What is the real story around heat pumps?

[Someone]

The whole idea of these systems to pay for themselves is kind of bullshit. Sure it can reduce on your energy bill, but it will still cost money. Depending on the type of system and the cost to install it can take a long time before any savings start to come.

Remember that expensive systems such as quoted for you are a kind of specialty of wealthy societies and wealthy households. Energy solutions are being sold exceeding their true value, because there is market for that and people still buy. My air-to-water heat pump installation was less than 4000EUR all parts included, although I did the install work myself but it would have been less than 1000EUR for work if I just paid for hourly rates for electrician and plumber; and the end result is way better than how a typical 15000EUR complete one size fits all solution would have been.

Typical cost for air-to-water retrofit was around 8000-9000 EUR here but nearly doubled to 14-15000 EUR almost overnight after a 4000EUR subsidy come into place. The market does not reflect actual costs, and any subsidies further twist the market. Enough people are willing to pay outrageous prices when they feel good about it.

In Japan air-to-air heatpump costs something like 500EUR installed so one can easily afford one per each room. They do pay back for themselves, that's literally why they were developed in 1980's in the first place, to save cost of fossil fuels.

Even when I would get a cheap monoblock heat pump and do the work myself and spend say the 4000 euro you mentioned yours costed, it would still take a very long time to see a so called "return on investment" or reach a break even point.

What I pay now for my heating is 24m3 of fire wood at 55 euro the m3 is 1320 euro.
On average loss of interest on 4000 euro in a savings account lets say 80 euro. (At the moment we get more then 2% here in France, but it will vary)
Needed heat energy 16500KWh at SCOP 3.5 is ~4714KWh at an average electricity price of 20 euro cents comes to 942,8 euro.

So saving comes down to 1320 - 942,8 - 80 = 297,2 euro per year so comes down to about 13,5 years. At that time it might be needed to buy and install a new heat pump. If not you will have to save up the money you save and it will take another 10 years, with interest on interest, or so to get the initial 4000 euro back in the bank.

This is not taking into account the cost of owner ship like maintenance or replacing defective parts if needed, nor is it taking into account the rise in electricity price that comes round once in a while. The latter would also effect the price of fire wood, so not really needed to adjust for.

And that is why I said that living costs money.

It might be different for others who have much higher heating costs with their current system, but still you will never really get your investment back.

To me there is a distinction between saving money and making money. With PV solar panels it might be a different story when you harvest way more energy than you consume and can actually sell the remainder to the energy company. But then still you have to take cost of owner ship into account.

Well you did start this thread on the basis that you had to get something to replace the wood burning, or perhaps you'd like to add labour for someone to come and cut/dry/handle/load the wood for you?  We've seen this before with people claiming they get their wood for "free" so it's not a cost.... in their shallow analysis.

"profit" can be real for heat pumps where someone has an ongoing need for some quantity of thermal heating, even if that is immediately replacing or augmenting an existing fully functional heat source. Of course the number varies wildly around the world. What is more common is your situation where a new heater is needed as an existing unit is absent/expired/unserviceable and the choice is now investing one way or another. Higher upfront investment can produce cheaper lifecycle costs, but as you found it needs careful analysis of the available options as salespeople generally only care about their immediate profit while you have some different (varying from person to person) horizon in mind for the investment. Easiest just to state where you want those analysis to sit as you have and then it's clear to everyone!

[nctnico]

The whole idea of these systems to pay for themselves is kind of bullshit. Sure it can reduce on your energy bill, but it will still cost money. Depending on the type of system and the cost to install it can take a long time before any savings start to come.

Remember that expensive systems such as quoted for you are a kind of specialty of wealthy societies and wealthy households. Energy solutions are being sold exceeding their true value, because there is market for that and people still buy. My air-to-water heat pump installation was less than 4000EUR all parts included, although I did the install work myself but it would have been less than 1000EUR for work if I just paid for hourly rates for electrician and plumber; and the end result is way better than how a typical 15000EUR complete one size fits all solution would have been.

Typical cost for air-to-water retrofit was around 8000-9000 EUR here but nearly doubled to 14-15000 EUR almost overnight after a 4000EUR subsidy come into place. The market does not reflect actual costs, and any subsidies further twist the market. Enough people are willing to pay outrageous prices when they feel good about it.

In Japan air-to-air heatpump costs something like 500EUR installed so one can easily afford one per each room. They do pay back for themselves, that's literally why they were developed in 1980's in the first place, to save cost of fossil fuels.

Even when I would get a cheap monoblock heat pump and do the work myself and spend say the 4000 euro you mentioned yours costed, it would still take a very long time to see a so called "return on investment" or reach a break even point.

What I pay now for my heating is 24m3 of fire wood at 55 euro the m3 is 1320 euro.
On average loss of interest on 4000 euro in a savings account lets say 80 euro. (At the moment we get more then 2% here in France, but it will vary)
Needed heat energy 16500KWh at SCOP 3.5 is ~4714KWh at an average electricity price of 20 euro cents comes to 942,8 euro.

Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

[pcprogrammer]

Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

Not really as it is already set reasonably low. I'm thinking about heating up more during the night at a reduced rate, but not sure if the offered pump will supply enough energy to reach the needed temperature rise on the coldest days when profit would be biggest.

That is part of the experiment.

Well you did start this thread on the basis that you had to get something to replace the wood burning, or perhaps you'd like to add labour for someone to come and cut/dry/handle/load the wood for you?  We've seen this before with people claiming they get their wood for "free" so it's not a cost.... in their shallow analysis.

I never claimed the wood to be free, but do still have about 12m3 from one of our own trees. It was a hell of a job to take it down, partly due to my disease, but also because it was a very big oak tree to close to the house. Cutting up all the branches and the trunk took us weeks. Apart from that labor and the petrol for the chainsaw and electricity for the splicer it is "free" wood. 

The thread was started to find out if sales people are lying about air to water heat pumps having far worse performance then ground to water heat pumps, and what the noise levels are.

And as with everything on the net you have to filter and analyze the given answers to get to the bottom. Conclusion is that the two systems are not far apart and definitely not the factor two that one of the sales people claimed.

