Field Test Results of Green Roofs, Cool Roofs, and ...
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Field Test Results of Green Roofs, Cool Roofs, and Conventional Roofs CNY Engineering Expo Oncenter, Syracuse, NY November 9, 2015 Hugh I. Henderson, Jr. P.E CDH Energy Corp. Cazenovia, NY
Transcript of Field Test Results of Green Roofs, Cool Roofs, and ...
Field Test Results of Green
Roofs, Cool Roofs, and
Conventional RoofsCNY Engineering Expo
Oncenter, Syracuse, NY
November 9, 2015
Hugh I. Henderson, Jr. P.E
CDH Energy Corp.
Cazenovia, NY
Project Goals
• Side-by-Side Comparison of Different Roofing
Systems
– EPDM w/ 4 inches of foam (UNIT 1)
– TPO w/ 4 inches of foam (UNIT 2)
– Vegetative Roof with 4 inches (UNIT 3)
– TPO w/ 8 inches of foam (UNIT 4)
• Measure Performance Impacts
– Compare thermal losses / energy impacts
– Compare water retention performance
• Jamesville provided 4 similar roof applications
Four Different Roofs at the Same
Facility
Unit 1
EPDM, 4 in
Unit 2
TPO, 4 in
Unit 3
Veg, 4 in
Unit 4
TPO, 8 in
Approach
• Install dataloggers to continuously monitor performance
– Two independent measurement locations on each roof
– Collect data continuously at 15-minute intervals
– Directly measure temperature differences through roof assembly
– Measure weather conditions
– Direct measurement of HVAC energy use was not practical at this site
Roof Assemblies
Location Insulation Surface
Unit 1 4 inches Poly Iso1 foam board
(R22)
EPDM rubber2
Unit 2 4 inches Poly Iso1 foam board
(R22)
TPO White3
Unit 3 4 inches Poly Iso1 foam board
(R22 + vegetative laver)
EPDM w/ Vegetative
Surface
Unit 4 8 inches Poly Iso1 foam board
(R45)
TPO White3
Notes: 1- Polyisocyanurate foam board applied in 2 inch layers
2- Black EPDM (Ethylene Propylene Diene Monomer) single-ply rubber roof membrane
3- White TPO (Thermoplastic Polyolefin) roof membrane
Vegetative Roof
• Carlisle Roof
Garden System
• Light-weight
assembly
Instrumentation
Point Description Instrument Eng
Units
Locations
TRO Roof Temperature
(on top of insulation, under roof brd)
Type-T
Thermocouple
ºF At each station
TRI Roof Temperature
(under roof insulation, above deck)
Type-T
Thermocouple
ºF At each station
TAI Indoor Temperature
(just below the roof)
Type-T
Thermocouple
ºF At each station
Point Description Instrument Eng
Units
Locations
TAO Outdoor Temperature Type-T
Thermocouple
ºF Station 2A
ISH Solar Insulation
(horizontal)
Licor LI200x W/m2 Station 2A
TGR Green Roof Temperature
(in middle of soil layer)
Type-T
Thermocouple
ºF Station 3A
MGR Green Roof Moisture Content
(in middle of soil layer)
Campbell
Scientific CS616
0-1 Station 3A
RAIN Rainfall Texas
Electronics 525
Inches Station 2A
WF Water Flow from Green Roof
Mockup
Hydrolynx 5050 Gal/h Station 2A
Roof Sensor Location/Station
Thermocouple TRO Thermocouple TRI
Thermocouple TAI
Sensors Installed During
Construction
Insulation
Board
Thermocouple
Probe
Thermocouple on Top of Insulation
(station 1B)
Indoor Thermocouple
A & B Stations on Each Unit
1A
1B
Results for Sunny November Day
EPDM TPO
Unit 1: 4 in, EPDM
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
20
40
60
80
100
Tem
pera
