Cold Climate household Heat Pump (not a mini split)

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peakbagger

Minister of Fire
Hearth Supporter
Jul 11, 2008
8,979
Northern NH
Looks like the mainstream heat pump industry is finally trying to compete in the cold climate heat pump business.
 
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Indeed. Step 1 is build them. Step 2 is sell them at an affordable price.

The Carrier Infinity is already giving great performance down to 5F/-15C, it just cost 2X what the current cheapest models of the same tonnage cost.
 
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The problem is sad to say, a US built consumer unit is going to cost more than lookalike Chicom piece.
 
Living in a house that is under insulated with a heatpump that has huge duct losses and nonfunctional heating strips the first winter was not fun. We, for the coldest 5 days had a space heater in the master bedroom and did everything there we could. It not how I want to live life everyday but 5 days a year we managed. (Heat strips are now working, making other home improvements has helped and we will keep making them.).

My point if we are all going to use heatpumps we need to get more comfortable being uncomfortable. It’s a hard sell to spend 200% more for an HVAC unit for 100% capacity down to 15 or 0 or -15F. If going the all electric route we need to think about secondary heat sources for the 1% of the time we are below design temp and have that honest discussion that they will be needed. Electric baseboards are cheap to install. Power hungry when used but are a great option.
 
Bring them on. I would be happy to buy another American-made HP when replacing our American Standard. It has given us zero problems with nothing more than filter changes. My installer friend spoke highly of the new Carrier units too.
 
My point if we are all going to use heatpumps we need to get more comfortable being uncomfortable. It’s a hard sell to spend 200% more for an HVAC unit for 100% capacity down to 15 or 0 or -15F. If going the all electric route we need to think about secondary heat sources for the 1% of the time we are below design temp and have that honest discussion that they will be needed. Electric baseboards are cheap to install. Power hungry when used but are a great option.

I disagree. Modern heat pumps are perfectly comfortable when properly installed. Comfort issues are a defect of the envelope.

All that is needed is to have a (perhaps region-dependent) HSPF minimum rating. My 2014 unit is HSPF = 8. Current best is 12. Mandate 10 then 12 going forward, and prices will drop with scale to about what they are now, installed. And cost far less TCO.

There is no engineering reason why the HSPF 12 units need to cost 2X that of the 8's. Inverter drive costs and power electronics are much cheaper now than they used to be.
 
Our HP is rated at HSPF 9.5 and it has been a good fit for most of our heating needs. It switches to resistance heating coils at 25º which is once or twice a year in colder winters and not at all in milder winters. The house comfort is fine, it's able to keep the house at 72º all the time if need be. For the past 2 days with our outside temperature ranging between 47º and 52º, it's handling all the heating load.

The real issue with comfort in an old house like ours is that in cold weather, the walls and windows get a lot colder. That makes one "feel" colder even though the indoor air temperature is the same. I'm fairly warm-blooded so this is not a big deal for me, but my wife is the opposite. With poorer blood circulation she gets cold just by hearing the weather forecast and usually has cold hands and feet unless the room temperature is higher. Thus the woodstove with me in a t-shirt when it's freezing outside. In the summer it's just the opposite.
 
Living in a house that is under insulated with a heatpump that has huge duct losses and nonfunctional heating strips the first winter was not fun. We, for the coldest 5 days had a space heater in the master bedroom and did everything there we could. It not how I want to live life everyday but 5 days a year we managed. (Heat strips are now working, making other home improvements has helped and we will keep making them.).

My point if we are all going to use heatpumps we need to get more comfortable being uncomfortable. It’s a hard sell to spend 200% more for an HVAC unit for 100% capacity down to 15 or 0 or -15F. If going the all electric route we need to think about secondary heat sources for the 1% of the time we are below design temp and have that honest discussion that they will be needed. Electric baseboards are cheap to install. Power hungry when used but are a great option.
There is no need to be uncomfortable. If you cheap out and undersize your equipment so that it can’t do the job then you are choosing to be uncomfortable. Hardly a requirement.

There are lots of ways to build your system. Combinations of technologies work fine.

