EcoSolar Energy Conscious Design Limited
46
Figure 24. Mains pressure drainback system using a closed loop system
Mains pressure hot water drainback system using a heatstore cylinder – see figure 25 below, these
systems are becoming more common as again they offer significant advantages over closed loop
systems. The cost of installing these systems is much lower than a conventional closed loop system
using glycol and therefore these systems are often being installed with an instantaneous gas heater to
boost the water temperature upon demand. This results in a seamless hot water demand for the
client at a cost similar to those for conventional systems and without the maintenance issues
associated with propylene glycol.
The heatstore cylinder is a low pressure copper cylinder with around 45 metres of mains pressure
copper coil heat exchanger inside. The solar collectors can be installed above the water level in the
cylinder and provided the system is installed properly the system should operate similar to the low
pressure system with the header tank as described above. The hot water however is supplied at mains
or high pressure, the cold water enters and is heated as it passes through the coil to be supplied to the
points of use. See the next article on options for boosting the water temperature for details of
installing an instantaneous water heater.
