It's now been one full winter since my geothermal heat pump system was installed so I can evaluate its performance. For the details on what was installed see part 1.
This was a good winter to test it in, as you know if you live around here. We had some pretty cold stretches. Let's see how the system did. Note, I won't be talking about operating cost in this post. That will be part 3 because it's not a simple topic and this post is long enough already.
Noise
As part of the crawlspace encapsulation that was done as part of this install, the fiberglass insulation was removed from under the living floors. The geo equipment was all placed in the crawlspace under the master suite, which is where the previous equipment was. The geo equipment is quieter than the equipment it replaced, but without insulation in the floors more of the noise came through, so the noise in the house is a wash.
Well it is now. At first it was very noisy, with a loud pulsing sound that sounded like there was a washing machine running. I had the contractor back out to troubleshoot and he discovered that the noise was due to the desuperator pump. One of the desuperator lines was resting on a PVC drain line from the master bath, so when the desuperator pump ran the noise and vibration was transmitted right up into the bedroom through the tub in the master bath! Once that was fixed the noise level was equivalent to the old system.
However in the future I may have insulation put back under the master suite floor to quiet it more. By nature the geo system is quieter, but removing the underfloor fiberglass insulation as a result of crawlspace encapsulation has cancelled that out.
Outside noise is non-existent. In the previous system the compressor was outside in an assembly with a big cooling fan and whenever it kicked in, relaxing outside was interrupted. Now the outside is perfectly quiet at all times, which is how we like it in the country!
Comfort
Well comfort is the real bottom line, right? The job of the system is to keep the house at a comfortable temperature and humidity after all. And on this score the new system is an A+!
With the previous system my master bedroom was always too cold because the thermostat was on a living room wall opposite a south facing wall of windows. So in the winter the sun would shine on the thermostate and heat it up, so the system would shut off before the master bedroom was warmed up.
In the summer the previous system couldn't keep the main room where the thermostat is cool enough so the system ran all day and froze out the master bedroom.
At first I wanted to solve this with a dual-zone system but my installer talked me out of that. He pointed out that a dual zone system is suited for a house with roughly equal zones, but in my house the master bedroom zone is only about 20% of the house so a dual zone system would be inefficient (the rest of the house is pretty much one big open space so no other zone definitions were practical). Instead he suggested changing the thermostat to one with multiple remote sensors. I placed the sensors around the house, out of the direct sun, and the thermostat uses the average of them to control the system.
This worked much better than I expected! My house now maintains a consistent, comfortable temperature throughout. The temperature in any one room has not varied by more than 2 degrees in the most extreme cold, and usually not at all.
Cold weather heat pump performance
So was my contractor right when he said I wouldn't need backup heat with my geothermal system? Bottom line, yes. We had a bitter winter this year with one of the coldest Februaries on record and the geothermal heat pump maintained the 70 degree set point all the way down to about 10-12 degrees F outside. There was one morning that got down to 8 degrees F and then the system could only maintain 68 degrees against the 70 degree setpoint. I ran 30 minutes of backup propane heat to boost the house up, switched back to the geo system, and it maintained the house at 70 for the rest of the day.
It's worth noting that during that 8 degree morning the air coming out of the vents while the heat pump was running felt just as warm as usual, so it was still generating the full amount of heat. It's just that, when it got that cold outside, that amount of heat became not quite enough.
So I could have lived without the backup heat and just been slightly uncomfortable on one exceptionally cold (for NC) morning. But that wasn't the only reason I had the backup heat installed, as I discussed in part 1.
Power outage protection
I had the propane backup heat installed so I could run it on a cheap generator to keep my house warm during ice storm power outages. I was anticipating more and longer power outages since Duke Energy took over Progress Energy. However I was pleasantly surprised. We had one power outage that lasted about five hours during windstorm, but through two significant ice events our power never flickered, even while many areas of the state had lengthy power outages. Over half the customers in my county were out for over a day, but I never was. So, so far, I haven't had to run the backup heat on the generator as I expected. This means that at this point, the propane backup heat is only providing peace of mind, and has only been run for 30 minutes since the system was installed this past fall.
The next installment will analyze the operating cost savings of the system.
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