My super cheap heat pump has an hspf of 10. It’s been heating my old shack the last couple of days. The woodstove is loaded and ready when cooler weather returns, or I could just let the heat pump do the job. None of my choices require discomfort.
 
I disagree. Modern heat pumps are perfectly comfortable when properly installed. Comfort issues are a defect of the envelope.

All that is needed is to have a (perhaps region-dependent) HSPF minimum rating. My 2014 unit is HSPF = 8. Current best is 12. Mandate 10 then 12 going forward, and prices will drop with scale to about what they are now, installed. And cost far less TCO.

There is no engineering reason why the HSPF 12 units need to cost 2X that of the 8's. Inverter drive costs and power electronics are much cheaper now than they used to be.
The South will mandate 16 SEER units come the first. My installer was booked solid with 12 and 14 SEER change outs before the the cold weather hit. Many people will go with the lowest price. The quality of work is often reflected by the price. If sized correctly they are under sized for a 1% of an average year. One can not expect a correctly sized unit to maintain set point during record or near record cold spells.

I agree with your envelope statement but I’ve lived in this home since 2010 and the owners before me and the ones before them did nothing to the envelope. Broken equipment gets replaced. falling down crawl space insulation not so much. So I stand behind my statement about backup heat for the simple reason that an equipment change outs often don’t address the envelope.

I did the math for a 14 SEER vs a 16 Seer two years ago and the ROI of the more efficient unit was something like 15-20 years. I don’t like 80-85 degree air blasting from my vents. It’s not comfortable. And it get colder the colder it gets outside. Yea this is a 13 year old unit but it it’s still being sold today!

We have to change our expectations of comfort when one switches to a heatpump from another heat source.
 
We have to change our expectations of comfort when one switches to a heatpump from another heat source.
I did that when changing from propane furnace to the heat pump. I expected to save money, but with the increasing price of propane and decreasing quality of delivery service locally by Amerigas, my expectations have been far exceeded. My sister in North Carolina agrees. She put in Daikin mini-splits and has been delighted by their performance during the recent cold snap when it dropped into the teens for a night.
 
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With modern variable speed equipment it is now much easier to correctly size for all normal expected weather. Even unexpected extremes. Our heat pump is 20 seer and output temps are quite hot.

Time to check out the new stuff. The old single stage equipment had a much narrower band of acceptable performance so you might be uncomfortable without emergency heat.

I did peel back my lineset insulation and bubble tested for leaks today just because pressures should be high and I always wanted to double check. No leaks.
 
I recently looked up the BTU output versus outdoor temps for the new HSPF 12 units, specifically the Carrier Infinity. The output was MUCH flatter down to about 10°F than conventional. I had thought the new units were just oversized with a variable speed (inverter) compressor. I have since learned that they have some plumbing and valve innovations that boost low temp BTUs... this is what 'cold weather heat pumps' are.

This translates to easily being able to size a system to 10°F (good for much of the US warmer than Boston), and getting high outlet temps (bc the BTUs are higher per CFM).

@EbS-P, you are behind the technology curve. All we need to see is these new units becoming the standard and the price falling with that. I also recently learned that the IRA does have a HSPF cutoff for heat pump rebates.
 
I recently looked up the BTU output versus outdoor temps for the new HSPF 12 units, specifically the Carrier Infinity. The output was MUCH flatter down to about 10°F than conventional. I had thought the new units were just oversized with a variable speed (inverter) compressor. I have since learned that they have some plumbing and valve innovations that boost low temp BTUs... this is what 'cold weather heat pumps' are.

This translates to easily being able to size a system to 10°F (good for much of the US warmer than Boston), and getting high outlet temps (bc the BTUs are higher per CFM).

@EbS-P, you are behind the technology curve. All we need to see is these new units becoming the standard and the price falling with that. I also recently learned that the IRA does have a HSPF cutoff for heat pump rebates.
I wouldn’t say I’m behind the curve, rather looking at what the average system that will be installed in the next 2 years will look like. I agree there are decent cold weather units available now. But they won’t be marked south of Washington DC. There are lots of natural gas furnaces that may be changed out for a heat pump in that region.

