phatboy Posted October 12, 2019 Share Posted October 12, 2019 Long story short, we still get mould behind the bed with MHRV running. It's held 5" away from the wall with wooden blocks, but with the bedside units air circulation is still limited. And the headboard is tall. And it's the north wall. My current thinking is 1 or 2 12v silent computer fans running all the time, or maybe a on a timerswitch on some programme. Is this the best way, or am I missing an obvious trick? Thanks! Tim Link to comment Share on other sites More sharing options...
ProDave Posted October 12, 2019 Share Posted October 12, 2019 Mould usually means condensation which usually means cold wall and high humidity. What is the house construction and age? Link to comment Share on other sites More sharing options...
Cpd Posted October 12, 2019 Share Posted October 12, 2019 Might be worth investing in one of these, then measure the temp of the wall at different locations to see if you have some nasty cold spots. Then work out what to do. Image was just the first one of the internet, not recommending it but they are all very similar. Link to comment Share on other sites More sharing options...
phatboy Posted October 12, 2019 Author Share Posted October 12, 2019 Thanks guys, The house is a 1950's bungalow, 9" solid block walls. I have insulated under the suspended floors with 50mm Celotex (I know it should have been a bit more), loft topped up to 300mm, 90mm EPS EWI. I used extra loft insulation to go right over the block work, so the house should be in a 'tea cosy' really. So we are pretty well insulated now. It is the bedroom, a room that has its door closed and so is cooler. I suspect it's moisture from the shower... previous years we have run a dehumidifier for 2 hours a day to stop it, but this year I've not started yet and hoped the MHRV would resolve things. Based on seeing the EWI being installed, I am quite confident there are no cold spots on the walls, and I did the floors and loft myself. I assumed it was just that some moisture would always be around, and it would find the coldest surface (north) and there always would be a coolest surface. The lack of air movement behind the bed caused it to settle and not get moved on. But if you think otherwise, I'm all ears....! Tim Link to comment Share on other sites More sharing options...
SteamyTea Posted October 12, 2019 Share Posted October 12, 2019 Give the fans a go, it is a cheap way to eliminate one thing. Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 12, 2019 Share Posted October 12, 2019 How far into the room is the supply air valve? Link to comment Share on other sites More sharing options...
Temp Posted October 12, 2019 Share Posted October 12, 2019 Gap under the door? Link to comment Share on other sites More sharing options...
phatboy Posted October 13, 2019 Author Share Posted October 13, 2019 10 hours ago, Nickfromwales said: How far into the room is the supply air valve? It's in the furthest corner from the door (about 4.6m), in the north - east corner 10 hours ago, Temp said: Gap under the door? About 10mm. Boost flow rate for that room is 6l/s Thanks Tim Link to comment Share on other sites More sharing options...
Mr Punter Posted October 13, 2019 Share Posted October 13, 2019 14 hours ago, phatboy said: I suspect it's moisture from the shower Where is the shower? If possible have a separate extract from the shower located in the ceiling above the shower tray and leave it to overrun for at least 20 mins. Link to comment Share on other sites More sharing options...
phatboy Posted October 13, 2019 Author Share Posted October 13, 2019 Sorry I've not made things very clear! With the MHRV I cannot have an extra extracts (presumably), nor should I need to I don't think? Please see attached room with issue, and whole house MHrV design. The problem room is Bedroom 1. Thanks again... Tim Link to comment Share on other sites More sharing options...