[Siwastaja]

This is not taking into account the cost of owner ship like maintenance or replacing defective parts if needed, nor is it taking into account the rise in electricity price that comes round once in a while. The latter would also effect the price of fire wood, so not really needed to adjust for.

Yeah. Calculate the cost for maintaining the wood burner and especially the time and effort you need to spend burning wood, and it not only evens out but exceeds that of the heatpump because the monoblock heatpump is nearly maintenance-free. I have had mine running for three years with no maintenance, unless you include the few seconds of my time used to pick a stuck leaf out of the evaporator coil. End-of-life for such heatpumps is typically around 10 - 20 years, maybe 12-15 median. Calculate the savings with a slightly pessimistic 10 years and you won't go too wrong.

In your case, you will again reach optimum with a hybrid system (as you don't have to invest in wood burner): burn wood when COP < 2 or so, and this effectively brings the SCOP of the heatpump up, and thus total energy cost down a bit.

[Siwastaja]

I never claimed the wood to be free, but do still have about 12m3 from one of our own trees. It was a hell of a job to take it down

Now the question really is, do you want to burn the results of your hard work in one winter, or maybe use it in a hybrid solution for the next 5 winters?

I started renovation of upstairs by just dismantling everything before putting in new materials, and that produced a few m^3 of 2x4" and 1x5" from 1950's, good untreated wood (spruce most likely). My wife spent a lot of time removing all the nails before I cut it to fixed length pieces. So in the same sense, this is also "free" wood, but carries some emotional attachment.

In addition to random sauna use, I have used this wood to heat the house for two winters now and it feels good to use this "waste". If I only heated by wood, it would have been gone in the first winter even before the first seriously cold weeks. During that time, the heatpump on the other hand produced heat with excellent COP and little electricity.

salespeople

Salespeople are funny. Expensive turnkey solutions:

What salespeople sell to the customer: theoretical savings of the best case installation +30%, payback in 2 years
How you are billed: Heavily customized solution tailored for your specific needs, with the best-in-class oversized heatpump
What you actually get: underdimensioned, one-size fits all installation, with some unoptimal flaw which wastes half of the savings, payback in 30 years except the pump doesn't last that long.

Then again, if you know something about the market and products and how they are useful, you still don't have to DIY, but you have to manage the project. This way cost is less and end result better than with most turn-key solutions.

[nctnico]

Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

Not really as it is already set reasonably low. I'm thinking about heating up more during the night at a reduced rate, but not sure if the offered pump will supply enough energy to reach the needed temperature rise on the coldest days when profit would be biggest.

Sorry I wasn't clear, I was hinting at adding insulation so you can reduce the amount of energy going out of the home.

[tszaboo]

Paving the planet with solar panels or harvesting all the lithium in the world, etc, might only make things worse.

Don't take it too extreme, but there is something to this. Efficient solutions should be preferred and e.g. a simple air-to-air heatpump which costs 500€ to buy and uses a few dozen kg of common materials like plastics, iron, aluminum, copper, yet harvests 1kW (input power) * 2 (SCOP-1) * 24*365 * 0.5 (duty cycle) * 12 (years lifetime) = 100 000 kWh of free, renewable energy. A 4-5kWp PV system would then harvest say 5000 kWh/year * 20 year lifetime = roughly the same 100 000 kWh of free, renewable energy.

But the environmental cost of manufacturing the heatpump is probably smaller, it is significantly cheaper to buy, and it harvests energy during winter nights, too. This doesn't mean PV is bad, just something to think about for the priority list.

Lithium ion battery storage is then again at least an order of magnitude worse again. Especially if you have any low-hanging fruit like controlling the usage of electric hot water production which can easily store 20kWh worth of energy by just adding 500€ worth of control to an existing system. Compare the ecological footprint and install cost to li-ion battery system of the same size!

Then again, maybe such low-hanging fruit is not available. I'm not saying never to install battery systems. Just something to think about for priorities.

See, this is what makes sense. Using easy to install technologies to save energy on the existing houses. Building new houses with the new technology in mind. Leveraging technology without bankrupting ourselves.
The same way, we don't want to ban spark plugs for cars, just because we want people to switch to electric. And tell people who need a new boiler "just buy electric".
If OP installs an air to air heatpump maybe he can reduce the heating season here from 4-5 month to say 2 month. Buy installing heatpump on 2-3 rooms and using it additionally to the heating he has. Save 40-50-60% of the bill (and reduce CO2) with 1/20th the investment.

[Siwastaja]

See, this is what makes sense. Using easy to install technologies to save energy on the existing houses.

Fair enough, but in specific case of OP, air-to-water heatpump is such easy-to-install retrofit. It's a perfect match because of the existing under-floor and low-temperature radiators. The problem is only navigating past overly expensive turn-key solutions and either do-it-yourself or find the right contractors to do it with sensible cost. Total cost should be only marginally larger than 2-3 room air conditioner units (1000EUR each installed). If price difference is more than 2-3x (let alone 20x as you suggest) then something is wrong and you are not looking hard enough for the right supplier.

[Zero999]

Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

Not really as it is already set reasonably low. I'm thinking about heating up more during the night at a reduced rate, but not sure if the offered pump will supply enough energy to reach the needed temperature rise on the coldest days when profit would be biggest.

That is part of the experiment.

Well you did start this thread on the basis that you had to get something to replace the wood burning, or perhaps you'd like to add labour for someone to come and cut/dry/handle/load the wood for you?  We've seen this before with people claiming they get their wood for "free" so it's not a cost.... in their shallow analysis.

I never claimed the wood to be free, but do still have about 12m3 from one of our own trees. It was a hell of a job to take it down, partly due to my disease, but also because it was a very big oak tree to close to the house. Cutting up all the branches and the trunk took us weeks. Apart from that labor and the petrol for the chainsaw and electricity for the splicer it is "free" wood. 

The thread was started to find out if sales people are lying about air to water heat pumps having far worse performance then ground to water heat pumps, and what the noise levels are.

And as with everything on the net you have to filter and analyze the given answers to get to the bottom. Conclusion is that the two systems are not far apart and definitely not the factor two that one of the sales people claimed.

Oak is quite expensive. It might have been more economical to sell the wood and use the money to by pellets, or scrap offcuts, than burn that tree!

