Condensation and 3G windows

[Russdl]

@Adsibob  I installed them but overlooked the measuring of duct lengths that I’d installed. 
 

When it was finally all ready to be turned on (long after the ducts had been installed) I used a vacuumed cleaner to suck a bit of foam tied to a length of string down each duct (worked brilliantly) and then measured how much string zipped down each duct. They definitely all go where I think they go. 

[Adsibob]

39 minutes ago, Russdl said:

@Adsibob  I installed them but overlooked the measuring of duct lengths that I’d installed. 
 

When it was finally all ready to be turned on (long after the ducts had been installed) I used a vacuumed cleaner to suck a bit of foam tied to a length of string down each duct (worked brilliantly) and then measured how much string zipped down each duct. They definitely all go where I think they go. 

Well that's reassuring. I think that given your MVHR machine is just on factory settings, if you were to get a professional commission, it would probably fix things for you. Maybe they just need to install those variable terminals that allow you to have different flow rates in different rooms, and then they can play around with it to get a more optimal flow rate in the rooms in question. They could hopefully also check your machine is working properly.

[Russdl]

9 minutes ago, Adsibob said:

professional commission, it would probably fix things for you

Yep, that’s on the cards but I’m a bit grumpy that I can’t work it out myself. 
 

10 minutes ago, Adsibob said:

variable terminals that allow you to have different flow rates in different rooms,

Got those. All set to 0 at the moment which allows maximum airflow. 

[LA3222]

I keep coming back to it, get an Industrial dehumidifier, dry the house then see what happens from there.

 

I had major issues with moisture as already said. My MVHR was on full and it didn't touch the sides so to speak. I thought the MVHR could dry the house. It can't. Once I dried it out there have been no issues since and the humidity steadily dropped from around 65% (after drying) to circa 45% now.

 

My MVHR is on, always has been, at 35% not balanced. I havent touched it other than to turn it on.

 

I dont see how balancing it will solve your issue.

[Roundtuit]

21 minutes ago, Russdl said:

Yep, that’s on the cards but I’m a bit grumpy that I can’t work it out myself.

Should be able to do it yourself with a hired meter.  Was the system designed for you by the supplier?  If so, they should be able to give you the design air flow rates for each terminal.

 

21 minutes ago, Russdl said:

Got those. All set to 0 at the moment which allows maximum airflow. 

That won't be helping IMO.  Air will take the easiest route, so you need to restrict the 'easy' routes to force air through the longer, bendier ducts, otherwise the route of air flow through the house as a whole won't be as intended.

[Russdl]

3 hours ago, LA3222 said:

I keep coming back to it, get an Industrial dehumidifier, dry the house then see what happens from there.

 

I hear you, I hear you, and I'm very grateful for your (and everyone else) input but I honestly don't think the house is or could still be 'wet' despite what the RH levels say,  If it transpires that that is the problem then I will whack some Humble Pie in the microwave and scoff it live on air.

 

3 hours ago, LA3222 said:

I dont see how balancing it will solve your issue.

 

I kind of agree there. I can't see how it's going to change much.

 

I'm looking suspiciously at the enthalpy heat exchanger but others on here seem to be using those without issue. The only other culprit (if it's not a 'wet' house) has to be the machine itself. It was a 'special order' so perhaps it's been put together incorrectly...

 

3 hours ago, Roundtuit said:

Air will take the easiest route, so you need to restrict the 'easy' routes to force air through the longer, bendier ducts

 

That restriction is done in the manifolds at the MVHR end of things with the red restrictor rings, popping out as many as the supplier dictated. I got those restrictor calculations checked twice so I'm fairly confident in them, I'm also fairly confident the correct restrictor ring is over the correct duct in the manifold.

 

 

 

The valves in the room also have adjustment, which in theory shouldn't be required, it's those that are set to 0 at the moment, so they can be adjusted to restrict flow further as required

 

 

 

3 hours ago, Roundtuit said:

Should be able to do it yourself with a hired meter.

 

That'll hopefully happen soon with the help of a very kind man who has also lent me a CO2 monitor which has been up and monitoring for a few hours.

 

That CO2 monitor shows that when the MVHR is on a low setting the CO2 readings are high, when the MVHR is on a high setting the CO2 reduces quickly - so air is moving in the right direction.

