Pumped versus Thermosyphon System

The energy transferring fluid in a Solar Water Heating System can be circulated in the solar loop (between the collector and the tank) in two ways, namely by a pump (actively) or through the density differential of water (thermosyphon). Each circulation method has certain advantages and suitability’s and consequently their application must be appropriate to the installation.

Pumped

A pumped system, also known as an active or split system, uses a pump to circulate the water between the collector and water storage tank. In split systems, the circulation of water is controlled by an automated controller which drives the pump. Given that the water between the collector and tank is actively pumped, the configuration of the system is much more flexible. The control panel and pump together provide an enhanced system that offers far greater control over maximum and minimum temperatures and includes features such as freeze protection and overheat tempering.

Pumped Solar System

Thermosyphon

A thermosyphon system, also known as a passive system, does not require a pump to circulate the water but instead relies on density differentials where the warmer water rises to the highest point. For this system to function the tank must be mounted above the collector, relative to the horizontal.

Thermosyphon Solar System

The cycle works as the water in the collector is heated. This water becomes less dense and rises within the system, collecting at the highest point in the system, which is the tank. The cooler water in the tank will be displaced due to its higher density and forced to the lower parts of the system, namely the collector. As this system relies on a principle of physics, it means there is no direct control over the circulation of the water and hence limited control over the temperature of the water in the tank. In typical thermosyphon systems, EFA Solar recommends that a tempering valve is used that would govern the maximum temperature of the hot water delivered.

Advantage of Pumped over Thermosyphon Advantage of Thermosyphon over Pumped
Greater control over system Simple System setup
Superior efficiency More Cost Effective
Flexibility in positioning of storage tank Operates without power
Easier to overcome freezing Can be used with both low pressure
and high pressure systems
Easier to avoid an overheating system  

↑ Back to top