ture
(F
)
Unit 2: 4 in, TPO
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
30
40
50
60
70
80
Tem
pera
ture
(F
)
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
0
200
400
Inso
lation (
W/m
^2)
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
-2
0
2
Heat
Loss
(B
tu/f
t^2-h
)
Unit 3: 4 in, Veg
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
30
40
50
60
70
80
Tem
pera
ture
(F
)Unit 4: 8 in, TPO
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
30
40
50
60
70
80
Tem
pera
ture
(F
)
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
0
200
400
Inso
lation (
W/m
^2)
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
-2
0
2
Heat
Loss
(B
tu/f
t^2-h
)
Ambient Temperature, Top of Insulation, Bottom of Insulation, Indoor Temperature
Heat Transfer Analysis
TAO
TRO
TRI
TAI
Rinsulation q Insulation
Board
Concrete Deck
Veg roof (optional)
Deck Board membrane
Where:
Rinsulation - R-value for Insulation layer
(ºF-h-ft2/Btu)
q - Heat flux through the roof
assembly (Btu/h-ft2)
q = (TRI-TRO) Rinsulatiion
Insulation Layer
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
8 9 10
Nov
2009
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
He
at
Lo
ss R
ate
(B
tu/f
t^2
-h)
Unit 1: 4 in, EPDM
Unit 2: 4 in, TPO
Unit 3: 4 in, Veg
Unit 4: 8 in, TPO
Impact on Heat Transfer(solid line = station A / dotted line = station B)
q = (TRI – TRO)/Rins
Summer Sunny, 71F pkMay 29
Summer, Sunny, 71F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
28 29 30
40
60
80
100
120
140
160
Tem
pera
ture
(F
)
Summer, Sunny, 71F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
28 29 30
-4
-3
-2
-1
0
1
2
Heat
Loss
(B
tu/f
t^2-h
)
Summer, Sunny, 59F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
15 16 17
20
40
60
80
100
120
140
160
Tem
pera
ture
(F
)
Summer, Sunny, 59F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
15 16 17
-6
-4
-2
0
2
4
Heat
Loss
(B
tu/f
t^2-h
)Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Summer Sunny, 59F pkMay 16
Summer, Sunny, 71F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
28 29 30
40
60
80
100
120
140
160
Tem
pera
ture
(F
)
Summer, Sunny, 71F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
28 29 30
-4
-3
-2
-1
0
1
2
Heat
Loss
(B
tu/f
t^2-h
)
Summer, Sunny, 59F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
15 16 17
20
40
60
80
100
120
140
160
Tem
pera
ture
(F
)
Summer, Sunny, 59F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
15 16 17
-6
-4
-2
0
2
4
Heat
Loss
(B
tu/f
t^2-h
)
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Summer Cloudy, 44F pkMay 12
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Summer, Cloudy, 44F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
11 12 13
20
30
40
50
60
70
80
90
Tem
pera
ture
(F
)
Summer, Cloudy, 44F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
11 12 13
-2
0
2
4
Heat
Loss
(B
tu/f
t^2-h
)
Fall, Sunny, 38F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
1 2 3
0
20
40
60
80
100
Tem
pera
ture
(F
)
Fall, Sunny, 38F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
1 2 3
-2
-1
0
1
2
3
Heat
Loss
(B
tu/f
t^2-h
)
Fall Sunny, 38F pkNov 2