 

And I'm sure the house isn't 'wet'. ?

 

[joe90]

Well I suffer from a little condensation on my 2g windows. I confess I never got round to balancing the MVHR it appears to work ok ?. I also have an enthalpy unit but where I live, an old moor, it is permanently damp and near the Atlantic and the RH is always fairly high (inside and out).

[Russdl]

6 minutes ago, joe90 said:

I confess I never got round to balancing the MVHR

 

That was going to be my default position but the damn things backed me into a corner, I've got a patio to do, I don't have time for this niff-naff and trivia! Plus work want me to 'work'! There's not enough hours in the day.

[Roundtuit]

10 minutes ago, Russdl said:

That restriction is done in the manifolds at the MVHR end of things with the red restrictor rings, popping out as many as the supplier dictated.

 

Fair enough!  apologies, only familiar with using room vents to control the flow.   The mystery continues...

(and I agree, the fabric of the house shouldn't still be drying out).

[dpmiller]

if the airflow haven't been checked, you've no idea if there actually *is* flow in all and every room...

[Russdl]

@dpmiller whilst it’s not been properly commissioned it supplies where it should supply and extracts where it should extract.
 

What I don’t know is if it is supplying and extracting the amount of air it should be. 

[dpmiller]

no I mean can you prove there's flow at each grille? With your restrictor setup you're working on someone else's guess... Id be dangling a bit of tissue in front of each vent or using a smoke pencil to confirm it, personally.

Airflow is a funny animal, I've spent too many years measuring and setting up fumecupboards and the like,  all the calcs might say there will be flow but one extra tight bend in a duct and...

[Mr Punter]

Do the offending windows have heavy curtains?

 

I don't have MVHR and RH here is about 50%.  No condensation on the windows.

[Russdl]

29 minutes ago, dpmiller said:

can you prove there's flow at each grille?

All extracts will suck a bit of tissue against the valve and on all supplies you can feel the flow (when it’s on a high setting). 
 

12 minutes ago, Mr Punter said:

 

Do the offending windows have heavy curtains?

 

As it happens the main offender does, an almost identical window in the room directly below doesn’t have thick or heavy curtains and on cold days it will also have condensation on it, so I don’t think curtains have any part to play in it.  

[AliG]

If you Google - How long does for a house to dry put - the first answer from the NHBC is 18-24 months to get fully dried out.

 

I didn't really track it in my house, but thE RH nowadays is much lower than was in the first year.

 

Considering the low heat input you have, the house could easily take over a year to fully dry out and will have more humidity than normal until  then. The dehumidifier is the answer.

 

I also suspect that running your heating at 21-22C will dry it out much faster as it would considerably increase the differential between outside and inside and increase how long the heating runs for.

 

It would also warm the windows up more and stop the condensation in the mean time.

[Mr Punter]

I am with @AliG on this.  Lots of natural ventilation this summer and the MVHR properly commissioned and SWMBO is happy and you will be fine.

[Russdl]

1 hour ago, AliG said:

the first answer from the NHBC is 18-24 months to get fully dried out

 

I take your point, probably aimed at brick and block and we're timber frame but the point is - it takes a long time.

 

1 hour ago, AliG said:

running your heating at 21-22C will dry it out much faster

 

Can't do that, the UFH doesn't seem to be working properly. I'll start another thread on that little issue when I get a roundtoit (the house isn't cold though)

 

55 minutes ago, Mr Punter said:

I am with @AliG on this.

 

I'm starting to feel bullied, I'm off to Tesco's to get some Humble Pie to pop in the fridge ready in case I need it.

 

57 minutes ago, Mr Punter said:

SWMBO is happy

 

Which is the number one priority. When that box is ticked nothing else really matters (its just a bloody difficult box to tick!)

[Radian]

2 hours ago, AliG said:

If you Google - How long does for a house to dry put - the first answer from the NHBC is 18-24 months to get fully dried out.

 

 

Our extension's foundations were poured in 2019. The blockwork was completed in 2020 with floor screed and wet plaster finished in April that year. It went all through the summer of 2020, and 2021 - by the end of which RH levels were still up as high as 80%. I got fed up and bought a dehumidifier which has been running constantly ever since xmas. 3 Litres a day is still coming out. But outdoor humidity is currently in the 90's so I don't know if its a massive air leak or just still drying out. I think the latter because the attached garage does occasionally drop below 70%

So yes, there's a stupid amount if water in the fabric of new buildings and it sticks around for years.