scottishjohn Posted October 13, 2019 Share Posted October 13, 2019 (edited) 19 hours ago, phatboy said: The house is a 1950's bungalow, 9" solid block walls. I have insulated under the suspended floors with 50mm Celotex (I know it should have been a bit more), so you have a solid wall -- not 2 walls with a void between them ? is it hard plastered onto that wall? I am guessing you fitted mvhr because you had a damp problem before can you see the damp course from outside of house? how far above the ground are the air bricks -damp course sdhould be below them and visible --not banked up with soil or anything Edited October 13, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
Mr Punter Posted October 13, 2019 Share Posted October 13, 2019 I know you have the light switches in place, but could you try rotating the bed and have it against the internal west wall? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 13, 2019 Share Posted October 13, 2019 21 minutes ago, Sensus said: Whatever the PassivHaus bunnies will try to tell you, the level of ACH and distribution of air circulation that you can achieve with MVHR is woefully inadequate even for very well insulated, modern properties (though in these the bigger problem is build up of pathogens rather than moisture). Interesting point, as one very common observation from those living in houses fitted with MVHR is how much "fresher" the air feels. Mind you, I've never met a "PassivHaus bunny", so perhaps they have different views. Be interesting to hear from others if they feel that MVHR similarly makes the air feel "fresher" or not. I have some evidence from comparative measurements made over a two year period between the air quality (in terms of humidity and CO2 concentration) for in our old house and our new build. The old house was a 3 bedroom, 1980's bungalow, block and brick construction, with a solid concrete floor, that had been improved a bit with ~300mm of loft insulation, bonded bead CWI and pretty average uPVC doors and windows. Ventilation was a mix of trickle vents (pretty useless in terms of providing effective ventilation - the measured air flow rates were very low), extraction fans in the kitchen, bathroom and WC, and a couple of permanently open small windows. There was also a fireplace and chimney, although the fireplace was fitted with a gas coal effect fire (but did use the flue). The new house exceeds the PHI standard for a PassivHaus, but isn't certified as one. It has MVHR as the only means of ventilation. In the old house the CO2 concentration in any room would usually pretty closely track the RH. The worst room for ventilation was the main bedroom, even though the windows had trickle vents that were always open and a small window that was also left open 24/7. It was common for the CO2 concentration to reach a level of between 1500ppm and 2000ppm overnight, with very noticeable dips whenever the bedroom door was opened. There was a fair gap (~8mm) under the bedroom door, but it seemed clear from the data that this was insufficient to allow effective cross ventilation. That room was also the worst for condensation, and the corner between the North and East walls suffered from mould, until I rigged up a small computer fan and time switch to blow air around behind the chest of drawers that was in that corner. There was no external moisture ingress, it seems that the mould was just down to that corner being both a bit cold and a ventilation dead space. In the new house the CO2 concentration sits around 500ppm pretty much all the time, and is damned near the same in every room. I think the highest CO2 concentration I've ever seen was ~800ppm, when we had several visitors around, just before the MVHR started to boost because the RH had risen above the boost threshold. I'm currently running the MVHR at a background ventilation rate of about 0.4 ACH. That seems to be fine for the two of us, and keeps both the RH and CO2 concentration within acceptable limits. Because the incoming fresh air is filtered through a F7 filter the air stays pretty clean, and we seem to get much less dirt and dust around, and very little pollen (something I'm thankful for, as a hay fever sufferer). On balance I'd say that a house with MVHR, even if the airtightness isn't to PHI levels, is likely to have better air quality than one without. MVHR isn't going to fix problems caused by internal surfaces dropping below the local dew point through, especially if they happen to be located in a ventilation dead space. Something like the small fan and timer I knocked up might be a solution for such a problem, if it isn't practical to improve the insulation in that area. Link to comment Share on other sites More sharing options...
Mr Punter Posted October 13, 2019 Share Posted October 13, 2019 Where do you dry the laundry? Link to comment Share on other sites More sharing options...
ProDave Posted October 13, 2019 Share Posted October 13, 2019 We live in a new modern near passive house level house with mvhr. There is a complete absense of condensation or mould anywhere, and I share others views that the air always feels fresh inside. Smells, e.g from cooking disperse very quickly. Back to the OP. You mention "moisture from the shower" Do you just have the 1 bathroom, or are you saying there is an en-suite shower in this bedroom? One thing that strikes me is you have 5 fresh air points but only 2 stale air extract points. I would try adding an extra stale air extraction point to bedroom one at the opposite corner to the existing fresh air point. Link to comment Share on other sites More sharing options...
Declan52 Posted October 13, 2019 Share Posted October 13, 2019 My house is no where near a passiv level but compared to my last home the mhrv makes such a difference. I get no condensation on the windows or no mould anywhere now the house has dried out. My previous house during the winter my 2g windows used to freeze shut when the condensation on the inside froze. I have my extractor fan vented out so cooking smells isn't an issue either. I have had issues with my sinuses for years , every member of my family have the same issue, and once we moved in to the new house it made such a difference. The way mhrv can deliver fresh air in my house is it's main benefit for me. If I recover some heat then great but I don't really worry about that aspect. Link to comment Share on other sites More sharing options...
