Air Source Heat Pump (ASHP)

[dspp]

How do you ensure that your immersion only kicks in when the solar PV panels are producing energy? Do you have some sort of relay switch being triggered by the electricity generation?

These scavenger systems have a CT clamped on the house's import cable, and a relay on the second immersion coil. When current flows outwards to grid they switch the coil on unless overriden by the tank thermostat. See https://www.marlec.co.uk/product/solar- ... cba1185463 for the Marlec version and immersun are the main competitor. Early versions were cable coms to the CT, later ones are wireless.

regards, dspp

[GoSeigen]

Let me try again.

[...]

To summarise, with my setup, I think it would take over 24 hours to get the house from 15 degrees to 21 degrees when outside is at 0 degrees. I think it would take about 7 hours to get from 19 degrees to 21 degrees overnight when outside is at 0 degrees. All of these timescales reduce drastically as the outside temperature increases.

It is hard to measure any of these things and come up with concrete figures as there are so many variables, the primary of which is the fluctuation in outside temperature.

I hope that clarifies somewhat.

Thanks fisher, that certainly is clearer. I'm guessing that you have insulated the house really well and reduced most of the draughts. Our house is a similar size but older with open chimneys and other draughts. With an ASHP our bills are much higher, even with the heating set to 17º for much shorter periods. On cold days it struggles to get above 15 except in the kitchen where the AGA is on.

My impression is ASHP is only sensible if heat losses from the house are minimal.


GS

[fisher]

Thanks fisher, that certainly is clearer. I'm guessing that you have insulated the house really well and reduced most of the draughts. Our house is a similar size but older with open chimneys and other draughts. With an ASHP our bills are much higher, even with the heating set to 17º for much shorter periods. On cold days it struggles to get above 15 except in the kitchen where the AGA is on.

My impression is ASHP is only sensible if heat losses from the house are minimal.


GS

Yes, I have reduced most drafts and insulated massively. Something like 500mm of loft insulation in lofts, as much sheet insulation as i could get into the roof slopes, something like 100mm or 120mm where possible without compromising air flow through the eaves. This required ripping the plasterboard off and getting the roof slopes reboarded and replastered after insulation. All floors downstairs sealed to the walls using expanding foam to remove drafts from under skirting (of course can only really be done when removing skirting). My house has been 90% renovated over the last 9 years and the remaining 10%will be done by end of next year. I still have some airflow coming from somewhere but I think it is a small amount and helps ventilate the house. We have one open chimney only. I have even insulated under first floor in the ceiling void where easy to do during renovations, concentrating mainly near the outside walls.

If your ASHP is having to work very hard then I'm guessing it is heating the water in your rads to a relatively high temperature and that then reduces its efficiency. At low efficiency your ASHP will cost nearly as much as electric heaters would.

Can you monitor what the target radiator temperature of the ASHP is and how often it gets the water to that temperature? Does it have any logging features so you can log what it's doing and analyse it? Mine has a USB socket where you can insert a memory stick to log to.

[DrFfybes]

A very interesting thread, as we also considered ASHP.

Talking to the eager sales lad at a local Home show - it was the best thing ever, especially as "gas boilers are going to be banned in 6 years".

I pointed out the error in his understanding of the legislation.

One thing that confuses me is the COP - as I understand it the figure relates to the relationship of heat energy produced compared to electricity used.

If so then surely it needs to be about 3 to compete with gas, as the electricity price per kWh is about 4 times that of gas (although efficiency is better?

I must admit to chuckling at this though...

We switch on wash machines, dishwashers and tumble driers only when the sun shines.

I only tend to use the tumble drier when the sun ISN'T shining

Paul

[fisher]

A very interesting thread, as we also considered ASHP.

Talking to the eager sales lad at a local Home show - it was the best thing ever, especially as "gas boilers are going to be banned in 6 years".

I pointed out the error in his understanding of the legislation.

One thing that confuses me is the COP - as I understand it the figure relates to the relationship of heat energy produced compared to electricity used.

If so then surely it needs to be about 3 to compete with gas, as the electricity price per kWh is about 4 times that of gas (although efficiency is better?

Paul

Yes - I think your understanding is right. I reckon I must average about a 3 times increase in performance but rather annoyingly, although I can get a whole raft of statistics out of my ASHP via its logging function it doesn't tell me the current consumed or the energy being produced at the back end. I can see current being consumed at any given point on its display but I can't log it. So I don't have a way to accurately measure its performance at the moment.

Here are the official NIBE COP specifications for my heat pump which is a F2040-16. It shows what the COP is for a given outside temperature and required Water Temperature - i.e. the temperature the radiators need the water to be in order to heat the house effectively. Note that the required Water Temperature will vary depending on what the outside temperature is on any installation. This is what is known as the heat curve. The figures given in the table are examples only and not recommended settings. The settings for each installation will vary.



