EdieCampbell Posted December 16, 2022 Share Posted December 16, 2022 I have a new build house, completed January 2021. No gas available, so the house has a Mitsubishi Ecodan ASHP. I then have a second Ecodan to power ancillary accommodation. Initially, having come from a gas boiler 1bed flat, I treated the house as if it was still running off cheap, quick-reacting gas. So I had to alter my behaviour, obviously. All fine for a year and a half until this cold snap. My radiators are constantly calling for heat, the house is cold, my kWh usage is very high considering I have my thermostats set to 16degrees, and most rooms are currently measuring 14/14.5 degrees. What am I getting wrong?! It feels like something has either been poorly spec’d, poorly installed, or poorly commissioned. I’ll be the first to admit I have a limited understanding of how heat pumps work, but I am slowly getting to grips with it. Any leads or suggestions gratefully received! Link to comment Share on other sites More sharing options...
ReedRichards Posted December 16, 2022 Share Posted December 16, 2022 Heat pumps installed to MCS specifications are sized to provide sufficient heat 99.6% of the time at minimum (you may have some headroom). Look-up tables enable a calculation of an outside temperature that is exceeded 99.6 % of the time. If the calculation was accurate and your heat pump was sized to exactly match this specification then when it is 2 degrees colder outside than the specified 99.6% temperature then the inside of your house will fall 2 degrees below its specified temperature - and so on. Therefore it's possible you did nothing wrong except not leave yourself any headroom when sizing your heat pump. You will have to reconcile yourself to needing auxiliary heating during particularly cold weather. Gas boilers are usually greatly oversized for the demand of the building but have a greater range of modulation than a heat pump. So for a gas boiler cold weather is not such an issue and they may be able to modulate down enough to avoid cycling in warmer weather. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 Interesting, Thankyou. I’m asking my architects to refer back to the M&E spec to try to get to the root of the problem. As an example, last night my bedroom was 14.5 degrees, and calling for heat to get up to the required 16degrees. This morning it’s 13.9degrees and still calling for heat. My smart meter says I have been consistently using between 2.5-3.5KWH every 30 minutes all night. Link to comment Share on other sites More sharing options...
akjos Posted December 17, 2022 Share Posted December 17, 2022 What’s your calculated heat loss and what’s your HP capacity? Also, UFH or rads and what flow temperature are you running? Link to comment Share on other sites More sharing options...
Conor Posted December 17, 2022 Share Posted December 17, 2022 Are the rads heating up? If the rads are warm, but room stays colds, suggests that heat loss rate is higher than what the system can match. What insulation and airtightness did you achieve? What size is the heat pump? Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 52 minutes ago, akjos said: What’s your calculated heat loss and what’s your HP capacity? Also, UFH or rads and what flow temperature are you running? I’m gonna have to apologise in advance for my ignorance on this! (And if you know of some useful guide that can bring me a bit more up to speed on ashp functioning, that would be much appreciated. I’m trying to troubleshoot and learn about the system at the same time) how do I see what my flow temp is? no idea what calculated heat loss is. have rads, no UFH Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 51 minutes ago, Conor said: Are the rads heating up? If the rads are warm, but room stays colds, suggests that heat loss rate is higher than what the system can match. What insulation and airtightness did you achieve? What size is the heat pump? Rads are warm to touch but not very warm. airtightness should be pretty good - new build bungalow that is mostly triple glazed glass. I don’t even know what size heat pump I have. I apologise again for my ignorance Im attaching images of the unit - it’s pretty frozen over too. I guess it’s spending all its time defrosting. Link to comment Share on other sites More sharing options...
ReedRichards Posted December 17, 2022 Share Posted December 17, 2022 Your Ecodan has a nominal 11.5 kW of output. That's the same size as I have for my 1980 bungalow so it's a lot for a new well-insulated house unless it's a large one. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 1 minute ago, ReedRichards said: Your Ecodan has a nominal 11.5 kW of output. That's the same size as I have for my 1980 bungalow so it's a lot for a new well-insulated house unless it's a large one. It’s a compact 4 bed bungalow, can’t remember exact square footage but 2500/3000 sqft Link to comment Share on other sites More sharing options...
ReedRichards Posted December 17, 2022 Share Posted December 17, 2022 New build bungalow yet you have radiators rather than underfloor heating. That's a bit surprising. I suspect that new builds are the most likely type of dwelling to have heat pumps installed by people who don't really know what they are doing. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 12 minutes ago, ReedRichards said: New build bungalow yet you have radiators rather than underfloor heating. That's a bit surprising. I suspect that new builds are the most likely type of dwelling to have heat pumps installed by people who don't really know what they are doing. That was my reaction. Having done some very superficial research. the radiators aren’t wall mounted - they’re coiled trench heaters. it’s a new build, but bespoke and should have been properly spec’d. I’ve asked my architects the question about UFH vs rads, as during the build there was a discussion about the two options, but I can’t remember the details. Obviously it’s the weekend so I’m waiting for a response from them! Link to comment Share on other sites More sharing options...
