Maybe "super-cold" ASHP will never be a thing ?

Dave Carpentier

My area design temp is -20f.
Im replacing my heating system, and it would have been nice to incorporate ASHP but you pretty much need a full heating system in addition to the ashp due to the current limitations of technology. I cant afford a fancy ccASHP *and* a modcon boiler at the same time.
So then I wondered.. maybe there isnt enough people living in "extreme" cold areas to drive manufacturers to develop further ?

GGross

Manufacturers are actually pushing inverter technology further all the time. LG has rated capacities down to -13f and they will continue to run much lower, they just have not tested the actual capacities at that range.

EDIT: for frame of reference we have design temps between 0f and -10f in my region and while I generally do not advise heat pumps as a sole heat source we have quite a few new constructions that have ASHP as the only source of heating.

Hot_water_fan

Why mess with a modcon for a handful of hours per year? Use a cheaper backup 

fentonc

If it’s only running when it’s below -10, you probably won’t be modulating or condensing very much. 

Jamie Hall

The problem isn't just inverter technology and other electrical tricks. The problem is the properties of the refrigerants, which are not tweakable. To get lower source temperatures, you have to run at a lower pressure -- you can't change the boiling point/pressure relationship. A different refrigerant may have a lower boiling point at a given temperature -- but it probably will also have a lower boiling point at the high pressure (condensing) end of the system for any given pressure (parenthetically, water is one of the best refrigerants around -- except that it is what might be called a high end refrigerant, with a very useful range from about 40 F up to 300 F or so at reasonable pressures -- an unusually wide range).

I expect that a number of people are working on it. I also expect that the total market is small -- your target market is lots of buildings and lots of people -- and even in Canada the big population centres are around -3 F t0 -10 F, except the prairie provinces. In the US there isn't much of a market north of New York City, realistically, so the bottom line is a machine which will go to -10 is going to cover almost all of the market.

Dave Carpentier

Good points on the modcon being used only in the extreme cold. I would still need some kind of gas boiler (likely propane), as the insurance companies seem to be preferring that we not use oil.
Electric grid heat would be a $ upgrade. The electric co tends to bill for transformer upgrades, plus I'd have to swap out my drop and panel (we have 125a service currently).
Govt grants wont help either, as they're all "replace with" ASHP and not "add to" so I couldnt just integrate an ashp into my existing system.

jumper

Hot_water_fan said:

Why mess with a modcon for a handful of hours per year? Use a cheaper backup 

Thinking along those lines I'm surprised that nobody seems to be talking about thermal storage.
Long long ago there were electric thermal storage heaters. Many places still have excess electricity during certain hours.
Another idea nobody ever talks about is dual source heat pumps. Air most of the time and geo or water for those cold days.

GroundUp

Are you running a hydronic system and are talking about an A2W system? A typical ASHP can be added to almost any standard ducted forced air system at only a small markup compared to a regular central heat/air system, in which case the gas or electric furnace automatically takes up the demand when outdoor temp drops below X. This is very typical in MN, possibly the coldest climate in the US.

If you're referring to an A2W system for hydronic heat, most are offered with electric resistance backup for these few days where the ASHP can not perform above 100% efficiency. While those days will often cost more than burning gas, the couple bucks extra per day saved with a mod/con would take an eternity to recover in most cases. Given the small customer base, I don't think anybody is actively rushing to develop a hybrid A2W HP system with gas backup. I also don't think they'll get much further than they already are with low temp ASHP, without developing a different refrigerant.

Hot_water_fan

Another idea nobody ever talks about is dual source heat pumps. Air most of the time and geo or water for those cold days. 

You run into the same heating degree day distribution problem - few days are beyond the capabilities of air source, so spending $$$ for a handful of days makes less sense than better insulation, storage, solar, hybrid backup, etc. Using a water source heat pump with ice would be interesting to me, but probably not economic at all. 

JakeCK

Speaking of a2w heat pumps does anyone have any experience with those Arctic heat pumps or has seen one in the wild?

jumper

Hot_water_fan said:

Another idea nobody ever talks about is dual source heat pumps. Air most of the time and geo or water for those cold days. 

You run into the same heating degree day distribution problem - few days are beyond the capabilities of air source, so spending $$$ for a handful of days makes less sense than better insulation, storage, solar, hybrid backup, etc. Using a water source heat pump with ice would be interesting to me, but probably not economic at all. 

A shallow backyard glycol loop is not so expensive but it cannot heat home entire winter. And it may even work better in A/C mode briefly.

Hot_water_fan

A shallow backyard glycol loop is not so expensive but it cannot heat home entire winter. And it may even work better in A/C mode briefly. 