It's not just sales. I don't completely trust everything people say on forums such as these, when it comes to heat pumps, because it has the potential to be shaped by ones political stance. I'm not accusing anyone of lying, just bias, which many people are unaware off. This is true for both those who are strong advocates, as those who are against. Another thing is everyone's usage and climate is different.

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

This laboratory test shows a COP of between 3 and 5, at 5°C, but it was done under very dry conditions. I live in a very humid climate and COP does down with high relative humidity, when the air temperature is 5°C.
https://www.nrel.gov/docs/fy23osti/85081.pdf

This Italian study is probably more relevant, as inland areas of Northern Italy have similar winter temperatures and relative humidity as Southern England. The downside is it's over ten years old and heat pump efficiency might have improved since then.
https://www.sciencedirect.com/science/article/pii/S187661021400071X?ref=pdf_download&fr=RR-2&rr=85afe559b8a379b5

A quote which I find concerning.

The energy consumption due to the defrost cycles has to be considered in calculating the heat pump performance but the calculation methods proposed by the European standards ignore this effect.

Given this can I trust data based on European standards, or is this not the case and this is out of date information?

This one from Strathclyde shows slightly lower COPs.
https://www.esru.strath.ac.uk/EandE/Web_sites/10-11/ASHP_CO2/ccl-potential.html

Someone on a British forum complaining about a COP of 2.3 for space heating and 2.5 for water.
https://forum.buildhub.org.uk/topic/34775-is-my-cop-rubbish/

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

I've also realised I didn't take into account the fact that if I can stop using gas, which would also involve replacing my cooker with an induction hob, I can reduce my standing charge (a flat rate daily connection fee, which independent of usage), but then I have to factor in the fact it probably costs a bit more to run.

[tszaboo]

See, this is what makes sense. Using easy to install technologies to save energy on the existing houses.

Fair enough, but in specific case of OP, air-to-water heatpump is such easy-to-install retrofit. It's a perfect match because of the existing under-floor and low-temperature radiators. The problem is only navigating past overly expensive turn-key solutions and either do-it-yourself or find the right contractors to do it with sensible cost. Total cost should be only marginally larger than 2-3 room air conditioner units (1000EUR each installed). If price difference is more than 2-3x (let alone 20x as you suggest) then something is wrong and you are not looking hard enough for the right supplier.

"Should be" is a keyword. It's not.
I've quickly looked up air to hot water pumps, they start at 3500. You get a subsidy, but only if they install it.

[nctnico]

This one from Strathclyde shows slightly lower COPs.
https://www.esru.strath.ac.uk/EandE/Web_sites/10-11/ASHP_CO2/ccl-potential.html

Someone on a British forum complaining about a COP of 2.3 for space heating and 2.5 for water.
https://forum.buildhub.org.uk/topic/34775-is-my-cop-rubbish/

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

In the end nothing beats getting information about hands-on experiences with the equipment. On a forum you can get a good list with prospects with some pros & cons but from there you have to start reading reviews about the various pieces of equipment out there. A good source may be looking for a forum where installers of heatpump systems hang out (likely a forum for AC installers as these are related) to get some info about maintenance problems for various models / brands.

[zilp]

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

This laboratory test shows a COP of between 3 and 5, at 5°C, but it was done under very dry conditions. I live in a very humid climate and COP does down with high relative humidity, when the air temperature is 5°C.
https://www.nrel.gov/docs/fy23osti/85081.pdf

The funny thing is that the effect of humidity is actually both beneficial and detrimental. On the one hand, there is a lot of latent energy to be had from condensing water vapor. On the other hand, if you get to the freezing point at the evaporator surface, the condensed water freezes and clogs up the evaporator, requiring energy to be expended for defrosting. Though it should be noted that the phase transition from liquid to frozen also releases latent energy, so the energy "spent" for thawing the ice was previously extracted from the ice by the heat pump. It's just that the heat pump will release more energy than would be absolutely necessary for thawing the ice, and also, the heat might be taken from a different place than where the extracted energy was pumped, both of which will generally make the freeze/defrost cycle a net energy loss and thus reduce COP. This is probably the primary thing that reduces COP around the freezing point with high humidity.

A quote which I find concerning.

The energy consumption due to the defrost cycles has to be considered in calculating the heat pump performance but the calculation methods proposed by the European standards ignore this effect.

Given this can I trust data based on European standards, or is this not the case and this is out of date information?

I have no idea as to the current requirements in the relevant standards, but I guess it isn't really possible to specify a representative way to include defrost energy in one generic COP number, as that, as you yourself said, depends on humidity, and also on rather specific weather patterns. Specifically: It's not something that is well captured by average values, because the COP (including defrost energy) will often be better at -5°C than at +3°C at the same relative humidity, so, the amount of time during a year spent in the critical region determines the influence of defrosting on COP.

At the same time, more transparency wrt defrost energy certainly would be useful, because there certainly is optimization potential. My own heat pump, for example, defaults to defrosting with a resistive heater. Or more specifically, it takes heat from the storage tank (that's kept at DHW temperatures) for defrosting, but switches on the resistive heater in the tank during the process to re-add the energy it extracts from the tank during defrost. But you can just disable the resistive heater and it will happily take the heat from the tank anyway, which was pumped there at a COP of ~ 2 or so (during winter), thus halving the electricity used for defrosting. (You just have to manually re-enable the resistive heater when it is actually needed, which obviously wouldn't be necessary if the controller were just smart enough to do this automatically ...)

Equally, COP doesn't reflect standby consumption of the heating system. My own heat pump uses 12 W in standby, i.e., all pumps off, compressor off, just watching tank and room temperature, eats 100 kWh in a year. Obviously, that should be possible at sub 1 W, right? Given that the system sits idle ~ 70% of the year ... that should be an easy improvement to make for a ~ 3% reduction in power consumption, shouldn't it?

Someone on a British forum complaining about a COP of 2.3 for space heating and 2.5 for water.
https://forum.buildhub.org.uk/topic/34775-is-my-cop-rubbish/

Well, did you read the thread?

