Not even that: If the non-existent party wall dividing the lounge had the same temperature both sides, the heat loss through it would be exactly zero. You would have less than half the loss for each part. It would probably have been more accurate to model one radiator of double the output.
1 Like
Iâve only recently come to appreciate this, I used air change rates around 1-1.5 in my original heat loss. In actual fact itâs more likely that my air change rates are more like 0.43 ACH. I had a blower door test done which measured the permeability at 60 Pa = 8.677 m3/h/m2. The divide by 20 rule suggests an air change rate of 0.43 ACH. Iâve since been experimenting with CO2 decay rate monitoring (will do another post about this soon) and am quite reliably getting figures around 0.35 ACH when windows & doors are all closed and itâs not blowing a gale outside. Figures are higher when windy but I think with a little attention to draught proofing I should be able to keep them below <0.6 ACH.
This makes the difference between 4.5 kW and 3 kW in my case. The maximum continuous heat Iâve put into our house over a 24h period is 2.9 kW.
1 Like
Yep,
When it is really cold I would isolate the conservatory for a lot of the day.
I estimated my heat loss at somewhere between 4 and 5kW based on our gas consumption.
I donât think it is far off.
Hi Robert,
Iâm sorry I donât understand your comment?
The heat loss of the lounge was calculated as accurately as any of the others. He just added it in twice into the schedule of radiators.
As Marko suggests, itâs a manual operation and therefore subject to human error.
He did not include an extra room as you seem to be suggesting?
I should add I do think thereâs a need to be careful not to sail too close to the wind with sizing (unless you have some form of additional backup heat). What I dont feel I have a clear grasp of yet is what is the real world capacity reduction of heat pumps under freezing fog conditions that are a regular occurrence in the UK. How much spare capacity should we build in to deal with this? I have a lot of spare room on my 5kW heat pump so itâs not been an issue for me. @ColinS has some interesting analysis on this which Im sure he will share soon.
2 Likes
By adding the room twice, once per radiator, he got more than the correct heat loss for two radiators each heating half the room.
For the sake of simplicity, letâs say that your lounge is completely symmetrical, so that when you divide it into two, each part is a mirror image of the other, each with one radiator. The temperature of each half is the same, so thereâs no heat transfer between the two halves. You then calculate the heat loss for each half, but the hypothetical 4th side thatâs common to both halves transfers no heat to the other side - it is lossless, perfect insulation. So the heat loss for one half is less than half the heat loss for the two halves added - i.e. less than the loss for the whole room.
Hi Robert,
I thought that was what you were saying but that isnât what he did I donât think.
He calculated the heat loss of the lounge.
Then he just included that figure twice so the total heat loss was overstated by the heat loss of the lounge.
He didnât include it as two separate rooms getting the calculation of each of them wrong by ignoring or adding walls.
You would have thought there would be alarm bells going off all over the place with this.
First the size of the house and the EPC rating?
Second, what they fit to similar houses?
Third, my lounge represented 37% of the total heat loss even though it is only 16% of the total floor area?
1 Like
I agree âalarm bellsâ. Could this possibly be down to a lack of experience, methinks?
My point comes down to the surveyor should have a method to deal with more than one radiator per room. The obvious ways (to me) are either take the room as one space and add up all the radiators to get one big one, or divide up the room to give one space per radiator, with zero (or only a very small, if you accept a âcold endâ and a âwarm endâ) heat loss on the sides adjacent to another heated space. And to my engineerâs brain, two small radiators spaced apart should be more effective than a single large one (based on âWhy did you have two in the first place?â), therefore you actually need less than 2 Ă radiators of the size he used in the calculation.
1 Like
Thatâs for 1-1.5 ACH vs 0.6 ACH?
Or for the (ridiculous) 3 ACH that MCS defaults to and the clueless clowns donât change vs 0.6 ACH?
3 Likes
Yes this one!
I know!