Sounds like a lot of 0s for something to back up an ASHP for a few days 

Dave Carpentier

jumper said:

I'm surprised that nobody seems to be talking about thermal storage. Long long ago there were electric thermal storage heaters. Many places still have excess electricity during certain hours.

I tried a bit of an experiment when I built this place. It's slab on grade, but with a 5ft deep foundation. Just some airfoil under the radiant slab. The idea was to store some heat to bridge over fuel outages and very cold days, and maybe coast a little during spring. It does seem to work, but without building the same place w/o the mechanism, I have no way to know for sure. Had I been thinking better, I would have buried some tubing inside the filled space or at least some temperature sensors.
I guess there's no free lunch though.. extra btu heats the space up in the first place.

DanHolohan

https://cleantechnica.com/2022/06/21/u-s-doe-announces-breakthrough-in-residential-cold-climate-heat-pump-technology/

hot_rod

The technology is already available, efficiencies and capacities drop at extreme conditions so sizing is critical.

Solid_Fuel_Man

I did one new construction home a few years back with 4 ASHP, and good old 1970s electric baseboard. Could not talk the guy out of it. He was dead set of the cheapest (to install) backup possible. 

Here in northern Maine, we have a design temp of -35F

Was a 200A 1ø service, and around 3,000 square feet I think. Never heard one complaint from him. I may ask him about his utility bills next time I see him, just for cost comparison. 

jumper

Solid_Fuel_Man said:

I did one new construction home a few years back with 4 ASHP, and good old 1970s electric baseboard. Could not talk the guy out of it. He was dead set of the cheapest (to install) backup possible. 

Here in northern Maine, we have a design temp of -30F. 

Was a 200A 1ø service, and around 3,000 square feet I think. Never heard one complaint from him. I may ask him about his utility bills next time I see him, just for cost comparison. 

A modern Canada2000 house does not need that much heat even with generous windows. Those good old 1970s electric baseboard are not the best form of electric resistance heating in my opinion.

Solid_Fuel_Man

@jumper what is better for electric resistance heat? 

pecmsg

They make freezers that reach -160*C. 
That can make heat pumps. 

All it takes is money. 

ChrisJ

pecmsg said:

They make freezers that reach -160*C. 
That can make heat pumps. 

All it takes is money. 

I've heard rumor that the minisplits do not seem to hold up very long when heating at low temperatures.
I.E. if they see a lot of time in the single digits you can expect a life of 5 years or less.

Is there any truth in that?

GGross

@ChrisJ
Design day is 0f here. We don't have mountains of mini splits sold up here, but so far we haven't done a replacement for any unit under the warranty period (10-12 years depending) It is possible that people are changing them out with online items, but I would think they would at least pursue warranty before doing that. I am sure harsh environments can play a part, but it seems to me that properly sizing, and installing them is most important. I would be perfectly comfortable selling these for heating right up to the rated temp of -13f and they go lower.

Jamie Hall

pecmsg said:

They make freezers that reach -160*C. 
That can make heat pumps. 

All it takes is money. 

As I said up there somewhere, it's a problem of finding the best refrigerant for the desired condensing and evaporating temperatures at reasonably achievable pressures. Then, as you say, just add money... I used to tell my students that if you give an engineer enough money, he can do pretty much anything!

pecmsg

Jamie Hall said:

They make freezers that reach -160*C. 
That can make heat pumps. 

All it takes is money. 

As I said up there somewhere, it's a problem of finding the best refrigerant for the desired condensing and evaporating temperatures at reasonably achievable pressures. Then, as you say, just add money... I used to tell my students that if you give an engineer enough money, he can do pretty much anything!

Then we get to make it work! 

archibald tuttle

DanHolohan said:

https://cleantechnica.com/2022/06/21/u-s-doe-announces-breakthrough-in-residential-cold-climate-heat-pump-technology/

and @hot_rod

that announcement is really low on specifics. I'm not saying it isn't possible that they have technically accomplished this. they love to play PR and never delve into the difficulties presented. repeatability in the field over service life could be achilles heal. fine they are off to test it.

I tend to think that the competing parameters are problematic. what's more important the global warming potential of refrigerants or their efficiency? The toxicity and flammability of refrigerants or their performance.

Obsessing about stand alone with air source heat pumps in canada or canadian weather, e.g. @Solid_Fuel_Man 's climes, seems is really only useful to the extent what we are actually doing is better centering the technology on the majority of applications. And not unironically, climate zone 5 has its derating problems with defrosting.

so what i'm wondering is why the HC push stalled. seems like signifcant efficency, lower charges and way more practical working pressures balanced admittedly against flammability (and the 0 ODP and 20 GWP satisfies the bureaucrats to the extent that you get an exception for refrigerant release albeit accidental contained leak is the flammability worry, but still have to laugh that we pushed out R-22 with .034 ODP and 1700 GWP for R410A with 0 ODP and 3000 GWP, not to mention inferred and empirical loss of efficiency and equipment life across the range of technologies from lower critical temperature and higher working pressures. maybe i should forget about HC and start a campaign to go back to R22).

