EcoSolar Energy Conscious Design Limited
45
Figure 23. Low pressure drainback system with header tank.
Mains pressure drainback with receiver
– these systems are uncommon in New Zealand but
offer many more advantages than conventional closed loop circuits with propylene glycol whilst
costing about the same to install.
The closed loop is charged with water so that the receiver is a maximum of about two thirds full of
water. Provided the system is installed properly the system should operate as follows. When there is
a heat demand and there is heat to gain from the collector, the pump is switched on, this draws water
out of the receiver, pumping it through the heat exchanger and through the solar collector. When the
heat demand is satisfied or when there is no longer heat in the collector, the pump is switched off
and the water drains back to the receiver. A sightglass on the outside of the cylinder indicates the
water level which should be periodically checked.