I aim to keep the water temperature as low as possible in my system by setting its heat curve so that the water temperature is the lowest it can be with the house occasionally getting to its target temperature but most of the time being very close, but not quite there. This means the machine is working more often but being as efficient as it can be when it runs.

I guess what salesmen won't tell you it that you need to do a lot of calculations to work out the energy heat loss in your house and then get an ASHP which can produce this much energy. For example, I worked out my house lost about 12KW of heat at -3 degrees outside temperature, so my ASHP is a 16KW heat pump. To work out the 12KW total I did detailed heat loss calculations for each room which took me days. As has been touched on above, your house needs to be well insulated to get the most out of an ASHP and to live comfortably with one.

The heat pump will also benefit from detailed ongoing analysis and tweaking of its settings at least for the first year. The installer will set it up with what you hope will be sensible settings but no-one really knows until you start using it. My heat loss calculations gave a higher figure than we see in practice which has allowed me to reduce the water temperature in the rads making the system even more efficient than we envisaged.

[Gan020]

Hi I am thinking of trying to go green. Our house is a 3 bed detached built in the early 2000s with an EPC of C/D. It is not suitable for a ground heat pump. Does anyone have any experience of installing an Air Heat Pump? Did the economics stack up?

427

Moderator Message:
Thread title altered. - Chris

If you are currently on a main gas supply then on a purely cost based analysis based on £, almost certainly not. If you are on LPG or oil then definitely yes.

I've had an ASHP for 8 years along with solar PV and solar thermal panels. The solar PV and solar thermal panels have been fantastic. The ASHP whilst financially well worthwhile has been a little disappointing in terms of the drawbacks.

[dspp]

I guess what salesmen won't tell you it that you need to do a lot of calculations to work out the energy heat loss in your house and then get an ASHP which can produce this much energy. For example, I worked out my house lost about 12KW of heat at -3 degrees outside temperature, so my ASHP is a 16KW heat pump. To work out the 12KW total I did detailed heat loss calculations for each room which took me days.

As you can imagine this is going to come as quite a culture shock to the average British sales person !

As has been touched on above, your house needs to be well insulated to get the most out of an ASHP and to live comfortably with one.

This bit is always skipped over by the average British salesperson, just as with a gas/oil boiler. The less insulation you have, the bigger the bit of kit they get to sell you.

The heat pump will also benefit from detailed ongoing analysis and tweaking of its settings at least for the first year. The installer will set it up with what you hope will be sensible settings but no-one really knows until you start using it. My heat loss calculations gave a higher figure than we see in practice which has allowed me to reduce the water temperature in the rads making the system even more efficient than we envisaged.

As you can imagine this is going to come as quite a culture shock to the average British plumber !


And all of this is coming as a culture shock to the average British consumer, so the more discussion like this that takes place the better.

regards, dspp

[fisher]

I guess what salesmen won't tell you it that you need to do a lot of calculations to work out the energy heat loss in your house and then get an ASHP which can produce this much energy. For example, I worked out my house lost about 12KW of heat at -3 degrees outside temperature, so my ASHP is a 16KW heat pump. To work out the 12KW total I did detailed heat loss calculations for each room which took me days.

As you can imagine this is going to come as quite a culture shock to the average British sales person !

As has been touched on above, your house needs to be well insulated to get the most out of an ASHP and to live comfortably with one.

This bit is always skipped over by the average British salesperson, just as with a gas/oil boiler. The less insulation you have, the bigger the bit of kit they get to sell you.

The heat pump will also benefit from detailed ongoing analysis and tweaking of its settings at least for the first year. The installer will set it up with what you hope will be sensible settings but no-one really knows until you start using it. My heat loss calculations gave a higher figure than we see in practice which has allowed me to reduce the water temperature in the rads making the system even more efficient than we envisaged.

As you can imagine this is going to come as quite a culture shock to the average British plumber !


And all of this is coming as a culture shock to the average British consumer, so the more discussion like this that takes place the better.

regards, dspp

I guess on new builds - provided the insulation has been done to building regs (big caveat!) then fitting an ASHP in every house in an estate would be possible with settings already defaulted to be the optimum. For retrofit to older houses I think it works best if you are renovating every room and are prepared to be a perfectionist with the insulation and you are a control freak like I am with monitoring the settings. I don't monitor so much now - 5.5 years since installation but if I'd left it how it was set up it'd be costing me a lot more money.

[fisher]

For completeness, below is a table of the values in the heat curve I am currently using - it is a NIBE predefined curve (curve No. 9). The target temperature is the temperature the ASHP is trying to get the water in the rads to. It will overshoot this temperature in a lot of cases and will then shut down for a while and come on again once the rads are well below this temperature and repeat the cycle. In the colder weather (down below 0) it will run more constantly and will only rarely overshoot.