With the dual bureaucratic imperatives of ODP and GWP blindly applied (and the great bureaucratic love for never having a refrigerant that doesn't require licensing) we are fighting this war, such as it is, with both hands tied behind our back. come back here and i'll bite your kneecap off . . . just sayin.

So we see small charge appliances flourish in Europe. Small penetration in the MVAC world where close monitoring revealed HC air conditioning is not one more way to turn cars into bombs.

Of course split systems would have higher charges and the more complexities and connections the more likelihood of problems, albeit at pressures we're much more used to stemming such tides. Or, how about building the heat pump equivalent of self contained HC chillers and we focus our technological hunt for a practical heat transfer fluid. Just blue sky over here. Maybe yawl see more promise in other approaches.

the other thing we really need to work on, maybe or maybe not short of a secondary vapor cycle, to allow partial contribution to heating during conditions that degrade the ability to fully condition the building through typical heat pumping. As soon as you warm the space with any secondary contribution this creates a circumstance where ambient is higher than condensing temps and can't take even the degraded extent of heat being produced.

It also seems to me residing in seasidish climate zone 5 that intelligent defrost control is a critical area that has only been marginally advanced on typical modest sized residential systems under 6 tons. and reps don't seem to have a really good grasp of how currents systems are controlled or what the future holds in this arena, nevermind attention to location to take advantage of 'solar defrost' and protections against precipitation, i.e. 100% humidity! much as I detest digital control in simple appliances, refrigerators began using digitally cued counts of door openings as a better surrogate for defrosting than the old fashioned analog timer. (these days, it seems like it would be pretty damn easy to add a humidity sensor as well to that algorithm, but we don't seem to see this problem and analogous sensing receiving the kind of attention in residential heat pumps that use far more energy than refrigerators.

Oh, I forgot, its heat pumps uber alles, just like it was modcon boilers uber alles a couple years back, regardless of whether emitters gave you condensing conditions with any regularity.

hot_rod

Solid_Fuel_Man said:

@jumper what is better for electric resistance heat? 

If I had to go electric resistance my choice would be panel rads. I like the feel of the heat from panel radiators better than baseboards. the radiant effect.

Dave Carpentier

hot_rod said:

If I had to go electric resistance my choice would be panel rads. I like the feel of the heat from panel radiators better than baseboards. the radiant effect.

Really ? Not electrically heater water into hydronic flooring ?

jumper

hot_rod said:

Solid_Fuel_Man said:

@jumper what is better for electric resistance heat? 

If I had to go electric resistance my choice would be panel rads. I like the feel of the heat from panel radiators better than baseboards. the radiant effect.

I as well. More comfortable at lower air temperature.

jumper

Dave Carpentier said:

hot_rod said:

If I had to go electric resistance my choice would be panel rads. I like the feel of the heat from panel radiators better than baseboards. the radiant effect.

Really ? Not electrically heater water into hydronic flooring ?

No. Too expensive. And the essergy/entergy people disapprove of using high grade energy to make low temperatures. OTH if you have a generous time-of-day rate or pay mainly for demand then hydronic makes opportunity to store heat.

hot_rod

Radiant floors, always??

It depends a bit on the building and heat loads. Modern well insulated homes will have heat loads in the single digits. As such you will never have warm floors.

75° floor temperature would give you 10 btu/ sq ft in a 70° space. (2 btu/sq.' for every degree difference). But 75 floor surface would not feel warm against 82° or so skin temperature. So the panels would be more comfortable. The space would be warm but the floor would feel cool.

Panel radiators with TRVs come close to the perfect heat emitter, hydronically speaking. Easy to zone with proportional, non electric valves. Easy to setback, fast ramp up. Hundreds of sizes, colors and styles.
With ODR and TRVs you get constant circulation.


Definitely radiant floor in baths and kitchen tile. Shower walls also.

Dave Carpentier

I dont think I would describe my radiant floor (tile and laminate on slab) as "warm", but I suspect the floor would feel much colder if I was using rads/panels instead. I was actually kind of let down a bit during the first winter after we built. Where's the warm floors, I thought.

Shower walls eh ? We're going to rip out our old tub in the upper bathroom and put in a stall soon. You have planted a seed now lol. Something like a zone on a timer perhaps ? (the room has forced air for normal heating)

hot_rod

To feel heat out of a radiant surface it needs to be warmer than skin temperature, your hand or barefoot, somewhere around 82F is the number often used.