During the time apparently covered by those numbers, they had huge holes in the wall, the flow sensor was broken, the total thermal energy they report is significantly lower than what they used in previous years (which might well be because of the broken flow sensor), ... i.e., for all we can tell, that COP is just complete nonsense?

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

I don't think anyone estimated a COP for you? Obviously, noone here knows the specifics of your heating system, so it would be nonsensical to estimate a COP for you based on no information. The 350% mentioned by me and others is a good general assumption about heat pumps on average, i.e., a useful basis for discussing, say, general policies as to how to switch energy supply of a country to renewable energy. But obviously, it would be nonsensical to use such a general average to make investment decisions for a specific house. And it is equally nonsensical for you to just assume 250% instead. 350% is fine for a first back-of-the-envelope calculation. Beyond that, you need to measure the actual properties of your heating systems and look at the COP curves published by heat pump manufacturers to get a reasonably accurate estimate as to what you could achieve with a particular heat pump model in your particular home.

I've also realised I didn't take into account the fact that if I can stop using gas, which would also involve replacing my cooker with an induction hob, I can reduce my standing charge (a flat rate daily connection fee, which independent of usage), but then I have to factor in the fact it probably costs a bit more to run.

Chances are it doesn't. Gas stoves are very inefficient as far as heating the stuff you put on them is concerned, they primarily heat the room they are in. Whether that's a loss obviously depends. If you are at the same time heating with gas anyhow ... well, you might as well burn it in an open flame in the kitchen? Though the increased CO (and CO2) concentration might be a reason to open the window, so maybe it's net negative still. But then, during summer, you might increase cooling load and thus pay more for getting rid of the waste heat than you saved from the cheap-ish energy source. Or at least it might make things more uncomfortable if it is too hot for your comfort already.

[pcprogrammer]

I never claimed the wood to be free, but do still have about 12m3 from one of our own trees. It was a hell of a job to take it down

Now the question really is, do you want to burn the results of your hard work in one winter, or maybe use it in a hybrid solution for the next 5 winters?

We have a small wood burner in the kitchen/living that is going to consume that wood. That space has to much volume to be heated with only the underfloor heating also due to the chestnut floor we have on top of it. Ceramic floor tiles would have been better, but we like the wooden floor. 

Inexperience with underfloor heating when designing the system made this happen. Should have added some radiators, but in stead there is the wood burner to lift it from ~17 to >20.

Oak is quite expensive. It might have been more economical to sell the wood and use the money to by pellets, or scrap offcuts, than burn that tree!

Only when you buy it as ready made planks from a DIY store. 

No sawmill owner over here will come to only take a single oak tree.

[jmelson]

The thread was started to find out if sales people are lying about air to water heat pumps having far worse performance then ground to water heat pumps, and what the noise levels are.

Many years ago my wife had a house that had an air to air heat pump.  It also was a "brick frame" house, not "brick veneer", meaning the walls were a single course of bricks with no air space or insulation from exterior to interior.  It had tons of insulation in the attic, but that was pretty useless.  In the moderate winter climate of Missouri, the place was impossible to heat!
Where we live now, some neighbors have air-air heat pumps.  When I am outside near their property, I can hear the unit running, and hear the valves changing over for defrost, but it is no louder than a typical air conditioner.  But, NO QUESTION, a ground-source heat pump will do the job on 1/10th the energy.  A friend did have a modern log cabin out in the woods with a ground source heat pump, and he used to brag about the CRAZY low energy bills!
Jon

[Siwastaja]

I've quickly looked up air to hot water pumps, they start at 3500. You get a subsidy, but only if they install it.

But 3500 is not that much at all IMHO. Sure I'd like to see them start at 2000, but . 3500EUR is quite easily recovered already during halfway of the lifetime of the product. It gets nasty when the heatpump is 7000 (some sort of premium brand name which isn't that much better in reality) and then the install cost another 7000, or even more.

[Zero999]

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

This laboratory test shows a COP of between 3 and 5, at 5°C, but it was done under very dry conditions. I live in a very humid climate and COP does down with high relative humidity, when the air temperature is 5°C.
https://www.nrel.gov/docs/fy23osti/85081.pdf

The funny thing is that the effect of humidity is actually both beneficial and detrimental. On the one hand, there is a lot of latent energy to be had from condensing water vapor. On the other hand, if you get to the freezing point at the evaporator surface, the condensed water freezes and clogs up the evaporator, requiring energy to be expended for defrosting. Though it should be noted that the phase transition from liquid to frozen also releases latent energy, so the energy "spent" for thawing the ice was previously extracted from the ice by the heat pump. It's just that the heat pump will release more energy than would be absolutely necessary for thawing the ice, and also, the heat might be taken from a different place than where the extracted energy was pumped, both of which will generally make the freeze/defrost cycle a net energy loss and thus reduce COP. This is probably the primary thing that reduces COP around the freezing point with high humidity.

Going from what I've read, humidity can both increase, as well as decrease the COP. If the temperature is above 6°C, high humidity generally increases the COP. At temperatures below 6°C, high humidity deceases the COP, which is worse around freezing, then becomes less of an issue below freezing, since freezing air holds less moisture.

In my specific situation, I expect the heat pump to mostly run when the temperature is around 0°C to 6°C, hence why I believe the humid climate where I live is a hindrance, rather than a help. If I were going to use it for hot water, say to heat a pool in summer, then it would be different.

A quote which I find concerning.

The energy consumption due to the defrost cycles has to be considered in calculating the heat pump performance but the calculation methods proposed by the European standards ignore this effect.

Given this can I trust data based on European standards, or is this not the case and this is out of date information?

I have no idea as to the current requirements in the relevant standards, but I guess it isn't really possible to specify a representative way to include defrost energy in one generic COP number, as that, as you yourself said, depends on humidity, and also on rather specific weather patterns. Specifically: It's not something that is well captured by average values, because the COP (including defrost energy) will often be better at -5°C than at +3°C at the same relative humidity, so, the amount of time during a year spent in the critical region determines the influence of defrosting on COP.

