The Search For An AC That Doesn't Destroy The Planet

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Heat pumps are just AC's run in reverse. It just takes some relatively minor mechanical and control systems upgrades to make an existing AC to also be a heat pump. My portable air conditioner has the "heat pump" feature and the whole unit costs less than $500 US.

Sure, a huge stand alone heat pump could cost thousands of dollars, but in context of the article, ADDING heat pump functionality to existing AC designs to build new units is relatively inexpensive.

Heat pumps are just AC's run in reverse. It just takes some relatively minor mechanical and control systems upgrades to make an existing AC to also be a heat pump.

Plus capping off the gas line.

Another reason some people don't want a heat pump is that gas is cheaper in many places. California, for example, has this tiered billing system for electric and gas, where you pay a *lot* more for usage above a certain threshold. Electricity and gas have separate tiers. So if you're already using a decent amount of electricity, getting your heat from gas means that most of that cost is billed at the bottom gas tier, whereas electricity to heat your home would be billed at the top electrical tier. So you are penalized for being energy efficient, because by doing everything with electricity, you miss out on the cost savings from the baseline gas price. There are formulas to calculate the breakeven point where a heatpump and gas cost the same amount. It's generally around a COP of about 2-3 or so, and in California's climate, a heatpump can easily get a COP of 5+ when heating.

There are formulas to calculate the breakeven point where a heatpump and gas cost the same amount. It's generally around a COP of about 2-3 or so, and in California's climate, a heatpump can easily get a COP of 5+ when heating.

I don't have my bill handy to verify the gas prices, but the average cost of natural gas in PG&E territory is about $2.40 per therm. Last I checked, every extra kWh I add will be billed at 38 cents per kWh. So heat pumps would be expected to cost about two-thirds more [apogee.net] than burning gas.

Like I said, the extortionate electrical rates make heat pumps infeasible.

In the southern US, where "air conditioner" is synonymous with "whole house air conditioning system" a standard 3-ton unit (enough to cool around 1,500 square feet) costs about $6,000, assuming your house already has ducts in place. So while the author was lazy in their description, for many, it's not wrong. It's also not relevant, since current units cost just as much.

A lot of places that use the most AC ahave ground that is almost all rock under the thin dirt layer.

It's why you don't see many basements in Texas.

That's not true. I live in Houston, where basements are quite rare. You will hit the water table long before you hit bedrock.

There are two reasons why basements are rare here:

1) Basements are effectively required in northern climes because building codes require foundations to be below the frost line. So, if you are in Minnesota and the foundation already has to be a few feet below grade, you might as well go ahead and dig a few more feet and do a basement stead of 4 feet of crawl space. In South Texas, there is no frost line, so this is not an issue.

2) The water table is high and flooding is an issue. Contrary to popular belief, it is possible to have a basement here (and there are a limited number of homes with them), but keeping the water out is a big problem that is generally not worth the headache.

I live in Houston, where basements are quite rare. You will hit the water table long before you hit bedrock.

Same for here in Virginia Beach -- where the reason for the lack of basements here should be obvious from just the name. :-)

Guess I am assuming San Antonio is all of Texas :)

I wish we had that much water here

Depends on which side of Texas you are talking about.

There are parts of Texas that have rocky soil, but the part that is "not true" is that as an explanation for why basements are rare here. The point is that basements are similarly rare even in places that don't have rocky soil.

Not really. The frost line issue is the case throughout the sate (and throughout the South). Digging is expensive (more so than building up). Builders won't do it unless it is effectively required.

This whole plan of building big cities in low lying areas is going to turn out to be a big problem everywhere it has been done... not just in Texas, but there too.

Well, then all we have to do ship a few billion pounds of earth to places like Texas or Florida so we can raise the height above sea level. Plus it has the added advantage that global warming can melt as many glaciers as it wants and both states will still be above sea level!

Sitting in my basement in MA and it is currently 79 degrees in here with 62% relative humidity, not exactly comfy considering it is only 81 outside now, and was down to 68 last night. It's nice up until mid July until the ground heats up and then it starts to get warmer and retaining. Plus water heaters and often washer/dryers are often in the basement and they generate waste heat which gets trapped unless you have good ventilation. And god help you if you need to run a dehumidifier.

