Manual J Residential Load Calculations Eighth Edition, Version 2.10 September 9, 2011
ISBN # 1-892765-35-7 The Eighth Edition of Manual J (MJ8 – ACCA/ ANSI) is the American National Standard for residential heating and cooling load calculations.
Version Two of Manual J reorganizes the presentation of material provided in previous versions, and provides guidance on using an abridged version of Manual J (MJ8AE), which supports hand calculations for a subset of Manual J applications.
Submit all comments to
[email protected] by 11:59pm (EST) 24 October 2011 on the ACCA RESPONSE FORM available from www.acca.org/ansi.
Abridged Edition Check List ¯ A 'yes' for all line items indicates MJ8AE is an appropriate calculation tool, otherwise use the full version of Manual J. The structure is a single family detached dwelling; the total window, glass door and skylight area does not, or shall not, exceed 15 percent of the associated floor area. The glass is, or shall be, equitably distributed around all sides of the dwelling – the dwelling appears to have obvious and sufficient exposure diversity. Heating and cooling is, or shall be, provided by a central, single-zone, constant volume system. The dwelling has no, or shall have no, radiant heating system. The comfort conditioning system is not, or shall not, be equipped with a ventilation heat exchanger or a ventilating dehumidifier. The indoor design condition shall be: Heating 70 oF; Cooling 75 db oF and 45%, 50% or 55% RH; unless superceded by code. The outdoor design conditions shall be equal to the values in Table 1A (exactly), unless superceded by code. Windows and glass doors have, or shall have, clear 1-pane, 2-pane or 3-pane glass. Skylights shall be flat and shall have clear 1-pane or 2-pane glass. Curbs shall default to uninsulated wood 2x4. Skylights shall not be equipped with a light shaft or an internal shade. For heating, the default U-values for fenestration assemblies shall be those listed in Table 2A. For cooling, the default U-values and SHGC values shall be those listed in Table 3A and 3C. The foreground reflectance shall default to 0.20. All conventional windows and glass doors shall default to internal shade (medium-color blind with slats at 45 degrees); except purpose-built daylight windows and skylights, which shall have no internal shade. Bug screen, French door and projection adjustments shall be made when such devices and construction are observed during a site inspection or appear on the building plans. Windows and glass doors are not, or shall not, be equipped with external sun screens. Overhang adjustments shall be evaluated and applied to all windows and glass doors. Above grade, the dwelling has, or shall have, wood frame walls or empty-core block walls (no metal framing, no filled core block). The exterior finish shall default to brick veneer, stucco or siding. The interior finish shall default to gypsum board. Below grade, the dwelling has, or shall have, empty-core block walls (with or without board insulation; with or without framing and blanket insulation). Framing shall be wood (not metal), when applicable. The dwelling has, or shall have, a dark shingle roof over a vented attic (not encapsulated), a beam ceiling, or a roof-joist ceiling. An attic or attic knee wall space is, or shall be, vented to FHA standards, no radiant barrier, no encapsulating foam. Slab floors shall have no edge insulation, or 3 feet of vertical insulation that covers the edge. Basement floors shall default to no insulation below slab, no sensitivity to width. Floors over a closed space shall default to no insulation on the walls of the closed space. Floors over a closed space shall be insensitive to the tightness of the closed space. Table 5A shall be used to estimate infiltration loads, which shall be appropriate for the dwelling of consideration (three or four exposures, class 4 wind shielding, no blower door test or component leakage estimate). The sensible appliance load is 1,200 or 2,400 Btuh; the number of occupants equals the number of bedrooms plus one. The duct system (when applicable) is, or shall be, installed in one horizontal plane; entirely in a conditioned space, in an attic that has no radiant barrier, no encapsulating foam, or in a closed crawlspace or unconditioned basement. Attic duct runs shall default to round, spider pattern; supplies in room centers, large return close to air handler or return in closet door; or rectangular trunk and branch, supplies near inside walls, large return at floor of conditioned space. Below-floor duct runs shall default to trunk-branch; perimeter supplies; large return close to air handler. The duct system (if applicable) is, or shall be, sealed to the Manual J default (0.12 / 0.24) leakage scenario. Credit for a tighter system requires a leakage test. Leakier systems should be sealed.(Leakage greater than 0.35 / 0.70 is unacceptable.) Ducts in an unconditioned space have (or shall have) R-2, R-4, R-6 or R-8 insulation. There is no engineered ventilation; or such ventilation is, or shall be provided by piping outdoor air to the return side of the duct system (pressurization effect on infiltration is ignored). No other type of ventilation system shall be installed in the dwelling. A blower heat adjustment shall be made when manufacturer’s performance data is not discounted for blower heat. The blower heat adjustment shall be 500 Watts. Note 1: The abridged edition of Manual J (MJ8AE) shall not be used to estimate heating and cooling loads for dwellings unless such dwellings are totally compatible (100 percent yes) with this checklist and the descriptions and caveats provided by Appendix 2 and Appendix 3. Use the full version of Manual J for all other scenarios. Note 2: A qualified practitioner may substitute a full version HTM for an abridged version HTM (see Section A1-6).
Section 2 n
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In general, take full credit for the rated (or tested) performance of construction materials, insulation materials and construction features. a) As specified for new construction. b) As installed (verify the installation conforms to methods and materials protocols). c) As tested (see quality control programs for new construction, investigate existing construction) Take full credit for the tightness of the envelope construction. a) As specified by builder or code. b) As installed (verify the installation conforms to methods and materials protocols). c) As tested (see quality control programs for new construction, investigate existing construction). Follow Manual J procedures for infiltration and ventilation a) Use the Table 8A procedure to evaluate the fresh air requirement. b) Use Table 5A to estimate infiltration rates for heating and cooling (ignore intermittent exhaust fans). c) Decide on the installation of an engineered ventilation system (mandatory if the code fresh air requirement is larger than an honest estimate of the Manual J infiltration rate). d) Intermittent bathroom and kitchen exhaust fans are not “ventilation devices” or “ventilation systems.” Take full credit for duct system sealing and duct insulation when such efforts are confidently anticipated or certifiable. a) Use the default (0.12/0.24) scenario for (untested) ducts that are reasonably sealed. b) Take full credit for sealing efforts that are certifiably tighter than the default scenario for sealed ducts. c) If the duct sealing work is deficient – seal the ducts and take credit for sealed ducts (use unsealed options to show why the sealing work is required). Match location as close as possible when selecting a duct load table (use Table 7 unabridged if the MJ8AE tables do not provide a satisfactory match). a) For attic ducts, match roof material, roof color, use of radiant barrier or foam, and attic ventilation. b) For closed crawlspace locations, match crawlspace tightness, crawlspace wall insulation and crawlspace ceiling insulation. Match duct system geometry (radial and spider systems tend to have less surface area than extended plenum and trunk and branch systems). Match return system geometry (use advanced Manual J procedures when the system has more than one or two large returns or when the returns are not located close to the air handler).
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Be sure to use the duct wall insulation correction if the R-value of the insulation is not R-6. Be sure to use the surface adjustment factor for the exposed duct surface area when the surface area of the actual duct system is significantly different than the defaults listed in Table 7. Make sure the occupancy and internal loads are compatible with the MJ8AE defaults (use Manual J, Worksheet F if MJ8AE does not provide a satisfactory match). Add blower heat to the sensible load if equipment performance data is not adjusted for blower heat (if equipment manufacturer or blower power is unknown, assume 1,707 Btuh for indoor blower motor heat). Educate consumers: Sit down with your customers or clients and educate them on these issues.
Manual J Don’ts (Mandatory Requirements) n Do not use Manual J (any version) for: a) Any type of commercial application (even if located in a residential structure). b) Large multi-family buildings or residential high rise structures. c) A room or space containing an indoor swimming pool or hot tub. d) Earth-berm or earth covered dwellings. e) Solar homes that have passive features. n Do not use MJ8 AE to estimate heating and cooling loads for applications that are not compatible with the "Abridged Edition Check List" (see the page that precedes Section 1). n Do not design for record breaking (or news making) weather conditions. n Do not add a “safety factor” to the Table 1A design conditions. n Do not design for abnormally low or high indoor temperatures or humidity conditions (unless there is a certified medical reason for doing so). n Do not assume that there will be no internal shade on ordinary windows and glass doors (bare glass is an acceptable assumption for glass specifically installed for “day-lighting”). n Do not fail to take credit for overhangs. n Do not assume that the load for the worst case site orientation can be used for other orientations. (Rotating the dwelling on a site can change the cooling load by a half ton or more. Room airflow requirements change as the orientation changes. If the same design is used for any orientation, some rooms may have too much supply air and other rooms will not have enough supply air for temperature control and comfort.) n Do not reduce known ceiling, wall or floor R-values “just to be safe.”
Section 4 Opaque Panel Heating Load Examples The following calculations are made for a 70°F indoor temperature in a location that has a -5°F outdoor design temperature: HTD = 70 – (-5) = 75° F. a) A metal door with a polystyrene core fits a 21 SqFt opening. The panel heating load is 551 Btuh. Table 4A construction number = 11N Table 4A U-value = 0.35 HTM = U x HTD = 0.35 x 75 = 26.25 Net load area = 21 SqFt Heating load = HTM x Load area = 26.25 x 21 = 551 Btuh
b) An exposed wall has brick veneer, R-2 insulation board sheathing, wood studs, R-19 cavity insulation and interior finish. There is 240 SqFt of gross area with 70 SqFt of window and door area. The panel heating load is 803 Btuh. Table 4A construction number = 12E-2b-w Table 4A U-value = 0.063 HTM = U x HTD = 0.063 x 75 = 4.725 Net area = Gross area – Opening area = 240 - 70 = 170 SqFt Heating load = HTM x Net area = 4.725 x 170 = 803 Btuh
Note: Metal framing significantly affects wall performance. Use advanced Manual J procedures for this type of construction.
c) An exposed block wall has brick veneer, no insulated cores, R-6 board insulation and interior finish. There is 240 SqFt of gross area with 70 SqFt of window and door area. The panel heating load is 1,454 Btuh. Table 4A construction number = 13A-6oc-b Table 4A U-value = 0.114 HTM = U x HTD = 0.114 x 75 = 8.55 Net area = Gross area – Opening area = 240 - 70 = 170 SqFt Heating load = HTM x Net area = 8.55 x 170 = 1,454 Btuh
Note: Core insulation significant affects wall performance. Use advanced Manual J procedures for this type of construction.
d) An exposed block wall has wood siding, empty cores, R-2 board insulation, wood 2x4 studs, R-11 blanket insulation and interior finish. There is 240 SqFt of gross area with 70 SqFt of window and door area. The panel heating load is 1,020 Btuh. Table 4A construction number = 13B-2oc-w Table 4A U-value = 0.080 HTM = U x HTD = 0.080 x 75 = 6.0 Net area = Gross area – Opening area = 240 - 70 = 170 SqFt Heating load = HTM x Net area = 6.0 x 170 = 1,020 Btuh
e) A basement wall has empty cores, R-2 board insulation extending from the sill plate to the floor and no interior finish. The wall is 8 ft high and has 320 Ft² of gross wall area. The basement floor is 6 feet below grade (2 feet of the wall is above grade). There is 240 SqFt of below-grade area and 80 SqFt of gross above-grade area with 16 SqFt of window area. The heating load for the below grade wall area is 1,854 Btuh, and 1,291 Btuh for the above grade strip. Table 4A construction number = 15A-2sfoc-6 Table 4A below grade U-value = 0.103 Below grade HTM = U x HTD = 0.103 x 75 = 7.725 Below grade area = Gross area = 240 SqFt Below grade heating load = HTM x Gross area = 7.725 x 240 = 1,854 Btuh Table 4A above grade U-value = 0.269 Above grade HTM = U x HTD = 0.269 x 75 = 20.175 Net above grade area = Gross area – Opening area = 80 – 16 = 64 SqFt Above grade heating load = HTM x Net area = 20.175 x 64 = 1,291 Btuh
f) A below grade block wall has no insulation in the cores, R-4 board insulation extending to 3 feet below the sill plate, wood 2x4 studs, R-11 blanket insulation and interior finish. The wall is completely below grade with a 240 SqFt area. The basement floor is 8 feet below grade. The panel heating load is 828 Btuh. Table 4A construction number = 15A11-4ocw-8 Table 4A U-value = 0.046 HTM = U x HTD = 0.046 x 75 = 3.45 Net area = Gross area = 240 SqFt Heating load = HTM x Gross area = 3.45 x 240 = 828 Btuh
23
Section 12 Worksheet E Infiltration Loads Smith Residence HTD = 76 oF
CTD = 15 oF
Design Grains = 38
Elevation = 955 Ft
Table 10A ACF = 0.97
Step 1 — Table 8 Outdoor Air Requirement Operating Mode
Above Grade Volume AGV (CuFt)
Number of Bed Rooms
Number of People
Default Burner Btuh
Installed Burner Btuh
OA Cfm for 0.35 ACH
OA Cfm for People
OA Cfm for Furnace
Table 8 OA Cfm
Heat
20,355
3
4
0
75,000
119
80
0
119
Cool
20,355
3
4
119
80
AGV for each level = Floor area X Average ceiling height The above grade portion of a conditioned basement is one level. AGV = Total of the volumes for all levels Default Occupancy = Number of bedrooms + 1
Furnace input defaults: Direct Vent = 0 Btuh Atmospheric = 100,000 Btuh Recalculate, using actual input Btuh, if the total heating load exceeds 80,000 Btuh.
For Smith: AGV = 8 x 56 x 32 + 188 x 32 = 20,352 CuFt
119
Cfm @ 0.35 = 0.35 x AGV / 60 Cfm for people = 20 x Number of people Cfm for Burner = 0.50 x Input Btuh / 1,000 Table 8 OA Cfm = Largest of the three Cfm values. Cfmoa determined by code requirement or designer decision to use the Table 8 OA Cfm value.
Step 2, Option 1 — Table 5 Defaults Operating Mode
Floor Area (SqFt)
Type of Const.
Space ACH
AGV (CuFt)
Space ICFM
Fireplace ICFM
Total ICFM
Heating
2,848
Average
0.32
20,355
109
0
109
Cooling
2,848
Average
0.16
20,355
85
1) For default estimates use Table 5A or 5B to find ICFM values for the conditioned space and fireplace. 2) The component leakage area method or the blower door method may be used to estimate ICFM values.
(Note 1) (Note 2)
Table 8 OA CFM
Table 8 Vent CFM
119
64
54
Total ICFM = Space ICFM + FP ICFM Space ICFM = ACH x AGV / 60 Use the AGV from the Table 8 procedure.
T8 vent-CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 2, Option 2 — Component Leakage Area Method Operating Mode
HTD and CTD
Wind Velocity (MPH)
Heating
76 oF
15
Cooling
15 oF
Table 5C ELA4 (SqIn)
Cs
Shielding Class
Cw
85.6
0.0299
2
0.0121
Table 5D
ICFM
Table 8 Vent CFM
119
28
191
7.5
Default heating season velocity = 15 MPH Default cooling season velocity = 7.5 MPH
Table 8 OA CFM
91 Detail from Worksheet E1
ICFM = ELA4 x ( Cs x TD + Cw x V2 ) 0.50
T8 vent CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 2, Option 3 — Blower Door Method Operating Mode
HTD and CTD
Wind Velocity (MPH)
Heating
76 oF
15
Cooling
15 oF
Blower Door ELA4
Table 5D
ICFM
Cs
Shielding Class
Cw
0.0299
2
0.0121
Table 8 Vent-CFM
119
53
139 62
7.5
Default heating season velocity = 15 MPH Default cooling season velocity = 7.5 MPH
Table 8 OA-CFM
66 Provided by field test
ICFM = ELA4 x ( Cs x TD + Cw x V2 ) 0.50
T8 vent-CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 3 — Infiltration Loads on Central Equipment Type of Load Heat Load
Wrksht. H Value for Vent CFM
Exhaust CFM
CFMimb
ICFM (Option 3)
Net Infilt. CFM NCFM
H&C Loads (Btuh)
70
70
0
139
139
11,237
70
70
0
66
66
Sens Load Lat Load
1,054
CFMimb = CFM exhaust - CFMvent
The ± sign in the NCFM equation is determined by the sign of the Heat Load = 1.1 x ACF x NCFM x HTD CFMimb Sensible Load = 1.1 x ACF x NCFM x CTD value. Latent Load = 0.68 x ACF x NCFM x Grains
NCFM = (ICFM1.5 ± CFMimb1.5 ) 0.67 NCFM = 0 if (ICFM1.5 - CFMimb1.5) < 0
1,651
The room infiltration load equals the load on the central equipment multiplied by the gross wall area ratio (WAR). WAR = Gross room wall area / Gross wall area for all rooms served by the central equipment
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Section 13 B
B
C South
Tops of B windows are 1.0 foot below a 1.5 foot overhang. Entire House 56 x 32 x 8
A
East
Top of glass door is 0.75 feet below a 1.5 foot overhang. West
D D windows equipped with external sun screen
Skylight S2
North
Bedroom 1 14 x 17
Bedroom 3 14 x 16
D
Combination Living and Dining Room 28 x 18
Bedroom 2 14 x 15
Kitchen and Utility 21 x 14 Hall and Two Closets 14 x 9 Entry 7 x 14
A
B
Skylight S1
Bath 2 5x7
Bath 1 9x7 A
A
A
A
A
A
Figure 13-3
13-2 Walker Residence Solution Figure 13-4 compares the sensible cooling loads for the three roof construction options. Based on this information and a preference for the appearance of roof tile, the home will have a white tile roof. Form J1 (next page) summarizes the equipment sizing calculations for this dwelling. In the column for the entire house, Line 21 shows that the total heating load is 6,142 Btuh, the total sensible load is 22,573 Btuh and the total latent load is 3,282 Btuh. (The latent load would be much larger without the ventilating dehumidifer.) Form J1 Line Items Lines 3 and 4 show that the gross wall area is 1,408 SqFt and that the floor plan area is 1,792 SqFt. Line 5 shows that the ceiling has no slope, so the ceiling area is 1,792 SqFT. Lines 6A and 6B show directional HTM values and load areas for windows, glass doors and skylights. The HTM values are copied from Worksheets B and C. Load areas are determined by multiplying the Figure 13-1 or Figure 13-2 areas by the number of occurrences on the floor plan. The associated heating and sensible cooling loads are determined by multiplying the HTM values by the load areas.
