Using solar energy to air-condition your home

Wrapped in a layer of aluminum foil and surrounded by a cadre of inquisitive investors, the machine hums mysteriously. Somber-faced technicians dressed in lab coats and eyeing clipboards add to the intrigue. So does the shape of the machine, which stretches across the floor of the large room like a down-sized linear accelerator.

But the device is less a mystery than an anomaly: a sun-powered air conditioner.

The unit on display here for a group of analysts is the prototype of a residential air-conditioning unit that American Solar King of Waco, Texas, expects to market by 1985.

The machine employs a three-step process to condition air. First, incoming air passes through a desiccant wheel. (Desiccants are drying agents that remove moisture from the air.) Next, the dry air passes through a heat-exchange wheel. This removes almost all of the heat in the air.

In the third stage, the air passes through a moist element that replaces the moisture - rehumidifies it through evaporation - which has the effect of cooling the air. The process is reversed for outgoing air to dry the desiccant wheel. The power needed to run the system would be provided by solar panels mounted on a homeowner's roof.

Desiccant cooling technology is not new and is not exclusive to American Solar King. Various solar air-conditioning techniques have been the subject of experiments for decades, but scientists say the desiccant system is most promising.

Exxon began experimenting with desiccant solar air conditioning about four years ago. Department of Energy officials say Exxon's research advanced the technology by roughly 50 percent over the state of the art. But a variety of factors caused the company to quit the solar field in late 1981.

Two parties stepped into the breach: American Solar King and the Gas Research Institute in Chicago. Each negotiated separate deals with Exxon for rights to the technology Exxon had developed. Along with the Solar Energy Research Institute near Denver, the three are the leaders in solar air-conditioning technology.

The Gas Research Institute has just begun construction of a laboratory prototype. Keith Davidson, manager of advanced energy systems for the institute, says that with lab and field testing it will likely be 1987 before the organization develops a marketable desiccant cooling system. Even then it will probably be an all gas-powered version that will slowly incorporate solar technology as the price of gas rises.

What is new about solar air-conditioning technology is progress evident in the design of the machine and in improvements to the desiccants themselves.

Cost is critical to the ultimate success or failure of solar air conditioners. Conventional central air-conditioning units cost a homeowner roughly $3,000 to $4,000 installed. American Solar King's air conditioner of similar size will cost approximately $6,500. The 50 percent federal solar tax credits would reduce the net cost to about $3,250.

But that's only the beginning, company officials say. The greatest savings come in operating costs. Including the costs of a built-in backup system (for the days when the sun doesn't shine), homeowners can expect to save an average of 63 percent on their monthly air-conditioning bills by using the new machine. The cooling apparatus would be compact and fit easily into a basement or against the side of a house.

The market potential for a solar air conditioner appears to be considerable. A study by Arthur D. Little Inc., the Cambridge, Mass., consulting firm, concluded that a $1 billion market potential could exist by the year 2000, given cost competitiveness and favorable consumer acceptance.

Currently, an average of 1.2 million new homes a year are being built, of which 40 to 50 percent are equipped with central air-conditioning units. Only about 30 to 40 percent of existing homes have air conditioning, providing a large retrofit market.

Independent observers, not privy to American Solar King's corporate secrets, generally confirm that solar air conditioning may indeed be reaching a market stage.

''I know it's possible because we're only a step behind,'' says Dennis Schlepp, project manager of the desiccant cooling research division of the Solar Energy Research Institute.