[Adsibob]

32 minutes ago, Radian said:

 

Our extension's foundations were poured in 2019. The blockwork was completed in 2020 with floor screed and wet plaster finished in April that year. It went all through the summer of 2020, and 2021 - by the end of which RH levels were still up as high as 80%. I got fed up and bought a dehumidifier which has been running constantly ever since xmas. 3 Litres a day is still coming out. But outdoor humidity is currently in the 90's so I don't know if its a massive air leak or just still drying out. I think the latter because the attached garage does occasionally drop below 70%

So yes, there's a stupid amount if water in the fabric of new buildings and it sticks around for years.

I'm now getting nervous about installing our oak herringbone floor, which the manufacturer has recommended should be glued directly to the screed. Screed was poured precisely three months ago. Where it is being covered in oak, it is about 80mm deep, so probably won't have fully cured for another 20 or so days. I think my builder is planning to wait until then, but won't wait any longer. UFH has been on low over the past 3 weeks so I'm hoping that will help. Perhaps I should turn it up a couple of degrees. 

[Radian]

1 minute ago, Adsibob said:

I think my builder is planning to wait until then, but won't wait any longer.

 

They say this kind of thing but then bugger off for a couple of months IME. Perhaps ask flooring mfr. what they think, get answer in writing...

[Adsibob]

1 hour ago, Radian said:

 

They say this kind of thing but then bugger off for a couple of months IME. Perhaps ask flooring mfr. what they think, get answer in writing...

The manufacturer will just say the floor had to be dry. So not really that helpful.

[AliG]

The drying time for screed is usually given as 1mm/day up to 40mm and 0.5mm/day above this. So you are looking at 100 days.

 

However, this is without UFH. Everyone says that heating will speed it up, but does not quote by how much.

 

To dry it out with heating you should start with a flow temperature of 25C which you can slowly raise to avoid cracking the screed, so you can probably be gradually increasing the temperature over the next 20 days, I think by 5C every 7 days. You will also need to turn it off before they start.

 

https://www.mpaliquidscreed.co.uk/latest-news/need-know-drying-times

 

From what I can see online, you need a minimum of 75% humidity to put flooring down, but for bonded flooring a level of 65% seems to be what is needed. So I would get a hygrometer which looks like it will cost about £15 on Amazon.

 

You should probably also put the wood into the house to acclimatise before it is laid.

[Adsibob]

Thanks. The wood has been in the house for about 3 weeks already, albeit it is still in its polythene and cardboard wrapping.

 

 Why should humidity be lower for installing a bonded floor? Is the concern that if it is too high the bonding won’t glue properly?

 

I will increase the UFH temp if i can persuade the builder to. I mentioned it to the foreman, but he wasn’t keen. I guess his boss is liable if it causes the screed to crack, so they must be being risk averse. 

[Adsibob]

Returning to the point of @Russdl’s original thread, I wonder Russdl if the issue is that you have an enthalpy exchanger when you don’t need one.

 

 This article, suggest you don’t, assuming you live in the UK of course:

 

“The average relative humidity in the UK is between lows of 70% and highs of 90% which is considered high, suggesting humidity recovery is not that big an issue in the UK”  
 

https://cvcsystems.co.uk/relative-humidity/

 

Maybe the solution is to swap out the enthalpy exchanger for a regular one.

Edited January 12, 2022 by Adsibob

[Russdl]

9 minutes ago, Adsibob said:

I wonder Russdl if the issue is that you have an enthalpy exchanger when you don’t need one.

Thats my gut feeling but it still doesn’t quite add up as others on here have enthalpy units and don’t seem to experience the same problems, @joe90’s experience is similar but his windows are 2g so that may explain his occasional condensation. It was cold again last night and there was condensation on most windows (some with thick curtains, some without) 
 

We went for the enthalpy expecting future occupancy to be low as I work away a lot. Maybe that was a mistake. 
 

Maybe the house does need to dry out further as suggested in this thread (I hope not, humble pie sounds revolting). 
 

Investigations are ongoing, but at a slight pause as I’m out of area at the moment.