At the same time, more transparency wrt defrost energy certainly would be useful, because there certainly is optimization potential. My own heat pump, for example, defaults to defrosting with a resistive heater. Or more specifically, it takes heat from the storage tank (that's kept at DHW temperatures) for defrosting, but switches on the resistive heater in the tank during the process to re-add the energy it extracts from the tank during defrost. But you can just disable the resistive heater and it will happily take the heat from the tank anyway, which was pumped there at a COP of ~ 2 or so (during winter), thus halving the electricity used for defrosting. (You just have to manually re-enable the resistive heater when it is actually needed, which obviously wouldn't be necessary if the controller were just smart enough to do this automatically ...)

Equally, COP doesn't reflect standby consumption of the heating system. My own heat pump uses 12 W in standby, i.e., all pumps off, compressor off, just watching tank and room temperature, eats 100 kWh in a year. Obviously, that should be possible at sub 1 W, right? Given that the system sits idle ~ 70% of the year ... that should be an easy improvement to make for a ~ 3% reduction in power consumption, shouldn't it?

I understand that it's not a simple calculation. It's similar to car mileage, in that it depends on how it's being used.

Yes, your standby consumption does sound high. I would have hoped that minimising it would have been an important design goal.

Someone on a British forum complaining about a COP of 2.3 for space heating and 2.5 for water.
https://forum.buildhub.org.uk/topic/34775-is-my-cop-rubbish/

Well, did you read the thread?

During the time apparently covered by those numbers, they had huge holes in the wall, the flow sensor was broken, the total thermal energy they report is significantly lower than what they used in previous years (which might well be because of the broken flow sensor), ... i.e., for all we can tell, that COP is just complete nonsense?

To be honest, no I didn't read the whole thread in detail. I concentrated my efforts on reading objective studies. Whilst forums can be useful and a lot can be learned from them, much of it is anecdotal. The only reason why it caught my attention was the numbers were similar to studies in areas with a similar winter climate, to where I live.

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

I don't think anyone estimated a COP for you? Obviously, noone here knows the specifics of your heating system, so it would be nonsensical to estimate a COP for you based on no information. The 350% mentioned by me and others is a good general assumption about heat pumps on average, i.e., a useful basis for discussing, say, general policies as to how to switch energy supply of a country to renewable energy. But obviously, it would be nonsensical to use such a general average to make investment decisions for a specific house. And it is equally nonsensical for you to just assume 250% instead. 350% is fine for a first back-of-the-envelope calculation. Beyond that, you need to measure the actual properties of your heating systems and look at the COP curves published by heat pump manufacturers to get a reasonably accurate estimate as to what you could achieve with a particular heat pump model in your particular home.

I thought reading objective studies about heat pumps in areas with a similar winter climate, to my location would give me a reasonable figure. I accept that it will be different, depending on how I use the heat pump, but I would have thought it would by closer, than a general ballpark of 350%, which doesn't even take into account the local climate.

I'm not sure how much I trust COP figures given by manufactures, given there are numerous different factors and they are likely to be skewed in the manufacture's favour. I've seen this with component data sheets, audio amplifiers and vehicle mileage, although I've also had instances when it's better than expected, such as my motorcycle doing more miles per tank, than expected. I suppose I'm more careful, because it would be a big investment, it's not something I'm overly familiar with and then there's the political side to it, which doesn't help.

I've also realised I didn't take into account the fact that if I can stop using gas, which would also involve replacing my cooker with an induction hob, I can reduce my standing charge (a flat rate daily connection fee, which independent of usage), but then I have to factor in the fact it probably costs a bit more to run.

Chances are it doesn't. Gas stoves are very inefficient as far as heating the stuff you put on them is concerned, they primarily heat the room they are in. Whether that's a loss obviously depends. If you are at the same time heating with gas anyhow ... well, you might as well burn it in an open flame in the kitchen? Though the increased CO (and CO2) concentration might be a reason to open the window, so maybe it's net negative still. But then, during summer, you might increase cooling load and thus pay more for getting rid of the waste heat than you saved from the cheap-ish energy source. Or at least it might make things more uncomfortable if it is too hot for your comfort already.

I'm aware of the fact that gas stoves aren't very efficient, I've read 40% is reasonable, but don't forget electricity costs four times as much for me, as gas, so an induction hob will still be more expensive for me to run. I doubt it will make much of a difference since, only a tiny part of my energy usage is for cooking, but it's something to consider.

I doubt it'll make any difference to ventilation. I have a CO detector, which never goes off and I only use the fume extractor when I'm cooking something smelly.

I generally avoid cooking in hot whether and summer is generally cool where I live, so unwanted heat is less of a big deal.

I've quickly looked up air to hot water pumps, they start at 3500. You get a subsidy, but only if they install it.

But 3500 is not that much at all IMHO. Sure I'd like to see them start at 2000, but . 3500EUR is quite easily recovered already during halfway of the lifetime of the product. It gets nasty when the heatpump is 7000 (some sort of premium brand name which isn't that much better in reality) and then the install cost another 7000, or even more.

I agree. That doesn't sound expensive for the heat pump itself. It's the rest of the installation and associated labour which is expensive. Subsidies are only given if you use an approved contractor and it has to meet certain criteria. I don't even know if it's legal for you to do it yourself. I would expect a licenced refrigeration tech will be required, or at the very least an electrician with the appropriate qualifications.

[Siwastaja]

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

I agree the information is not that easy to find. You need to combine bits and pieces and measurements by individuals. One helpful advice that I have repeated and do it once again: differences between heatpumps (cheap vs. premium) are surprisingly small, and effect of condensing temperature (i.e., water temperature you need to get into your radiators/floor circuits/etc.) is just massive, regardless of brand. Therefore, while we roughly know the climate you live in, not knowing your water distribution temperature, we can't say whether your SCOP will be 2.0 or 5.0. Very unlikely anything outside this range. Maybe you have underfloor heating pipes and good insulation and need water temperature of +27degC. Then your SCOP can easily be 5.0. Maybe you have tiny radiators that act as the name suggest, primarily radiating the heat instead of natural convection, and maybe you need +80degC water to feel warm. Then SCOP would plummet to 2.0 or so, as you would run on resistive aux heating at COP=1, large part of the winter.