Weirdly at 21 and 22 outside its target is lower than the outside temperature - not that it matters as the heating would be switched off before it got to these temperatures.

[fisher]

I've had an ASHP for 8 years along with solar PV and solar thermal panels. The solar PV and solar thermal panels have been fantastic. The ASHP whilst financially well worthwhile has been a little disappointing in terms of the drawbacks.

Out of interest, what do you see as the drawbacks?

[dspp]

As has been touched on above, your house needs to be well insulated to get the most out of an ASHP and to live comfortably with one.

This bit is always skipped over by the average British salesperson, just as with a gas/oil boiler. The less insulation you have, the bigger the bit of kit they get to sell you.

I guess on new builds - provided the insulation has been done to building regs (big caveat!) then fitting an ASHP in every house in an estate would be possible with settings already defaulted to be the optimum. For retrofit to older houses I think it works best if you are renovating every room and are prepared to be a perfectionist with the insulation and you are a control freak like I am with monitoring the settings. I don't monitor so much now - 5.5 years since installation but if I'd left it how it was set up it'd be costing me a lot more money.

UK building standards get updated periodically, and various things get changed. The level of insulation that is required is one of the things that gets changed. Unfortunately it still is not set as high as it ought to be, and certainly is still not as good as the level of insulation you have retrofitted to your house. Which, in my opinion, is the level of insulation that is required in order to get a good match between an ASHP and a house in a UK climate.

I am afraid that the reason for this is the very active lobbying by the construction industry of politicians. If you recall Cameron's "cut out the green crap" quote then you know where to pin the blame. Pickles was one of the main culprits as well. Matters have not improved since, and this is stuff that we know how to do correctly now, on both newbuild & extensions, but still are not doing. Thus it is left to a few private consumers to raise awareness.

regards, dspp

[doug2500]

Our salesman is selling us 2 medium sized heat pumps for a large ish house. Apparently they run more efficiently at higher loads and so one medium pump flat out works better than a large one ticking over most of the time and only running flat out in the coldest temps. They will be connected in series.

[UncleEbenezer]

I'd see the great advantage of an air source heat pump as the ability to use it both ways. Warm the house in winter, cool it in summer.

Can't speak for noise or efficiency.

[Gan020]

I'd see the great advantage of an air source heat pump as the ability to use it both ways. Warm the house in winter, cool it in summer.

Hi, I'm a bit puzzled. Unless you know something I don't ASHP don't work this way. They are heating only. I'd be happy to learn something new.

[Gan020]

I've had an ASHP for 8 years along with solar PV and solar thermal panels. The solar PV and solar thermal panels have been fantastic. The ASHP whilst financially well worthwhile has been a little disappointing in terms of the drawbacks.

Out of interest, what do you see as the drawbacks?

The major drawback is the time the system takes to heat up in combination with the noise of the unit.

I have a Mitsubishi 3 phase unit which apparently is the maximum size you can put on a domestic supply. It is sited on an outside wall of the house. In the depths of winter when the temperature drops below zero, the noise it makes on the defrosting phase is in my opinion unacceptably loud. (when it's cold the back of the heat exchanger gets covered in ice so this has to be removed by heating it up else there is no air flow for the ASHP). The noise volume is probably less loud at this point when the ASHP is running continuously but after a while you don't listen or hear the fan noise in continuous operation as it's a constant drone in the background. The noise of the defrost cycle is more noisy because of the way the noise kicks in and out. It doesn't seem to bother my sleep when the temperature is above about -3 but anything below that and it disturbs me. It doesn't bother my wife at all.

Because of this I do not run the unit 24 hours a day and avoid running it overnight. I do use it from 3-4am to heat the hot water on overnight tariff, but somehow the defrost cycle doesn't bother me then presumably as I'm in deep sleep. I then start it up at 6am in Nov through Mar but of course it can't raise the temperature in the house as quickly as I would like. I do route the water through my rads to the rooms I want heated first which helps but it's not as warm as I'd like it first thing.

What you need with an ASHP is a modern well insulated house. Mine was built in the 60's with later extensions and whilst the heat losses from the house are such that the ASHP can keep it warm with ease in everything but the Beast from the East (when I suspect it wouldn't matter what you have for heating), getting it raised to tickover temperature can take 2-3 hours in Oct/Nov/Mar/Apr. For the coldest 20 days or so of the year when I heat all the rooms when the kids are home from University and we have visitors staying it really struggles and takes 4+hours. If a couple of rooms aren't being used and I turn the radiators off in those rooms the temperature in the rest of the house picks up much more quickly which is telling me my house it getting close to the point if I put some more insulation in, change some windows or curtains or floor underlay or whatever the ASHP would be alot better to live with.

