My eco 4 heat pump fun

[robertXX]

hello chaps ,

this january , i had the eco 4 installation done on my derelict red brick 1865 4 on 4 farmhouse .

they fitted 4" insulation inside the external walls , a thick layer of loft insulation , and filled the one cavity wall with balls .

panels ,battery , and a heat pump ,12kw harnitek combo .


http://www.harnitek.com/products/html/137.html

http://file.site.biggreenbeard.co.uk/si ... 469279.pdf

https://www.theheatpumpwarehouse.co.uk/ ... -guide.pdf

https://www.theheatpumpwarehouse.co.uk/ ... r-tank.pdf


my concern is , i cannot seem to get any response from anyone who knows auything about setting up this pump , through the lcd screen , and what are the best settings for lowest power usage .

heres my power usage graphs over a couple of days recently ..


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IMG_8551.PNG (198.62 KiB) Viewed 5628 times

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IMG_8553.PNG (190.45 KiB) Viewed 5628 times

as you can see ,a lot of on and offing going on , i have the heat curve around 25-30c over its range , i have the water on 45 and turn it up to 53 for a bath , i have the hs set to 16.5c ,and if i get cold i light the wood burner .


i have the water deltas set to 1 degree ,and also pump speed delta at 1c .


i have the instructions, but they only tell you what each thing does, not what is the best setup . the lcd screen only shows tater temp ,room temp and ambient temp , no way to see scop .


i also have the transmitter for the remote contact , but no software i can find to download .

i do have the password to get into the installers settings .

i can set it so the rad water temp on the lcd creates a ripple pattern , or so it goes up and falls for a while then goes up again , but i dont know whats the best pattern to save leccy !



regards
robert

[hitman2]

Solar pv?

How many panels (wattage)
Location
Battery size
Ambient air temperature, day, night
Rads or underfloor

Notwithstanding the above I'd be tempted to set it up to YOUR comfort levels and see how it goes, with the insulation you have you could well be pleasantly surprised, if underfloor have it running 24/7

[Gilbertd]

Can't help with any of your questions but, as Simon mentioned it, my experiences. I always said I wasn't going to work beyond 65 which would have happened in July 2020 but I then found that from a tax point of view, it was better to retire at the end of the financial year. So, after over 45 years as a communications engineer, I put my notice in with the intention of retiring at the end of March 2020. I had a pretty decent workplace pension but would need to wait 15 months before the State pension kicked in so figured I would see if Euro Car Parts or similar needed a van driver for 2 or 3 days a week to top up the income.

However, March 2020 saw the start of the first Covid lockdown so nobody needed anybody meaning I was dipping into the pension lump sum to keep myself in the manner to which I had become accustomed. You may remember that the weather got particularly hot that summer and those that were still working were mostly working from home, including my daughter. She had re-purposed a spare bedroom into an office only to find that with it facing south and with a 6 foot wide window, it was getting up to 35-36 degrees so she asked if I could install air conditioning. My immediate response was, "buggered if I know", but agreed to look into it. That was when I found that I needed to be F-Gas qualified and registered to even buy air conditioning units. A mate had recently done a course to do mobile air con refills and he suggested the place he had done his course. So I did the F-Gas course, passed the City and Guilds exam (the first actual pass or fail exam I'd done in over 40 years!), registered, opened a trade account and installed a system for my daughter. 2 days later she's on a Skype call with her boss who looks and says, "is that an air con unit on the wall behind you?". Being a little stirrer, she replies "Yes, 22 degrees, bloody lovely". As his spare room was up in the mid 30's I ended up putting a system in for him the following week and, after a free advert on facebook, started doing multiple garden offices, summer houses and garage conversions being re-purposed as home offices.