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Sensible Cooling Load (Btuh) Form J1 Line Item
Ceiling Duct Total Effect
Roof Construction White Shingle No RB
White Shingle With RB
White Tile
2,004
1,549
865
896
851
826
2,900
2,400
1,691
Figure 13-4 Lines 7 through 11 show HTM values and load areas for opaque surfaces. The HTM values are copied from Worksheet D. The load area for a door is equal to the 21 SqFt default value. The load area for walls and ceilings is equal to the net surface area. The associated heating and sensible cooling loads are determined by multiplying the HTM values by the load areas. Line 12 shows the infiltration loads, as copied from Worksheet E. In this case the wall area ratio equals 1.0 because the calculation is for the entire house. Line 15 shows the effective load factors (EHLF and ESGF) for the duct system, as copied from Worksheet G. The heating and sensible load values are equal to the
Section 13 1 Name of Room Walker Residence 2 Running Feet of Exposed Wall 3 Ceiling Height (Ft) and Gross Wall Area (SqFt) 4 Room Dimensions (Ft) and Floor Plan Area (SqFt) 5 Ceiling Slope (Deg.) and Gross Ceiling Area (SqFt) Type of Panel HTM Const.. Exposure Faces Number Htg. Clg.
6a
6b
7
8
9
10
11
12
13
14 15 16 17 18 19 20 21
West 7.92 15.01 Windows a 1G Unit A and Glass b 1G Unit A East 7.92 15.01 Doors c 1G Unit C oh South 8.28 7.14 d 1G Unit B oh South 7.56 7.09 e 1G Unit B North 7.56 7.09 f 1G Unit A North 7.92 7.36 g 1G Unit D West 8.10 10.98 h I j North 16.74 84.33 Skylights a 9C Kitchen b 9C Living South 12.78 78.33 c a 11N 6.30 10.50 Wood and Metal b 11N 6.30 10.50 Doors c a 14C-5 All 1.24 1.01 Above Grade b Walls and Partitions c d e f g a Below Grade b Walls c 0.47 0.49 Ceilings a 16F-39tw b c Floors a Rad 22D-5rl 12.34 b c d 0.137 Infiltration Heating Load (Btuh) Effct. Sensible Load (Btuh) ACH 0.00 Latent Load (Btuh) a Occupants at 230 and 200 Btuh Internal b Scenario Number Option 3 c Default Adjustments d Custom Appliances tv & computer e Plants Sum lines 5 through 12 Subtotals 0.066 Duct EHLF & ESGF Loads ELG 0 Ventilation Loads Vent Cfm 50 E Cfm Winter Humidification Load Gal / Day Piping Load Blower Heat AED Excursion & Latent Moisture Migration Load Sum Lines 13 Through 19 Total Load
8 56 x 32 0
Entire House 176 1,408 1,792 1,792 Btuh
Area or Length
Heating
S-Clg.
8.75 17.50 58.00 28.00 14.00 43.75 31.50
69 139 480 212 106 347 255
131 263 414 199 99 322 348
8.00 32.00
134 409
675 2,507
21.0 21.0
132 132
221 221
1,165
1,446
1,773
1,752
820
865
176
2,172
L-Clg.
Area or Length
Btuh Heating
S-Clg.
L-Clg.
< Line 2 factor x line 5 adjustment >
1.330 0.233 0.293
Step 3) Leakage Rate Correction (LCF) 8
For heat loss =
1.75
For heat loss =
1.75
9
For sensible gain =
1.91
For sensible gain =
1.91
10
For latent gain =
4.02
11 12 13
Adjusted heat loss factor = Adjusted sensible gain factor = Adjusted latent gain (Btuh) =
0.048 0.559 2,416
For latent gain = < Line 6 factor x line 8 adjustment t > < Line 7 factor x line 9 adjustment > < Line 3 value x line 10 adjustment >
4.02 0.048 0.559 2,416
Step 4) Surface Area Adjustment 14
Installed supply area (SqFt) =
275
15
Default supply area (SqFt) =
312
16
Rs = Installed area / default area =
17
Installed return area (SqFt) =
18 19 20 21 22
Default return area (SqFt) = Rr = Installed area / default area = Ks =
0.676
DSF for Sect 23-18 Shortcut
0.881
Installed supply area (SqFt) = Default supply area (SqFt) =
0
Rs = Installed area / default area =
~
120
Installed return area (SqFt) =
95
Default return area (SqFt) =
1.263
Kr =
0.324
SAA (heating and sensible cooling) = LGA (latent cooling) =
1.005 1.263
Rr = Installed area / default area = Ks =
0.676
Kr =
0 120 95 1.263 0.324
< Ks (L20) x Rs (L16) + Kr (L20) x Rr (L19) > < Latent LGA = Rr (L19) >
0.409 1.263
< Line 11 Factor x Line 21 SAA value > < Line 12 Factor x Line 21 SAA value > < Line 13 gain x Line 22 LGA adjustment >
0.167 0.229 3,052
Step 5) Heat Loss and heat gain factors and latent gain (Btuh) 23 24 25
Effective heat loss factor (EHLF) = Effective sensible gain factor (ESGF) = Effective latent gain Btuh (ELG) =
0.410 0.562 3,052
Figure 23-2
197
Section 23 Return Side Loads The J1 Form converts duct load factors to duct loads. The return side loads for this example are as follows: The heating load for the space served by the duct system converts the return side heat loss factor to a heating load. For example, if the space heating load is 52,000 Btuh (per line 14 on the J1 form), the heating load for the return-side of the duct system is 0.167 x 52,000 = 8,684 Btuh. The sensible cooling load for the space served by the duct system converts the return side sensible gain factor to a sensible cooling load. For example, if the sensible space load is 22,000 Btuh (per line 14 on the J1 form), the sensible cooling load for the return-side of the duct system is 0.229 x 22,000 = 5,038 Btuh. The return side latent load is provided by Worksheet G.
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Dry-Bulb and Wet-Bulb at the Exit of the Return Duct The sensible heat equation (below) converts a sensible return duct load (sensible Btuh) to a dry-bulb gain, or dry-bulb loss (±DT). Then the dry-bulb temperature (DB) of the air that exits the return duct equals the indoor dry-bulb temperature plus the return duct gain. Indoor DB temperature = Given DT (°F) = ± Sensible Btuh / (1.1 x ACF x Rcfm ) Exiting DB (°F) = Indoor DB ± DT
Where: ACF is an altitude correction factor (see Table 10A) Rcfm = Return air Cfm = Blower Cfm
Note: Return air Cfm may be equal to the blower Cfm, or may be somewhat larger or smaller. For the purpose of this calculation, Rcfm defaults to blower Cfm
An indoor humidity ratio (grains of moisture per pound of air value) is provided by altitude sensitive psychometrics (based on the indoor dry-bulb and relative humidity values). Then the latent heat equation (below), converts a latent return duct load (latent Btuh) to a grains of moisture gain (DGR). Then the exiting grains value equals the indoor grains value plus the latent moisture gain Indoor Grains = Psychometric value DGR = Latent Load Btuh / 1.1 x ACF x Rcfm Exiting Grains = Indoor Grains + DGR
Altitude sensitive psychometrics converts an exiting dry-bulb temperature and grains value to a exiting wet-bulb temperature, and converts an indoor dry-bulb temperature and relative humidity value to an entering wet-bulb temperature. The wet-bulb rise (DWB) equals the difference between the two wet-bulb values. Exiting WB (°F) = Psychometric value Indoor WB (°F) = Given psychometric state point DWB (°F)= Exiting WB - Indoor WB
Duct System Efficiency The heating and sensible cooling loads generated by duct systems are sensitive to a collection of variables and interactions such as piping geometry, the location of the duct runs, the condition of the air in the duct runs, the condition of the air surrounding the duct runs, the tightness of seams and joints, and the amount of duct-wall insulation. Duct loads also depend on the size of the dwelling and construction details because equipment size, blower CFM, the size of the duct airways and the total surface area of the duct system depend on the size of the heating and sensible cooling loads. Leakage at seams and joints produces a latent cooling load and creates pressure differentials that affect the dwelling’s infiltration rate.
198
Duct load calculations are complex and recursive, and should be performed on a case by case basis by "Powered by Manual J" software. This manual provides solutions for a collection of default scenarios (see Table 7). As demonstrated by Sections 7, 8 and 9, these solutions reduce to a heat loss factor, a sensible heat gain factor and a latent gain value. The loss and gain multipliers for heating and sensible cooling loads are expressed as a percentage of the envelope load. The latent heat gain value is expressed in Btuh units. The information presented here pertains to the duct loss and gain models used to generate the Table 7 values. These models are compatible with information published in ASHRAE Standard 152.
Section 23
23-10 Adequate Insulation is Required Comparison of the wall insulation correction factors (see Table 7B-R, for example) indicates that there is a significant increase in the size of the sensible duct load if the wall insulation is reduced from R-6 to R-4 and that an unacceptably large increase is associated with R-values that are less than R-4. Alternatively, performance is noticeably improved when the wall insulation is upgraded to R-8. (Depending on the circumstances, replacing R-6 with R-8 produces a 3 to 6 percent reduction in the sensible duct load and a 2 to 9 percent reduction in the duct heating load.)
23-11 Surrounding Environment Attics are a hostile environment because the dry-bulb temperature is significantly higher than the outdoor temperature in the summer (white shingles, tile roofs, radiant barriers, attic fans, extra vent area and certain types of attic construction moderate this condition), and almost as cold as outdoors during winter. In addition, the absolute humidity in a properly vented attic is approximately equal to the outdoor humidity. Open crawlspaces are undesirable because there is little difference between the crawlspace temperature and humidity and the condition of the outdoor air. Enclosed crawlspaces and unconditioned spaces produce environments that range from benign to hostile, depending on construction details (tightness, insulation placement and insulation R-value). Information gained by a limited effort to investigate the affect of location is summarized by Figure 23-3. This figure shows that the loads for open crawlspaces
and uninsulated crawlspaces can be comparable to or greater than the loads for attic locations. (The crawlspace system has more exposed duct wall area than the attic system because the crawlspace runouts extend to the perimeter of the floor plan and attic runouts only ran to the center of a room.) This figure also indicates that radiant barriers (or white shingles or tile roofs) reduce the cooling load for attic duct systems. Duct heat transfer to an unconditioned space can be significantly reduced if the surface area of the system is minimized. In this regard, research performed at the National Renewable Energy Laboratory (NREL) indicates that when the thermal envelope is efficient, an acceptable level of comfort can be provided by an attic duct system that features a central air handler and short supply runs that feed supply air diffusers located near the interior walls of the rooms. Duct loads are eliminated when duct runs are in a conditioned space, and significantly reduced when in an encapsulated attic.
23-12 Duct Load Factors Depend on Design Procedures The model used to generate the duct factor tables for this manual applies to designs that are compatible with Manuals J, S, and D procedure. This is important because duct surface area estimates are based on the assumption that the blower CFM is compatible with the calculated loads and that duct airway sizes are compatible with the blower performance and the total effective length of the duct system. In other words, default surface areas for Manual J duct tables do not apply to duct systems that have been designed by using whimsical guidelines and unreliable rules of thumb (the surface area correction procedure adjusts for these cases).
Comparison of Duct Load Factors — Radial Duct System In Vented Attic Under Dark Shingles Range of Duct Load Factors Scenario
Grille Location
Sensible Cooling
Latent Btuh
Heating SAT = 110 °F
Supply
Return
Ordinary Vented Attic Mostly Sealed Not Sealed
0.11 > 0.27 0.20 > 0.58
136 > 1,044 483 > 3,930
0.06 > 0.20 0.11 > 0.41
Center room
1,000 cfm per grille, short ducts
Vented Attic With Radiant Barrier Mostly Sealed Not Sealed
0.09 > 0.20 0.18 > 0.36
131 > 851 368 > 2,399
0.06 > 0.20 0.11 > 0.41
Center room
1,000 cfm per grille, short ducts
Open Crawl Space Mostly Sealed Not Sealed
0.12 > 0.40 0.25 > 1.18
241 > 2,217 1106 > 9,094
0.13 > 0.48 0.27 > 1.35
Perimeter
1,000 cfm per grille, short ducts
Closed Crawl Space, No Insulation Mostly Sealed Not Sealed
0.06 > 0.15 0.11 > 0.27
125 > 972 1068 > 8,787
0.12 > 0.38 0.25 > 1.28
Perimeter
1,000 cfm per grille, short ducts
Figure 23-3
198
Section 27 humidity level that produces condensation on a visible surface. The following equation is used to evaluate the temperature distribution across a structural panel. This equation shows that the temperature at a concealed surface (Tc) depends on the R-value for the layers of material between the surface of interest and the outdoors (Rc), the total R-value across the sandwich (Rt), the outdoor design temperature (To), and the indoor temperature (Ti).
Dew point 37% RH
Tc - Ro + (Ti - To) x (Tc / Rt)
43 oF
For example, the following guidance compares the condensation potential at the inside surface of a cinder block wall that has insulation on the indoor side of the block with the condensation potential of a block wall with the same amount of insulation installed on the outdoor side of the block. These calculations are based on data provided by Figure 27-2, which shows the thermal resistance of the path between the concealed surface and the outdoor air is R-2 for indoor insulation and R-10 for outdoor insulation. Figure 27-2 also shows that the total thermal resistance for both walls is R-12 and the indoor and outdoor temperatures are 70 oF and -5 oF.
Figure 27-1
R-12
-5 °F
Tc = -5 + ((70 - (-5)) x 10) / 12 = 57.5 oF
For a 57 oF dew point, the psychometric chart for normal temperatures indicates that indoor air with
220
R-2
Concealed Surface
70° F
-5 °F
70°F
Overall resistance of both walls is R-13 with Interior finish and air films
Tc = -5 + (70 - (-5)) x (2 / 12) = 7.5 oF
Insulation on Outside Surface This equation provides the value for the temperature at indoor surface of the cinder block if the insulation is installed on the outdoor surface of the wall.
R-12
R-2
Insulation on Inside Surface This equation provides the temperature at indoor surface of the block (under the insulation) if the insulation is on the indoor side of the wall.
For a 7.5 oF dew point, a low-temperature psychometric chart indicates that indoor air with 8 Grains of moisture will produce condensation on the concealed surface of the block (an absolute humidity of 8 Gr/Lb is associated with a 7.5 oF dew point). A psychometric chart for normal temperatures shows that the relative humidity of the indoor air must be 8 percent or less to prevent condensation at the indoor surface of the block wall (8% RH is compatible with 70 oF dry-bulb and 8 Grains of moisture). These calculations show that concealed condensation is almost certain if the insulation is installed on the inside surface of the block wall.
