radiant cooling design .pdf

PerformancePredictionandModeling JingjuanFeng,PhDCand.

GGASHRAERadiantEnergySeminar 1

Center for the Built Environment October 2013 1Center for the Built Environment October 2013

Radiant Cooling Design: Performance Prediction and Modeling Methods

Jingjuan (Dove) Feng, PhD CandidateCenter for the Built Environment

University of California Berkeley

Center for the Built Environment October 2013 2

Agenda

Background

Cooling load prediction methods and tools

Whats available and whats been used? Are they accurate? Investigation by experiment and simulationDesign recommendations

Cooling load prediction method Modeling tool selection Implications for sizingModeling for code compliance and LEED

Coolingload

analysis

Coolingload

analysis

Radiantsystemsizing

Radiantsystemsizing

Modelingtools

Modelingtools




Backgrounds: Air systems vs. Radiant systems

Air systems 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


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?




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)

Case studies + Survey

5 case studies 11 responses from designers from

Europe and North America

1)ASHRAEHOF;2)ISO11855(2012)

Casestudybuildinglist

Building names

Bankok Airport

David Brower Center

Walmart at sacramento

Manitoba Hydro

NREL Research Support FacilityWilliam Jefferson Clinton

Presidential LibraryLobby of Hearst headquarters

SMUD building office area

St Meinrad Archabbey church

applications Load features Rad system type

Lobby/atrium solar + stratification radiant floor

office Typical radiant ceiling slab

retail with skylight Typical radiant floor cooling

office Typical TABS ceiling

office Typical radiant slab ceiling

Lobby/atriumTypical

load+stratification radiant floorLobby/atrium solar + stratification radiant floor

office Typical radiant ceiling slab

ChurchTypical

load+stratification radiant floor


Available cooling load prediction methods/tools

Method Tools

#1 Heat gain Ignorethermalmasseffect Spreadsheet

#2 Simplifiedmethods

RTS,CLTD/CLF/SCL,weightingfactormethod, etc.(airsystemonly)

TRACE,DOE2,eQUEST,etc.

#3 HB method Radiantsystemsimulatedwith dynamicsimulationtool

EnergyPlus,IESVE,TRNSYS,etc.

#4 Nontraditional

Usedmostlyfor applicationswithintensivesolarandstratification

Solar simulationtools,CFD

#5 ISO11855(2012)

Diagrambasedondesigndayenergygain,operationhour,andetc. (TABSonly)

Proprietarytools




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

Directly use heat gain 37%

Simplified method (Trane

Trace) 38%

ISO 11855 method

0% Dynamic simula on

tool 19%

Nontradi onal method (CFD,

etc) 6%

Typical design

N=16


Differences between Heat gain and cooling load

Thermalmasseffectforconvectionbased(air)system(source:ASHRAEFundamental2013)




Space cooling load definition

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

What is the difference in cooling load for radiant vs. air systems?


Are they the same?

Cooling loadRADIANT Cooling loadAIR

Laboratory testing and simulation study will compare the following:

Instantaneous cooling rate

peak cooling rate




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


Test chamber configurations

Feng,J.Bauman,F.andSchiavon,S.(2013)Experimentalcomparisonofzonecoolingloadbetweenradiantandairsystems,TobesubmittedtoEnergyandBuilding.




Experimental results: Operative temperature

Maintain the same thermal comfort level

Control to the same operative temperature at 24C (75.2 F )


Experimental results: Instantaneous cooling rate

Radiant system has a higher cooling rate than the air system

18% higher during hour 6 (peak cooling load)




Radiant system removes heat faster during heater-on period

Radiant system removes 82% of total heat gain

Air system removes 63.3%of total heat gain

Experimental results: Total energy removal

Heateronperiod


Simulation study of different design cases

Radiant system types

Radiant panel/Lightweight radiant slab/Heavyweight radiant slab

Parameters studied Thermal insulation Building mass Radiative/convective

split of internal load

Solar heat gain Active ceiling/floor Cooling design day simulation

Window Window

BC: adiabatic

Window Window

BC: adiabatic

BC: adiabatic

hw_r2: R=2.20 (m2-K/W)hw_r1: R=1.20 (m2-K/W)

BC: adiabatic

Wall: L1: Concrete block L2: Foam insulation

L1: Concrete slab

L2: Insulation

L3: Wood sidingFlr:

hw_r2: heavyweight Lw_r2: lightweightWall: L1: Plaster board

L2: Fiberglass quilt

L1: Timber flooring

L2: Insulation

L3: Wood sidingFlr:

