Placing a pan of ice chunks in front of a small electric fan indoors and wearing a white hat outdoors—great-grandma knew a thing or two about keeping cool on the hottest summer days.
Her simple, low-tech ideas are the inspiration behind two new strategies for summer comfort. One system uses ice as part of the air-conditioning system for a whole building. The other idea uses white and other light colors for reflective roofs.
These new technologies can help lower the amount of electricity used during afternoon peak-demand times. That’s an important step in helping utilities manage their existing power plants more efficiently. Reducing daytime demand could also help delay the need to build new power plants. These technologies also mean lower monthly energy bills for consumers.
In most air-conditioning systems used today, a pump compresses a special gas within coils of tubing. The temperature of the gas regularly moves back and forth between cold and warm. These recurring cycles use a lot of electricity.
Air conditioning with ice
Using ice instead of a gas can change that. At night, electricity powers icemakers that freeze water. During the day, when demand for power is high, there’s no need to use more electricity to refreeze the water.
In one version of the new system, air passes over the ice, becomes chilled, and then travels through the building. The ice-making cycle is repeated during the next night, using the water over again.
In the basement of the 1.9-million-square-foot Credit Suisse office building in New York, machines turn the water in sixty-four 800-gallon tanks into ice each night. During the hottest part of the afternoon, air passing across the ice cools the interior of the huge skyscraper.
In another kind of ice-based system, ice cools water instead of air. Under a parking lot at California’s Stanford University, a 4-million-gallon tank of water becomes a huge block of ice. Water in a separate system passes over the ice, then 360 miles of pipes circulate the chilled water to buildings all over campus to cool them. Each night, the water is refrozen for a fresh supply of ice the next day.
Shifting electricity use to nighttime hours helps utilities manage their generating systems, and it can also help large energy consumers. Commercial and industrial electricity users typically pay different rates for their power depending on the time of day. For really large spaces such as a towering skyscraper or a sprawling campus, using an ice system at night when electricity is cheaper can be an important money-saving strategy.
For the small- to mid-sized commercial buildings common in Kentucky, a third style of ice system may be more useful.
Up on the roof
Instead of putting huge water tanks and ice-making equipment in the basement or underground, a mini icemaker system can be mounted on the roof of a one- or two-story commercial building. Other mini systems allow the ice tank to be installed in the ground outdoors instead of inside a basement.
Computer controls allow the building’s owner to program the ice system to work with the normal HVAC system according to local weather conditions and electric rates. The existing gas compressor system cools the building during off-peak times. The mini ice system kicks in for four to six hours during peak times.
Homeowners and commercial property managers are also taking another look at roof materials and construction methods for other opportunities to reduce summer air-conditioning use.
For homes with little or no natural shade, a light-colored “cool” roof may help. In a typical angled household roof, there is attic space between the roof and the home’s interior. Proper ventilation of this buffer space, plus proper insulation, helps moderate heat transfer from the outermost roof surface to the living space. That can reduce the number of times an air-conditioning system needs to cycle on during the hottest part of the day.
In a flat roof on a commercial building, the roof and its various layers of insulation touch each other in a weatherproof sandwich. Each of those layers can absorb heat from the sun and quickly transfer it to the building, adding to the amount of effort it takes to cool the interior.
Investigators testing products for the federal ENERGY STAR label and independent labs such as the Cool Roof Rating Council measure roofing materials according to two standards. The rating for “solar reflectance” measures how well sunlight bounces off a roof. The rating for “thermal emittance” tells how well a roofing material can radiate any heat it does absorb back into the atmosphere. Higher numbers are better.
Upgrading to one of these new materials when an existing roof needs to be replaced may be the quickest way to lower monthly energy use during the summer in Kentucky.
KNOW YOUR CONTRACTOR
Kentucky HVAC contractors must pass a licensing exam and meet certain standards. For more information about the program, visit www.dhbc.ky.gov/hvac.
However, there is no state licensing requirement for residential roofing contractors. Mike Sasse, owner of Louisville-based Commonwealth Roofing and past president of the Kentucky Roofing Contractors Association, says, “To help consumers, in 2001 KRCA began a certification program for roofers that is described on our Web site at www.krca.org. KRCA-certified contractors must stay up-to-date about materials, procedures, and safety practices.”