It's plenty inexpensive to partially trench, then berm. You'll get a big portion of the benefits. If you insulate well and install rooftop solar, you can save a bundle on energy loss from the roof (and not having to cool as much due to reduced insolation.)

That works in the northern US, but not in the south, where daytime temperatures often reach 100 degrees, and many nights never goes below 80. Even an underground house would be uncomfortably hot.

Depends on how deep you go. Underground caverns remain a constant cool temperature regardless of how hot it gets above ground. But yes, a house only partially under ground wouldn't stay comfortably cool.

Normal HVAC unit fan motor: $100. Decent chance it will last the life of the unit. High efficiency unit fan motor >$1,200. Variable speed motor. Decent chance it will have to be replaced before the unit dies.

These Daikin and Carrier commercial high efficiency units are an ideal product to sell. They carry a large price premium. The compressor and coils have 5-10 year warranties. Everything else is 1 year. 2-3 years into ownership, VFD drives, fancy circuit boards and sensors start failing. The profits on the replacement parts is huge. Plus, Daikin and Carrier design everything to be proprietary to their units. You can't buy a cheap generic motor to get you back up. You're locked in.

High efficiency unit fan motor >$1,200. Variable speed motor. Decent chance it will have to be replaced before the unit dies.

The variable-speed DC motor in my Trane air handler, installed in 2005, lasted 12 years, was $1,600 (parts+labor) to replace in 2017.

I got a quote for a AC fan motor on an 18 year old unit, and it was $2500 parts+labor. We ended up not fixing the old AC unit and selling the house without AC.

I was with the tech as he replaced the motor and I could probably do the actual work myself -- unplug/unbolt things, swap the fan onto the new motor, re-bolt/re-plug things -- but having them do it comes with testing the entire unit and a 1-year warranty on their labor (in addition to the inherent parts warranty), etc... The bulk cost was for the motor itself (probably the electronics) anyway. I have a maintenance contract, which includes 2 annual cleanings/checkups (fall and spring) as well as parts/labo

I assumed the two quotes were mostly high bids for people who didn't want to do the work. Seems like most places want to install new systems,and possibly pressure test duct work and insist on new work to seal them up or whatever. Just a new unit might have been fine, but I doubt I would have gotten out with just that.

Daikin has been selling them to consumers in Japan for a while now, with 10 year warranties on everything.

Note: I said "commercial high efficiency units"

Yeah. They sell the high efficiency units to consumers in Japan.

Our AC's blow hot air, not cold air.

Both companies created ACs with higher internal performance that used less environmentally damaging refrigerants; the new units could reduce their impact on the climate by five times.

Refrigerants only impact the environment if (when) they escape into the atmosphere. If they can keep that from happening, it shouldn't matter what refrigerant is used.

It's a virtual certainty that some percentage of refrigerant in use will eventually leak to atmosphere, despite all attempts otherwise. Some fraction of units will have poorly installed lines, or the lines will rust, or an evaporator core will crack from heat cycling, or something will impact them.

Not to mention how many unscrupulous technicians end up not following the law and just venting to atmosphere or I can imagine how much leaks by people buying those cans at the auto parts store and not using it right or just continually filling a leaky system rather than getting it fixed. Impossibl problem to solve unfortunately.

Granted, of course. Good points about practical vs. ideal situations.

This article is terrible. It leaves facts and logic behind due to criminally atrocious editing, or the willful agenda pushing on clueless idiots.

Heat pumps are reversible air conditioners. In the summer they cool the inside air In the winter, they cool the outside air. Zero environmental difference either way. ZERO!

A heat pump replacing an oil burning furnace does possibly provide greater efficiency than individual furnaces. But, the heat pump is ineffective in near freezing conditions or below, so they are

But, the heat pump is ineffective in near freezing conditions or below, so they are completely unfit for purpose in many(most?) environments.

That's no longer true. Heat pumps become more inefficient than just burning fuel at around -20C.

Citation needed. Residential heat pump coils freeze up at 0C.

https://youtu.be/MFEHFsO-XSI?t... [youtu.be] - he has a full video with references. All the modern heatpumps can go past freezing with no issues whatsoever. I switched to a heatpump last year and it worked at -10C this winter just fine.

