Cool Roofing …Cutting Through the Glare

Atlanta May 2005
“Cool Roof Coatings to Reduce Energy Demand and Temperature in an Urban Environment”
Liz Robinson, Director ECA
Michael Blasnik and Associates, APPRISE Incorporated
Bill Kirn RRC, Technical Director, National Coatings Corporation

Abstract

The Energy Coordinating Agency is a Philadelphia based private non-profit corporation
dedicated to ensuring that low and moderate income people have access to safe,
affordable and reliable sources of energy and water. ECA works to develop a sustainable
energy future for the region through energy conservation and renewable energy. ECA
coordinates and provides energy conservation services to thousands of households in the
Philadelphia area every year.

In 2000 ECA began a pilot program to investigate the potential for “cool roof coatings”
as a means of reducing cooling energy costs and providing passive cooling to row homes.
Results of energy monitoring as well as roof and interior temperatures proved that this
technology was viable and could be part of a more comprehensive program to reduce
overall energy costs to residents.

The success of the early experiments was followed up with a more comprehensive
program called “Cool Block” where an entire city block of row homes was coated.
Monitoring in this study included actual outside temperatures in the alley which ran the
length of the block Peak temperatures were compared to a control block with black
uncoated roofs and found to be lower as a result of the reflective coating. Thus the
reflective coating actually had an impact on lowering the “urban heat island”
temperature.

Actual case histories and performance data will be detailed, including an update on this
program and efforts to replicate the program in other urban areas.

Background

The Energy Coordinating Agency is a Philadelphia based private non-profit corporation
dedicated to ensuring that low and moderate income people have access to safe,
affordable and reliable sources of energy and water. In the mid 1990’s, ECA began
exploring ways to assist their clients in dealing with issues relating to summertime
cooling. While some homeowners had air conditioners, the cost of electricity relative to
their income sometimes prevented them from operating them. In addition, extreme
summertime heat events in Chicago and other major urban areas caused ECA to consider
alternative methods to assist their clients. These “killer heat waves” achieved dubious
notoriety when in 1995, 435 people died in Chicago due to heat related illnesses. In
Philadelphia, these heat waves were directly responsible for 118 deaths in 1993, 61
deaths in 1995 and 67 in 1999. The most vulnerable are comprised mainly of low income
seniors who have a higher risk of heat related health problems due to poor general health
status, social isolation, physical limitations, and safety concerns that detract from their
ability to manage high temperatures.

Early Experiments:

Research published by Rohm and Haas, National Coatings Corporation and Oak Ridge
and Lawrence Berkeley National Laboratories 1-18 showed that some cooling and
reduction in air conditioning load and electricity required to condition buildings could be
realized by coating low slope roofs white to reflect the infra red portion of solar radiation.
The studies also showed energy and life cycle benefits for reflective roof coatings.
Almost all of ECA’s clients live in densely populated urban two story row homes, with
low slope asphalt built up or modified bitumen roofs.

“Cool Homes” Program

ECA began a pilot program coating several homes in Philadelphia. Each home was
equipped with recoding thermometers placed strategically in the structure. A set of
uncoated “control” homes were also monitored to determine the effect of the reflective
coating. Electricity demand was also monitored. However, it would be preferred to
reduce the temperatures in these homes without or minimum mechanical/electrical
cooling. The homes had blown-in insulation in the cavity spaces under the roof deck and
above the 2nd floor ceilings. The R values ranged from 8-12. The reflective roof coating
used in the project had solar reflectance of 0.83 and thermal emittance of 0.89.
The Cool Home pilot collected temperature and humidity with data loggers at 35 houses.
Six of these houses were logged in the summer 2001 and treated before the summer of
2002. Six more houses were designated for the comparison group and did not receive
coating during the summer, leaving 23 houses with potential for short-term pre/post
analysis. Three of these houses did not have any data from the second floor bedroom
wall and one of the remaining houses did not receive any major coatings during the
summer, leaving 19 houses for the pre/post analysis. All but two of these 19 houses
have air conditioners.

Temperature Time Series Profiles

There were few days with similar outdoor temperatures between the pre and post coating
periods, but July 2nd and July 16th were fairly similar with peak temperatures in the mid-
90s and clear skies. Both also had similarly warm days preceding them (reducing the
potential impact of thermal mass effects).

The figure below (Figure 1) shows the temperature data for four houses where the data
for each of these two days is overlapped. The dashed lines show the July 2nd data
(representing the “pre-coating” condition) and the solid lines show the July 16th data (post
coating). The bold lines show the 2nd floor bedroom indoor air temperatures while the
lighter lines show the outdoor temperatures. (Note: In all cases “indoor air
temperatures” refers to the temperature measured at chest height.) “T in Pre” is
interior (chest height) temperature prior to coating, “T in Post” is interior (chest height)
temperature after coating, “T out Pre” is exterior temperature prior to coating, and “T out
Post” is exterior temperature after coating.

Contact Information
National Coatings Corporation
info@nationalcoatings.com
http://www.nationalcoatings.com
800-423-9557