2 Likes
Yes, much as the ârubbish COP in warmer conditionsâ situation is galling, at least the place is warm. Having the nominally oversized Daikin lose its composure completely at -2 because itâs covered in ice is, from a domestic politics PoV, a Big Deal, especially as it would contrast strongly with the other end of the performance envelope. @ColinS 's analysis of the defrost cycle would be most instructive, even if it means we have to dump this HP - but for which one?? Thereâs a comment on this or a related Daikin thread about a âwell-respectedâ German manufacturer whose real-world defrost performance is abysmal!
1 Like
Hi Robert,
Lack of experience?
Iâll tell you about Doug the surveyor.
He freely admitted he knew nothing about heat pumps, he was an ex BG employee
He couldnât draw the floor plan of the house, I had to do it for him.
He was already in trouble with his employer for drawing the floorplans back to front, they needed to be looking at the house from the front, he could only do them backwards and got yet another telling off from the office at my survey.
He originally calculated over 12kW of heat loss and wasnât in the least bit surprised even though I told him I expected around 5kW.
The office laughed at him when he submitted the calculation for verification and told him off yet again, I could hear the conversation as it was on speaker phone.
He had put the house down as solid walls.
I did inform Octopus that I knew he was clueless and had no faith in his work and my comments were duly noted.
What were they thinking sending somebody of that quality to do the most important part of the job?
He was a nice guy though.
Two weeks before the installation I had a visit from an installer to make sure everything was OK, I questioned the choice of heat pump and heat loss but still no alarm bells.
That visit was from someone who was leaving the employment that week I subsequently found out.
And no questions from any of the five employees that were present during the install, two installers, two electricians and a few visits from a supervisor to check the quality of the work.
Two further visits post installation, I was laughed at when I asked about OEM monitoring and told that I really didnât need it and if it was his house he would just use it.
The second installation quality auditor seemed to think my heat pump was doing quite well even though I showed him all the other heat pumps here. Again I questioned the install but still no response.
How did I know it was the wrong heat pump, Iâm an accountant, these people do this all day every day, you would have thought one of them would notice?
1 Like
Zero!
Design it down to the wire and rely on other crutches if you need to.
-
Wear an extra jumper on the odd occasion itâs actually that cold for a sustained period.
-
Low temperature radiators are handy when it gets cold. Drop your room temperature to 17C from 20C (say because it couldnât quite keep up with the heat loss) and your rad output at a given flow temperature will pop up.
I laughed out loud when doing the calc for âfrost modeâ (could the heat pump stop the place from freezing when itâs -20C out - which is design condition here) and "reheat from frost mode (if flow temp at steady state design condition is 40C but youâre starting with a room at 5C not 20C the rads really kick out more heat)
-
Plan on the insulation of the property getting better not worse over time. Itâs unlikely that this is the only measure youâll take.
-
Any fix any stuffups withâŚan AC. We have fitted one of these to knock the edge off in summer. (a fortnight of 30C and 100% humidity knocked back to 24C and DRY is bliss). Noddy basic (doesnât even have an electronic expansion valve; just a capillary tube) 9000 BTU class minisplit.
âŹ630 inc VAT minsplit. Vac pump, gauges, flaring tool, and heated diode leak detector another âŹ250 inc VAT if you donât have these already. Lineset, cable, drain hose, floor mounts say âŹ200 inc VAT. A round âŹ1000 worth of bits. Call it âŹ2000 fitted if you didnât DIY it.
Eurovent figures?
On paper itâll chuck in 2.1 kW at -7C with a COP of just over 3 (need not worry about defrost at that temperature); 1.3 kW @ +2C with a COP of 4.6; 0.8 kW @ +7C with a COP of 5.5
Bit chilly at design condition (or beyond?)
Blast that into the house somewhere and open the doors and youâll be fine.
Bit sticky in June/July?
1.1 kW of cooling @ 25C for an EER (COP) of 10.8; 1.75 kW @ 30C for an EER of 6.6 - hardly a criminal amount of electricity and at a time of year when itâs easy to offset against PV
Wanna heat back up from frost setting faster?