Then again, if you read a complaint that COP is bad when one has a massive hole in the wall and they are producing steaming hot water at full power 24/7 during winter, I would just ignore the whole discussion and try to find more useful data points. Unless, of course, you have a large hole in your wall, too.

I live in a very humid climate and COP does down with high relative humidity, when the air temperature is 5°C.

I can say from own experience that COP most definitely goes up in high humidity conditions when the air temperature is +5°C. You can easily see this from the fact that Tpipe (evaporator internal temperature) as measured by the heatpump is closer to ambient temperature in such conditions (e.g.: dry air, Ta=5.0, Tpipe=-0.5, ice is forming; RH=100% humid conditions: Ta=5.0, Tpipe=3.0, it rains under the outdoor unit).

More heat can be extracted because turning water vapor into liquid releases a lot of latent heat. At +2 or so things get different - even the high humidity is not able to keep dT low enough, and freezing will start to occur. At medium humidity, freezing can occur already at +5 or so.

Defrosting is fundamentally not a bad thing: if you calculate the total enthalpy you are seeing the sum is actually better than in completely dry lab conditions! You get extra heat by making ice from water vapor in the first place, and during defrost you don't turn it back to vapor, mostly liquid, so you gained more than lost! In reality of course significant losses are involved, e.g. because the compressor is used to transfer the heat round-trip, and because, even with fan stopped, the evaporator (now condenser during defrost) sits hot in the outdoors air, possibly in windy conditions, for a minute or two, so defrosting reduces true COP below the level of dry testing, but given decently working decision algorithms (which they usually are), the effect is much smaller than many assume.

Specifically air-to-water units are very efficient at defrosting because they have better source of stored heat, in form of hundreds of liters of warm water, than air-to-air units which can only utilize the tiny amount of thermal energy stored in the indoor unit coil (copper with aluminum fins) and therefore heat the outdoor unit with worse COP during defrost. This is easy to see from the power consumption of e.g. my heatpump, which, for the 2300W input power unit, is just between 300-600W during defrost, and it only lasts for 3-5 minutes.

But sure, there is a small dent in COP curve around +5degC. It doesn't get progressively worse, as very cold air will be dry. The loss for every defrost cycle is higher when very cold, but fewer are needed, so there is just a small jump of about -0.2..-0.3 near +5degC compared to dry testing which keeps quite constant down to however low temperatures.

A quote which I find concerning.

You can keep being a concerned citizen, but then again, this is how reality works. Your car consumes more fuel than the official numbers, just like every other car in existence, and just like they always did. Your condensing boiler performs worse compared to marketing material, I'm 100% sure about that. This is human nature. The big question is, are you making sensible decisions based on best effort of obtaining true data, or just using your concerns and uncertainties as coping mechanism?

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

SCOP of 2.5 in British weather, which is pretty optimal for air source heatpumping (at least from Finnish perspective), would require some massive blunder. It's not impossible to do that badly, but it would be an outlier. I'm close to 2.5 (don't have exact measurement but very good guesstimates) in Finnish climate which is significantly colder.

However, important fundamental fact to understand is that COP is not a constant over year. We talk about annual COP, SCOP, defined simply as annually produced thermal energy divided by annually consumed electricity. We do this because we are interested about how much money we are putting in the long run. Heatpumps are not suitable for those who only have £100 on their bank account and are struggling to pay a single bill on February, because of the cost nonlinearity, which makes the effect of time-of-the-year on the bill even larger than it already is with linear systems (basically everything else than heatpumps).

I've also realised I didn't take into account the fact that if I can stop using gas, which would also involve replacing my cooker with an induction hob, I can reduce my standing charge (a flat rate daily connection fee, which independent of usage), but then I have to factor in the fact it probably costs a bit more to run.

This is indeed another (albeit small) downside in gas-based systems, you rely on another contract and someone supplying you with this product every day. Compare with wood or oil (I use both as auxiliary heating methods) which can be locally stored for years, and if you mainly do heatpump, the volumes that need to be stored are modest.

[Marco]

Wood is clearly the cheapest per kwh if you have the space to have ton's worth delivered by truck.

Though on truly modern homes so little heating is required that it would almost never be worth the effort unless you enjoy fuelling the stove.

[nctnico]

I'm not sure how much I trust COP figures given by manufactures, given there are numerous different factors and they are likely to be skewed in the manufacture's favour.

The nameplate COP / SCOP number is a standarised value at a standard indoor / output temperature. However, there should be more detailed information available. The service manual for the Panasonic airco unit I have, has extensive tables that show COP/SCOP for combinations of indoor / outdoor temperatures.

[Zero999]

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

I agree the information is not that easy to find. You need to combine bits and pieces and measurements by individuals. One helpful advice that I have repeated and do it once again: differences between heatpumps (cheap vs. premium) are surprisingly small, and effect of condensing temperature (i.e., water temperature you need to get into your radiators/floor circuits/etc.) is just massive, regardless of brand. Therefore, while we roughly know the climate you live in, not knowing your water distribution temperature, we can't say whether your SCOP will be 2.0 or 5.0. Very unlikely anything outside this range. Maybe you have underfloor heating pipes and good insulation and need water temperature of +27degC. Then your SCOP can easily be 5.0. Maybe you have tiny radiators that act as the name suggest, primarily radiating the heat instead of natural convection, and maybe you need +80degC water to feel warm. Then SCOP would plummet to 2.0 or so, as you would run on resistive aux heating at COP=1, large part of the winter.

Then again, if you read a complaint that COP is bad when one has a massive hole in the wall and they are producing steaming hot water at full power 24/7 during winter, I would just ignore the whole discussion and try to find more useful data points. Unless, of course, you have a large hole in your wall, too.

You raise some interesting points, but I won't quote everyone of them and reply to save space. Note that just because I've not responded to and quoted them all, it doesn't mean they were unhelpful or that I have ignored them.

I know for certain that my current heating system is completely incomputable with a heat pump. The pipes are too thin and radiators too small. The whole lot will need to be replaced, which will be very costly. Although I don't use hot water myself, I still need the option, for when I have guests over and no one else would buy the house, which doesn't have hot water. At the moment it's heated on demand, by the boiler. A heat pump would require a tank and associated plumbing, which would be expensive. I haven't looked at how much it would cost, but I've seen £12 000 mentioned in this thread.

