Cold Climate Heat Pumps being developed

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peakbagger

Minister of Fire
Hearth Supporter
Jul 11, 2008
8,977
Northern NH

Despite various manufactures claims, existing cold climate heat pumps just do not perform well at lower temps. The industry knows it and the DOE knows it. Sounds like they are finallly starting to get their hands around the problem. I read somewhere that with the phase out of the current refrigerants that the new propane based refrigerant has a lower working range.

With the new incentives kicking in for heat pumps (currently scheduled for late spring in NH), I will be looking at upgrading my units but sounds like I may be better off giving it a year.
 
Yes, I read that yesterday. It's good to see some additional manufacturers coming on board. I'm watching this closely too and may hold off for another year in upgrading our system if the tech makes a large difference. If not, or if the cost is too high then we may go with existing tech. In our climate zone we will never see these extreme temperatures. I think the coldest it has been in the past 30 yrs has been around 15º.
 
I need to factor in my income in the mix, now that I am retired, my taxable income is low for a few years so I can grab the best incentives ;)
 
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Yes, I read that yesterday. It's good to see some additional manufacturers coming on board. I'm watching this closely too and may hold off for another year in upgrading our system if the tech makes a large difference. If not, or if the cost is too high then we may go with existing tech. In our climate zone we will never see these extreme temperatures. I think the coldest it has been in the past 30 yrs has been around 15º.
Last year my weather station showed overnight low temps here below 10 dF for a week or so. It was a unusually cold winter.
 
Yes, I read that yesterday. It's good to see some additional manufacturers coming on board. I'm watching this closely too and may hold off for another year in upgrading our system if the tech makes a large difference. If not, or if the cost is too high then we may go with existing tech. In our climate zone we will never see these extreme temperatures. I think the coldest it has been in the past 30 yrs has been around 15º.

Yeah, it’s not really your climate zone but your specific near waterfront location. I should be in your same zone but we’ve seen 4 degrees and blowing.

Glad to see progress in cold weather heat pump tech. Now if they would just spend more effort on air to water.
 
We installed a new heat pump combo unit before last winter. Needed a unit and tax incentives/rebates didn't play into my purchase. Our unit has natural gas as the auxiliary heat, works great for us and last Christmas it was below zero, heat pump switches over below freezing.
 
Ours switches over to resistance heating at 25º, but by then it is running continually with defrost cycling. The next system will have full output at 17ºF.
 
I had a York heat pump installed in October of 2023 that states in the manual that "The unit provides compressor heat down to an outdoor ambient temperature of -5 degrees F." So far it's operated just fine and we've hit single digits a handful of times. My electric bill has increased significantly versus running an oil boiler, but I'm still pleased with the installation.

Like others, I constantly want to wait "one more year" to do major projects hoping the technology and efficiencies will further improve but in this case I think the differences over one year are negligible.

The total cost for the heat pump, upgraded ductwork in the attic, and a new air handler was 15k. That was a lot, but I never have to fill my 1000 gallon oil tank again and it does qualify for the $2000 tax credit.
 
I had a York heat pump installed in October of 2023 that states in the manual that "The unit provides compressor heat down to an outdoor ambient temperature of -5 degrees F." So far it's operated just fine and we've hit single digits a handful of times. My electric bill has increased significantly versus running an oil boiler, but I'm still pleased with the installation.

Like others, I constantly want to wait "one more year" to do major projects hoping the technology and efficiencies will further improve but in this case I think the differences over one year are negligible.

The total cost for the heat pump, upgraded ductwork in the attic, and a new air handler was 15k. That was a lot, but I never have to fill my 1000 gallon oil tank again and it does qualify for the $2000 tax credit.
Sounds great. Does the heatpump system have backup resistance heaters or is this on the heat pump alone?
 
Sounds great. Does the heatpump system have backup resistance heaters or is this on the heat pump alone?
There's probably some clever back and forth going on in order to satisfy the thermostat in those temperatures but it does say "compressor heat down to....." so I think that means just the heat pump. It has a 10kW auxiliary resistance element which was installed as an accessory to the air handler but I can't say for certain exactly how everything interacts.
 
There's probably some clever back and forth going on in order to satisfy the thermostat in those temperatures but it does say "compressor heat down to....." so I think that means just the heat pump. It has a 10kW auxiliary resistance element which was installed as an accessory to the air handler but I can't say for certain exactly how everything interacts.

