Anybody in northern europe/UK or other cold place running air source heat pump

[fourtytwo42]

Hi all looking to find a way to reduce my winter fuel costs, I had seen some ASHP's apparently spending a lot of time defrosting but then I see claims of 2.0 for COP even at -1C so maybe there not so bad. Here in the UK there is still a subsidy available so I am kinda tempted if nothing else to replace the woodburner. Anybody got any small scale domestic installation they want to share (I am thinking 4-16Kw range air heating only).
My oil costs on my elderly boiler are about 8.2p/Kwh and including the subsidy looks like ashp could be around 7.2p/Kwh (capital amortised over 5 years).

[sokoloff]

In Boston, MA area (97.5% heating design temperature of 9°F/-13°C), air source heat pumps are not used as the sole source of heat for most buildings, but are commonly used as supplemental, either with combustion appliances for backup, or with electric strip [resistance] emergency heat. It's still cost effective on a seasonal basis, even with electricity costing $0.20/kWh.

To be frank, I suspect a lot of the draw is that with the reversing valve, it allows for summer air-conditioning, meaning an end user is willing to give up some in-winter efficiency for the year round comfort and lack of window-shakers in the summertime.

[rhb]

I live in central Arkansas.  Most of the time a heat pump would work just fine, but we occasionally have cold spells where it gets down to -10 C.  So while heat pumps are used here, they are not as popular as say Dallas or Houston.  I'm also sitting in the middle of the Fayetteville shale dry gas play, so natural gas prices are low.

If you have an auxiliary  heat source and your average temperature is above 0 C then an air exchanger should be a good setup.  If you have the space, a geothermal system with horizontal heat exchangers below the frost line is a relatively inexpensive installation.   Drilling wells tends to cost a lot more, mostly because the equipment has to travel a long way to the job.  Backhoes are much more common than rotary drilling rigs most places.  Installing a horizontal heat exchanger in the ground is also a great opportunity to build a really good garden plot when you backfill.

If you're going to have a heat pump for heat, you might as well have it for cooling also.  It's just some additional valving and controls.

[jc101]

We have a Daikin ASHP split unit (11kW total) that can run 3 indoor units, we only have two fitted.  It basically is used to heat/cool a conservatory and ground floor of the house.  In the winter we will often flip this on for heating rather than run the Combi Boiler, as with solar panels running it is effectively free.  With both 3kW indoor units pumping out heat I've never seen it draw more than 1.75kW of electric (we have real time power monitoring as part of the solar PV system).

The lowest external temp we've had it on was -10 (which is pretty cold for Cambridge) and it pumped out plenty of heat, it did defrost itself when it needed to but not enough to cause a problem.

I know a couple of people who have been mulling installing a Daikin Altherma system to replace old oil boilers, they have no Gas where they are and don't want a gas pressure vessel installed.  These can run a typical wet CH system and create hot water much more efficiently that oil.  Worth taking a look at.

[kaz911]

my dad put a Single Panasonic SZ9 in his 80 sqm house in Denmark to "complement" his wood burner and stop using the electric radiators.

So far it has been the coldest winter in DK in a long time - and his costs are down to 1/3 compared to the year before - while using the wood burner a LOT less.

The Panasonic and Daikin factories have made great progress in low temperatures ASHP's.

I got a Daikin Ururu Sarara for my office - and it was electric heat before - and that cut my electric bill a lot as well. 

But with both Daikin and Panasonic - the remote and internet integrations are both terrible. Kind of 1990's hardware roughly connected to the Internet with a hack'ed interface.

[fourtytwo42]

Thank you for all your replies, I should have added it is unlikely if ever it would be used for aircon as we don't need that here in the UK except for a way of wasting fuel and polluting the atmosphere in cars  I seem to remember there is not much chance of a straight swap for a boiler as the hot water flow temperature has to be low to maintain anything like a reasonable COP so either you have to go for underfloor heating or vastly oversized radiators. That is why I am considering air to air.
I am interested in supplying 1.5Kw to an ASHP in winter from PV, may I ask what sized PV system is that, 10Kw+ ?

These websites (Daikin & Panasonic) are a bit of a nightmare to navigate and I have yet to find COP charts for any product on either of them Apparently I heard somewhere they are even more sensative to external humidity than temperature (in heating mode). I see there are various convelutions of COP on data sheets now presumably invented to obscure the truth so definetly a case of tread very carefully and spend plenty of time investigating methinks.