70 oF
R-2 between the concealed surface and the outdoors
R-12 between the concealed surface and the outdoors
Figure 27-2
70 Grains of moisture will produce condensation on the concealed surface of the block. This chart also shows that 62% RH is compatible with 57 oF dry-bulb and 70 Grains of moisture. Therefore, condensation will not occur until the indoor humidity exceeds 62% RH. These calculations show that concealed condensation is prevented (or will be unusual) if the insulation is installed on the outdoor side of the block wall.
27-3 Duct Condensation Condensation on interior duct surfaces will not occur if the dew-point temperature of the ducted air is lower than the temperature of the airway surface. The
Section 27 following equation shows that airway surface temperature (Ts) depends on duct air temperature (Ti) and ambient temperature (To), the overall R-value (Rt) of the duct wall (duct material, insulation and air film resistence), and the resistance of the inside air film (Ri).
If the ambient temperature is 0°F and the duct air temperature is 105°F, the temperature for the duct airway surface is about 76.8°F, so supply duct condensation will not occur. A similar calculation shows that return duct condensation will not occur.
Ts = Ti - (Ti - To) x (Ri / Rt) Where: Ri equals the air film coefficient for airway air: Ri is about 0.25 for typical air velocities Ri is about 0.68 for no air velocity (blower off)
For example, sea level dwelling has winter humidification added to supply air, and the dew-point of space air is 37.3°F for 70°F dry-bulb and 30% RH. If the blower is off, space air may siphon through an attic duct system. Uninsulated metal duct is used to demonstrate the calculation procedure. If the blower is off, the total R-value of a sealed metal duct that has no insulation is about 1.36 (metal resistance is negligible, Ri is about 0.68, and Ro is about 0.68). If the ambient air temperature (To) is 0°F and the duct air temperature(Ti) is 70°F, the temperature for the duct airway surface is about 35°F, so condensation is possible. Dew-point for duct air = 37.3 °F Ts = 70 - (70 - 0) x (0.68 / 1.36) = 35.0°F
When the blower operates, 1,400 CFM of 105°F air moves through the supply side of the duct system. The Manual J humidification load was determined to be 4,760 Btuh for the winter design condition, so the humidifier must add 4.5 pounds of water per continuous hour of operation. But the furnace only operates for 42 minutes per hour because it is oversized, so the humidifier must add moisture at a rate of 6.5 pounds (Lb) of water per hour when the furnace operates. This means that return air enters the return duct at 70°F and 32.5 Grains (Gr) and leaves the supply duct at 105°F and 39.7 Grains, so the dew-point (DP) of the supply air is about 42.3°F. ACF for sea level = 1.0 Return air at 70 °F and 30% RH = 32.5 Grains Latent heat added to air = 6.5 x 1,054 = 6,851 Btuh Grains rise = 6,851 / (1.0 x 0.68 x 1,400) = 7.2 Supply air grains = 32.5 + 7.2 = 39.7 Supply air at 105 °F and 39.7 Grains = 42.3 °F DP
If the blower runs, the total R-value of a sealed metal duct that has no insulation is about 0.93 (metal resistance is negligible, Ri is about 0.25, and Ro is about 0.68).
Dew-point for supply air (105°F, 12% RH) = 42.3 °F Ts = 105 - (105 - 0) x (0.25 / 0.93) = 76.8°F Dew-point for return air (70°F, 30% RH) = 37.3 °F Ts = 70 - (70 - 0) x (0.25 / 0.93) = 51.2°F
In general, duct runs installed outside of the conditioned space should be insulated (R4 is common, R6 or R8 is good practice, and ma be a code requirement). For winter humidification, the amount of duct wall insulation must assure that the duct airway surfaces will be warmer than the dew-point of ducted air. In general, duct runs installed outside of the conditioned space should be comprehensively sealed (this is good practice, and may be a code requirement). For winter humidification, exposed duct runs must be as tight as possible (much better than the 0.12/0.24 Cfm per SqFt of duct surface area default for sealed duct per Table 7). n
n
Reactively humid air leaking out of a supply duct may condense (and possibly freeze) on a nearby surface. Cold air leaking into a return duct can cause condensation (and possible freezing) at the leakage point.
27-4 Moisture Migration Water vapor rapidly migrates throughout an enclosed space, finding its way into every gap, crack and cavity that has an air-path connection to a humid space. This means that when humidification is done locally, the contiguous spaces — as defined by the exterior walls and/or interior walls — will be humidified. Therefore, the maximum acceptable (non condensing) humidity level in any room or zone depends on the construction of the room or zone. Also note that moisture can be mechanically dispersed throughout a home, by a forced-air heating system. For example, if return air is drawn from a room that contains a pool or hot tub, the entire home will be humidified. Even if the blower is not operating, moisture will migrate through any duct run (supply or return) that connects a humid room with the other rooms served by the air distribution system. Condensation also can occur inside of air distribution systems located in unconditioned spaces. For example, homes equipped with baseboard heat and a cooling
221
Section 27 system installed in the attic may have problems with duct wall condensation or air handler cabinet condensation during cold weather. In extreme cases water may drip from the ceiling supply outlets or returns. This moisture is generated when humid, buoyant room air migrates to the attic duct system (through a supply or return), loses sensible heat and moisture (the water vapor in the air condenses on cold surfaces), loses buoyancy and falls back into the room (through a supply or return), which draws more room air into the duct system. This continuous, gravity-driven circulation process is called thermosiphoning (see Section 27-3).
27-5 Humidifier Water Requirement Winter humidification loads are generated by natural infiltration, by mechanical ventilation, by duct leakage, and by moisture migration (ignoring the affect of internal moisture gains). Because the infiltration and ventilation loads are similar, they are combined into a single outdoor air load. Then the default humidification load for outdoor air is increased by a moisture migration load, and/or a duct leakage load, but good construction practices prevent significant migration and leakage loads. Provide a comprehensive vapor retarding membrane for structural surfaces. Duct runs and equipment cabinets in an unconditioned space must be tightly sealed. Section 28-6 guidance pertains to the moisture migration load for winter humidification. Section 27-7 provides guidance for calculating humidification loads caused by duct leakage.
n
n
n
n
The following equations show that the default humidification load depends on the total flow of outdoor air (infiltration CFM plus the ventilation CFM), the absolute humidity difference between the indoor air (at the indoor design condition) and the outdoor air (at the winter design temperature and 80 percent RH), and the altitude correction factor (ACF) from Table 10A. Outdoor Air CFM = ICFM + VCFM Pounds of Water Per Hour = 0.000645 x Outdoor CFM x (Indoor Grains - Outdoor Grains) x ACF
Figure 27-3 provides moisture content values for a range of outdoor air temperatures and moisture content values for a variety of indoor humidity values. This information is used when the elevation is 2,500 feet or less. For higher elevations, moisture content values are read from Table 12, a psychometric chart for the altitude of concern, or they can be obtained by using altitude sensitive psychometric software.
Moisture Content at Sea Level Outdoor Dry Bulb °F
Outdoor Grains
Indoor Humidity % RH
Indoor Grains @ 70 °F
-10 or lower
2.6
10
10.8
-9 to -1
3.4
15
16.2
0
4.4
20
21.6
5
5.7
25
27.1
10
7.3
30
32.5
15
9.4
35
38.0
20
12.0
40
43.5
25
15.2
45
49.0
30
19.2
50
54.5
35
23.8
55
60.0
40
29.0
45
35.2
Figure 27-3 Humidifier Capacity Requirement Gallons of Water per Day per 100 CFM of Outdoor Air At Seal Level Conditions Outdoor Design Temperature - °F
Indoor RH -20
-10
0
10
20
30
40
20 %
3.52
3.37
3.37
2.65
1.78
0.44
NA
30 %
5.54
5.39
5.21
4.67
3.80
2.47
0.65
40 %
7.58
7.43
7.25
6.71
5.84
4.50
2.69
Figure 27-4 For example, sea level calculations show that 4.67 gallons of water per day are required to humidify 100 CFM of outdoor air when the outdoor design temperature is 10 oF and the indoor design condition is 70 oF dry bulb and 30 percent RH. For convenience, Figure 27-4 summarizes the result of a similar set calculations for a range of outdoor temperatures and indoor humidities. Outdoor Grains = 7.3 (10 oF, 80% RH) Indoor Grains = 32.5 (70 oF, 30% RH) Pounds per Hour = 0.000645 x 100 x (32.5 - 7.3) x 1.0 = 1.625
The following equation converts pounds of water per hour to gallons of water per day: Gallons per Day = 2.874 x Pounds Water per Hour
222
Section 27 Therefore, the 1.625 Lb/Hr water requirement is equivalent to 4.67 gallons per day. Gallons per day = 2.874 x 1.625 = 4.67
27-6 Humidifier Heating Load The humidification load on central heating equipment depends on the type of humidification equipment. If a humidification device has its own (self contained) source of heat, there is no humidification load on the central equipment. If a humidification device does not have a source of heat, the heat of evaporation is a load on the central heating equipment. This equation determines the humidification heating load (HHL) generated by evaporative humidification devices. HHL (Btuh) = 1,054 x Pounds Water per Hour
For example, an evaporative device that processes 1.625 pounds of water per hour produces a 1,713 Btuh load on the central heating equipment. 1,713 Btuh = 1,054 x 1.625
The following equation provides a value for the heating load produced by evaporative humidification devices. For this equation, CFMoa is the total flow of outdoor air (infiltration plus ventilation) and Grains Added is the grains of moisture added to the flow of outdoor air. HHL (Btuh) = ACF x 0.68 x CFMoa x Grains Added x ACF
For example, adding 15 Grains of moisture to 100 CFM of outdoor air produces a 1,020 Btuh humidification load (at sea level). HHL = 1.0 x 0.68 x 100 x 15 x 1.0 = 1,020 Btuh
27-7 Winter Humidification Load for Duct Leakage This calculation procedure evaluates the winter humidification load for duct leakage. It is offered as investigative-demonstrative tool. To avoid possible condensation problems, humidified air should not flow through leaky ducts installed in a cold space. For this calculation, altitude determines the altitude correction factor (ACF from Table 10A), and affects the psychometric properties of outdoor air and indoor air (per Table 12, or use psychometric software). Table 7 provides default values for supply duct surface area and return duct surface area (or use values specified by the practitioner). The supply and return leakage values (Cfm per SqFt of surface area) are
those used for the Manual J duct load calculation per Worksheet G (or use different values for what-if investigations). This procedure is for moisture added to supply air, so the grains of moisture in the supply duct is greater than the grains of moisture in the return duct. The supply-side moisture loss due to duct leakage is relative to dry outdoor air. The return-side moisture load due to duct leakage depends on the moisture in the ambient air in contact with the return duct. n
n
Assume that ambient air moisture equals outdoor air moisture if the unconditioned space is not sealed from outdoor air. Duct moisture leakage to an unconditioned space that is tightly sealed from outdoor air may not cause a significant humidification load (a regain issue), but may cause a structural condensation problem for the unconditioned space.
These equations determine the supply-side heating load (SHL) and moisture load (SML) for supply-side leakage, and the return-side heating load (RHL) and moisture load (RML) for return-side leakage. The total heating load (THL) and total moisture load (TML) for the duct system is equal to the sum of the supply and return values. LHS (Btuh) = 1,054 x Pounds Water per Hour DSG (grains) = HLS / (0.68 x ACF x Bcfm) SG (grains) = RG + DSG LScfm = SA x SLR LRcfm = RA x RLR SHL (Btuh) = 0.68 x ACF x LScfm x (SG - OG) RHL (Btuh) = 0.68 x ACF x LRcfm x (RG - AG) THL (Btuh) = SML + RML SML (Lb water per Hr) = SHL / 1,054 RML (Lb water per Hr) = RHL / 1,054 TML (Lb water per Hr) = SML + RML Where: LHS is the latent heat (Btuh) added to supply air. For the first iteration, pounds water per hour is the moisture requirement for infiltration and engineered ventilation at the winter design condition, per Section 27.5 guidance. For the second and final iteration, pounds water per hour is equal to the Section 27.5 value plus the TML value from the first iteration. DSG is the grains of moisture added to supply air. ACF is the altitude correction factor (Table 10A). Bcfm is the blower Cfm. SG is the grains of moisture in the supply air . RG is the grains of moisture at the return grille (which defaults to the grains value for the conditioned space).
223
Section 27 This value is determined by Table 12, or use altitude sensitive psychometric software. LScfm is the supply-side leakage Cfm. SA is the surface area of the exposed supply duct (SqFt). SLR is the leakage rate (Cfm/SqFt) for the supply duct. LRcfm is the return-side leakage Cfm. RA is the surface area of the exposed return duct (SqFt). RLR is the leakage rate (Cfm/SqFt) for the return duct. SHL is the latent heating load for supply moisture loss. OG is the grains of moisture for outdoor air at the winter design condition. This value is determined by Table 12, or use altitude sensitive psychometric software. RHL is the latent heating load for return moisture loss. AG is the grains of moisture in the ambient air that contacts the return duct . This defaults to OG if the unconditioned space is not tightly sealed (no regain), or may be about equal to RG if the unconditioned space is tightly sealed. (100% regain). THL is the total latent heating load . SML is the supply-side moisture loss. RML is the return-side moisture load . TML is the moisture load for both sides of the duct system.
For example, the outdoor design temperature for a sea level dwelling is 0°F, and the indoor design condition for winter humidification is 70°F and 30% RH. Per Table 12, there are 4.4 grains for outdoor air and 32.5 grains for indoor air. The design humidification load for infiltration and ventilation is 6.5 Lb/Hr. The duct runs are in a vented attic, and 1,400 Cfm flows through the duct system. The supply-side surface area is 255 SqFt and the return-side surface area is 175 SqFt. Humidification loads are compared for ducts that are exceptionally tight (0.06/0.06 Cfm/SqFt), default sealed (0.12/0.24 Cfm/SqFt), and default unsealed (0.35/0.70 Cfm/SqFt).
224
Figure 27-5 shows the solutions for the first iteration and for the second and final iteration. Note that the humidification load is very sensitive to duct leakage (and much less sensitive to the iteration). Duct Leakage Loads -- Iteration 1 6.5 Lb Water per Hr for Infiltration and Ventilation Sealed 0.06/0.06
Sealed 0.12/0.24
Unsealed 0.37/0.70
Supply Btuh
Return Btuh
Supply Btuh
Return Btuh
Supply Btuh
Return Btuh
367
201
734
803
2,142
2,341
Duct System Btuh
Duct System Btuh
Duct System Btuh
568
1,537
4,483
Duct System Lb/Hr
Duct System Lb/Hr
Duct System Lb/Hr
0.54
1.46
4.25
Duct Leakage Loads -- Iteration 2 Lb Water per Hr for Infiltration, Ventilation and Duct Leakage 7.04
7.96
10.75
Sealed 0.06/0.06
Sealed 0.12/0.24
Unsealed 0.37/0.70
Supply Btuh
Return Btuh
373
201
Supply Btuh
Return Btuh
768
803
Supply Btuh
Return Btuh
2,428
2,341
Duct System Btuh
Duct System Btuh
Duct System Btuh
574
1,571
4,769
Duct System Lb/Hr
Duct System Lb/Hr
Duct System Lb/Hr
0.54
1.49
4.52
Total Humidification Load (Lb/Hr) Sealed 0.06/0.06
Sealed 0.12/0.24
Unsealed 0.37/0.70
7.04
7.99
11.02
Figure 27-5
Section 28
Moisture Migration Load Procedure Moisture migration can have a significant affect on the latent cooling load and the winter humidification load. In addition, it can cause concealed condensation with attendant mold and mildew or structural damage problems.
28-1 Moisture Migration for Cooling Moisture migrates through permeable building materials (structural panels) when there is a difference in the moisture content (vapor pressure) of the air that is in contact with each side of the material. This flow of water vapor produces a latent moisture migration load (MML) on cooling equipment during the cooling season. This load shall be evaluated when one or more of the dwelling's opaque panels (ceilings, walls and exposed floors) has permeable construction that is not protected by a vapor retarding membrane..
28-2 Moisture Migration Load The (latent) moisture migration load depends on the permanence (Perm) of the material in Btuh per 100 SqFt per grains difference units, the net panel surface area (NA) in SqFt, and the grains difference across the panel. Refer to Table 13 for permanence values that are compatible with this equation and the Table 1 grains difference value for the site location. MML (Btuh) = Permanence x Grains Difference value x NA / 100 (SqFt) Where: Permanence = Btuh / (100 SqFt ´ Grain Difference) Table 1A or 1B provides the grains difference value for cooling Table 12 provides the grains difference value for winter humidification NA (SqFt) = Net area of the permeable surface (gross area minus fenestration area)
28-3 Perm Unit Conversion Handbooks may list material Perm ratings in Grains/(HR´SqFt´InHg) units (grains of moisture flow per hour, per square foot of surface area, per inches of mercury pressure difference). Such values are approximately converted to Btuh/(100 SqFt´Grain Difference) units (Btu per hour per 100 square feet of surface area per Table 1 grains difference) by dividing the handbook value by 10.0. For example, a handbook value of 50.0 Grains/(HR´SqFt´InHg) converts to 5.0 Btuh/(100 SqFt´ Grain Difference).
