Condensation and 3G windows

[Russdl]

@IanR ok, that’s well below ours and may be what’s causing the problem.

[joe90]

Our RH was high after the build was finished, not sure what it is now, perhaps I need to check. It’s always a bit high this close to the Atlantic.

[SteamyTea]

It takes lot of energy and time to dry a house out.

 

I don't consider Salisbury the SW

[Bonner]

1 hour ago, SteamyTea said:

I don't consider Salisbury the SW

 

Just for my understanding, where is the border?

[Russdl]

1 hour ago, SteamyTea said:

 

I don't consider Salisbury the SW

 

No offence intended ?

 

4 minutes ago, Bonner said:

Just for my understanding, where is the border?

 

Wiltshire/Hampshire border for a bit of it.

 

 

[SteamyTea]

3 minutes ago, Bonner said:

 

Just for my understanding, where is the border?

I was always told that if you draw a line from Bristol down to Weymouth, then anything west of that is the South West.

I once heard a radio program where they referred to Oxford as in the South West.

When I lived in Bournemouth (west of Salisbury), it was always refereed to as Southern England, and was on the South Coast.

Much of this is to do with how the UK is orientated on a map.  It is easy to assume that where I am, 5°W is above France, but it is actually more than halfway across Spain.

 

[Russdl]

It's not as cold this morning, and there is no condensation. 

 

5° outside and if my IR thermometer is to be believed the inner panes of glass are around 16° so in theory well above the point that condensation would form according to @IanR. 

 

The humidity is up to 67%!

 

One difference to our set up from most, I suspect, is that we went for an enthalpy MVHR working on the theory that when the kids are finally gone and it's just the two of us the house would get too dry in the winter.

 

I'm guessing that if it isn't just a simple case that the house hasn't dried out yet then it could be that the enthalpy heat exchanger that is causing problem?

[IanR]

2 minutes ago, Russdl said:

The humidity is up to 67%!

 

If internal temp is still at 20°C, then dew point is up to 13.7°C with 67% RH. So, yes, inner pane is above dew point.

 

https://www.calculator.net/dew-point-calculator.html

[Russdl]

1 minute ago, IanR said:

If internal temp is still at 20°C

 

It's down to 19°

 

Thanks for the link.

 

[SteamyTea]

8 minutes ago, Russdl said:

One difference to our set up from most, I suspect, is that we went for an enthalpy MVHR working on the theory that when the kids are finally gone and it's just the two of us the house would get too dry in the winter.

 

I'm guessing that if it isn't just a simple case that the house hasn't dried out yet then it could be that the enthalpy heat exchanger that is causing problem?

I remember that there was a guy on eBuild that that had trouble getting his RH down.  He kept opening windows putting the MVHR on and off, heated etc.

Don't think there was an outcome.

 

Have you got any lime in your build?

Edited November 24, 2021 by SteamyTea

[Adsibob]

How close are your MVHR air supply vents to your windows?

[Russdl]

20 minutes ago, SteamyTea said:

Have you got any lime in your build?

 

Nope, none.

 

4 minutes ago, Adsibob said:

How close are your MVHR air supply vents to your windows?

 

They're on the gable end, 6+ meters away from the nearest kitchen window, closer to others. Closest being the en-suite at about 2m away from the intake.

[Conor]

It's the enthalpy heat exchanger. it's retains a lot more humidity than a standard counterflow. Turn it up a notch and see if that makes any difference. But you'll always have a higher RH.

 

We've just got the house water and airtight and some heating on. No MVHR yet... currently 89% RH  

[ProDave]

43 minutes ago, Russdl said:

One difference to our set up from most, I suspect, is that we went for an enthalpy MVHR working on the theory that when the kids are finally gone and it's just the two of us the house would get too dry in the winter.

I have an enthalpy MVHR as well and it does not lead to condensation on the windows (other than my rogue one already mentioned)

[joe90]

I too have an enthalpy unit and get a little condensation on very cold days (but don’t think it’s the MVHR). And mine is only double glazing.

[Russdl]

2 minutes ago, Conor said:

Turn it up a notch and see if that makes any difference

 

I'll give that a go. 

 

3 minutes ago, ProDave said:

I have an enthalpy MVHR as well

 

Interesting. Thanks.

[Russdl]

1 minute ago, joe90 said:

I too have an enthalpy unit

 

And there was me thinking I was the odd one out! It seems that everyone who's anyone has an enthalpy unit ?

[SteamyTea]

3 minutes ago, Russdl said:

enthalpy

The enthalpy H of a thermodynamic system is defined as the sum of its internal energy and the product of its pressure and volume:^[1]

H = U + pV,

where U is the internal energy, p is pressure, and V is the volume of the system.

 

As you are trying to change H, but do not know U, and cannot control p, the only thing you can change is V, by putting more air though the system.

[Russdl]

@SteamyTea I'm going to have to take your word for that ?

 

Turning it up as we speak sir!

[joe90]

2 minutes ago, SteamyTea said:

The enthalpy H of a thermodynamic system is defined as the sum of its internal energy and the product of its pressure and volume:^[1]

H = U + pV,

where U is the internal energy, p is pressure, and V is the volume of the system.

 

As you are trying to change H, but do not know U, and cannot control p, the only thing you can change is V, by putting more air though the system.

Duh, don’t know, just upped the fan speed to see if it made a difference, it didn’t.

[Marvin]

23 minutes ago, Russdl said:

It seems that everyone who's anyone has an enthalpy unit

That makes me a nobody. ?

[SteamyTea]

18 minutes ago, Russdl said:

Turning it up as we speak sir!

Just washed my hair, will it dry it for me?

[Marvin]

5 hours ago, SteamyTea said:

Just washed my hair, will it dry it for me?

If you stand under the inlet valve and you have as much hair as me, then yes in about 50 seconds.

Edited November 24, 2021 by Marvin
minor change.

[Russdl]

Just a quick update. We turned the MVHR up 24/7 for several weeks, RH still remained high and on cold mornings condensation was on the inside of some windows, most noticeably the large frameless window in the main bedroom that faces east. 
 

I splashed out on a dehumidifier because there is clearly a lot of water in this house. So far I’ve taken about 6 litres out in about 15-20 hrs of dehumidifier action. (so we have no shortage of window cleaning water). 
 

One morning the RH in the main bedroom was over 70%. I put the dehumidifier in there and bought it down to the mid 50’s% relatively quickly and then the moved the dehumidifier to the next room that needed attention. The following morning the RH was back up above 70% (and we’ve re-run that little sketch twice now). Is that an indication of something fundamentally wrong somewhere or just an indication that the house is wet and needs to be dried out. 
 

One other thing that really surprised me, that I’m sure our resident scientists will be able to explain with lots of confusing equations:

 

Running the dehumidifier in a room aside from drying it, also warms the room. There is little to no heat from the dehumidifier, is this temperature rise ‘latent heat’ or something to do with ‘dry/saturated adiabatic lapse rates’? Or none of the above?

[joe90]

RH in our house has always been fairly high, 67% this morning, but outside thick mist and drizzle so not surprising. I get a little condensation around my double glazing, especially the bedrooms, (people breathing at night?) I tried upping the MVHR a little but it appeared to make little difference.