To transfer heat energy, the surface needs to be warmer than ambient and the objects in the room. The wider that differential the greater the heat exchange.

I'll make a radiant surface out of anything that doesn't move, or move much.

I've done walls, ceilings, floors, desktops, concrete counter tops, concrete dogs, anything I can get tube in or under.

You can get higher output from a wall or ceiling radiant, as you don't typically walk on them, 90F or warmer. So radiant ceilings or walls could be 30- 35 btu/ sq, ft or more.

Walls get you the highest output, ceilings tend to stratify a bit and that lowers output.

JakeCK

I legit just LOL'd when I seen the concrete dog. 

Beagle right?

Dave Carpentier

JakeCK said:

I legit just LOL'd when I seen the concrete dog.

Turned Old Roy into a hotdog.

archibald tuttle

conversation is definitely not reserved to a some kind of straight line here, but it's funny that radiant is where this discussion has focused when they got a hard enough time making 100 degrees for a 30 degree split at the indoor minisplit unit vs. 120 to 130 you usually expect from a furnace or other circulating air type system (with setback our fan coil units running all the time generally can range up to 150 during coldest temps.

now with a good exchanger refrigerant to hyrdonic (i.e. costly and possibly needs even higher filtration installs to preserve if plate style) could you get 100 degree water out of heat pump much of the time? @hot_rod seems to say 92 works on radiant (well anything warmer than ambient but you need to get up into the 90s to get much warming of objects if i'm reading right. that coordinates with my experience that you need a fairly vast emitter surface to stay under 100 when it gets cold. now it looks like he makes every surface he can into emitter. i'm kinda down with that in theory but i've spent a lifetime trying to figure out how to get that much emitter economically installed. i mean how many people without serious money to spend are really installing even a minimally radiant approach? And that neverminds that the most practical heat exchange would somehow be to have the emitter in the refrigerant circuit rather than convert to hydronic. but that is going to be complicated by pressures and refrigerant flow and oil problems. i'm sure companies with hydronic equipment are trying like hell to figure out ways to make heat pumps hydronic but that seems a step beyond even these 'future pumps'. or am i too pessimistic?

hot_rod

JakeCK said:

I legit just LOL'd when I seen the concrete dog. 

Beagle right?

Foxhound, about 400 lbs.

GGross

@hot_rod
I've been sitting here all day thinking about the radiant dog, I just can't get over it. I truly hate to be a bother but I just really need details

hot_rod

GGross said:

@hot_rod
I've been sitting here all day thinking about the radiant dog, I just can't get over it. I truly hate to be a bother but I just really need details

A company near me made those concrete lawn ornaments. Bird baths, statues, dogs, all sorts of stuff.
I dropped by one day with am small coil of CSST with the yellow jacket removed. I asked if they could put the tube inside the two piece rubber mold they use to cast the objects.

Tube went up one front leg, wrapped around a rebar "rib cage" down a rear leg. You can see the transition fittings to pex at the base.
It was great for towels and putting clothes on to warm for cold mornings.

My mother in law did the dog paint job. He didn't quite make the last move several legs broke where the tube was and could no longer support the 400 lbs of concrete.

I made a radiant statue and sent it back east to one of the wallies also.

I'm itching to build another, maybe a pony or elephant this time

JakeCK

The Predator would be truly confused by this concrete hotdog. Lol

archibald tuttle

@Hotrod so, what you are saying is: "that dog won't hunt, but it will heat"

ChrisJ

it's looking like a 3 dog night............

Dave Carpentier

archibald tuttle said:

conversation is definitely not reserved to a some kind of straight line here

Threads wouldn't make a very good training tool sometimes, but gems do pop in.

.. you need to get up into the 90s to get much warming of objects if i'm reading right.

Everything above ambient will be bleeding btu into the structure, generally afaik the closer to ambient it is, the slower the bleed. Preventing heat loss thru insulation and sealing reduces the velocity of ambient loss due to winter, so the amount of btu required to make up for it is reduced. At some point, even "warm" feeling floors via hydronic will have to be a thing of novelty.

.. i've spent a lifetime trying to figure out how to get that much emitter economically installed. i mean how many people without serious money to spend are really installing even a minimally radiant approach?

When I was building, a pipefitter buddy convinced me that he/we should do hydronics. I had no quote or idea of the end cost, I just kept grabbing the supply house invoices from him and sendings the bank's money over. Death by 1000 cuts kinda thing. I absolutely love it, but had I known the cost I probably would have gone simple forced air. Most people I know that built new houses just went with run of the mill forced air. Im not sure how much of that is due to lack of knowledge about it, and how much is rejection of the cost. Its not very widely known about in the general public, I think. For the most part, mainstream thinking is decades behind current tech. (is that because people prefer to read FB instead of Popular Science etc ? )