ten years of cool roofing research at the florida solar … · ten years of cool roofing research...
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FLORIDA SOLAR ENERGY CENTERA Research Institute of the University of Central Florida
Danny ParkerDanny Parker
Consortium for Energy Efficiency Consortium for Energy Efficiency Workshop on Cool Roofing Workshop on Cool Roofing
San Francisco, December 2005San Francisco, December 2005
Ten Years of Cool Roofing Ten Years of Cool Roofing Research at the Research at the
Florida Solar Energy CenterFlorida Solar Energy Center
Attic Thermal Processes
Altered attic heat transfer mechanisms; Radiant Barrier
Radiant Barrier Pilot Project
Site #199 attic temp before and after retrofit – June 22, 2000
Julian Date160 165 170 175 180 185 190
Atti
c A
ir Te
mpe
ratu
re (o F)
70
80
90
100
110
120
130RBS Retrofit
Site #199 RBS retrofit impact on attic air temp and AC cooling demand
Hour of Day (Standard Time)0 2 4 6 8 10 12 14 16 18 20 22 24
Tem
pera
ture
(o F)
70
80
90
100
110
120
130
Coo
ling
kW
0
1
2
3
4
5Attic Temp (pre):avg=91.0; max=113.7Attic Temp (post): avg=88.3; max=101.5AC (pre): avg=2.23 kW;max=3.79 kWAC (post): avg=1.79 kW; max=2.69 kW
SummerPeak
Overall Results: 9 Sites
o Average cooling energy savings: 3.6 kWh/day (9.3%)
o Peak demand reduction; 420 W (16%)o 8.4o drop in avg. max daily attic temp.o Improved load shape: most reduction
during day; nighttime demand elevatedo Improvements to customer comfort
RBS impact on summer attic air temp and AC cooling demand in eight homes
Hour of Day (Standard Time)0 2 4 6 8 10 12 14 16 18 20 22 24
Tem
pera
ture
(o F)
70
80
90
100
110
120
Coo
ling
kW
0.0
0.5
1.0
1.5
2.0
2.5
3.0Attic Temp: (pre):avg= 89.4; max= 114.8Attic Temp:(post):avg= 87.0; max= 106.4AC(pre):avg=1.61 kW;max= 2.64 kWAC(post):avg= 1.46 kW;max= 2.22 kW
SummerPeak
Reflective Roof Retrofits
Experiments: 1993 - 1998Dark roofed attics can reach 130 - 140EF on summer afternoons. A white color will reflect much of this heat back to the sky. Reducing the temperature in the attic is doubly importantbecause of the presence of the cooling ducts.
Pre-post experiments in 19 homes:- 19 % average reduction in cooling energy use- 23 % average reduction in peak demand
Reference:Parker, D.S., Chandra, S., Barkaszi, S.F. and Beal, D.J., 1995B. "Measured Cooling Energy Savings from Reflective Roofing Systems in Florida: Field and Laboratory Results," Thermal Performance of the Exterior Envelopes of Buildings VI, p. 489, December 4 _ 8, 1995, Clearwater, FL.
Dark Gray vs. White?
Big Differences Seen…
Roof Whitened
Atti
c A
ir Te
mpe
ratu
re F
.
