Connecting solar hot water system to geothermal HVAC

Discussion in 'Solar and Geothermal Water Heating Forum' started by Kevin homeowner, Feb 9, 2011.

  1. Kevin homeowner

    Kevin homeowner New Member

    Feb 9, 2011
    I have an existing closed horizontal loop geothermal heatpump HVAC system using glycol, and an existing solar hot water system also using glycol. The glycol loops are not connected to each other in any way. In the winter when my hot water pre-heat tank is hot enough, the pump to the solar panel stops the flow of glycol to the roof panels, which could otherwise be generating glycol heated above 100 degrees. This happens for a significant portion of the sunlight hours. At the same time (in the winter), my geothermal HVAC is trying to extract heat from at best 55 degree glycol from the ground loops.

    Question: Can I install some type of switch connecting the two glycol loops such that; if the water tank is already hot, and if the HVAC is in heating mode, and if the glycol from the roof panels is hotter than the glycol from the ground loops, then the glycol from the roof panels is directed to the heat pump? If this is possible, would this be done by the solar guy or the geothermal guy? Who makes the switch?

    Thanks, Kevin
  2. WellWaterProducts

    WellWaterProducts In the trades

    Feb 23, 2011
    Northwood NH
    Not certain but this sounds like a good application for a heat exchanger and keep the glycol loops separate.
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  4. buhrly

    buhrly DIY Junior Member

    Jun 10, 2011
    Consulting, Management
    Bend, Oregon
    The glycol mixes are probably different between the two systems. Sounds possible with some three way valves and a boiler control that could prioritize the calls. It would be much more efficient to extract heat from 100 degree water then 55 degree. I have done this using exchangers and control as Wellwaterproducts suggested with success. The idea of having them linked together would be simialar to how a solar system supplies heat to domestic and radiant floors but definitely check on the mixes first as this could cause problems on the solar side with freezing if mixed to low and on the geo side with pumping if the mix is to high.

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