Heat Pump vs. Geothermal Heat Pump

[willow_hiller]

Dave - I agree. My variable speed indoor fan is night and day better. My A/C unit sits beside the house near the Master Bedroom but there are no windows. I can barely hear it.

Just as a quick aside, are variable speed fans known for noise from harmonics? The outside unit of the Bosch is very quiet (standing next to it), but for some reason it creates a bit of vibration noise indoors. I'm tempted to call my installer back and ask to have something like this installed on the coolant line:

 

[Feathermerchan]

You may have a bare refrigerant line touching the framing somewhere. My outdoor unit is only two speed. And it has to stop to switch speeds. I have no noise issues.

 

[iPlug]

Our central air ducted heat pump with variable-speed compressor is much quieter than the one speed it replaced a few years ago, both the compressor unit and the indoor fan/venting noises.

There is one noise caveat, however. During the coldest pre-dawn winter mornings (California cold) it will briefly run the defrost cycle to remove frost from the outdoor coil and this is not so quiet an event. Still very pleased with the sound improvements. Efficiency gains, gentle air movement, ditching the natural gas furnace, what's not to like?

 

[willow_hiller]

There is one noise caveat, however. During the coldest pre-dawn winter mornings (California cold) it will briefly run the defrost cycle to remove frost from the outdoor coil and this is not so quiet an event. Still very pleased with the sound improvements.

This may explain the vibration we heard this morning; it was a low of 37 F last night, and the fans haven't run as fast since then.

Also, with the efficiency gains from this new unit, I'm wondering if our solar may be slightly oversized...

 

[DFibRL8R]

Reviving this thread for 2021. After much research about mini-splits, geothermal, and variable speed air-to-air heat pumps, we finally settled on an interesting option I hadn't heard anyone else mention.

Today we just had a Bosch BOVA 2.0 inverter ducted split system installed. Product information here: Inverter Ducted Split System (IDS 2.0) | Air-to-Air Heat Pump Systems | Heat Pump Systems | Products | Residential

It's a really fascinating device. My HVAC tech said it's basically mini-split technology applied to a ducted system. Really quiet at 56 dB. SEER 20.5. Inverter-driven variable speed fans on both the condenser and the air handler. And most interesting, it's variable speed without the need for a special thermostat or running new lines for signalling. From my understanding, the heat pump control board just monitors the pressure of the coolant coming back from the air handler, and from there it can tell how much heating/cooling is needed. And likewise the air handler monitors the pressure coming from the condenser and adjusts the fan speed accordingly. So my Ecobee controls it as if it's a single stage device. It's also meant to operate down to -5 F! I'll be surprised if my resistive heat ever turns on again.

3 ton system installed for just over $10k.

How's the Bosch system suiting you? Based on your recommendation, I had a technician come to give a quote today and he was recommending the 18 SEER system over the 20 SEER that you went with due to the 18 SEER using a Mitsubishi compressor with a long reliable history while the 20 SEER unit is a newer LG design. Any thoughts on this (did your installer share any concerns along these lines)? Having an installer steer me towards lower-priced equipment was interesting.

 

[willow_hiller]

How's the Bosch system suiting you? Based on your recommendation, I had a technician come to give a quote today and he was recommending the 18 SEER system over the 20 SEER that you went with due to the 18 SEER using a Mitsubishi compressor with a long reliable history while the 20 SEER unit is a newer LG design. Any thoughts on this (did your installer share any concerns along these lines)? Having an installer steer me towards lower-priced equipment was interesting.

It's been going well! It's been keeping our home consistently more comfortable, and at about a third of the energy consumption. And no mechanical issues so far.

I had actually originally asked for the 18 SEER as well, but for some reason my installer was able to get the BOVA 2.0 quickly and installed it for us at the same price.

 

[willow_hiller]

It's been going well! It's been keeping our home consistently more comfortable, and at about a third of the energy consumption.

Just following up on this with some concrete data. I don't have average temperatures for these months, but I believe this year has been colder overall. Here's how the new heat pump has affected my monthly consumption in the winter:

December 2020: 1,740 kWh
January 2021: 1975 kWh

Heat pump installed March 2021

December 2021: 1,207 kWh (-30.6%)
January 2022: 1,565 kWh (-20.8%)

 

[David_Cary]

December was like the 3rd hottest ever in NC - close enough to MD to matter. It was warmer than November. Shorter heat pump run times.
So you might want to throw out that comparable. My usage numbers
Dec 2020 1.6 mwh
Dec 2021 1.32 mwh (17.5% decrease)
No changes in equipment/driving pattern etc.

Now Jan was pretty flat for me so that is probably a better month to look at. But I find my usage gradually decreases for other reasons as you are more careful. So some of the decrease my be something else entirely.

Highly recommend Ecobee stat. Gives you runtimes and a whole bunch of good data. Also great control over aux heat.