Day
AC
Pow
er D
eman
d: W
atts
Attic Temp AC Energy
0 2 4 6 8 10 12 14
80
90
100
110
120
0
500
1000
1500
2000
2500
3000
3500
4000
4500
FPL Demonstration Project: Ft. Myers, FL
Study Homes: RGS, RWM, RWB, RWF
Study Homes: RTB, RWS, RSL
Detailed Instrumentation
Attic Air Temps
Time of Day (EST)
0 2 4 6 8 10 12 14 16 18 20 22 24
Ave
rage
Tem
pera
ture
s (o F)
70
80
90
100
110
120
RWB: Max = 89.0 FRWF: Max= 87.8 FRWM: Max= 91.7 FRWS: Max= 103.6 FRSL: Max= 83.2 FRGS: Max= 110.2 FRTB: Max= 98.8 F
SummerPeak
Period
Influence on Peak Attic Temperatures
Max Daily Air Temperature (oF)84 85 86 87 88 89 90 91 92 93 94 95
Max
Atti
c Te
mpe
ratu
re (o F)
80
85
90
95
100
105
110
115
120
125
130
135
140
80
85
90
95
100
105
110
115
120
125
130
135
140RGS
RWS
RTB
RWB
RWF
RWM
Avg. Cooling over Unoccupied Period
Time of Day (EST)
0 2 4 6 8 10 12 14 16 18 20 22 24
Ave
rage
Ele
ctric
al D
eman
d (W
atts
)
0
200
400
600
800
1000
1200
1400RWB Avg = 13.3 kWh/dayRWF Avg = 13.3 kWh/dayRWM Avg = 12.2 kWh/dayRWS Avg = 15.6 kWh/dayRSL Avg = 14.9 kWh/dayRGS Avg = 17.0 kWh/dayRTB Avg = 16.2 kWh/day
SummerPeak
Period
Impact of East facing glass(RWB, RWF, RWS)
West facing glass(RGS,RTB,RSL, RWM)
Final Results Summary: Best Estimates
Table 21 Summary of Normalized Savings and Demand
Reductions from Regression Estimates
Case DescriptionCooling Savings Peak Demand ReductionkWh Percent kW Percent
RGS (Control) 0 0% 0 0%RWS (White Shingle) 300 4% 0.48 17% RSL (Sealed Attic) 620 9% 0.13 5%RTB (Terra Cotta Tile) 180 3% 0.36 13%RWB (White S-Tile) 1,380 20% 0.92 32%RWF (White Flat Tile) 1,200 17% 0.98 34%RWM (White Metal) 1,610 23% 0.79 28%
* Percentages relative to typical values for average sized detached South Florida homes detailed in Appendix H.
Table 21 Summary of Normalized Savings and Demand
Reductions from Regression Estimates
Case DescriptionCooling Savings Peak Demand ReductionkWh Percent kW Percent
RGS (Control) 0 0% 0 0%RWS (White Shingle) 300 4% 0.48 17% RSL (Sealed Attic) 620 9% 0.13 5%RTB (Terra Cotta Tile) 180 3% 0.36 13%RWB (White S-Tile) 1,380 20% 0.92 32%RWF (White Flat Tile) 1,200 17% 0.98 34%RWM (White Metal) 1,610 23% 0.79 28%
* Percentages relative to typical values for average sized detached South Florida homes detailed in Appendix H.* Percentages relative to typical values for average sized detached South Florida homes detailed in Appendix H.
Flexible Roof Facility
Time of Day: June 16, 19970 2 4 6 8 10 12 14 16 18 20 22 24
Mea
sure
d At
tic A
ir T
empe
ratu
re (F
.)
60
70
80
90
100
110
120
130
140White tileBlack shngl, RBS, 1:150 ventBlack shngl, RBS, 1:300 ventRed tileBlack shngl, 1:300 ventWhite metal: 1:300 ventAmb. air temperature
FRF Roof /Attic Testing
o Roofs/Ventilationo Cool roofing systemso Measured heat fluxo Attic air temperatureo Weather conditionso Summer 2002-2003:
Unfinished vs. Finished metal roofing systems
o Long-term testing of unfinished metals
Emittance/reflectance
FRF Testing 2003
o Metal Roofing long term exposure
Unfinished Galvanized Unfinished GalvalumeIR Reflective Metal shinglesWhite metal roofControl= Dark shingles
Attic Temps over Summer
Average Temps Over Summer
Time of Day: June 1 - September 30, 2003
0 2 4 6 8 10 12 14 16 18 20 22 24
Mea
sure
d At
tic A
ir Te
mpe
ratu
re (o F)
70
75
80
85
90
95
100
105
110
115
120
125Galvalum metal: Max= 99.2o
Sealed attic(dbl roof): Max= 83.5o
Brown IR Selective Metal Tile: Max= 101.5o
Galvanized Metal: Max= 103.6o
Dark Shingle: Max=116.7o
White Metal: Max= 94.6o
Ambient Air: Max= 85.2o
Max Attic TemperaturesMax Attic Temperatures
o Galvalume Metal111 oF
o Dbl Roof, sealed85 oF
o IR Reflective Shingle106 oF
o Galvanized Metal114 oF
o Black Shingle (Control)140 oF
o White Metal Panel104 oF
o Outdoor Air Temp= 95 oF
Ceiling Flux…Different StoryCeiling Flux…Different Story
Time of Day: June 5- September 30, 2002
0 2 4 6 8 10 12 14 16 18 20 22 24
Mea
sure
d C
eilin
g H
eat F
lux
(Btu
/hr/f
t2 )
-0.5
0.0
0.5
1.0
1.5
2.0
2.5Galvalum 5-vee metal (Avg= 0.43)Dbl Roof w/Sealed Attic/Insulated deck (Avg= 0.98)Ivory IR Reflective Metal Shingle (Avg= 0.39)Galvanized 5-vee metal (Avg= 0.53)Black Shingle (Avg= 0.70)White standing seam metal (Avg= 0.30)Zero Heat Flux Line
Change in PerformanceFRF Test Results for Summer 2003
Increase in Avg Max Mid Attic Air Temperaturefrom 2002
Test Cell Description
Galvalum Galvanized Std Shingle White Mtl Air Temp
Max
Atti
c Te
mpe
ratu
re C
hang
e (o F)
-1
0
1
2
3
4
5
NoChange
Journal of Light Journal of Light ConstructionConstruction, June 2003
Information to the public…Information to the public…
Roof Research: What Next?
