Indy Posted November 22 Share Posted November 22 (edited) Pertinent details of our build 260sq m masonry build to BR standards and emphasis on airtightness. U Values Floor: 0.14 Walls: 0.15 Roof: 0.11 Doors/windows: 1.2 Wet UFH heating on both floors – ground and first. 22mm system for the first floor due to height restrictions. Missus likes feeling extra warm all the time - wants temperatures of upto 22C in the rooms. No carpets through the property. Tiles in the living/hallway etc and then engineered wood in the bedrooms Digital thermostats for each bedroom, study, living/dining area (8 in total) ASHP – most likely 10kW 3-400l UVC MVHR Solar PV – 16 panels (7.1kW) Solar battery storage – maybe, depending on price but 5-10kWH battery to be added later. This is generally straightforward and easily speccable. Where things start to get confusing is my desire to add some sort of cooling to the property. This would be in 5 rooms (4 bedrooms + living/dining area) or 8 rooms (adding studies) if we can find a system big enough. Plan A – add a separate air con system using a 5-8way multi split system. One big external unit that sits outside and wall mounted units within the rooms – both to be added in 2 years time when we regenerate funds. Part of the build would be to have power and ducting/pipework to allow the external and internal units to be connected so that we’re not ripping open walls again. Rough cost of £10-£15k for a system like this. Plan B – get a heat hump that runs cooling as well. Not eligible for grant but price difference won’t be that much. Dissuaded against this as running heat pump in reverse means issues with condensation. Plan C – get an MVHR system that also does cooling. BPC quote for standard MVHR parts is £5k for Zehnder Q600(parts only) and £20k for 2 x Q600s with Enthalpy exchanger and ductwork for cooling option. Not going to be as good as active air con but the price differential is quite significant. Plan D – get a Fan Convector unit/Fan coil unit. I’ve picked this up reading these forums and had no idea of the existence of these. But it seems that this look like radiators and can be floor or wall mounted and can do heating as well as cooling? Does this mean I only get the standard MVHR unit, wet UFH heating on ground floor and then install these FCUs in the bedrooms on the 1st floor? Do they work like air con in the summer and radiators in the winter? What additional pipework do I have to get done for these – if I decide only to get the pipework done now and the actual units added later? Make it make sense please! Would really appreciate some guidance as trying to find a company that pulls this all together in a simple package has been an exercise in futility mostly. They all want to quote or sell products that they stock and not really looking at what would be the most effective option – both in terms of installation and running costs. Thanks in advance. Edited November 22 by Indy Link to comment Share on other sites More sharing options...
JohnMo Posted November 22 Share Posted November 22 57 minutes ago, Indy said: Digital thermostats for each bedroom, study, living/dining area (8 in total) Be careful here. Most thermostats are really rubbish with with UFH as the hysteresis is huge and you end up with big under and overshoot of room temp. When we first build I had loads of issues and found it unmanageable, and uncomfortable. Running weather compensation without thermostats works best for us. 1 hour ago, Indy said: ASHP – most likely 10kW That sound huge with MVHR and your U values are you sure, have you calculated the heat loss. 1 hour ago, Indy said: UFH heating on both floors I am not impressed with UFH in bedrooms, would do fan coils, way better cooling also, plus response time is good. Hate hot bedrooms, once the bedroom is warm its staying that way with UFH. 1 hour ago, Indy said: Plan A – add a separate air con system using a 5-8way multi split system. One big external unit that sits outside and wall mounted units within the rooms – both to be added in 2 years time when we regenerate funds. Part of the build would be to have power and ducting/pipework to allow the external and internal units to be connected so that we’re not ripping open walls again. Rough cost of £10-£15k for a system like this. Sounds a waste of good money 1 hour ago, Indy said: Plan B – get a heat hump that runs cooling as well. Not eligible for grant but price difference won’t be that much. Dissuaded against this as running heat pump in reverse means issues with condensation. No restriction come with grant that says you cannot cool. It is related to permitted development, but you will have express planning permission with a new build so, make sense to go with option for heat and cool. 1 hour ago, Indy said: Plan C – get an MVHR system that also does cooling. Another waste of cash, it doesn't do much in the UK, check the datasheets for you flow rates you will get about 0.5kW max at super low flow temps. 1 hour ago, Indy said: Plan D – get a Fan Convector unit/Fan coil unit. I’ve picked this up reading these forums and had no idea of the existence of these. But it seems that this look like radiators and can be floor or wall mounted and can do heating as well as cooling? Does this mean I only get the standard MVHR unit, wet UFH heating on ground floor and then install these FCUs in the bedrooms on the 1st floor? Do they work like air con in the summer and radiators in the winter? What additional pipework do I have to get done for these – if I decide only to get the pipework done now and the actual units added later? Install in bedroom instead of UFH. Fun UFH and fan coils on same WC flow rates for heating and cooling. No additional piping needed. So standard MVHR (its ventilation only) ASHP with cooling ability Heat pump cylinder Fan coils in bedrooms, they will manage room temps in auto mode or you can run in manual fan mode on WC UFH on ground floor and upstairs wet room. Electric towel rads in wet rooms also. If you can add more insulation to floor. Keep ventilation separate from heating - different suppliers, installers, they are vey different things Think simple not complex, simple is easier to run, cheaper to buy and run 3 Link to comment Share on other sites More sharing options...
