What is the real story around heat pumps?

[pcprogrammer]

At the moment we are looking for a heat pump system to replace our wood burner. Asked three companies to come and give a quotation. The responses vary quite a bit.

The first one suggested that heat pumps and specifically air to water systems are no good for where we live. They would consume more energy due to colder winters up here. (~500m above sea level) His advice was to look into fuel or pellet burners. Would be cheaper to install and on par with what we now pay per year for fire wood.

Well guess again, his quotations for a fuel based system came out to be on par with a geothermal heat pump system, and the pellet based system even much higher, so no to those. Would also not solve my wife's problem with the smells.

The second one suggested more or less the same for air to water heat pumps, due to the usage of additional direct electrical heating on very cold days. Annual energy consumption would be more then twice of what a geothermal system would use.

The third one told us the opposite. Big fan of Mitsubishi Electric air to water heat pump. They would dimension it such that no additional direct electrical heating would be needed. They were also dismissive about the brand of heat pump offered by the second party. (De Dietrich) Did not receive their quotation yet, since they only came by yesterday.

The problem I found with comparing all the data is the way the coefficient of performance is specified. There are tables that show the relations between outside temperature and requested inside water temperature, but to make a more or less correct calculation on energy consumption is not easy to do. I do know how much energy our house uses based on the data collection from my computer controlled heating system.

The COP in the general data sheets is given mainly for 35 degree Celsius output water, and an input temperature that varies for the different systems. +7 and -7 for air to water systems and 0 for geothermal systems. (Based on glycol in the water)

Sure they give the seasonal COP, but again at 35 degree Celsius. On colder days how ever our house needs the water to be between 45 and 55 degree Celsius, which is possible, but at what expense.

So not an easy decision also given the fact that it is about a lot of money. (Between 15 - 40K euro)

Any thoughts on what to believe and how to make a better decision between an air to water and a geothermal system?

[RoGeorge]

Heat pumps are advantageous when there is enough temperature difference, otherwise they'll become less efficient, or might not work at all.  If a company selling heat pumps advice against buying a heat pump, better listen to them.  Won't work.

Anyway, if you decide to replace the current wood burner, do not remove it, and keep a way to switch back to burning wood if necessary.  Heat pumps do not work without electricity, and electricity can not be stored, while a pile of wood is trivial to store indefinitely.

[ebastler]

Here's an online calculator with data for many real-world heatpump units, which lets you select the water output temperature and plots efficiency as a function of building heat loss. It assumes British weather though, which -- depending on where you are -- may distort the calculations somewhat. (Since you mentioned 500m altitude, I assume that's not in the Netherlands?)

https://tools.bregroup.com/heatpumpefficiency/index.jsp

[pcprogrammer]

Heat pumps are advantageous when there is enough temperature difference, otherwise they'll become less efficient, or might not work at all.  If a company selling heat pumps advice against buying a heat pump, better listen to them.  Won't work.

Anyway, if you decide to replace the current wood burner, do not remove it, and keep a way to switch back to burning wood if necessary.  Heat pumps do not work without electricity, and electricity can not be stored, while a pile of wood is trivial to store indefinitely.

Thanks for the input, but my central heating system as is also needs electricity to work 

The task of feeding the wood burner is daunting for me with my Fibromyalgia, and my wife hates the smell it gives. She loves to work outside in the garden and that becomes difficult on the days I have to burn the wood. In the colder periods it needs to burn every other day.

It is not that a heat pump would not work, it is a question about who is telling the "truth". Geothermal will work for sure, but is more expensive due to in our case the need for vertical loops. Drilling is expensive.

With geothermal the source is far more stable in temperature then when using air to water. But the COP goes down when you need 45 or 55 degrees Celsius of heating water to fulfill the need of the house. So both systems are less efficient when it is cold outside. Hence the seasonal COP being lower then the COP in ideal circumstances.

The question is how big the difference is in annual energy consumption between the two systems. Air to water and geothermal. I know it depends on a lot of factors, like the local climate, the size of the house, the insulation of the house, etc.

