Pumps for Solar Hot Water Systems

Pump or no pump?

Water or liquid can be circulated around a solar water heating system using a pump, or it can be circulated using a thermosiphon system.

Systems that utilize natural circulation, such as a thermosiphon, are often referred to as "passive" systems. In this type of system, the hot water cylinder is typically located above the rooftop collector panels. The fluid moves from the cylinder to the cold or cool collector panels, then, once heated by the sun, it returns to the cylinder.

Systems that use a pump to circulate water or liquid are often referred to as "operating" systems.

Natural circulation by thermosiphons requires no pumps, and pump systems, on the other hand, have the advantage of not relying on electricity.

With a pump system, the hot water cylinder is located below the collector panels. This can be helpful if you are installing a solar water heating system in an existing home and wish to use the existing cylinder, or if the cylinder is located on the roof. It is essential that this pump be used with a controller (see below) to ensure proper operation only when the pump is present.

Controller

The controller manages the use of auxiliary ('booster') gas or electric heating and controls the pump in the pump system. The heating controller has a significant impact on the overall system performance, so it is important to set it correctly.

There are two types of auxiliary heating controllers: time-trigger controllers and minimum temperature controllers.

A time-trigger controller can be used to keep the booster heating off during the day, avoiding paying for electricity or gas to heat the water when the sun is available. A timer can also be set to turn on the auxiliary heating before periods of high water usage. This can significantly increase the efficiency of the system.

The minimum temperature controller simply triggers auxiliary heating whenever the cylinder temperature drops below a minimum predefined temperature.

Regardless of the controller, you can't go without hot water at any time of day. You should consult with your installer or supplier about the type of controller you need.

Building codes require that the water temperature in the cylinder reach 60 degrees Celsius at least once a day. Make sure your system is set up to meet that requirement.

It's also worth checking your electricity bill when installing a solar water heating system to ensure you're paying the best price for supplemental heating.