solar hydronic and heat pump thermostat controls

SlowJoeSlowJoe Registered Users Posts: 1
Is it possible to use my new heat pump thermostat to control the hydronic solar heat?

I have a solar-hydronic heat system and have added an air-source heat pump for cooling in the summer and additional heat during storms.

Is there a way to use the heat pump thermostat (Trane TCONT802AS32DAA) to turn on the solar first, and then add the heat pump if the temperature continues to drop?


  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: solar hydronic and heat pump thermostat controls

    Since the thermostat has 3 heating stages it probably could be wired to make the heat pump the second stage. The way the thermostat controls the 1st and 2nd stage switch over is by outdoor temperature ( Balance Point ). Most all these newer thermostats use a digital outdoor controller that won't have the range needed to control hydronic ( water temperature ). There might be a way to set it up as a duel fuel concept like you would a electric / gas, this way it would shut the hydronic off so they wouldn't both run at the same time.

    I'v tried it a few ways over the years, my hydronic is in the forced air duct. I don't have enough storage or a high enough water temperature to make it sustainable so I use the heat pump and augment it's output. I control it's run with a ductstat. It runs with the HP until the duct air is 100°. When the HP goes into the defrost, the hydronic will carry the load. The duct air temperature and the HP coil is about 20° differential ( HP coil 120°, air 100° ) with the return air at 73°. It takes about 6-7 minutes for the HP to get the coil to 120°.
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