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Reference Publication: Parker, D., Fairey, P., McCluney, R., Gueymard, C., Stedman, T., McIlvaine, J., "Rebuilding For Efficiency: Improving the Energy Use of Reconstructed Residences in South Florida", Prepared for U.S. Department of Energy, Florida Energy Office, and Florida Power & Light Company, FSEC-CR-562-92, December 1992.

Disclaimer: The views and opinions expressed in this article are solely those of the authors and are not intended to represent the views and opinions of the Florida Solar Energy Center.

REBUILDING FOR EFFICIENCY:
Improving the Energy Use of Reconstructed
Residences in South Florida

Appendix E
Reflective Roof Research at FSEC

Background Information

  • Florida Solar Energy Center (FSEC), began testing various residential roof finishes on small scale roof models in January of 1991. The tests were designed to determine the difference in heat build-up at the roof substrate.’

    Results compared various clay and concrete tile scenarios with white and darklgray shingles. Gray shingles painted with a white elastomeric coating (Flex-Tech in Sarasota, FL) were also included in the test and were found to perform very well.2

    The shingles painted with the elastomeric coating registered a sub-strate temperature about 50°F lower than the uncoated gray shingle and about 40°F lower than the white shingle.
  • Based on these findings, two full-size houses in Cocoa Beach, Florida were retrofitted with white elastomeric coating over shingles.

    Residence 1: pitched, gray shingle roof over plywood decking and R-19 ceiling insulation (Figures 1-4).

    Residence 2: flat, tar paper roof and no ceiling insulation (Figure 6).

    Prior to the retrofit, the two houses were monitored for one month. The air conditioning load of each house was measured every 15 minutes. The thermostats were left on a constant settings. After the retrofit was done on July 7, 1992 and the houses were monitored for another month (Figure 7).
  • An infra-red scanner (Figure 6), used to evaluate changes in heat gain, revealed greatly reduced heat flux from the attic in the home with the pitched roof (Figure 4).

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Preliminiry Results

  • The measured roof solar reflectance in both homes changed from about 20% to 70% after the coating was applied.
  • Comfort increased significantly in the flat-roofed home without ceiling insulation.
  • Maximum attic temperatures under the pitched roof dropped by at least 15°F. This potentially has a substantial impact on heat transfer to duct work located in attics, particularly if the duct work has any supply or return leaks.
  • Residence 1: Measured air conditioning consumption was reduced by over 20%. Figure 7 shows A/C energy consumption on the vertical-axis and day of experiment on the horizontal-axis. Attic temperatures are shown by the solid line; the diamonds show the 15-minute recorded electrical demand. The graph shows an eight day period of the two month monitoring (four days before the retrofit and four days after). Seventy-two to ninety-six represents the last 24-hour period before the retrofit and 96 to 120 represents the first day after the retrofit.
  • Residence 2: Figure 8 shows the reduction to air conditioning energy and improved interior comfort in the coated flat-roofed home. A 72-hour period during which the coating was applied is plotted. Before the roof is coated on July 31st, the 2.5-ton air conditioner runs constantly each summer day from 11 AM - 8 PM. After the coating, the air conditioner cycles on and off producing energy savings with greatly improved interior comfort conditions.
  • Results verify findings of other researchers.

Figure 7

Figure 8

FLORIDA SOLAR ENERGY CENTER
DSET Report No.: 4043203.01O
DSET No.: 40432
Date: September 3, 1992

Hemispherical Spectral Reflectrance Test Report

3.0 Observations, Deviations, and Waivers:

The measurements were made with the uncoded side of the specimens to the source.

The disparity at 350 and 400 nm in the spectral reflectance charts is attributed to normal pen response coupled with an automatic filter change in the Beckman 5240 Spectrophotometer. This disparity generally occurs only in regions of rapid change in percent transmittance.