The new cold weather tech is great but still expensive. A large pot of consumers will just buy the lowest price option available and it won’t be the new technology. I don’t have numbers but I’m guessing close to or under 50% of the whole house heat pumps installs will variable speed compressor tech. So i stand by my statement that heatpumps should have backup heat even if it’s resistive strips.

Have the efficiency requirements for the IRA been released yet? Last I heard they were going to come out soon but we’re going to redo the tiered rating system so more ( less efficient) units would qualify.
 
So i stand by my statement that the lowest price, oldest technology, or undersized heatpumps should have backup heat even if it’s resistive strips.
You said much more than that to demonstrate that you weren't considering the newer equipment . Maybe your above statement could benefit from my green edit. Resistive strips are a great answer for an undersized heat pump. Often a cheaper decision than sizing the heat pump for all conditions even after considering the extra electric costs for using them. That's some tough math though and requires some deep understanding of how often the coils take over.

I agree that every home should have some sort of backup. We're on a wood heating website after all and it's pretty uncommon for anybody here to be 100% wood heat with no other source. Each heating device can be sized properly for the task at hand if the owner wants to.
 
Resistive strips are a great answer for an undersized heat pump.
That's exactly how our system is setup. It is optimized for about 90-95% of our normal weather with backup resistive coils for the remaining anomalous winter weather. This is a high-end, 2-stage system, albeit from 2006. Where it is undersized is for cooling which up until a couple of years ago was a non-issue in our cooler maritime climate.
 
That's exactly how our system is setup. It is optimized for about 90-95% of our normal weather with backup resistive coils for the remaining anomalous winter weather. This is a high-end, 2-stage system, albeit from 2006. Where it is undersized is for cooling which up until a couple of years ago was a non-issue in our cooler maritime climate.

As are most older traditional heat pump systems in our area, or worse where the coils are needed for more than 75% of the weather. The older heat pump tech just didn't do the job when it got cold so you didn't have a furnace unless you had frequently used resistance coils along with your heat pump. These days it's looking very easy to "optimize" the system for 100% of our weather since the efficient operating window is huge in comparison. It's still extremely cheap and easy to install backup resistance coils inside a central heat pump system and I think it's worth doing even if your heat pump is capable of 100% of the heating because those coils become a second furnace. High operating cost but extremely cheap to install as a backup/emergency heat source instead of part of normal operations.

I have to be careful to not compare minisplits to traditional split systems too much. The technology from minis has only recently arrived inside the central heat pumps. This thread was specifically not about minisplits.

I'm off to climb onto the roof and reseal my storm collar. The last roofer apparently didn't think silicone was the right stuff.
 
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I wouldn’t say I’m behind the curve, rather looking at what the average system that will be installed in the next 2 years will look like. I agree there are decent cold weather units available now. But they won’t be marked south of Washington DC. There are lots of natural gas furnaces that may be changed out for a heat pump in that region.

The new cold weather tech is great but still expensive. A large pot of consumers will just buy the lowest price option available and it won’t be the new technology. I don’t have numbers but I’m guessing close to or under 50% of the whole house heat pumps installs will variable speed compressor tech. So i stand by my statement that heatpumps should have backup heat even if it’s resistive strips.

Have the efficiency requirements for the IRA been released yet? Last I heard they were going to come out soon but we’re going to redo the tiered rating system so more ( less efficient) units would qualify.

Ofc heat pumps come with resistive strips... even 'cold weather' heat pumps in the future will have those, they will just get called a lot less often.

I was responding to your statement that switching the heat pumps will require an adjustment to lower comfort levels. The cold weather tech that boost low outdoor temp BTUs boosts temps from the registers as well.

South of the Mason-Dixon line heat pumps are a very common source of heating, on a par with natgas, IIRC. If people want to save money and put in a cheapo system and then be uncomfortable while spending more money very year, then so be it. But that is not a technology problem.

And you seem to think that it will take a loooong time for the new tech to roll out into cheap heat pumps. The right govt incentives will take care of that, as they have with other tech, when it became possible to achieve lower TCO.
 
I want the resistance coils in the air handler not only for extreme weather but also as a backup heat source in case of a compressor failure.
 