Then I started getting asked about larger systems in houses, one of which already had an air source heat pump system installed. It was on an ex-MoD housing estate that had been sold off to a developer. The houses had originally been built in the 1960's so the developer installed cavity installation, external insulation, new double glazed windows and doors and the ASHP system. Now looking at the spec of what you have, it is vastly superior to what they fitted. Yours uses the same R32 refrigerant as the AC units I fit but still only has a COP of 4.3 compared with the Fujitsu AC units I install with an average of 4.7 (some going up to 5.2). His used a different refrigerant (don't remember what though) and a COP of 3.5. In a large kitchen/dining/living room he had three 2m double width radiators which on the day I went to survey it, were at 48 degrees and the room was at 18 degrees. His complaint was that, not only was the house permanently cold, he had 3 kids who all wanted a shower in the morning but as the system could only supply heating or hot water, not both at the same time, the house was freezing cold and his smart meter was off the scale as the 6kW immersion heater had kicked in as the heat pump wasn't capable of keeping up with demand. I installed a 18,000 Btu wall unit in the combined ground floor room and a 7,000 Btu unit in each of the 3 bedrooms all running off a single outdoor unit. He was astounded at how quickly air at 65-70 degrees with a fan behind it could warm up the room, so the ASHP system is only used for hot water and the AC units for heating. When I went to survey another house on the same estate shortly afterwards, I called in to see him and he told me the house now stays at 22 degrees and his electricity bill has almost halved. As the ASHP system is no longer supplying heating, it can heat the hot water tank and the immersion rarely kicks in.

I saw something in the media where they were saying that to meet the Government targets, a huge number of additional installers would be needed. As the qualification would simply be an add on to my F-Gas, I thought about it but from that experience, decided not to bother. Unless the building is perfectly suited and the modern systems are better than the one I saw, I wouldn't be able to sell a system to someone with a clear conscience. It strikes me that they have their place in a new build with excellent insulation properties (although in saying that, I've installed AC units in new builds where the insulation is so good, the bedrooms get ridiculously hot in summer and the customer wants it purely for cooling) but in anything else they aren't as suitable as some make out.

I can install an AC wall unit in a house with naff all insulation and while it might have to work a bit harder, it will still work. When running flat out, the evaporator runs at 65-70 degrees and with a fan behind it to distribute the warm air, it soon fills the room. I've also installed ducted systems where a single indoor unit is mounted in a loft with ducts to each room and vents in the ceiling. On a new build, it would be possible to run the ducts for the ground floor between the joists above the ceiling and below the first floor flooring, so the whole house could be catered for by two indoor units. It also means no radiators which, lets face it, aren't an ideal way of spreading heat around a room. There's a bit of convection, a bit of radiation and nowhere to put your sofa unless you have a really big room and it can sit in the middle.

[robertXX]

Solar pv?

How many panels (wattage)

15 x 415 watts ... facing 233d south west .

Location,,, on barn roof ..... just west of shrewsbury ,.


Battery size

4.8kw

Ambient air temperature, day, night

a lot af variation lately ,but ..

day -2 to +12

night -6 - +6

Rads or underfloor

rads , all new ,and fitted for the pump .

Notwithstanding the above I'd be tempted to set it up to YOUR comfort levels and see how it goes, with the insulation you have you could well be pleasantly surprised, if underfloor have it running 24/7

i have been doing that to a degree , most comfy is 18.5 c , but my leccy went to 23 kw in a day , so am trying to reduce that , but the regime to get the best from my system seems hard to define , andtheres nothing out there to help .


pre heat pump i would average 6 untits a day , but i was using 1000 to 1500 litres of oil a year .


here is my years usage since the fitment of the system ..

IMG_8626.PNG (165.08 KiB) Viewed 5621 times

which worksout on average at 4.55 units a day over the year , so better than before , and thats not counting the solar i have fed back which is 1991 x .15 ppu ...298 quid .


thanks hitman

regards
robert

[robertXX]

thank you gilbert that an interesting comparison , in my case i felt like it was worth it to try and see how well i could make it work , i would not have considered it without the panels , and the battery was an unexpecteed bonus .

[hitman2]

Your main problem is those minus temperatures, might as well just plug an electric radiator in when you get that low as the efficiency is down to 1 in 1 out....

I'd try cranking your buffer tank temperature up to the bath water setting and leaving it there for a good while, set up your main room stats to 21, bedrooms 17, see how it goes for a few days, don't be tempted to chase your tail too quickly, wait until your eyes are watering at the potential cost

Ashps work great here as we hardly ever drop below freezing, just been for my morning walk and comfortable in shorts and tee shirt, overnight temperature of about 13 daytime up to 19.

Its a pity the UK government has taken the stance of moving from gas as its going to be expensive for most folk unless the building they live in has been constructed recently and with the viewpoint of having ashp as the main heat source...

