Hybrid GSHP

[tomsbradford]

I'm looking at a direct exchange DX ground source heat pump. The ground loop is copper tubing with R-410A. Why wouldn't be better to run the refrigerant through an air-source coil before it goes to the ground loop? The air is always going to be warmer or cooler than the refrigerant as it is heading to the ground loop. Wouldn't a greater heat transfer surface increase the efficiency of the system? There are many hours during the year that the air would be at a higher temperature than the ground when heating, and vice versa when cooling. Also, it would help keep the ground from getting thermal saturation. I suppose that controls could be added to bypass the air coil if it started to collect frost. Is this too simplistic thinking?

[Rob White]

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DX ground loops aren't too popular in the UK because
the copper reacts with the soil and corrodes which leads
to leaks and pollution.

We tend to put a secondary water loop in and then transfer
the heat through the treated water in the ground loop.

Combining air and ground in principle will work but may
prove difficult to control.

Do you intend to divert the two circuits or are you just
going to put the air coil before the ground loop?

The air coil will freeze in certain low temperature conditions
so defrosting it will require a heat source and because you are
thinking of using the ground loop you won't be able to reverse
the flow of refrigerant (you could but it would be complicated).

Also the ground is going to be at a constant temp and constant
but the air will fluctuate wildly and that will throw the heat transfers
out all over the place.

Pick one and go with it, in my opinion don't mix the two.

Rob

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