Chilled Water Plant Seminar - 04-2014

The PG&E Pacific Energy Center Presents:

Optimizing the Design and Control of Chilled Water Plants

Presented by:

Mark Hydeman Steve Taylor

Taylor Engineering LLC Alameda, CA http://www.taylor-engineering.com

April 3, 2014

Logistics Safety Restrooms Recycling Cell phone etiquette Lunch Review forms Webinar etiquette PG&E Resources

• • •

Rebates Tool Lending Library Marlene Vogelsang ([email protected]) 2

Handouts You can get a copy of the handouts in PDF format as follows:

• Type the following link into your web browser: http://www.taylorengineering.com/ftp/PECClassHandouts.html

• Click on the link for the Chilled Water Plant Class on 4/3/2014 to download the Acrobat file of the presentation.

3

About Mark Hydeman Founding Principal, Taylor Engineering Education

• •

Stanford University, BS General Engineering, 1982 Stanford University, MS Mechanical Engineering, 1983

ASHRAE

• • • • • • • •

Fellow Exceptional Service Award Standard 90.1 Energy Standard, two tours of duty, Vice-Chair Technical Committee 1.5, Computer Applications, Past Chair Technical Committee 9.9, Mission Critical Facilities Technical Committee 9.10, Laboratory Systems Electronic Communications Committee, Vice-Chair SPC 205, Vice Chair

Research

• • • • • •

Developed a simulation and assessment toolkit for data centers with LBNL Principal Investigator for NBI PIER project on Large HVAC System design Principal Investigator for ASHRAE RP 1455, Best of Class Control Sequences Developer of the Universal Translator Principal Investigator for the CoolTools™ Market Transformation Project PMSC Lead for ASHRAE Research on Humidity Control for Data Centers and Alternate Gas for Hood Testing (ASHRAE 110)

Other • Lead author of Title 24 HVAC compliance and acceptance requirements • Design and commissioning experience on dozens of chilled water plants

4

About Steve Taylor Principal, Taylor Engineering Education

• •

Stanford University, BS Physics, 1976 Stanford University, MS Mechanical Engineering, 1977

ASHRAE

• • • • • • • • • •

Fellow Standard 62 Indoor Air Quality, 8 years, chair Standard 90.1 Energy Standard, Chair HVAC Subc., 14 years Standard 55 Thermal Comfort Guideline 16 Economizer Dampers, chair Guideline 13 Specifying Direct Digital Control Systems, chair TC 4.3 Ventilation, vice-chair TC 1.4 Control Theory & Applications, chair Author “Fundamentals of Design and Control of Central Chilled Water Plants” Course Distinguished Lecturer

USGBC LEED

•

Indoor Environmental Quality TAG, vice chair

UMC/IAPMO (California Mechanical Code)

•

Mechanical Technical Committee, member and ASHRAE Liaison

CSU

•

Mechanical Review Board, member 5

Who are You? Consulting Engineers? Design/Build Engineers? Contractors? Energy/Green Building Consultants? Building Owners/Engineers? Equipment rep/supplier/manufacturer? Commissioning authority? Other? 6

Agenda Introduction CHW Distribution Systems Break CHW Distribution System Balancing CW Distribution Systems Lunch Selecting CHW Distribution Systems Selecting CHW ∆T Selecting CW ∆T Selecting Chillers Optimizing control sequences Questions Completion

9:00 AM 9:15 AM 10:45 AM 11:00 AM 11:45 AM 12:00 PM 1:00 PM 1:30 PM 2:00 PM 2:30 PM 3:00 PM 4:15 PM 4:30 PM

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Articles (1 of 2) Available at this URL: http://www.taylor-engineering.com/publications/articles.shtml

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Articles (2 of 2) Available at this URL: http://www.taylor-engineering.com/publications/articles.shtml

9

Design Guide and Tools Available at this URL: http://www.taylor-engineering.com/publications/design_guides.shtml

10

Design Guide Scope New Construction

• • • • •

Hydronic design Chiller selection Cooling tower selection Control optimizations Commissioning