Good luck finding the sweet spot

[LPGC]

messed up my editing

[LPGC]

Your main problem is those minus temperatures, might as well just plug an electric radiator in when you get that low as the efficiency is down to 1 in 1 out....

That's what I used to think but Gilbert said modern systems are efficient (1in 4.5out) almost regardless of external temp.

@Gilbert do you reckon your AC systems work better than the usual type (radiator) heat pump setups because the air is blown instead of relying on radiators to radiate and convect heat then? That's assuming both types are of similar efficiency, reading through this your type and Rob's type are similar efficiency, both more efficient than earlier heat pump setups?

[Gilbertd]

Personally I think they do. Take a double width, 2000x600 mm radiator that sits against a wall, the spec shows it to give 11,823 Btu or 3.464 W (as Btu depends on the difference between ambient and radiator temperature) and comparing that with a 12,000 Btu unit that I would supply. The room will warm up eventually but the further you are from the radiator, the lower the temperature until the heat has spread around the room. The wall unit I would supply is 834mm wide by 270mm high and is fitted to a wall around 100mm below the ceiling so can go under a sofa rather than behind one. The output varies depending on the difference between ambient and desired temperature and is rated at between 0.9 and 5.3 Watts. So you set the temperature you want and depending on the difference between that and ambient, depends on how hard it needs to work.

I've installed one today, a single unit in a garden office (for my sister who has recently moved house). Ambient was 7.1 degrees and I set it for 22 degrees, so initially it ran at full power until the room got up to around 19 degrees when both the compressor and fan slowed until it reached 22 degrees. That took just over 10 minutes. The vent on the unit is adjustable but if you leave it to its default, when heating, the airflow is angled downwards towards the floor, hot air rises so it circulates over the whole room and is then drawn in through the top of the unit to be circulated again. In my opinion, that has got to be better that having a 'hot spot' against a wall with nothing to move the air around other than convection. Think of it much the same as comparing the heat from a bonfire with heat from a fan heater.

[LPGC]

I think blowing warm air is going to heat a room quicker and to a warmer temp than a radiator at the same temperature too.

But are there no radiators that have switchable fan assistance to aid with convection?

If the efficiency isn't always 5x regardless of temperature then, what is the efficiency curve from (say) -15C to +20c external temp assuming we always want the room to be (say) 15>22C?

Is there a maximum temperature shift? I.e. If for input temp of (say) -5C the radiators / output fan can only output at max 50C that would be a temp shift of 55C, if 55C is the max shift it would mean for input temp of -10C output temp would be +45C. There is kind of a max shift with burning gas or hot wire electric heaters too, but on those the max shift is hundreds of degrees so input temp change is negligible compared to max shift.

I suppose ideally ground source would work better when external temp is below around 10C, air source when external temp is above around 10C? Since underground temp doesn't change much from around 10? But ground source too involved and costly to fit and not always possible to fit...

[Gilbertd]

There may well be fan assisted radiators which would definitely be a good idea, but it isn't something I've ever looked into.

The efficiency is going to vary with the input/outputs, as some power consumed is going to be used for the control electronics and that will be the same no matter if the unit is working flat out or idling. The unit I supply more than any of is the lowest power unit of them all, a 7,000 Btu unit rated at a nominal 2.5kW as that is all that is needed for an average size UK room (length x width x ceiling height in cubic feet x 5, gives the Btu figure required). That will give up to 3.4kW of heat for 555W of electrical input, so giving a COP of 6.12, at the lowest the output will go down to 0.9kW but the manufacturers don't quote a minimum power consumption when running at that level. The quoted COP is 4.6 (average), so it obviously takes into account the power consumed by the overhead when running at lower output. There is also a high spec version that will give 5.2kW output for 500W input but with a quoted COP of 5.2 but they are more expensive and most people don't want to spend the extra.

It may well be that the heat generated in the condenser will be lower when the ambient is lower but it isn't by much. When doing a commissioning test the unit is first run flat out cooling and the temperatures at both indoor and outdoor units are checked and then the same is done with it running flat out heating. The airflow temperature does vary slightly from around 65 degrees up to over 70 but in saying that I've installed multi-split systems (a number of indoor units running from a single outdoor unit) and the output on the indoor units will vary by a couple of degrees from one unit to another.

