F113tch Posted January 23, 2022 Share Posted January 23, 2022 Hi, I am new to the forum so please be kind! Having recently been advised that there are supply issues with my GSHP I stumbled across this forum whilst searching for an alternative supplier. After lots of reading on this forum I am now swayed towards an ASHP. My original GSHP design proposed a 12kW unit therefore am I correct in assuming (if the calcs were right!) that I would exchange the 12kW GSHP for a 12kW ASHP? The property is c. 350m2 with the following level of insulation: 100mm PIR in 150mm cavity walls. 100mm PIR underfloor. 170mm PIR (TBC) in roof (cold-construction). I have had a SAP report completed however, I do not understand how the report can help me in sizing my heat pump, if this is indeed possible therefore any help on sizing a ASHP would be much appreciated? Kind Regards, Steve. Link to comment Share on other sites More sharing options...
ProDave Posted January 23, 2022 Share Posted January 23, 2022 Who sized the GSHP at 12kW? If that is correct then an ASHP would also be 12kW. There are reported shortages of ASHP's as well so best of luck. some suggest the last gasp of the RHI is producing a demand peak to get systems in before that runs out. 1 Link to comment Share on other sites More sharing options...
F113tch Posted January 23, 2022 Author Share Posted January 23, 2022 Thanks for the reply ProDave. The GSHP was sized by NuHeat, but after reading on here, 12kW seems much bigger than most are using. I am aware that the house is only ‘reasonably’ well insulated compared to what others have, however I am just wanting to check that 12kW is the correct size unit for the size and type of construction of my new-build? Hopefully supply with return to some form of normality once the RHI deadline has passed. Link to comment Share on other sites More sharing options...
ReedRichards Posted January 23, 2022 Share Posted January 23, 2022 I have a 12 kW heat pump but I live in a bungalow built in 1980. As part of the requirement to qualify for the RHI my installer came and surveyed the house and calculated the heat loss for every room and added it all together. On top of that they add a margin for the time the heat pump is heating the water (or defrosting) and a little bit of headroom. I have subsequently found out that heat pumps seem to be most efficient when operating at moderate levels of their maximum capacity so I'm not sure what the optimum amount of "headroom" should be. Link to comment Share on other sites More sharing options...
Conor Posted January 24, 2022 Share Posted January 24, 2022 If anything your pump might be slightly undersized, not over. I've double the insualtion you have and are under 300m² and we are going for a 9kW pump (double our peak head demand) Search the forum for the heatloss calculator and give it ago. 1 Link to comment Share on other sites More sharing options...
F113tch Posted January 24, 2022 Author Share Posted January 24, 2022 Thanks for your replies gents. I will have a go with the heat loss calculator tomorrow. Out of interest Conor, have you selected the manufacturer of your ASHP please? If so, what have you selected and why? Link to comment Share on other sites More sharing options...
Conor Posted January 24, 2022 Share Posted January 24, 2022 16 minutes ago, F113tch said: Thanks for your replies gents. I will have a go with the heat loss calculator tomorrow. Out of interest Conor, have you selected the manufacturer of your ASHP please? If so, what have you selected and why? Cool Energy. Was set on an Mitsubishi ecodan but couldn't find one in stock. Cool energy was competitively priced and got a package with tank, buffer, controls etc so didn't have to think beyond the order. Tank is plumbed in but not got the ashp connected yet. @dpmiller seems happy with his. Link to comment Share on other sites More sharing options...
F113tch Posted January 24, 2022 Author Share Posted January 24, 2022 Who completed the design of the system for you please or is this something you did yourself? @Conor PS. I have found the heat loss calculator - many thanks for the heads up. Link to comment Share on other sites More sharing options...
Iceverge Posted January 24, 2022 Share Posted January 24, 2022 On 23/01/2022 at 20:29, F113tch said: he property is c. 350m2 with the following level of insulation: 100mm PIR in 150mm cavity walls. 100mm PIR underfloor. 170mm PIR (TBC) in roof (cold-construction). Is the house built yet?.......... Link to comment Share on other sites More sharing options...