Indy Posted November 23 Author Share Posted November 23 Thanks for the detailed reply. Just to make sure I understand, I'm going to break it down step by step - and please correct me if I've got this wrong. 1. Standard MVHR - no cooling added 2. ASHP with cooling function - may or may not be eligible for grant but if we have only 1 unit, then we can put this outside without going back to planning and do it under PD rules. 3. Heat pump cylinder - 300 to 400l for 3 bathrooms and 1 cloak room. 4. Wet UFH heating on the ground floor 5. Can I also put fan coils in certain rooms on the ground floor with the wet UFH? This will make them work as air con units in the summer when we run the ASHP in reverse. 6. Any modifications needed to the ASHP to make sure running in reverse doesn't cause issues? 7. Wet UFH only in bathrooms upstairs, and not bedrooms? Will the fan coils work enough on their own to provide heating up to say 22-23C to keep the rooms at that temp? And what temp can they cool down to in the summer? 8. I currently have towel rads that run off the ASHP and then an immersion element that can be turned off or on. I assume this is the equivalent of electric towel rads? 9. Stupid question: the fan coil units will have plumbing connections to them I assume - i.e. a pipe coming in and a pipe going out? 10. Why not have thermostats in the rooms? Or can we replace the thermostat with the fan coil unit which I assume will have some sort of manual control on it rather than running of a central system? With regards to floor insulation - we did speak to the architect about adding more but his opinion is that BR regs are pretty good these days, and coming from my baseline of a 1930s semi with no cavity walls at all - it's going to be a massive step up. This is what I have so far Floor construction: U Value = 0.14 W/m².K 65mm. sand: cement screed 500g. Polythene separation layer 120mm. Celotex XR4000 insulation Polythene DPM Concrete beam & block floor to manufacturer's design Wall construction: U Value = 0.15 W/m².K Render 100mm. Thermalite Hi Strength 7 blockwork 50mm. clear cavity 100mm. Celotex CW4000 insulation 100mm. Thermalite Hi Strength 7 blockwork 12.5mm. plasterboard on dabs dry lining, plus skim Pitched roof construction (insulation at rafter level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters fully filled with 150mm. Celotex XR4000 insulation 25x47mm. battened services void beneath rafters Celotex PL4060 (60+12.5) insulated plasterboard plus skim Proprietary felt support tray Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters Unventilated loft space 19mm. plywood decking or flooring plywood for loft storage 75mm. Celotex GA4000 insulation above ceiling joists 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation Visqueen High Performance vapour barrier 12.5mm. plasterboard plus skim COLD Flat roof construction: U Value = 0.11 W/m².K GRP weather surface 18mm. plywood deck Firrings to give 1:40 fall 195mm. joists with 150mm. Celotex XR4000 between joists 90mm. Celotex GA4000 insulation below joists 12.5mm. plasterboad plus skim Link to comment Share on other sites More sharing options...
JohnMo Posted November 23 Share Posted November 23 2. Permitted development does not exist under planning permission. So if doing a new build permitted development only come after build control sign off. 5. Yes 6. Some need a widget adding such as Valiant, most will do it out the box, Daikin some will cool some will not. So be careful with choice. 7. You need to size for heat pump flow temps. 9. Yes 10. Thermostats mean you need a buffer, because you restricted flow from heat pump. Buffers unless very big are useless. Floor insulation, the more the better with UFH. Your floor is hotter than the room, so downwards heat loss can be high. 1 Link to comment Share on other sites More sharing options...
