Post and beam Posted September 5 Share Posted September 5 I have just had a heat loss calc done by our proposed supplier of UFH & ASHP. With regard to the emitters, they have a term '3.1 (HEG) ' . Quite apart from not expecting to need emitters of the size they specify which is a question i have raised with them. Can anyone shed light on this please? Link to comment Share on other sites More sharing options...
marshian Posted September 5 Share Posted September 5 54 minutes ago, Post and beam said: I have just had a heat loss calc done by our proposed supplier of UFH & ASHP. With regard to the emitters, they have a term '3.1 (HEG) ' . Quite apart from not expecting to need emitters of the size they specify which is a question i have raised with them. Can anyone shed light on this please? 3.1 Oversize factor (from the Heat Emitor Guide) They are trying to improve the Heat pump efficiency by ensuring the operational flow temp is 45 deg is my guess so 3.1 x oversize for the room heat loss https://zlcenergy.co.uk/wp-content/uploads/2013/08/MIS-3005-Supplementary-Information-2-Heat-Emitter-Guide-v2.0.pdf Link to comment Share on other sites More sharing options...
JohnMo Posted September 5 Share Posted September 5 1 hour ago, Post and beam said: proposed supplier of UFH & ASHP Other than UFH, where are you installing radiators? Your low energy house should be running pretty cool flow to the UFH, circa 30 ish at your lowest outside temp. If you are have radiators 1. Do you really need them? Upstairs bedroom unlikely to need them 2. make sure they have a design temp pretty close to your UFH Then run the whole system open loop. Remember No buffer No mixers or UFH pumps in the system. Both the above will have a direct impact on CoP Link to comment Share on other sites More sharing options...
Post and beam Posted September 5 Author Share Posted September 5 John Mo Well, there are other questions that i did not include in the original post. I have consistently said i want a flow of <35 degrees and ideally no more than 30 on 150mm centres for the ground floor only UFH. They have designed for 45 degrees flow on 300mm centres which is beginning to make me worry if A: they know what they are doing and B: have taken into account what i have asked for. In fact, also C Have they understood the design of this Potton house. Yes i have written back to them asking for clarification. I do not expect to need radiators upstairs at all and certianly not large ones. I have also always said i want single zone Link to comment Share on other sites More sharing options...
Post and beam Posted September 5 Author Share Posted September 5 Some time ago i tried to do my own heat loss calculation using the spreadsheet on this forum. I dont really know if i have done it correctly though and therefore have no confidence in the numbers. They may or may not be valid. But now i also dont have confidence in this proposed solution. I have a full design SAP calculation from Potton so it should be possible to generate a good set of data via the spreadsheet. Link to comment Share on other sites More sharing options...
Post and beam Posted September 5 Author Share Posted September 5 I found and have updated with some missing windows i forgot last year. Would anyone that understands the spreadsheet please look at these numbers and give their views. Heat loss - Caxton j DG 5 Sep 24.xls Link to comment Share on other sites More sharing options...
marshian Posted September 5 Share Posted September 5 1 hour ago, Post and beam said: I found and have updated with some missing windows i forgot last year. Would anyone that understands the spreadsheet please look at these numbers and give their views. Heat loss - Caxton j DG 5 Sep 24.xls 33 kB · 2 downloads 330 m3 is a big house - are you really going to replace all that air in the house every hour? Seems a bit high? 21 Deg for all rooms also seems a bit high - if the house is relatively well designed and sealed then a target temp of 19 is fine for me Link to comment Share on other sites More sharing options...
JohnMo Posted September 6 Share Posted September 6 Air changes can set at 0.3 to 0.5. A big house not many people set at 0.3 so the air doesn't dry too much in winter. If you want to heat the house house from just the ground floor you are likely going to need 150 to 200mm centres. Maybe time to look at a different supplier? Link to comment Share on other sites More sharing options...
Post and beam Posted September 6 Author Share Posted September 6 8 hours ago, marshian said: 330 m3 is a big house I need to look again at my spreadsheet because the house is 201 sq metres, storey and a half. Link to comment Share on other sites More sharing options...
