Lol…the AC it replaced was from 1992.
Heat Pump in Northern Climates?
- Thread starter tbm5690
- Start date
Fascinating thread (for this energy nerd). We did without AC for our first 16 summers here. Although we are a cold-weather city, with a much longer heating than cooling season, the summers are hot and humid.
I held off for a number of years, thinking that geothermal would come down in price. And meanwhile our mid-efficiency furnace continued to age. So I figured I could deduct the cost of new AC and a replacement furnace from the cost of new geothermal, for an effective upgrade cost of only a few thousand dollars.
That turned out to be very optimistic; as I learned, the HVAC ductwork for a conventional forced-air system is considered to be too small for geothermal. Because the geothermal-sourced heat is cooler than that produced by a natural gas furnace, more air has to be moved through the ducts to transfer the heat. More air moving through the same ducts means more air velocity, resulting in whistling. To increase the size of the ducts would have meant ripping out our finished basement. Yikes! All in, we were looking at about $35K. The payback ($50/month, or less) would not have covered the interest on the loan.
So Plan B was to look at air-to-air heat exchangers. Unfortunately, we experience very cold winters, and the refrigerants of the day (c. 2007) were not rated much below freezing. Therefore, although the heat exchanger would have worked fine during the knee seasons, for most of the winter it would have consumed more energy than it could have provided. Furthermore, at that time the government incentives were not available for air-to-air, as they considered it no more efficient than pure electric heating. So, I would have been out-of-pocket $15K for something that wouldn't have actually done much. Natural gas heat is much cheaper than electric here, despite the recent spike in natural gas.
I talked to an energy advisor at our public electric utility. He had been out in private for a long time, and knew his stuff. He recommended leaving the furnace alone, and going with a conventional AC system. He also warned against the really high SEER units, saying that they tended to fail early due their exotic refrigerants.
My last shot at it, before opting for the conventional AC, was to consider buying a unit that could be switched to heat. That would have been an $800 upgrade. The HVAC company I dealt with advised against it; the tech said that to be sized large enough to make any significant heat contribution during the knee seasons, the unit would be way oversized for cooling. That is, it would not run long enough in the summer to dehumidify, but rather would quickly cool without dehumidifying, acting as a "chiller". (I can tolerate dry heat, but can't stand high humidity.)
So, $2300 in 2007 for a stand-alone AC system, and it's been problem-free so far. And meanwhile, the old furnace is still going strong. I have replaced a couple of motors, and the fan control board, and the high-limit switch, but it's been cheap compared to a new one.
The recommendation here is to invest in upgraded insulation rather than putting money into more efficient heating and cooling systems. May get the attic spray-foamed next summer.
Anyway, thanks all for this very interesting discussion - I've learned a lot.
I held off for a number of years, thinking that geothermal would come down in price. And meanwhile our mid-efficiency furnace continued to age. So I figured I could deduct the cost of new AC and a replacement furnace from the cost of new geothermal, for an effective upgrade cost of only a few thousand dollars.
That turned out to be very optimistic; as I learned, the HVAC ductwork for a conventional forced-air system is considered to be too small for geothermal. Because the geothermal-sourced heat is cooler than that produced by a natural gas furnace, more air has to be moved through the ducts to transfer the heat. More air moving through the same ducts means more air velocity, resulting in whistling. To increase the size of the ducts would have meant ripping out our finished basement. Yikes! All in, we were looking at about $35K. The payback ($50/month, or less) would not have covered the interest on the loan.
So Plan B was to look at air-to-air heat exchangers. Unfortunately, we experience very cold winters, and the refrigerants of the day (c. 2007) were not rated much below freezing. Therefore, although the heat exchanger would have worked fine during the knee seasons, for most of the winter it would have consumed more energy than it could have provided. Furthermore, at that time the government incentives were not available for air-to-air, as they considered it no more efficient than pure electric heating. So, I would have been out-of-pocket $15K for something that wouldn't have actually done much. Natural gas heat is much cheaper than electric here, despite the recent spike in natural gas.
I talked to an energy advisor at our public electric utility. He had been out in private for a long time, and knew his stuff. He recommended leaving the furnace alone, and going with a conventional AC system. He also warned against the really high SEER units, saying that they tended to fail early due their exotic refrigerants.
My last shot at it, before opting for the conventional AC, was to consider buying a unit that could be switched to heat. That would have been an $800 upgrade. The HVAC company I dealt with advised against it; the tech said that to be sized large enough to make any significant heat contribution during the knee seasons, the unit would be way oversized for cooling. That is, it would not run long enough in the summer to dehumidify, but rather would quickly cool without dehumidifying, acting as a "chiller". (I can tolerate dry heat, but can't stand high humidity.)