G and J Posted November 23 Share Posted November 23 2 hours ago, Indy said: 7. Wet UFH only in bathrooms upstairs It’s a personal thing I guess but I’ve read on here many times that electric mat UFH in bathrooms gives warm wet toes even when the rest of the house doesn’t need heating. Zoning ASHP based UFH appears to be bad news. My history is boiler and wet rads with zines which works well in my wind tunnel house. So it took me a while to get my head round heated slab, slow reaction time, different control methodology entirely. Talking of which….. Link to comment Share on other sites More sharing options...
G and J Posted November 23 Share Posted November 23 2 hours ago, Indy said: Floor construction: U Value = 0.14 W/m².K 65mm. sand: cement screed 500g. Polythene separation layer 120mm. Celotex XR4000 insulation Polythene DPM Concrete beam & block floor to manufacturer's design I think you may benefit from a bigger slab to benefit from more thermal mass. (To the pedants, I know that there is scientifically no such thing but it is a useful concept in such debates. So there.). Now I appreciate that someone with letters after their name has decreed stuff but you are the client, so actually, what you want tops their sometimes odd preferences. And remember sometimes the guys doing the drawing are driven more by how quickly they can get onto the next job than they are by your long term happiness. I’m looking at slightly lowering our bnb and increasing our screed to 100mm (75mm in drawings) and maybe upping the insulation from the 150mm PIR as drawn. Might use an insulated bnb to help that. Link to comment Share on other sites More sharing options...
G and J Posted November 23 Share Posted November 23 2 hours ago, Indy said: Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters Unventilated loft space 19mm. plywood decking or flooring plywood for loft storage 75mm. Celotex GA4000 insulation above ceiling joists 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation Visqueen High Performance vapour barrier 12.5mm. plasterboard plus skim We’ve not had our as designed SAP done yet but we’ve designed out lots of PIR on the basis that it gives a more echoey house and is bad for the planet (and our carbon score). So we are going for loads of soft fluffy stuff in the loft that will take me no time at all to deploy (c.f. many miserable hours trimming PIR to fit between trusses) and a raised walkway so as not to compress the fluff. I’m hoping it will mean the rooms are quieter and feel nicer. Certainly PIR is not the most popular stuff in here with everyone. Link to comment Share on other sites More sharing options...
G and J Posted November 23 Share Posted November 23 On 22/11/2024 at 14:02, Indy said: Solar battery storage – maybe, depending on price but 5-10kWH battery to be added later I’ll be wiring to make adding a battery later easy, but I can’t for the life of me build a case for it right now. There appears to be no eco benefit and there won’t be a financial one for us. But prices will come down…. Link to comment Share on other sites More sharing options...
jfb Posted November 23 Share Posted November 23 On 22/11/2024 at 15:19, JohnMo said: No restriction come with grant that says you cannot cool Are you sure about that? I was under the impression that if you are including cooling with the ashp you can’t get the grant Link to comment Share on other sites More sharing options...
G and J Posted November 23 Share Posted November 23 10 minutes ago, jfb said: Are you sure about that? I was under the impression that if you are including cooling with the ashp you can’t get the grant I’ll let you know if and when I get the grant, for my ASHP that cools too! (Perhaps sometime next summer). Link to comment Share on other sites More sharing options...
JohnMo Posted November 23 Share Posted November 23 9 minutes ago, jfb said: Are you sure about that? Yes. You need to split some of thought processes out. New build is covered by express planning permission, a retrofit is normally covered by permitted development. Permitted development does not allow cooling. Permitted development is not applicable to a new build until sign off is complete. Also permitted development is not applicable if you want cooling, you need planning permission. None of the above has anything to do with grant. For grant applicability read up of Ofgem website. You need to read source information. If you find cooling isn't allowed I will happily eat my hat. Link to comment Share on other sites More sharing options...