28-4 Perm-Permeability Conversions Permanence [Grains/(HR´SqFt´InHg)] is for the listed thickness of a material (i.e. less or more than one inch). Permeability [Grains/(HR´SqFt´InHg)/In] is for one inch of material. Use the following equations to convert a Perm or Permeability rating to a Perm rating for a desired thickness. Perm for desired thickness = Permeability for one inch / Inches of thickness Perm for desired thickness = Perm for listed thickness x (Listed thickness / Desired thickness)
Example A dwelling in Charleston, SC has a 2,000 SqFt gypsum board ceiling that is 5/8 of an inch thick. The ceiling is covered by blanket insulation that has negligible resistance to moisture migration. There is no vapor retarding membrane. The perm value for a 3/8 inch thick gypsum board is 5.0 Btuh/(100 SqFt´Grain Difference). For 50% RH indoor humidity, the Table 1 grains difference value is 54. The latent load is 3,305 Btuh MML = 5.0 x (0.375 / 0.625) x 54 x (2000 /100) = 3,305 Btuh
28-5 Altitude Effect The 10.0 conversion factor for handbook Perm ratings (see Section 28-3) is for sea level. This value increases somewhat with altitude, but this effect is relatively small, and may be ignored. n
n
A latent cooling load is not an issue for higher elevations (see the Table 1 grains difference values). A winter humidification load is a design possibility for any elevation.
28-6 Moisture Migration for Heating The moisture migration equation (see Section 28-2) applies to winter humidification (latent loss), but this calculation is not needed for approved construction (see Section 28-7). For unapproved construction, the moisture migration load (MML) is evaluated by using Table 12 to obtain a grains difference value for the winter design condition and the site elevation (or use altitude sensitive psychometric software)
28-7 Approved Construction Cold climate and balanced climate dwellings normally have a vapor retarding material near the inside surface of the panels that define the envelope of the conditioned 225
Table 1
Table 1A Outdoor Design Conditions for the United States Location
Elevation Latitude
Winter
Summer
Feet
Degrees North
Heating 99% Dry Bulb
Cooling 1% Dry Bulb
Coincident Wet Bulb
Design Grains 55% RH
Design Grains 50% RH
Design Grains 45% RH
Daily Range (DR)
Alexander City
686
33
22
93
76
39
46
52
M
Anniston AP
612
33
24
93
76
39
46
52
M
Auburn
776
32
22
93
76
39
46
52
M
Birmingham AP
644
33
23
92
75
34
41
47
M
Decatur
592
34
16
93
74
27
34
40
M
Dothan AP
401
31
32
93
76
39
46
52
M
Florence AP
581
34
21
94
75
31
38
44
M
Gadsden
569
34
20
94
75
31
38
44
M
Huntsville AP
629
34
20
92
74
28
35
41
M
Mobile AP
218
30
30
92
76
41
48
54
M
Mobile CO
26
30
29
93
77
46
53
59
M
Montgomery AP
221
32
27
93
76
39
46
52
M
Ozark, Fort Rucker
356
31
31
94
77
44
51
57
M
Selma-Craig AFB
166
32
26
95
77
42
49
55
M
Talladega
528
33
22
94
76
37
44
50
M
Tuscaloosa AP
170
33
24
94
77
44
51
57
M
Adak, NAS
19
52
23
57
53
-18
-11
-5
L
Anchorage IAP
144
61
-9
68
57
-20
-13
-7
L
Anchorage, Elemendorf AFB
212
61
-8
69
57
-21
-14
-8
L
Anchorage, Fort Richardson
342
61
-13
71
58
-20
-13
-7
M
Annette
110
55
17
70
59
-14
-7
-1
L
Barrow
44
71
- 36
52
49
-25
-18
-12
L
Bethel
123
61
-24
68
57
-20
-13
-7
M
Bettles
643
67
-44
75
59
-22
-15
-9
M
Big Delta, Ft. Greely
1277
64
-39
75
58
-27
-20
-14
M
Cold Bay
98
55
10
57
53
-18
-11
-5
L
Cordova
42
60
1
67
57
-18
-11
-5
M
Alabama
Alaska
Deadhorse
61
70
-34
61
54
-21
-14
-8
M
Dillingham
86
59
-13
66
56
-21
-14
-8
M
Fairbanks IAP
434
64
-41
77
59
-26
-19
-13
M
Fairbanks, Eielson AFB
545
64
-31
78
60
-23
-16
-10
M
Galena
152
64
-31
74
59
-21
-14
-8
M
Gulkana
1579
62
-39
73
56
-32
-25
-19
M
Homer
78
59
4
62
55
-18
-11
-5
L
Juneau IAP
19
58
7
69
58
-17
-10
-4
L
Kenai
92
60
-14
65
55
-23
-16
-10
M
Ketchikan IAP
88
55
20
68
59
-11
-4
2
L
King Salmon
57
58
-19
67
56
-22
-15
-9
M
Kodiak
73
57
12
65
56
-19
-12
-6
L
Kotzebue
11
66
-31
64
58
-9
-2
4
L
McGrath
337
62
-42
73
58
-23
-16
-10
M
Middleton Island
87
59
21
60
51
-31
-24
-18
L
Nenana
362
64
-44
76
59
-24
-17
-11
M
Nome AP
37
64
-26
65
55
-23
-16
-10
L
Northway
1716
62
-32
74
57
-29
-22
-16
M
Port Heiden
105
56
-2
61
52
-29
-22
-16
L
Saint Paul Island
63
57
3
52
50
-22
-15
-9
L
Sitka
21
57
21
64
58
-9
-2
4
L
Talkeetna
358
62
-21
73
58
-23
-16
-10
M
Valdez
120
61
7
66
55
-25
-18
-12
L
Yakutat
33
59
2
63
55
-20
-13
-7
L
225
Table 1
Table 1A Outdoor Design Conditions for the United States Location
Elevation Latitude
Winter
Summer
Feet
Degrees North
Heating 99% Dry Bulb
Cooling 1% Dry Bulb
Coincident Wet Bulb
Design Grains 55% RH
Douglas AP
4173
31
31
95
63
-34
Flagstaff Ap
7011
35
8
83
55
-54
Fort Huachuca AP
4716
31
28
92
62
-34
Kingman AP
3446
35
27
97
63
Nogalas
3932
31
32
96
64
Page
4310
36
24
97
62
Design Grains 50% RH
Design Grains 45% RH
Daily Range (DR)
-27
-21
H
-47
-41
H
-27
-21
H
-38
-31
-25
H
-32
-25
-19
H
-43
-36
-30
H
Arizona
Phoenix AP
1133
33
37
108
70
-21
-14
-8
H
Phoenix, Luke AFB
1101
33
38
107
71
-14
-7
-1
H
Prescott AP
5042
34
20
91
60
-42
-35
-29
H
Safford, Agri. Center
3176
32
26
99
66
-25
-18
-12
H
Tuscon Ap
2641
32
24
103
66
-39
-30
-24
H
Winslow AP
4938
35
14
93
60
-46
-39
-33
H
Yuma AP
213
32
44
109
72
-15
-8
-2
H
Blytheville AFB
264
36
18
95
77
42
49
55
M
Camden
130
33
23
96
76
34
41
47
M
El Dorado AP
277
33
23
96
76
34
41
47
M
Fayetteville AP
1251
36
13
93
75
33
40
46
M
Fort Smith AP
469
35
19
96
76
34
41
47
M
Hot Springs
540
34
23
97
77
39
46
52
M
Jonesboro
262
35
15
94
77
44
51
57
M
Little Rock AP
260
34
21
95
77
42
49
55
M
Pine Bluff AP
206
34
22
97
77
39
46
52
M
Texarkana AP
389
33
25
95
77
42
49
55
M
Alameda, NAS
15
37
42
79
64
-6
1
7
M
Bakersfield AP
507
35
35
101
69
-15
-8
-2
H
Barstow
1927
34
32
105
67
-32
-25
-19
H
Blue Canyon
5280
39
24
81
57
-41
-34
-28
M
Blythe AP
397
33
33
110
71
-18
-11
-5
H
Burbank AP
775
34
41
95
69
-6
1
7
M
Chico
238
39
30
101
68
-22
-15
-9
H
Concord
23
38
27
97
68
-14
-7
-1
H
Covina
575
34
35
95
68
-11
-5
2
H
Crescent City AP
57
41
33
65
59
-6
1
7
M M
Arkansas
California
Downey
110
34
40
89
70
9
15
22
El Cajon
387
32
44
80
69
19
26
32
H
El Centro AP
-30
32
38
110
74
-3
4
10
H
Escondido
660
33
41
85
68
5
12
18
H
Eureaka/Arcata AP
217
41
32
67
59
-10
-3
3
L
Fairfield-Travis AFB
62
38
34
94
67
-15
-8
-2
H
Fresno AP
328
36
32
101
70
-10
-3
3
H
3
38
32
84
66
-4
3
9
H
Laguna Beach
35
33
43
80
68
0
3
6
M
Lemoore, Reeves NAS
237
36
32
101
71
-4
3
9
H
Livermore
500
37
27
97
68
-14
-7
-1
M
Lompoc, Vandenburg AFB
87
34
38
70
61
-5
2
8
M
Long Beach AP
30
33
43
88
67
-5
2
8
M
Los Angeles AP
97
34
45
81
64
-9
-2
8
L
Los Angeles CO
270
34
40
89
70
10
17
23
M
Marysville, Beale AFB
119
39
34
98
69
-10
-3
3
H
Hamiltion AFB
226
Table 1
Table 1A Outdoor Design Conditions for the United States Location
Elevation Latitude
Winter
Summer
Feet
Degrees North
Heating 99% Dry Bulb
Cooling 1% Dry Bulb
Coincident Wet Bulb
Design Grains 55% RH
Design Grains 50% RH
Design Grains 45% RH
Daily Range (DR)
St. Augustine
10
29
35
89
78
59
66
72
M
St. Petersburg
11
28
47
93
79
59
66
72
M
Sanford
55
28
38
93
76
39
46
52
M
Sarasota/Bradenton
30
27
43
92
79
61
68
74
M
Tallahassee AP
55
30
28
93
76
39
46
52
M
Tampa AP
19
28
40
91
77
49
56
62
M
Valpariso, Eglin AFB
85
30
33
90
78
57
64
70
M
Vero Beach
13
27
43
90
78
57
64
70
M
West Palm Beach AP
15
26
47
90
78
57
64
70
M
Albany, Turner AFB
223
31
30
95
76
49
56
62
M
Americus
466
32
25
94
76
37
44
50
M
Athens
802
34
25
92
75
34
41
47
M
Atlanta AP
1010
33
23
91
74
30
37
43
M M
Georgia
Augusta AP
148
33
25
94
76
37
44
50
Brunswick
20
31
34
91
79
62
69
75
M
Columbus, Fort Benning
232
32
27
94
76
37
44
50
M
Columbus, Lawson AFB
971
32
24
93
76
39
46
53
M
Columbus, Metro AP
397
32
27
93
75
33
40
46
M
Dalton
710
34
22
93
76
39
46
52
M
Dublin
310
32
25
93
76
39
46
52
M
Gainesville
1275
34
21
91
74
30
37
43
M
Griffin
980
33
22
90
75
38
45
51
M
La Grange
693
33
23
91
75
36
43
49
M
Macon AP
354
32
27
94
75
31
38
44
M
Marietta, Dobbins AFB
1068
34
26
91
74
30
37
43
M
Moultrie
292
31
30
95
77
42
49
55
M
Rome AP
637
34
21
94
74
25
32
38
M
Savannah, Travis AP
49
32
29
93
76
39
46
52
M
Valdosta, Moody AFB
233
31
34
94
77
44
51
57
M
Valdosta, Regional AP
203
30
31
94
76
37
44
50
M
Waycross
151
31
32
94
76
37
44
50
M
Ewa, Barbers Point NAS
34
21
61
90
72
19
26
32
M
Hilo AP
36
19
63
84
74
41
48
54
L
Honolulu AP
16
21
63
88
73
29
36
42
L
Kahului
56
20
61
88
74
35
42
48
M
Kaneohe Bay MCAS
18
21
68
85
74
40
47
53
L
Lihue
148
21
62
85
74
40
47
53
L
Molokai
449
21
61
87
73
30
37
43
M
Wahaiwa
900
21
59
85
72
28
35
41
L
Hawaii
Idaho Boise AP
2838
43
9
94
63
-34
-27
-21
H
Burley
4150
42
2
90
62
-22
-15
-9
H
Coeur D’Alene AP
2320
47
-1
86
61
-30
-23
-17
H
Idaho Falls AP
4741
43
-6
89
60
-39
-32
-26
H
Kamiah
1196
46
15
93
64
-28
-21
-14
H
Lewiston AP
1413
46
15
93
64
-28
-21
-15
H
Moscow
2583
46
0
87
62
-27
-20
-13
H
Mountain Home AFB
2996
43
5
96
62
-42
-35
-29
H
Mullan
3317
47
7
84
61
-27
-20
-14
H
229
Table 4A
Table 4A Heating and Cooling Performance for Opaque Panels U-Values and Group Numbers or CLTD Values Heating Application
Heating Load HTM = U-Value x (Indoor Design Temperature - Outdoor Design Temperature) Heating Load (Btuh) = HTM x Reference Area Default indoor design temperature = 70 °F. Outdoor design temperature provided by Table 1. Reference area provided with construction number. Heating Exceptions Number 15 — Basement walls may be partly above grade and partly below grade: Below Grade Heating HTM = Below Grade U-Value x HTD; Heating Load = HTM x Below Grade Wall Area Above Grade Heating HTM = Above Grade U-Value x HTD; Heating Load = HTM x Net Above Grade Wall Area Above Grade Cooling HTM = Above Grade U-Value x CLTD; Cooling Load = HTM x Net Above Grade Wall Area Number 19 — Passive or radiant floor over enclosed craw space: HTM = U-Value x Floor TD From Table 19 Number 20 — Radiant floor over open crawlspace: HTM = U-Value x (HTD + 25) Number 22 — Passive slab floor: HTM = F-Value x HTD; Heating Load = HTM x Running Feet of Exposed Edge Number 22 — Radiant slab floor: HTM = F-Value x (HTD + 25); Heating Load = HTM x Running Feet of Exposed Edge Table 4C — Partition wall for closed garage Table 4D — Partition wall for closed sunroom Table 4E — Ceiling below and encapsulated attic Cooling Application
Cooling HTM = U-Value x Table 4B CLTD Value Cooling Load (Btuh) = HTM x Reference Area Default indoor design temperature = 75 oF. Outdoor design temperature and daily range provided by Table 1. Design Temperature Difference = Outdoor Design Temperature - Indoor Design Temperature Use the CLTD provided by Table 4A or use the Table 4A group number and the Table 4B CLTD. Reference area provided with construction number. Cooling Excpetions Table 4C — Table 4D — Table 4E —
Partition wall for closed garage Partition wall for closed sunroom Ceiling below an encapsulated attic
Construction Number 11 Wood and Metal Doors Reference Area = Area of Rough Opening (SqFt)
Wood Door
U-Value
A. Hollow Core B. Hollow Core with Wood Storm C. Hollow Core with Metal Storm D. Solid Core E. Solid Core with Wood Storm F. Solid Core with Metal Storm G. Panel H. Panel with Wood Storm I. Panel with Metal Storm Metal Door
0.47 0.30 0.32 0.39 0.26 0.28 0.54 0.32 0.36 U-Value
J. K. L. M. N. O. P. Q.
Fiberglass Core Fiberglass Core with Storm Paper Honeycomb Core Paper Honeycomb Core, with Storm Polystyrene Core Polystyrene Core with Storm Polyurethane Core Polyurethane Core with Storm
0.60 0.36 0.56 0.34 0.35 0.21 0.29 0.17
CLTD Values Medium Color Wood or Metal Doors
L
10 M
L
15 M
H
L
20 M
H
M
25 H
30 H
35 H
25.0
21.0
30.0
26.0
21.0
35.0
31.0
26.0
36.0
31.0
36.0
41.0
Wood and metal doors do not have a group number.
