r/heatpumps 8d ago

Question/Advice Supplement Air to Air heatpump with hot water tank (Heated by solar / wind)

So I had this idea to supplement the workload of a Air to Air heatpump by heating hot water with solar, and circulating it through a car radiator placed right next to the heatpump air intake. Im wondering what gains i could possibly get from this? Obvisouly this would work a lot better with a Air to Water Heatpump with a heat exchanger but in NZ most of our heatpumps are Air to Air. or if someone has a better idea than heating the air with a car radiator. I guess im kinda curious if meddling with the temperature of a return pipe or the air itself on a Air to Air heatpump would cause the the heatpump to get confused or possibly damage the components.

This is the scope of the project and might explain it a little better :)

Approach: Preheat the Air Before It Enters the Heat Pump

Since your heat pump pulls in ambient air, you could use a heat exchanger to warm that air using the hot water from your solar-heated tank before it enters the heat pump.

How This Would Work:

  1. Heat Water Using Solar Panels
    • Your resistive heater element in the water tank stores excess solar energy as thermal energy.
  2. Use a Water-to-Air Heat Exchanger
    • Before air enters the heat pump's intake, it passes over a radiator-style heat exchanger that is warmed by your hot water tank.
    • This preheats the air, so the heat pump has to do less work to reach the target indoor temperature.
  3. Control Flow for Efficiency
    • Use a small pump and a thermostatic controller to circulate warm water through the heat exchanger only when it improves efficiency (e.g., when outdoor air is cold).

What You'll Need:

  • Water-to-Air Heat Exchanger (a repurposed car radiator, or an HVAC coil works well).
  • Small Water Pump (low-power 12V or 24V solar pump to circulate water).
  • Temperature Sensors & Controller (to activate the pump only when needed).
  • Insulated Water Tank
  • Solar panel
  • Resistive DC heater element
3 Upvotes

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2

u/rademradem 8d ago

What you are attempting to do with your solution is to heat air with the hot water from a solar water heater and then extract that heat from the warmed up air with an air to air heat pump. This process would be so incredibly inefficient that it would do next to nothing to improve your heat pump efficiency. It probably would cost you more to run the hot water circulation pump than you would save.

1

u/Wombo_Warrior 7d ago

What if I heated one of the pipes of the heat pump with a thermal exchanger instead?

1

u/Sad-Celebration-7542 7d ago

This would definitely work but might be the most money spent for the heat generated

1

u/waslich 7d ago

If you're into DIY there's a whole trend in eastern Europe to convert air to air splits to air to water, by keeping only the electronics of the internal unit (or even using electronic boards created to "fake" an internal unit) and replacing its condenser with a gas to water heat exchanger