To put it into perspective, my energy bill both gas and electricity last year was £545.30. I used 1472kWh in total (including both gas and electricity) last year. Most of my bill is standing charges at £253.78.

Regarding the hole in wall comment, no I don't take that forum thread too seriously. I do add more weight to the other articles I linked, which involve real data from Scotland and Northern Italy, especially the latter which is very comprehensive.

The big question is, are you making sensible decisions based on best effort of obtaining true data, or just using your concerns and uncertainties as coping mechanism?

A coping mechanism for what?

Given the high upfront cost of replacing my current system, which works perfectly, it's perfectly reasonable I'm going to be overly cautious, especially given it's possible the new system won't necessarily be cheaper to run or more reliable, than the current one. This is why it's just a thought experiment at this stage and I have no intention of changing. I wouldn't expect someone to buy a new car, when their current one works fine. I don't see why this is any different.

[zilp]

Going from what I've read, humidity can both increase, as well as decrease the COP. If the temperature is above 6°C, high humidity generally increases the COP. At temperatures below 6°C, high humidity deceases the COP, which is worse around freezing, then becomes less of an issue below freezing, since freezing air holds less moisture.

The point is that COP doesn't get magically worse around 6°C, COP gets worse due to freezing. Or more accurately, COP gets worse with lower outdoor temperature, but the dip somewhere around 6°C is due to freezing and the required defrost.

Which also means that this is not somehow specifically at a magic 6°C, but rather at whatever outdoor temperature that happens to cause the evaporator surface temperature to dip below the freezing point of water. Which depends on, among other things, the thermal power that you are extracting from the evaporator. And on the amount of air being blown through the evaporator. And on the geometry of the evaporator. And who knows what.

So, it is possible that you might be seeing defrost cycles at 6°C with some heat pumps in some setups. But really, you mostly shouldn't, because the heat pump will generally be dimensioned for sufficient thermal power to keep your house warm (without resistive heating) at -15°C or whatever (depends on your location, obviously), so the thermal power you are drawing from the evaporator at +6°C (assuming a modulating/inverter heat pump) should be relatively low and should not be sufficient to pull it to below 0°C, especially not with humid air that provides significantly more heat per volume than dry air would.

Here, we had rainy wheather and temperatures in the 4 to 8°C range the last few days, but effectively no defrost. I say "effectively" because the controller does a defrost cycle shortly after startup at outdoor temperatures around ~ 5°C or lower (no clue what the exact decision criteria are), but then it keeps going 8 hours or whatever without any further defrosting, until it shuts off because the target temperature was reached, and the ~ 250 Wh of heat it dumps into the evaporator for that don't matter all that much overall (especially given that it probably recovers a significant part of that). (And also, there really is no ice forming, so it's not like COP is dropping but the controller just fails to do a defrost cycle.)

Around 3°C with humid air is where things get into terrible territory here, i.e., where you get ~ hourly defrosting.

In my specific situation, I expect the heat pump to mostly run when the temperature is around 0°C to 6°C, hence why I believe the humid climate where I live is a hindrance, rather than a help. If I were going to use it for hot water, say to heat a pool in summer, then it would be different.

I mean, it's certainly not ideal, but I suspect it wouldn't be quite as bad as you are imagining it. But if you were to ever go that route, it certainly would make sense to see whether you can set it up such that the heat pump can extract the heat for defrosting from your house.  As mentioned, mine pulls from the DHW temperature storage tank, and even defaults to resistive heat for defrost, which is kinda bad. But at higher heating water temperatures, it could potentially also pull from under-floor heating, for example. Some other heat pumps can also do so at lower temperatures. There will always be some cut-off, because a source with insufficient thermal power would risk freezing up and thus damaging the refrigerant/water heat exchanger, but if you somehow can arrange for defrost energy to be pulled from some low-ish temperature thermal mass in your heating system, then that is the most efficient way to go.

Yes, your standby consumption does sound high. I would have hoped that minimising it would have been an important design goal.

Well, yeah, the thing has two separate transformer-based (i.e., mains frequency transformers) power supplies. That seems to be the result of the thing being a bit of Frankenstein's monster built from the heating controller of an old German manufacturer of heating systems and the actual heat pump from Daikin. Certainly doesn't help with efficiency ...

I thought reading objective studies about heat pumps in areas with a similar winter climate, to my location would give me a reasonable figure. I accept that it will be different, depending on how I use the heat pump, but I would have thought it would by closer, than a general ballpark of 350%, which doesn't even take into account the local climate.

Well, the problem is that the required heating water temperatures have a significant effect on efficiency. And the 350% does take "local" climate into account. Being more accurate wrt local climate doesn't really help much if the details of the heating system remain a variable with a lot of potential variability.

I'm not sure how much I trust COP figures given by manufactures, given there are numerous different factors and they are likely to be skewed in the manufacture's favour. I've seen this with component data sheets, audio amplifiers and vehicle mileage, although I've also had instances when it's better than expected, such as my motorcycle doing more miles per tank, than expected. I suppose I'm more careful, because it would be a big investment, it's not something I'm overly familiar with and then there's the political side to it, which doesn't help.

What I am talking about here are detailed tables or graphs that specify COP at specific outdoor and heating water temperatures, not something like yearly averages. Just as with specs in component  datasheets: They tend not to be outright lies, they just tend to be measured under ideal circumstances, or typical rather than worst case, that sort of stuff. So, a Vf of 0.2 V on the title page of a data sheet might be for 10 mA for a 2 A diode, say. But the Vf vs. I graph won't be completely made-up bullshit. And the same seems to apply for heat pump specs.

I'm aware of the fact that gas stoves aren't very efficient, I've read 40% is reasonable, but don't forget electricity costs four times as much for me, as gas, so an induction hob will still be more expensive for me to run. I doubt it will make much of a difference since, only a tiny part of my energy usage is for cooking, but it's something to consider.

Yeah, my point was more that it's not worth the base fees to keep cheap gas for cooking, and that the advantage probably isn't huge. And 40% might be a bit optimistic, but it's the right ball park.