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Summer, Cloudy, 44F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
11 12 13
20
30
40
50
60
70
80
90
Tem
pera
ture
(F
)
Summer, Cloudy, 44F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
11 12 13
-2
0
2
4
Heat
Loss
(B
tu/f
t^2-h
)
Fall, Sunny, 38F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
1 2 3
0
20
40
60
80
100
Tem
pera
ture
(F
)
Fall, Sunny, 38F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
1 2 3
-2
-1
0
1
2
3
Heat
Loss
(B
tu/f
t^2-h
)
Winter Sunny, 3F pkJan 24
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Winter, Sunny, 3F, Min temp of -13F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
23 24 25
-10
0
10
20
30
40
Tem
pera
ture
(F
)
Winter, Sunny, 3F, Min temp of -13F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
23 24 25
1.0
1.5
2.0
2.5
3.0
3.5
Heat
Loss
(B
tu/f
t^2-h
)
Winter, Cloudy, 25F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
18 19 20
-10
0
10
20
30
40
Tem
pera
ture
(F
)
Winter, Cloudy, 25F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
18 19 20
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Heat
Loss
(B
tu/f
t^2-h
)
Winter Cloudy, 25F pkJan 19
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Winter, Sunny, 3F, Min temp of -13F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
23 24 25
25
30
35
40
45
Tem
pera
ture
(F
)
Winter, Sunny, 3F, Min temp of -13F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
23 24 25
1.0
1.5
2.0
2.5
3.0
3.5
Heat
Loss
(B
tu/f
t^2-h
)
Winter, Cloudy, 25F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
18 19 20
25
30
35
40
45
Tem
pera
ture
(F
)
Winter, Cloudy, 25F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
18 19 20
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Heat
Loss
(B
tu/f
t^2-h
)
Spring Rainy, 41F pkApr 17
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
Spring, Morning, 41F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
16 17 18
35
40
45
50
55
60
Tem
pera
ture
(F
)
Spring, Morning, 41F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
16 17 18
0.0
0.5
1.0
1.5
2.0
Heat
Loss
(B
tu/f
t^2-h
)
Spring, Sunny, 49F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
13 14 15
0
20
40
60
80
100
120
140
160
Tem
pera
ture
(F
)
Spring, Sunny, 49F
22: 0: 2: 4: 6: 8: 10: 12: 14: 16: 18: 20: 22: 0:
13 14 15
-4
-2
0
2
4
Heat
Loss
(B
tu/f
t^2-h
)
Rain
Impact of
Snow &
Rain
30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Nov Dec
0
20
40
60
Te
mp
era
ture
(F
)
30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Nov Dec
0.0
0.5
1.0
1.5
2.0
2.5
3.0H
ea
t L
oss (
Btu
/ft^
2-h
)
Unit 1: 4 in, EPDM, Unit 2: 4 in, TPO, Unit 3: 4 in, Veg, Unit 4: 8 in, TPO
30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
December
0.00
0.05
0.10
0.15
0.20
0.25
Wa
ter
(in
ch
es) Rainfall
Drainage
RainSnow
(no drainage)
Ambient
Daily Heat Loss
0 20 40 60 80 100
Outdoor Temperature (F)
-40
-20
0
20
40
60
He
at
Lo
ss (
Btu
/ft^
2-d
ay)
Unit 1: 4 in, EPDM
Unit 2: 4 in, TPO
Unit 3: 4 in, Veg
Unit 4: 8 in, TPO
Impact of
Snow Cover
Heat Loss
Heat Gain
Monthly
Heat Loss
Month
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
November-09 675.2 930.2 815.8 603.1