Just look online, most units are fine at -4F or -20C

https://hvacdirect.com/aciq-3-... [hvacdirect.com]

They defrost the coils by just running as normal cooling mode every couple hours and melting the ice

https://www.youtube.com/watch?... [youtube.com]

But whats the difference if all of those buildings already have traditional AC systems anyway for cooling? If heat pumps are a bomb than every building in america already has a bomb in it with terrible GWP. We already have methods and protocols to restrict what gets released and it is never perfect but the knowledge and tools already exist, even for flammable. A lot of commercial systems now are using propane as refrigerant, the regulations will slowly catch up for residential.

Just to compare to R32 thou

Tesla vehicles use HFO-1234yf for their heat pump/AC. It has a global warming potential of close to 1. "Small problem" with it is it is moderately flammable. Tesla addresses this by confining its use to a small "inner heat pump loop" in a fully contained device, which then transfers heat to/from conventional radiator fluid for use elsewhere in the car (batteries, cabin temperature).

All of the major car makers are moving to 1234yf as R-134a is due to be phased out. R-32 never really made it into automotive applications. It would take a phase out of R-32 to get the building AC market to switch, which I suspect will eventually happen as governments push for even lower impact coolants. That said, I think it's disingenuous to say that heat pumps are a flawed idea for building heating today, mainly because so many homes already have air conditioning. So that "delayed-fuse climate bomb" is

Einstein had a patent on a refrigerator with no moving parts, used ammonia and butane. Just required a heat source...

https://en.wikipedia.org/wiki/... [wikipedia.org]

Absorption refrigeration [wikipedia.org]. Closely related: adsorption refrigeration [wikipedia.org]. Both are driven by heat input. Not very efficient unless your heat source is cheap/free. Like industrial waste heat or solar.

A solar powered AC unit would seem to make a lot of sense, since one tends to need cooling when the sun is out.

Every air conditioner sold in most of the world since the 1980s has supported "reverse cycle", i.e. what the article calls a heat pump. North Americans discussing this like it is new technology really unscores just how parochial that continent is.

And the comments that say they don't work in cold climates show equal ignorance. Daikin specifically make models for places like Hokkaido.

hydrocarbons like Propane and isobutan make excelent refrigerants. They transfer heat more efficiently, require less refrigerant, and work at lower compression pressures than CFC and HCFC refrigerants currently used. Also of note is that HC refrigerants are still widely used outside North America and have been for almost a century safely and effectively.

GWP (Global Warming Potential) [wikipedia.org] is a messure of how effective a gas is at retaining heat heat from the sun. The baseline is CO2 at 1.0, everything else is referenced to how much more or less effective the compound is at retaining heat. For example Methane has a GWP of 25, while the HCFC refrigerant R-134a* currently used in most refrigerators and car A/C systems in North America has a GWP of 1430, Propane has a GWP of just 9.4, plus a shorter life once released into the atmosphere, and when mixed with a small amount of Isobutane (GWP 6.5) can be used as a direct drop in replacement for R-134a, no retrofit required.

yes, there are some safety concerns, HC refrigerants are flammable when vented into an enclosed space and an ignition source is present. However, HC refrigerant usually contain an odurant just like household natural gas and any leak of the A/C system can be easialy detected and steps taken to prevent a dangerous situation. And to be fair it should be mentioned that when R-134a is exposed to high temperatures it becomes a toxic and carcinogenic gas. Plus in both cases the lubricating oil also released when an refrigeration system is vented is also highly flammable on it's own when vaporized during the release and mixed with air.

Some references I've got in my bookmark list if your interested; https://en.wikipedia.org/wiki/... [wikipedia.org] https://www.danfoss.com/en/abo... [danfoss.com] http://www.possumliving.com/20... [possumliving.com] http://www.ener-save.biz/Airco... [ener-save.biz] https://redtek.com/12a/ [redtek.com] https://hychill.com.au/ [hychill.com.au]

* R-134a is also known as 1,1,1,2-Tetrafluoroethane, the stuff used in "canned air" dusters that everyone uses. It is illegal in most of the USA to vent R-134a car A/C systems but it is fine to release it into the atmosphere to keep our keyboards clean. The amount of R-134a in you car is about a can and a half of "compressed air".

