Posted by: @carrownisky

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It’s subjective but we find the radiant heat from the old AGA and the IR panels much more pleasant than radiators.

That's true!

What your body is telling you is factually correct.

There are three main types of heat, as you will no doubt know from your science background

• convection: typically experienced by warm air rising from a 'radiator'
• conduction: heat being passed directly from a warmer material to a colder one
• radiation: underfloor heating (ufh) radiates Far Infra-red radiation with a wavelength of around 3–100 μm

And it's radiation which the human body finds most pleasant. 🙂 

Posted by: @carrownisky

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So my understanding (which may be completely incorrect, that’s why I'm posting here 🙂) is that the heat pump will be most efficient if our target temperature and our fall back temperature are quite close together, say 20 degrees and 17 degrees and that all the rooms are heated at least to around the fall back temperature. The heat pump will also be more efficient if it runs on an “open loop” system with no individual radiator control,  buffer tank or volumiser. 

 

That is true, there are the most efficient ways to run a heat pump, although not always the cheapest because ToU tarrifs can distort the picture.

Posted by: @carrownisky

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So the question I hope you can help with is which system would use the least electricity given the fact we are at home all day and only use a few rooms. The ease of control of the IR panels may mean we would be using less Kw at any one time than a heat pump.The one quote we have so far for a heat pump is for a 14kw Mitsubishi high temperature ashp. Heating our largest room with IR panels would use about 2Kw. Most rooms use much less. We would only use more at times when the internal room temperature drops below 13 degrees (our setback IR temp) 

Its difficult to be certain and anyone who tells you otherwise is either magic or not telling the truth.  Here are some considerations.

As you have a background in science/engineering you will know that heat loss (from the house) is proportional to the temperature difference between the inside and the outside.  And of course the laws of thermodynaics mean that the heat loss from the house has to be exactly matched by energy from your heating system otherwise the house temperature will change.  Thats the starting point.

In general terms its very difficult to keep rooms at substantially different temperatures which means that, in most tolerably well insulated houses the savings from only heating a subset of the rooms is much less than one would at first think.  So consider a situation that half the area is 'heated' to 20C.  Most likely the other half will settle at no less than say 16C when its 0C outside, so the average temperature is 18C, which represents just a 20% saving on energy when the outside is at freezing, nothing like the 50% one might crudely think.

Now consider the fact you are home all day and so presumably want the house (or at least those parts of the house you use) heated all day.  So you arent going to want 'instant on/off' heating in those parts of the house used most of the time.  Some parts will be more or less continuously heated.

Taking this into account I would imagine that much of your house will in reality be at between 16-20 most of the time, and therefore the amount of heat you need to put in is equal to the heat loss hat corresponds to this figure.

Now consider that the IR panels have an efficiency of 100%, so for each kWh you put in you get 1kWh out, whereas the heat pump produces roughly three times as much heat as you put in, so for each kWh you put in you get 3kWh out. 

Is it plausible that, with the IR heating, only one third as much energy is lost from the house to the outside world, because the average temperature is so much lower so the average temp difference inside to outside is one third as much?  Thats is what would need to be the case for the IR heating to work out cheaper.

I think the most likely scenario where this might be the case is if the air temperature of even the parts of the house you use is much lower with the IR heating than with the ASHP, because you feel comfortable with a much lower air temperature. It would have to be quite a lot lower though to account for a factor of 3 reduction in energy loss from the house.  Now it is true that if you go out in the sun when its say 10C outside, you can still feel comfortable, but are you go to run your house at this air temperature?  The alternative scenario where this might be the case is if the house is so poorly insulated that the rooms are effectively separate thermally.  

Thats not an answer, I admit, but it hopefully gives you something to think about and in particular think about what the air temperatures in your house (including the bits you dont use) are.

What you will get with a properly designed ASHP is constant consistent heat.  This may not suit you, only you can tell.

Please feel free to come back with thoughts/questions.

Do you know your current annual heating energy consumption, even approximately?

Can you provide any detail of the house construction and how old is it and floor area.  What insulation do you have Extensions can quite often reduce the loss of old houses, because the building standards have improved.  

@jamespa Thanks so much for this James, some of what you suggest is new to me and needs to be taken into consideration. I will put together some figures and get back to you - our current use is about 25000 Kwh for last  year. Thanks again for your time.

Posted by: @carrownisky

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@jamespa Thanks so much for this James, some of what you suggest is new to me and needs to be taken into consideration. I will put together some figures and get back to you - our current use is about 25000 Kwh for last  year. Thanks again for your time.

I look forward to the further info and will do my best to help.

The thing about heating is that the physics is extremely simple indeed but the application of that extremely simple physics becomes complicated by the myriad of configurations.  Sometimes it helps to simplify it down again when thinking about things.  The most useful 'tool' in the armoury of thinking is conservation of energy.  Very simple, very universal and very unavoidable.

25kWh would tend to suggest your house loss is in the 8-12kW region, although this is a rough and ready estimate based on various approximations which may not be true.  With multiple extensions there is a distinct risk that surveyors overestimate the demand (which may or may not matter).  Mine, for example, is a 1930s house with solid walls, two modern extensions and piecemeal fabric upgrades. Two surveyors got to 16kW, the measured loss is 7kW.  That made a big difference to the choice of ASHP and to radiator size!

