I know others have made a case against air source vs. geothermal in the past on some posts. However, I'm wondering what more info can I get.

What I'm wondering is about how long the system lasts, and how effective/efficient are they when they are set to run down to an outdoor temp of 0 deg. F.?

Some contractors here in our area are installing these hybrid air source/propane furnace systems and running the air source units down to 0 or 5 deg. F. It's my guess that this will hurt the equipment and wear it out far before it should.

What type of data or proof is there that I'm guessing right? Or am I guessing wrong?

Does anybody have experience with ASHP failures due to over-working the equipment?

Our own company has lots of experience with ASHP failures in the past. These were systems installed in the 1970s, and we've replaced a lot of them. However, the ASHP manufacturers are telling the HVAC contractors that these new systems can run down to 0 deg. F. without problems like the ones in the '70s had. I think that's a bogus claim, but I have no proof. What do you think?

The addressing of these choices are site specific. Would one ask a Ford dealer what is better Ford or Honda? A proper study of the site to determine the most suitable alternatives would have to include but not be limited to the cost of energy from the utility, available space, soil and rock conditions, geology, hydrology, vertical heat exchanger installation prices, horizontal heat exchanger installation prices, and heat gain and loss.

Downsource Heating and Cooling
2345 Route 390
Mountainhome, PA 18342
Email: [email protected]
(570) 242-8750 (24/7 Cell)

At $.08 per KWh, $3.00/gallon propane, and temperatures that sit around 0 to -10 for weeks at a time, I don't think our area is the place for it.

I guess what I'm after is the proof that it's not a good setup for an area like mine. Proof (or educated opinions) that it's harder on the equipment than any benefits gained are worth for running them down to such low temperatures.

Another part of why I'd like to know, is that I usually show up to 10 years payback on the hybrid propane/ashp system vs. geothermal, and 15-20 yrs. on ashp/electric vs. geothermal. If the compressor of the ashp is going to need to be changed out before that payback, then that needs to be taken into consideration for a more accurate comparison.

Clark,
This question came up at Senecarr's. In doing the math we found that a $4,000 ashp paid for itself in 4 years and an $8,000 ashp paid for itself in 4 years (assuming a reduction in usage didn't change the price they paid for propane). Of course a $20,000 gshp paid for itself in 4 years, so which would you rather have?
J

huh? He's asking about ASHP, what do the rock and soil conditions have to do with anything? My goodman ASHP lasted about 10 years before it had to be replaced, and the replacement one is pushing 7 years now.  

TG,

Remind me where you're located.

Galloway, New Jersey. (it's close to Atlantic City, New Jersey) I'm about 5 miles from the bay, so i'm not sure how much salt air there is to affect the life expentancy of outside equipment, but I would expect there is some impact. Actually there some evidence of this, when they get snow / ice storms farther west, we usually escape with rain. I'm sure the amount of salt air would depend on the direction the wind is blowing, I'm sure I have a lot less salt air then someone with a house in a beach / barrier island community.  

 

 

What failed on your previous ASHP? The compressor or the condenser? If it was the compressor, the salt air likely had nothing to do with it.

Addressing the original question of operating air source equipment down to 0 F:

My educated guess is that newer compressors, variable speed blowers and smarter controls widen the performance envelope of air source equipment. Still, one can't escape physics, specifically psychrometric considerations. ASHPs produce less heat as ambient temp drops, and at the same time building load rises. Expensive defrost cycles are inevitable, particularly in cold wet climates.

In a hybrid installation the economic balance point has to be carefully calculated and probably recalibrated yearly to reflect anticipated Btu costs of the two fuels. Who will actually do that correctly every year? Especially nifty would be a smart thermostat or controller wherein the installer or even homeowner enters cents per kWh, dollars per therm of gas and / or dollars per gallon for propane, and the system calculates a balance point based on the cost entries. Does any hybrid system manufacturer offer that?

I think the question of compressor overwork is a non-issue. As ambient temps drop, the system will cycle longer, and system pressures will drop - both effects should lengthen rather than reduce, compressor lifetime.

I don't know, The house was build in 1991, the existing heat pump was installed in 2001, I'm the 2nd owner of the house, so I don't know what failed on the original system. Thismorning it felt more humid then normal upstaris, I'm wondering if it's not dehumidifying right. I have to get gauge to tell me if its a problem or just me.

As cooling loads drop with the onset of cooler weather, it is not uncommon for humidity to increase owing to shorter compressor run times and less dehumidification

Yeah, I had to have a small debate with my wife when she saw the cost difference between the two systems. In the end though, she understands the math, which is what you need to look at, so long as you have some method for paying for it. Also, it helps that she hated even being on natural gas at our last home, and always wanted us to try to get our dryer switched to electric, let alone the idea of having a giant tank of gas sitting in our yard. Really if you GSHP guys could get the IGSHP rolling out enough advertising, you should be able to get things like insurance companies to lower bills for GSHP users. After all, a GSHP can't give you carbon monoxide poisoning, and I do know some home owner's insurance companies discount if you have a detector installed. Why not a discount on not being able to produce it?