Declan52 Posted October 13, 2019 Share Posted October 13, 2019 4 hours ago, phatboy said: Sorry I've not made things very clear! With the MHRV I cannot have an extra extracts (presumably), nor should I need to I don't think? Please see attached room with issue, and whole house MHrV design. The problem room is Bedroom 1. Thanks again... Tim Could you open the ceiling vent up a bit more to try to increase the flow rate a bit more. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 13, 2019 Share Posted October 13, 2019 56 minutes ago, Sensus said: We've had this discussion before, JS, and I provided plenty of evidence at the time. You'll find it if you look far enough back in my posting history, and I don't intend to revisit the matter with you. Let's stick to the point on this thread, shall we? I don't recall ever being involved such a discussion with you here before, and cannot seem to find any thread in my posting history where the topic of ventilation/MVHR and air quality has been debated with you. All I can find from a quick general search is a thread from October 2016 (when I was away and not posting here) where you seem to have been debating this with others here. It's not something I'd read before, TBH, as it seems the thread was locked for some reason. I also believe this is very much "on topic", given that the OPs problem seems related to ventilation, plus, I suspect, the internal surface of an external wall that is dropping below the local dew point. Link to comment Share on other sites More sharing options...
Cpd Posted October 13, 2019 Share Posted October 13, 2019 12 minutes ago, JSHarris said: I suspect, the internal surface of an external wall that is dropping below the local dew point. This was my feeling and why I suggested getting a cheep IR temperature measurer to eliminate this. Link to comment Share on other sites More sharing options...
ToughButterCup Posted October 13, 2019 Share Posted October 13, 2019 1 hour ago, Sensus said: [...] Whatever the PassivHaus bunnies will try to tell you, the level of ACH and distribution of air circulation that you can achieve with MVHR is woefully inadequate even for very well insulated, modern properties [...] Evidence? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 13, 2019 Share Posted October 13, 2019 6 minutes ago, Cpd said: This was my feeling and why I suggested getting a cheep IR temperature measurer to eliminate this. Could also be that, as it's behind the bed headboard, the local RH is slightly higher, from exhaled moisture. The combination of a cool wall, plus a dead space as far as ventilation is concerned, and a locally elevated RH could well be the cause. The fix I used in our old house for a problem area like this (behind a chest of drawers) was to fit a small, low voltage, computer fan behind the chest, run from a DC power supply that was plugged in to a time switch, so that the fan ran during the daytime to ventilate that area, but turned off (for noise reasons) at night. Seemed to work well. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted October 13, 2019 Share Posted October 13, 2019 1 hour ago, AnonymousBosch said: Evidence? As I'd no recollection of ever having discussed this topic before, despite the incorrect assertion by @Sensus that I had, I took the time to locate the thread in question: It appears to have been posted here, and locked for some reason, during the time I was away from here, in October 2016. Link to comment Share on other sites More sharing options...
ToughButterCup Posted October 13, 2019 Share Posted October 13, 2019 1 hour ago, Sensus said: As per my post above, I discussed it in some depth a good while ago, including referencing research from the worlds most recognised authority on building ventilation. I have no interest in spending hours rehearsing the same information over again, for those who were unwilling to accept it previously. That's - for me - is quite an uncomfortable reply. As I understand it, you are an architect. And that implies authority. To refuse to reference an important statement diminishes your argument. A simple hyperink to the discussion would suffice. No need for rehearsal. Link to comment Share on other sites More sharing options...
jamiehamy Posted October 13, 2019 Share Posted October 13, 2019 9 minutes ago, Sensus said: You will appreciate from our past correspondence that I'm not especially interested in your comfort. If you're interested, you won't have too much difficulty finding it yourself. I find it interesting that as an administrator of this site, you see trolling as part of your role. I see that JS has saved you the trouble and posted a link to the relevant thread, above. ? No need to be so rude mate. JS saved YOU the trouble. There's only one troll on this thread buddy and it's you. Link to comment Share on other sites More sharing options...
Declan52 Posted October 13, 2019 Share Posted October 13, 2019 Could we all take this down a notch please. 1 Link to comment Share on other sites More sharing options...
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