 

[willow_hiller]

December was like the 3rd hottest ever in NC - close enough to MD to matter. It was warmer than November. Shorter heat pump run times.
So you might want to throw out that comparable. My usage numbers
Dec 2020 1.6 mwh
Dec 2021 1.32 mwh (17.5% decrease)
No changes in equipment/driving pattern etc.

Now Jan was pretty flat for me so that is probably a better month to look at. But I find my usage gradually decreases for other reasons as you are more careful. So some of the decrease my be something else entirely.

Highly recommend Ecobee stat. Gives you runtimes and a whole bunch of good data. Also great control over aux heat.

It's interesting which things influence memory.

Dec 2020: Baltimore, MD Weather History | Weather Underground

Dec 2021: Baltimore, MD Weather History | Weather Underground

So this last Dec had a lower minimum low. But a slightly higher average everywhere else.

Also I also have an Ecobee, but the runtime stats aren't really comparable between a single speed and variable speed heat pump. The variable speed is running much more frequently, but at lower speeds. And the way the Bosch works, the Ecobee still thinks it's driving a single speed, so I don't have recorded data about the intensity.

On the flip side, it looks like January 2022 had slightly lower averages than January 2021.

 

[Feathermerchan]

When multiple/variable speed systems came on the market, the efficiency rating systems were thrown into an uproar. Efficiency is higher at part load but varies with load. So if you set your thermostat higher in the summer or lower in the winter, the unit runs longer cycles and is much more efficient lowering energy consumption considerably. That made it much more difficult for testing/rating to accurately calculate efficiency.

 

[willow_hiller]

How big is your home? I looked at these a few years ago and couldn't find one big enough for our house. 3800 sqft. Seems like the only good brand in our area was Mitsubishi.

About half the size of yours, to be honest. But we've got a 3 ton system that's a little oversized for our home, and I think they make a 5 ton heat pump. Or people also swear by mini-splits, and you'd be able to install as many as you need in that case.

 

[Cal1]

Thanks!

 

[JRP3]

It's actually very common and mine is the same way. On aux heat when temperature outside is below 45 degrees. And this is a pretty new unit. I have yet to have a heat pump that works at low temps except the ones in a tesla.

I installed 2 Mr.Cool DIY 24K heat pumps, one in my garage and one in my house. The one for the garage heats fine down into the teens, the one for the house is a bit undersized but still does fine into the 20's. I supplement it with wood. House has some air leaks and if I ever chase them all down the heat pump might be fine on it's own.

 

[willow_hiller]

I know Ecobee thermostats came up in this thread earlier, and for anyone who has one with a heat pump I'd highly recommend a free third-party application called beestat.io. They've actually come up with an algorithm that lets you estimate your system's thermal balance-points, here's the chart of mine:

So the Y-axis is the change in inside temperature per hour, and the X-axis is the outside temperature. In theory, you can find where the orange line (representing times when the heat pump is in heating mode) intersects the Y-axis at 0 F, and the corresponding X-axis point tells you the outside temperature at which you need to switch to an auxiliary form of heating. But my recorded data for the last year only goes down to 12 F outside, where the heat pump is still able to provide + 0.4 F per hour inside. Oddly enough, on the AC side of things, the data is suggesting that 94 F is the point at which my heat pump is only able to maintain the interior temperature, it cannot cool things down when it's that hot outside.

And then the grey-line they call the "Resist," which is calculated from the data points where the system isn't running at all. Seems like my home is built such that at 59 F it can maintain a steady inside temperature without heating or cooling, but down at 29 F my home loses 1 degree per hour, and up at 89 F my home gains 1 degree per hour.

 

[Sudre]

I have both a split system (works down to -5f) and a GEO-thermal closed loop well system. The geothermal heats and cools my first floor and the split system is a four head system that handles the upper floor bedrooms. It is nice that each person has individual control over the room temperature with the split system.

I have found the GEO-thermal unit to be a pain. Maybe it was a bad installer. It needs slight amounts of water added every 3 months or the water pressure drops to zero. The blower failed in the second year and this year the thermal freeze senor went out during the coldest winter week and naturally with today's parts shortages the part took a while to come in. I would suggest at least never buying a Carrier unit. The unit is also noisy compared to a HP system IMO.

The Toshiba split system has worked flawlessly. Depending of the room, temps indoor range from 72 to 68 in winter while the outdoor temps have dropped to +5f. No service needs except to spray off the outside condenser every now and then.

Overall is you are in a climate that stays above the 0f temps most of the time, I would go with a heat pump.

Do other geo owners with closed loop wells have to top up the glycol 3 or 4 times a year... I am talking like less than a cup... 8oz each time?

 

[JRP3]

Maybe it was a bad installer. It needs slight amounts of water added every 3 months or the water pressure drops to zero.

Definitely sounds like a leak in the system.

 

[David_Cary]

Thanks willow_hiller. Just what I need - more time to waste over analysizing my stat!
I already like the decimel temperature readout. The delta temp per hour is good for estimating when to fire up the unit when returning from vacation.