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Using Heat Pump thermostat to control solar heat wiring help needed

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  • Using Heat Pump thermostat to control solar heat wiring help needed

    Sorry for the long post. let me know if it is not clear. Thanks in advance.

    The solar hot water system is connected to an solar-heated-water-to-air-coil in the duct of the heat pumps' air handling units (AHUs). I want to open the valves to the solar-heated-water-to-air-coils when the heat pumps' thermostats call for heat. When the temperature drops and the emergency heat is called for, I want to bring on the heat pumps too. Can someone help with the thermostat wiring?

    The thermostat is a Traine 802 for one heat pump
    The second heat pump has two Traine 802s connected to a Honeywell Total Zone 4 with the zones controlling dampers and the heat pump
    Should the solar-pump relays be connected to the W1&R terminals and the heat pumps to the W2?
    Currently, the W2 and Y2 are jumpered at the Honeywell. There are two unused wires to the thermostats.

    FWIW, the solar-heated-water-to-air-coils are installed so the air flows through them after it flows through the heat pump coils in the AHUs.
    The solar-heated-water-to-air-coils are valved off if the solar antifreeze loop is cool, by a pipe-thermostat which is on the antifreeze loop after the valve taps to the solar-heated-water-to-air-coils. The pipe-thermostat breaks the solar-heated-water-to-air-coil valves' transformer circuit, so the coils are not cold when there is a call for heat.

    The circulator pump and coil valves will be controlled by DPDT relays which are attached to the room thermostats or Honeywell controller.

    There is a pressure regulated antifreeze bypass around the solar-heated-water-to-air-coils. This is so that when the solar-heated-water-to-air-coil valves are both closed, and the circulator is running, it is not pumping against the valves and the solar/air coils are not cold when there is a call for heat. (I think I should add a fan control too so that the coils are hot before the fans start...)

    I did not install the heat pump system and am not sure why the primary and secondary heat terminals are shorted.

    I tried to upload some photos of the wiring but was unsuccessful. Send me an email for photos if needed.

  • #2
    On heatpump thermostats the o/b terminals control the reversing valve in the heat pump mode in conjunction with the W1 terminal. That being said your heat pump will only function if wired to the W1 terminal. The W2 terminal will bring on the 1 st stage auxiliary ( electric strip ) heat, W3 will bring on the 2nd Stage auxiliary heat.
    If the thermostat is switched to emergency heat the W1 & the o/b terminal are removed from the circuit and only stage 1 & 2 auxiliary heat can be energized.
    The average heat pump discharge temp is around 90-110 degrees depending on the outdoor temperature. Your solar HW coil should have a min. 130 degree water circulating through it at 5 gallons per min .
    The only way I can see this system working is just running the the HW coil or the heat pump seperately not simultaneously.
    Or run the HW as the auxillary connected to W2.
    If you want to run them individually this requires a thermostat with a DPDT switch mounted to your hw storage tank set at 130 degrees, the w1 and o/b wire would broken through the NC & common contacts, your solar pump relay would be connected to the NO contact that would close when the water reaches 130 degrees.
    How many gallons of storage do you have and how many square ft of collector do you have?

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    • #3
      Thank you LucMan

      I will see if I can do this.

      I don't know the sizes. Sorry.

      Have a happy and safe New Year.

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