Notes on open loop geothermal
After living with our geothermal heat pump for a few months, and coming into winter, there are a few thoughts I'd like to share. Note that ours is a water system, open loop, and shares water with the house from our one standing well. As you will recall, due to regulatory conflicts between plumbing board and state we had to ask permission to use this type of system. The one thing we were asked to do at the end of all the hoo-hah was to install a backflow valve—a CYA move that satisfied everyone, although they also agreed it was unnecessary.
A backflow valve is a safety device that sits between the intake of water to the geothermal and the intake of water to the house. It works like a trapeze artist; the balance between water pressure to the geo and water pressure to the house keeps it quiet. If this balance is affected, however, it kicks in, draining backflow from one side or the other. Things that may affect this balance include a leaky toilet, or a clogged pipe somewhere, or the pressure variation from your well. In our case, our "constant pressure" well pump is constant to within 5 GPM, which is great except that it may vary within that 5 GPM. When it does, the backflow valve drips.
If you have a drain under your backflow valve, well and good. If you don't, however, it can cause you headaches. Our valve, being close to the floor, does not have adequate height to drain with gravity. If we put a basin under it, we'd have to pump it. If we don't have a pump, we have to empty it. You can imagine this can be inconvenient for travel.
So if you are planning a dual use geo/house supply well, beware. Place your backflow valve over a drain, or of adequate height to drain elsewhere via gravity.