Conor Posted September 6 Share Posted September 6 (edited) I've never used that sheet but at a glance your wall U value is way off at 0.33. should be something like 0.15? I used loopcad to design mine. While it was generally very good, it basically said you can't have any rooms without some sort of heat source. I just don't think the typical modelling software can accurately predict heat transfer between rooms. Had to ignore those issues and ensure the emittance in other areas totaled up to what was required by PHPP. Your designers will be seeing the same thing which is why they are specifying rads. If you want my single honest price of advice, stick UFH in every room at 150-200mm CC. Edited September 6 by Conor Link to comment Share on other sites More sharing options...
marshian Posted September 6 Share Posted September 6 11 hours ago, Post and beam said: I have consistently said i want a flow of <35 degrees and ideally no more than 30 on 150mm centres for the ground floor only UFH. They have designed for 45 degrees flow on 300mm centres which is beginning to make me worry if A: they know what they are doing and B: have taken into account what i have asked for. In fact, also C Have they understood the design of this Potton house. Yes i have written back to them asking for clarification. I do not expect to need radiators upstairs at all and certianly not large ones. I have also always said i want single zone I honestly think you need to find another supplier - if they aren't listening you are almost certainly going to get what you don't want I am assuming here that you are going for the BUS grant? Link to comment Share on other sites More sharing options...
Dave Jones Posted September 6 Share Posted September 6 11 hours ago, Post and beam said: John Mo Well, there are other questions that i did not include in the original post. I have consistently said i want a flow of <35 degrees and ideally no more than 30 on 150mm centres for the ground floor only UFH. They have designed for 45 degrees flow on 300mm centres which is beginning to make me worry if A: they know what they are doing and B: have taken into account what i have asked for. In fact, also C Have they understood the design of this Potton house. Yes i have written back to them asking for clarification. I do not expect to need radiators upstairs at all and certianly not large ones. I have also always said i want single zone you want 100mm centres max for low flow. Kick this lot into touch and do it yourself/sub in the trades. You will get a superior setup for half the cost. 1 Link to comment Share on other sites More sharing options...
Post and beam Posted September 6 Author Share Posted September 6 2 hours ago, Conor said: I've never used that sheet but at a glance your wall U value is way off at 0.33. should be something like 0.15? Then that is clearly a mistake i need to check. The wall value is .16 Link to comment Share on other sites More sharing options...
marshian Posted September 6 Share Posted September 6 58 minutes ago, Post and beam said: Then that is clearly a mistake i need to check. The wall value is .16 That is the value for the wall but for the section below it looks like averages the wall Window and Door area by the U value for each by area then divides it by the total area Link to comment Share on other sites More sharing options...
Nick Laslett Posted September 6 Share Posted September 6 (edited) 17 hours ago, Post and beam said: I found and have updated with some missing windows i forgot last year. Would anyone that understands the spreadsheet please look at these numbers and give their views. Heat loss - Caxton j DG 5 Sep 24.xls 33 kB · 13 downloads It looks fine to me. The “average wall U value = 0.33” is calculated and includes the windows. I take it you are planning to have a better air tightness than 1 air change per hour? Target should be 0.6, but anything below 1 is good. You will need a blower door test to get actuals for this. If you change this number you will see how big an effect, air tightness has on the heat loss. I also take it that you have got the mean minimum monthly temps from the MET office from your nearest weather station? Edited September 6 by Nick Laslett Link to comment Share on other sites More sharing options...
Nick Laslett Posted September 6 Share Posted September 6 (edited) oops, double post Edited September 6 by Nick Laslett Link to comment Share on other sites More sharing options...
Post and beam Posted September 6 Author Share Posted September 6 20 minutes ago, Nick Laslett said: It looks fine to me. The “average wall U value = 0.33” is calculated I have looked at it again and it is indeed as you say a calculated figure and not a slip of mine on the keyboard. I have to assume its correct. 22 minutes ago, Nick Laslett said: I also take it that you have got the mean minimum monthly temps from the MET office from your nearest weather station Yes. 22 minutes ago, Nick Laslett said: I take it you are planning to have a better air tightness than 1 air change per hour And yes i am. But i used 1 in case my score is not actually any better when i get that far. 1 Link to comment Share on other sites More sharing options...
