Active Closed Loop Solar Water Heating for
Radiant Underfloor Space Heating by Heat Exchanger

A Closed Loop system can be used to link domestic hot water (DHW) and space heat to the same collector. It is normal to include domestic hot water in any multiple application as it is a year round requirement.


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.

The Solar Collector System is capable of contributing significantly to space heating requirements in many areas. The best use for solar energy is to heat a building by radiant underfloor hydronic heating, which requires water at a maximum temperature of 140ºF. This system usually uses a concrete floor slab with special water pipes running through it, to provide a pleasant, even, low temperature radiant heat. The floor slab will also provide heat storage. There are several methods of retrofitting these systems to existing houses without adding a floor slab.
More benefit can be gained from the solar system if space heating is linked to a summer application, e.g. a swimming pool, so that the solar system is in use year round. Some linking suggestions are shown here, but when using really hot water, as VM can provide, many different combinations are possible.


1. Solar Storage Tank
3. Radiant Underfloor Manifolds
5. Heat Exchanger
2. Electric or Gas Boiler
4.Cold Feed and DHW Out
6. Supply and Return to Collector



  • In the Solar Loop priority is given to the DHW tank by an aquastat (A) controlling the solar zone valves. When the tank reaches temperature the flow switches to the heat exchanger (2).
  • In the Radiant Underfloor Loop the pump is activated when either thermostat (T) calls for heat for it's area, and the end switch in the zone valve activates the pump.
  • This loop flows through the heat exchanger. If the heat exchanger is below, say, 100ºF the aquastat "A" redirects the flow through the boiler, activating the boiler at the same time.
  • The bypass, incorporating a mixing valve and a check valve, ensures that the floor system cannot overheat by mechanically recirculating it when a set temperature is reached.








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