Wondering if it would make my heat pump more effective if I built an enclosure around it?

Hey @Marc0324 

One of our very knowledgeable Heat Pump volunteers, juliamc has left some great advice and a handy video for you.

We’ve also got a lot of topics on Heat Pump efficiency that could also be helpful to you:

Hopefully some of this can be of use to you.🙂

hi Abby

thanks for the vid, but that’s not quite what I had envisioned, I’m thinking of actually building an entire little room if  you can picture it, but the air intake for that room will be coming from a tunnel I’ll dig in the ground. Dig it down 20-30 feet or so in order to get to air that is stable and much warmer than the ambient air. Is that something that has been tested or tried?

I think what you’ve described would be  untested to date. If you have the time and energy to do it then please report here how you get on.
My point with the video was that the heat pump tested seemed to defy the theory as recirculating cold air back into it made little difference to its efficiency. 

There are three possible issues that I can think of straight away.

When you start pulling cold air through the tunnel it will cool down the inside wall and the only thing warming the surface will be the thermal conductivity of the soil. The inside of the tunnel could end up very near the same temperature as the incoming air so you may not have gained very much at all. The temperature will obviously recover a bit between operating cycles but that will depend upon the thermal conductivity of the soil which varies depending upon its type.

Another effect is that the viscosity of the air, although small, will produce a pressure drop at the air con unit reducing the rate of flow of air over the heat exchanger. This will impair the COP of the unit as it won’t be operating at its deigned level of air flow.

If the tunnel goes below the water table or it rains it will fill up and will need to be drained with a pump possibly negating what you gained in the first place. What you are actually progressing towards is a horizontal ground source heat pump and it takes a very large area to run a house simply because of the poor thermal conductivity of soil. You have the right idea and if there is a large enough area the GSHP does work with a higher and much more stable source of heat and it is easier to get the required COP (or SCOP).