Post and beam Posted September 6 Author Share Posted September 6 During a conversation with these guys this morning, when i questioned the flow temp and pipe centres i was told that 150mm centres might result in too much energy going into the floor resulting in cycling. They dont appear to grasp that that would be true if they stuck to their 45 degree flow temperature but would not be true if the flow temperature was reduced to a suitable value!! If i can find a company that will just install the ASHP/UFH and ignore the grant i think i might do that. Easier said than done though. Link to comment Share on other sites More sharing options...
marshian Posted September 6 Share Posted September 6 42 minutes ago, Post and beam said: During a conversation with these guys this morning, when i questioned the flow temp and pipe centres i was told that 150mm centres might result in too much energy going into the floor resulting in cycling. They dont appear to grasp that that would be true if they stuck to their 45 degree flow temperature but would not be true if the flow temperature was reduced to a suitable value!! If i can find a company that will just install the ASHP/UFH and ignore the grant i think i might do that. Easier said than done though. I think that tells you all you need to know - they are working to a one size fits all script and complies with the BUS grant criteria I’d find someone who actually will design a system that meets your criteria which I don’t think is impossible at all No local “heat geek” trained installer??? Link to comment Share on other sites More sharing options...
JohnMo Posted September 6 Share Posted September 6 2 hours ago, Nick Laslett said: take it you are planning to have a better air tightness than 1 air change per hour It's actually air changes per hour not air tightness, that goes in the box in the spreadsheet. Different things. If you have MVHR that air change figure is close enough. Link to comment Share on other sites More sharing options...
JohnMo Posted September 6 Share Posted September 6 1 hour ago, Post and beam said: 150mm centres might result in too much energy going into the floor resulting in cycling They are wrong. I get some cycling, which I can manage, because I have 300mm centres. By default closer centres has way more water in the system, this prevents cycling to a good degree. You also have more contact area with the screed so heat gets carried away easier. You manage energy by flow temp. Which can go down to a flow temp of 25. Link to comment Share on other sites More sharing options...
Post and beam Posted September 6 Author Share Posted September 6 17 minutes ago, JohnMo said: They are wrong. I know, i was illustrating the fact that they dont appear to know what they are talking about. This was not their technical guy so i am giving them a chance next week to see if they can say anything to restore their credibility. Link to comment Share on other sites More sharing options...
SBMS Posted September 6 Share Posted September 6 2 hours ago, Post and beam said: I know, i was illustrating the fact that they dont appear to know what they are talking about. This was not their technical guy so i am giving them a chance next week to see if they can say anything to restore their credibility. For those of us not in the know, and who are setting out on UFH design with an ASHP can you summarise the point regarding centres and flow temp? Link to comment Share on other sites More sharing options...
ReedRichards Posted September 7 Share Posted September 7 8 hours ago, SBMS said: can you summarise the point regarding centres and flow temp? Surely it's just about the amount of warmed water you have per unit area of floor? The closer you make the pipes then the more warmed water per unit floor area so the more heat it can give out for any given water temperature. Since what you want is a fixed amount of heat for any given outside temperature then the closer the pipes the cooler you can make the water so the more economically you can run your heat pump (provided it's not also having to provide heated water for radiators elsewhere in the building). Link to comment Share on other sites More sharing options...
SBMS Posted September 7 Share Posted September 7 21 minutes ago, ReedRichards said: Surely it's just about the amount of warmed water you have per unit area of floor? The closer you make the pipes then the more warmed water per unit floor area so the more heat it can give out for any given water temperature. Since what you want is a fixed amount of heat for any given outside temperature then the closer the pipes the cooler you can make the water so the more economically you can run your heat pump (provided it's not also having to provide heated water for radiators elsewhere in the building). Yes, it was more about the cycling that JohnMo mentioned that I was trying to understand. Link to comment Share on other sites More sharing options...
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