BC: adiabatic

rad0: 0% radiant

BC: adiabatic

rad0.6: 60% radiantrad0.3: 30% radiant

rad1.0: 100% radiant

BC: environment

G1: insulation G2: building mass

G3 :Int. heat gain G4 :ceiling with solar

cl_noshade: No shade cl_shade:Exterior shade

flr_noshade: No shade flr_shade:Exterior shade

G5 :floor with solar

Real Window

BC: adiabatic

G6 :typical

cl_shade_rad0.6

Feng,J., Schiavon,S.andBauman,F.(2013)Coolingloaddifferencesbetweenradiantandairsystems,EnergyandBuildings,65,310321.




Results: Peak cooling load

Higher peak cooling load for studied cases:

Interior space: 7-27% Perimeter space without solar: 12-35% Perimeter space with solar: 48-85%

Implications

Minimize solar load for design Especially effective for removing solar load High peak load high energy consumption!


Why are they different?

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Comparison of cooling load profiles

Caseexample:Internalloadonly_radiative fraction=0.6

AirSystem RadiantSystem


What about cooling load prediction methods and

modeling tools?




ASHRAE cooling load prediction methods

Heat balance (HB) method

Based on first principles EnergyPlus 8.0Radiant time series (RTS) method/weighting factor method

Convective heat gain instantaneous cooling load Radiative heat gain convective cooling load with delay CTF/RTF Generator and excel (or TRACE )

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Quote: ASHRAE HOF chapter 19




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


Measured vs. Prediction based on RTS method

RTS method cannot predict cooling load correctly for the test chamber configuration




Modeling tool selection

Tools Modeling method Capabilityto capturetheradiantdynamic

IES (VE) HBmethodTRNSYS HBmethodEnergyPlus HB method

ESPr HBmethodDOE2 Weighting factormethodeQUEST Weighting factormethodTRACE RTSmethod orTFmethod

Makesureto:1)Modeltheradiantsourceasaroomsurface;2)Definecoolingloadcorrectly


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)

With solar: 100 W/m2 (32 Btu/h.ft2)

Akronartmuseum,OH

B.Olesen,ASHRAEJournal(2008).




Simulated capacity vs. standard without solar

Simulated capacity matches well with standard capacity curve without solar


Simulated capacity vs. standard with solar

Cooling capacity can reach 130 W/m2 (42 Btu/h.ft2)




Air system size: Simulated: 20 W/m2 (6.4 Btu/h.ft2)

Guideline: 86 W/m2 (27.5 Btu/h.ft2)

Impact on air system sizing

Coolingcapacityhighlimitwithoutsolar42W/m2

peakcoolingload:128W/m2 (41Btu/h.ft2)Radiantcoolingcapacity:108W/m2 (34.5Btu/h.ft2)


Modeling for code compliance and beyond code program




Title 24 (2013): Radiant floor cooling system

Modeling requirements for compliance evaluation

EnergyPlus will be available for code compliance (CBECC-Com) , Jan 2014, http://www.bees.archenergy.com

Items ModelingInputRestrictionsTemperaturecontrol MeanairtemperatureHydronic TubingInsideDiameter Betweenaminimumof1/2andamaximumofTemperatureControl FixedatMeanAirTemperatureforcompliancecalculationsCondensationControlDewpointOffset

MinimumcoldwatersupplyTemperaturefixedat2Fabovedewpoint

CoolingLowWaterTemperature 55F


LEED

LEED topics PossiblepointsEnergy& AtmosphereCredit1:OptimizeenergyperformanceCredit 3:EnhancedcommissioningCredit4:EnhancedrefrigerantmanagementCredit5:Measurement&verification

26

IndoorEnvironmentalQualityCredit1:OutdoorairdeliveringmonitoringCredit2:IncreasedventilationCredit3:ConstructionIAQplanCredit6.2:Controllabilityofsystems thermalcomfortCredit7:Thermalcomfort Design&Verification

6

Innovationindesign 5




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).


Acknowledgments

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.




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]


Questions?

Jingjuan (Dove) Feng

[email protected]

Fred Bauman

[email protected]

Stefano Schiavon

[email protected]

radiant cooling design .pdf

Documents

radiant cooling design

radiant layer

single peak cooling

tools whats available

performance prediction

case studies survey

code compliance

phd candidatecenter