The units can be set for a target temperature between 18 and 30 degrees and that is what they will achieve if the ambient is within the limits of -15 to +24. I had one customer who took no notice of the advice I gave him or the operating manual and complained that when it was -4 outside the unit could only get his room up to 20 degrees and would then pause. It turned out that he had set the unit for 30 degrees target, thinking that would make it warm up faster, and the unit was trying to achieve that. He was also using the Powerful function which is intended for a rapid change between one target temperature and another, not for a change from Off to On. That meant that the temperature of the outdoor unit was dropping so low that it was icing so would shut itself down to defrost before resuming. When he set the target at his desired 22 degrees (and didn't use the Powerful function), it reached it almost immediately as it didn't run flat out (to try to achieve 30 degrees) but ran at a lower compressor speed and temperature. Had he left it long enough, it would have got the room up to 30 degrees but in stops and starts as it had to keep pausing to defrost the outdoor unit. So from that point of view, in the case of a heat pump system, ground source would be better as the outdoor unit would be at a more stable temperature but for the vast majority of people, it will work fine unless you try to abuse it (as he did).

[LPGC]

Wouldn't have thought control electronics would use much power?

Seems quite the bloke thing to think 'set it to full power, that should warm the room fastest' lol but some of us would realise the pausing wasn't going to help.

Wonder if they could make multi-stage setups for extremely cold climates like the antarctic, first stage most efficient shifting temp from say -40 to 0, the 0 output being the input temp for the 2nd stage, 2nd stage capable of 0 to 40 but leave it set to 22? If so would each stage use a different type of refrigerant? Maybe the kind of thing people planning manned Mars missions would need to look into? Or would something like what you're already using with single stage work?

[LPGC]

Are there any heat domestic heat pumps that could easily be modified to be turned by a separate motor/engine instead of the (presumably) built in electric motor?

Mentioned this idea before...

Gas and electricity are measured in kwh, if we burn 1kwh worth of gas we get 1kwh worth of heat from a boiler, if we use 1kwh of electricity in a hot wire heater we get the same amount of heat, if we use 1kwh of electricity to power a heat pump we get the 1kwh x the heat pump's scop worth of heat. Electricity costs around 3x more than gas per kwh.

Engines are only around 33% efficient at turning fuel kwh into rotational power, the remaining 67% of the fuel's heat is usually wasted because it goes out the exhaust or is radiated/convected by the radiator, exhaust and block. If electricity costs 3x more than gas per kwh then even if the engine is only 33% efficient at turning gas kwh into rotational energy it would still be just as cheap to power a heat pump from an engine running on gas as to power a heat pump running from grid electricity - this is before we even consider making use of the heat that the engine is making. If we can make use of the engine's 'waste' heat we get 67% of the heat we'd get from running a boiler on the amount of gas the engine is using to power the heat pump for free. Normally we want an engine to produce rotational power so we think of an engine as 33% efficient at turning input kwh into rotation kwh, but if the idea is to generate heat we could think of the engine as 67% efficient at producing heat with 33% bi-product rotational power. If we can make direct use of the heat to heat radiators and use of the rotational power to turn a heat pump then (due to gas versus electricity prices) we can spend less on energy to make more heat by combining an engine with heat exchangers with a heat pump.

Example figures...

Let's say a heat pump uses on average 1kw of electricity costing 25p per hour and the heat pump has scop of 4 so produces 4kw of heat. If instead of running the heat pump on electricity from the grid we used an engine to power the heat pump the engine would also need to produce 1kw to turn the heat pump, so would normally waste 2kw of heat. The engine (at 33% efficiency) would need to burn 3kw worth of fuel to produce the 1kw of power for the heat pump but this would cost the same as running the heat pump from grid electricity because the gas costs 1/3rd as much as electricity per kwh. If we can make use of the 2kw of 'waste' heat from the engine our total heat output to the house from running our heat pump from the engine (4kw) plus the heat from the engine (2kw) becomes 6kw. You can look at these results in different ways - The 6kw output is a 50% improvement in heat output, or is we still only wanted 4kw heat output we throttle back the engine so it's using less gas so it's the equivalent to running the heat pump at lower cost than 25p per hour for same output.