This doesn't make sense. A heat pump works in the same way as an air conditioner when cooling a home. A heat pump is no more efficient or environmentally friendly for cooling than an AC-only unit. I don't see how that is an option for more efficient or cleaner cooling,

True for cooling, but they provide more efficient heating than fossil-fuel / electric, which a house with an A/C only cooling unit would probably have, so having a heat pump would be better all around. For extreme heating needs, heat pumps (usually) have a secondary source, like electricity or gas. My 17 SEER Trane unit has a 2-stage compressor for heating/cooling and electric strip elements for 3rd-stage heating, but the first 2 stages seem to be able to provide, at least some, heat down into the low teen

In general, it's not the unit itself but the whole heading and cooling system. With an AC only system, you have cooling, but if you need heating, then you have to use some other form - maybe resistive or burning a fossil fuel.

When I had central A/C installed, it was about $3500 for A/C only. That reversing valve must be made of gold and platinum because the heatpump version was $12000.

Yeah that's nuts. Saw a youtube video not that long ago where I guy modified an AC-only condenser unit to add a reversing valve and some other necessary fittings to make it into a true reversible heat pump. Obviously required some existing HVAC skill and knowledge, but certainly not $8500 worth. Seems like this could be an opportunity for some HVAC guys to go in and modify units to be reversible. They could do it for less than the original quote I'm sure.

I think the quote in the summary is just cut off in a weird way. That part of it is probably talking about heating rather than cooling. Heat pumps are far more efficient than resistive heating and don't come with the global warming impact of natural gas. (And yes, an air conditioner is a heat pump)

They are saying you can use a heat pump for your heating needs. They are more efficient than resistive heating, and unlike gas boilers they don't have to run on fossil fuels.

OK in a moderate climate, but completely useless in any area with very hot or very cold temperatures.

Not true, at all anymore. You can easily find units that work down to negative temperatures

Heating: 100% Capacity at -5F and 78% Capacity at -22F* [mrcool.com] Cooling: 100% Capacity at 115F and 78% Capacity at 130F*

Efficient heating from -22F to 75F outdoor temperatures [hvacdirect.com]

OK in a moderate climate, but completely useless in any area with very hot or very cold temperatures. Not true, at all anymore. You can easily find units that work down to negative temperatures Heating: 100% Capacity at -5F and 78% Capacity at -22F* [mrcool.com] Cooling: 100% Capacity at 115F and 78% Capacity at 130F* Efficient heating from -22F to 75F outdoor temperatures [hvacdirect.com]

OK in a moderate climate, but completely useless in any area with very hot or very cold temperatures.

Not true, at all anymore. You can easily find units that work down to negative temperatures

Heating: 100% Capacity at -5F and 78% Capacity at -22F* [mrcool.com] Cooling: 100% Capacity at 115F and 78% Capacity at 130F*

Efficient heating from -22F to 75F outdoor temperatures [hvacdirect.com]

The issue I have with the "push heatpumps everywhere" campaign is the grid simply isn't ready for it, and they represent a significant challenge to the grid in periods where the grid is already unstable. Take that -22F day with the heat pump you list above. It'll work, great. But the unit's efficiency drops, and it's likely making up the difference with (extremely inefficient) resistive heating elements. So the unit's power draw spikes. Additionally at temperatures that cold, in my anecdotal experience, people like to turn up the heat just because it's so hard to feel warm. And even well insulated houses will notice drafty spots when it's that cold. Which translates into even more power draw.

What does that mean for the grid? Well extremely cold polar lows are already the most challenging grid scenario. Solar output is poor that time of year, winds can stall over vast areas, and even fossil units just run into operational issues at those temperatures (crap gets brittle and breaks, coal piles freeze, etc.). And now you've lumped all these heat pumps, which represent a huge variable load, onto that already somewhat brittle electric grid. I'm just not sure it can be sustained.

Heat pumps in California, or the American Southeast, make a lot of sense. Heat pumps in Minnesota and Iowa, or really any of the plains states? They're more efficient on average, but a disaster waiting to happen in the dead of winter.

By it's nature by itself the heatpump isn't using more electricity than it owuld as an air conditioner.

Also if your home has a gas line ran into it chances are you are not going to just cap it off, you would buy a heat pump with a traditional emergency gas furnace, especially in a cold climate.

