SOLAR HOT WATER SYSTEMS
HOT-WATER RADIANT HEATING)
AT SOLAR HAVEN
EQUIPMENT - COSTS - INSTALLATION
POSITIVES AND NEGATIVES OF SOLAR HOT WATER SYSTEMS
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The heart of this system is a Thermomax solar hot water heating unit (made in Great Britain) which has been installed on the south facing roof section of the greenhouse. In the picture below, 9 of 30 heat tubes have been set in place and connected to a "manifold" at the top of the unit where the water actually circulates:
Thermomax "Evacuated Heat Pipe Solar Collectors" (tubes) operate quite differently than other solar collectors available on the market. They are more sophisticated; they have higher heat output; and they are more expensive.
These solar collectors consist of a heat pipe (called a "heat diode") inside a vacuum sealed tube, as shown below:
How the Termomax works: Each tube contains a sealed copper pipe (heat pipe). The pipe is then attached to a black copper fin that fills the tube (absorber plate). Protruding from the top of each tube is a metal tip attached to the sealed pipe (condenser). These tubes are mounted, the condensers up, into a heat exchanger (manifold). As the sun shines on the black surface of the fin, alcohol in the heat pipe is heated and hot vapor rises to the top of the pipe and collects in each condenser. Water flowing through the manifold picks up the heat from the tubes.
THE WHOLE SYSTEM
Hot water from the Thermomax unit is circulated in the main manifold for the hydronic heating system (see below). It supplies both domestic hot water and hot water for radiant heating system in the new straw bale house (and formerly for heating our mobile home). No propane gas is needed to supplement this hot water system.
The radiant heating system uses special hot water plastic (PEX) tubing which has been installed under the adobe brick floor of our new straw bale house. In our mobile home the PEX was attached to the underneath surface of the floor boards in the spaces between the floor joists. See our Radiant Heating Installations page for the details about how this was done.
Here is a picture of the "manifold" which connects all the "PEX" hot water tubing together as well as the five small 12 volt pumps which circulate the water. Also shown is the hot water storage tank and the 12 volt battery system used to power the circulating pumps.
The circulating manifold is built from 1 3/4" copper tubing, five shut off valves, five circulating pumps, and numerous fittings. The manifold connects the hot water pipes in the floor of the straw bale house, the loop up to the Thermomax to bring hot water down from the roof, and the loop to the hot water storage tank and back. It was built by Rod Hyatt of Eden, Utah as mentioned above. It has been mounted on a 4' x 8' sheet of plywood in one corner of the greenhouse and has been insulated with special foam insulation made for hot water pipes.
SPECIAL CIRCULATING PUMPS
There are five pumps which circulate water in the system, all of which run on DC power and draw an incredibly low amount of power (only 10 watts per pump). These are state-of-the-art "El-SID" pumps designed by Ivan Labs, Inc. of Jupiter, Florida.
A separate 12 volt DC system has been installed (see picture above) consisting of a deep-cycle storage battery to provide direct DC power for the circulating pumps and one 40-watt solar panel on the roof on the greenhouse to charge the battery. This is a much more efficient source of power than an AC wall cube which converts 110 VAC to 12 VDC. (An AC wall cube, of course, is running from power which had to to "inverted" from our main 48 volt battery bank to regular household current.) A charge controller, an on/off switch and fuse for each pump, a 12 volt timer, and a battery desulfator complete this system. Click here for a detailed diagram.
COSTS OF SOLAR HOT WATER SYSTEM
(including the hydronic heating system in the new straw bale house)
POSITIVES AND NEGATIVES OF A
SOLAR HOT WATER SYSTEM
On the positive side: The 30 Thermomax tubes produce enough hot water to meet all of our domestic hot water needs (taking showers, washing dishes, etc.) and to heat our mobile home even on very cold days with the hot water circulating under the floors. There is also plenty of hot water left over, and this has been used to heat the water in the 15' "doughboy" above-ground pool we are using for water storage out back. This extra "heat sink" for the system turns out to be a necessity to keep the water in the system from getting too hot and in fact melting the PEX tubing and bursting it (see "on the negative side" below). A 20 tube Thermomax unit would be sufficient for meeting out domestic hot water and house heating needs. The 30 tube unit was in fact purchased in order to heat the water in a lap pool in the greenhouse which we were never able to build. (We we could not get county approval for the kind of pool we had designed and could afford.)
One of the most spectacular pluses of the system is that it produces virtually the same amount of hot water on cold, windy days (providing the sun is out, of course) as it does in fair, warm weather. Since the heat elements are protected in a vacuum tube, they just aren't affected by ambient conditions. When there is sun, we have hot water... On one memorable blustery day, we had mixed clouds and sun with some rain. The Thermomax still pumped out the hot water when it was getting rained on.
Conventional solar heating units with water circulating in tubes in an enclosed, black box don't produce nearly as much hot water when it is cold or windy outside . The Thermomax unit was in fact designed in Great Britian where the weather is anything but favorable for solar hot water heating. Even on semi-cloudy days, the unit works very well.
On the negative side: It is absolutely necessary to use all or most of the high heat produced by the Thermomax unit or the water will actually BOIL as it circulates. PEX tubing is rated at a maximum water temperature of 180 degrees. PEX can tolerate hotter water only for a short time after which the tubing melts and bursts open as shown in the picture.
"Should you happen to be walking underneath
when this happens, you get a nice scalding hot shower.
Been there... done that... not eager to repeat the experience."
The answer to this problem is obviously to size the system correctly and to provide a place for all the energy generated to be used. We also installed three feet of copper pipe (see left) where the hot water emerges from the Thermomax manifold on the roof and goes down through the roof into the greenhouse. This is where the water is the hottest and most likely to burst the PEX. Installing copper for the entire loop between the Thermomax and the main circulating manifold would not be a bad idea. This has helped a great deal avoid trouble when the system does get too hot...
Also highly recommended is a thermostat which reads the temperature of the water in the unit, and which turns on the circulating pump when the sun is up high enough in the morning to begin heating the water and turns it back off again in the evening or when clouds roll in and there is little hot water to circulate. These are available from In Hot Water Heat and Power. We use a simple on/off timer at the moment (less expensive) which we have set to turn the unit on first thing in the morning and turn it off at night. The timer obviously must be reset periodically to match the rising and setting of the sun.
Finally on the negative side, there is still the need to heat water with some other source (a conventional water or more specialized boiler unit) at night. Adjusting your schedule so that most showering and washing dishes is done during daylight hours when the sun can do your water heating for you is one obvious way to offset this. Establishing some way to store some of the day's hot water for night time use is another. We are collecting old water heaters to hook in series which no longer work but their tanks are still intact to do this.
Passive solar heating is a further solution. The large "thermal mass" of our adobe floors in the new straw bale house (or a concrete slab in a conventional home) will absorb the sun's energy which stream in through it's south facing windows and doors during the day and radiate it back out again at night to help heat the house...
"At last!! Won't be cold no more in the Winter."
©2003-2014 by Jim Phypers