Performance Prediction and Modeling
Radiant Cooling Design: Performance Prediction and Modeling Methods
Jingjuan Feng, PhD Cand.
Jingjuan (Dove) Feng, PhD Candidate Center for the Built Environment University of California Berkeley
Center for the Built Environment Oc October 2013
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Center for the Built Environment Environment October 2013 2013
Agenda Background Cooling load prediction methods and tools •
What’s available and what’s been used?
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Are they accurate?
•
Investigation by experiment and simulation
Cooling load analysis
Design recommendations recommendations •
Cooling load prediction method
•
Modeling tool selection
•
Implications for sizing
Modeling tools
Radiant system sizing
Modeling for code compliance and LEED
Center for the Built Environment Oc October 2013
GGASHRAE Radiant Energy Seminar
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Backgrounds: Air systems vs. Radiant systems Air systems •
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Ventilation + space conditioning Design to meet a single peak cooling load value Remove heat using convection
Radiant systems •
•
•
Decoupled ventilation and space conditioning Allow pre-conditioning the radiant layer Remove heat using convection + radiation
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1. Is the cooling load the same for radiant systems as for air systems? 2. Can we use the same method to size radiant system as air system? 3. Which modeling tools can be used to assist design?
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
What methods and tools are available and being used ? Literature review
ASHRAE HOF (2013)
ISO 11855 (2012)
RHVEA Guidebook
Price Engineer's HVAC Handbook (2011) 1) ASHRAE HOF ; 2) ISO 11855 (2012)
Case studies + Survey
5 case studies 11 responses from designers from Europe and North America
Building names
appli cations
Load f e at ur es
Bankok Airport
Lobby/atrium
sola r + stratif icatio n
radia nt floor
David Brower Center
office
Typical
radiant ceiling slab
Walmart at sacramento
retail with s ky li gh t
T yp ic al
r ad ia nt floor cooling
Manitoba Hydro
office
Typical
TABS ceiling
NREL Research Support Facility
office
Typical Typical load+stratific ation sola r + stratif icatio n
radiant slab ceiling
WilliamJeffersonClinton Presidential Library Lobby of Hearst headquarters
Lobby/atrium Lobby/atrium
R ad system type
radia nt floor radia nt floor
SMUDbuilding office area
office
Typical
radiant ceiling slab
St MeinradArchabbey church
Church
Typical load+stratific ation
radia nt floor
Case study building list
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Available cooling load prediction methods/tools Method Heat gain
#1 #2
Tools
Simplified methods
Ignore thermal mass effect
Spreadsheet
RTS,CLTD/CLF/SCL, weighting TRACE, DOE‐2, factor method, etc. eQUEST, etc. (air system only)
#3
HB method
Radiant system simulated EnergyPlus, IES‐VE, with dynamic simulation tool TRNSYS, etc.
#4
Non‐ traditional
Used mostly for applications with intensive solar and stratification
Solar simulation tools, CFD
#5
ISO‐11855 (2012)
Diagram based on design day energy gain, operation hour, and etc. (TABS only)
Proprietary tools
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Thermal load analysis method/tool in practice •
•
13 out of 16 designers we interviewed assume the same cooling load for radiant systems as air systems Radiant cooled surfaces were not directly modeled Typical design ISO 11855 method 0%
Dynamic simula on tool 19%
Simplified method (Trane Trace) 38%
Non‐tradi onal method (CFD, etc) 6%
Directly use heat gain 37%
N=16
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Differences between Heat gain and cooling load
Thermal mass effect for convection based (air) system (source: ASHRAE Fundamental 2013)
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Space cooling load definition What is the difference in cooling load for radiant vs. air systems? All-air systems
Cooling load •
Heat gain removed by convection only
•
Maintain fixed setpoint temperature
Radiant heat gain •
Absorbed by non-active thermal mass
•
Released as convective heat gain after time delay
Radiant systems
Cooling load •
Heat gain removed by radiation and convection at active chilled surface
•
Maintain operative temperature within comfort zone
Radiant heat gain •
Becomes cooling load instantly
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Are they the same?