Retrofit

• • • •

Replacement chillers Addition of VSDs Control optimization Commissioning

11

Optimizing Energy Usage Chillers

•

Type, efficiency, size, VSD

Cooling Towers

•

Fan type, efficiency, approach, range, speed control, flow turndown

Chilled Water Pumps

•

Arrangement, flow rate (delta-T), pressure drop, VSD

Condenser Water Pumps

•

Flow rate (delta-T), pressure drop

Air Handling Units

•

Coil sizing, air-side pressure drop, water-side pressure drop

12

Pop Quiz 1 What happens to component energy usage if we lower CWS setpoint?

• Chiller • Towers • Pumps

Pop Quiz 2 What happens to component energy usage if we lower CW flow?

• Chiller • Towers • Pumps

Pop Quiz 3 What happens to component energy usage if we lower CW flow AND the CWS setpoint?

• Chiller • Towers • Pumps

Optimizing CHW Plant Design Ideal: Design a plant with lowest life cycle costs (first cost plus lifelong operating costs) accounting for all the complexities and interaction among plant components Practical: Design plant subsystems to be near-life cycle cost optimum using techniques that are simple and practical enough to be used without a significant increase in design time

16

Chilled Water Distribution Systems

17

Water Distribution System Classes Constant Flow

• •

No control valves 3-way control valves

Variable Flow

• • • •

Primary-Only Primary/Secondary (/Tertiary) Primary/Distributed Secondary Primary/Variable Speed Coil Secondary

18

Constant Flow Single Chiller, Single Coil, No Control Valve SUPPLY WATER TEMPERATURE CHW PUMP CHILLER

SUPPLY AIR TEMPERATURE OPTIONAL STORAGE TANK COIL

Works also for boilers that have modulating burners and very good turndown, e.g. ≥10 to 1

19

Constant Flow Two Chillers, Single Coil, No Control Valve SUPPLY WATER TEMPERATURE

CHW PUMP CHILLER #2

CHILLER#1

VFD

SUPPLY AIR TEMPERATURE OPTIONAL STORAGE TANK COIL

20

“Constant” Flow 3-Way Valves

3-Way Mixing Valve

∆P

Bypass Balance Valve

Item

Pressure at constant flow Flow at constant Pressure (20’)

Pressure Drop @ 100 GPM 100% to Coil 50% to Coil 0% to Coil

Pipe/Valves Coil and/or Bypass Globe Control Valve Total GPM @ 20’ ∆P*

2 8 10 20

2 2 7.5 11.5

2 6 12 20

100

132

100

*actual ∆P available may change 21

Constant Flow Single Chiller, Multiple Coils CHW PUMP CHILLER

3-WAY VALVES COIL

22

Partially Variable Flow Single Chiller, Multiple Coils SUPPLY WATER TEMPERATURE

CHW PUMP CHILLER

Where to locate 3-way valves?

VFD

COIL 2-WAY VALVE

At the very end: • Engages mass to reduce cycling • More constant pressure so flow is more constant • Still self-balancing Close to pump: • Lower pump energy

DP SENSOR

3-way valves sized for minimum chiller flow

3-WAY VALVE

23

Constant Flow Multiple Parallel Chillers, Multiple Coils SUPPLY WATER TEMPERATURE CHILLER CH1 240 #1 gpm CHW PUMPS

How many chillers do we need to run?