December-09 1,063.2 1,253.3 1,078.4 823.1
January-10 1,089.5 1,231.3 1,090.0 824.1
February-10 939.6 1,043.6 999.0 728.1
March-10 629.8 900.5 883.9 623.6
April-10 138.8 496.9 550.2 379.4
May-10 (178.1) 248.0 339.3 216.3
June-10 (261.0) 75.4 178.5 117.5
July-10 (437.9) (22.2) 135.8 59.6
August-10 (302.7) 34.4 174.5 83.6
September-10 (8.8) 306.7 313.3 221.0
October-10 394.8 641.0 621.6 445.9
November-10 724.2 946.5 874.8 636.2
December-10 968.7 1,101.0 1,013.5 729.2
January-11 970.8 1,178.0 1,035.6 734.1
February-11 879.4 1,074.0 942.2 679.1
2010 Htg Season 4,885.5 6,360.8 6,032.8 4,366.6
(Oct to April) 1,475.3 1,147.4 (518.8)
30% 23% -11%
2010 Clg Season (1,188.5) 642.2 1,141.3 698.0
(May to Sep) 1,830.7 2,329.9 1,886.5
Heat Loss (Btu/ft^2)
Monthly Heat Loss
(600)
(400)
(200)
-
200
400
600
800
1,000
1,200
1,400Ja
n-1
0
Feb
-10
Mar-10
Apr-
10
May-
10
Jun-1
0
Jul-10
Aug-1
0
Sep-1
0
Oct
-10
Nov-
10
Dec-
10
He
at
Lo
ss
(B
tu/f
t^2
)
Unit 1: 4 in EPDM
Unit 2: 4 in TPO
Unit 3: 4 in Veg
Unit 4: 8 in TPO
Heat Gain
Heat Loss
Seasonal Cost Analysis
• Heating Season Assumptions:
– 80% efficient, $1 per therm
• Cooling Season Assumptions:
– 0.9 kW per ton, 12¢ per kWh
Heating and Cooling Costs
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
4.9 6.4 6.0 4.4
61.1 79.5 75.4 54.6
61$ 80$ 75$ 55$
(18)$ (14)$ 6$
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
152.6 194.2 157.2
137.3 174.7 141.5
16$ 21$ 17$
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
(2)$ 7$ 23$
COOLING
COMBINED
Savings per 1000 sq ft
Reduced Cooling (ton-hrs/yr per 1000 sq ft)
Reduced Cooling Power (kWh/yr per 1000 sq ft)
NET Savings per 1000 sq ft
Annual Gas Use (therms per 1000 sq ft)
Annual Cost per 1000 sq ft
Savings per 1000 sq ft
Annual Heat Load (MMBtu per 1000 sq ft)
HEATING
Water Retention
Testing
Long Term Retention Impacts
0 2 4 6 8
Rainfall (in)
0
2
4
6
8D
rain
ag
e (
in)
Retention Rate
is about 75-80%
Vegetative Roof Provides
Evaporative Cooling
22: 0: 2: 4: 6: 8: 10:12:14:16:18:20:22: 0:
40
60
80
100
Am
bie
nt
Tem
pera
ture
(F
)
22: 0: 2: 4: 6: 8: 10:12:14:16:18:20:22: 0:
0.0
0.2
0.4
0.6
0.8
1.0
Insola
tion (
W/m
^2)
22: 0: 2: 4: 6: 8: 10:12:14:16:18:20:22: 0:
0
5
10
15
20
25
Soil
Mois
ture
Conte
nt
(%)
22: 0: 2: 4: 6: 8: 10:12:14:16:18:20:22: 0:
60
65
70
75
80
Roof
Tem
p (
F)
July 20, 2010
July 27, 2010
More Recent Work
• Is simplistic heat transfer model accurate?
– Does heat transfer into roof deck = heat into space
• Longer term results (2009 to 2015)
– Impacts of aging
• Snow Retention on roof compared to ground
– Are the roof surfaces different?
A More Detailed Heat Transfer Model
• Developed EnergyPlus (E+) model of roof assembly
with finite difference option (not default CTF)
– Provides temperatures within layers
– Provides heat flux at both inside and outside surfaces
• Massive concrete layer confounds simple method
74
76
78
80
82
84
86
88
90
92
1 2 3 4 5 6 7 8 9
Tem
pe
ratu
re (F
)
7/1/2014 12:00
Insulation Layer
Tro
Tri
Comparison of Heat Loss through Concrete and Insulation layers
-200 -100 0 100 200 300
Concrete Layer Heat Loss (Wh/m2-day)
-200
-100
0
100
200
300
Insu
latio
n L
aye
r H
ea
t L
oss (
Wh
/m2