I disagree that it means that.

With a variable speed compressor it is really hard to tell what is going on. With my (old) single speed, I can just listen to it cycle on and off, and know that it starts to run 100% around 21-22°F. Below that the compressor continues to run 100%, but the aux strips cycle. I have the compressor set to keep running down to 0°F (which I see for an hour or two every few years), but down there it is only providing a fraction of my BTUs

My guess is that your system is calling backup strips at some temperature well above -5°F. You either need to get info from your tstat (my ecobee system gives me graphs) or put a monitor on your strips to be sure.

PS: Funny story, when I got this system together back in 2017, the ecobee3 did a funny thing: when it cycled off the strips, it ALSO cycled off the compressor, and then had neither run for a lockout period (of 5 minutes) to protect the compressor. This is really dumb, and was a feature of all smart stats at that time running two-stage, due to the setup of legacy systems. The shutdown ofc just limits the BTUs you can get out of your HP, costing you more energy. The cycling of the HP also wears the startup system, and has a negative comfort effect.

This is ofc contra to the ecobee company's mantra of saving you energy, and I ended up on a webforum with the CEO of ecobee (a much smaller company at that time) and griped about this issue that is costing customers tons of energy (I estimated >500kWh/yr) and comfort, while also being a firmware fix. The guy was responsive, and admitted that it needed to be fixed (to leave the HP at 100% and cycle the strips) while telling me that ALL the smart stats still operated that way.

A couple years later I noticed that the same stat started running the right way... HP 100%, cycling the strips. Updated the firmware wirelessly at some point. :)
 
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I want to know what research is being done to reduce defrost times. My last math said my unit in a defrost consume as much power as it did for the rest of the hour it was cycling on and off. Now it is likely that a good portion of that time is was in first stage consuming 1.8 kw. But during a defrost consumption goes up to 10.2 kw. (Indont know how my 10 kw heaters are wired they may be 8+2 I’m not sure).

One thought I had was would an oversized unit running at lower output result in a higher outdoor coil temp thus reducing the amount of defrost needed?

But at any rate don’t expect any of these new technologies to do much better than cop of 2 at temps below 0F. But I could be wrong.
 
I want to know what research is being done to reduce defrost times. My last math said my unit in a defrost consume as much power as it did for the rest of the hour it was cycling on and off. Now it is likely that a good portion of that time is was in first stage consuming 1.8 kw. But during a defrost consumption goes up to 10.2 kw. (Indont know how my 10 kw heaters are wired they may be 8+2 I’m not sure).

One thought I had was would an oversized unit running at lower output result in a higher outdoor coil temp thus reducing the amount of defrost needed?

But at any rate don’t expect any of these new technologies to do much better than cop of 2 at temps below 0F. But I could be wrong.

I have done a lot of thinking and work on defrost. There are two things... when in reverse cycle (to defrost) the fluid temps and thus pressures are higher, so the compressor load goes up. In many cases, there is also a strip heater that kicks on to prevent 'cold blasts' from the indoor coil.

Keep in mind that the outdoor coil might only run 5-7°F below the outdor air temp. If the outdoor dew point is low enough, zero frost forms, and the unit just does a short defrost cycle on the 'dry' coil to make sure. That is, most units have defrost timers, not frost detectors.

So, your numbers make sense. If that defrost cycle was 2 minutes every 60 run minutes (1/15th) then the total wouldn't be affected much. If it defrosted every 30 minutes, it would be a bigger effect. If the defrost cycle took 5 or 8 minutes, it would be a HUGE effect.

In my case (a single speed Goodman HP from 2013), the defrost runs every 60 compressor run minutes.

1. My installer set that switch to 30 minutes, and I changed it to 60 mins to reduce defrost losses.

2. Keep in mind that most of the time, there is no frost on the coil at all. So the reverse cycle just heats the outdoor coil until its exit fluid temp reaches 40°F (meaning it is not encased in ice) and then resets to normal heating. In my unit that takes about 2-2.5 minutes. So I thermal compounded the defrost stat and wrapped it in foam, which shaved 30-45 seconds off the dry cycle time (removing the delay from poor thermal contact). This saves MORE defrost energy.