CHILLER CH2 240#2 gpm

COIL

Ballroom A 240 gpm 3-WAY VALVE

Ballroom B 240 gpm

Ballroom A 240 gpm 100% Loaded

Ballroom B 0 gpm Unoccupied 24

Variable Flow Vary Flow Through Coil Circuit

• Two-way valves • Variable speed coil pump Configurations

• Primary-secondary • Primary-secondary variations • Primary-only

25

Variable Flow Chilled Water Systems Old Paradigm

• Controls respond to changes in CHW • •

temperature Variable flow causes low temperature trips, locks out chiller, requires manual reset (may even freeze) Hence: Maintain constant flow through chillers

26

Primary/Secondary

27

Primary/Secondary 100 gpm ON

100 gpm

ON

100 gpm

0 gpm OFF

ON

100 gpm

100 gpm 28

Variable Flow Primary/Secondary, Multiple Chillers and Coils

CHILLER #1 PRIMARY PUMPS CHILLER #2

COMMON LEG (DECOUPLER)

VFD

VFD

SECONDARY PUMPS

COIL 2-WAY VALVE DP SENSOR

29

Variable Flow Primary/Secondary, Series Flow, Multiple Chillers

30

Variable Flow Primary/Distributed Secondary

31

Variable Flow Primary/Secondary/Tertiary

32

Variable Flow Chilled Water Systems New Paradigm

• Modern controls are robust and very •

responsive to both flow and temperature variations Variable flow OK within range and rate-ofchange spec’d by chiller manufacturer

33

Variable Flow Primary-only, Multiple Chillers PRIMARY PUMPS CHILLER #1 VFD

CHILLER #2 VFD

FLOW METER BYPASS

COIL 2-WAY VALVE DP SENSOR

34

Variable Flow Primary, Bypass Valve

Location • Near chillers Best for energy Controls less expensive Control more difficult to tune – fast response

•

Remote Smaller pressure fluctuations (easier to control) Keeps loop cold for fast response Less likely to unequally load chillers

Sizing • Sizing critical when at

•

chillers/pumps Different size if pump has VFD or not

Flow measurement • Flow meter Most accurate Needed for Btu calc for staging

•

DP across chiller Less expensive Accuracy reduced as tubes foul One required for each chiller 35

Primary CHW Pump Options

Dedicated Pumping Advantages: • Less control complexity • Custom pump heads w/ unmatched chillers • Usually less expensive if each pump is adjacent to chiller served • Pump failure during operation does not cause multiple chiller trips

Headered Pumping Advantages: • Better redundancy • Valves can “soft load” chillers with primaryonly systems • Easier to incorporate stand-by pump 36

Balancing Variable Flow Systems See “Balancing Variable Flow Hydronic Systems” ASHRAE Journal Oct 2002

37

Variable Flow Balancing Issues Ensure “adequate” flow available at all coils to meet loads

•

Less than design flow may be “adequate” most of the time

Ensure differential pressure across control valves is not so high as to cause erratic control

• •

“Two-positioning” Unstable control at low loads

Cost considerations

• • •

First costs (installed costs and start-up costs) Pump energy costs (peak demand and annual) Rebalancing costs (if any) as coils are added to system

Reference

•

“Balancing Variable Flow Hydronic Systems,” Steve Taylor and Jeff Stein, October 2002, ASHRAE Journal 38

Variable Flow Balancing Options No balancing

1.

•

Relying on 2-way control valves to automatically provide balancing

Manual balance

2.

• •

Using ball or butterfly valves and coil pressure drop Using calibrated balancing valves (CBVs)

Automatic flow limiting valves (AFLVs) Reverse-return Oversized main piping Undersized branch piping Undersized control valves Pressure independent control valves

3. 4. 5. 6. 7. 8.

•

Not studied in our ASHRAE paper 39

Piping Systems Analysis Heating system

• • • •

540 gpm 400 VAV reheat coils Constant speed pumps Based on actual building in Oakland

Cooling system

• • •

1,200 gpm 20 Floor-by-floor AHUs Variable speed pumps

All valves: 2-way modulating Analyzed using Pipe-Flo 40

HW Piping Floor Plan

41

Typical Coil Piping

Options 1, 4, 5, 6, & 7

Option 2

42

Typical Coil Piping Option 3

Option 8

43

Option 1: No Balancing Advantages

• •

No balancing labor Coils may be added/subtracted without rebalance

Disadvantages

• •

Imbalance during transients or if setpoints are improper Control valves near pumps can be overpressurized, reducing controllability