309
Table 4A
Table 4A Heating and Cooling Performance for Opaque Panels U-Values and Group Numbers or CLTD Values
Construction Number 15 Basement Walls Block (open or filled core), brick, concrete, insulated concrete form and plywood panel Insulation options: None, closed cell foam board, framing with cavity insulation (blanket or fill) and board-cavity combinations Insulation coverage code: From sill plate to 3 feet below grade = s3, from sill plate to floor = sf Core condition code: oc = open core; fc = filled core Framing code: w = wood, m = metal (studs 16 Inches on center, 75% cavity, 25% framing) Soil path code: (for distance from grade line to basement floor): x = 2, 4, 6, 8 or 10 feet A foundation wall that drops from grade to a floor that is at least 2 feet below grade is a below grade wall. Below Grade Reference Area = Distance From Grade To Floor x Length A foundation wall that is less than 2 feet below grade is part of the above grade wall (add below grade height to above grade height). Above Grade Reference Area = (Effective Above Grade Height x Length) - Area of Window and Door Openings Construction Description of Number Construction
Insulation R-Value and Coverage
Type of Stud
Below Grade Wall Performance U-Value for Basement Floor Depth 2’
Above Grade Performance
4’
6’
8’
10’
U
Group
15B Eight Inch Brick, Stone or Concrete Wall with Framing and Cavity Insulation 15B11-0w-x 15B11-0m-x 15B13-0w-x 15B13-0m-x 15B15-0w-x 15B15-0m-x 15B19-0w-x 15B19-0m-x 15B21-0w-x 15B21-0m-x
Eight inches brick or stone, framing with R-11 in 2 x 4 cavity, no board insulation, plus interior finish Eight inches brick or stone, framing with R-13 in 2 x 4 cavity, no board insulation, plus interior finish Eight inches brick or stone, framing with R-15 in 2 x 4 cavity, no board insulation, plus interior finish Eight inches brick or stone, framing with R-19 in 2 x 6 cavity, no board insulation, plus interior finish Eight inches brick or stone, framing with R-21 in 2 x 6 cavity, no board insulation, plus interior finish
R-11 cavity sill to floor
R-13 cavity sill to floor
R-15 cavity sill to floor
R-19 cavity sill to floor
R-21 cavity sill to floor
Wood
0.071
0.062
0.056
0.051
0.047
0.099
J
Metal
0.087
0.074
0.065
0.059
0.054
0.125
J
Wood
0.068
0.059
0.053
0.049
0.045
0.093
K
Metal
0.083
0.071
0.063
0.057
0.052
0.118
K
Wood
0.065
0.057
0.051
0.047
0.043
0.088
K
Metal
0.079
0.068
0.061
0.055
0.050
0.112
K
Wood
0.052
0.047
0.043
0.040
0.037
0.069
K
Metal
0.075
0.065
0.058
0.053
0.048
0.105
K
Wood
0.051
0.046
0.042
0.039
0.036
0.067
K
Metal
0.073
0.064
0.057
0.052
0.048
0.102
K
15B Eight Inch Brick, Stone or Concrete Wall with Framing and Cavity Insulation Plus Board Insulation 15B11-4w-x 15B11-4m-x 15B11-8w-x 15B11-8m-x 15B13-4w-x 15B13-4m-x 15B13-8w-x 15B13-8m-x 15B19-4w-x 15B19-4m-x 15B19-8w-x 15B19-8m-x
Eight inches brick or stone, framing with R-11 in 2 x 4 cavity, R-4 board insulation, plus interior finish Eight inches brick or stone, framing with R-11 in 2 x 4 cavity, R-8 board insulation, plus interior finish Eight inches brick or stone, framing with R-13 in 2 x 4 cavity, R-4 board insulation, plus interior finish Eight inches brick or stone, framing with R-13 in 2 x 4 cavity, R-8 board insulation, plus interior finish Eight inches brick or stone, framing with R-19 in 2 x 6 cavity, R-4 board insulation, plus interior finish Eight inches brick or stone, framing with R-19 in 2 x 6 cavity, R-8 board insulation, plus interior finish
R-11 cavity sill to floor, plus 3 feet R-4 board
Wood
0.053
0.050
0.048
0.045
0.042
0.071
K
Metal
0.062
0.058
0.054
0.051
0.047
0.083
K
0.043
0.043
0.043
0.041
0.039
0.055
K
0.048
0.048
0.048
0.046
0.043
0.063
K
0.051
0.048
0.046
0.043
0.041
0.068
K
0.059
0.056
0.053
0.049
0.046
0.080
K
R-11 cavity sill to floor, plus 3 feet R-8 board
Wood Metal
R-13 cavity sill to floor, plus 3 feet R-4 board
Wood Metal
R-13 cavity sill to floor, plus 3 feet R-8 board
Wood
0.041
0.042
0.042
0.040
0.038
0.053
K
Metal
0.046
0.047
0.047
0.045
0.042
0.061
K
R-19 cavity sill to floor, plus 3 feet R-4 board
Wood
0.042
0.040
0.038
0.036
0.034
0.054
K
Metal
0.055
0.052
0.049
0.046
0.043
0.074
K
R-19 cavity sill to floor, plus 3 feet R-8 board
Wood
0.035
0.035
0.035
0.034
0.032
0.044
K
Metal
0.044
0.044
0.044
0.042
0.040
0.057
K
321
Table 4A
Table 4A Heating and Cooling Performance for Opaque Panels U-Values and Group Numbers or CLTD Values
Construction Number 16A through 16F Insulated Ceiling Under Attic or Attic Knee Wall (see Table 4E for encapsulated attic) Ventilation options: Unvented or vented to FHA specifications, or attic fan, or extra attic vent area. Roofing material options: Asphalt shingles, wood shakes, tile, slate, metal, concrete, tar and gravel or membrane. Roof color options: Dark, red or solid bold color; light color, light gray, silver or unpainted metal and white (see absorptivity notes). Reference Area = Gross Area - Skylight Area (SqFt) Number 16A 16A-0 16A-7 16A-11
Construction Notes
Insulation R-Value
U-Value
CLTD Values Ceilings Under an Attic or Attic Knee Wall
Attic temperature = 150 °F when outdoor temperature = 95 °F Unvented Attic, No Radiant Barrier, Any Roofing Material, Any Roof Color 16A Unvented attic over ceiling or same type of air space behind an attic knee wall.
16A-13
None
0.408
R-7
0.112
R-11
0.081
R-13
0.070
Design Temperature Difference and Daily Range 10
15
20
L
M
H
L
M
H
M
H
H
H
69
65
74
70
65
79
75
70
80
75
80
85
30
35
R-15
0.061
16A-19
R-19
0.049
16A-21
R-21
0.044
16A Roofing material code: None required Roof color code: None required
16A-25
R-25
0.038
16A-28
R-28
0.034
16A-30
R-30
0.032
16A-38
R-38
0.026
16A-44
R-44
0.022
16A-56
R-56
0.018
16B-7 16B-11 16B-13 16B-15 16B-19 16B-21 16B-25
Attic temperature = 130 °F when outdoor temperature = 95 °F 16B = Vented Attic, No Radiant Barrier, Dark Asphalt Shingles or Dark Metal, Tar and Gravel or Membrane 16BR = Unvented Attic with Radiant Barrier, Any Roofing Material, Any Roof Color 16B FHA vented attic with no radiant barrier over ceiling or same type of air space behind an attic knee wall. 16BR Unvented attic with radiant barrier over ceiling or same type of air space behind an attic knee wall.
None
0.408
R-7
0.112
R-11
0.081
R-13
0.070
Design Temperature Difference and Daily Range 10
15
20
25
L
M
L
M
H
L
M
H
M
H
H
H
49
45
54
50
45
59
55
50
60
55
60
65
R-15
0.061
Roofs and ceilings do not have a group number.
R-19
0.049
R-21
0.044
16B Roofing code: a = asphalt shingles, m = metal, x = tar/gravel, z = membrane Roof color code: d = dark (absorptivity of roofing material exceeds 0.75) Red or solid bold color shingle = dark color
R-25
0.038
16B-28
R-28
0.034
16B-30
R-30
0.032
16B-38
R-38
0.026
16B-44
R-44
0.022
16B-50
R-50
0.020
16B-56
R-56
0.018
326
35
M
Roofs and ceilings do not have a group number.
16B-0
30
L
16A-15
16B 16BR
25
16BR Roof material code: None required Roof color code: None required
Table 4A
Table 4A Heating and Cooling Performance for Opaque Panels U-Values and Group Numbers or CLTD Values
Construction Number 16A through 16F Insulated Ceiling Under Attic or Attic Knee Wall (see Table 4E for encapsulated attic) Ventilation options: Unvented or vented to FHA specifications, or attic fan, or extra attic vent area. Roofing material options: Asphalt shingles, wood shakes, tile, slate, metal, concrete, tar and gravel or membrane. Roof color options: Dark, red or solid bold color; light color, light gray, silver or unpainted metal and white (see absorptivity notes). Reference Area = Gross Area - Skylight Area (SqFt) Number 16C 16CR
Construction Notes
Insulation R-Value
CLTD Values Ceilings Under an Attic or Attic Knee Wall
U-Value
Attic temperature = 120 oF when outdoor temperature = 95 oF 16C = Vented Attic, No Radiant Barrier, White or Light Color Shingles, Any Wood Shake, Light Metal, Tar and Gravel or Membrane 16CR = Vented Attic with Radiant Barrier; 16CF = Attic Fan; Dark Asphalt Shingles or Dark Metal, Tar and Gravel or Membrane 16C FHA vented attic with no radiant barrier over ceiling or same type of air space behind an attic knee wall.
None
0.408
R-7
0.112
R-11
0.081
L
M
L
M
H
L
M
H
M
R-13
0.070
39
35
44
40
35
49
45
40
50
16CR FHA vented attic with radiant barrier over ceiling or same type of air space behind an attic knee wall.
R-15
0.061
Roofs and ceilings do not have a group number.
R-19
0.049
R-21
0.044
R-25
0.038
16C Roofing code: a = shingles, w = shakes, m = metal, x = tar/gravel, z = membrane Roof color code: l = light (absorptivity of roofing material 0.50 to 0.75) Light gray shingle, unpainted metal or silver membrane = light color
16CF Dark roof, FHA vented attic with attic fan; or extra attic vent area.
R-28
0.034
R-30
0.032
R-38
0.026
16C-44
R-44
0.022
16C-50
R-50
0.020
R-56
0.018
16C-0 16C-7 16C-11 16C-13 16C-15 16C-19 16C-21 16C-25 16C-28 16C-30 16C-38
16B-56 16D 16DR
Design Temperature Difference and Daily Range 10
15
20
25
30
35
H
H
H
45
50
55
16CR or 16CF Roof material code: a = asphalt shingles, m = metal, x = tar/gravel, z = membrane Roof color code: d = dark (absorptivity of roofing material exceeds 0.75) Red or solid bold color shingle = dark color See glossary for definition: • Attic fan • Extra attic vent area
Attic Temperature = 110 oF when outdoor temperature = 95 oF 16DR = Vented Attic, No Radiant Barrier, Dark Tile, Slate or Concrete 16DR = Vented Attic with Radiant Barrier, White or Light Color Shingles; Any Wood Shake; Light Metal, Tar and Gravel or Membrane 16D FHA vented attic with no radiant barrier over ceiling or same type of air space behind an attic knee wall.
None
0.408
R-7
0.112
R-11
0.081
L
M
L
M
H
L
M
H
M
R-13
0.070
29
25
34
30
25
39
35
30
40
16DR FHA vented attic with radiant barrier over ceiling or same type of air space behind an attic knee wall.
R-15
0.061
Roofs and ceilings do not have a group number.
R-19
0.049
R-21
0.044
R-25
0.038
16D Roofing code: t = tile (terra cotta, slate or concrete) Roof color code: d = dark (absorptivity of roofing material exceeds 0.75) Red or solid bold color tile = dark color
16DF Light roof, FHA vented attic with attic fan; or extra attic vent area.
R-28
0.034
R-30
0.032
R-38
0.026
16C-44
R-44
0.022
16C-50
R-50
0.020
16D-0 16D-7 16D-11 16D-13 16D-15 16D-19 16D-21 16D-25 16D-28 16D-30 16D-38
Design Temperature Difference and Daily Range 10
15
20
25
30
35
H
H
H
35
40
45
16DR or 16DF Roofing code: a = shingles, w = shakes, m = metal, x = tar/gravel, z = membrane Roof color code: l = light (absorptivity of roofing material 0.50 to 0.75) Light gray shingle, unpainted metal or silver membrane = light color See glossary for definition: • Attic fan • Extra attic vent area
327
Table 4A
Table 4A Heating and Cooling Performance for Opaque Panels U-Values and Group Numbers or CLTD Values
Construction Number 16A through 16F Insulated Ceiling Under Attic or Attic Knee Wall (see Table 4E for encapsulated attic) Ventilation options: Unvented or vented to FHA specifications, or attic fan, or extra attic vent area. Roofing material options: Asphalt shingles, wood shakes, tile, slate, metal, concrete, tar and gravel or membrane. Roof color options: Dark, red or solid bold color; light color, light gray, silver or unpainted metal and white (see absorptivity notes). Reference Area = Gross Area - Skylight Area (SqFt) Number
16E 16ER
Construction Notes
Insulation R-Value
U-Value
CLTD Values Ceilings Under an Attic or Attic Knee Wall
Attic Temperature = 105 oF when outdoor temperature = 95 oF 16E = Vented Attic, No Radiant Barrier, Light Tile, Slate or Concrete 16ER = Vented Attic with Radiant Barrier, Dark Tile, Slate or Concrete 16E FHA vented attic with no radiant barrier over ceiling or same type of air space behind an attic knee wall.
None
0.408
R-7
0.112
R-11
0.081
R-13
0.070
16ER FHA vented attic with radiant barrier over ceiling or same type of air space behind an attic knee wall
R-15
0.061
Roofs and ceilings do not have a group number.
R-19
0.049
R-21
0.044
R-25
0.038
16E Roofing code: t = tile (terra cotta, slate or concrete) Roof color code: l = light Light gray tile = light color (absorptivity of roofing material 0.50 to 0.75)
16E-28
R-28
0.034
16E-30
R-30
0.032
16E-38
R-38
0.026
16E-44
R-44
0.22
R-50
0.20
16E-0 16E-7 16E-11 16E-13 16E-15 16E-19 16E-21 16E-25
16E-50 16F 16FR 16F-0 16F-7 16F-11 16F-13
Design Temperature Difference and Daily Range 10
15
20
25
30
35
L
M
L
M
H
L
M
H
M
H
H
H
24
20
29
25
20
34
30
25
35
30
35
40
16ER Roofing code: t = tile (terra cotta, slate or concrete) Roof color code: d = dark (absorptivity of roofing material exceeds 0.75) Red or solid bold color tile = dark color
Attic Temperature = 95 oF when outdoor temperature = 95 oF 16F = Vented Attic, No Radiant Barrier, White Tile, Slate or Concrete; White Metal or White Membrane 16FR = Vented Attic with Radiant Barrier, Light or White Tile, Slate or Concrete; White Metal or White Membrane 16F FHA vented attic with no radiant barrier over ceiling or same type of air space behind an attic knee wall.
None
0.408
R-7
0.112
R-11
0.081
R-13
0.070
Design Temperature Difference and Daily Range 10
15
20
25
30
35
L
M
L
M
H
L
M
H
M
H
H
H
14
10
19
15
10
24
20
15
25
20
25
30
R-15
0.061
Roofs and ceilings do not have a group number.
R-19
0.049
R-21
0.044
16F Roofing code: t = tile (terra cotta, slate or concrete), x = metal, z = membrane Roof color code: w = white (absorptivity of roofing less than 0.50)
R-25
0.038
16F-28
R-28
0.034
16F-30
R-30
0.032
16F-38
R-38
0.026
16F-44
R-44
0.022
16F-50
R-50
0.020
16F-15 16F-19 16F-21 16F-25
328
16FR FHA vented attic with radiant barrier over ceiling or same type of air space behind an attic knee wall
16FR Roofing code: t = tile (terra cotta, slate or concrete), x = metal, z = membrane Roof color code: l = light (absorptivity of roofing material 0.50 to 0.75) w = white (absorptivity of roofing material less than 0.50) Light Gray tile = light color
Table 4C
Table 4C Approximate Ambient Temperature in a Closed Garage The temperature rise values provided by Table 4C are approximations (see the table notes) that can be used to estimate partition heating load and cooling load for the listed scenarios. Rough estimates for ambient space temperatures are suitable for this task because partition loads are relatively small when compared to the total load. For example, if the partition load is 3 percent of the total load, a 20 percent error in the partition load translates to a less than 1 percent error in the total load. The temperature rise values for scenarios that are significantly different than the listed scenarios are provided by the heat balance procedure that appears in Section 18 of the unabridged version of Manual J. Garage 1: Two car garage, no significant glass area, one insulated partition wall, garage walls have no insulation, uninsulated garage ceiling under vented attic.
