Build Your own Passive Solar Water Heater
(Page 3 of 7)
October/November 2007
By David A. Bainbridge
In the standard batch heater, cold water enters the solar collection tank through a side inlet near the bottom or through a “dip tube” that enters at the top and discharges cold water near the bottom. The heated water exits through an outlet near the top where the water is warmest, then moves to a backup conventional heater (fueled by gas, electricity or wood) where it’s heated all the way to the desired temperature. Batch heaters use waterline pressure for circulation, eliminating the need for expensive pumps and controls. During the summer months, or where it is warm and sunny year-round, the backup heater often can be turned off and bypassed, with the batch heater providing all your hot water needs. In Davis, Calif., my three-tank heater provided all our hot water for nine months.
RELATED CONTENT
On-demand water heaters provide an “endless supply” of hot water, but are they really “green”? Ther...
How Hot Is HOT? February/March 2004
The Other Chile Peppers
Where does the h...
Conventional water heaters heat water and store it until it’s used, but a lot of that heat is waste...
Want to know how to build your own photovoltaic system, how to construct a solar water pump, or eve...
It’s not every day that you get a chance to tour a green home. Well, here’s your opportunity! Every...
The relatively low temperature of the collector minimizes expansion and contraction of components, reducing wear and tear. The mass of the water in the system helps protect it from freezing and extreme high temperatures that can harm materials, which leads to long system life. Research in Europe suggests that up to 20 percent of the water in the collector can freeze without damaging the tank, but keep in mind pipes are still at risk unless protected or drained.
The 6 Commandments of passive solar water heaters
If your heater’s specifications and installation follow these six commandments, it will work admirably and will supply inexpensive solar-warmed water, no matter which specific design you choose.
1. Locate your heater for maximum solar exposure. Find a sunny, south-facing location, preferably close to the backup heater to minimize piping distance. You might have to do some calculating to be sure your solar collector will be exposed to the sun when you want hot water, but placement and orientation are the single most important considerations. Remember the sun is high in summer, low in winter. Specific optimum angles for your location during any month of the year can be found here. (Click “Data Services,” then select “Altitude and Azimuth of the Sun or Moon During One Day.”)
Next, determine where your heater will be installed — roof, platform, wall or ground — keeping in mind that a filled three-tank 90-gallon system can weigh more than 800 pounds when full of water. For most applications, it’s best to keep a large solar heater on the ground or on a specially built platform. A rooftop installation may be placed above a load-bearing wall or reinforced section of roof. Ground mounting is easiest, and eliminates the weight problem.
2. Make the collector and storage tank(s) as efficient as you can. First, decide on the type of tank(s) you’ll use for your heater. Tanks come in a wide variety of shapes and sizes, but long, thin cylinders are the most efficient (they have the greatest ratio of surface area to water volume). The cheapest and easiest of these to obtain are used electric water heater cores. Examine the “sacrificial anode,” a rod made of metal with a low resistance to corrosion that is inserted into the tank from the top to attract any corrosive elements in the water. Replace it if substantial corrosion and/or consumption is evident. A new one costs only a few bucks, and it will add measurably to the longevity of your system. Check carefully for leaks, and never use a tank that you have doubts about. Wire-brush it and paint it with rust-resistant flat black paint, or apply a selective surface coating if you can afford it.
Page:
<< Previous 1 |
2 | 3 |
4 |
5 |
6 |
7 |
Next >>