o Continue test of spectrally selective roofing materials
o Innovative roofing systems (e.g. sealed roofs, ventilation systems)
o Integrated Power Roofs (PV, solar, thermal control etc).
Night Sky Cooling Potential
oo Cool Night SkyCool Night Sky30 oF below ambient40-50/W/m2 in FloridaRoof: 1 ton coolingClear, calm nightsClouds, wind, reduce impact
Measured Night Cooling Potential: FRF
o FRF Test Cell with White metal Roof
o Roof surface temperature
o Average over Summer of 2001
o Shows sizeable cooling potential most nights
Flexible Roof Facility:Average Metal Roof Temperature Depression
Summer 2001
Time of Day: June - September 2001
0 2 4 6 8 10 12 14 16 18 20 22 24
Mea
sure
d Te
mpe
ratu
re (o F)
70
80
90
100
110Ambient air temp: Min= 72.2oFWhite metal roof: Min= 69.0oF
Interior Setpoint (77 oF)
NightCooling
NightCooling
NightCool Schematic
NightCool Simulation
o Modified Givoni-IngersollModel
o Simulate major influences with model
o Evaluate for sealed attic model with exposed metal roof
o Florida, Tampa= ~2 kW cooling potential under typical night conditions
Use two small buildings for test of concept
o Control and experimento Full exposed metal roof
on battens (no decking) with sealed attic
o Channel air to space when cooling conditions are met
o Use dehumidfier with heat rejection to attic
o Fully instrumented
Evaluation Sensitivity for Tampa, FL
o Major factorsCFM air flow and fan powerAmbient dewpoint(limiting factor on roof temperature)Wind if low dewpointInlet air temperature
o Minor factorsRoof tiltSurface emissivity
Excellent Predicted Performance…
o Tampa, FloridaHot humid climate challenge for conceptDaily summer cooling reduction of 15 kWhSEER of 37 Btu/Wh
o Atlanta, Georgia50 kWh/day coolingSEER = 71 Btu/Wh
o Phoenix, ArizonaVery hot arid climate23 kWh of daily summer coolingSEER of 61 Btu/Wh
Two small buildings for test of concept
o Control and experimento Full exposed metal roof
on battens (no decking) with sealed attic
o Channel air to space when conditions met
o Use dehumidfier with heat rejection to attic
o To be fully instrumented
Two Test Buildings Completed…
Experimental has open metal roof…
Other issues in Florida…Other issues in Florida…
Exposed White Metal Roof Runs Cooler…
o Runs 2 oF cooler without space conditioning
o Runs up to o4 F cooler on clear summer days
o Instrumentation with conditioning/dehumidifica-tion system to begin later in autumn 2005
Getting advantages on Getting advantages on the street…the street…
o More reflective roofing is no cost option within any roofing type, but…
o Need to influence decision at time of construction or re-roof
o Metal will have greatest reflectance longevity
o Chinese menu approachReflective roofRadiant BarrierMore insulation, interior ductsSealed attic with cool roofing
o Savings will be ~20-25% for cooling with very reflective roof
o 10 – 15% with moderately reflective tile roof with good venting
o ~10% for radiant barrier with good ventilation
o Peak savings are larger
Thank you!