So, $2300 in 2007 for a stand-alone AC system, and it's been problem-free so far. And meanwhile, the old furnace is still going strong. I have replaced a couple of motors, and the fan control board, and the high-limit switch, but it's been cheap compared to a new one.
The recommendation here is to invest in upgraded insulation rather than putting money into more efficient heating and cooling systems. May get the attic spray-foamed next summer.
Anyway, thanks all for this very interesting discussion - I've learned a lot.
That is likely an Alternating Current Heat Pump -- suggest you look at Direct Current Heat Pump systems as we run these both in the Arctic and South Florida.
They come these days as whole house systems, not only of the mini split variety.
Big night tonight as it's the coldest it's been since the HP was installed! It's 18F outside and I set the crossover temp to 10F. The heat came on at 62F (it's set for 64F) and ran for 16mins but the first 5 were totally cold and I believe it was in defrost mode. The supply temperatures were 99F after that and 11 mins later the heat shut off with an inside temp of 66F.
Only 11 mins of "real" heating runtime and still putting out 99F air at 18F. This thing will easily go to 10F.
Only 11 mins of "real" heating runtime and still putting out 99F air at 18F. This thing will easily go to 10F.
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Here’s what I have coming. The temps are in deg F. This doesn’t happen all that often so wouldn’t expect a heat pump to go this low. Certainly 10 F would be an awesome set point here. I spoke with one of the contractors and they are putting together a list of HP to show to the government group looking at placing 30 heat pumps in my area.
shocking
A couple of "general" points worth considering/researching when in the market for Mini Split systems. (I noticed that people discussed them above)
1) SEER numbers are often exaggerated. Especially when there is a large temperature differential. SEER 35 might be possible "IF" it's 55 outside and you want 60 inside. Otherwise SEER numbers fall much more in line with modern high efficiency systems when real work is required. Research/understanding is required! Don't be surprised if your Mini Split home costs as much to heat as a conventional system when a large temp differential is required. (10 outside, 70 inside)
2) The larger and more capable the Mini Split, the lower the SEER numbers are.
3) Heat pumps are efficient when considering purchased electricity in KWH. But when considering how much gas the Combined Cycle Power Plant consumes to heat your home, there is very little difference between a modern furnace burning fuel directly in your home, and a heat pump consuming electrical power generated by the gas burning plant. The stack of losses exists between power plant and the home. Over unity is possible, but it requires the very best of equipment at all stages.
1) SEER numbers are often exaggerated. Especially when there is a large temperature differential. SEER 35 might be possible "IF" it's 55 outside and you want 60 inside. Otherwise SEER numbers fall much more in line with modern high efficiency systems when real work is required. Research/understanding is required! Don't be surprised if your Mini Split home costs as much to heat as a conventional system when a large temp differential is required. (10 outside, 70 inside)
2) The larger and more capable the Mini Split, the lower the SEER numbers are.
3) Heat pumps are efficient when considering purchased electricity in KWH. But when considering how much gas the Combined Cycle Power Plant consumes to heat your home, there is very little difference between a modern furnace burning fuel directly in your home, and a heat pump consuming electrical power generated by the gas burning plant. The stack of losses exists between power plant and the home. Over unity is possible, but it requires the very best of equipment at all stages.
My house was built int 1987, it is 2x4 with fiberglass insulation and at best average construction. The doors have worn our weather stripping and need to be replaced and many of the double-pane windows have lost their seals. We have two large fireplaces with drafty flues and 5 skylights which I believe are single pane. This system has no problems heating my drafty home at 15F.
Bring back nuclear which can be done safely. At this point all I care about is I'm spending about $180 dollars less per month to heat my house.
I wanted to touch on price as well. This Bosch IDS 2.0 is a 4-ton HP and it was $1500 less than four other quotes for mid-level 16 SEER ACs from Goodman, Ruud, and Trane. That is before the insane HP rebates. The other systems were about $12K and this one was $10,500 - $6250 = $3750. Because they only come in two physical sizes (2-3 tons and 4-5 ton units - the difference is just a dip switch setting) you get credit for either the 3-ton or 5-ton even if you have a 2-ton or 4-ton. This plus $180 per month so far in savings could be another $1000 in heating savings this year. Factor in the +$100 per month savings for cooling in summer and this things pays for itself in 2-3 years. Not to mention can keep the house cool and dry at 68F when it's 95F outside and warm when it's 15F.
