Installing an All Weather Closed Loop Antifreeze System

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Build Your Own Solar Water Heater

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Closed-loop, active, antifreeze systems are the most versatile and failsafe of all the systems. Most new solar homes features a variation of one kind or another (see Figure 12-5).

A special water-heater tank incorporating a heat exchanger works in conjunction with one or more flat-plate, roof-mounted collectors (see Chapter 10 for details on flat-plate collectors). Glycol, or some equivalent antifreeze fluid, fills the collector and associated routing pipes. A controller measures the temperature in the collector fluid, as well as the temperature in the hot water tank. When heat's available for transfer, pumps are activated to move the collector fluid. The hot water heater tank also has a backup means for independent heating, either gas or electric.

Figure 12-5:

A closed-loop, solar water heating system.

Figure 12-5:

A closed-loop, solar water heating system.

Back-up Water Heater

Solar Storage Tank

Back-up Water Heater

Solar Storage Tank

The flat-plate collectors can be mounted in almost any configuration, at great distances from the exchanger. The closed loop is always full of fluid, so the pump pressure requirements are much easier than those for a drainback system.

The pump can be very small, with very little head pressure, which means you can opt for lower power and better efficiency. Running these types of pumps off a PV panel is practical, which increases efficiency even more. (At night, when no sunlight can power the PV panel, there's no hot water to be pumped anyway, so it's a good match.)

You can get complete kits. Installation of the parts is no more difficult than for other systems, but charging the closed-loop isn't straightforward, and doing it incorrectly can damage the system and give you inefficient performance. I recommend that you don't install one of these systems yourself, even if you're a skilled do-it-yourselfer.

The major limitation of these systems is the tendency of the antifreeze fluid to degrade over time. When the fluid gets really hot (it's always in the collector, at all times) it degrades very quickly, resulting in inefficiency and buildup of deposits on the interior walls of the pipes and collector. For a properly maintained system, you should need to change the antifreeze fluid only every ten years. Have a qualified serviceperson inject new fluid into the system — it has to be done just right.

The best way to prevent the fluid from overheating is to make sure that the fluid in the closed-loop is circulating at all times when it's sunny out. Therefore, you can get really hot water in your domestic tank, and a tempering valve is critical. You need to use copper pipe — it's the only material that can withstand very high temperatures.

Make sure that the copper pipe is well insulated wherever children may touch it. The pipe can get extremely hot.

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