Novice Posted June 27, 2016 Share Posted June 27, 2016 In the middle of finalising the detail on our new build passive house (425m2). I had originally thought of putting UFH but not sure if it is required? It will be a MBC build so UFH in slab. The question is whether to install UFH or use duct heater/cooler (wet) in the MVHR? If we stay with the UFH are there systems available off the shelf to control it? Other information which may be relevant - large solar array(10kW), ASHP, towel rails in bathrooms (low power) and Sunamp PV I have promised SWMBO a warm house and she has made several compromises from her wish list (No aga or wood burner), so do not want to regret any decision! Link to comment Share on other sites More sharing options...
IanR Posted June 27, 2016 Share Posted June 27, 2016 What does PHPP say is your peak heat load? Can you easily supply that through Duct Heating. How about cooling? Is there any risk of overheating, if so what strategies do you have for dumping heat. It's much cheaper to instal UFH in the slab than retrofit... Link to comment Share on other sites More sharing options...
Novice Posted June 27, 2016 Author Share Posted June 27, 2016 According to PHPP peak heat load is 7w/m2. It has been suggested that a duct heater could also be used to cool(using ASHP in reverse), is that correct? In theory I should not need the UFH but would love to hear from anyone who has/hasn't UFH in passive house (or nearly ph) thanks D Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 27, 2016 Share Posted June 27, 2016 @jack has mentioned that he had issues with unheated areas. Can't recall if it was the entire first floor or just the bathrooms. He'll see I've mentioned him and perhaps he can recall the thread Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 27, 2016 Share Posted June 27, 2016 Oh, fwiw, you may want to read @JSHarris blog regarding using the Ufh pipes in the slab to dump hear from areas with solar gain, and also about cooling the slab via the ASHP. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 27, 2016 Share Posted June 27, 2016 I'd very definitely fit the UFH, no question. In theory we can supply plenty of cool or warm air from our active MVHR (a Genvex with an air-to-air heat pump built in) but in practice it doesn't move enough air to be particularly effective. The UFH is far more effective, although 90% of the time it's used for cooling the floor, rather than heating it. We're in a very sheltered location, cut back into a hill, with the north and lower part of the east elevations protected by a high retaining wall just a few feet away. The house very rarely needs any heat at all, in cold weather the heating might come on for an hour or so every two or three days. We do need a great deal of cooling though. As I'm typing this the underfloor cooling in running and the MVHR air cooling turned an about half an hour ago. The house is just over 23 deg C inside. Link to comment Share on other sites More sharing options...
IanR Posted June 27, 2016 Share Posted June 27, 2016 While 7w/m2 is very low, on 425m2 that's a 3kW requirement to maintain 21 degrees. A higher input would be required if the house had been allowed to drop in temperature. A wet duct heater may be able to supply 3-5kW through the MVHR, but it will likely need +60 degree water temperature (at least that's what I found). Where do you plan to get the hot water from for the wet duct heater? ie. direct from the ASHP? or a buffer? May be only 2.5kW from the wet duct heater is realistic (again, that's what I have found) However it's not very often that this peak heat will be required. A higher cost lower capital solution may therefore be appropriate so perhaps an electric pre-heat on the MVHR rather than UFH. Personally I need the cooling so I've installed UFH. Even if I didn't I think I would still go with UFH. Note: I'm only at install stage, so my opinion is only theory... Link to comment Share on other sites More sharing options...
Novice Posted June 27, 2016 Author Share Posted June 27, 2016 Thank you for your responses, great feedback. Looks like my original thoughts are correct - best install UFH The UFH would be ground floor only but because of the size (190m2) there will be several loops. Can you recommend a system to control it and how would it work with the ASHP for cooling/heating? Thanks D Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 27, 2016 Share Posted June 27, 2016 I think most of it's written up in my blog here. All I have are two wireless room stats, one for setting the heating on temperature and one for setting the cooling on temperature. They are low hysteresis stats, +/- 0.1 deg C, so provide the fine level of control needed to reduce overshooting the set temperature. The manifold is a standard Wunda one with all the ports commoned so there are no zones (no point in zones, as the heat input is tiny, and rarely needed). The Wunda pump set and remote sensing thermostatic valve does a good job of running the floor at a low enough temperature, unlike some others. There's a need for valves to shut switch from heating (where the ASHP heats both the floor and the buffer that pre-heats hot water) and cooling where the ASHP cools the floor but the buffer is isolated. I used motorised ball valves, because they give a guaranteed 100% shut off, unlike most central heating motorised valves that don't close 100%. This is important as you need to be able to completely isolate the warm buffer (35 deg to 40 deg C) from the floor cooling (around 12 deg C for us). 1 Link to comment Share on other sites More sharing options...