People with electric only heat are already using resistive heating all the time regardless, heat pumps will help them use less so the only increase in grid capacity comes from people with gas systems moving to heatpum

By it's nature by itself the heatpump isn't using more electricity than it owuld as an air conditioner.

What's deltaT in summer? Typically 10-35 degrees. Winter? More like 40-80 degrees. Not only is more energy required to address a temperature gradient a few times higher during winter than it in summer more energy is required to extract the same unit as energy due to higher volume of high energy molecules from a pool of much lower energy molecules which makes the process for an air source heat pump inherently less efficient in winter than summer.

Where I live it's quite rare. You would have to be insane

Not only is more energy required to address a temperature gradient a few times higher during winter than it in summer more energy is required to extract the same unit as energy due to higher volume of high energy molecules from a pool of much lower energy molecules which makes the process for an air source heat pump inherently less efficient in winter than summer.

"air source heat pump" though. A heat pump does not have to be air source. A lot of the regions where there are the kind of persistent, very low temperatures where air source heat pumps might be problematic also have fairly low population density, which also usually translates to cheaper land and therefore the average person having more of it available, which means potential room for ground-source or - in some cases - water-source heat pumps. Those sources never get too cold unless you maybe live in Antarct

If you replace your AC with a heat pump it's going to be the same grid load.

The primary concern when it comes to heating and cooling is good insulation. Otherwise you'll waste a lot of energy.

The building where I lived in Toronto, a 38 story condo tower, all the units had heat pumps. They worked in conjunction with a water cooling tower on the roof. Even with water pumps, I think that shared workload helped reduce energy consumption. Sometimes old tech is still good tech. Some buildings in the Toronto get their cooling heat exchange from water pipes looped way out into Lake Ontario, down a few hundred feet to the quite cold bottom. But that is sharing a common utility. How socialist.

The one part you're missing is that in large swathes of the country, the heat pump is replacing other resistive heating which is far less efficient. In my old house (western WA) I replaced baseboard with a 4-room Daikin mini-split, and it was fantastic. I gained A/C in the summer, and I replaced my baseboards entirely, dramatically lowering my heating bill in the winter, because heat pumps are FAR more efficient than baseboard.

In my area, a great number of older houses don't have natural gas, so all the h

"But the unit's efficiency drops, and it's likely making up the difference with (extremely inefficient) resistive heating elements."

Actually the way mine works is to cycle on more often when it's colder. It cycles on and off just like a regular furnace. The biggest problem is when the humidity is high, then it ices up and sometimes the defrost cycle doesn't completely defrost it, then it shuts off on an error. I've woken up to a pretty cold house. A quick reset in five minutes it's going again.

I have the baseboard heaters still installed. That thermostat is set to 55 F. If the heat pump trips while I'm away the pipes won't freeze.

That's great until you hit -23F and the unit fails completely.

Do heatpups put out as much heat at once as gas? No shot, nothing beats gas on that metric but thats a math problem. If your system is undersized for your home it doesn't matter what system you have. Heat pumps come in up 5 ton+ and it's easy to add on with mini splits because all you need is an electric circuit.

Even in that scenario running the heat pump longer to get up to temp is more efficent on most days.

Also if you live in a climate that gets to -40C you are going to have emergency heat either ele

Do heatpups put out as much heat at once as gas? No shot, nothing beats gas on that metric but thats a math problem.

No, it's a physics or engineering problem. You can certainly build a heat pump that is as powerful as any arbitrary gas furnace but there are electrical power and space issues. a 5-ton unit is not going to cut it though - you need over 8-tons at low temperatures which probably means well over 10-tons at "normal" temperatures.

If your system is undersized for your home it doesn't matter what system you have.

My point is that getting a heat pump large enough for a house in a cold climate is currently either unfeasible due to space and electrical power needs (air-source) or much more expens

Ground source is great for extreme seasonal temperature swings, but even Fairbanks, AK has only ~250 degree-days under -20F per year. That means ~97% of your heating needs can be accommodated by a heat pump. The remaining 3% you can use something supplemental.

That is only hitting -40 the equivalent of 12 days per year, but it is spread out over ~3 months. I wouldn't want to live there, but it is survivable. Point being that you can reduce your heating oil needs by 90% and even provide cooling during mosquito season with a lower energy cost.

