Task Air-conditioning For Sleeping
The Sun Frost “Sleep Genie”

In a hot humid climate, keeping comfortable by passive strategies is often difficult and sometimes not possible. Passive strategies, such as high ceilings and large operable windows to increase ventilation, can make conventional air conditioning more difficult because of increased heat gains. Sun Frost has developed an air-conditioner to provide comfortable sleeping conditions even in an airy uninsulated building. The strategy to accomplish this feat is to create a relatively small, insulated space around the bed. This space can then be air-conditioned and dehumidified with a very small air-conditioner. A diagram of the air-conditioner and enclosure is shown in the accompanying figure. Here the structure is installed over a small single bed. Since cold air is heavier than hot air, the space above the occupant’s head can be left open.

The compressors we are currently using to power the cooling system can be run off either a 12-volt or a 24-volt battery bank. We will also be building a 120-volt model. The typical load in a 12-volt system will be about 7 amps or 84 watts. With 8 hours of sleep, the nightly electrical load at 12 volts will be about 56 amp-hours or 672 watt-hours. To power this air conditioner with photovoltaic panels, a 200-watt array would typically be required.

In addition to homes, this concept could find wide application in long-haul trucks with sleeper compartments. Currently, drivers idle their trucks all night to keep cool in hot weather. This burns up about 1 gallon of diesel fuel per hour and causes a great deal of noise and air pollution. Idling trucks all night is becoming illegal in a great many states for these reasons. With Sun Frost’s “Sleep Genie”, idling would not be necessary because the air-conditioner could be run off the truck’s starting batteries.

In some tropical countries like Singapore, many of the buildings are concrete and use no passive strategies for cooling. As a result of poor design, heat from sun-baked walls will begin to penetrate into an apartment several hours after sunset creating the most uncomfortable conditions as you are getting ready to go to bed. In Singapore, air-conditioners are often only used at night to make a bedroom more comfortable. Instead of cooling a high thermal mass, uninsulated space, a task air-conditioner like the “Sleep Genie” would be a much more energy efficient solution. Of course, it would make the most sense to combine strategies, incorporate the “Sleep Genie”, insulate the building and put windows in the most appropriate locations with effective shading devices and then use the “Sleep Genie” when necessary. “Task” air conditioning is a simple strategy for cutting the air conditioning electrical loads for the 1/3 of your day you are off your feet and making solar cooling more practical.

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