Crack it on at 2.9 kW at +7C with a COP of 4.5 (the COP drops at full load vs part load)
Better IMO to size the wet system to the wire (to maximise the everyday performance of it) and rely on being able to fudge it in extremis with an minisplit.
Put the split in the living room NOT the conservatory. That way you can heat the house with it with conservatory doors shut; and itâs no problem if you open the doors to the conservatory for the cold air to get into the conservatory if for some bizarre reason you wanted to use that in the summer rather than sitting in the garden under the shade of some PV panels / vines.
Not all is plain sailing mind.
Bolt it in. Flare up the pipework. Hook up the wires. Light the woodburner to warm up the indoor unit so that moisture evaporates at a sensible temperature. Vacuum it down. Release the refrigerant. Leak check.
Balls. Thought Iâd made a bad flare until I realised that the unit was leaking from an internal braze (and the gas coming down the insulation sleeve) rather than my flare:
Those sniffers detect leaks down to 3g/year. (about what leaks from a car AC compressor rotating seal even by design). Cracking bits of kit for ÂŁ60 or so. Donât bother with soapy water etc. Nitrogen pressure test is nicer but lots more kit to have for the odd installation; and wouldnât have made identifying the location of the (tiny) leak and showing it to the supplier easy.
Shut the liquid line, fun the split in full cooling override until youâve drawn the refrigerant back into the outdoor unit, shut the vapour line and knock the power off. Call the supplier.
Local distributor to be fair took one look at the vid and asked whether Iâd like to pickup a new indoor unit myself or for them to come swap it and weight out the refrigerant/weight in the correct amount in the event that a material quantity had leaked.
Not easy then but canât grumble at that on a âŹ630 widget.
Shouldnât really do that in the UK because F-Gas regs. (you need a certificate to know that you shouldnât let all the gas out before youâre allowed to touch these) Rest of Europe and the USA are less fussed. Can buy the units and the kit to fit them properly at B&Q. Donât be irresponsible though and do get the tools including one of those heated diode detectors if you are fitting them.
4 Likes
Itâs nuts eh @TrystanLea?
Default assumption: house has no glass in the windows
They should leave it bloody blank in my opinion so that the installing company are forced to put their neck on the line to a degree by estimating a number.
Not that their necks are on the line. Like heck are RECC or MCS are ever going to dare terminate Octopus registrations. Those outfits exist now for the purpose of preventing the smaller players that are good at heating and donât care for box ticking from entering the market.
Iâd REALLY like DESNZ to offer the BUS grant to anybody who can PROVE theyâve fitted the kit correctly via a yearâs worth of operating data. Buy the kit outright. (on a 0% card if you have to) Prove it works well. (with OEM etc) Get your VAT back and the BUS at the end of the year.
They donât need to allocate much funding to that track but imagine the benchmark it would set for installation quality / the look of fear on Ian Rippinâs face if they were to do so. 
4 Likes
Haha, love it 
2 Likes
Can this be fitted (in UK) without planning permission?
At Trystanâs prompting Iâve put my thoughts and measurements on the defrosting issue in a separate thread. Iâd value all inputâŚand corrections!
Hope Iâve got this link rightâŚ
2 Likes
Nope.
Itâs not an air source heat pump installed by an MCS union member. Youâre allowed to fit gas boilers and stinky oil boilers wherever you like. The MCS union successfully lobbied government to make it illegal to fit heat pumps of any description unless you use MCS labour. MCS donât do air conditioning so it isnât permitted development.
However if you throw it on the wall anyway and nobody moans for four years itâs effectively legal from a planning consent perspective.
Unless your neighbours are awful people I would, given the price point, install it somewhere that it canât be seen or heard and roll the dice on planning consent.
4 Likes
Yes, absolutely. For now, I would usually point people towards John Cantorâs website - https://heatpumps.co.uk/ - as a fantastic place to start their research. His book is a great read too.
2 Likes