I have no doubt they are very competative with electric heating BUT I feel ASHP is going to have a tough time competing with my elderly oil boiler Typical winter temperatures here are -10C or colder for days at a time, -5C for weeks at a time and below zero for a couple of months and of course thats when the maximium heating power is required.

Back to trying to find real information in websites vs marketing bs!!

[coppice]

Has anyone here tried heating their home with a gas powered air sourced heat pump? I've seen these things at exhibitions, and they seem interesting, but I haven't seen anyone comment about how they work out in the real world.

[coppice]

Hi all looking to find a way to reduce my winter fuel costs, I had seen some ASHP's apparently spending a lot of time defrosting but then I see claims of 2.0 for COP even at -1C so maybe there not so bad.

I've used Daikin heat+cool air cons in Hong Kong, where the temperature can go down to 4C or 5C for a few days in the winter. The exterior unit goes way below zero when its operating, but those cold spells are also periods of low humidity. Things never freeze over, and the appliances work great.

in the UK the cold spells are also periods of near 100% humidity. It puzzles me how an ASHP could function in those conditions. Once one gets frozen over it just won't defrost if the ambient temp is below 0C, so its stuck until the weather warms up. Do the systems supplied in the UK have a thawing cycle, or something?

[fourtytwo42]

in the UK the cold spells are also periods of near 100% humidity. It puzzles me how an ASHP could function in those conditions. Once one gets frozen over it just won't defrost if the ambient temp is below 0C, so its stuck until the weather warms up. Do the systems supplied in the UK have a thawing cycle, or something?

This is the dreaded "defrost cycle" where the heatpump works in reverse to heat the external unit thus de-icing it. Of course the effect is to reduce the effective COP and dramatically reduce the heat delivered into the house! Quantifying this aspect is what concerns me

[jc101]

Our Solar system is 2.5kWp, so we only use the ASHP on the sunny days, so there is an initial hit where it gets going then it is just topping up.  According to the smart meter still cheaper than turning on the Combi on bright days.

A few years ago now I was staying in a converted railway carriage for a few days ahead of going to a wedding.  It was a steady -10 to -18 outside at the time and the gas boiler in the carriage blew a pipe whilst we were there (interesting design flaw, but that is another story!).  It also had ASHP mainly for Air Con in the summer months, but that became our only heating for 3 days.  The outdoor unit was under the carriage and it did keep us warm, every few hours you would hear it go into a defrost cycle for 10 mins or so, then switch back to heating.  It had its work cutout as you can imaging the insulation in the carriage wasn't the best - but it managed very well considering.

A number of new buildings I've worked on in Cambridge recently have deployed GSHP, once tuned they have been very effective at keeping the running costs for the buildings down. The pipes are within the piles under the buildings.

When I put the ASHP in the house, and a smaller one in my office, I gave up with the websites and just went to see a couple of local installers, they can normally get more detail out of the manufacturer.  Following a few discussions both my systems are Daikin and haven't missed a beat in the years they have been installed.  Follow up on any references they give and ask the owners how they get in, it's the only way to really know how a system performs.

[coppice]

in the UK the cold spells are also periods of near 100% humidity. It puzzles me how an ASHP could function in those conditions. Once one gets frozen over it just won't defrost if the ambient temp is below 0C, so its stuck until the weather warms up. Do the systems supplied in the UK have a thawing cycle, or something?

This is the dreaded "defrost cycle" where the heatpump works in reverse to heat the external unit thus de-icing it. Of course the effect is to reduce the effective COP and dramatically reduce the heat delivered into the house! Quantifying this aspect is what concerns me

I don't think the models Daikin sells in Hong Kong have a defrost function. You have to do really dumb things to get a radiator to freeze over there. In the UK its not even hard to get an air con to freeze over on a hot rainy day in summer, but I have no experience of heat+cool air cons in the UK providing winter warmth.

[fourtytwo42]

Our Solar system is 2.5kWp, so we only use the ASHP on the sunny days, so there is an initial hit where it gets going then it is just topping up.  According to the smart meter still cheaper than turning on the Combi on bright days.

Now I understand thank you

When I put the ASHP in the house, and a smaller one in my office, I gave up with the websites and just went to see a couple of local installers, they can normally get more detail out of the manufacturer.  Following a few discussions both my systems are Daikin and haven't missed a beat in the years they have been installed.  Follow up on any references they give and ask the owners how they get in, it's the only way to really know how a system performs.

That sounds like very good advice But I will also keep digging and try find some figures.....