I imagine a setup with engine completely enclosed in an insulated box, it's coolant passing through a heat exchanger, most of the exhaust including the manifold being part of a heat exchanger, most water from these heat exchangers directly heating some radiators. Further exhausts heat exchangers, the idea being that the exhaust gets progressively cooler toward the tailpipe so we don't waste any heat out of the tailpipe. Pump evaporator refrigerant passes first through the heat exchanger closest to the exhaust tailpipe (so the final exhaust gas temp is same as atmospheric temp, so we're making full use of all the heat produced from burning the gas in the engine without wasting any heat), refrigerant may be heated further by a heat exchanger a bit closer to the engine in the exhaust. Seems likely to me that by using some of the engine heat output to warm the evaporator of the heat pump we'd push up the heat pump scop efficiency when external temperatures are very cold, whilst simultaneously making use of some exhaust heat we couldn't make use of without the heat pump - If it wasn't for the heat pump the exhaust gas would exit at at least the same temperature as the inside of the house... The heat pump and engine enhance each other's effective heat output, an efficient condensing boiler might still have flu gas temp above 40degC but with this setup 'flu gas' (engine exhaust) temp could be lower than atmospheric temp because the heat pump made use of most of that heat, whilst at the same time the heat pump evaporator is warmer than it would be if only heated by atmospheric air and this temp might be warm enough to improve the heat pump's scop. Not only does it improve the heat pump's scop, if internal radiator temp is at all relative to evaporator temp it also increases the temp of the radiators in the house heated by the heat pump.

Easy to add capacity for extra heating - connect an electricity generator to the engine and you could run oldskool hotwire electric heaters from the generator... Every time you put an extra 1kw electrical load on the engine you also get an extra 2kw equivalent heating from a gas boiler. You plug in 1kw hotwire heater somewhere in the house and there's another 2kw of heat going to the radiators connected to the engine's heat exchangers.

Run your other household electrical appliances from the generator, if you paid a standing charge for electricity you no longer need to do so because now you can create your own electricity at same as grid price, if you have a storage battery use the generator to charge the battery.

[Pinger]

Are there any heat domestic heat pumps that could easily be modified to be turned by a separate motor/engine instead of the (presumably) built in electric motor?

Mentioned this idea before...

Gas and electricity are measured in kwh, if we burn 1kwh worth of gas we get 1kwh worth of heat from a boiler, if we use 1kwh of electricity in a hot wire heater we get the same amount of heat, if we use 1kwh of electricity to power a heat pump we get the 1kwh x the heat pump's scop worth of heat. Electricity costs around 3x more than gas per kwh.

Engines are only around 33% efficient at turning fuel kwh into rotational power, the remaining 67% of the fuel's heat is usually wasted because it goes out the exhaust or is radiated/convected by the radiator, exhaust and block. If electricity costs 3x more than gas per kwh then even if the engine is only 33% efficient at turning gas kwh into rotational energy it would still be just as cheap to power a heat pump from an engine running on gas as to power a heat pump running from grid electricity - this is before we even consider making use of the heat that the engine is making. If we can make use of the engine's 'waste' heat we get 67% of the heat we'd get from running a boiler on the amount of gas the engine is using to power the heat pump for free. Normally we want an engine to produce rotational power so we think of an engine as 33% efficient at turning input kwh into rotation kwh, but if the idea is to generate heat we could think of the engine as 67% efficient at producing heat with 33% bi-product rotational power. If we can make direct use of the heat to heat radiators and use of the rotational power to turn a heat pump then (due to gas versus electricity prices) we can spend less on energy to make more heat by combining an engine with heat exchangers with a heat pump.

Example figures...

Let's say a heat pump uses on average 1kw of electricity costing 25p per hour and the heat pump has scop of 4 so produces 4kw of heat. If instead of running the heat pump on electricity from the grid we used an engine to power the heat pump the engine would also need to produce 1kw to turn the heat pump, so would normally waste 2kw of heat. The engine (at 33% efficiency) would need to burn 3kw worth of fuel to produce the 1kw of power for the heat pump but this would cost the same as running the heat pump from grid electricity because the gas costs 1/3rd as much as electricity per kwh. If we can make use of the 2kw of 'waste' heat from the engine our total heat output to the house from running our heat pump from the engine (4kw) plus the heat from the engine (2kw) becomes 6kw. You can look at these results in different ways - The 6kw output is a 50% improvement in heat output, or is we still only wanted 4kw heat output we throttle back the engine so it's using less gas so it's the equivalent to running the heat pump at lower cost than 25p per hour for same output.

