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Drain
Back
Solar Water Heating Systems
| A circulating pump operated by a
differential control is turned on when the collector outlet is
at least 20°F (11°C) warmer than the tank outlet. Water or an
antifreeze solution is lifted from a small reservoir tank and
circulated through the collectors and back to the tank. Heat is
transferred to the domestic water via a heat exchanger in the
reservoir tank. The circulation loop through the collectors is a
closed loop. The water or antifreeze solution is installed at
the time of installation, and does not present a recurring
supply of oxygen. |
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A drainback system
requires a large pump. It must have sufficient capacity to lift
the fluid to the highest point in the system. When there is no
more heat to be collected, the controller turns the pump off,
and all the fluid drains back to the reservoir tank. The
collectors are empty. They can't freeze, and they can't overheat
the antifreeze. As a Do It Yourself homeowner, you won't need a
special charging pump either. When it comes time to change the
antifreeze, you can just drain and refill the reservoir tank.
Drain Back Systems are suitable
for single and multiple
applications. They are suitable for areas with questionable
water quality and moderate climate conditions. They are
particularly suitable for single
application pools and spas. Domestic hot water and multiple
application systems require heat exchangers. These can be small
vented reservoirs with separate heat exchangers, or preheat
tanks with single or multiple integral heat exchangers. Heat can
be thermosyphoned from the reservoir or it can be pumped using a
second pump. Single application pool and spa systems can
circulate the pool/spa water directly through the collector,
using the existing circulating pump and a simple bypass.
Reliable freeze protection is provided by the fact that when the
pump is switched off, or in the event of a power outage, water
in the collector circuit drains back, leaving no water in the
collector to freeze. |
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