Conor Posted January 25, 2022 Share Posted January 25, 2022 8 hours ago, F113tch said: Who completed the design of the system for you please or is this something you did yourself? @Conor PS. I have found the heat loss calculator - many thanks for the heads up. I did it on loopcad. The ground and top floors were done precisely to meet the heat load requirements and I used the optimal spiral pattern. Sprayed out the pipe routes in advance. Took two days to do 175m². For the basement, we basically skipped all the design and went straight to simply marking out the pipe centres in each room and roughly calculating the loop runs in our head. Laid using the serpentine pattern. Much easier and faster. 115m² done in half a day. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 17 hours ago, Iceverge said: Is the house built yet?.......... It is to the point in the build where the only insulation I can increase is in the roof. I assume the advice would have been to increase the insulation if I could have? Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 10 hours ago, Conor said: I did it on loopcad. The ground and top floors were done precisely to meet the heat load requirements and I used the optimal spiral pattern. Sprayed out the pipe routes in advance. Took two days to do 175m². For the basement, we basically skipped all the design and went straight to simply marking out the pipe centres in each room and roughly calculating the loop runs in our head. Laid using the serpentine pattern. Much easier and faster. 115m² done in half a day. I have just had an UFH design completed by the screeding guys as the previous design appeared to have lots of issues i.e. 200mm centres and pipe runs way in excess of 100m. Did you also calculate the size of your ASHP, buffer tank, etc or did you get a company to complete this please? I ask as there seems to be a great disparity in the quality of the quotes and information I am receiving. All good fun though! Link to comment Share on other sites More sharing options...
ProDave Posted January 25, 2022 Share Posted January 25, 2022 4 minutes ago, F113tch said: I have just had an UFH design completed by the screeding guys as the previous design appeared to have lots of issues i.e. 200mm centres and pipe runs way in excess of 100m. Did you also calculate the size of your ASHP, buffer tank, etc or did you get a company to complete this please? I ask as there seems to be a great disparity in the quality of the quotes and information I am receiving. All good fun though! And what is "wrong" with 200mm pipe spacing? Care to post the design? Link to comment Share on other sites More sharing options...
SteamyTea Posted January 25, 2022 Share Posted January 25, 2022 3 minutes ago, ProDave said: Care to post the design And the heat loss calculations for each room, along with the power of the heat source. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 6 minutes ago, ProDave said: And what is "wrong" with 200mm pipe spacing? Care to post the design? Hi Dave, in the design using 200mm spacing it was suggested I would need supplementary heating in the bathrooms as the desired temperatures could not be achieved. I am assuming, but happy to be corrected, that reducing the centres in these rooms will increase heat output and I therefore may not need additional heating? I am expecting the design anytime now and will be happy to post for critique. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 6 minutes ago, SteamyTea said: And the heat loss calculations for each room, along with the power of the heat source. Hi Steamy Tea, Unfortunately I have not been given the heat-loss calcs by the company that completed the first design. I was pointed in the direction of a heat-loss calculation tool last night that a lot of people have used on here that will hopefully help me estimate the heat loss. I do have the SAP report but do not fully understand it at present... The heat-source specified was a 12kW GSHP. Link to comment Share on other sites More sharing options...
