Probably the most vulnerable component of an active (pumped) solar water heating system,is the pump. It is therefore very important to ensure that a good quality pump is used and that it is correctly installed. Just about any pump will do when the system is running normally;the problem comes in when the system is not running normally. If the system is in stagnation due to a power failure or water supply problem,poor quality pumps will not withstand the resulting heat.
Even good quality pumps though should be installed in a manner that provides maximum protection to the pump in the event of abnormal operation. There are 4 important principles to apply when installing the pumps:
- Protect the pump with a non-return valve.
- Install the pump below the water level in the hot water cylinder.
- Install the pump as close to the hot water cylinder and as far from the collector as possible.
- Correct orientation of the pump as per the manufacturer’s instructions.
Let us unpack these 4 guidelines:
- The pump is always installed on the flow side of the solar loop and should have a non-return valve fitted between the pump and collector. The non-return valve should be solar rated and able to withstand very high temperatures including steam. If the system goes into stagnation,steam can build up to very high temperatures in the manifold and this heat can be conducted down the pipe to the pump. The non-return valve prevents steam from pushing backwards through the flow pipe and pump. Component 6 on Fig 1.
- One of the worst things for a pump is for it to run dry. Where at all possible,try and install the pump below the top of the water level in the hot water cylinder. Should the water supply to the house be interrupted,if the pump is below the water level,it will prevent the pump running dry. Component 5 on Fig 1.
- Having the pump situated as close to the hot water cylinder and as far from the collector as possible will also help protect the pump from the very high temperatures the solar collector can generate,especially when the system stagnates. Fig 1 pump position.
- Pumps must be oriented as per manufacturer’s instructions.
- Generally pumps that have a shaft should be installed with the rotor shaft in a horizontal position. See Fig 2.
- The Laing DC pumps do not run on a shaft but on a magnetic field. If installed on a horizontal pipe,the motor should be facing downward. See Fig 3.
Adhering to these guidelines and using a good quality pump with a brass housing should ensure many years of trouble free service.
Fig 2. Salmson AC Pump Orientation
Fig 3. Laing DC Vario &Solar Pump Orientation