Hi again James - just got a full survey booked with ARIA for Thursday 06/03. So we should have a better picture soon. The original house dates to 1860 but there is very little of that left. There are 2 1960's extentions and one from about 2000. The total floor area is around 200sqm. The walls are almost all (apart from small original patches which in total would only be 2 or 3 sqm) insulated cavity wall. The outside of the house is rendered. The floors are almost all insulated and most are finished with engineered wood. The windows are all double glazed. The roof is mostly insulated but not to modern standards - last done around 2000. There upstairs floors are floorboards with mostly engineered wood on top of them.

The kitchen we have the IR panels in is 20sqm with just over 5sqm of double glazing and one internal door. There are three rendered external cavity walls and a very thick internal wall which was the outside wall of the original build. The floor is insulated and the ceiling has floorboards and engineered wood over the top. We heat this room with 2 800w panel heaters. It heats up faster than the central heating rooms. A wall thermostat controlls the panels and we find an indicated air temperature 18 is as warm as we need it. The thermostat is not facing either panel. The position and orientation of the panels is from experience crucial. We tried a couple of portable panels in the room to get the best position, before buying the fixed ones.

Thanks again for your time James - looking forward to the ARIA survey on Thursday and will let you know what they suggest.

Peter

Posted by: @carrownisky

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. The total floor area is around 200sqm. The walls are almost all (apart from small original patches which in total would only be 2 or 3 sqm) insulated cavity wall. The outside of the house is rendered. The floors are almost all insulated and most are finished with engineered wood. The windows are all double glazed. The roof is mostly insulated but not to modern standards - last done around 2000.

Thats better insulated than my 1930s house of about the same size, apart from the loft which is easily and cheaply upgraded (so I would recommend doing it!). 

Im a bit surprised you are burning 25MWh/yr to heat it, mine was 18-20MWh/year.  That said mine was 24MWh/yr until about 4 years ago when I turned down the gas flow temperature so it actually condensed, put the heating on 24x7 (ie I basically ran it as close as I could to how I would run an ashp), upgraded the loft insulation to 300mm and changed out many of the double glazing glass units (but not the 30 yr old frames) for low e/argon filled.

Beware the surveys, they may well ignore fabric upgrades they cant see even if you tell them.  Mine did, which is part of the explanation as to why they came out at 16kW estimated instead of 7kW actual loss.

I do think you need to think carefully about what the average temperature of your house is.  A 3:1 ratio in energy out from the heat pump vs energy out from the IR panels (for the same cost) will be challenging to overcome.  It sounds like you might be happy with the house at 18C with the radiant panels, rather than perhaps 21C with a warm fabric.  Even if the 'unheated' rooms are at 10C you are still averaging perhaps 14C as opposed to 21C when its cold outside.  Thats not a 3:1 difference, even if outside is say 7C, a typical season average.  If you had a very low loss house then the effect of waste and body heat might help tip the balance, but you don't.  However these things are pretty much impossible to work out as I say above, so in the end you will have to make a choice.

That said its a condition of the grant that the heat pump is capable of heating the whole house, so you wont be able to benefit from that if you omit radiators in rooms with panels.

Hi James

Aira came Thursday and did a heat loss survey which came out at just over 10kw 

They quoted us £9264 for a 12 kw ashp and 10 new radiators including fitting etc

The two Aira surveyors were excellent and answered all the questions we asked, we were very impressed.

Following the visit and the new information you provided me here James an ASHP solution is looking more likely than the IR panel route. Just the Octopus survey to come on the 20th.

Thanks again for your help

Peter

Hi,

We have TWO potential ASHP property projects: one at our Perthshire 5 bed, timber frame 270sq.m house, UFH throughout with a dead oil boiler (10 weeks now); the other a 45yo. 90sq.m stone cottage right on the coast in west Ireland needing an overhaul.  Now retired we'll spend time between the two.

I'll post two threads to explain each separately but have already learned a good bit from your site this morning (wish I'd found it months ago!).  Two quotes received for the house include buffer tanks (seen your great video).  Have bought the books so will spend the day soaking up your experience and knowledge and start again on both projects!

Mark

Hi @dowallydrifter

The key explanation of how buffer tanks are meant to operate is encapsulated in this diagram posted by @heacol

Start with the diagram,
read the clarifications which follow...
... and then go back one page to check the context of why Brendon was asserting they shouldn't be used.

As you have UFH, it's even less likely that any sort of storage tank would be required for space heating.
You don't need a higher temperature differential across the radiating surface due to it being too small! 🤔 

Posted by: @dowallydrifter

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Two quotes received for the house include buffer tanks (seen your great video).  Have bought the books so will spend the day soaking up your experience and knowledge and start again on both projects!

Thank you for your support in buying the books. I hope that they're helpful to you.

Would you like me to connect you with credible installers that cover Perthshire?

@carrownisky where are you based? Would you like me connect you with some reputable installers in your neck of the woods?