I imagine a setup with engine completely enclosed in an insulated box, it's coolant passing through a heat exchanger, most of the exhaust including the manifold being part of a heat exchanger, most water from these heat exchangers directly heating some radiators. Further exhausts heat exchangers, the idea being that the exhaust gets progressively cooler toward the tailpipe so we don't waste any heat out of the tailpipe. Pump evaporator refrigerant passes first through the heat exchanger closest to the exhaust tailpipe (so the final exhaust gas temp is same as atmospheric temp, so we're making full use of all the heat produced from burning the gas in the engine without wasting any heat), refrigerant may be heated further by a heat exchanger a bit closer to the engine in the exhaust. Seems likely to me that by using some of the engine heat output to warm the evaporator of the heat pump we'd push up the heat pump scop efficiency when external temperatures are very cold, whilst simultaneously making use of some exhaust heat we couldn't make use of without the heat pump - If it wasn't for the heat pump the exhaust gas would exit at at least the same temperature as the inside of the house... The heat pump and engine enhance each other's effective heat output, an efficient condensing boiler might still have flu gas temp above 40degC but with this setup 'flu gas' (engine exhaust) temp could be lower than atmospheric temp because the heat pump made use of most of that heat, whilst at the same time the heat pump evaporator is warmer than it would be if only heated by atmospheric air and this temp might be warm enough to improve the heat pump's scop. Not only does it improve the heat pump's scop, if internal radiator temp is at all relative to evaporator temp it also increases the temp of the radiators in the house heated by the heat pump.

Easy to add capacity for extra heating - connect an electricity generator to the engine and you could run oldskool hotwire electric heaters from the generator... Every time you put an extra 1kw electrical load on the engine you also get an extra 2kw equivalent heating from a gas boiler. You plug in 1kw hotwire heater somewhere in the house and there's another 2kw of heat going to the radiators connected to the engine's heat exchangers.

Run your other household electrical appliances from the generator, if you paid a standing charge for electricity you no longer need to do so because now you can create your own electricity at same as grid price, if you have a storage battery use the generator to charge the battery.

Interesting...
I dropped all my 2T plans when it was announced that only EVs would be for sale after 2030/2035 but picked them up again when I envisaged the grid being unable to supply all that is needed for rapidly increasing electrification and an engine for a stand-alone generator came to mind. Like you I considered using the excess heat to usefully heat the house. My thinking got a bit muddled though as to what to do with said excess heat in summertime when electricity is required but not heat. That in my mind imposed two 'cooling' systems on an engine.
I was open minded as to fuel (but was not contemplating diesel - but never say never) and had mains gas in mind for the very simple reason of not having to transport a flammable liquid fuel and, if that fuel was petrol, avoid fuel duty. Is it mains gas you have in mind LPGC?
Other thoughts were suitability re different house types but concluded it would be no worse than any other stand-alone generator set and, if more thoroughly integrated then the risk of theft could be eliminated. Multi-storey properties didn't figure in my thinking. And trying to figure out scale ie, how much power is required, and at what rpm, noise and vibration considerations, any emission regulations to comply with, portable or fixed, etc.
As you've likely already deduced my thinking got stuck between emergency use only (in which case using excess heat is tricky) and as an 'off-grid' solution supplying all of the house's energy requirement and in that environment the adaptation to a house's existing heating system needed to be considered. At no point though did I contemplate using a heat pump. If I have understood your post correctly you have in mind a system that can be as I envisage (retro fit) or, more pertinently, applicable to new build. Do you intend pursuing your ideas as outlined and if so, for own use only or with a view to commercialisation?

[LPGC]

Commercialisation would be the idea. Running from piped methane for those that have it, propane for those that don't.

It's something I'm going to look into. Retrofit as I don't imagine persuading house builders to use this, especially not those that won't be having a mains gas supply fitted.

In summer room heating wouldn't be used but hot water is still needed, coincides with less use of electricity too. Charge a battery while heating a hot water storage tank (and one such battery could be in an EV). Wonder if old style washing machines that use piped hot water are still available.

From an emissions standpoint a 4 stroke would usually be better than a 2T? A 4 stroke running on methane or LPG is going to have low emissions anyway and probably quieter than a 2T too? We're not so concerned about fuel economy (which largely comes down to engine heat efficiency) if one of our aims is to use that heat produced by the engine. But if someone achieved the impossible of a 100% engine heat efficient engine we could still use that engine for this purpose because it's easy to convert kinetic energy into heat energy.