Ambient Temperature in Unconditioned Space Garage 1 Winter
Table 1A heating drybulb with no adjustment
Summer
Table 1A Daily Range Low
Medium
High
Table 1A cooling db + 22°F
Table 1A cooling db + 17°F
Table 1A cooling db + 12°F
Detail Used for Garage 1 Estimate Garage: Slab floor area: 22 Ft wide x 24 Ft deep Ceiling height = 8 Ft Exterior wall insulation: None Exterior finish: Brick, siding or stucco Interior finish: Plasterboard Glass in exterior walls: 0% to 5% of wall area Ceiling type: Below vented attic Attic roof: Dark asphalt shingles Ceiling insulation: None Ceiling finish: Plasterboard 20 Ft, uninsulated metal door Winter ACH = 1.0; Summer ACH = 0.5 Duct system regain: None Adjustment for vehicle cool-down: None
Partition: Wall area = 192 SqFt R-value of insulation: R-13 Finish: Plaster board on both sides Glass area: None Entrance door: Insignificant issue
Temperature rise values are daily averages. Hourly values may be larger or smaller.
Garage 2: Two car garage, no significant glass area, conditioned space above garage, insulated ceiling partition, one insulated partition wall, garage walls have no insulation. (Note: A conditioned space above a garage should be a separate zone.)
Ambient Temperature in Unconditioned Space Garage 2 Winter
Table 1A heating drybulb + 5 °F
Summer
Table 1A Daily Range Low Table 1A cooling db + 11°F
Medium
High
Table 1A cooling db + 6°F
Table 1A cooling db + 1°F
Detail Used for Garage 2 Estimate Garage: Slab floor area: 22 Ft wide x 24 Ft deep Ceiling height = 8 Ft Exterior wall insulation: None Exterior finish: Brick, siding or stucco Interior finish: Plasterboard Glass in exterior walls: 0% to 5% of wall area Ceiling type: Below vented attic Attic roof: Dark asphalt shingles Ceiling insulation: None Ceiling finish: Plasterboard 20 Ft, uninsulated metal door Winter ACH = 1.0; Summer ACH = 0.5 Duct system regain: None Adjustment for vehicle cool-down: None
Partitions: Ceiling area; R-value of ceiling insulation: R-19 Wall area = SqFt R-value of wall insulation: R-13 Finish: Plaster board on both sides Glass area: None Entrance door: Insignificant issue
Temperature rise values are daily averages. Hourly values may be larger or smaller.
349
Table 4D
Table 4D Approximate Ambient Temperature in an Isolated Sunroom
Sunroom 1: Primary exposure faces South, 24 Ft wide by 12 Ft deep, sunroom walls are 60 percent double-pane clear glass (no external or internal shade), sunroom walls and ceiling are insulated, one insulated partition wall with sliding glass door. Note: Sunrooms should be architecturally and mechanically isolated from the main living space. If conditioned, heating and cooling should be provided by a separate system.
Ambient Temperature in Unconditioned Space Sunroom 1 Winter
Table 1A heating drybulb with no adjustment
Summer
Table 1A Daily Range Low
Medium
High
Table 1A cooling + 27°F
Table 1A cooling db + 22°F
Table 1A cooling db + 17°F
Detail Used for Sunroom 1 Estimate Sunroom: Slab floor area: 24 Ft wide x 12 Ft deep Ceiling height = 8 Ft Exterior wall insulation: R-11 Exterior finish: Brick, siding or stucco Interior finish: Plasterboard Glass in exterior walls: 60 % of exposed wall area Type: Double-pane clear; wood frame, no shades Overhang adjustment: None Window position: Closed Ceiling type: Below vented truss space. Roof: Dark asphalt shingles Ceiling insulation: R-19 Ceiling finish: Plasterboard Winter ACH = 0.50; Summer ACH = 0.25
Partition: Gross wall area = 192 SqFt R-value of insulation: R-13 Finish: Plaster board on both sides Glass door area: 42 SqFt Type: Double-pane clear; wood frame Overhang: Shaded by sunroom ceiling Glass door is closed.
Temperature rise values are daily averages. Hourly values may be larger or smaller. Sun Room 2: Primary exposure faces South, 24 Ft wide by 12 Ft deep, sunroom walls are 60 percent spectrally-selective glass (no external or internal shade), sunroom walls and ceiling are insulated, one insulated partition wall with sliding glass door. Note: Sunrooms should be architecturally and mechanically isolated from the main living space. If conditioned, heating and cooling should be provided by a separate system.
Ambient Temperature in Unconditioned Space Sunroom 2 Winter
Table 1A heating drybulb with no adjustment
Summer
Table 1A Daily Range Low
Medium
High
Table 1A cooling db + 14°F
Table 1A cooling db + 9°F
Table 1A cooling db + 4°F
Detail Used for Sunroom 2 Estimate Sunroom: Slab floor area: 24 Ft wide x 12 Ft deep Ceiling height = 8 Ft Exterior wall insulation: R-11 Exterior finish: Brick, siding or stucco Interior finish: Plasterboard Glass in exterior walls: 60 % of exposed wall area Type: NFRC U = 0.30; SHGC = 0.45, no shades Overhang adjustment: None Window position: Closed Ceiling type: Below vented truss space Roof: Dark asphalt shingles Ceiling insulation: R-19 Ceiling finish: Plasterboard Winter ACH = 0.50; Summer ACH = 0.25
Partition: Gross wall area = 192 SqFt R-value of insulation: R-13 Finish: Plaster board on both sides Glass door area: 42 SqFt Type: NFRC U = 0.30; SHGC = 0.45 Overhang: Shaded by sunroom ceiling Glass door is closed.
Temperature rise values are daily averages. Hourly values may be larger or smaller.
350
Table 4E
Table 4E Approximate Ambient Temperature in an Encapsulated Attic
Encapsulated Attic: Attic space roof and gable ends sprayed with R-19 insulating foam. Attic space sealed (no vents, infiltration 0.15 ACH or less). Attic floor is uninsulated plasterboard (ceiling of conditioned space below the attic).
Ambient Temperature in Unconditioned Space Encapsulated Attic Winter
Table 1A Heating Drybulb (°F) -20
0
20
40
57°F
61°F
64°F
66°F
Summer
Table 1A Cooling Drybulb (°F) 85
95
105
115
78°F
79°F
80°F
81°F
Detail Used for Encapsulated Attic Estimate Attic: Attic floor area: 40 Ft wide x 60 Ft long Ridge height = 8 Ft Gable wall insulation: R-19 Gable wall finish: Brick, siding or stucco Ceiling type: Below encapsulated attic Attic roof: Dark asphalt shingles Attic roof insulation: R-19 Attic floor: See partition ceiling Winter ACH = 0.15 Summer ACH = 0.15 Duct system regain: None
Partition ceiling: Load area = 2,400 SqFt R-value of insulation: No insulation Finish: Plaster board
The ambient air condition depends on the actual construction details. Section 18-5 provides guidance for estimating the temperature of an unconditioned space (buffer zone). Tables 4E, 7M and 7N apply when the air condition in the actual space is similar (say ± 5 °F) to the Table 4E values.
Ceiling Load Calculation
Duct Loads
The ceiling below an encapsulated attic is a partition that separates a conditioned space from an unconditioned space. So, the ceiling load for heating depends on the U-value of the ceiling panel, on the partition temperature difference for heating (PTDH), and the ceiling area; and the ceiling load for cooling depends on the U-value of the ceiling panel, on the partition temperature difference for cooling (PTDC), and the ceiling area.
Table 4E shows that the ambient temperature in an encapsulated attic is benign and relatively constant for heating and cooling. Foam seals attic cracks, so attic humidity is similar to indoor humidity.
Heating Btuh = Uceiling x PTDH x Aceiling Cooling Btuh = Uceiling x PTDC x Aceiling
Tables 7M and 7N provide duct load factors and latent loads for ducts runs in an encapsulated attic. Comments on these tables are provided here. n n
Where: Uceiling = (Btuh/(SqFt x °F) Aceiling = SqFt
n
Table 4E provides default values for PTDH and PTDC. Or, use other values for PTDH and PTDC (calculated per Section 18-5, or measured on a design day).
n
Default U-value for 5/8" plasterboard and air films = 0.60 Or, use the U-value for the actual ceiling construction (plus air film resistance values for lower and upper sides).
n
Attic behavior should be similar to Table 4E. For heating, the ambient temperature is relatively steady as outdoor temperature increases, so the duct load is a lager portion of the total load as outdoor conditions moderate. For cooling, the ambient temperature is relatively steady as outdoor temperature decreases, so the sensible duct load is a lager portion of the total sensible load as outdoor conditions moderate. For cooling, the latent duct load is based on some envelope leakage (the grains difference for computing the duct load is 20% of the Table 1 value). Include a surface area adjustment when duct surface areas are known or estimated.
351
Table 7C-AE -- Trunk and Branch Supply System in 16B Attic, Return Riser In Floor to Ceiling Chase 7C-AE
Ambient drybulb temperature = Outdoor db + 11 (heating) and Outdoor db + 35 (cooling) Supply location = Core of floor plan, near airhandler Nominal return Cfm = Blower Cfm Return location = Floor of conditioned space Duct leakage Cfm per SqFt of duct surface area (supply / return) = 0.06/0.06; 0.09/0.15; 0.12/0.24; 0.24/0.47; 0.35/0.70 Duct wall insulation R-value = 2, 4, 6 and 8
Base Case Heat Loss Factor (BHLF) R6 Insulation, ASHRAE Sealed (Supply = 0.12, Return = 0.24) Square Feet of Floor Area OAT 1000 1500 2000 2500 3000 -10 0.138 0.157 0.176 0.195 0.217 0 0.131 0.145 0.164 0.184 0.199 10 0.118 0.133 0.148 0.166 0.188 20 0.111 0.122 0.138 0.150 0.170 30 0.098 0.119 0.129 0.141 0.153 40 0.085 0.103 0.120 0.135 0.148
R-Value Correction (WIF - Heat Loss)
R2 2.02
R4 1.28
Leakage Correction (LCF) for Heat Loss Leakage R2 R4 R6 0.06 / 0.06 0.87 0.83 0.78 0.09 / 0.15 0.92 0.89 0.86 0.12 / 0.24 1.00 1.00 1.00 0.24 / 0.47 1.40 1.56 1.68 0.35 / 0.70 1.84 2.21 2.47
R6 1.00
R8 0.84
R8 0.75 0.86 1.00 1.81 2.76
Base Case Sensible Gain Factor (BSGF) R6 Insulation, ASHRAE Sealed (Supply = 0.12, Return = 0.24)
OAT 85 90 95 100 105
1000 0.137 0.146 0.157 0.158 0.160
R-Value Correction (WIF - Sensible Gain)
Square Feet of Floor Area 1500 2000 2500 0.170 0.200 0.220 0.161 0.203 0.220 0.175 0.203 0.220 0.180 0.203 0.220 0.185 0.207 0.224
3000 0.240 0.240 0.240 0.247 0.252
R2 2.19
R8 0.80
R6 1.00
Leakage Correction (LCF) for Sensible Gain Leakage R2 R4 R6 0.06 / 0.06 0.90 0.85 0.80 0.09 / 0.15 0.95 0.91 0.90 0.12 / 0.24 1.00 1.00 1.00 0.24 / 0.47 1.26 1.35 1.42 0.35 / 0.70 1.56 1.74 1.88
Default Duct Wall Surface Area (SqFt) Floor Area Look-Up Value 1000 SqFt 1500 SqFt 2000 SqFt 2500 SqFt Supply Return Supply Return Supply Return Supply Return 189 50 276 70 361 90 431 110 See Sections 6-8 and 23-6 for instruction for determing the floor area look-up value.
3000 SqFt Supply Return 481 120
Surface Area Adjustment Factor (SAA) for Heat Loss or Sensible Gain SAA = Ks x (Actual supply area / Default supply area) + Kr x (Actual return area / Default return area) Example: Floor area lookup value = 2,000 SqFt; duct leakage = 0.09 / 0.15; default areas = 361 and 9 SqFt. Actual system has 285 SqFt on supply side and 19 SqFt on return side Ks = 0.972, Kr = 0.028 SAA =0.972 x (285 / 361) + 0.028 x (19 / 9) = 0.826
Procedure for Heat Loss and Sensible Gain Factor Adjustment Step 1: Select the default heat loss factor or the default sensible gain factor. Step 2: Apply R-value correction to default value. Step 3: Apply leakage correction to Step 2 value. Step 4: Apply the surface area adjustment to the Step 3 value.
R4 1.30
R8 0.81 0.91 1.00 1.56 2.14
Base Case Latent Gain (BLG) R6 Insulation, ASHRAE Sealed (Supply = 0.12, Return = 0.24) Square Feet of Floor Area Grains 1000 1500 2000 2500 3000 10 111 166 214 264 297 20 157 234 303 373 420 30 205 306 395 487 549 40 255 280 492 606 683 50 307 458 592 730 823 60 361 639 697 859 968 70 417 624 806 994 1119
Leakage 0.06 / 0.06 0.09 / 0.15 0.12 / 0.24 0.24 / 0.47 0.35 / 0.70
Leakage Correction (LCF) for Latent Gain Any R-Value 0.28 0.62 1.00 2.81 4.88
Surface Area Factors Leakage Ks Kr 0.06 / 0.06 0.975 0.025 0.09 / 0.15 0.972 0.028 0.12 / 0.24 0.969 0.031 0.24 / 0.47 0.965 0.035 0.35 / 0.70 0.962 0.038
Surface Area Adjustment (SAA) for Latent Gain SAA = Actual return-side area / Default return-side area Example: Floor area lookup value = 2,000 SqFt; default duct surface areas = 229 and 51 SqFt. Actual system has 285 SqFt on supply side and 95 SqFt on return side SAA = 95 / 51 = 1.863
Procedure for Latent Gain Adjustment Step 1: Select the default latent gain factor. Step 2: Apply leakage correction to Step 1 value. Step 3: Apply surface area adjustment to the Step 2 value.
Notes 1) This table provides load factors for systems that features one large return because such designs are common (but not recommended by ACCA). 2) Multiple returns improve comfort and room air motion, stabilize room pressures and blower Cfm (as interior doors open and close) and reduce the noise level in the conditioned space. 3) The load factors in this table are compatible with duct systems that are designed according to Manual J , Manual S and Manual D procedures. 4) Duct systems designed by other procedures may not provide adequate air distribution (surface area adjustment does produce an acceptable duct load estimate for such systems). 5) ACCA recommends sealing duct systems that have leakage rates greater than the 0.12 / 0.24 scenario. Use the data for leakier scenarios to evaluate the benefit of the sealing work.
Table 7
Table 7 Summary of Duct Tables Location Unvented attic or attic knee wall space above 16A ceiling (150 °F attic when OAT = 95 °F). Vented attic or attic knee wall space above 16B ceiling (130 °F attic when OAT = 95 °F).
Supply System Geometry 1 Radial with outlets in center of rooms.
Trunk and branch with outlets in center of rooms. Radial with outlets at perimeter of rooms. Trunk and branch with outlets in center of rooms. Radial or trunk and branch with outlets at perimeter of rooms.
Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Single ceiling return close to air handler. Closet air handler, return in closet door. Grille at floor of conditioned space, return riser to attic air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial or trunk and branch, 400 CFM per return, returns close to air handler.
Radial or trunk and branch with outlets at perimeter of rooms. Trunk and branch with outlets at perimeter of rooms.
Radial or trunk and branch, 400 CFM per return, returns close to air handler. One or two floor returns, close to air handler.
Radial with outlets at room perimeter. No supply leakage. Sealing options apply to the return runs.
Return system in conditioned space. Radial system in attic, 400 CFM per return, returns close to air handler.
Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms. Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms. Radial with outlets in center of rooms.
