The second most widely used system is the drainback system. Fluid fills the collectors
when the pump starts and drains the collectors when the pump stops. The benefits
of a drainback system are it is protected from freezing down to -20°F, it is protected
from overheating during a period of time with no power, and water is used as a heat
It is important that you understand the basic principles and concepts of solar hot
water. As an informed client you will better understand and appreciate how the system
will function and how it will serve your needs.
There are two general types of solar hot water systems used in the United States–closed
loop and drainback systems. The system should be designed according to your needs
and budget. The goal is to make it as simple as possible, resulting in lower operation
costs, lower maintenance costs, fewer site visits, and lower energy consumption.
Both closed loop and drainback hot water systems use pumps and valves to control
the circulation of the fluid throughout the system. They allow the system to run
year round, without the threat of freezing. Protecting the system from freezing is
critical to the proper operation of any system.
Solar hot water systems collect energy from the sun in panels or tubes. Hot water
produced for use in a home or building is stored on site in tanks. A solar hot water
system can be a cost-effective way to reduce energy costs from oil, gas, electric,
or propane sources. The size of your system will depend on your hot water consumption
and storage capacity. It is important to calculate your needs to determine the correct
solar hot water system.
The most common domestic hot water system is the closed loop glycol system. This
is a sealed unit where a propylene glycol mixture transports the heat within the
system. The heat transfer fluid is a mixture of antifreeze and water, which can be
protected from freezing to -50°F. If overheated or stagnated, the fluid can go bad.