[fourtytwo42]

I don't think the models Daikin sells in Hong Kong have a defrost function. You have to do really dumb things to get a radiator to freeze over there. In the UK its not even hard to get an air con to freeze over on a hot rainy day in summer, but I have no experience of heat+cool air cons in the UK providing winter warmth.

I remember the extremely high humidity in HK,but as they were working as aircon it was the indoor units that were in danger of freezing up, as you say I cannot recall any particular defrost arrangement, just the usual condensate drain.

EDIT I found this indipendent report by the energy savings trust (UK) that makes interesting reading though it only considers water output systems http://www.energysavingtrust.org.uk/sites/default/files/reports/TheHeatisOnweb%281%29.pdf it also explains some of the new presentations of COP

[kaz911]

I think Norwegian consumer reports have tests of devices that work well in Norway

My dad used that for his selection.

[coppice]

I remember the extremely high humidity in HK,but as they were working as aircon it was the indoor units that were in danger of freezing up, as you say I cannot recall any particular defrost arrangement, just the usual condensate drain.

The humidity in HK is very high for most of the year. However, during the short period when domestic heating is a good idea the humidity can be very low. Low enough some people get cracked skin and nose bleeds.

Most air cons in HK are still of the cooling only type. Each year when the 2 weeks of cold arrive people empty the shops of any heaters, and say they will do something about properly heating their homes before next year. Then it warms up, and they forget about it. Most of the winter is maybe 15C. It only goes down to a temperature where you really want some domestic heating for a week or two, usually around Chinese new year.

[fourtytwo42]

You know I am discovering this whole heat pump thing is like solar but a hundred times worse!! The PV panel manufacturers are really good guys for publishing exacting specs for there panels but its hard to find good reliable insolation data for your location till eventually you turn up government sponsored survey data that allows you to estimate the potential performance. For heatpumps the manufacturers are total garbage, they don't publish proper specifications for there equipment and suggest you should trust the opinion of there installers which if PV installers are anything to go by know very little about the technology and simply want to make a fast buck! So I have challenged two of the manufacturers (Panasonic & Daikin) to provide proper specifications, let's see if they wan't to be honest and truthfull

I see many comments around both in support and against, I have to say like solar a lot of the supporters are those with systems installed after all we are only human I have DIY solar but so far it's crap from an economic standpoint at 3 times the cost of oil (don't tell the wife)!

Although my solar system is not good on numbers it's been an enjoyable hobby especially as I am retired, so somewhere in these things is a crossover between hobby/saving the planet and hard economics so the comparison is rather hard to quantify IMOP

[JohnnyMalaria]

I have an HVAC system for my house here in North Carolina (as does everyone else). It's great in the summer. It's okay in the spring/autumn but it sucks in the winter. The best temperature increase you can expect (measured between outside air and the air coming through the registers) is about 20F or so. Cooling by 20F in the summer is fine but trying to heat air at or below freezing to room temperature requires the auxiliary heat (i.e., forcing the air through what is nothing more than an electric bar fire). Another issue is that the heated air has a lower relative humidity that outside. My house gets horribly dry. Nasal passages dry up, skin flakes etc even with humidifiers. During a prolonged cold spell (5 days below freezing) I will have additional space heaters running as well. This past January my electricity bill for the month was $400.


I'd suggest you stick with a boiler (if you mean central heating/radiators etc). I miss having those to hang my clothes on to dry

And I'd expect maintenance/repair costs would be high in the UK.

[fourtytwo42]

The best temperature increase you can expect (measured between outside air and the air coming through the registers) is about 20F or so.

Ahh but were disgusting here (at least in my household) we re-circulate the air  so we only have to add some heat via the refrigerant circuit from outside Re-circulation is so ingrained we even use a de-humidifier in winter to avoid opening the windows

The boiler is dammed good, the flue heats the central lump of brickwork in our house like a heat store, what do people do without an airing cupboard with a big hot water cylinder in it and lots of hot pipes !! We could never manage winter without that!!

[james_s]

I live in the Northwestern US where the weather is very similar to the UK. I have an air source heat pump in tandem with a gas furnace and mine is set up to run the heat pump down to an outdoor temperature of about 35F and then switch over to the gas furnace which minimizes the annoying defrost cycles. A more conventional heat pump installation will use supplemental electric elements that come on with the defrost cycle to minimize the effects. Detecting frost on the outdoor coils is a difficult engineering challenge so most use a simple timer coupled with a defrost termination thermostat attached to the coils and typically this results in more frequent defrosting than is really necessary. In the process of experimenting with this I have also turned my outside coil into a solid block of ice. The thing a lot of people don't like about heat pumps is the air coming out of the register is not nearly as warm as you get with a conventional furnace. It warms the house up but it doesn't feel like hot air. The BTU/hr rating is much lower than you'd normally have with a furnace so the cycle times are longer. Short cycling gives a significant efficiency penalty.