ReedRichards Posted December 17, 2022 Share Posted December 17, 2022 24 minutes ago, EdieCampbell said: the radiators aren’t wall mounted - they’re coiled trench heaters. Fan-assisted heaters or the type that just rely on natural convection? Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 44 minutes ago, ReedRichards said: Fan-assisted heaters or the type that just rely on natural convection? Natural convection. I think it’s manufactured by Verano, but I’d have to double check that Link to comment Share on other sites More sharing options...
akjos Posted December 17, 2022 Share Posted December 17, 2022 Your flow temp has been set by whoever installed/commissioned your system. Usually the setup is weather compensated, meaning you have a higher flow temp when it’s colder outside, and lower flow temp when it’s hotter. Heatpumps work more efficiently with lower flow temps, so you can expect a higher energy consumption during winter as the flow temps would be higher too most likely. Now in regards to heating your house, just ballparking it I still think 11kw should be enough for you. So it can either be as easy as bumping the flow temp higher, or there might be an inherent flaw with how the system was installed. Or your heat emmiters aren’t powerful enough to emit heat. Bumping the flow temp is easy. You just do it via the controller inside, though I dont how how exactly on the Ecodan. Other people on this forum will know or a google search will help you figure it out too. Just bump the weather compensation curve up, i.e higher flow temps and see what happens. That’s the easiest thing without any changes to the system, but your efficiency will drop a little. Link to comment Share on other sites More sharing options...
akjos Posted December 17, 2022 Share Posted December 17, 2022 Found this manual on setting the WC curve on the Ecodan. Page 12: https://planetaklimata.com.ua/instr/Mitsubishi_Electric_PUHZ-W-HW_OPERATION_MANUAL_Eng.pdf Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 Thankyou, I’ll have a play Link to comment Share on other sites More sharing options...
ReedRichards Posted December 17, 2022 Share Posted December 17, 2022 53 minutes ago, EdieCampbell said: Natural convection. I think it’s manufactured by Verano, but I’d have to double check that Here's a catalogue, which might help with identification: https://veranoconvector.co.uk/images/en/VK15-202006-EN.pdf . Perhaps you have a controller like the ones shown on page 40. I hope whoever calculated the size of your heaters took the low flow temperatures from a heat pump into account. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 I got it wrong - it’s actually the Kampman Kathern NK system. I hope the same. It should have been properly spec’d by an M&E specialist but I’m having serious doubts. I read elsewhere that the thermostat should be set reasonably high (I.e not the 16 I have mine at), to reduce cycling. I don’t even know what cycling is, but do you have opinions on this? I’m feeling utterly deflated that the house is just not heating. It’s been calling for heat all day, and has produced none. The outside temperature has come above freezing now. This morning at 7am the heat pump was frozen solid without the fan working. It’s now defrosted and the fan is going. The rooms are all still calling for heat, in the past 5hours it’s managed to produce an increase of about 0.5 degrees in each room. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 Oh forgot to add - the hot water is working. There’s always a good supply of DHW. So something is working. Link to comment Share on other sites More sharing options...
Conor Posted December 17, 2022 Share Posted December 17, 2022 You say this is bespoke new build. Your project or somebody else's? If yours, surely you know all the details of the design and what was done? Then you can go chasing your builder/suppliers if something wasn't to spec or not setup properly. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 Not my project in some senses - I commissioned an architect to build it. I know, strictly speaking, this is a forum for self-builders, but you seem a knowledgeable bunch. Link to comment Share on other sites More sharing options...
EdieCampbell Posted December 17, 2022 Author Share Posted December 17, 2022 (I am chasing the architects and builders, but it’s the weekend and they’re not in the office, and it’s freezing and and and ….) Link to comment Share on other sites More sharing options...
Marvin Posted December 17, 2022 Share Posted December 17, 2022 (edited) Hi @EdieCampbell This may help to start with: Edited December 17, 2022 by Marvin Completely changed Link to comment Share on other sites More sharing options...
ReedRichards Posted December 17, 2022 Share Posted December 17, 2022 3 hours ago, EdieCampbell said: I read elsewhere that the thermostat should be set reasonably high (I.e not the 16 I have mine at), to reduce cycling. I don’t even know what cycling is, but do you have opinions on this? Okay, "cycling" is not an issue, short cycling could be. This where the heat pump comes on for just a few minutes then goes off again and this happens repeatedly. It's liable to give you inefficient operation because each time the heat pump comes in a certain amount of heat is wasted in getting parts up to temperature and it is wasteful if this happens too frequently and as too high a percentage of the total heat generated. Short cycling could happen if the heat demand from your radiators is too small, the return water gets too hot and causes the heat pump to cut-off. If everything it set up properly and working normally this could happen if the thermostat is set too low. But your problems imply that everything is not "normal" so no need to worry about short cycling as such yet. Link to comment Share on other sites More sharing options...
TW9 Posted December 17, 2022 Share Posted December 17, 2022 I suspect the radiators aren't able to put out enough heat because they're too small. Did you have a heat loss assessment done on the house before the heating system was specified? This will tell you how much heat each room needs so you can check this against the radiator specifications. Make sure you check the spec at the correct flow temperature. Link to comment Share on other sites More sharing options...
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