Saturday, May 19, 2012
White Roof Reduces Cooling Load
Today, as we have for the last 3 years, we put into practice our "green building" commitment by coating our Organic Food Depot grocery store roof white in Virginia Beach.
It is a fairly well established fact that having a white roof reduces heat load by 30% - 40% http://www.gizmag.com/white-roof-heat-island/21758/, and I know on our own house which has a white roof, it's what makes the difference between whether our undersized A/C system works or not.
For our grocery stores, the internal equipment heat load plus the external solar load can overwhelm an A/C unit, leading to premature failure, an expensive replacement I can tell you from experience. Therefore, anything we can do to lessen the summer heat load in a cost effective manner, is something we look for, and coating our roof white certainly makes a huge difference.
However, we don't "paint" our roof white, both because runoff might affect nearby wetlands, and because we actually want the coating to wash off by Winter.
So we use Kool Ray Liquid Shade from Continental Products.
It's made for greenhouses, is non-toxic and is designed to wash off over time. http://www.continentalprod.com/greenhouse/kool/kool.htm
As you can see from this first photo, after a winter, most of the previous year's coating has been removed by rain. This gives us radiant absorption during the winter. The roof, being back to black, acts like a solar collector. We get the best of both worlds - cooling in the summer, heat in the winter.
It took 4 of us about half a day to roll on the new coating. The roof is a black, 8,000 sq. ft. EPDM rubber membrane. We used three 5-gallon pails, mixed 1:1 with water, and a small amount of "extra stick" for longer adhesion. Cost was minimal, around $500.
The result is bright white and reflects sunlight well. The A/C units on the roof which had been running when we started, stopped during the installation, and only ran sporadically the rest of the day, so clearly the coating had an immediate effect.
We know it works, though we haven't tried to quantified it precisely.
If all the businesses and even homeowners in Tidewater were to adopt white roofs, the savings in cooling costs would be substantial, not to mention the fact that we would no longer need to build new power plants.
Getting homeowners to make their roof white is probably not going to happen. It has no aesthetic appeal. Businesses, however, are another story, and the payback could be calculated.