Solar Hot Water
by Lawson Schaller
Solar hot water for houses has been going on for a long time—more than a century in the southern warmer states. Like many things it is simple in concept. Simple batch-style systems can consist of painting a tank black, put it in an insulated box with glass on top and there you go. Sunlight shines through and warms the tank and the water.
Many would consider this a passive system with no electro-mechanical parts—i.e. valves, pumps etc. I'm sure many of you have taken the shower bag on camping or back packing trips. The one where you fill the bag with water, set it in the sun, and not long after—if you have sunshine—there is hot water for a shower. Well, sometimes warm, sometimes very hot. Ah, the simplicity.
Now, on the other extreme are the more sophisticated systems that have pumps, valves, etc. These can be quite complex for the novice and it is recommended one consider the professional contractor for consultation and installation.
In a nutshell, you have two main types of systems—open loop and closed loop.
Remember last month's geo thermal closed and open loop systems? Open loop systems circulate potable water through from an open source like a well. Closed loop systems circulate a heat transfer fluid through the system and utilize a heat exchanger to heat the domestic/potable water.
There are government and utility incentives for solar hot water systems, much like there are for other renewable energy systems, such as solar electric. The residential federal tax credit and many state and utility incentives require that the system be certified by the Solar Rating and Certification Corporation (SRRC ). Within the open and closed loop systems, the SRCC has four main classifications; integral collector storage (batch) system, thermosyphon, forced circulation, and self pumped systems. I will not go into the details of these four main classifications but will offer some information on the basic components.
The collector simply absorbs the sunlight and transfers heat to the fluid. Two main collector types are flat plate and evacuated tube.
Flat plates have been around a long time, are proven, reliable, and most the common. They have an absorber plate (typically black painted copper) that is connected to the pipes that have the fluid. These are encased in an insulated metal frame and have a top sheet of glass.
Evacuated tube collectors are a more recent technology. One characteristic of the evacuated tube is that the tube is inside a vacuum which is a better insulator than air. These collectors have better heat retention than flat plate collectors.
The typical size of collectors ranges from 24 to 48 square feet. One way to get an approximate estimate for sizing is about one square foot of collector space for every 1.5 gallons of water in a storage tank. This varies, depending upon what part of the country you are in and other parameters.
In addition to the collectors, there are storage tanks, and/or drain back tanks, expansion tanks, and/or backup water heaters. There are also circulation pumps, controls, and valves and gauges. Heat exchangers also come into the mix.
So, for some of us things can get a little complicated. For others with technical backgrounds it may be fairly straightforward. Don't forget about freeze protection either, and yes, yet still more variables exist. Ah, the simplicity.
You do not have to figure it all out for yourself. Qualified professionals offer system sizing and installation services. One can save a lot of energy costs and natural resources with a solar hot water system. Check it out.
|