Indy Posted November 24 Author Share Posted November 24 On 23/11/2024 at 16:53, JohnMo said: Yes. You need to split some of thought processes out. New build is covered by express planning permission, a retrofit is normally covered by permitted development. Permitted development does not allow cooling. Permitted development is not applicable to a new build until sign off is complete. Also permitted development is not applicable if you want cooling, you need planning permission. None of the above has anything to do with grant. For grant applicability read up of Ofgem website. You need to read source information. If you find cooling isn't allowed I will happily eat my hat. I do like your confidence but I have to say that my understanding was the same - i.e. anything related to cooling is not covered by the grant. I do know that PD doesn't cover cooling but this is one of those situations where it would be quite hard to police as the external unit is the same so how would anyone find out if you're using it for cooling as well as heating? As for PD not being applicable under sign off - something I'm acutely aware of. We have convoluted plans to do a number of things under PD as I have no desire to go back to planning for absolutely anything I don't have to - so we'll be building the house, get the sign off and immediately exercise our PD rights for a number of things - including a rear outbuilding, fencing, front boundary wall, ASHP etc. Link to comment Share on other sites More sharing options...
Indy Posted November 24 Author Share Posted November 24 On 23/11/2024 at 15:43, G and J said: I think you may benefit from a bigger slab to benefit from more thermal mass. (To the pedants, I know that there is scientifically no such thing but it is a useful concept in such debates. So there.). Now I appreciate that someone with letters after their name has decreed stuff but you are the client, so actually, what you want tops their sometimes odd preferences. And remember sometimes the guys doing the drawing are driven more by how quickly they can get onto the next job than they are by your long term happiness. I’m looking at slightly lowering our bnb and increasing our screed to 100mm (75mm in drawings) and maybe upping the insulation from the 150mm PIR as drawn. Might use an insulated bnb to help that. What change would that mean if we wanted a bigger slab? Link to comment Share on other sites More sharing options...
JohnMo Posted November 24 Share Posted November 24 1 hour ago, Indy said: I have to say that my understanding was the same - i.e. anything related to cooling is not covered by the grant Read the rules and state where it says anything with respect cooling not being allowed. Some rule about 10 years ago did exclude cooling but not the current ones. Link to comment Share on other sites More sharing options...
JohnMo Posted November 24 Share Posted November 24 1 hour ago, Indy said: I’m looking at slightly lowering our bnb and increasing our screed to 100mm (75mm in drawings) and maybe upping the insulation from the 150mm PIR as drawn. I did nearly exactly the same. Not BnB, but increased insulation to 200mm and slab above that to 100mm concrete instead of screed. 1 Link to comment Share on other sites More sharing options...
G and J Posted November 24 Share Posted November 24 3 hours ago, Indy said: What change would that mean if we wanted a bigger slab? Can you post a diagram of your foundation/beam and block detail? Link to comment Share on other sites More sharing options...
Andehh Posted November 25 Share Posted November 25 If you want meaningful cooling, and you should, 100% split system aircon. Only way, the rest are compromised. We did across 5 rooms powered from 3 external units and love it. The world is only getting warmer, and with your solar panels mean it'll be free to run when you need it, so you can go nuts with it. Premium feature for the home and massively impactful to your comfort on hot nights and if WFH on hot days. Installation for me was the lowest point of out build due to original firm not joining (crimping) the joints on the longer run, but only being found after they'd gone bust (with our money) and after 2nd fix.... Not fun. But utterly worth it now!! 2 Link to comment Share on other sites More sharing options...
Indy Posted November 26 Author Share Posted November 26 On 24/11/2024 at 23:56, G and J said: Can you post a diagram of your foundation/beam and block detail? Link to comment Share on other sites More sharing options...
G and J Posted November 27 Share Posted November 27 Forgive the crap drawing, but simply place the beams a brick lower, and use more stuff (be it insulation or screed) above it to make up the thickness. It may mean digging out more too, so beware of that as an unexpected extra cost. An insulated bnb is different in that the concrete blocks are replaced with polystyrene which gets more insulation into the same thickness, so the insulation sheet above the beams can be thinner for the same u value. Link to comment Share on other sites More sharing options...
G and J Posted November 27 Share Posted November 27 And having said all that I spoke yesterday with a BCO and when I mentioned a slightly thicker screed for improved UFH/house temp performance he expressed the opinion that it wouldn't help. He has a 65mm screed and that's fine - "you won't notice any difference". (His airtightness is circa 3, so that may be a factor). Maybe this is another thread.... Link to comment Share on other sites More sharing options...