Another issue is the noise. We are very sensitive for it, and with the large fans in the external units the make more noise. There are a couple of installations in the village and when we walk by it bothers us. Not sure how it would be inside the house. The geothermal units are well insulated and produce not a lot of noise.

It is hard to make a well informed decision.

[pcprogrammer]

Here's an online calculator with data for many real-world heatpump units, which lets you select the water output temperature and plots efficiency as a function of building heat loss. It assumes British weather though, which -- depending on where you are -- may distort the calculations somewhat. (Since you mentioned 500m altitude, I assume that's not in the Netherlands?)

https://tools.bregroup.com/heatpumpefficiency/index.jsp

Thanks.

Indeed we live in the middle of France.

Edit: We are Dutch though, that is why I use the Dutch flag. Not out of chauvinism, just to show that Dutch is my native language. 

[Bicurico]

Please check this channel, specifically the videos about heating and heat pumps.

It is in German but I think you would understand what they are saying.

https://m.youtube.com/@ProfRieck

After watching many videos on the subject, mainly for the political aspect of it, I would say that heat pumps are a scam in most cases. There might be some use cases, where they make sense, but in most they don't.

[Zarhi]

Short answer:

Upgrade Your utility power to 16 kW or more. Install electric boiler for 1500 euro and keep rest of the money to pay electric bills for next 7+ years.
Keep Your wood burner in event of electricity fail and install backup UPS for circulation pump.

Think for additional external insulation of house if possible. Upgrade windows with 4 Season Low-e 3 layer glasses.

Long answer:

Air source heat pump does not have problems with outside temperature, most will keep COP >2 and 50+ output (R32, R290) even in less that -10 outside.
They have problem with humidity. With outside temperatures from -5 to +5 COP will drop to <1, because outside evaporator freeze in minutes. Defrost cycle use internal heat to melt the ice.

Water source heat pump will need at least 1 to 3 kW to pump water from a well. If water level fall too deep, heat pump will stop completely. Sand and mud from a well will clog filters very fast. These filters will need cleaning every few days for first year ot two until a well settles down. Also a well water temp must be at least +7 and have 2 to 5 m3/hour capacity in winter.

Heat pumps compressors have expected life of about 7 to 10 years. Anyway after 5 years they will change refrigerant type and current compressors will be not available as spare part. So be prepared to have another 20k+ euro for new heat pump in about 7 years.

Make an simple calculation: If heat pump cost 20k euro to install and need to heat 6 monts/year:

For 7 years: 20000/42 = 476 euro/month + electric bills.
For 10 years: 20000/60 = 333 euro/month + electric bills.

[Kleinstein]

The heat pump can work well when it is not very cold. So it could make sense to keep the wood burner as an alternative and support for the few very cold days, when the heat pump is not working that well and high temperatures are needed. In a combination a air - water solution likely makes more sense. The main advantage of the geothermal heat pump is a more even temperature to start with. This is good for the few cold days, but bad for the not so cold days.
For the ground heat pump it really depends on the local conditions. The ground and available area can effect the costs a lot. The COP also changes with the size of the system and over the year, when the ground cools. On may have to expect the ground to reach freezing - without it the capacity is relatively limited.

Some upgrades to the house can make sense, to lower the needed temperature from the heat pump. This could be as little as fans under the radiators that are borderline sized.

[pcprogrammer]

Wow, these are grim perspectives.

I'm not someone who stands on one nights ice and do in depth research. That is why I asked this question here. I know this forum is more about electronics, but heat pumps are very technical too.

For geothermal there are basically three variants. Horizontal capture with a couple of long loops buried in the ground, vertical with closed loops in drill holes up to 100m deep and vertical with a well. The latter indeed needs filtering and have sufficient flow to sustain the pump. It does use a separate water pump to bring up the water but has, according to the documentation, a higher efficiency with the heat pump.

With air there is indeed the freezing of the evaporator that needs energy for defrosting. When resistance heating is used the COP will drop dramatically. But the latter seems to be optional in many systems.