3. Third thing is that I discovered that the 'cold blast' from my registers takes 2-3 minutes to arrive after the unit enters defrost. So I spliced a 2 minute delay timer on the wire that calls the strip heat on defrost. So on a 'dry cycle' that takes 90 seconds, no strip is called. But in frosty/icy weather when the coil can take 5 minutes to defrost, the strip IS called (for the last 3 minutes), and I still don't get an ice blast.

No problem in 10 years running with the above mods.

I reckoned that changes 2-3 boosted my SCOP from 1.9 to 2.2 or so, if I recall correctly. And netted me ~1500 kWh per season and about $250.

As installed, the unit might've been SCOP around 1.6 to 1.7? And probably would've cost me an extra $500/season.

Many installers don't care about SCOP, and do care about callbacks (e.g. for comfort). So they set the units up in ways that are inefficient, and if that costs the owner a few thousand dollars per decade more? Not their problem.

This is why **package** systems are great... bc the builder can set them up to work properly, versus a split system installer miswiring things, and setting up the stat wrong.
 
I have done a lot of thinking and work on defrost. There are two things... when in reverse cycle (to defrost) the fluid temps and thus pressures are higher, so the compressor load goes up. In many cases, there is also a strip heater that kicks on to prevent 'cold blasts' from the indoor coil.

Keep in mind that the outdoor coil might only run 5-7°F below the outdor air temp. If the outdoor dew point is low enough, zero frost forms, and the unit just does a short defrost cycle on the 'dry' coil to make sure. That is, most units have defrost timers, not frost detectors.

So, your numbers make sense. If that defrost cycle was 2 minutes every 60 run minutes (1/15th) then the total wouldn't be affected much. If it defrosted every 30 minutes, it would be a bigger effect. If the defrost cycle took 5 or 8 minutes, it would be a HUGE effect.

In my case (a single speed Goodman HP from 2013), the defrost runs every 60 compressor run minutes.

1. My installer set that switch to 30 minutes, and I changed it to 60 mins to reduce defrost losses.

2. Keep in mind that most of the time, there is no frost on the coil at all. So the reverse cycle just heats the outdoor coil until its exit fluid temp reaches 40°F (meaning it is not encased in ice) and then resets to normal heating. In my unit that takes about 2-2.5 minutes. So I thermal compounded the defrost stat and wrapped it in foam, which shaved 30-45 seconds off the dry cycle time (removing the delay from poor thermal contact). This saves MORE defrost energy.

3. Third thing is that I discovered that the 'cold blast' from my registers takes 2-3 minutes to arrive after the unit enters defrost. So I spliced a 2 minute delay timer on the wire that calls the strip heat on defrost. So on a 'dry cycle' that takes 90 seconds, no strip is called. But in frosty/icy weather when the coil can take 5 minutes to defrost, the strip IS called (for the last 3 minutes), and I still don't get an ice blast.

No problem in 10 years running with the above mods.

I reckoned that changes 2-3 boosted my SCOP from 1.9 to 2.2 or so, if I recall correctly. And netted me ~1500 kWh per season and about $250.

As installed, the unit might've been SCOP around 1.6 to 1.7? And probably would've cost me an extra $500/season.

Many installers don't care about SCOP, and do care about callbacks (e.g. for comfort). So they set the units up in ways that are inefficient, and if that costs the owner a few thousand dollars per decade more? Not their problem.

This is why **package** systems are great... bc the builder can set them up to work properly, versus a split system installer miswiring things, and setting up the stat wrong.
Is defrost even used in the efficiency ratings? I’m inclined to say it is not. I caught mine on a defrost cycle when I was quite sure there was no ice on the coil. It was 42 ish outside. I need to figure out what defrost mechanism I have. Not that it matters if I keep burning wood. All systems should be required to have frost sensors.
 
Is defrost even used in the efficiency ratings? I’m inclined to say it is not. I caught mine on a defrost cycle when I was quite sure there was no ice on the coil. It was 42 ish outside. I need to figure out what defrost mechanism I have. Not that it matters if I keep burning wood. All systems should be required to have frost sensors.

Estimated defrost is part of HSPF I think. And demand defrost was tried years ago and rejected as unreliable (if it malfunctions, it kills the unit).

Defrost timers are standard, and operate up to 40°F outside (bc a coil COULD grow frost at 31° dewpoint). Plus or minus because the hardware tstats have a manufacturing variation ±3°F or so.

This leads to LOTS of defrost cycles when there is no frost present, but the idea is that they run a short period and only use a little energy.