Also -22F is not that cold - here it gets down to below -40C (or -40F - the scales are the same at this point) so it will be under 78% capacity, possibly by a lot more since IIRC the drop-off is non-linear.

Fortunately, due to its inhospitality, Hoth has a permanent population of about 5-6 people (including you apparently). The rebel base is temporary and anyway they use hypermatter fusion reactors for heating so I assume efficiency is less of a concern.

In the contiguous 48, Grand Forks, ND is apparently one of the coldest cities.

https://weatherspark.com/y/835... [weatherspark.com]

The 90%ile winter night time temperature never drops even as low as -30C (around -22F), which according to the parent poster is the point at which their heatpump efficiency drops to a mere 78% of nominal. Given a CoP of 3.5 (a bit of a guess), that's down to 2.7, still 2.7 times better than resistive heating at the 90th percentile for the single coldest month of the year. And that's for one of the coldest cities in the contiguous 48.

In other words the vast majority of the time, such a heat pump would be absolutely fine and provide its rated output or close to, at very much greater efficiency than the alternatives. And you can still use the alternatives for supplementary heating just like now for the rare times when it's colder.

Heat pumps are useless in cold climates in the same way that electric cars are useless because you can't load up your entire house in a trailer then attempt a cannonball run. Maybe for the 0.24% of the population in Alaska or (Tuktoyaktuk if you're Canadian) they might be less useful. But really, for the vast, vast majority of the North Americans, heat pumps are a great idea.

In the contiguous 48, Grand Forks, ND is apparently one of the coldest cities.

It may come as a surprise but not everyone lives in the US. Try looking at Edmonton and Calgary in Alberta. Both are cities of around a million or so and Edmonton does hit -30C at the 90th percentile. Indeed, these data suggests that much of the population of Alberta and probably the BC interior, Saskatchewan and Manitoba. Alberta alone is about 10% of the Canadian population.

Heat pumps are useless in cold climates in the same way that electric cars are useless because you can't load up your entire house in a trailer then attempt a cannonball run.

Somehow despite owning a car I've never really wanted to try a Cannonball run something I suspect I have in common with most of the

Really? You're going for that? Did you actually read my post?

Yes, I did - it's the one where you pick a tiny 50k population city in the US and ignore the literally millions of people living well to the north and the only data you mention from Canada is an even smaller settlement and literally stated that this was problem that only the tiniest fraction of the population would ever encounter. I know it's hard to imagine millions of people living in the great white north but it's not fake news.

Which means, maybe 10% of the time in the single coldest month of the year, the heat pump can only reach 78% efficiency. That's hardly "useless".

Yes, it is useless because what you are conveniently forgetting that an AC

COP below 0F is about 2 in current systems. For -22F it is about 1.

than resistive heating at the 90th percentile for the single coldest month of the year. And that's for one of the coldest cities in the contiguous 48.

Relevant comparison is not between resistive heating and heat pumps it's between gas heating and heat pumps.

In other words the vast majority of the time, such a heat pump would be absolutely fine and provide its rated output or close to, at very much greater efficiency than the alternatives.

If you can find an air sourced heat pump that does 2.7 @ -22F by all means please share the details.

Not true, at all anymore. You can easily find units that work down to negative temperatures Heating: 100% Capacity at -5F and 78% Capacity at -22F*

Not true, at all anymore. You can easily find units that work down to negative temperatures

Heating: 100% Capacity at -5F and 78% Capacity at -22F*

There is always a catch with the low temperature ratings in air source heat pumps you just have to find it. Most often it's simply efficiency goes to crap. The -5F only works in their 2 ton model. It's +17 and +14 for the 3 and 4 ton models.

Some of them have internal schemes like running the compressor in such a way that heat is intentionally generated to make up shortfalls (e.g. "Hyper-Heating") which effectively turns the compressor into a resistive heater. With this technology there are inherent phys

OK in a moderate climate, but completely useless in any area with very hot or very cold temperatures.