Cooling loadRADIANT ≠ Cooling loadAIR Laboratory testing and simulation study will compare the following: •
Instantaneous cooling rate
•
peak cooling rate
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Laboratory testing: Cooling load comparison Objectives
Verify that cooling loads for radiant system are different from air system
Experimental approach
Concrete blocks (thermal mass) on floor with heating mats on top (internal heat gain)
Conduct 12-hour tests with heaters on for 6 hours and off for 6 hours •
Radiant chilled ceiling panels
•
Overhead air system
Maintain the same operative temperature
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Test chamber configurations
Feng, J. Bauman, F. and Schiavon, S. (2013) Experimental comparison of zone cooling load between radiant and air systems, To be submitted to Energy and Building.
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Experimental results: Operative temperature Maintain the same thermal comfort level
Control to the same operative temperature at 24°C (75.2 °F )
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Experimental results: Instantaneous cooling rate Radiant system has a higher cooling rate than the air system •
18% higher during hour 6 (peak cooling load)
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Experimental results: Total energy removal Radiant system removes heat faster during heater-on period Heater on period •
•
Radiant system removes 82% of total heat gain
Air system removes 63.3% of total heat gain
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Simulation study of different design cases Radiant system types •
Radiant panel/Lightweight radiant slab/Heavyweight radiant slab G1: insulation
G2: building mass
Parameters studied
Thermal insulation Building mass
hw_r2: heavyweight Lw_r2: lightweight
hw_r2: R=2.20 (m2-K/W) hw_r1: R=1.20 (m2-K/W)
BC:environment
Wall: L1:Plaster board L2:Fiberglass quilt L3:Wood siding
Wall: L1:Concrete block L2:Foaminsulation L3:Wood siding
Flr:
Flr:
L1:Concreteslab
L1:Timberflooring L2:Insulation
L2:Insulation
BC: adiabatic
BC: adiabatic
G3 :Int. heat gain
G4 :ceiling with solar BC: adiabatic
Radiative/convective rad0: 0% radiant
split of internal load
Solar heat gain
Active ceiling/floor
Cooling design day simulation
Window
Window
rad0.3: 30%radiant rad0.6: 60%radiant rad1.0: 100%radiant
cl_noshade: No shade BC: adiabatic
G5 :floor with solar
G6 :typical
Window
Window
flr_noshade:No shade
flr_shade:Exteriorshade
cl_shade:Exteriorshade
BC:adiabatic
RealWindow
BC:adiabatic
cl_shade_rad0.6
BC:adiabatic
Feng, J., Schiavon, S. and Bauman, F. (2013) Cooling load differences between radiant and air systems, Energy and Buildings, 65, 310‐321.
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Results: Peak cooling load Higher peak cooling load for studied cases: •
Interior space: 7-27%
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Perimeter space without solar: 12-35%
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Perimeter space with solar: 48-85%
Implications •
Minimize solar load for design
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Especially effective for removing solar load
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High peak load ≠ high energy consumption!
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Why are they different? Air1010System
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) 8 ) 2 2 8 m m / / W 6 ( W ( l l e6 e v e v L e L r 4 r e4 e w o w P o P 22
66 44
Cooling load from convective heat gain
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18:00
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6:00 6:00
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10 Radiant System
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Comparison of cooling load profiles •
Case example: Internal load only_ radiative fraction= 0.6 Air System
Radiant System
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What about cooling load prediction methods and modeling tools?