Vented attic or attic knee wall space above 16C ceiling (120 °F attic when OAT = 95 °F). Vented attic or attic knee wall space above 16D ceiling (110 °F attic when OAT = 95 °F). Vented attic or attic knee wall space above 16E ceiling (105 oF attic when OAT = 95 °F). Vented attic or attic knee wall space above 16F ceiling (95 °F attic when OAT = 95 °F). Open crawl space or garage (95 °F ambient when OAT = 95 °F). Closed crawl space below insulated floor, no wall insulation. Unconditioned basement or closed crawl space with: a) No wall or ceiling insulation b) Wall insulation only c) Wall and ceiling insulation Supply runs below ground slab. Return runs in conditioned space or in attic. Riser or drop in exterior wall.
Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms. Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms. Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms. Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms.
Rectangular or round airway
Encapsulated attic
Radial with outlets in center of rooms.
On roof
Trunk and branch with outlets in center of rooms. Radial with outlets in center of rooms.
-1 = Reflective surface in sun -2 = White surface in sun -3 = Dark surface in sun -4 = Any surface in shade
Return System Geometry 1
Trunk and branch with outlets in center of rooms.
Table Number 7A-R 7A-T 7B-R 7B-T 7A-AE 7B-AE 7C-AE 7C-R 7C-T 7D-R 7D-T 7E-R 7E-T 7F-R 7F-T 7G-R 7G-T 7H 7I 7D-AE 7J-1 7J-2 7K 7L
Rectangular or round airway Radial, 400 CFM per return, returns close to air handler. Trunk and branch, 400 CFM per return, returns close to air handler. Radial, 1,000 CFM per return, returns close to air handler.
7O-1: 7O-2; 7O-3; 7O-4
Trunk and branch,1,000 CFM per return, returns close to air handler.
7P-1; 7P-2: 7P-3; 7P-4
7M 7N
1)
Floor plan size and duct system geometry determine the default heating cooling loads, the default blower Cfm, and the duct surface area defaults.
2)
Duct wall insulation R-values = R2, R4, R6 ord R8 (use "Powered by Manual J" software for R0).
3)
Duct leakage Cfm per SqFt or duct surface area (supply-side / return-side) = 0.06/0.06, 0.09/0.15, 0.12/0.24, 0.24/0.47 or 0.35/0.70.
4)
The default surface areas for these duct tables are compatible with systems designed by Manual D procedures.
5)
ACCA recommends sealing duct systems that have leakage rates greater than the 0.12/0.24 scenario. Use leakier scenarios to evaluate sealing benefit.
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Table 7
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Table 7
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Table 7
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Table 7
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Table 7
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Table 7
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Table 7
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Table 7
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Table 7
Table 7 Notes 1) The Table 7 load factors account for the conduction loads and leakage loads that occur on the supply and return sides of the duct system. These factors also include an adjustment for an increase or decrease in the envelope infiltration load (per a set of power law equations), depending on the relative amount of supply-side and return-side leakage. 2) The Table 7 data is compatible with duct systems that have dominant supply-side leakage (with the exception of return runs located in exterior walls). The load factors and latent load values are compatible with duct system surface areas generated by theManual D sizing pro- cedure and the five default leakage ratesprovided by Table 7. Computerized duct load solutions (models) are required for duct systems that have dominant return side leakage or a leakage rate that is substantially different than the default values. 3) The Table 7 heat loss factors depend on the temperature of the supply air. These factors tend to get smaller as the discharge temperature increases because (by the sensible heat equation) the supply CFM values and airway sizes (exposed area) get smaller as the supply temperature increases. Table 7 uses a 100 °F default for discharge temperature because it produces conservative duct load values and because the heat loss factors are compatible with airway sizes required for cooling. Computerized duct load solutions (models) are required for other supply air temperatures. 4) Table 7 produces values duct load values if a duct system installation is reasonably similar to one of the default scenarios. The Table 7 data is based on assumptions pertaining to the floor plan of the home, the location of the air handler, the number of supply runs, the number of the return runs and a set of leakage rate values. These assumptions are listed here. • Rectangular floor plan with a 2:1 aspect ratio. • Air handler located in the center of the floor plan. • One supply branch per 100 CFM of supply air. • One return branch per 400 CFM of return air (the four AE tables and the eight O and P tables are for 1,000 cfm per return). • Supply ducts not sealed (0.35 / .070 scenario) have 35 CFM of leakage per 100 SqFt duct surface area. • Return ducts not sealed (0.35 / .070 scenario) have 70 CFM of leakage per 100 SqFt duct surface area. • Supply ducts sealed (0.12 / 0.24 scenario) have 12 CFM of leakage per 100 SqFt duct surface area. • Return ducts sealed (0.12 / 0.24 scenario) have 24 CFM of leakage per 100 SqFt duct surface area. • Duct runs below slab have an average of 3 CFM leakage per 100 SqFt duct system surface area. (Duct runs below the slab have no leakage and are water tight. The leakage occurs along the above grade duct runs). • Table 4E provides default dry-bulb temperatures for the ambient air in an encapsulated attic; and the default for grains of moisture difference (for the attic air and return air) is 20% of the Table 1A or Table 1B value. • For heating, the default value for ambient dry-bulb temperature for duct on a roof equals the Table 1A or1B value. • For cooling, the default value for ambient dry-bulb temperature for duct on a roof depends on the color of the outside surface of the duct, and weather the duct is in the sun or shade.
a) For a reflective surface in the sun, the ambient dry-bulb equals the Table 1A or 1B dry-bulb plus 20°F. b) For a white or light surface in the sun, the ambient dry-bulb equals the Table 1A or 1B dry-bulb plus 35°F. c) For a black or dark surface in the sun, the ambient dry-bulb equals the Table 1A or 1B dry-bulb plus 65°F. d) For any surface in continuous shade, the ambient dry-bulb equals the Table 1A or 1B dry-bulb plus 10° • For cooling, the default value for grains of moisture difference (for the outdoor air and return air) is equal to the Table 1A or Table 1B value.
5) The average leakage rate for duct systems that are carefully sealed by approved methods may be substantial lower than the sealed leakage rates listed by the previous note. Performance should be certified by test or quality control program before taking credit for this type of sealing effort. 6) When using Table 7, use the load factors and latent gain values for unsealed duct systems ( 0.35 / .070 scenario) when duct tape is used to seal the leakage points. (Duct tape is not and approved sealing method. Sealing work must conform to industry standards.) 7) If a duct run is located in a garage, use Table 7G. If a duct run is located behind an attic knee wall or between the joists in a roof-ceiling sandwich, use Table 7A. 8) The Table 7 load factors are compatible with the ambient temperatures listed by Figure 23-6. If the load estimating software performs an energy balance on an unconditioned space, the estimated space temperature should be used to generate load factors for the duct runs that pass through the space (providing the software use the Manual J duct load model, see note 12). 9) Table 7 can be used to produce load factors and latent gain values for duct runs that pass through different types of spaces, and run segments that have different leakage rates and insulation R-values. See Worksheet G1. 10) When duct runs are in an exposed wall, the duct load factor for the riser or drop is added to the load value for the system (see Worksheet G1). This procedure applies to all the exposed-wall load factors (heating percentage, cooling percentage or latent load value.). Note that the load factor for a two-story riser or drop is twice the single-story value, etc..
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Appendix 1
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same with the J1AE form. Then repeat the process for Sections 8 and 9. Refer to Sections 3 and 6; and Appendices 4, 7, 8 and 9, as required. Learn to use the MJ8AE spreadsheet (redo the example dwellings in the book, or investigate a simple dwelling that is available for survey). Read Sections 2 and Appendix 6 internalize this guidance Go to Appendix 2 and read the capabilities and sensitivities material. Make sure that you understand the limitations of MJ8AE. Use advanced Manual J procedures for applications that are not compatible with MJ8AE. Read Appendix 3 and make sure you understand these concepts. Make sure you understand the limitations of MJ8AE. Use advanced Manual J procedures for applications that are not compatible with MJ8AE. Read the Introduction of this manual and internalize this guidance. Read Section 10 and acquire the necessary knowledge and skills. Pay particular attention to the error checking procedure.
A1-6 Expanding MJ8AE Capability The HTM x Load Area concept applies equally to MJ8AE and to Manual J . Therefore, HTM values for
constructions exclusively supported by advanced Manual J procedures can be imported to Form J1AE, or the MJ8AE spreadsheet. See advanced procedures for: n n n n n
More types of opaque panels (Table 4A) NFRC glass (Table 3D-1) Alternative infiltration load methods (Section 21) More internal load options (Tables 6A and 6B) More duct system options (Table 7)
Note 1: AED excursions are common, even for fenestration plans that seem to have begin attributes. The AE procedure will not be equivalent to the full procedure if the dwelling's AED excursion is greater than zero. There is no simple way to simulate the information provided by the AED curve, and no simple way to estimate the AED excursion value. Note 2: When using Manual J for attic duct systems, make sure the Table 4A construction number for the attic ceiling and the Table 7 option (7A through 7F) are compatible. Note 3: For duct loads, "Powered by Manual J" software can be used to evaluate the attributes of the "as-installed" system (user-specified R-values, sealing options and surface areas).
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Appendix 2
MJ8AE Capabilities and Sensitivities MJ8AE is an abridged version of the Eighth Edition of Manual J. As such, it introduces the procedures used to estimate residential heating and cooling loads. Mastery of the material in MJ8AE is a prerequisite for using the Eight Edition of Manual J. Mastery of the material in MJ8AE is a prerequisite for using third party software products that perform Manual J calculations. This presentation assumes the practitioner is acquainted (or will become familiar) with the basic principles of mathematics and heat transfer; and is conversant with Manual S, Manual D and Manual T design procedures.
A2-1 Limitations and Guidelines System design plays an important role in the comfort, health and safety of the occupants. MJ8AE may be used to estimate heating and cooling loads for residential applications that have these attributes. Architecture and Occupancy Single family detached dwellings shall have a normal amount of fenestration (total area of windows, glass doors and skylights shall not be more than 15 percent of the floor area). n
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Windows and glass doors shall be reasonably distributed around the dwelling. There shall be no large skylights in any room (skylight load area does not exceed 5% of room floor area). The dwelling shall have adequate exposure diversity (see Appendix 3). There shall be no excursion adjustment for the sensible fenestration load (see Appendix 3). Simple default values shall be used for the occupancy loads and appliance load. Use advanced Manual J procedures for applications that do not have these attributes.
Comfort System n A central, single-zone air system, or electric baseboard elements shall provide heat. n Cooling shall be provided by a central, singlezone, constant volume system. n Use advanced Manual J procedures for zoned systems, variable volume systems and distributed equipment. Windows and Glass Doors n Window and glass doors shall have clear (single, double or triple pane) glass.
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Window and glass door framing shall be metal, metal with break, wood or vinyl. Windows can have a fixed or operable sash (sliding glass doors have an operable sash). Windows and glass doors shall not be equipped with external sun screens. The foreground reflectance for window and glass door heat-gain shall be 0.20. Use advanced Manual J procedures for Fenestration rated by the NFRC, for other internal and external shading options, for other foreground reflectance options, and for latitude-adjusted HTM's for generic fenestration.
Skylights n Skylights shall have clear (single pane or double pane) glass. n Skylight glazing shall be flat. n Skylights shall not be equipped with a light shaft. n Use advanced Manual J procedures for Fenestration rated by the NFRC, for internal shading options, for curb and light-shaft options, and for latitude-adjusted HTM's for generic fenestration. Walls n Above grade wall construction shall be woodstud frame or empty-core block. n Exterior finish options shall be brick veneer or stucco/siding. n Interior finish shall default to gypsum board (i.e. plaster board, dry-wall, sheet rock, etc.) n Below grade wall construction shall default to empty-core block. n Block walls may have board insulation and/or wood-stud framing with blanket or fill insulation. n Use advanced Manual J procedures for other structural material options (logs, stress-skin foam, concrete-foam matrix, aerated concrete, brick, poured concrete), insulation arrangements and R-value options, block with filled cores, and metal studs. Ceilings and Attic Knee Walls n The ceiling options shall be attic ceiling, ceiling on exposed beams or joist ceiling sandwich. n The roofing material shall be dark-shingles. n The roof deck material shall be plywood for all types of roof construction. n Attic construction shall be FHA-vented with no radiant barrier or attic foam.
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Appendix 2 n
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Knee walls shall be installed in a FHA-vented attic space. Insulation shall be blanket and/or board or fill (as appropriate for the type of roof construction). Use advanced procedures for other types of roofing material, roof color, attic with radiant barrier, encapsulated foam, unvented attic or knee-wall space.
Floors n All floors shall be passive (no heating elements below the floor). n Floors over an open space shall have carpet or tile cover with floor insulation options. n Slab floors shall have vertical insulation that covers the edge, or no insulation. n Slab floor soil conditions may be heavy-moist; heavy-dry; light-wet; or light-dry. n Basement floors shall be uninsulated. n Use advanced Manual J procedures for radiant floors, other combinations of crawlspace tightness and wall R-value, insulated basement floor, and other slab insulation options. Infiltration n All infiltration estimates shall be based on the ACH values provided by Table 5A of MJ8AE. n Dwellings shall be rated: very-tight, semi-tight, average, semi-loose and loose (definitions are provided). n There shall be no space pressure adjustment for engineered ventilation (50 Cfm or less). n Infiltration induced or reduced by duct runs in an unconditioned space is evaluated by the duct-table factors. n Use Section 21 procedures to estimate infiltration rates (and loads) by blower door test or component leakage method, or to adjust infiltration rate for pressurization (or depressurization) caused by an engineered ventilation system. Duct System n A duct system shall be entirely in the conditioned space, or shall be compatible with one of the system scenarios in Figure 1-1 of Section 1. n Duct systems (trunks and runouts) shall be (essentially) installed in one horizontal plane. n Use the unabridged version of Table 7 for other locations and combinations of airway shape and system geometry. Engineered Ventilation n Engineered ventilation may be provided by piping a small amount (50 Cfm or less) of fresh air to the return-side of the duct system.
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The engineered ventilation system shall not have a heat recovery device or a ventilation dehumidifier. Use advanced Manual J applications for engineered ventilation systems and ventilating dehumidifer equipment.
Other Loads n Internal load (choice of two default values) n Blower heat (one default value) n Use Section 22 procedures for other internal load options (occupants, appliances, lighting, etc.), any blower motor power, winter humidification load, hot-water piping loss, and moisture migration load.
A2-2 Procedural Defaults Procedural complexity increases in proportion to sensitivity to variations in construction detail. Defaults simplify the procedure and make hand calculations possible. The defaults that apply to Manual J and MJ8AE are listed here. Design Conditions n Indoor: Heating = 70 °F db; Cooling = 75 °F db and 50% RH, unless superceded by code. n Outdoor: Use values in Table 1A unless superceded by code. Windows and Glass Doors n Purpose-built daylight windows and skylights shall have no internal shade. n All other windows and glass doors shall have internal shade. n The default assumption for internal shade is a medium-color blind with the slats at 45 degrees. n An overhang adjustment shall be applied to all windows and glass doors. n When available, use the actual overhang geometry or use the default geometry. n The default length of the overhang is one foot; the default height above the glazing is one foot. n The sensible cooling load adjustment for any type of insect screen shall be 0.90. n The heating load and sensible cooling load adjustment for a bay window shall be 1.15. n The heating load and sensible load adjustments for a garden window shall be 2.75 and 2.00. n The sensible cooling load adjustment for a French door shall be 0.70. Skylights n Curb construction shall default to (un-insulated) wood 2x4; four inches high. n Skylights shall not be equipped with an internal shade or light shaft.