A couple observations. Well three. or four.

1. I am a statistical outlier.

2. Local I am paying 21 cents per kwh on the last bill I can lay my hands on, I just paid $4.68 per gallon for #1 boiler fuel and bootleg green spruce, as unseasoned splits, is currently on local CL at $300/cord.

Ass/u/me-ing the bootleggers are delivering full cords, $1 in electricity delivers 16.2k BTU to my home, $1 in boiler fuel delivers 29.5k BTU to my home, and $1 in green cordwood delivers 60k BTU to my driveway. FWIW it is currently 'illegal' to retail green cordwood in my area, retail cordwood must be certified at or under 20% MC and sold by a licensed reseller, with MC of the delivered cordwood specified on the sales receipt.

3. Having a heat pump that can deliver efficiency of 200% makes it (to me) about the same price to operate as running #1 oil through my existing boiler. The omniscient EPA has suggested I should burn ultra low sulfur diesel in my boiler next winter, I haven't looked up the price of that idea yet.

I get that my local economics (and air quality) are atypical for most of the country. I am glad to see the heat pump engineers pushing the performance envelope. For me to seriously consider a heatpump to handle even a portion of my climate control needs, I need a unit that doesn't have to be brought indoors in deep winter to prevent freeze up or related damage.

4. Envelope is still trump. It doesn't matter what source you are using for heat, if you have air leaks or inadequate blanket you are burning money. I am burning money. The rafters on my home pass withing 4 inches of my ceiling. Though I have 40" of blown cellulose in the middle of my attic, I only have 4" of insulation at the corner where the wall meets the ceiling.
 
A couple observations. Well three. or four.

1. I am a statistical outlier.

2. Local I am paying 21 cents per kwh on the last bill I can lay my hands on, I just paid $4.68 per gallon for #1 boiler fuel and bootleg green spruce, as unseasoned splits, is currently on local CL at $300/cord.

Ass/u/me-ing the bootleggers are delivering full cords, $1 in electricity delivers 16.2k BTU to my home, $1 in boiler fuel delivers 29.5k BTU to my home, and $1 in green cordwood delivers 60k BTU to my driveway. FWIW it is currently 'illegal' to retail green cordwood in my area, retail cordwood must be certified at or under 20% MC and sold by a licensed reseller, with MC of the delivered cordwood specified on the sales receipt.

3. Having a heat pump that can deliver efficiency of 200% makes it (to me) about the same price to operate as running #1 oil through my existing boiler. The omniscient EPA has suggested I should burn ultra low sulfur diesel in my boiler next winter, I haven't looked up the price of that idea yet.

I get that my local economics (and air quality) are atypical for most of the country. I am glad to see the heat pump engineers pushing the performance envelope. For me to seriously consider a heatpump to handle even a portion of my climate control needs, I need a unit that doesn't have to be brought indoors in deep winter to prevent freeze up or related damage.

4. Envelope is still trump. It doesn't matter what source you are using for heat, if you have air leaks or inadequate blanket you are burning money. I am burning money. The rafters on my home pass withing 4 inches of my ceiling. Though I have 40" of blown cellulose in the middle of my attic, I only have 4" of insulation at the corner where the wall meets the ceiling.

You're numbers seem sensible... Did you apply a nominal efficiency factor the boiler and woodstove to get BTU output? For oil, I would use 75-80%, not AFUE.

Also, the COP (or eff/100%) of the ASHP depends strongly on the outdoor temp. It is about 4+ when the outdoor temp is >40°F, making it cheaper than woodburning in your case. There is a step in COP around 30-35°F, bc the unit starts to defrost. Under low outdoor dewpoint conditions, this is not so severe, but under wet outdoor conditions, frosting pulls the COP down to 2.0 or so.

Here is one table, for an inverter drive ASHP with good low temp performance (Carrier Infinity):

The largest (and best tech) 5 ton unit has a BTU/h output chart on page 12, and a table on page 30. You can compute the COP from the BTU output and kW input, they were not kind enough to tabulate it.

