Active Open Loop Solar Water Heating System
With Preheat Tank


Open Loop Systems are suitable for single application domestic hot water (DHW) systems, in mild and moderate climates. One or two tanks can be used in various configurations and they retrofit easily into existing systems. An Open Loop System is for climates where there is no risk of freezing. Recirculation freeze protection can be provided by the Recirculation feature in the controller. At about 42ºF. the pump will turn on for a short time, circulating the water through the loop and preventing freezing. 


NOTE: The information presented in this page is for guidance only - no part of this may be used for any agreement, whether express or implied, or to form any contract. THERMO TECHNOLOGIES reserves the right to change specifications and prices without prior notice.

1. Solar Collector 6. Ball Valve 11. Existing DHW Tank
2. Freeze Protection Valve 7.Circulating Pump 12.Cold Feed
3. Collector Supply 8. System Drain 13. Hot Out to Cold In
4. Collector Return 9.Tank Drain Fitting 14. Tempering Valve
5. Non Return Valve 10. New DHW Tank 15. Hot Water to Taps

  • Easy to retrofit to existing tank with minimum disturbance of existing piping.
  • Versatile system - the preheat tank can be located away from the conventional tank.
  • Useful if the conventional tank is gas or oil fired. Many gas fired DHW tanks have high standby heat losses and will waste solar energy.
  • The "pretank" is usually cold in the morning and ready to receive solar energy.
  • Good control over the system and easily monitored performance.
  • Efficient if the house is occupied through the day. Solar heated water will frequently be drawn into the conventional tank, helping offset standby losses.
  • A well insulated standard DHW electric tanks is mass produced and reasonably priced.
  • This solar system can be disassembled easily, leaving the existing system intact, and moved to another location.

  • Solar energy heats only half of the available storage. If no-one is home through the day the solar heat remains in the preheat tank.
  • A larger pre-heat tank will be necessary than if a tank was added in parallel.
  • Stand-by losses are more than twice those of a single tank system.
  • Contact Thermo Technologies