For the past 8 years I've been slowly improving the heat losses from the house. What I can tell you here is that every time you sort the heat losses in one place they move elsewhere (or you become more aware of them). I've now got 3 rooms which heat up reasonably quickly and once that's done the TRV's on the radiators in those rooms turn off and there's more heat to spread around the remaining ones and the overall temperature in the house accelerates. If you are using radiators rather than underfloor coils you will need to make sure your rads are large enough and regrettably I've a couple that aren't even though they were sized by a professional. Finally my wife likes radiators that aren't the standard oblong ones. This isn't possible though as they don't have the heat output in relation to surface area.

I am thinking of getting some electronic TRV's so I can better control the on and off times by zone in each room. This would definitely help push the heat where I want it better. Regrettably they are still quite expensive when you compare with simply turning up the heating an extra 10% or spending the same amount on insulation. Nevertheless I shall probably try this out at some point.

It is cheap to run. My total electricity bill for everything this year is around £1400 although it has been mild and we went away for 10 days in Feb. Usually it would be £200 more. I have no gas but do have solar panels for both electricity and hot water. My house is a large 4 bed house. I'm not sure what large means but I have two rooms in which I can fit a snooker table in if that helps and a kitchen large enough to fit another although that of course would be a very strange thing to do indeed.

[GoSeigen]

I'd see the great advantage of an air source heat pump as the ability to use it both ways. Warm the house in winter, cool it in summer.

Hi, I'm a bit puzzled. Unless you know something I don't ASHP don't work this way. They are heating only. I'd be happy to learn something new.

Not all of them can, but many models can pump either way. Practically all Japanese homes have them because they need heat in winter and cool in summer. My mother had a similar unit in Australia.

GS

[richlist]

I've got one in Spain that does hot & cold.

Whilst it gets unbearably hot in summer it gets way below freezing in winter. So a heater that doubles as air con is very useful.

Just so there is no confusion......mine is an Inverter air conditioner. It doesn't provide hot water and heats/cools the room by fan.

[UncleEbenezer]

I've got one in Spain that does hot & cold.

Whilst it gets unbearably hot in summer it gets way below freezing in winter. So a heater that doubles as air con is very useful.

Just so there is no confusion......mine is an Inverter air conditioner. It doesn't provide hot water and heats/cools the room by fan.

I experienced similar in Italy. Not at home, but in the office.

That was not without its issues, but did the job of heating and cooling a whole lot more efficiently than some old-fashioned radiator.

[Itsallaguess]

I am thinking of getting some electronic TRV's so I can better control the on and off times by zone in each room. This would definitely help push the heat where I want it better.

Regrettably they are still quite expensive when you compare with simply turning up the heating an extra 10% or spending the same amount on insulation. Nevertheless I shall probably try this out at some point.

We wanted our bedroom radiator to have some automatic timer-controls, as we prefer a colder bedroom than the rest of the house in the evening and overnight.

I've had one of these Rondostat electronic TRV's installed for a number of years now, and I'm very happy with it -

https://www.amazon.co.uk/Homexpert-Heating-Controls-Electronic-HR20UK/dp/B007AQ71U4

They're £20 delivered, and it was a simple swap-out for the upper section of the previous TRV.

We've got ours set to turn off at 5pm and turn back on at 9pm, which may sound odd initially, but our central-heating goes off at 8pm anyway, and the benefit of it opening back up at 9pm is that it's a little noisy and I'm a very light sleeper, so we didn't want it opening up noisily too early in the morning to catch the first timer-period of our central-heating. It's not a loud noise, so don't let that put you off, but it's enough that it would wake me up, and finding a simple solution to that issue via the timing-cycle was too good an opportunity to miss...

It takes a couple of AA batteries which last around a year and a half.

You can spend any amount of money on app-controlled TRV's nowadays, but this simple electronic-timer version is great for my needs.

Cheers,

Itsallaguess

[fisher]

The major drawback is the time the system takes to heat up in combination with the noise of the unit.

I have a Mitsubishi 3 phase unit which apparently is the maximum size you can put on a domestic supply. It is sited on an outside wall of the house. In the depths of winter when the temperature drops below zero, the noise it makes on the defrosting phase is in my opinion unacceptably loud.

Mine can make a bit of noise when defrosting but it is not attached to the house directly - it has its own stand which is a few inches out from the side wall of the house. This isolation means we seldom hear the unit in operation from inside the house. Certainly having mine running overnight is advantageous in achieving my daytime target temperature.

My unit is a NIBE 16kw machine which is single phase I believe. It runs off an RCBO in the main Consumer unit.