For example, crunching some numbers... at 70°F indoor, and 7°F outdoor, the delivery is 33.65 kBTU/h and 4.93 kW total system power. This works out to be 33.65/(4.93*3.412) = 2.00, or as you estimated Eff = 200%.

This does NOT include defrost losses. Under dry conditions (no frost formation) the COP will likely be close to this. Under very wet/condensing conditions, they could be 20% worse.

Ofc, what you want is to know the seasonal average COP, or SCOP. This requires the integration (Monte Carlo) of COP with your outdoor temps and dewpoints. A non-trivial calculation. My SCOP is about 2.2 (from seasonal billing data) with an old tech system. The infinity would be closer to 3 in my climate.

What is the typical minimum outdoor temp encountered at your location? Or better, what temp do you typically spend less than 50 hours or so below per season? What is a typical low temp in January? Your SCOP will likely be a bit better than the tabulated COP at that last (average January low) temp. This ofc assumes that your backup strip usage is minimal.

---------------

There is no need to 'bring in' the outdoor unit. It is built to be outside, and fully capable of defrosting itself automagically as needed (using many kWh you pay for). The one concern is to avoid it being buried in snow (suffocating it). Thus, you should mount it higher than your maximum snow line, and someplace that snow sliding off a roof won't bury it. This often requires that it be mounted high on a wall, ideally under an eave, or a small rooflet for this purpose. Because vibration can then be coupled to the structure (vs a ground mount) some care can be made with vibration isolation and locating the unit away from bedrooms.

In my climate, my condenser is ground mounted on a earthen berm and plastic 'board' that is 6" higher than mean ground level with 8" plastic legs to keep it out of any snow (we seldom get more than 14" of snow). I also have 1" sorbothane pads between the condenser and all four legs to damp vibration, and a pile of stones on the plastic board to prevent it from acting as a sounding board. With this arrangement, the unit is reasonably quiet, just making a bit of a whoosh and whistling noise when the valving flips to switch it into defrost, once every run hour.
 
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A couple observations. Well three. or four.

1. I am a statistical outlier.

2. Local I am paying 21 cents per kwh on the last bill I can lay my hands on, I just paid $4.68 per gallon for #1 boiler fuel and bootleg green spruce, as unseasoned splits, is currently on local CL at $300/cord.

Ass/u/me-ing the bootleggers are delivering full cords, $1 in electricity delivers 16.2k BTU to my home, $1 in boiler fuel delivers 29.5k BTU to my home, and $1 in green cordwood delivers 60k BTU to my driveway. FWIW it is currently 'illegal' to retail green cordwood in my area, retail cordwood must be certified at or under 20% MC and sold by a licensed reseller, with MC of the delivered cordwood specified on the sales receipt.

3. Having a heat pump that can deliver efficiency of 200% makes it (to me) about the same price to operate as running #1 oil through my existing boiler. The omniscient EPA has suggested I should burn ultra low sulfur diesel in my boiler next winter, I haven't looked up the price of that idea yet.

I get that my local economics (and air quality) are atypical for most of the country. I am glad to see the heat pump engineers pushing the performance envelope. For me to seriously consider a heatpump to handle even a portion of my climate control needs, I need a unit that doesn't have to be brought indoors in deep winter to prevent freeze up or related damage.

4. Envelope is still trump. It doesn't matter what source you are using for heat, if you have air leaks or inadequate blanket you are burning money. I am burning money. The rafters on my home pass withing 4 inches of my ceiling. Though I have 40" of blown cellulose in the middle of my attic, I only have 4" of insulation at the corner where the wall meets the ceiling.

I also fit into that category.

$1 of electricity gets me 12,209 btu
$1 of natural gas 100,000 btu
$1 of wood pellets 51.327 btu

I looked an ASHP when I installed central AC in 2021. I didn't have to look very hard, financially it's a dumb investment here.
 
I also fit into that category.

$1 of electricity gets me 12,209 btu
$1 of natural gas 100,000 btu
$1 of wood pellets 51.327 btu

I looked an ASHP when I installed central AC in 2021. I didn't have to look very hard, financially it's a dumb investment here.
Have your gas prices dropped like they have down here??