IanR Posted June 27, 2016 Share Posted June 27, 2016 If you're not already aware, as soon as you reverse an ASHP for cooling, the installation is not applicable for RHI. Your predicted RHI payment may be so small that this is not relevant anyway. My experience of talking to installers for an ASHP install capable of cooling as well as heating makes JSHariss appear to have "discovered" the holy grail with his home-brew install. That's not entirely true, as I found some installers with commercial experience capable of designing a suitable solution. There's only a few manufacturers that state their UK pumps are capable of cooling, or sell a kit that can convert them. By no means the cheapest of these is Nibe who sell a cooling module to add to their ASHP's. I haven't bottomed out the control side yet, I'm being lead towards a rather expensive OJ Control system solution, but I'm working on the Home Automation system doing this directly, or understanding why the standard Nibe control is not capable. Link to comment Share on other sites More sharing options...
jack Posted June 27, 2016 Share Posted June 27, 2016 You'll need several loops, but you don't really zone this sort of system (in the sense of setting different operating times and flow temperatures for each zone). That actually makes things a lot easier. I personally just turned the temp right down on the manifold mixing valve and left it to the the ASHP to supply 25 deg C water to the slab as required (I put in a small heating curve so that was a bit higher when it was very cold, but not sure if that really made much difference). My issues were with upstairs heating, specifically in bathrooms. I thought we could do without, but we found it just a little too chilly getting out of the shower over winter. The tiles, in particular, are surprisingly chilly underfoot, as much because they are conductive as due to their actual temperature. 1 Link to comment Share on other sites More sharing options...
joe90 Posted June 27, 2016 Share Posted June 27, 2016 Hi, just to say we plan UFH in our slab from our ASHP and thanks to Jeremy he has worked out how to reverse engineer the ASHP to cool the slab if required. We plan to take a loop from the ASHP to the MVHR so we could instal a wet heater in the duct which again could cool the air if required. I will also cable to the MVHR in case we decide to install an electric heater. Cable and pipe in at first fix as its better than retro fitting in a finished house ?. Link to comment Share on other sites More sharing options...
MarkH Posted July 17, 2016 Share Posted July 17, 2016 Is there a significant advantage to installing the UFH/cooling in the slab rather than in the screed (which I understand is the norm?). I can see the former would best utilise the whole body of concrete but for me sticking it in the screed would simplify things - we want to get our slab poured soon and have limited time to get the pipework and insulation done as it is without dealing with a stack of UFH pipings... Link to comment Share on other sites More sharing options...
Nickfromwales Posted July 17, 2016 Share Posted July 17, 2016 It's the norm if your screed is over insulation. The way you describe it is with the screed over your slab. How far along are you with the floor build up? What's the proposed insulation / total thickness of all layers etc? Link to comment Share on other sites More sharing options...
PeterW Posted July 17, 2016 Share Posted July 17, 2016 26 minutes ago, MarkH said: Is there a significant advantage to installing the UFH/cooling in the slab rather than in the screed (which I understand is the norm?). I can see the former would best utilise the whole body of concrete but for me sticking it in the screed would simplify things - we want to get our slab poured soon and have limited time to get the pipework and insulation done as it is without dealing with a stack of UFH pipings... It depends what your floor build up is ..? In slab tends to be for heavily insulated (i.e. 250mm plus) of insulation under a reinforced slab that becomes the floor. For in screed heating, you've normally got insulation between the concrete slab and the screed, so you need to be careful to make sure you have enough space to get the insulation and screed build up right to keep the losses down. what is the current build up ..? Link to comment Share on other sites More sharing options...
MarkH Posted July 18, 2016 Share Posted July 18, 2016 8 hours ago, Nickfromwales said: It's the norm if your screed is over insulation. The way you describe it is with the screed over your slab. How far along are you with the floor build up? What's the proposed insulation / total thickness of all layers etc? 8 hours ago, PeterW said: It depends what your floor build up is ..? The current proposed build up is for insulation (200mm) under the slab (100mm) with 50mm screed. The design we inherited called for over slab, under screed insulation but under slab seems to make more sense... I'm operating under the assumption that the screed layer is a strong, smooth layer that finishes the floors ready for final coverings? Am I right? Link to comment Share on other sites More sharing options...
