Solar Water Heaters

By Jeffery M. Wolf, General Contractor, St. Petersburg, Florida

When we remodeled our house last summer I wanted to practice what I preach to my clients (with great conviction and to great excess according to my wife) about sustainable and energy efficient construction. We incorporated high efficiency air conditioning, LED lighting, better insulation, low water use fixtures, and Solar Water heating.
We are very happy with the results. Our power usage has been lower every month than it was for the same month the previous two years.

Solar Panel on Roof

This is what I learned about Solar Water Heating:

 

System Types: There are two basic system types, open loop (direct pump) where the potable water supply passes through the panel and back into the water tank, and closed loop (indirect pump) systems that have an antifreeze solution that circulates through a heat exchanger inside the tank and up through the collector. The anti-freeze solution (often glycol) transfers heat to the water through contact with the heat exchanger.
Closed loop systems can be more resistant to freezing so they are favored in colder climates. Open loop systems are simpler and more efficient but they can freeze so they are better for warm climates. In St. Petersburg, Florida where we live, hard freezes are infrequent so we used an open loop system. Within the two systems there are also drain-back types that drain all the water or glycol back into the tank when the temperature approaches freezing. This keeps the pipes from freezing.


Collector location and angle: Solar collectors work best when facing due south or within 30° to 45° east or west of due south. In regards to the tilt of the collector, the collector should be mounted at an angle ± 15° parallel to the site's latitude.
If your roof has the proper slope and exposure you can mount the panels on stands that mount directly to the roof. This is ideal as it gives the panel a low profile to resist high winds. In our case we used hinged mounts. One side of the panel is mounted close to the roof and the other side is raised on angle struts to provide the correct angle to the sun.


Tank size: The size of the tank should be matched to the size of the collector and the number of occupants of the home. In our case we used an 80 gallon tank with a four foot by ten foot collector panel.

Water Heater Tank

Valves: A solar water heating system will have more piping, four inlets at the top of the tank instead of two and possibly a connection at the bottom of the tank for a recirculating system. Valves should be installed to isolate the roof-top collector, to isolate the tank from the house water supply, and if there is a recirculating pump, to isolate the pump so it can be serviced. This makes for a lot of valves.
If you install a solar water heater you should make sure your installer labels the valves and explains their function. They should also explain any special procedures, such as shutting off valves to isolate the system, in the event that you need to drain your water lines for other plumbing work such as remodeling or repairs.


Circulation pump: Most solar water heating systems include a circulating pump to circulate the water or anti-freeze solution between the collector and the tank. The pump may be controlled by a controller that senses temperature in the collector, or by a photo voltaic panel that powers the pump when the sun is out.


Freeze valve: All solar water heating systems should have a method to prevent freezing water from damaging the collector or water pipes. In an open loop system that may be accomplished with a freeze valve that opens when the temperature drops to 50 degrees or lower. The valve allows a small amount of hot water to circulate through the collector and drain off to prevent the water in the pipes from freezing. You should know where the valve is located and check during and after cold weather episodes to make sure that the valve has closed. A typical valve may bleed off three or four gallons of water but if you have a steady stream coming off your roof you need to have the valve checked to make sure it is not stuck open.


Maintenance: The system should be inspected annually and if you have a freeze valve it is a good idea to inspect after very cold weather.

 

# # #Copyright © 2011 by Jeffery M. Wolf All rights reserved.# # #

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