44

Option 2: Manual w/CBVs Advantages • •

Valves can be used for future diagnosis (flow can be measured) Reduced overpressurization of control valves at low flow

Disadvantages • Added cost of calibrated • • • • •

balancing valve Higher balancing cost Complete rebalance may be required if coils added/subtracted Slightly higher pump head due to balancing valve Coils may be starved if variable speed drives are used without DP reset Slightly higher pump energy depending on flow variations and pump controls

45

Starved Loads with CBVs and Fixed DP Setpoint: Design Condition 70

PRESSURE PSIG

60 50 40

45 PSID

38 PSID

12 PSID

30 20 10 0 PUMP

CLOSE LOAD

REMOTE LOAD

VFD

Load

Load

100 GPM 5 PSID

100 GPM 5 PSID

DP 5 PSID

5 PSID

28 PSID, Cv=19

2 PSID

46

Starved Loads with CBVs and Fixed DP Setpoint: No Remote Flow Condition 70

PRESSURE PSIG

60 50 40 19 PSID

12 PSID

12 PSID

30 20 10 0 PUMP

REMOTE LOAD

Load

Load

VFD

CLOSE LOAD

56 GPM 1.6 PSID

0 GPM 0 PSID

DP 1.6 PSID

12 PSID

8.8 PSID

0 PSID

47

Option 3: Automatic Flow Limiting Valves Advantages • No balancing labor • Coils may be added/subtracted without rebalance

Disadvantages • Added cost of strainer and • • • • •

flow limiting valve Cost of labor to clean strainer at start-up Higher pump head and energy due to strainer and flow limiting valve Valves have custom flow rates and must be installed in correct location Valves can clog or springs can fail over time Control valves near pumps can be overpressurized, reducing controllability 48

Option 4: Reverse-return

49

Reverse Return Configurations

C/C

H/C

H/C

C/C

H/C

H/C

H/C

H/C

C/C

C/C

Reverse return riser (elevation)

Reverse return on floor (plan) 50

Option 4: Reverse-return Advantages • No balancing labor • Coils may be • •

added/subtracted without rebalance No significant overpressurization of control valves close to pumps. Usually lower pump head due to reverse-return piping having lower pressure drop than mains (due to larger pipe)

Disadvantages • Added cost of reverse•

return piping Not always practical depending on physical layout of system

51

Option 5: Oversized Main Piping C/C

C/C 2”

2”

3” C/C

C/C 4”

4” C/C

C/C 6”

6”

C/C

C/C 3”

6”

6”

Standard main design

6”

6”

Oversized main riser

52

Option 5: Oversized Main Piping Advantages • No balancing labor • Coils may be • • •

added/subtracted without rebalance Reduced overpressurization of control valves close to pumps Lowest pump head/energy due to oversized piping, no balance valves Increased flexibility to add loads due to oversized piping

Disadvantages • Added cost of larger piping

53

Option 6: Undersized Branch Piping Advantages • No balancing labor • Reduced cost of smaller • •

piping Coils may be added/subtracted without rebalance Reduced overpressurization of control valves close to pumps where piping has been undersized

Disadvantages • Limited effectiveness and • • • •

applicability due to limited available pipe sizes High design and analysis cost to determine correct pipe sizing Reduced flexibility to add coils where piping has been undersized Coils may be starved if variable speed drives are used without DP reset Slightly higher pump energy depending on flow variations and pump controls 54

Option 7: Undersized Control Valves Advantages • No balancing labor • Reduced cost of smaller • •

•

control valves Coils may be added/subtracted without rebalance Reduced overpressurization of control valves close to pumps where control valves have been undersized Improved valve authority which could improve controllability where control valves have been undersized

Disadvantages • Limited effectiveness and • • •

applicability due to limited available control valve sizes (Cv) High design and analysis cost to determine correct control valve sizing Coils may be starved if variable speed drives are without DP reset Slightly higher pump energy depending on flow variations and pump controls

55

Option 8: Pressure Independent Control Valves Advantages • No balancing labor • Coils may be • • • •

added/subtracted without rebalance No over-pressurization of control valves close to pumps Easy valve selection – flow only not Cv Perfect valve authority will improve controllability Less actuator travel and start/stop may improve actuator longevity

Disadvantages • Added cost of strainer and • • • •

pressure independent control valve Cost of labor to clean strainer at start-up Higher pump head and energy due to strainer and pressure independent control valve Valves have custom flow rates and must be installed in correct location Valves can clog or springs can fail over time

56

PICVs May Improve ∆T?