For me the primary use is air conditioning in the summer. People say it's not really necessary up here and very few have AC, but for the month or two of hot weather we typically get in a year it's totally worth it to be able to sleep in comfort rather than laying on top of the sheets sweating. At the peak of summer I typically spend about $20 a month in electricity running the AC for a ~2300 sq-ft house, a small price to pay IMO.

[JohnnyMalaria]

At the peak of summer I typically spend about $20 a month in electricity running the AC for a ~2300 sq-ft house, a small price to pay IMO.

Did you miss a zero there? Good grief, Charlie Brown, I spend that much when it's 70F outside! Must be a better breed of electrons they sell around these here parts.

[james_s]

Did you miss a zero there? Good grief, Charlie Brown, I spend that much when it's 70F outside! Must be a better breed of electrons they sell around these here parts.

No it's about $20, maybe $30 on a really hot month. My typical gas/power (combined) bill is about $80/month in the summer and $130 in the winter. Electricity is around 8.2c/kWh and gas was last I checked around $1/Therm. The heat pump is a 3 ton (36k BTU) 14 SEER unit that typically runs for a few hours a day to keep the temperature down. My house is surrounded by large trees so that does likely help considerably in the summer as it receives relatively little direct sun.

[nctnico]

For me the primary use is air conditioning in the summer. People say it's not really necessary up here and very few have AC, but for the month or two of hot weather we typically get in a year it's totally worth it to be able to sleep in comfort rather than laying on top of the sheets sweating.

For that purpose I have a large tree in front of my house where our bedroom is.

[Fungus]

For me the primary use is air conditioning in the summer. People say it's not really necessary up here and very few have AC, but for the month or two of hot weather we typically get in a year it's totally worth it to be able to sleep in comfort rather than laying on top of the sheets sweating.

For that purpose I have a large tree in front of my house where our bedroom is.

You climb out the window and sleep in the tree? 

[NiHaoMike]

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[Nauris]

Hi all looking to find a way to reduce my winter fuel costs, I had seen some ASHP's apparently spending a lot of time defrosting but then I see claims of 2.0 for COP even at -1C so maybe there not so bad.

I have seen claims of 2 COP at -30C!

But typically you get COP of 3 at 0C including defrosting.
They are really popular here many houses even have more than one.

One big importer get some units measured by independent lab attached are some results (vertical axis is avarage output power/input power (COP))
First Mitsubishi Electric MSZ-FH35VE we have two of these in this house


Second MSZ-LN25VGW, the newest and greatest one.


Figures include defrosting, outdoor relative humidity about 80%, units are operating at partial load above aprox. -10C outdoor temperature, room temperature 20C
Further details are in the report but it is in finish.

Here is more graphs and models(in finish):
https://www.scanoffice.fi/fi/tuotteet/tuoteryhmat/ilmalampopumput/raportit-ja-sertifikaatit/vttn-testiraportit

[CatalinaWOW]

As OP says the performance depends heavily on the details.  I am NW US and at my location winter temps average around 0C for many weeks, with dips to -5 to -8 C.  All at high relative humidity.  So not too different from OPs conditions.  My house has older (I wasn't there when they were installed but they appear to be late 1980s to 1990s units) air source heat pumps and the cost of operating them caused me to switch to fuel based sources.  Way too much time was spent defrosting.  Might work better with newer technology pumps, but I couldn't prove it to myself.

They are handy for the few hot days of the summer which can't be dealt with with shade, good insulation, thermal mass,  overnight cooling and the like.  And because site details and the house efficiency details work for me the cost of operation is similar to what james_s mentions.

[Nauris]

Might work better with newer technology pumps, but I couldn't prove it to myself.

It certainly does. There has been very big leap forwards since '90. Like actually working defrosting, inverter driven twin rotary compressors, electronically controlled expansion valves, different refrigerants, oils that do not freeze in the evaporator, inverter driven outdoor and indoor unit fans, bigger heat exchangers and so on...

[CatalinaWOW]

Actually I should have said that I couldn't prove that savings in operating costs would cover the installation costs.  Or that I wouldn't be better off waiting for a few more years of improvements.  And I am not saying it wouldn't, just saying that with the amount of research I did it wasn't obvious to me.