That’s why BC and Quebec run on Hydro electricity and Ontario mostly on Nuclear. Every area has their own thing going on. For now I’d recommend every one calculate their energy cost by the GJ and make decisions based on that. For AC of course there is only one practical choice, which is electricity. For heat pumps vs propane in my area, it’s hands down for heat pumps. For heat pumps vs natural gas, usually natural gas will win, but even then a person should know the numbers. As for saving the plant, one needs to take a look at where the power comes from. There are a lot of coal powered Tesla’s in Alberta.
I can’t help wonder when I read about these low temperatures people are posting and heat pumps working great are they taking into account the auxiliary built in back up electric resistance heat coils that may be kicking in because the heat pump can’t keep up?
I’m not doubting the posts but I am wondering if the posters are aware of the back up coils.
At any rate it would be interesting as each month goes by in the winter to see the actual electric bill for heating costs.
I’m not doubting the posts but I am wondering if the posters are aware of the back up coils.
At any rate it would be interesting as each month goes by in the winter to see the actual electric bill for heating costs.
Good point. I hope we are all talking about situations where the compressor is running and not using the backup system. This is easy enough to check just by checking for the compressor noise.
I have a relatively recent (~3 years old) 3 ton Lennox 14HPX and it has had no issue handling the 20's we see here a handful each winter season. I monitor my Nest app when its running in lower temps and I don't ever recall seeing it on AUX heat, I have it setup to allow heat pump at any temp and the "heat pump balance" set to most efficient which prevents AUX as much as possible.
I'm intrigued now. I might get a little IR thermometer to have on hand to see how it handles things when we have some mornings in the 20's. We might get lucky (well unlucky) and it might be a year we see some teens again.
I'm intrigued now. I might get a little IR thermometer to have on hand to see how it handles things when we have some mornings in the 20's. We might get lucky (well unlucky) and it might be a year we see some teens again.
Since mine is dual-fuel there is no auxiliary heat and you can see if "emergency heat" is on.
I will say tonight I did find a bit of an Achilles heel. The temp outside is 27F and the temp inside was set to 62F. I jacked the heat up to 74F and the system did not even attempt to heat with HP and it immediately went to the emergency oil heat. I turned off dual-fuel to force it to use only the heat pump and the following happened.
Mins 1-5 was in defrost and so blowing cold air which brought the temp down to 60F
Mins 5-20 was in second stage heat mode and the temp went from 60F to 66F
Mins 20-25 was back to defrost mode and blowing cold air and so temp went down to 64F
Mins 25-40 was in second stage heat mode and temp went from 64F to 70F
Mins 40-45 back in defrost mode and so temp back to 68F
Mins 45-60 in second stage heating and finally we reached 74F.
I let the upstairs cool back down to 62F and turned dual-fuel back on and set the temp at 74F and the oil heat came on and hit 74F in like 13 mins. So for large heat calls it turns out the HP is less efficient and it seems to do best just needing to maintain a set temp which requires less time than is needed to trigger the defrost mode.
This has been my experience with various heat pumps through the years, if the setpoint and actual difference is too high it just automatically kicks to AUX/Emergency no matter the outside temp. Some of my older basic programmables you could set the temp differential to trigger AUX, IIRC you could go as high as 3 or 4 degree differential or as low as 0 degrees to use AUX all the time. Even the old slider style thermostats with the AUX heat light on the front you could see where the AUX would kick in when bumping up the temp, then you could back it off until the "Aux. Heat" light turned back off. Remember these things?
Excellent post, details are great
Here is a pic of what happens when it’s snowing out and the outdoor temp drops to my cutoff point. Since then the temp has risen to above 27 F and my pump started up again and blew away the rest of the crusty snow.
10F here and supply temps are 95F (edit: 90.6F - I'm an idiot and was looking at a temp in memory) with no issues but clearly starting to lose the ability to produce maximum temps (previous supply temps were 99-100F). It also almost immediately went into stage 2 and it took about 20 mins to reach set temp. We had 7" of snow yesterday and felt the cold air during a defrost cycle and went to the window to watch. Within 2 mins there was steam coming out of the top of the outdoor unit and you could watch the snow melt within a min or two on the top and sides and even on fan blades inside. Do I dare go to 5F?
The defrost cycle does suck as it is basically turning the AC on in the middle of the winter for 5 mins. The entire house drops 1-2F during that time and you can really feel the cold air during that time which is about 5 mins at 10F. I think it is not timer based but based on temp of the outdoor unit.
The defrost cycle does suck as it is basically turning the AC on in the middle of the winter for 5 mins. The entire house drops 1-2F during that time and you can really feel the cold air during that time which is about 5 mins at 10F. I think it is not timer based but based on temp of the outdoor unit.
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