Inside the collector is an absorber to which are attached tubes filled with liquid. A
pump circulates this fluid through the absorber removing the trapped heat to a solar
Water is normally used for storage, because it can be used for many purposes and it
stores a large amount of heat in a fairly small volume.
A Simplified Solar
The collectors and exposed piping require protection against freezing in cold
climates. If water is used to remove the heat from the collectors, it must be drained
on cold nights or cold, cloudy days to prevent it from freezing. Two ways to do this
are called "drainback" and "draindown." These are described in more detail in
Sections 2.3 and 2.4.
In other systems, a non-freezing fluid is used in the collector loop. In this case, a
heat exchanger must be used to transfer the heat from the collector fluid to the
water in storage. This type of system is called "closed-loop," and is described in
All the different types of systems use the same type of control. The control uses two
sensors. One sensor is installed at the collectors, and the other is located at the
storage. The control continually compares the temperature of the two sensors.
2.1 BASIC SYSTEM CONFIGURATION