Geothermal HVAC

[buckeyefarmer]

I am surprised by your EWTs. In winter I reach 27-29 deg by the season end. Summer I never get above 60 deg. But even at 80 deg summer and 40 deg winter, the DHW generator output is close to the same number, not really favoring summer.

Do you have bore holes or a ground loop ? Ay 80-90 deg EWT in the summer is not much improvement over a conventional air-air heat pump.

paul

Never compared to anyone else. My loops are horizontal slinkys, buried 5' - 6' deep. I just put a probe in, my EWT is 30 right now, but it has been very cold the last couple weeks, more than normal. My electric backup has only been on a few hours when the temps have been below 0.

 

[s219]

One thing I like over conventional systems is the temp does not swing as much as the old school natural gas. Of course more modern energy efficient gas units are probably not at hot when running as systems from 25 years ago.

That's what I noticed once we started heating with geo for the first time this fall -- the system runs for fairly short durations to get the temperature up, and the air coming out of the registers is very even and doesn't feel that much warmer than the interior temperature. If I put a bare foot on a floor register it feels warm, but the overall air temperature blowing out is not too much warmer than the interior to my senses. At our old house with NG furnace, the heat used to blast out of the vents like a hot rocket exhaust, yet the house still felt very unevenly heated with drastic swings.

I do think our new thermostats, and their placement, may have something to do with this, along with 2x6 walls and spray foam. The new house clearly loses heat much more slowly than the old house, despite many more windows. So the geo system really sort of leisurely comes on every so often to maintain temp (we normally set to 70F during the day and 68F at night) without having to go bonkers.

The only time it took a while to run was back a few weeks ago when we lost power for 4 hours when it was 12F outside. I didn't bother to fire up the generator since the power company had a firm estimate for restoration (it was a cold weather equipment failure) and our fireplace was keeping us fairly comfortable. It got down to 64F inside by the time power came back on. The geo system ran for about 2 hours to get us back up to 70F on the first floor.

One thing I did in our new house was to place one of the HVAC return registers up near the peak of our fireplace room that has a vaulted ceiling. After running the fireplace for a couple hours to the point where we have a good bed of embers and it starts belting out the heat, I can turn the thermostats to "off", then switch on the fan only. That will suck the warm air from the fireplace room and push it out to the rest of the house. It's pretty neat to feel warm air blowing out of vents at the opposite corner of the house from fireplace heat only. I bet if we installed a wood stove instead of fireplace, it would work even better.

 

[s219]

Our EWTs were pretty much in the 55-58F range during summer, and only drop slightly during winter so far, into the lower 50s when it gets real cold (can't say I have looked at the readout when we had single digit temps last week though). Our loop circulates through 5 bore holes at about 150 ft deep each, and then runs about 100 ft to get into the house, buried about 30" down. The frostline here is generally at 12-14" depth. So it looks like our geo system is seeing fairly steady EWT compared to some of you.

At a 55F EWT, our system looks to be doing about 2600 BTUh HWC in heating mode and 1400 BTUh in cooling mode according to the tables (ours is a ClimateMaster 22).