[theoldwizard1]

Apologies for jumping in late ...

Heat pumps are a classic case of "BUYER BEWARE".  This is especially true with mini-split heat pumps !  You have to learn how to read the specifications.

Many heat pumps will actually supply heat from below -20C WITHOUT USING A RESISTIVE HEAT STRIP !  Cheaper models use resistive heat strips when the temp gets down to about 10C and your power bill goes up, A LOT.

Again, BUYER BEWARE.  Even the top brands (Mitsubishi, Fujitsu, etc) sell units that will work at low temperatures, but they also sell units that rely on heat strips.

[james_s]

There's no magic here, it's all a matter of the size and efficiency of the unit and how it's set up. If the heat pump is too small or the efficiency too low then it will require supplemental electric heat to keep up.

[kaz911]

Just a follow up:

Denmark - heat pump installed for 1 1/2 years. No issues at all even in -10c in February '18. Energy savings compared to old electric storage heaters - about 2/3- so TOTAL electric consumption is now 1/3 of what it was before with same avg. indoor temperature. One single Panasonic SZ9 for 80 SQM house with big windows and one outlet. Had to reset it ONCE during the summer probably due to a thunderstorm making it slightly confused.

UK - Daikin Ururu Sarara thing - over sized for the room but - kept my 25m2 lab  hot during winter and cold during summer. Savings > 50% less TOTAL electricity consumption in my lab over 1 year and 3 months. That is despite cooling running a lot this year! during summer and Ururu spends some extra energy pulling in "real" fresh air from outside. And since it is over sized next door have not even noticed it is there as fans run VERY silent - despite it being about 30cm from our fence in a terraced house and about 3 meters from neighbors outside "entertainment table".....

So thumbs up for heat pumps from me. They will earn their installed cost back in about 3-4 years worst case.

[cdev]

So heat pumps are much more efficient than resistive heating for heating?

Are you serious? How is this done? How does one tell the difference?

Apologies for jumping in late ...

Heat pumps are a classic case of "BUYER BEWARE".  This is especially true with mini-split heat pumps !  You have to learn how to read the specifications.

Many heat pumps will actually supply heat from below -20C WITHOUT USING A RESISTIVE HEAT STRIP !  Cheaper models use resistive heat strips when the temp gets down to about 10C and your power bill goes up, A LOT.

Again, BUYER BEWARE.  Even the top brands (Mitsubishi, Fujitsu, etc) sell units that will work at low temperatures, but they also sell units that rely on heat strips.

[cdev]

Nauris - could you summarize the gist of the report?

I have seen claims of 2 COP at -30C!

But typically you get COP of 3 at 0C including defrosting.
They are really popular here many houses even have more than one.

One big importer get some units measured by independent lab attached are some results (vertical axis is avarage output power/input power (COP))
First Mitsubishi Electric MSZ-FH35VE we have two of these in this house


Second MSZ-LN25VGW, the newest and greatest one.


Figures include defrosting, outdoor relative humidity about 80%, units are operating at partial load above aprox. -10C outdoor temperature, room temperature 20C
Further details are in the report but it is in finish.

Here is more graphs and models(in finish):
https://www.scanoffice.fi/fi/tuotteet/tuoteryhmat/ilmalampopumput/raportit-ja-sertifikaatit/vttn-testiraportit

[AndyC_772]

So heat pumps are much more efficient than resistive heating for heating?

Are you serious? How is this done? How does one tell the difference?

Yes, absolutely. The search term you'll need is "Coefficient of Performance", or COP, which is the ratio of useful heat output to energy consumed.

The COP for a good domestic air con / heat pump system is around 4 to 5.

[bingo600]

We have a Swedish IVT Air/Air pump in the summerhouse in SE , COP = 5+  ,  Efficient to -25
IVT Nordic Inverter 12 KHR-N


Our choice was based on "Get one made for the Cold climate, by the Swedes" , and the 10C - "keep house at standby heat".

Lot's of "Cheap" pumps can not go below 18C , but that's only an issue in a summerhouse i guess.



Bosch - Bought IVT in 2013 , and our's is now a : 8000 AA

https://www.bosch-thermotechnology.com/dk/da/ocs/compress-8000-aa-758044-p

Others to looked as was

Daikin & Mitshubishi.  Where Daikin prob was #2


/Bingo

[james_s]

So heat pumps are much more efficient than resistive heating for heating?

Are you serious? How is this done? How does one tell the difference?

