An Experimental Solar Water Heater Design

Kenneth Whetzel came up with his own recirculating, closed loop solar water heater design as an experiment to study first hand the possibilities of solar heating.
May/June 1973
http://www.motherearthnews.com/renewable-energy/solar-water-heater-design-zmaz73mjzraw.aspx
Left: Ken Whetzel poses with  his completed unit. Right: An illustration of the heater's parts and fittings.


PHOTO/ILLUSTRATION: MOTHER EARN NEWS STAFF

Ever wonder whether you could put the sun's energy to work for you where you live? Well, a former neighbor of MOTHER EARTH NEW asked himself that question, and to find the answer he built a solar water heater right here in northern Ohio.

Though Kenneth Whetzel describes his little machine as "experimental", there's nothing tentative about the hot water it produces. Ken likes his shower about 105°, and there wasn't one day in all the time the test system was running that he couldn't have washed comfortably in the device's output (had he been equipped to do so). That's not bad for 60° weather. It should be noted, however, that since Ken didn't intend actually to use his heater's product, the contents of the tank are routed back through the collector — an arrangement that makes the model operate more efficiently than a working system in which the warmed liquid is frequently drained off.

The collector that produced these results is a 2' X 4' piece of sheet metal with about 24 feet of half-inch copper tubing soldered to it in a zigzag pattern. This whole heat-absorbing area is contained inside a wooden frame sealed over with clear plastic sheeting. The tubing that carries hot water away from the enclosure is insulated with a layer of half-inch foam rubber and leads to a raised 11 1/2 gallon reservoir protected by a styrofoam jacket one inch thick. (Whetzel built the contraption entirely of scraps scavenged from his construction job, so it's hard to say just how much it would cost you to fabricate a similar unit.)

One feature of Ken's design that really cuts the device's cost, and which should be pointed out, is the fact that it needs no mechanism to force water through the collector and into its storage tank. Why? Because of a basic fact of thermodynamics: Water, like air, expands and becomes lighter per cubic measure as its temperature increases. Rather than use electricity to run a pump, Ken took advantage of this principle and set up his creation so that the warmer and lighter H20 rises through the cooler layers and on up the pipe into the top of the tank, where the liquid sinks down into the collector again for reheating as it cools.

A very simple, streamlined experiment, isn't it? And best of all, it works. The first day Ken set up his invention (pointed 10° west of south and tilted 30° downward from the horizontal) the water temperature at 7 a.m. was 60°. By the time the experimenter got home from work at 5 p.m., the contents of the tank had been heated to 128° ... too hot to put your hand into. And—because of some nearby trees—the sun's rays hadn't even hit the collector until about 10 in the morning.

Overnight, Ken's hypothetical bath cooled only to 96°, and when the second day turned out warmer and sunnier than the first (with a high near 70°), Whetzel knew he could look forward to some really impressive readings. Sure enough, by evening his system's water temperature had climbed to 138°, nearly twice as hot as the surrounding air! Thereafter the tank's 5 p.m. temperatures ranged from a low of 108° (a cloudy day) to a high of 148° — and on top of that record, the inventor thinks he might be able to pick up 30% in efficiency by the use of reflectors.

Ken was convinced. The last we heard—when he and his wife left for their five-acre homestead in Florida—he intended to employ the results of his experiment to set up two practical solar heating systems: one to warm the house in winter and another for domestic hot water. He figured that three 2' X 8' collectors mounted on the garage roof would supply at least 72 gallons of bath or wash water (1 1/2 gallons to the square foot) per day, and probably a lot more, considering Florida's fabled weather.

Our ingenious neighbor also thought his winter heating system might be used to cool the house in summer by circulating cold water from a well, but when we last talked to him he hadn't worked out all the details of that modification. Let us know when you do, Ken!