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
ASHRAE cooling load prediction methods Heat balance (HB) method •
Based on first principles
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EnergyPlus 8.0
Radiant time series (RTS) method/weighting factor method •
Convective heat gain
instantaneous cooling load
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Radiative heat gain
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CTF/RTF Generator and excel (or TRACE )
convective cooling load with delay
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Quote: ASHRAE HOF chapter 19
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Measured vs. Prediction based on HB method
EnergyPlus v8.0 model was developed to apply the HB method
Match well with air system cooling load
Radiant system cooling load: heat removed by the radiant ceiling panels
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Measured vs. Prediction based on RTS method
RTS method cannot predict cooling load correctly for the test chamber configuration
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Modeling tool selection Tools
Modeling method
IES (VE)
HB method
TRNSYS
HB method
EnergyPlus
HB method
ESP‐r
HB method
DOE‐2
Weighting factor method
eQUEST
Weight ing factor method
TRACE
RTS method or TF method
Capability to capture the radiant dynamic
Make sure to: 1) Model the radiant source as a room surface; 2) Define cooling load correctly
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Design radiant floor cooling systems with solar load Applications
Spaces with large glazed surfaces, such as atria, perimeter areas, etc.
Guidance is limited with solar
Maximum cooling capacity in standard: 42 W/m2 (13 Btu/h.ft2)
Akron art museum, OH
With solar: 100 W/m2 (32 Btu/h.ft2)
B. Olesen, ASHRAE Journal (2008). Center for the Built Environment October 2013
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Simulated capacity vs. standard without solar
Simulated capacity matches well with standard capacity curve without solar
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Simulated capacity vs. standard with solar
Cooling capacity can reach 130 W/m2 (42 Btu/h.ft2)
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Impact on air system sizing Air system size: Simulated: 20 W/m2 (6.4 Btu/h.ft2) Guideline: 86 W/m2 (27.5 Btu/h.ft2)
peak cooling load: 128 W/m2 (41 Btu/h.ft2) Radiant cooling capacity: 108 W/m2 (34.5 Btu/h.ft2) Cooling capacity high limit without solar 42W/m2
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Modeling for code compliance and beyond code program
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Title 24 (2013): Radiant floor cooling system
Modeling requirements for compliance evaluation Items
Modeling Input Restrictions
Temperature control
Mean air temperature
Hydronic Tubing Inside Diameter Temperature Control
Condensation Control Dewpoint Offset Cooling Low Water Temperature
Between a minimum of 1/2” and a maximum of ¾ ” Fixed at Mean Air Temperature for compliance calculations Minimum cold water supply Temperature fixed at 2°F above dewpoint 55°F
EnergyPlus will be available for code compliance (CBECC-Com) , Jan 2014, http://www.bees.archenergy.com
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LEED
LEED topics
Possible points
Energy & Atmosphere Credit 1: Optimize energy performance Credit 3: Enhanced commissioning Credit 4: Enhanced refrigerant management Credit 5: Measurement & verification
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Indoor Environmental Quality Credit 1: Outdoor air delivering monitoring Credit 2: Increased ventilation Credit 3: Construction IAQ plan Credit 6.2: Controllability of systems – thermal comfort Credit 7: Thermal comfort‐ Design&Verification
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Innovation in design
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Key takeaway
Cooling load prediction and modeling method for radiant systems • Use design tools based on heat balance approach • Define cooling load as heat removed by actively cooled surface(s),i.e. , radiant source should be modeled • RTS or weighting factor method, may lead to incorrect results
Peak cooling loads may be higher than air systems, but… • Radiant systems are known to be more energy efficient • Under some operating strategies radiant systems will have lower peak cooling loads (e.g., nighttime pre-cooling).
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Acknowledgments •
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California Energy Commission (CEC) Public Interest Energy Research (PIER) Buildings Program. Center for the Built Environment, University of California, Berkeley (www.cbe.berkeley.edu ). Julian Rimmer, Brad Tully, and Tom Epp of Price Industries for the use of their Hydronic Test Chamber in Winnipeg.
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Performance Prediction and Modeling
Jingjuan Feng, PhD Cand.
Radiant system building project Link to the map: http://bit.ly/RadiantBuildingsCBE Link to the form: http://bit.ly/RadiantFormCBE Contact:
Caroline Karmann,
[email protected] Fred Baumann,
[email protected]
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Questions? Jingjuan (Dove) Feng
[email protected]
Fred Bauman
[email protected] Stefano Schiavon
[email protected]
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