4.0 Results

Specimen Code
% Reflectance
% Absorptance
Solar
UV
VIS
NIR
Solar
UV
VIS
NIR
Aged Elastomeric
72.7
17.4
78.5
73.1
27.3
82.6
21.5
26.9
Cement Tile
24.8
9.7
18.1
32.8
75.2
90.3
81.9
67.2
Lo Mit
54.1
50.9
53.3
55.2
45.9
49.1
46.7
44.8
Grey Shingle
21.7
10.1
23.1
21.7
78.3
89.9
76.9
78.3
White Shingle Flex-tec Elastomeric
65.0
14.1
69.4
66.3
35.0
85.9
30.6
33.7


FLORIDA SOLAR ENERGY CENTER
DSET Report No.: 4043203.01O
DSET No.: 40432
Date: September 3, 1992

Total Emittance Test Report

4.0 Results

Specimen Code
Reflectance Measured
Emittance Calculated
Aged Elastomeric
.14
.86
Cement Tile
.10
.90
Lo Mit
.58
.42
Grey Shingle
.09
.91
White Shingle Flex-tec Elastomeric
.11
.89


FLORIDA SOLAR ENERGY CENTER
DSET Report No.: 4043203.01O
DSET No.: 40432
Date: September 8, 1992

Directional Hemispherical Solar
Reflectance Test Report

4.0 Results

Date of Test: September 8, 1992
Start Time: 11:00 MST
Finish Time: 11:35 MST

Specimen
% Reflectance
Built-Up with Gravel
30.6
Smooth Built-Up
5.9
Gray EPDM
23.0
White EPDM
66.2
Black EPDM
6.0



FLORIDA SOLAR ENERGY CENTER
DSET Report No.: 4043203.01O
DSET No.: 40432
Date: August 4, 1992

Hemispherical Spectral Reflectance Test Report

4.0 Results

Specimen Code
% Reflectance
% Absorptance
Solar
UV
VIS
NIR
Solar
UV
VIS
NIR
Galvanized
71.3
75.0
74.0
68.7
28.7
25.0
26.0
31.3
Aluminum
60.9
29.3
49.4
73.5
39.1
70.7
50.6
26.5
Grey EPDM
23.1
13.5
27.2
20.2
76.9
86.5
72.8
79.8
White EPDM
68.7
16.7
68.3
75.0
31.3
83.3
31.7
25.0
Black EPDM
6.2
6.7
6.4
6.0
93.8
93.3
93.6
94.0
Hypalon
75.5
17.3
81.2
76.4
24.5
82.7
18.8
23.6
T-EPDM
80.6
16.7
88.7
79.8
19.4
83.3
11.3
20.2
Smooth Bitumen
5.8
4.2
5.2
6.6
94.2
95.8
94.8
93.4
Granular Surface Bitumen
25.8
9.3
28.4
25.0
74.2
90.7
71.6
75.0
Black Shingles
5.0
4.6
5.3
4.8
95.0
95.4
94.7
95.2
White Fiberglass Shingles
25.3
9.9
27.0
25.2
74.7
90.1
73.0
74.8


FLORIDA SOLAR ENERGY CENTER
DSET Report No.: 4043203.01O
DSET No.: 40432
Date: August 3, 1992

Total Emittance Test Report

3.0 Observations, Deviations, and Waivers

All measurements were performed on the uncoded surface. The values reported represent the average of at least five measurements.

4.0 Results

Specimen Code
Reflectance Measured
Emittance Calculated
Galvanized
.96
.04
Aluminum
.75
.25
Grey EPDM
.13
.87
White EPDM
.13
.87
Black EPDM
.14
.86
Hypalon
.09
.91
T-EPDM
.08
.92
Smooth Bitumen
.14
.86
Granular Surface Bitumen
.08
.92
Black Shingles
.09
.91
White Fiberglass Shingles
.09
.91
Smooth Built-Up
.09
.91


MEMORANDUM

Date: November, 1, 1991
To: Subrato Chandra, Jim Cummings, Bob Abernathy, Danny Parker
From: Jody Cummings
Subject: Measured solar absorptances of IHP surfaces
_________________________________________________________________________

On September 19, Jim Cummings and Bob Abernathy measured the solar absorptances of the IHP model roof structures and the IHP prototype walls using a PSP (serial #14392). The results of these tests are:

Dark grey shingle model roof
a = .88
Single batten red concrete
tile model roof
a = .86
Red metal model roof
a = .79
Elastomeric coated model roof
a = .41
Ceramic coated model roof
a = .41
Base prototype wall
a = .36
Dome prototype wall
a = .41
Dow prototype wall
a = .41
IHP cement slab
a = .71
Ceramic coating (different manufacturer)
Cummings house roof
a = .27

These measurements may overestimate the absorptance of the ceramic and elastomeric coated model roofs because a fraction of the roof surface is shaded by the PSP and beacase the small area of the model roofs cannot fill the full field of view of the PSP. The true values for the white coated model roofs may be closer to the measured value of .27 for the Cummings house roof. Jim suggested that measurements of larger surfaces with similar white coatings should be done.