The house is reasonably well insulated. Average annual energy consumption for heating the house, based on my experience with the wood burner is ~16500 KWh. Worst day average this season is about 8.75 KWh. It is a big house with 240m2 of living surface.

[Zero999]

What's the mean temperature in the coldest months?

My understanding is, the problem with heat pumps is are least efficient, when the air temperature is above freezing and it's humid. Moisture condenses on the evaporator and freezes, causing it to ice up. This can be alleviated by only running at night, when its colder, but much of Southern and Western Europe's average overnight lows in the coldest months are still above freezing.

Perhaps a more efficient wood gasifier system is a good idea? Wood is a very dirty fuel, which releases lots of nasty carcinogens such as benzine and particulates, when not completely burnt. Gasifier systems pyrolyse the wood. to release flammable gases, which are cleaned before burning.

[Gyro]

Skill Builder channel has a nice down to earth approach, with a healthy hint of skepticism about government initiatives. He has recently done a series of videos on viewer 'John', who has been through a nightmare with his heat pump and enough maintenance and other bills to have paid his energy costs for years to come. If you get them in chronological order, it covers the initial problems and then analysis by several more experienced companies and solutions.

I have included the search term 'Heat pump John'...

https://www.youtube.com/@SkillBuilder/search?query=Heat%20pump%20John


P.S. He also has a couple of videos on wood burners.

[pcprogrammer]

What's the mean temperature in the coldest months?

Over here based on my own measurements for this season the lowest average is about -4 degree and the total somewhere around 5 or 6 degrees Celsius. (day and night average) It is not as cold anymore and we hardly see snow. Last winter season maybe one week or so, and this season up till now none.

Perhaps a more efficient wood gasifier system is a good idea? Wood is a very dirty fuel, which releases lots of nasty carcinogens such as benzine and particulates, when not completely burnt. Gasifier systems pyrolyse the wood. to release flammable gases, which are cleaned before burning.

Pellet burners, I think, are based on this principle and will be cleaner then what we have, but these installations are very expensive. They also need regular upkeep like removing ashes and still produce fumes. A problem is that when we use our extractor hood the fumes are drawn down the chimney of a small wood stove we have in our kitchen/living area, despite the other ventilation holes in the house. This chimney is sitting right next to the one from the basement for the big wood burner and would have to be used for the pellet burner too. 

[Zarhi]

My understanding is, the problem with heat pumps is are least efficient, when the air temperature is above freezing and it's humid. Moisture condenses on the evaporator and freezes, causing it to ice up. This can be alleviated by only running at night, when its colder, but much of Southern and Western Europe's average overnight lows in the coldest months are still above freezing.

Air humidity does not drop to 0% below 0 °C. Evaporator temperature is below -30 °C and will build ice even in -10 °C "dry" air.

[nctnico]

Heat pumps are advantageous when there is enough temperature difference, otherwise they'll become less efficient, or might not work at all.  If a company selling heat pumps advice against buying a heat pump, better listen to them.  Won't work.

Anyway, if you decide to replace the current wood burner, do not remove it, and keep a way to switch back to burning wood if necessary.  Heat pumps do not work without electricity, and electricity can not be stored, while a pile of wood is trivial to store indefinitely.

Thanks for the input, but my central heating system as is also needs electricity to work 

The task of feeding the wood burner is daunting for me with my Fibromyalgia, and my wife hates the smell it gives. She loves to work outside in the garden and that becomes difficult on the days I have to burn the wood. In the colder periods it needs to burn every other day.

It is not that a heat pump would not work, it is a question about who is telling the "truth". Geothermal will work for sure, but is more expensive due to in our case the need for vertical loops. Drilling is expensive.

With geothermal the source is far more stable in temperature then when using air to water. But the COP goes down when you need 45 or 55 degrees Celsius of heating water to fulfill the need of the house. So both systems are less efficient when it is cold outside. Hence the seasonal COP being lower then the COP in ideal circumstances.

How about installing underfloor heating? That way you don't need the water to be very hot and you get better efficiency from there on.