Not true, at all anymore. You can easily find units that work down to negative temperatures

Heating: 100% Capacity at -5F and 78% Capacity at -22F* [mrcool.com] Cooling: 100% Capacity at 115F and 78% Capacity at 130F*

Efficient heating from -22F to 75F outdoor temperatures [hvacdirect.com]

Your definition of very cold temperatures is different than mine. -5F is typically what we see here in southern New Mexico. Places up north get well below that.

And you absolutely missed the point, and to some point so did the GP.

Heating is 100% of its normal efficiency at -5F, only dropping down to 78% efficiency at -22F.

I live in 'places up north', and yes, we sometimes do get down to -22, sometimes lower. But we're only talking about the efficiency here. We're not talking about whether or not it's adequate to heat the space. If I know it can get cold enough to get my heat pump down to 50% efficiency, I just choose the one that is sized to heat my space at that temperature and efficiency.

The question that you both missed is, "when the efficiency drops in the cold, how does the cost, over the course of the year, knowing that it's really efficient 95% of the time, compare to other heating/cooling methods?"

Heating is 100% of its normal efficiency at -5F, only dropping down to 78% efficiency at -22F.

No, it's capacity not efficiency. This means the unit provides 2 tons of heating up to -5F and 78% of 2 tons of heating at -22F.

Note this is ONLY for the 2 ton version which is too small for most homes in northern climates. The 3 ton version will only provide 100% @ +17F and 50% of 3 tons at -22F.

The colder it is the more efficiency goes to shit. Efficiency is NOT communicated in the CAPACITY figures on Mr Cool's website.

No, capacity loss very much means inadequate. When it occurs the heat must be supplemented to maintain indoor temperatures.

If I know it can get cold enough to get my heat pump down to 50% efficiency, I just choose the one that is sized to heat my space at that temperature and efficiency.

This is bad advice, never oversize HVAC equipment. Not that it will even do you any good. Go for the giant 5 ton model 100% to 23F and 50% @ -15F (2.5 ton).. they don't even bother to tell you what -22 is.

The CAPACITY figures in the datasheet on Mr Cool's site have NOTHING to do with EFFICIENCY.

Yeah I live in Minnesota and we use natural gas for heating the air, water (tankless water heater) and for cooking. Our gas bill in the dead of winter is about $150 on the high side.

Whereas, in the summer, our AC cost can hit twice that amount.

An air conditioner is a heat pump.

A ground source heat pump doesn't care much about ambient air temperature, obviously.

>Thermodynamics dictates that the most efficient way to get heat from fuel is to burn it directly.

But a heat pump uses fuel to squeeze cold (or hot) from the air around it. Thus achieving efficiencies better than the carnot cycle permits, if judged by the power coming from the grid against the temperature change achieved inside the house.

>Burning fuels at a remote location, converting the heat to electricity (at a minimum loss as dictated by the Carnot Cycle), then line losses in transmission, then ad

"A minisplit typically runs off a 30A 240V circuit. So 7KWish. That is less than a typical solar array and you mostly need it when the sun is shining. AC couples very well with solar, if you can stand the capital cost."

You mostly need the mini split in winter, when the sun is not shining, or when you are under an inversion layer and the solar panel is putting out 1/14 of its rated capacity for the whole 8 hours of alleged daylight. (Actual data.)

Heat pump in cool mode for part of 9 day

That is only true in generating heat/energy from the fuel.

Heat pumps get around that becuase they are not generating energy at all, only moving it for one place to another.

The coefficent of heating for a heatpump is usually between 2 to 4. For burning gas directly on site is always less than 1 since it can only ever be theoretically 100% efficent.

https://www.nrcan.gc.ca/energy... [nrcan.gc.ca]

The major benefit of using an air-source heat pump is the high efficiency it can provide in heating compared to typical systems like furnaces, boilers and electric baseboards. At 8C, the coefficient of performance (COP) of air-source heat pumps typically ranges from between 2.0 and 5.4. This means that, for units with a COP of 5, 5 kilowatt hours (kWh) of heat are transferred for every kWh of electricity supplied to the heat pump. As the outdoor air temperature drops, COPs are lower, as the heat pump must work across a greater temperature difference between the indoor and outdoor space. At –8C, COPs can range from 1.1 to 3.7./i?