[Pinger]

Commercialisation would be the idea. Running from piped methane for those that have it, propane for those that don't.

It's something I'm going to look into. Retrofit as I don't imagine persuading house builders to use this, especially not those that won't be having a mains gas supply fitted.

In summer room heating wouldn't be used but hot water is still needed, coincides with less use of electricity too. Charge a battery while heating a hot water storage tank (and one such battery could be in an EV). Wonder if old style washing machines that use piped hot water are still available.

Kinda passed me by the new builds wont have mains gas - oops!
Good point re hot water.
Any thoughts as to which engine - type, power output, torque characteristics, size, etc? (When I gave this thought I figured generator rpm would dictate an engine running at its speed or, the necessity of a reduction gear).
Looks like washing machines that use hot water are available - and for the same reason as your gas vs electric for driving a heat pump.
https://www.google.com/search?q=washing ... e&ie=UTF-8

[LPGC]

I reckon the engine needs to be big enough to make around 5kw crank power at low rpm (say below 1500rpm), so not as small as most portable generators that make 5kw at around 3000rpm full throttle on petrol. A simple design like a pushrod engine, fit a cam that gives best breathing at the unusually low rpm so probably opening and closing valves at nearly bang on TDC/BDC. Simple design and low rpm = quiet, low maintenance, easy maintenance, long life. At 33% efficiency if it makes 5kw crank power (to drive a generator and/or heat pump) it makes 10kw heat while using 15kw worth of gas but it could be throttled down/up.

The engine rpm might not be compatible with necessary pump or generator rpm but could use belt drive to correct that. Belt drives are less efficient than direct drive but the belts are inside the insulated engine box so any heat belts produce isn't lost, likewise any heat the alternator etc produce isn't lost.

[Pinger]

At a guess, both generator and heat pump compressor will require hefty torque at low speed to get them moving so I see the logic in your proposed engine. Aren't these the characteristics of marine (eg, outboard) engines? Or only in larger units where they are expected to accelerate a boat to planing speed whereupon they are throttled back?

[LPGC]

I wasn't thinking about the torque to get the pump or generator going, just like I said was thinking about noise and reliability. Would expect a beefy enough starter motor to get the engine started even if the loads were not switched off / disconnected... But a generator alternator could easily be electrically disabled during engine starting (and it's load gradually connected when the engine was running) and the heat pump drive could have a vehicle AC compressor style electric clutch.

In a boat you've effectively got only one gear and in that gear you've got to be able to reach top speed whilst also have enough torque at lower rpm to have the boat to climb over it's own wake to get onto the plane or it will never reach that top speed. But I don't think torque is a major consideration if we're talking conventional design engines.. Could have an engine that makes 200hp at 4500rpm, another engine that makes 200hp at 9000rpm but if they both make 100hp at half rpm we could compensate completely by adjusting the gear ratio (the probably smaller less torquey engine being twice as low geared compared to the probably bigger torquier engine). It would be different if we were talking a less conventional engine that made little torque at low to mid range rpm and suddenly came on cam at higher rpm. I had a boat with a 2T engine rated at 70hp, was around 800cc and had red line at around 6000rpm... The figures seem like the redline was low and the engine was relatively big to only make 70hp for a 2T, it was an older design engine but even the newer 2T outboards have similar figures.

[Gilbertd]

Are there any heat domestic heat pumps that could easily be modified to be turned by a separate motor/engine instead of the (presumably) built in electric motor?

I know you've mentioned this before and only just got around to replying but how would you control your engine? The pumps in a heat pump don't run at a constant speed, speed is adjusted depending on demand. So if ambient is 10 degrees and you decide you want the room at 20 degrees, it will run flat out initially until the room temperature gets up to around 17-18 degrees and then slow down until the temperature gets up to 20 degrees. At this point it will just be 'ticking over' (for want of a better expression) or even stopped, ready to speed up, or restart, the compressor and fan speed to maintain the target temperature. So your engine would need to be able to generate the same torque at differing revs and be stop/start controllable.

But surely a far cheaper option would be solar panels and a storage battery? That way you needn't even think about the differing costs of mains gas and electricity.....