And how about getting an LNG tank and use a natural gas burner? It sounds like you are retired so you don't need a solution which lasts for another 50 years.

Either way, I'd look at a solution which is most commonly used in your area. That way availability of parts and maintenance will be way better compared to getting some kind of outlandish setup which nobody knows about. As far as my experience goes, installers of heating systems know less than zero about what they are doing.

[fourtytwo42]

I can tell you from actual experience of an "ECO" office building heated by ASHP that in winter here in the UK they are useless!! Meaning they spend a huge proportion of time in energy gobbling "defrost mode" defrosting the outdoor unit, not just once but all day on a cold day, so just when you need the heat there is none.

Whats wrong with a gas or oil condensing boiler ?

I wouldn't touch an electric boiler with a bargepole, those poor people in Scotland who were experimented on with the things complained loudly of horrendous electricity bills.
Don't be tempted by fancy electric tariffs either, here today, gone tomorrow.

You might call me skeptical but if I am to make a large investment and trust my comfort to something I investigate very thoroughly, especially if they are being pushed by politicians whom as we all know are not adverse to a bit of industry/expert-crank lobbying 

[Zero999]

My understanding is, the problem with heat pumps is are least efficient, when the air temperature is above freezing and it's humid. Moisture condenses on the evaporator and freezes, causing it to ice up. This can be alleviated by only running at night, when its colder, but much of Southern and Western Europe's average overnight lows in the coldest months are still above freezing.

Air humidity does not drop to 0% below 0 °C. Evaporator temperature is below -30 °C and will build ice even in -10 °C "dry" air.

It's true that air below freezing still contains some water, but going from what I've read, it's much less of a problem, when it's below freezing, especially once the ground is frozen, so no water can evaporate into the air. I've noticed that in winter, when the wind is blowing from the east, off the cold continent, the air is do dry, ESD is a problem and I feel my sinuses drying up.

[Siwastaja]

Get a sensibly priced monoblock (refrigerant is sealed in at factory, only water pipe connections are needed) and have a plumber/electrician install it for you. For example Swedish company ES imports Chinese Amitime heatpumps. Mine, a 9kW unit cost less than 3000EUR with all the accessories I had to get. I installed it myself. Panasonic also does some Monoblock units which are not more expensive.

By all means leave the existing burner. You can choose to use it during the coldest days, and it's a good idea to have a spare system. I left my dual oil-wood boiler and keep using it; the 9kW ES/Amitime monoblock reaches approx. COP=1.5 around -15degC outdoors / +40degC water; if this condition lasts longer than a day or two, then I switch to oil/wood.

People in much colder climates use heatpumps no problem. Netherlands is obviously totally fine. The only exception is if your distribution system (radiators) is super crappy (i.e. small surface area) i.e. requires high water temperature already in modest weather. You may be able to replace some radiators for bigger ones. That's what I did, radiators are not expensive.

Finally, just normal air-to-air units might be a better idea, especially if your home has large central "open concept" area. Models designed for heating in colder environments, not the cheapest ass "mostly for cooling" units. A good one is still below 1000EUR. They don't have the problem of high distribution temperature, and you can also use them for summertime cooling. You can probably get them for less than 1500EUR installed so if air-to-water guys give ridiculous quotes over 15000EUR, you could get five(!) air-to-air units for half(!) the cost, and get better COP!

I would guess actual SCOP (annual COP correctly weighed for more consumption during coldest months, calculated simply annually_produced_heat / annually_consumed_electricity) for Netherlands is at very least 2.0 for super crappy mini radiators, 3.0 for OK-ish radiators and 4.0 for underfloor or fan coil distribution.

There are two simple questions for you:
* What is the coldest "not unusual" temperature in your region which you experience every winter, for more than a few hours a day, for more than a few days? E.g. something that lasts for a week or two (nearly) every winter,
* In said weather condition, to maintain comfortable room temperature, how hot is the water flowing into the radiators - you can measure it using infrared thermometer (bonus point for measuring the water temperature as it leaves the radiators)

Answers to these questions vary so much it's hard to guess.