Edit…

Did a quick look at average electricity price predictions. Looks like they might see a slight increase next year or two then hold flat for a decade then drop by a bit by 2040. At any rate there does not seem to be much predicted change. In the nation averages
 
You're numbers seem sensible... Did you apply a nominal efficiency factor the boiler and woodstove to get BTU output? For oil, I would use 75-80%, not AFUE.

Also, the COP (or eff/100%) of the ASHP depends strongly on the outdoor temp. It is about 4+ when the outdoor temp is >40°F, making it cheaper than woodburning in your case. There is a step in COP around 30-35°F, bc the unit starts to defrost. Under low outdoor dewpoint conditions, this is not so severe, but under wet outdoor conditions, frosting pulls the COP down to 2.0 or so.

Here is one table, for an inverter drive ASHP with good low temp performance (Carrier Infinity):

The largest (and best tech) 5 ton unit has a BTU/h output chart on page 12, and a table on page 30. You can compute the COP from the BTU output and kW input, they were not kind enough to tabulate it.

For example, crunching some numbers... at 70°F indoor, and 7°F outdoor, the delivery is 33.65 kBTU/h and 4.93 kW total system power. This works out to be 33.65/(4.93*3.412) = 2.00, or as you estimated Eff = 200%.

This does NOT include defrost losses. Under dry conditions (no frost formation) the COP will likely be close to this. Under very wet/condensing conditions, they could be 20% worse.

Ofc, what you want is to know the seasonal average COP, or SCOP. This requires the integration (Monte Carlo) of COP with your outdoor temps and dewpoints. A non-trivial calculation. My SCOP is about 2.2 (from seasonal billing data) with an old tech system. The infinity would be closer to 3 in my climate.

What is the typical minimum outdoor temp encountered at your location? Or better, what temp do you typically spend less than 50 hours or so below per season? What is a typical low temp in January? Your SCOP will likely be a bit better than the tabulated COP at that last (average January low) temp. This ofc assumes that your backup strip usage is minimal.

---------------

There is no need to 'bring in' the outdoor unit. It is built to be outside, and fully capable of defrosting itself automagically as needed (using many kWh you pay for). The one concern is to avoid it being buried in snow (suffocating it). Thus, you should mount it higher than your maximum snow line, and someplace that snow sliding off a roof won't bury it. This often requires that it be mounted high on a wall, ideally under an eave, or a small rooflet for this purpose. Because vibration can then be coupled to the structure (vs a ground mount) some care can be made with vibration isolation and locating the unit away from bedrooms.

In my climate, my condenser is ground mounted on a earthen berm and plastic 'board' that is 6" higher than mean ground level with 8" plastic legs to keep it out of any snow (we seldom get more than 14" of snow). I also have 1" sorbothane pads between the condenser and all four legs to damp vibration, and a pile of stones on the plastic board to prevent it from acting as a sounding board. With this arrangement, the unit is reasonably quiet, just making a bit of a whoosh and whistling noise when the valving flips to switch it into defrost, once every run hour.
After reading your attached table and the same required tables for my heat pump I believe that the total input kw and total output DOES include defrost cycles. It’s a gross input figure, not net of defrost. Why do you think defrost is not included when the temperature is below zero and defrost will obviously be required? The purpose of these required tables is to disclose expected total performance at each temperature point. The humidity is standardized so that the defrost expectations can be known.
 
After reading your attached table and the same required tables for my heat pump I believe that the total input kw and total output DOES include defrost cycles. It’s a gross input figure, not net of defrost. Why do you think defrost is not included when the temperature is below zero and defrost will obviously be required? The purpose of these required tables is to disclose expected total performance at each temperature point. The humidity is standardized so that the defrost expectations can be known.
The footnote on the table says that defrost losses are not included.

While it would be nice to include them (from a design point of view) the defrost losses vary wildly with the outdoor dew point, precipitation and wind. Maybe some minimum loss is included?

Also, my installer always set up the unit to defrost every 30 run minutes. This was cray-cray. I moved the jumper to defrost every 60 minutes, and cut the defrost losses in half, and reduced the wear on the reversing valve at the same time.