I agree. That doesn't sound expensive for the heat pump itself. It's the rest of the installation and associated labour which is expensive. Subsidies are only given if you use an approved contractor and it has to meet certain criteria. I don't even know if it's legal for you to do it yourself. I would expect a licenced refrigeration tech will be required, or at the very least an electrician with the appropriate qualifications.

IIRC, Siwastaja was talking about a monoblock system, so the refrigerant loop is a closed system within the outdoor unit and only electricity and water need to be hooked up, which is why you in most places don't need a licenced refrigeration tech, which is why they are popular with DIYers.

[Siwastaja]

Wood is clearly the cheapest per kwh if you have the space to have ton's worth delivered by truck.

Maybe / possibly somewhere, but I'd say usually not.

Fun fact: two years ago due to events that did not actually affect Finland that much in any meaningful way, people got hysteric and got an impression that cost of electricity would skyrocket to 2x, 3x, 5x, 10x, 20x, whatever insane value. Mass media poured buckets of gasoline into the fire. A few were gullible enough to get colossally expensive 2-year fixed contracts in irrational fears of increasing prices which never happened, but this con did not affect the majority of people.

In reality electricity prices rose by 25% (typical cost; energy 0.05€ --> 0.08€ /kWh, transmission+tax 0.07€ --> 0.07€, total 0.012€ --> 0.015€), but those selling wood, mainly small individuals who own some forest, in a cascading effect took advantage of the impression of expensive electricity so that m^3 of wood (around 1000 kWh including typical losses) went from like 30-40€ to well over 100€. So the individuals who criticize large corporations from causing greedflation by increasing prices by 10% for no reason themselves increased prices by 200% almost overnight without blink of an eye.

But it's free market, sure. In some cases, burning wood became more expensive than resistive electric heating with COP=1. Wood transitioned from the "cheapest" form of heating to the most expensive one!

In mid-European climate though, heatpumps easily get COP between 3.0 and 5.0, so electricity needs to be specially expensive, or wood specially cheap for wood to be "clearly the cheapest".

[pcprogrammer]

Wood is clearly the cheapest per kwh if you have the space to have ton's worth delivered by truck.

Only if you can source it cheaply, and in the Netherlands you most likely can't.

It also involves a lot of work. The truck load is usually dumped somewhere accessible and not necessarily near the space where it is stocked. So wheelbarrow to the stocking is needed and when the time comes you have to bring it inside to the burner. For sure it keeps you warm multiple times. 

I know someone who bought a truck load of of-cuts from a barrel maker down here and transported it to the Netherlands to sell it with quite a bit of profit. 

[tszaboo]

I've quickly looked up air to hot water pumps, they start at 3500. You get a subsidy, but only if they install it.

But 3500 is not that much at all IMHO. Sure I'd like to see them start at 2000, but . 3500EUR is quite easily recovered already during halfway of the lifetime of the product. It gets nasty when the heatpump is 7000 (some sort of premium brand name which isn't that much better in reality) and then the install cost another 7000, or even more.

I agree. That doesn't sound expensive for the heat pump itself. It's the rest of the installation and associated labour which is expensive. Subsidies are only given if you use an approved contractor and it has to meet certain criteria. I don't even know if it's legal for you to do it yourself. I would expect a licenced refrigeration tech will be required, or at the very least an electrician with the appropriate qualifications.

Keep in mind this is the cheapest I was to find in a particular Dutch webshop. Let's assume the installation costs and the subsidies cancel each other out. The installation is relatively painless compared to exchanging the entire heating system. Then we are at 3500 EUR investment which is only for hot water, not for heating. Upon double checking the shop, it's not on stock, might be one of those things that is never on stock to just get your attention with good price. Anyway, let's move on.
I take my summer hot water costs, it's 0.5GJ/month/person. Which is billed for me at 22EUR, excluding the fixed costs. And that's 140KWh per month energy. The same would cost me 56 EUR with direct electric heating (0.4EUR/kWh). District heating is incredibly expensive because of bad regulations here, and the monopoly, but that's just a sidenote.
Let's assume SCOP of 5 which would put this at 12 EUR/month, saving of 10 EUR per month. That would place it at 30 year ROI. For 4 person, 7.5 year ROI. This is, if I have to buy the electricity.
If I can use my own electricity to heat it up, the story changes. I can oversize my solar system by 1500KWh per year, which is about 1000 EUR investment here. About 2-3 panels will do that much. We have to assume yearly net metering for this to work. Then The investment is 4500 EUR, and the monthly saving is 22 EUR. ROI is 17 year for one person, 10 year for 2, 6 years for 4 person. That also assumes that you can place an extra 6000KWh/year solar capacity on your roof, that's about 11 panels here. That's assuming that the cheapest heatpump will even suffice for a family of 4, looking at the supplied tank size, I don't think so, it's tiny compared to what I've seen. And it's capacity is only 5kW. Net metering is also being phased out. The regulation around district heating is changing, so I expect much lower prices next years.
So I only see this to be valuable for large families.

Wood is clearly the cheapest per kwh if you have the space to have ton's worth delivered by truck.

Only if you can source it cheaply, and in the Netherlands you most likely can't.

It also involves a lot of work. The truck load is usually dumped somewhere accessible and not necessarily near the space where it is stocked. So wheelbarrow to the stocking is needed and when the time comes you have to bring it inside to the burner. For sure it keeps you warm multiple times. 

I know someone who bought a truck load of of-cuts from a barrel maker down here and transported it to the Netherlands to sell it with quite a bit of profit. 

Yeah someone in the neighborhood was buying wood for cooking in the garden and that sort of things, and I was seriously questioning his sanity when he told me how much it cost. I think there is an issue when people are just uninformed how much something should cost, and companies are praying on us with extra profit. The good prices are not easily accessible. That's why we have internet at 70 EUR a month, while the same speed and accessibility, costs less than 20 in other countries.

[tom66]

A monobloc can be installed by someone without a refrigerated gas (F-Gas) license in the UK because the system is 'pre-gassed' -- only hot water passes out of the unit.  There are other types of air conditioners which can be installed by people without F-Gas certification, like propane based mini-splits as propane has a GWP of 3 and ODP of 0 so its release into the atmosphere is not considered particularly hazardous.