FLORIDA TESTING
CONTRACT REPORT
Measured Air Conditioning Electricity Savings
From Reflective Roof Coatings Applied to Florida Residences
FSEC-CR-596-93
February 1993
Submitted to Florida Energy Office
2740 Centerview Dr. Tallahassee, FL 32399
Submitted by
D.S. Parker
J.B. Cummings
J.S. Sherwin
T.C. Stedman
J.E.R. McIlvaine
The Building Design Assistance Center
Florida Solar Energy Center
300 State Road 401
Cape Canaveral, Florida 32920
ENERCHRON TEST RESULTS:
More recently, the Sacramento Municipal Utilities District (SMUD) in conjunction with the Lawrence Berkeley Laboratories (LBL) has measured the cooling energy savings of reflectively coating two buildings in its service territory (Akbari et al, 1992). One building was an occupied residence located in an older section of Sacramento with R-11 ceiling insulation over a composite shingle roof. The initial roof reflectivity was measured at 0.18, which was altered to 0.81 by application of a roof coating (ENERCHRON®).
The air conditioning cooling load in the building virtually disappeared after the coating was applied (100% cooling energy savings).
Picture 1 (Below): Roof before testing with ENERCHRON®.
Picture 2 and 3 (Below): Albedo test equipment.
Picture 4 (Below):
With an air temperature of 86°F ENERCHRON® lowered the temperature to 99°F (13°F above air temperature) when covered with dirt and to 89°F (3°F above air temperature) when washed clean. ENERCHRON® lowered HVAC energy use with a very high level of dirt build up (10°F difference between clean and dirty), which was critical to long term energy savings.
The small amount of cooling still measured was due to occupant-related changes to the cooling set point. The building cooling thermostat was initially set to 80°F although occupants later changed the thermostat down to 75°F. The savings amounted to an energy use reduction of approximately 12 kWh per day with a 2.3 kW reduction in peak power demand. The second building evaluated was a test bungalow at a school site. The building's corrugated metal roof was insulated from the interior space by R-19 insulation. The roof albedo and that of the building's southeast wall was altered from 0.08 to 0.68. Measured air conditioning energy use was reduced by approximately 50%
short term testing 46% long term testing (covered with dirt).
AZTEC 100 TEST RESULTS:
The reflective roof was applied on September 5, 1991 with approximately 37 gallons of Insulating Coatings Corporation's Aztec 100, applied to the 2,300 square foot roof surface. The roof reflectivity was measured to increase from 0.22 to 0.73 after the coating was applied. Spot measurements under full sun at mid-summer showed shingle surface temperatures of 160-170°F prior to the roof treatment as compared with 100°F after the coating was applied. As shown in Figure 3, recorded roof deck and attic air temperatures clearly evidence how the white coating reduced thermal loads on days with similar weather conditions. Since the roof reflectivity was changed late in the cooling season, analysis of cooling energy savings was accomplished by correlating the daily recorded air conditioning electricity use to average ambient air temperature. Data for 24 days from the "before" period were eliminated to yield 44 days with a similar average level of solar insulation to that recorded in the 14 day period after the coating was applied. A plot of the resulting data is shown as Figure 4 with least-squares best-fit lines drawn through the data points for the before and after periods. The difference in the regression lines indicates the savings of the reflective roof coating.
Evaluated at an average summer temperature of 81°F, the analysis indicated a 10.5% savings of the reflective roof coating (38.7 kWh/day vs. 34.7 kWh/day).
