dogman Posted June 11, 2017 Share Posted June 11, 2017 I was speaking to an engineer today about cooling our house should it need it. He was talking about fan coils when i mentioned cooling the slab with underfloor heating. His advised me not to due to condensation and the risk to the floor and concrete. He stated that it was due to the dew point/humidity in the house and the condensation around the pipes and on the floor. He stated it would form not just on the floor surface but under tiles and around the pipes Now i don't pretend to know anything about this but i am sure that those who have looked into cooling a slab must have considered this issue and mitigated against condensation forming. Can anyone help with this issue(if it is one) Link to comment Share on other sites More sharing options...
MikeSharp01 Posted June 11, 2017 Share Posted June 11, 2017 Interesting point @dogman. Let's see what every body thinks but I suspect that the amount / rate of change of temperature drop you can drive with the sort of cooling systems discussed here won't get to dew point under floor although I suppose it might in parts of the above ground pipework. If you have a 200 Kw chiller and you can pump that around in 100mm pipes you will probably get there. He may be used to large building HVAC systems rather than the systems for energy efficient homes where ASHP systems are driving UFH. Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 Was this a HVAC engineer by any chance? I have received similar feedback about slab cooling AND my MVHR cooling. However, I cant see that either reach temperatures where condensation will form? 1 Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2017 Share Posted June 11, 2017 There isn't enough moisture in a slab for condensation to form round a pipe so that's not correct..! You could get floor condensation but the RH would need to be fairly high to get to dew point and cause dampness Link to comment Share on other sites More sharing options...
TerryE Posted June 11, 2017 Share Posted June 11, 2017 2 hours ago, dogman said: was speaking to an engineer today about cooling our house should it need it ... I mentioned cooling the slab with underfloor heating. His advised me not to due to condensation and the risk to the floor and concrete. He stated that it was due to the dew point/humidity in the house and the condensation around the pipes and on the floor. He stated it would form not just on the floor surface but under tiles and around the pipes Martin, do the maths. Do the (over) heat calcs and see how much heat you need to suck out of the slab to maintain an overall thermal equilibrium. For a typical MBC house, it will be at most a few kW (unless you've got silly solar gains). If you've got 100m2, say of slab, then you'll need the slab at 18°C instead of the normal room environment of 21°C, say. At an RH of 40 - 55 %, that's way above the dew point. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 In practice, slab cooling isn't a risk in the UK climate at all. We run water at 12 deg C around the slab when the system is in cooling mode, and the slab surface never, ever gets below 18 deg C. Even that cool is rare, and most of the time the slab is around 19 to 19.5 deg C in warm weather. At 18 deg C, the relative humidity would need to be well over 90% for there to be a condensation risk, and that is just never going to happen during warm weather in the UK. Link to comment Share on other sites More sharing options...
dogman Posted June 11, 2017 Author Share Posted June 11, 2017 Many thanks everyone. As @Barney12 stated it was a HVAC engineer. I would rather go with practical experience rather than the engineers view. I suppose in his defence he was talking about the supply to the system being at 7 deg or less not 12 and above. Ill stick with my plan of cooling the slab with a small cooler in the MVHR supply to lower the air temp coming in a few deg. I am plumbing the house for fan coil rads in case i do need more cooling. Being a northerner my idea of heaven is 2 foot of snow and minus temperatures. Anything over 18 is far too hot for me. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 In his defence, I'd guess that he was thinking about cool air in ducts, where there is a very real risk of condensation when it's cooled down to 7 or 8 deg C. The difference with a slab is that although there may be water at 12 deg C circulating around the pipes, the surface of the slab will always be a fair bit warmer, and it's only the slab surface where condensation could form. Slab cooling is very unusual, I've not heard of many who have done it, and when I first installed our slab cooling system I couldn't find any information at all about it. I have to say that when I asked a few questions on various HVAC related forums I did get lots of condemnation for the idea - because of the sort of person I am I took that as encouragement to give it a go............. Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 1 hour ago, dogman said: Many thanks everyone. As @Barney12 stated it was a HVAC engineer. I would rather go with practical experience rather than the engineers view. I suppose in his defence he was talking about the supply to the system being at 7 deg or less not 12 and above. Ill stick with my plan of cooling the slab with a small cooler in the MVHR supply to lower the air temp coming in a few deg. I am plumbing the house for fan coil rads in case i do need more cooling. Being a northerner my idea of heaven is 2 foot of snow and minus temperatures. Anything over 18 is far too hot for me. Did you manage to find those right angle floor connectors for your UFH pipe upstairs (ready for the fan cooled rads if needed)? Link to comment Share on other sites More sharing options...
dogman Posted June 11, 2017 Author Share Posted June 11, 2017 I found 15mm that are in a sort of fitting. However you can just use a 22mm to 3/4inch elbow Hep20 do a plastic one. They did do a brass version if you can find them still. eBay link Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 23 minutes ago, dogman said: I found 15mm that are in a sort of fitting. However you can just use a 22mm to 3/4inch elbow Hep20 do a plastic one. They did do a brass version if you can find them still. eBay link Thanks. So how have you left then in the room? Just below the floor with their locations carefully recorded? Or have you got them above FFL with a cap? Sorry for being inquisitive! Link to comment Share on other sites More sharing options...