Yes that's the whole point. For 1kW of electricity in you get about 3kW of heat into your house. 1kW comes from the electricity, the other 2kW comes from refrigerating the outdoors. Not to be confused with some kind of free energy scheme, there's no energy being created from nothing, you're just consuming some energy to shove other energy around to where you want it. While electric resistance heat is 100% efficient at turning electricity into heat, that's only part of the process. Generating and transporting the electricity is far less than 100% efficient and dumps a lot of heat into the atmosphere and a heat pump can be thought of as recovering a portion of that.

[coppice]

So heat pumps are much more efficient than resistive heating for heating?

Are you serious? How is this done? How does one tell the difference?

Yes, absolutely. The search term you'll need is "Coefficient of Performance", or COP, which is the ratio of useful heat output to energy consumed.

The COP for a good domestic air con / heat pump system is around 4 to 5.

4 to 5 is a bit optimistic. 3 to 4 is more like the figure you usually get.

[woodchips]

Good luck!

We have an old GEC Nightstor electric boiler running wet radiators. It is brilliant, but we also get through 16MW electricity per year, that is everything, heat, domestic, workshop. It seemed sensible to look,again, at a heat pump.

After spending a long time searching, there are many websites to look at, from the UK posting feedback and comments ASHP is not a great way to go. This means the total cost not only of running, but also buying and maintaining it.

Doing the sums I came to the conclusion that I could save more money by running a diesel generator into the Nightstor. It seems that diesel is available for £0.70 per litre, so £0.075 per kWh. Diesel is 11.6 kWh per kg, sg of 0.8. The genset is about 60-70% efficient but the losses are heat, so you put it in a shed and plumb the radiator into the house. If the shed is insulated then it to will be warm, like my workshop! It would be cheaper if you can use heating oil in the engine, but savings might be more illusatory than real.

The one unknown in these ASHP calculations is how much they cost in maintenance. The Nightstor costs nothing per year in maintenance, unlike a gas or oil boiler. I once cansidered a log gassification boiler, we have a wood so the fuel is free, other than the cost of felling, shifting and cutting up, which is significant. The cost of buying the gassification plant was horrendous, can't really remember, £10k? And then you have the chimney sweeping etc etc. Simply didn't add up.

[timgiles]

Currently living in a small village in the middle of Sweden on the East coast (Umeå). We have a small heat pump by Mitsubishi and it manages ok down to about -15oC and stops working at -30oC. It is stated that it is an 'extended temperature' model - the normal ones stop providing more than they consume around -15oC if I remember. Air source works well but ground source works better.

Ground source work well but if you need to heat a large house you are looking at multiple units, where each unit requires an internal large heat transfer unit and an externally mounted radiator / fan unit. As stated, if you are going to get properly cold weather, you need to make sure you purchase an extended temperature model - that has a better compressor. Else when it is cold, you are basically switching over to standard resistive load type costs. Ground source will normally have a single hole bored 150m (ish) deep and requires only a single unit mounted inside. Since winter cold only penetrates about 35 meters - they are effected by changes in surface temperature as much.

[james_s]

The diesel generator idea has some appeal, at least as supplemental energy. If all you want is heat then it's going to be more efficient to burn the diesel in a boiler but if you can use the electricity and pipe the heat into the house then it could start to look pretty favorable. On top of that you could recover a sizable amount of heat from the exhaust.

I wouldn't go out and buy a new genset to do that but in parts of the world where diesel passenger cars are common it ought to be easy to get an engine from a salvage yard and couple it to a surplus alternator. Could be a fun project.

[NiHaoMike]

What about a CHP generator plus a heat pump to extract the last bit of heat that can be realistically extracted from the exhaust?

[Nauris]

What about a CHP generator plus a heat pump to extract the last bit of heat that can be realistically extracted from the exhaust?

Does work, that is sometimes used to boost heat recovery from exhaust washing units in smaller biomass fired district heating plants, profitability depends on things like return water temp, fuel moisture content and electricity price.

[soldar]

I am running heat pumps in central Spain and they definitely produce much more heat than a resistive space heater. It is cheaper to heat each room as needed than to heat the entire house with the central boiler.

They do have one problem, if I can call it that, and it is that condensation on the outside coil freezes solid and then the unit goes into a defrost cycle which is inefficient (ice outside needs to be melted) and uncomfortable because you are not getting any heat during that time.

It could be that colder air is dryer and the problem diminishes as the air gets colder but if the air is slightly above or below freezing and humid then you get a lot of defrosting.