PeterW Posted July 18, 2016 Share Posted July 18, 2016 That's correct, although a screed isn't structural and the slab is. You could easily drop the screed on that and go for another 50mm of insulation. That would give you around 0.12 with EPS, and if you use a self compacting concrete or a power float the floor is tile ready. The other missed benefit is time to dry. Screed is around 1mm per day so you have 50 days drying time. With the concrete going down before the shell is built you will effectively have a "dry" floor within the average build time. Lots to consider I know ..!! Link to comment Share on other sites More sharing options...
IanR Posted July 18, 2016 Share Posted July 18, 2016 45 minutes ago, MarkH said: The current proposed build up is for insulation (200mm) under the slab (100mm) with 50mm screed. The design we inherited called for over slab, under screed insulation but under slab seems to make more sense... In the design you inherited, the insulation was probably not designed to be load bearing, since it was only under the screed. Since you are moving this to under the slab, it is now load bearing. What type of insulation are you going with? Just to be sure...is what you are calling the slab load bearing? ie. is there a thicker ring beam and internal beams where the load bearing walls are? Link to comment Share on other sites More sharing options...
MarkH Posted July 18, 2016 Share Posted July 18, 2016 11 hours ago, IanR said: In the design you inherited, the insulation was probably not designed to be load bearing, since it was only under the screed. Since you are moving this to under the slab, it is now load bearing. What type of insulation are you going with? Just to be sure...is what you are calling the slab load bearing? ie. is there a thicker ring beam and internal beams where the load bearing walls are? I have been looking at PIR insulation but in all honesty I've not had much time to research fully (the downside of earning all your money in the summer...) The 'slab' isn't load bearing, no ring beam and no internal beams (we have no internal load bearing walls). I believe what we're building is a called ground bearing slab? I was under the impression that screed was a thing you did regardless of how the rest of the 'floor' was made up... it seems I was wrong there - we can get a 'screed' finish on the slab concrete. Link to comment Share on other sites More sharing options...
joe90 Posted July 19, 2016 Share Posted July 19, 2016 I am having a 100mm ground bearing slab on 300mm eps with steel and UFH pipes in it, I am going to power float it to give a "screed" finish. Mine is not supporting any walls as these will be built on normal foundations ( well nearly, see Golcar passive house on the green building store site). Link to comment Share on other sites More sharing options...
PeterW Posted July 19, 2016 Share Posted July 19, 2016 Similar to mine but its 250mm EPS with 100mm fibre reinforced concrete with a power float finish. Comes in about 0.12 uValue IIRC Link to comment Share on other sites More sharing options...
MarkH Posted July 25, 2016 Share Posted July 25, 2016 On 19 July 2016 at 13:11, joe90 said: I am having a 100mm ground bearing slab on 300mm eps with steel and UFH pipes in it, I am going to power float it to give a "screed" finish. Mine is not supporting any walls as these will be built on normal foundations ( well nearly, see Golcar passive house on the green building store site). On 19 July 2016 at 13:14, PeterW said: Similar to mine but its 250mm EPS with 100mm fibre reinforced concrete with a power float finish. Comes in about 0.12 uValue IIRC OK, I'm beginning to get my head around this! I don't need the screed and leaving it out will allow a more rapid progression once the slab is down. Our architect doesn't specify any steel in the 100mm slab (dimensions approx. 5 by 12m for the largest section). Do the UFH pipes need to be suspended within the slab concrete or attached to the underlying insulation as with screed-installed pipes? Link to comment Share on other sites More sharing options...
jack Posted July 25, 2016 Share Posted July 25, 2016 No steel? Is it fibre reinforced? I'd have thought you'd need one or the other as an anti-crack measure. Link to comment Share on other sites More sharing options...
PeterW Posted July 25, 2016 Share Posted July 25, 2016 Pipes get pinned to the insulation. And fibre is cheap these days but I would watch out as it also makes the concrete less liquid. Link to comment Share on other sites More sharing options...
MarkH Posted July 25, 2016 Share Posted July 25, 2016 8 hours ago, jack said: No steel? Is it fibre reinforced? I'd have thought you'd need one or the other as an anti-crack measure. No reinforcement as specced by the architect, just a couple of movement joints, I have wondered about sticking steel in anyway... 8 hours ago, PeterW said: Pipes get pinned to the insulation. And fibre is cheap these days but I would watch out as it also makes the concrete less liquid. Ok, thanks for that info Peter. I assumed the pipes would have to be within the 100mm of concrete and wasn't sure how that was acheived. Our local concrete people do offer fibre filled but I'd heard it makes the mix less workable - steel seems sensible. Link to comment Share on other sites More sharing options...
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