[pcprogrammer]

How about installing underfloor heating? That way you don't need the water to be very hot and you get better efficiency from there on.

And how about getting an LNG tank and use a natural gas burner? It sounds like you are retired so you don't need a solution which lasts for another 50 years.

Either way, I'd look at a solution which is most commonly used in your area. That way availability of parts and maintenance will be way better compared to getting some kind of outlandish setup which nobody knows about. As far as my experience goes, installers of heating systems know less than zero about what they are doing.

We already have underfloor heating and low temperature radiators in the rooms that don't have underfloor heating. That is not the issue. My 8 years with the wood burner system with a 5000 liter heat storage has shown that on the really cold days the system wants ~55 degree Celsius coming from the heat storage mostly for the radiators to keep the rooms up to set temperature. On warmer days it can work with lower temperatures down to 30 degree Celsius.

And indeed it does not have to last for 50 years. I'm 60 and the wife is 59, so another 25 or so, if we manage to keep living here.

Down here a lot of fuel (diesel) is used for heating, but the government wants it gone, and we thought the sale of these type of burners had stopped in 2022, but one of the installers told us the regulation has been delayed.

Gas could be an option, but it is not used much around here.

[Siwastaja]

It's true that air below freezing still contains some water, but going from what I've read, it's much less of a problem, when it's below freezing, especially once the ground is frozen, so no water can evaporate into the air. I've noticed that in winter, when the wind is blowing from the east, off the cold continent, the air is do dry, ESD is a problem and I feel my sinuses drying up.

A practical example: my ES/Amitime 9kW unit runs defrost cycle around 20-25 times a day with temperatures around 0degC. This is the worst case. At -15 .. -20 degC, the heatpump easily makes 2 - 3 hour stretches so just around 10 defrosts per day, even when the RH is the same or even higher.

If the heatpump implements detection of frost properly, defrosting is not a dealbreaker even in very cold environment, because the situation indeed gets better as it gets colder. There are stories of bad products which overdetect the need of defrosting, e.g. doing it every 40 minutes in -20degC, which then totally kills the COP.

[nctnico]

How about installing underfloor heating? That way you don't need the water to be very hot and you get better efficiency from there on.

And how about getting an LNG tank and use a natural gas burner? It sounds like you are retired so you don't need a solution which lasts for another 50 years.

Either way, I'd look at a solution which is most commonly used in your area. That way availability of parts and maintenance will be way better compared to getting some kind of outlandish setup which nobody knows about. As far as my experience goes, installers of heating systems know less than zero about what they are doing.

We already have underfloor heating and low temperature radiators in the rooms that don't have underfloor heating. That is not the issue. My 8 years with the wood burner system with a 5000 liter heat storage has shown that on the really cold days the system wants ~55 degree Celsius coming from the heat storage mostly for the radiators to keep the rooms up to set temperature. On warmer days it can work with lower temperatures down to 30 degree Celsius.

And indeed it does not have to last for 50 years. I'm 60 and the wife is 59, so another 25 or so, if we manage to keep living here.

Down here a lot of fuel (diesel) is used for heating, but the government wants it gone, and we thought the sale of these type of burners had stopped in 2022, but one of the installers told us the regulation has been delayed.

Gas could be an option, but it is not used much around here.

Well, going for a diesel burner is a no-brainer then. The French will be hell-bound on keeping those systems as these are likely cheap to operate, so they will be around long enough for you.

[Siwastaja]

We already have underfloor heating and low temperature radiators in the rooms that don't have underfloor heating. That is not the issue. My 8 years with the wood burner system with a 5000 liter heat storage

Given underfloor + low temperature radiators, your situation is optimal for air-to-water heatpump.

I would also consider utilizing your existing energy storage system to benefit from varying market prices of electricity (if such contracts are available in NL, I don't know). I have 1200-liter storage and would kill to have your 5000-liter reservoir! That's a huge asset on its own.

