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Solar Hot-Water System Speaks to You

March 02, 1986|TERENCE M. GREEN

Talking automobiles have been around for a while now but it is still a little surprising to drive down the street and have your car tell you: "Please fasten your seat belt"--and then, when you do, say, "Thank you!"

(Judging by the voices, some cars are male and some are female; does this mean that machines can have gender?)

But this reporter had never heard of a solar domestic hot-water system that would give you the time of day--literally. According to Mike Robinson, sales coordinator for Exam Exemplar Inc. of Hickory, N.C., the device, which can be mounted on the roof of the house or in the yard, is managed by a programmable control that is basically a mini-computer operating off a microchip.

On demand, it will tell you, by spoken words, the time of day and the relevant temperatures. For programming, when the proper button has been pushed, it tells you to push this button and then push that button, leading you by the hand through the programming process. (The interviewer forgot to ask about its gender.) If a mother is home all day with children, it would be programmed only to shut off at night; if no one is home during the day, it would run morning and evening.

The company calls it the "Energy Garden" and describes it as a self-contained solar collection and energy-storage system that hooks up to the spigot of the water heater and can be installed by the homeowner in two to four hours.

"During the day," the company's description says, "Energy Garden sends the heater water to the water tank for use that evening. At night, it uses extra energy accumulated and stored during the day to heat water again for yearly morning use." This is accomplished through use of a phase-change material.

Such materials basically "freeze" and "melt," absorbing and releasing heat as they do so. Almost all materials have this property; everyone knows how water will freeze into ice, releasing its heat supply to freeze and absorbing heat to melt; or liquid water can absorb more heat and change to its gaseous phase, steam, then can release heat and go back to being a liquid.

But water has two drawbacks: The temperatures involved are too far apart for most of our needs, and its capacity to store heat is not great. Certain chemical compounds, called eutectic salts, will store and release many times the amount of heat that water will, and will change within a much narrower temperature range.

But, Robinson said in a telephone interview, such salts have a drawback: After a certain amount of changes their chemical composition breaks down and they have to be replaced. "We wanted a device that never needs servicing," he said.

The Energy Garden's heat storage material is a paraffin-based wax developed by NASA and used in Skylab, Robinson said. He added that one pound of it will store and release as much heat as 96 pounds of water; the Energy Garden has about 150 pounds of the wax inside it.

The device is plumbed into the tank at the drain spigot at the bottom--"where the cold water collects in the tank"--with coaxial tubing, essentially a pipe within a pipe. Cold water goes from the tank through one of the tubes, is warmed and returned through the other. Hot water is drawn off the top.

What about a backup heating system for bad weather?

"Don't need it," Robinson said. "For one thing, we use a black-chrome collector plate that's 200% more efficient on cloudy days than the conventional collectors. It keeps the water at 120 to 130 degrees all the time.

Another advantage Robinson mentioned is that it is portable. If you sell your house, you can take it with you (that would have to be in the sales contract, of course). Also, he said renters can use it and take it with them when they move (an agreement with the landlord seems obvious here).

The retail price is $2,495, he added. The company has distributors along the East Coast and as far wst as Oklahoma but none in the Far West. However, it can be ordered from the factory for $1,988.

More information can be obtained by writing to Exemplar Inc. at P.O. Box 9027, Hickory, N.C.

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