NBCIP Test Lab (as reported by manufacturer) 57

Controllability & Transients Balancing Method

Maximum pressure drop of control valve required for design flow, feet CHW

1

No balancing

2

Manual balance using calibrated balancing valves

3

Automatic flow limiting valves

4

HW

Percent of design flow (percent of design coil sensible capacity) with all control valves 100% open Maximum flow through closest coil CHW

HW

Minimum flow through most remote coil CHW

HW

20.5

44.4

143% (106%)

212% (119%)

73% (89%)

75% (96%)

0

0

100% (100%)

100% (100%)

100% (100%)

100% (100%)

20.5*

44.4*

100% (100%)

100% (100%)

100% (100%)

100% (100%)

Reverse-return

1.2

10.4

103% (100%)

150% (109%)

99% (100%)

85% (97%)

5

Oversized main piping

7.0

20.9

122% (103%)

173% (112%)

94% (99%)

82% (97%)

6

Undersized branch piping

19.5

NA

142% (106%)

NA

73% (100%)

NA

7

Undersized control valves

8.0

NA

120% (103%)

NA

86% (89%)

NA

58

Energy & First Costs Balancing Method

Pump head, feet CH W

Annual Pump Energy, $/yr

HW

CHW

HW

Incremental First Costs vs. Option 1 $ per design gpm

$ CHW

HW

CHW

HW

1

No balancing

58.5

82.7

$1,910

$3,930

–

–

–

–

2

Manual balance using calibrated balancing valves

60.3

83.6

$1,970

$3,970

$7,960

$47,530

$6.60

$88.00

3

Automatic flow limiting valves

66.6

90.8

$2,170

$4,310

$11,420

$50,750

$9.50

$94.00

4

Reverse-return

55.3

80.0

$1,810

$3,800

$28,460

$17,290

$23.70

$32.00

5

Oversized main piping

45.0

59.3

$1,470

$2,820

$12,900

$7,040

$10.80

$13.00

6

Undersized branch piping

58.5

NA

$1,910

NA

($250)

NA

($0.20)

NA

7

Undersized control valves

58.5

NA

$1,910

NA

($2,340)

NA

($2.00)

NA

59

Ranks Balancing Method

Controllability (all conditions)

Pump Energy Costs

First Costs

1

No balancing

7

3

3

2

Manual balance using calibrated balancing valves

4

6

6

3

Automatic flow limiting valves

4

Reverse-return

5

Oversized main piping

6

Undersized branch piping

7

Undersized control valves

7 2 3 6 5

7 2 1 4 4

7 5 4 2 1

8

Pressure independent control valve

1

78

8

60

Conclusions & Recommendations for Variable Flow Hydronic Systems Automatic flow-limiting valves are not recommended on any variable flow system

•

They only limit flow for transients which has little or no value

Calibrated balancing valves are also not recommended for balancing variable flow systems

•

But useful for future diagnostics on small low pressure drop coils – just leave them wide open (no throttling)

Oversized mains may have reasonable pump energy savings payback on 24/7 chilled water systems Undersizing piping and valves near pumps improves balance and costs are reduced, but significant added engineering time required Pressure independent valves should be considered on very large systems (>100 ft head) for coils near pumps

• •

Cost is high but going down now with competition When costs are competitive, this may be best choice for all jobs

For other than very large distribution systems, option 1 (no balancing) appears to be the best option