[pcprogrammer]

There are two simple questions for you:
* What is the coldest "not unusual" temperature in your region which you experience every winter, for more than a few hours a day, for more than a few days? E.g. something that lasts for a week or two (nearly) every winter,
* In said weather condition, to maintain comfortable room temperature, how hot is the water flowing into the radiators - you can measure it using infrared thermometer (bonus point for measuring the water temperature as it leaves the radiators)

Answers to these questions vary so much it's hard to guess.

To answer these questions I have to search my backed up databases from the heating system. I have a Raspberry PI measuring and controlling the whole system. All the pipes have sensors taped to them. Not super precise but it gives insight in what is going on. At the moment two sensors are dead so the readings of my departure of the heat storage and after the mixing valve are gone, but these don't matter that much.

I have a mixing valve in the system to reduce the >85 degrees Celsius the storage can reach, down to the needed temperature. There is a guard system to make sure the underfloor heating stays below 40 degrees Celsius.

Attached is a screen capture of the web interface I have for it.

[watchmaker]

The cost equations differ across the world.  I am in the US, about 150 miles north of Boston.  Here in New Hampshire electricity rates are among the highest in the US. 

Oil is also not cheap and then there is the fossil fuel thing.

We decided to install a solar system for our electricity this coming summer.  In the interim, we installed a heat pump in late 2022.  It is used in conjunction with our oil-fired hot water forced-air furnace.

While of course our electricity went up, our oil bill was more the halved.  We have noticed the heat pump still contributed even at -3 degrees F. 

Also, unlike the old heatpumps (had one in the 90s), this system is very comfortable.  We installed a humidifier with it and keep the house at 40% so we are happy at 62 degrees F.

Hope this helps.

[Siwastaja]

To answer these questions I have to search my backed up databases from the heating system. I have a Raspberry PI measuring and controlling the whole system. All the pipes have sensors taped to them. Not super precise but it gives insight in what is going on. At the moment two sensors are dead so the readings of my departure of the heat storage and after the mixing valve are gone, but these don't matter that much.

I have a mixing valve in the system to reduce the >85 degrees Celsius the storage can reach, down to the needed temperature. There is a guard system to make sure the underfloor heating stays below 40 degrees Celsius.

Nice, I would recommend this process:
* Buy monoblock heatpump,
* Connect monoblock's water inlet in parallel with the radiator/infloor heating return pipe, the one that connects to the bottom of the 5000l tank,
* Connect monoblocks water outlet near the top of 5000l tank.
* Normally, let the heatpump control the water output temperature based on curve from outdoor temperature, and force the mixing valve fully open to avoid loss of temperature (which costs you some COP)
* When transitioning to wood, just shut down the heatpump and let the mixing valve gradually close to regulate the water temperature,
* When transitioning back to heatpump, just turn it on and let it start heating once the big tank cools down to the setpoint of the heatpump. Let the mixing valve open and force it fully open again.

This is how I do it.

[pcprogrammer]

We already have underfloor heating and low temperature radiators in the rooms that don't have underfloor heating. That is not the issue. My 8 years with the wood burner system with a 5000 liter heat storage

Given underfloor + low temperature radiators, your situation is optimal for air-to-water heatpump.

I would also consider utilizing your existing energy storage system to benefit from varying market prices of electricity (if such contracts are available in NL, I don't know). I have 1200-liter storage and would kill to have your 5000-liter reservoir! That's a huge asset on its own.

Heating 5000 liters with my 38 KWh wood burner takes between 10 to 12 hours and on the cold days it only lasts for 36 hours coming from ~85 down to ~30 degrees. With a heat pump you probably won't reach much higher then 55 to 60 degrees and it will have to work the whole night to get there. It would save on the high charge days though. We live in France, but are Dutch and here we have a setup from the EDF called tempo. On 22 days in the winter electricity is 3 times the normal price during the day. On 44 days the reduction is about 20% during the day and on the remainder it is about 30% reduction. During the nights there is always a reduction but varies depending on the type of day ranging from ~15% to 40%.

But keeping on the wood burner for the 22 expensive days is not an option for me. I'm struggling with it as is and it is not going to get better unfortunately. That is the whole reason for the change.