GaryChaplin Posted January 2 Share Posted January 2 (edited) I know this is a bit of a daft question as is subject to many factors, however I am currently getting quotes for an ASHP install and really don't have a baseline. We should qualify for the £7.5k grant, which I was rather hoping would cover the majority of the cost. I found a rather useful heat loss calculator on here, which I have completed and it suggests just over 2.5kW. Though one of my quotes has come back with their own heat loss figure of over 5kW. Seems way off! Anyway, assuming the 2.5kW heat loss is accurate, what size ASHP should I require and what price range should I expect? Edited January 2 by GaryChaplin Link to comment Share on other sites More sharing options...
JohnMo Posted January 2 Share Posted January 2 If it is 2kW, you don't really get a heat pump that small, if you did DHW would take to long to heat up. You need to look at the output at your design temp to see what matches, they all quote different kW outputs, one may do 5kW at -10, while the next may do 5kW at plus 15 and only kW at -10. And are rated as 5kW. MCS assume you don't have MVHR and will not include in the calculation. Realistically it's going to be an ASHP in the 4 to 6kW with a buffer Link to comment Share on other sites More sharing options...
joth Posted January 2 Share Posted January 2 31 minutes ago, GaryChaplin said: Though one of my quotes has come back with their own heat loss figure of over 5kW. Seems way off! Was the quote for 5kW heat loss, or a 5kW heat pump? It's usual to oversize the HP a bit (1.5x or so) to avoid it running 24/7 in cold weather and to give duty cycle time for DHW reheat. And some head room incase incase... But yes as per JohnMo 2.5kW is very low heat loss. To sense check it, how many m2 floor area and what build quality? What is your EPC? Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 2 Author Share Posted January 2 Please elaborate on the acronyms? I have very little knowledge on plumbing and am trying to wing it! The spreadsheet suggested 2.5kW heat loss. It’s only medium sized 1½ storey building and has huge amounts of insulation. I have no idea what figures to expect but hope for maximum efficiency. Waiting on an EPC. Link to comment Share on other sites More sharing options...
saveasteading Posted January 2 Share Posted January 2 1 hour ago, GaryChaplin said: I know this is a bit of a daft question No its not. And you are right to tell us off for acronyms without explanation. ,But you started it with ASHP. Good luck with the EPC currently TBC. 1 Link to comment Share on other sites More sharing options...
joth Posted January 2 Share Posted January 2 (A forum glossary wouldn't be a bad call, can't recall we have one) DHW = Domestic hot water. The stuff you shower / wash hands with HP = Heat pump MCS = Microgeneration Certification scheme. Bureaucracy heavy installer standards body that are gate keepers to government grant money MVHR = Mechanical ventilation with heat recovery. Provides fresh breathable condensation free air to the whole house without throwing hard-won heat out the window. Standard in most of western Europe but still considered dark magic by most of the UK building industry Link to comment Share on other sites More sharing options...
SteamyTea Posted January 2 Share Posted January 2 4 minutes ago, joth said: A forum glossary wouldn't be a bad call, can't recall we have one Of course we have one, just that the search facility on here is so bad we would be better of getting rid of it and just putting a link to Google up. 1 Link to comment Share on other sites More sharing options...
Tom Posted January 2 Share Posted January 2 (edited) 4 hours ago, GaryChaplin said: Anyway, assuming the 2.5kW heat loss is accurate, what size ASHP should I require and what price range should I expect? I'm just going through this process now actually. My heat loss came out at very similar to yours, but the calculations that various ashp suppliers came back with was anything from 5kW ro 15kW. Anyway, quotes for an ashp in the 8-9kW range came in at about £5.5k (after the 7.5k grant taken off). Seems like a nice little earner for a few days work... I questioned the EDF salesman why I would have to pay £1.5k for "design" and he just came up with a load of sales bollocks. Anyway, I've settled on a local-ish firm who will fit an 8.5kW ecodan for £2700 net. Edited January 2 by Tom 1 Link to comment Share on other sites More sharing options...
JohnMo Posted January 2 Share Posted January 2 16 minutes ago, Tom said: I'm just going through this process now actually. My heat loss came out at very similar to yours, Anyway, I've settled on a local-ish firm who will fit an 8.5kW ecodan for £2700 net. 8.5kW heat for 2.5kW sounds like overkill, you will need a decent sized buffer to keep it happy and no more than one zone. Or if you have UFH and decent depth of screed batch charge overnight. Link to comment Share on other sites More sharing options...
HughF Posted January 2 Share Posted January 2 It’s a shame the modulation ratio on 99% of heat pumps is so bad. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 2 Share Posted January 2 7 minutes ago, JohnMo said: 8.5kW heat for 2.5kW sounds like overkill Do you think that it is just what plumbers do. If unsure of the size, go bigger, then add a bit. Link to comment Share on other sites More sharing options...
HughF Posted January 2 Share Posted January 2 MCS does require the system to supply 100% of the dhw and heating requirement, and no-one wants to install a system that’s too small. Link to comment Share on other sites More sharing options...