JohnMo Posted November 27 Share Posted November 27 2 hours ago, G and J said: And having said all that I spoke yesterday with a BCO and when I mentioned a slightly thicker screed for improved UFH/house temp performance he expressed the opinion that it wouldn't help. He has a 65mm screed and that's fine - "you won't notice any difference". (His airtightness is circa 3, so that may be a factor). Maybe this is another thread.... Thicker screed does not improve UFH/house temp performance. It makes the UFH slow and very unresponsive. So depending how you assess the question, you will get different answers. Thick screed is a thermal store, so to change its temperature using a low flow temp takes an age, using high temps takes a while also. But once up to temp it stays there for an age. Not good if you want to move temperature similar to radiators - that will not occur, if you add to much heat you live with it for the rest of the day or open the windows. You can do WC, bounce off a thermostat and use it as a thermal store. You do not need a buffer as the floor is the buffer. Mine is currently being batch charged as a thermal store, topped up if needed. The energy is being used to heat the house, but circulation water continues to circlulate and I keep a summer house also heated by fan coil from the circulation water (currently at 24 degs) carrying heat from the floor. Summer house is currently 18 degs (-2 outside) heating went off at 6:30am and house at 21.2. Having a high flow temp and or a thermostat with a hysteresis of more that 0.1 will lead to big swings in house temperature. But: once you have the heat source in control - as well as your head, you can do things with a thick screed that are not really done well with a thin screed. You can stuff plenty of kWh's of energy in, at will and not affect house temp for many hours. I have added 20kWh's of heat from PV excess. It just delays the heat pump switching on later in the day. You can charge the floor on cheap rate energy and have stable house temps the rest of the day. You switch the heating on at midnight the house is the right temp for sleeping as the floor energy is depleting. Having the heating on overnight isn't an issue, as the floor takes a while to charge up, so it is about right for getting up in the morning. I set my thermostat high to start to the heat cycle, then after a few hours drop the temp to 0.5 degs below my target temp, two hours after the heating cycle is complete the house is at 21. If you want simple, but slightly less flexibility, go 65mm. 100mm and beyond is a bit of learning curve. Zones are an utter waste of time also with thick screeds, as its like trying to stop a two mile long train quickly, it isn't going to happen Link to comment Share on other sites More sharing options...
G and J Posted November 27 Share Posted November 27 I guess my head is full of the notion of using cheap rate periods to charge a big screed in a house that has a very constant pleasant temperature, (until I light the woodburner lol). The idea that for months on end we never have to think about the heating settings is very attractive. Couple that with exporting spare lecky and thus having good running costs and for me that’s worth using my mental crampons to ascend the slippery learning curve. Link to comment Share on other sites More sharing options...
JohnMo Posted November 27 Share Posted November 27 2 hours ago, G and J said: using cheap rate periods to charge a big screed Then the other side of that, is a heat pump sized for the heat loss, doesn't work for the high heat demand periods - so as way of an example, its -3 outside, you have a 4kW heat loss, you have a 4 kW heat pump. The heat pump needs to run 24/7 to keep up. If you have an 8kW heat pump it needs to run 12 hrs. Or you accept for most the heating season you batch charge during cheap electric rates, and when cold you burn expensive electricity as well. Link to comment Share on other sites More sharing options...
G and J Posted November 30 Share Posted November 30 On 27/11/2024 at 13:40, JohnMo said: Then the other side of that, is a heat pump sized for the heat loss, doesn't work for the high heat demand periods - so as way of an example, its -3 outside, you have a 4kW heat loss, you have a 4 kW heat pump. The heat pump needs to run 24/7 to keep up. If you have an 8kW heat pump it needs to run 12 hrs. Or you accept for most the heating season you batch charge during cheap electric rates, and when cold you burn expensive electricity as well. Looking like our 5kW heat pump will be needing to provide less than 2.5kW heat load at max (normal) temp difference if we don’t light the woodburner. Intuitively, against the various discussions on here, that feels sensible. Of course one piece of info that’s missing from my jigsaw puzzle is cost of screed. When I google I get handwavy £18 to £20 /m2 but no info as to how thick that figure refers to. Will there be much difference between 75mm and 100mm fibre reinforced screeds? Is there a budget rule of thumb I can refer to? Link to comment Share on other sites More sharing options...
JohnMo Posted November 30 Share Posted November 30 17 minutes ago, G and J said: Will there be much difference between 75mm and 100mm fibre reinforced screeds? I did our differently to anyone else, I have seen. I did the floor insulation, UFH and then 100mm fibre reinforced concrete, prior to any walls going up. Way easier, then the cost is concrete m3 prices, we needed a 36m concrete pump lorry also, and 2.5 lorries worth of concrete. Link to comment Share on other sites More sharing options...
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