ProDave Posted January 25, 2022 Share Posted January 25, 2022 6 minutes ago, F113tch said: Hi Dave, in the design using 200mm spacing it was suggested I would need supplementary heating in the bathrooms as the desired temperatures could not be achieved. I am assuming, but happy to be corrected, that reducing the centres in these rooms will increase heat output and I therefore may not need additional heating? I am expecting the design anytime now and will be happy to post for critique. You would only know that with a proper detailed heat loss room by room. This is the second house we have built, both with 200mm spaced UFH. The first one, 18 years ago was an "ordinary" timber framed house with 150mm insulation in the walls, 200mm under the floor and 300mm in the loft and there was no issue with cold rooms. Closer spacing does not create problems so no problem going closer just to be sure. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 3 minutes ago, ProDave said: You would only know that with a proper detailed heat loss room by room. This is the second house we have built, both with 200mm spaced UFH. The first one, 18 years ago was an "ordinary" timber framed house with 150mm insulation in the walls, 200mm under the floor and 300mm in the loft and there was no issue with cold rooms. Closer spacing does not create problems so no problem going closer just to be sure. Thanks for the reply Dave. I will complete a heat loss calc for the individual rooms. It is good to know that there is no detriment to 150mm spacing, other than cost. It is a steep learning curve for me at present! Link to comment Share on other sites More sharing options...
SteamyTea Posted January 25, 2022 Share Posted January 25, 2022 The pipe spacing is about power delivery, not energy. The only problem with wider spacing would be if you had to run at a higher temperature, increasing losses to the ground, or required a faster slab recharge time i.e running on an E7 time window. Link to comment Share on other sites More sharing options...
epsilonGreedy Posted January 25, 2022 Share Posted January 25, 2022 39 minutes ago, ProDave said: Closer spacing does not create problems so no problem going closer just to be sure. Plus a chance to redesign the pipe layout to get the loop lengths under 100m. Link to comment Share on other sites More sharing options...
epsilonGreedy Posted January 25, 2022 Share Posted January 25, 2022 42 minutes ago, F113tch said: It is good to know that there is no detriment to 150mm spacing, other than cost. Some try to avoid UFH pipe congestion at door thresholds because these are a weak point in the slab. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 (edited) 4 minutes ago, epsilonGreedy said: Some try to avoid UFH pipe congestion at door thresholds because these are a weak point in the slab. The updated 150mm centre design is to use 2 x manifolds downstairs which will help avoid the congestion you mention. Edited January 25, 2022 by F113tch Link to comment Share on other sites More sharing options...
Conor Posted January 25, 2022 Share Posted January 25, 2022 2 hours ago, F113tch said: I have just had an UFH design completed by the screeding guys as the previous design appeared to have lots of issues i.e. 200mm centres and pipe runs way in excess of 100m. Did you also calculate the size of your ASHP, buffer tank, etc or did you get a company to complete this please? I ask as there seems to be a great disparity in the quality of the quotes and information I am receiving. All good fun though! Architect did the PHPP modelling that said peak head load would be 3.5kW. also used loopcad that did room by room modelling. It was greatly over estimating heating requirements for some reason. As it's a passive-ish house and currently 5 small dehumidifiers are keeping it (top two floors) at 17c, I'm not too worried. Link to comment Share on other sites More sharing options...
epsilonGreedy Posted January 25, 2022 Share Posted January 25, 2022 12 minutes ago, F113tch said: The updated 150mm centre design is to use 2 x manifolds downstairs which will help avoid the congestion you mention. Sounds like you have this covered. When you get around to plumbing the manifolds up to the heat source I advise spending some time to fully comprehend posts from @Nickfromwalesabout ensuring the two feeds are hydrodynamically decoupled and the same applies to radiator circuits. I would be very interest to hear what heat loss down through the floor is predicted when you produce a detailed model. There has been some debate here recently about insulation thickness under a heated slab and your 100mm of PIR is a bit on the low side. You might find 15% of total heat loss is via the floor. Link to comment Share on other sites More sharing options...
F113tch Posted January 25, 2022 Author Share Posted January 25, 2022 1 hour ago, epsilonGreedy said: Sounds like you have this covered. When you get around to plumbing the manifolds up to the heat source I advise spending some time to fully comprehend posts from @Nickfromwalesabout ensuring the two feeds are hydrodynamically decoupled and the same applies to radiator circuits. Could you point me in the right direction for the post you are referring to please? Many Thanks, Steve. Link to comment Share on other sites More sharing options...
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