Tom Posted January 2 Share Posted January 2 42 minutes ago, JohnMo said: Or if you have UFH and decent depth of screed batch charge overnight. ^^ this, pipes set at the bottom of a 200mm concrete slab Link to comment Share on other sites More sharing options...
JohnMo Posted January 2 Share Posted January 2 55 minutes ago, Tom said: ^^ this, pipes set at the bottom of a 200mm concrete slab So on a design day you can run the heat pump for 7 hrs and get a full 24hrs worth of energy into the floor. 1 Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 3 Author Share Posted January 3 (edited) 13 hours ago, SteamyTea said: Do you think that it is just what plumbers do. If unsure of the size, go bigger, then add a bit. As far as I understand, this is what NOT to do. With conventional boilers you can do this, but heat pumps just will not be efficient if oversized. They need to be working quite hard to get optimum perfomance. It would appear that many authorised installers are just adding the grant to their profit margin! First quote includes £5600 for the install! Edited January 3 by GaryChaplin Link to comment Share on other sites More sharing options...
SteamyTea Posted January 3 Share Posted January 3 2 minutes ago, GaryChaplin said: They need to be working quite hard to get optimum perfomance. Are you sure about that? The way the physics works does not support that. Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 3 Author Share Posted January 3 3 minutes ago, SteamyTea said: Are you sure about that? The way the physics works does not support that. No, I'm not sure as it was what I was told by a refrigiration engineer. But I'll now go and do some reading. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 3 Share Posted January 3 3 minutes ago, GaryChaplin said: refrigiration engineer I bet he was not an engineer. Technician probably. Here is a good place to start. https://en.wikipedia.org/wiki/Heat_engine Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 3 Author Share Posted January 3 From memory it was to do with a bigger unit having to switch on & off, which is less efficient than a smaller unit working steadily. I just need to know the basics as want to make a reasonably informed decision. Link to comment Share on other sites More sharing options...
HughF Posted January 3 Share Posted January 3 (edited) There is a point at low compressor rpm (and hence a low output) where a greater efficiency is gained by moving to start/stop than by running the compresssor very slowly. I will check my Carel tech notes for the reference for this. But that’s why nearly all heat pumps have a poor modulation ratio, and why they’ll turn the compressor off when they drop below a certain output. Edited January 3 by HughF Link to comment Share on other sites More sharing options...
Alan Ambrose Posted January 3 Share Posted January 3 Hi Gary, the J Harris spreadsheet is good. I'm sure you will have the surface areas right but it might be worth checking the U-Values as 2.5 total seems a bit low. You can do a quick double check by taking the main insulation material thickness and ignoring the rest. Or you can put the whole stack-up (or just the bit that is actually doing insulation) into ubakus to get a bit more accuracy. You have some feel for your air tightness and your DHW need? Then assume the other thermal leaks roughly net out with the other misc gains from people / always on equipment etc and you won't be far wrong. Another way of double checking is to put a 3kW fan heater in there when its pretty cold outside and see whether it can bring the temperature up to something reasonable within say 1/2 a day. Link to comment Share on other sites More sharing options...
ReedRichards Posted January 3 Share Posted January 3 14 hours ago, HughF said: It’s a shame the modulation ratio on 99% of heat pumps is so bad. So why are we all talking about a 5 Kw heat pump (say) instead of a 1 to 5 kW heat pump and quoting the minimum output power as well as a maximum? Link to comment Share on other sites More sharing options...
HughF Posted January 3 Share Posted January 3 2 minutes ago, ReedRichards said: So why are we all talking about a 5 Kw heat pump (say) instead of a 1 to 5 kW heat pump and quoting the minimum output power as well as a maximum? The same reason everyone talks about a 30kW boiler? I dunno, a historical hangup from when everyone had on/off controls? Oh wait, they still do…. 🤣 Link to comment Share on other sites More sharing options...
saveasteading Posted January 3 Share Posted January 3 48 minutes ago, GaryChaplin said: told by a refrigiration engineer I've not met a refrigeration business ( in about 8 projecrs) who understood the science of it. Like many trades in the industry, they had been installers fof a while, then started their own business, which was joining up plumbing stuff and insulation panels. As implied, they were barely technicians, let alone engineers, even small e. I'm sure there are good ones who lose tenders to the cheap ones. This discussion is concerning. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 3 Share Posted January 3 (edited) 14 hours ago, HughF said: It’s a shame the modulation ratio on 99% of heat pumps is so bad. It is the way they work. While it is possible to make a heat pump modulate as much as you like, you loose efficiency and reliability. It is a bit like modulating an open fire. You can put less fuel on it, which reduces the thermal output, but at the same time, it reduces the temperature difference, which causes the smoke to rise less. Eventually there is no air movement up the chimney and the room fills with smoke. Edited January 3 by SteamyTea 1 Link to comment Share on other sites More sharing options...
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