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.

So far, so good.

Utilities:
Okay, we have a 2850 square foot home, four bedrooms, three baths, an electrically powered well which supplies both our electric geothermal heat pump and our house water. We cook with propane, and use propane for the dryer and hot water heater as well.
We have been living in the property, had house guests, ran all systems continuously.

So far:
Propane: the dryer is a big expense here, total so far is around $60 per month. We are looking to change our use of dryer with standard controls so that we don't "overdry" our clothing.
Electric: New electric bill just in for $201.71. This means our total utility cost for October was under $265. However, we need to look forward to midwinter, when the geothermal will be cranking a lot more.

Solar gain:
We do get some benefit here. Our south-facing house, even with the low-E windows, is warming the downstairs by around 3 or 4 degrees, so that our furnace, set at 65 degrees, is not kicking on.

SIPs:
The house holds heat beautifully. It also, however, holds cold. So if there is a sudden warming trend in the weather, you have to throw open the windows to get that benefit.

Insects:
We recently had the annual ladybug swarm, and the exterior of the south side was Covered with ladybugs. Only a handful got inside. The leaf-footed stinkbug we have here, which likes white pine cones (and boy do we have those) has also been seeking a winter home. Again, only a few made it in.