Appendix 4 and latent capacity. Supply-side gains reduce the cooling capacity of the airflow delivered by the supply air outlets. Duct loads are caused by conduction through the duct wall and by leakage. Duct leakage also causes negative or positive pressure in the conditioned space. The space pressure condition depends on the difference between the return side leakage rate and the supply side leakage rate. If the return side leakage rate is greater than the supply side leakage rate, there is a net flow of air from outside the conditioned space to the conditioned space. This causes a positive pressure in the conditioned space, exfiltration from the conditioned space and a direct load on the central equipment (the air that leaks into the return duct passes through the central equipment before it enters the conditioned space). If the supply side leakage rate is greater than the return side leakage rate, the flow rate through the return grilles is greater than the flow rate through the supply outlets. This causes a negative pressure in the conditioned space, the infiltration to the conditioned space is increased and the load on the central equipment is larger. The heating and sensible cooling loads generated by duct systems are sensitive to a collection of parameters and interactions that include the piping geometry, the location of the duct runs, the temperature and moisture content of the air in the duct runs, the temperature and moisture content of the air in the surrounding environment, the tightness of seams and joints and the amount of duct-wall insulation. Duct loads also depend on the size of the dwelling and the construction details because equipment size, blower CFM, the size of the duct airways and the total surface area of the duct system depend on the size of the heating and cooling loads. An attic is a hostile environment for duct runs if attic temperature is significantly higher than the outdoor temperature in the summer (white shingles, tile roofs, radiant barriers and foam encapsilation moderate this condition); and almost as cold as the outdoor air in the winter. In addition, the absolute humidity in a properly vented attic is about the same as the outdoor humidity (the absolute humidity in a foam encapsulated attic will be closer to the conditioned space value). Open crawlspace locations are undesirable because there is little difference between the crawlspace condition and the condition of the outdoor air. Enclosed crawlspaces and unconditioned spaces represent environments that range from benign to hostile, depending on the ambient conditions in the space. Duct heat transfer to an unconditioned space can be significantly reduced if the surface area of the system is
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minimized. In this regard, research indicates that if the thermal envelope is efficient, an acceptable level of comfort is provided by an attic system that has a central air handler and short supply runs that feed diffusers located near the interior walls of the rooms. There are no duct loads when a duct system is installed within a conditioned space. The model used to generate the default duct factor tables applies to system designs that are compatible with the procedures documented in Manuals J, S and D. This is important because duct surface area estimates are based on the assumption that the blower CFM is compatible with the calculated loads and that the size of the duct airways are compatible with the blower performance and the total effective length of the duct system. In other words, the duct factor tables do not apply to heating and cooling systems that have been designed by whimsical guidelines and unreliable rules of thumb.
A4-30 Duct Sealing Information pertaining to duct construction and duct sealing is provided by other documents. A partial list of sources is presented below. n
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The North American Insulation Manufacturers Association (NAIMA). The Sheet Metal and Air Conditioning Contractors National Association (SMACNA). Underwriters Laboratories (UL-181 and UL-181A). Air Diffusion Council (ADC).
In some cases a duct sealing effort can create a health hazard that can cause discomfort, sickness or death. The most dangerous condition occurs when the sealing work creates a negative pressure condition that causes a combustion appliance to back draft. Other undesirable scenarios involve transfer of contaminated air from space to space, reduced ventilation rates and objectionable pressure conditions. Information about this subject is found in documents that pertain to duct testing and duct sealing. Also refer to the safety-test procedures in the appendices of ASHRAE Standard 62 and the National Fuel Gas Code.
A4-31 Blower Heat Most of the electric power delivered to a furnace or air handler blower is used to move a flow of air against the resistance of the duct system. Some of this resistance is generated as moving air rubs against a duct wall or any other surface (the blower vanes, the fins of a coil or the plates of a heat exchanger, for example), the remainder of the resistance is caused by turbulence produced by fittings and air-side devices. All of this resistance is
Appendix 5
A5-3 Indoor Design Conditions Heating and cooling load estimates shall be based on the indoor design conditions listed below. Use of this set of conditions is mandatory, unless superceded by a code, regulation or documented health requirement. n n n
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Indoor drybulb temperature for heating = 70°F Indoor drybulb temperature for cooling = 75°F Indoor relative humidity for a dry-coil (insignificant latent load) climate = 45% RH Preferred indoor relative humidity for a wet-coil (latent load climate) = 50% RH Acceptable indoor relative humidity for a large latent load application = 55% RH
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A5-4 Plans, Sketches and Notes When available, up-to-date floor plans, elevations and detail sheets define architectural geometry, establish orientations, provide dimensional information and specify construction detail. If a set of plans is not available or if the plans no longer represent conditions at the site, sketches of the existing construction are used to record the information required for the load estimate. These sketches are drawn to scale or accurate dimensions are added to drawings that are not to scale. Sketches also provide an efficient way to record the information that is read from a set of plans. The collection of sketches and notes shall provide the following information.
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Sketches based on plan take-off or field observation n n n
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An arrow or directional rosette that points north. A dimensioned outline of the floor plan for each level. The location of stairwells, partitions, chases and cavities. The length, width and height of every room with the room name. An alphanumeric code (WN-1, WN-2, etc.) next to each type of window or glass door. An alphanumeric code (S1, S2, etc.) next to each type of skylight. An alphanumeric code (DR-1, DR-2, etc.) next to each type of wood or metal door. An alphanumeric code (CL-1, WL-2, FL-1, etc.) next to each type of ceiling, wall or floor. Room assignments for occupants, appliances, lighting, plants and equipment.
Record observations pertaining to: n
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The type of ceiling, ceiling construction detail (preferably with a Manual J construction number and overall R-value), the ceiling height (at the wall
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or at the wall and ridge), the type of space that is above the ceiling (include detail that will help determine the temperature in enclosed, unconditioned spaces); the type of vapor retarder; the air leakage that might occur at hard-wired lighting fixtures and ceiling penetrations, and the quality of the sealing and caulking effort at the top plate. The use of a radiant barrier under an attic roof, or encapsulated foam attic (if applicable). Attic vent locations, vent areas and powered attic ventilation equipment. A record of the location, size and type of skylights (preferably, with a Manual J construction number). Wall construction detail (preferably with a Manual J construction number and overall R-value), wall heights, the type of space that is on the nonconditioned side of a partition (include detail that will help determine the temperature in enclosed, unconditioned spaces); the type of vapor retarder, the type of infiltration retarder, the potential for leakage around electrical outlets and wall penetrations, and the quality of the sealing and caulking effort at plates, headers, sills, band joists and rough openings. The location, type and size of the window and glassdoor assemblies and wood and metal door assemblies, with notes pertaining to U-values, SHGCs, construction details, bug screens, sun screens, projections and tightness. Internal and external shading devices and overhangs. The type of floor, floor construction details (preferably with a Manual J construction number and overall R-value), the type of space that is under the floor (include detail that will help determine the temperature in enclosed, unconditioned spaces); the type of vapor retarder, the leakage that might occur at floor penetrations, and the quality of the sealing and caulking effort. Observed pathways that connect the conditioned space with an attic space, stud space, chase, crawl space or basement. The location of the appliances, display lighting, ceiling fans, waterbeds or any equipment that generates internal loads. The location of vents and exhaust equipment, with observations pertaining to the use of back draft dampers. The location and type of combustion equipment and fireplaces, with notes pertaining to the source of combustion air, type of vent or chimney and the use of vent dampers.
The preceding list applies to load estimates, but there are other items that should be noted during the survey.
Appendix 5 (U-value and SHGC) for window assemblies and sliding glass door assemblies. Rated values are preferred because they eliminate uncertainty about window and glass door performance. When such information is not available, use the Table 2A values. Also record the following information: n n n n n n
n n n
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The direction the glass faces Type of window (see Figure A5-11) The number of lites (panes) in the assembly The type of glass used in the assembly The frame material Frame conduction path (thermal break or no thermal break) The use of a storm window The type and color of internal shading devices The shading coefficient of external shade screens (when applicable and available) The X and Y dimensions (see Table 3E-1) of external overhangs (when applicable)
In regard to opaque doors, record observations pertaining to style (see Figure A5-12), construction material (wood or metal) and insulation. If a door has a rating label, record the tested U-value.
Also evaluate the tightness of the window and door assemblies. Collect data pertaining to tested leakage ratings — as listed in the manufacturer’s performance data, documented by the NFRC directory or displayed on a performance label. If quantitative information is not available, make notes that summarize the findings of a site inspection. Also try to evaluate the seal between the structural framing and the frame of the window or door assembly. Ceilings Ceiling performance depends on the type of construction (attic, roof-ceiling sandwich or ceiling on exposed beams) and the construction details associated with the ceiling assembly (or attic knee wall). Ceiling and attic knee wall performance is also depends on the temperature in the attic, which depends on the roofing material, the roof color, the use of a radiant barrier or encapsulating foam, and the amount of attic ventilation. Such observations are used to select a construction number (see Table 4A), to evaluate structural tightness and to estimate resistance to moisture migration. Record the following information: n n n n n
Sliding Glass Door
n n n n n
n n n
French Door
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Type of construction (attic, beamed or roof-ceiling) Size and type of framing Primary insulating material (type and R-value) Secondary insulating material Overall R-value of the attic-ceiling, partition-ceiling or roof-ceiling assembly Type of roofing material (shingles or tile with air space) Long-term roof color and texture Details pertaining to attic ventilation The use of radiant barrier in attic (when applicable) Description of an unconditioned space above a ceiling Secondary insulation (sheathing material and R-value) Type and quality of vapor retarder Sealing effort at seams, light fixtures and penetrations Sealing effort at partitions, wall cavities, chases and stair wells
Skylights For generic skylights, use qualitative observations and Table 2A to determine the U-value, SHGC value. Use Table 3C for the cooling HTM value. Wood or Metal Panel Door
Figure A5-12
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Table 3D (-1 through -4) procedures apply to all types of skylights. Always try to obtain the NFRC rating (U-value and SHGC) for skylight assemblies. Rated values are preferred because they eliminate uncertainty about window and glass door performance. When such information is not available, use the Table 2A values. Also record the following information:
Appendix 10 Worksheet E Infiltration Loads HTD =
CTD =
Design Grains =
Elevation =
Table 10A ACF =
Step 1 — Table 8 Outdoor Air Requirement Operating Mode
Above Grade Volume AGV (CuFt)
Number of Bed Rooms
Number of People
Default Burner Btuh
Installed Burner Btuh
OA Cfm for 0.35 ACH
OA Cfm for People
OA Cfm for Furnace
Table 8 OA Cfm
Heat Cool AGV for each level = Floor area X Average ceiling height The above grade portion of a conditioned basement is one level. AGV = Total of the volumes for all levels Default Occupancy = Number of bedrooms + 1
Furnace input defaults: Direct Vent = 0 Btuh Atmospheric = 100,000 Btuh Recalculate, using actual input Btuh, if the total heating load exceeds 80,000 Btuh.
Cfm @ 0.35 = 0.35 x AGV / 60 Cfm for people = 20 x Number of people Cfm for Burner = 0.50 x Input Btuh / 1,000 Table 8 OA Cfm = Largest of the three Cfm values. Cfmoa determined by code requirement or designer decision to use the Table 8 OA Cfm value.
Step 2, Option 1 — Table 5 Defaults Operating Mode
Floor Area (SqFt)
Type of Const.
Space ACH
AGV (CuFt)
Space ICFM
Fireplace ICFM
Total ICFM
Table 8 OA CFM
(Note 1) (Note 2)
Table 8 Vent CFM
Heating Cooling 1) For default estimates use Table 5A or 5B to find ICFM values for the conditioned space and fireplace. 2) The component leakage area method or the blower door method may be used to estimate ICFM values.
Total ICFM = Space ICFM + FP ICFM Space ICFM = ACH x AGV / 60 Use the AGV from the Table 8 procedure.
T8 vent-CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 2, Option 2 — Component Leakage Area Method Operating Mode
HTD and CTD
Wind Velocity (MPH)
Table 5C ELA4 (SqIn)
Table 5D Cs
Shielding Class
ICFM
Table 8 OA CFM
Cw
Table 8 Vent CFM
Heating Cooling Default heating season velocity = 15 MPH Default cooling season velocity = 7.5 MPH
Detail from Worksheet E1
ICFM = ELA4 x ( Cs x TD + Cw x V2 ) 0.50
T8 vent CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 2, Option 3 — Blower Door Method Operating Mode
HTD and CTD
Wind Velocity (MPH)
Blower Door ELA4
Table 5D Cs
Shielding Class
ICFM
Table 8 OA-CFM
Cw
Table 8 Vent-CFM
Heating Cooling Default heating season velocity = 15 MPH Default cooling season velocity = 7.5 MPH
Provided by field test
ICFM = ELA4 x ( Cs x TD + Cw x V2 ) 0.50
T8 vent-CFM = T8 OA CFM - Cooling ICFM If cooling ICFMis greater than T8 OA CFM, the T8 vent CFM is zero.
Step 3 — Infiltration Loads on Central Equipment Type of Load Heat Load Sens Load
Wrksht. H Value for Vent CFM
Exhaust CFM
CFMimb
ICFM Net (Option __ ) Infilt. CFM NCFM
H&C Loads (Btuh)
CFMimb = CFM exhaust - CFMvent
The ± sign in the NCFM equation is determined by the sign of the Heat Load = 1.1 x ACF x NCFM x HTD CFMimb Sensible Load = 1.1 x ACF x NCFM x CTD value. Latent Load = 0.68 x ACF x NCFM x Grains
NCFM = (ICFM1.5± CFMimb1.5 ) 0.67 NCFM = 0 if (ICFM1.5 - CFMimb1.5) < 0
Lat Load The room infiltration load equals the load on the central equipment multiplied by the gross wall area ratio (WAR). WAR = Gross room wall area / Gross wall area for all rooms served by the central equipment
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Appendix 12 eight-hour period beginning at 11 am and ending at 7 pm, standard time. This aggregate value is used for all roof-ceiling construction, regardless of exposure direction or time of day.
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ASHRAE Base-Case CLTD Values for Ceilings (8 Hour Average) Group
2
These averaging rules are applied to five types of wood deck roofs (ASHRAE Group 2, 5, 7, 10 and 13). The resulting collection of 8-hour averages are summarized by Figure A12 -13. (This figure lists base-case CLTD values, which means they are compatible with a 20 oF temperature difference and a medium daily range.) The HTM value for a specific type of construction is obtained by multiplying the appropriate CLTD value by the panel U-value:
5 7 10 13 1)
Construction 1" wood, 1" Insulation 1" wood, 2" Insulation 2-1/2" wood, 1" Insulation 2-1/2" wood, 2" Insulation 4" wood, 2" Insulation
Roof Deck On Beams
Roof-Ceiling Sandwich
66
50
55
45
39
31
35
30
27
27
Outdoor = 95 °F, indoor = 75 °F, medium daily range.
Figure A12-13
HTMpanel = CLTD x Uceiling
Ceiling Under Attic The cooling load temperature difference for an attic ceiling panel depends on the attic temperature, which depends on the amount of insulation above the ceiling, the amount of attic ventilation, the use of a radiant barrier, encapsulating foam, attic fan, or extra attic vent area, and the type of roofing. Since the absorptivity and emittance of roofing products may not be known, roofing is classified by material (asphalt shingles, wood shakes, tile, slate, concrete, metal, membrane or tar and gravel) and color. The attic temperature also is affected by attic duct runs, but the temperature moderating effect is conditional, so it is (conservatively) ignored. Figure A12-14 (next page) summarizes the attic temperatures used to generate CLTD values for ceilings under an attic. These values are for the peak (late afternoon) load condition. They are used to estimate ceiling loads for all Manual J applications.
case CLTD values for this type of construction. These values represent the average ceiling load condition that occurs during the afternoon. They are used to estimate ceiling loads for all Manual J applications.
A12-15 Floor Over Enclosed Crawl Space For sensible cooling load estimates, Table 4A (construction 19) provides partition temperature difference (PTDC) values for floors over a tight, enclosed crawl space and for floors over a loose or vented crawl space. These temperature differences depend on the outdoor design temperature, the indoor design temperature, the tightness of the crawl space (sealed or loose or vented) and are estimated by performing an energy balance on the unconditioned crawl space. The following assumptions are used for this work. The resulting floor temperature difference equations are provided on the next page by Figure A12-17 (ahead two pages). n
Ceiling on Exposed Beams The cooling load temperature difference for a ceiling on exposed beams depends on the type of deck material, the thickness of the decking, the amount of insulation in the deck sandwich, the type of roofing and color. Figure A12-15 (ahead two pages) summarizes the base case CLTD values for deck-on-beam construction. These values represent the average ceiling load condition that occurs during the afternoon. They are used to estimate ceiling loads for all Manual J applications. Roof-Joist-Ceiling Sandwich T h e co o l i n g l o a d te m p e r a t u r e d i f f e r e n c e f o r roof-joist-ceiling sandwich depends on the type of deck material, the thickness of the decking, amount of insulation on the deck, the amount of insulation in the joist space, the ceiling material, the type of roofing and color. Figure A12-16 (ahead two pages) summarizes the base
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The heat transfer through below grade walls and the crawl space floor is ignored. Crawl space duct runs do not produce a regain effect. The floor area of a tight crawl space is 4 times larger than the crawl space wall area exposed to the outdoor air (assume the crawl space floor has a 2:1 aspect ratio and that it has three feet of exposed wall height). For tight construction, the conductive heat flow through the crawl space ceiling equals the conductive heat flow through the crawl space walls, as indicated here: (U x A x TD)ceiling = (U x A x TD)wall
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A loose or vented crawl space has 500 square feet of wall exposed to the outdoor air and 2,000 square feet of floor area.