-da
y)
NRMSE=31.%
An Approximate Correction
• Use a simple mass
correction for the
concrete layer
• Demonstrated to work
with E+ results
• Applied correction to
the field data
Comparison of Heat Loss through Concrete layer, R22
-300 -200 -100 0 100 200 300
Energy Plus Model (Wh/m2-day)
-300
-200
-100
0
100
200
300
Sim
plif
ied M
odel (W
h/m
2-d
ay)
NRMSE=0.49%
Impact of Applying CorrectionUnit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
2010 Htg Season 4885.5 6360.8 6032.8 4366.6 4905.3 6364.3 6047.2 4320.5
(Oct to April) 1475.3 1147.4 -518.8 1459.0 1141.9 -584.8
30% 23% -11% 30% 23% -12%
2010 Clg Season (1188.5) 642.2 1141.3 698.0 (1217.8) 639.3 1140.3 714.4
(May to Sep) 1830.7 2329.9 1886.5 1857.1 2358.2 1932.3
2011 Htg Season 3958.3 5725.5 5153.8 3407.3 4790.9 6557.0 5935.2 4156.3
(Oct to April) 1767.2 1195.5 -551.0 1766.1 1144.3 -634.6
45% 30% -14% 37% 24% -13%
2011 Clg Season (1204.4) 476.7 1009.4 558.8 (1244.9) 459.4 1004.9 559.3
(May to Sep) 1681.2 2213.8 1763.3 1704.2 2249.8 1804.2
2012 Htg Season 4483.5 6478.7 5942.2 4089.5 4496.8 6464.9 5964.3 4108.0
(Oct to April) 1995.2 1458.7 -394.0 1968.2 1480.8 -375.5
45% 33% -9% 44% 33% -8%
2012 Clg Season (1333.5) 568.1 1178.2 627.6 (1352.7) 570.4 1191.6 643.8
(May to Sep) 1901.5 2511.7 1961.1 1923.1 2544.3 1996.5
2013 Htg Season 5333.6 7179.9 6507.5 4937.1 5357.4 7202.5 6509.8 5000.0
(Oct to April) 1846.4 1174.0 -396.5 1845.1 1152.4 -357.5
38% 24% -8% 34% 23% -7%
2013 Clg Season (943.2) 1050.3 1408.7 881.6 (928.6) 1082.1 1422.5 888.6
(May to Sep) 1993.5 2351.9 1824.8 2010.7 2351.0 1817.2
2014 Htg Season 4472.2 6128.9 5503.6 4258.0 4381.0 6095.1 5510.5 4251.6
(Oct to April) 1656.6 1031.3 -214.2 1714.0 1129.5 -129.5
37% 23% -5% 39% 26% -3%
2014 Clg Season (1036.9) 802.5 1292.9 833.2 (981.1) 822.9 1278.2 818.5
(May to Sep) 1839.4 2329.9 1870.2 1804.0 2259.3 1799.6
Heat Loss (Btu/ft^2), No Thermal Mass Heat Loss (Btu/ft^2), With Thermal Mass
Impact of Applying Correction
HeatingUnit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Avg Annual Heat Load (MMBTU per 1000 sq ft) 4.6 6.4 5.8 4.2 4.8 6.5 6.0 4.4
Annual Gas Use (therms per 1000 sq ft) 57.8 79.7 72.8 52.6 59.8 81.7 74.9 54.6
Annual Cost Per 1000 sq ft 58$ 80$ 73$ 53$ 60$ 82$ 75$ 55$
saving per 1000 sq ft (22)$ (15)$ 5$ (24)$ (17)$ 3$
Reduced Cooling (ton-hrs/yr per 1000 sq ft) 154.1 195.6 155.1 155.0 196.0 155.8
Reduced Cooling Power (kWh/yr per 1000 sq ft) 138.7 176.1 139.6 139.5 176.4 140.2
Savings per 1000 sq ft 17$ 21$ 17$ 17$ 21$ 17$
Net Saving per 1000 sq ft (5)$ 6$ 22$ (7)$ 4$ 20$
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Unit 1
4 in EPDMCombined Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Heat Loss (Btu/ft^2), No Thermal Mass Heat Loss (Btu/ft^2), With Thermal Mass
Cooling Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Unit 1
4 in EPDM
Unit 2
4 in TPO
Unit 3
4 in Veg
Unit 4
8 in TPO
Conclusions
• TPO or “cool roof” is energy cost neutral in
Central NY: benefit in summer, penalty in
winter
• Vegetative roof has cooling season benefit
(due to evaporation)
• More insulation is better (especially in the
winter)
• Vegetative roof retains 75-80% of rainfall