•

Low first costs with minimal or insignificant operational problems 61

Break

Problems caused by Degrading ∆T

Q= 500 X GPM X ∆T For a Given Load Q, When ∆T Goes Down, GPM Goes up Result:

• • •

Increases pump energy Can require more chillers to run at low load, or coils will be starved of flow Can result in reduced plant effective capacity: chiller capacity without the capability of delivering it

Resource January 2002 ASHRAE Symposium Paper, “Degrading Chilled Water Plant Delta-T: Causes and Mitigation

63

Primary/secondary “death spiral” Chillers staged by Load 80%

42oF 46oF 42 VFD

When ∆T Degrades, Secondary Flow Exceeds Primary VFD

50oF 52

64

∆T Degradation in Large Chiller Plant (January through March)

Design ∆Τ=10oF

9.5°F-10.0°F

Evaporator Delta T (°F)

Coincident Wet Bulb Ranges 7.0°F-7.5°F

35°F-40°F 40°F-45°F 45°F-50°F 50°F-55°F 55°F-60°F

4.5°F-5.0°F

2.0°F-2.5°F

0

100

200

300

400 Approximate hrs/yr

500

600

700

800

Causes of Degrading ∆T 1. Causes that can be avoided by proper design or operation of the chilled water system; 2. Causes that can be mitigated, but through measures that may not result in overall energy savings; and 3. Causes that are inevitable and simply cannot be avoided

66

Degrading ∆T #1. Causes that can be eliminated by design/operation

Improper Setpoints or Calibration

•

e.g. dropping coil SATsp by 2ºF will double the flow rate and halve the ∆T

Use of Three-way Valves

•

Instant response is not a valid reason for 3-way valves

No Control Valve Interlock

•

i.e. valve open when fan is off

Coils Piped Backwards (parallel flow vs. counter-flow) ...

67

Degrading ∆T #1. Causes that can be eliminated by design/operation (continued)

Uncontrolled Process Loads

•

need isolation valves

Incorrectly Selected Control Valves

• •

Oversized valves hunt and result in higher average flow Undersized actuators have insufficient close-off pressure

Incorrectly Selected Coils

•

Common problem when new buildings don’t follow the campus standard ∆T

Improper “Bridge” Connection & Control

•

Bridge valve cannot raise the CHWRT without starving the load

68

Degrading ∆T

#2 Measures that improve ∆T but energy trade-off

Chilled Water Reset to Lower Chilled Water Supply Temperature

• Lowering CHWST by 1ºF increases ∆T by 1 •

to 2ºF but reduces chiller efficiency Net effect could be better (if high pump energy) or worse (low pump energy)

69

Degrading ∆T

#2 Measures that improve ∆T but energy trade-off

Coil Pumps to Prevent ∆T Degradation at Low Flow Due to “Laminar Flow Effect”

• May (or may not) improve ∆T at low flow but coil pump energy is very high

70

Laminar Flow “Problem:” Real or Myth? 20 18

Dual Row, 5/8" Tubes Full Row, 5/8" Tubes Full Row, 1/2" Tubes

14 12 10 8 6 4 Laminar Flow

2 0

100%

80%

60%

40%

% Sensible Load

20%

0%

Delta-T (degrees-F)

16

Data from Major Coil Manufacturer’s ARI certified rating program developed from lab tests

Primary/Secondary vs. Primary/Secondary with Coil Pumps 50.00 45.00

P/S/T with constant ∆T

40.00

Pump kW

35.00 30.00 25.00

P/S with degrading ∆T

20.00 15.00 10.00 5.00 0.00 0%

20%

40%

60%

80%

100%

3-chiller/3-pump plant, total 1440 gpm

% Plant Load Conclusion: even if the laminar flow problem were real, coil pumps are not a good solution. They add to both first costs and energy costs.

72

Causes of Degrading ∆T #3. Causes That Cannot Be Eliminated

Air Economizers and 100% Outdoor Air Systems 42oF CHWST

60oF EAT

55oF SAT

(Design CHWRT of 62, based on design EAT of 80)