It's still more efficent to run a heat pump in almost all scenarios though. Modern gas turbines operate in the 50-60% efficency range, line losses are less than 5% and that is assuming all the electricity is coming from fossile sources. We are talking efficency improvements of 3-5x in some cases.

To hear your home with gas you have 1 option, using electricity it can come from any source, green or not and will fit right in with future sources of energy. If your town moxes more wind into the grid your heat pump will gladly use that.

Plus not having gas in the house eliminates a lot of fire hazard, carbon monoxide risk, air pollution etc

It's shockingly worse than that. Generation of electricity and delivery is about 40% efficient in the US. That's a major reason why natural gas and oil furnaces are still so common in homes. It should be noted that neither of those are 100% efficient in their delivery mechanisms though. Gas leaks and requires compression. Oil needs trucks to deliver it.

Even ignoring that though, for every KWh of energy available in a source, direct burning can only create 1 KWh of heat. A heat pump with a COP of 5 can generate 0.4*5= 2KWh of heat. Even at colder temperatures, as long as the COP exceeds 2.5, it still wins.

That's ignoring a major tangible side benefit of centralized generation - particulate control. If you're in any doubt of how important that is, consider the smogs in various cities from cars. (LA being a prime US example). They have serious health implications. Read about the London smog of 1952 that killed over 4000 people (likely closer to 12000 according to modern statistical analysis). The UK government responded with energy initiatives including insulation programs and the phasing out of coal fireplaces.

Burning fuels at a remote location, converting the heat to electricity (at a minimum loss as dictated by the Carnot Cycle), then line losses in transmission, then additional losses on conversion of the electricity back to heat at the destination - is the most inefficient and wasteful way to use fuel possible.

That's simply incorrect. You can gain over-100% efficiency end-to-end with regular heat engines. The trick is, the hot side of the heat power plant is around 300C and the cold side is the atmosphere (at around 0C). For a heat pump the cold side is the same atmosphere (at around 0C) but the hot side is at mere room temperature (20C). If you wanted to use a heat pump to get back to 300C then it indeed would be a very inefficient way of burning fuel.

I don't need to generate heat. I want to move heat from one place to another. And I can move a whole lot more heat than the energy it takes to create that heat from scratch. Which is why a heat pump is more cost effective than a furnace at heating a home. Turns out if it's really cold outside it becomes less efficient than burning fuel, rather than stops working entirely, and only for a few days year in the latitudes covered by the continental US.

Heat pumps are by their construction typically more efficient

Heat pumps are basically two air conditioners connected to each other.

Nope. They are just one single air conditioner. A reversing valve is used to change the direction of refrigerant flow. A $100(retail) valve plus the electronics to control it.

They do have to be stronger than a normal airconditioner. A normal air conditioner generally creates a 10-30 degree Farenheit change change in a house as compared to outside temperature, (i.e. 110->70) They rarely have to do more. A heat Pump also has to be able to raise 20 degree air to 70 degree air, a 50 degree change. So it DOES have to be a bit stronger than a normal air conditioner. Basically, if someone is charging you more than twice the cost a normal AC unit for a Heat Pump, they are overchar

They do have to be stronger than a normal airconditioner.

Nope. Besides the reversing valve, sensors, and control logic, the physical difference between an AC and a heat pump is that the evaporator and condenser are the same size, since they both have to be able to do the same job — each of them is both of those things.

Basically, if someone is charging you more than twice the cost a normal AC unit for a Heat Pump, they are overcharging.

If it costs more than a couple hundred bucks more, you are being ripped off. Welcome to capitalism.

Modern units do work below freezing and will defrost themselves, usually running in reverse.

Here is one defrosting in North Dakota, -12F, these units can work down to -22 (if it gets colder they have emergency heat)

https://www.youtube.com/watch?... [youtube.com]

I'd like to talk to your A/C guy. I just had to buy a new 3-ton unit for my house, enough to cool about 1,500 square feet. The cost was almost $6,000. Heat pumps certainly don't cost less than that.

Oh you mean, a window unit? Yeah, no, those don't work in the south.

They would if you had enough insulation. Also, they don't necessarily work anywhere, if it's hot enough, or at least one might not do the job. We used two Window ACs to cool a 3 bedroom house in Lake County, and it even had passive solar so it had proper overhangs... but also had an absolute ton of glass. There are some pretty big window units.

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