dogman Posted June 11, 2017 Author Share Posted June 11, 2017 Not in place yet. Am having a nightmare with the windows so everything has stopped. The plan is to fit them, so there is a hole in floor , test them, drain the pipes and leave them in place. If house is either hot or cold i will buy the units and fit them. Remember fan coils also need power. Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 Yes, I'm putting a radial circuit in for electric rads as a fail safe. Im minded to put the UFH pipe in too as you are doing as the first fix cost is minimal. My one concern is that I haven't actually seen a fan coil rad in the flesh and the ones I've seen online look bulky and akin to the aweful night storage heaters of the past. Windows; what a complete PIA they are. Ours are going in a week on Monday. Well they will be when MBC have adjusted almost all of the upstairs openings which are too small due to a manufacturing error in the factory. I'm glad @jack banged on at me to check all the openings to the window schedules! I also found a couple of errors downstairs too where the slab recess was wrong. Thankfully all of the errors are reasonably easy to put right but will certainly add to their workload. 1 Link to comment Share on other sites More sharing options...
jack Posted June 11, 2017 Share Posted June 11, 2017 I'm so glad my experience has helped someone else, and very pleased you found the issue now rather than later. MBC came out on the same day the errors were discovered by the window installers, to adjust the two or three worst of ours. The rest were fine, as there was quite a lot of tolerance built in (eg, window aperture was nominally 30mm taller than the external window frame dimension, but was built to 18-25mm). Interesting yours were mostly upstairs - ours were too. Was it vertical dimensions that were the problem? Good catch on the slab recesses. Fixing those after the fact could involve a world of unpleasantness. Link to comment Share on other sites More sharing options...
jack Posted June 11, 2017 Share Posted June 11, 2017 8 hours ago, dogman said: Can anyone help with this issue(if it is one) I'm sure my Panasonic Aquarea ASHP installation manual cautions against using cooling mode to cool UFH heating circuits. That may be arse-covering though. We haven't bothered with cooling yet. It's not that hot downstairs, and I doubt whether cooling the slab downstairs will have much impact on the bedroom temps (which are the only ones I'd really like to bring down at times). Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 1 hour ago, jack said: I'm so glad my experience has helped someone else, and very pleased you found the issue now rather than later. MBC came out on the same day the errors were discovered by the window installers, to adjust the two or three worst of ours. The rest were fine, as there was quite a lot of tolerance built in (eg, window aperture was nominally 30mm taller than the external window frame dimension, but was built to 18-25mm). Interesting yours were mostly upstairs - ours were too. Was it vertical dimensions that were the problem? Good catch on the slab recesses. Fixing those after the fact could involve a world of unpleasantness. A combination of width and height issues. Mostly width. The worst being a large height error of nearly 60mm. They're going to have to cut a glulam lintel to fix that one. Ecohaus only ask for a 10mm tollerance so that one would have more than a slight issue! Ive now been round every window and noted the window number and opening dimensions (as per the schedule) and written onto the smartply with a sharpie marker. 1 Link to comment Share on other sites More sharing options...
jack Posted June 11, 2017 Share Posted June 11, 2017 Ah, right. All widths were perfect for us, but we had quite a few height issues. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 12, 2017 Share Posted June 12, 2017 Interestingly, Munster asked for all apertures to be 10mm bigger all around than the window sizes, and came around as soon as the frame was stood up to check that the as-built apertures were the same as the schedule sheet with the order. A week after they checked the aperture dimensions the team arrived with the windows to fit them. Link to comment Share on other sites More sharing options...
Barney12 Posted June 12, 2017 Share Posted June 12, 2017 26 minutes ago, JSHarris said: Interestingly, Munster asked for all apertures to be 10mm bigger all around than the window sizes, and came around as soon as the frame was stood up to check that the as-built apertures were the same as the schedule sheet with the order. A week after they checked the aperture dimensions the team arrived with the windows to fit them. Ecohaus Internorm ask for 10mm for sides and top, nothing for bottom. For larger windows they ask for greater tolerances on the height. They did send their surveyor last week but unfortunately MBC were well behind schedule and didn't even have the first floor up (despite being on-site for a week) due to the atrocious weather so I agreed to do upstairs. Glad I did! As an aside MBC have done our entire build with a telehandler and hand balling. Due to the wind where we are they probably would have only been able to crane on 1 or 2 days over the past two weeks. I have a suspicion they might be glad when ours is done! Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 12, 2017 Share Posted June 12, 2017 We had a 100ft jib crane on site for a day and half, and that got all the wall panels up, plus the joists etc lifted up to the first floor level. We were lucky, in that the weather wasn't too bad, just one wet day, and we're sheltered in a valley, so there was no wind to speak of. Our frame arrived at 08:30 on the Tuesday morning, and MBC were off site at Saturday lunchtime, leaving us with a weathertight house. Link to comment Share on other sites More sharing options...
Barney12 Posted June 12, 2017 Share Posted June 12, 2017 On 6/12/2017 at 10:06, JSHarris said: We had a 100ft jib crane on site for a day and half, and that got all the wall panels up, plus the joists etc lifted up to the first floor level. We were lucky, in that the weather wasn't too bad, just one wet day, and we're sheltered in a valley, so there was no wind to speak of. Our frame arrived at 08:30 on the Tuesday morning, and MBC were off site at Saturday lunchtime, leaving us with a weathertight house. That's impressive. Brendan, Darren and their crew have finished tonight (just packing up). So it's taken them nearly 12 working days working 12 hour shifts. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 12, 2017 Share Posted June 12, 2017 (edited) Brendan led the team on our build, and similarly they were pulling 12 hour days. They broke our planning conditions on working hours, but luckily no one complained about it. Edited June 12, 2017 by JSHarris Link to comment Share on other sites More sharing options...
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