| A pump
circulates the water from the tank up to the
collector and back again. This is called a direct
(or open loop) system because the sun's heat is
transferred directly to the potable water
circulating through the collector tubing and
storage tank; no anti-freeze solution or heat
exchanger is involved.
This system has a differential controller that
senses temperature differences between water leaving
the solar collector and the coldest water in the
storage tank. When the water in the collector is
about 15-20° F warmer than the water in the tank,
the pump is turned on by the controller. When the
temperature difference drops to about 3-5° F, the
pump is turned off. In this way, the water always
gains heat from the collector when the pump
operates.
A flush-type freeze protection valve installed near
the collector provides freeze protection. Whenever
temperatures approach freezing, the valve opens to
let warm water flow through the collector. The
collector should also allow for manual draining by
closing the isolation valves (located above the
storage tank) and opening the drain valves.
Automatic recirculation is another means of freeze
protection. When the water in the collector reaches
a temperature near freezing, the controller turns
the pump on for a few minutes to warm the collector
with water from the tank. |
Saturday July 05, 2008 - 12:41 PM
