Does anyone with MVHR have annual internal temperature and humidity data?

[Mike]

As per the title, I'm wondering if anyone with MVHR has kept a log of internal temperature and humidity data.

 

I'm playing with the free version of WUFI, and while it can derive the internal climate by adjusting external climate data to take into account heating and aircon, there's nothing for MVHR. Which seems a surprising omission, unless it's only in the paid versions.

 

In the absence of that, the next best option would be to define sine curves for the internal temperature and humidity, but there seems to be a lack of easily discoverable data on that. I've posted my initial guess below, but it would be good to have something to validate / correct this against:

 

 

Edited June 11 by Mike

[JohnMo]

I have winter data for MVHR, but wouldn't you need to overlay on my external temp, external humidity, internal temp and ventilation rates?

 

On cold day I had internal humidity was as low as 36.5%, 14 days previously it was 45% and a couple of days later back to low 40s. House temp was pretty stable around 21 degs.

[Mike]

5 hours ago, JohnMo said:

wouldn't you need to overlay on my external temp, external humidity, internal temp and ventilation rates?

Yes, it soon gets complicated like that, and I'm going to have to be very unscientific this time. However the methods included with WUFI look detached from reality for MVHR:

• The ISO 13788 option has 'humidity classes' to choose (i.e. guess), and one mean internal temperature to pick (constant for the entire year). To get relative humidity into the kind of range that I'd expect for a year (35% to 50% or so) requires that temperature to be around 30°C, which clearly isn't realistic.
• ASHRAE 160 takes the external climate file and generates the internal climate from that. It can take into account air changes, but assumes pulling in air at external temperature & RH, modified only by heating or aircon - no heat exchange option. That makes it very driven by building volume, and for a small volume like mine the internal climate generated is sub-tropical - in my case forecasting year-round RH at about 70%. Or from 35% in winter to 70% in summer if I plug in a moisture generation rate of 0.00003 kg/s (which has no link to anything).
• EN 15026, if I choose a 'low moisture load', comes closest to my expectations, but relative humidity is capped at 55% from mid-June until the end of September. It may peak at that, but to stay that way for a third of the year? Seems unlikely, but maybe.
• The external climate file (based on real data) can also be used as-is, but that's not helpful unless designing a building without walls or a roof (not even a tent).
• It looks like the paid version may have the option to input your own data, which is fine If you've been monitoring an existing building for a while, or you have some other software in which to model the internal environment (edit: looks like WUFI Plus can do that), but no good to me.

The only other option is to 'best guess' one sine curve for temperature and another for RH, ignoring the fine detail. As the results from WUFI are only used a long time scales - months or years - such generalisation should work, I imagine. So data to (literally) help shape these would be useful - or just comments & opinions.

 

5 hours ago, JohnMo said:

On cold day I had internal humidity was as low as 36.5%, 14 days previously it was 45% and a couple of days later back to low 40s. House temp was pretty stable around 21 degs.

At the cold end that looks about in line with my attempt, which is encouraging. I've picked low RH of 32% in mid-March, and a high of 48% in mid September (the peak and high have to be 6 months apart; I've put the high one month after peak August temperatures) - does that seem plausible?

 

Edited June 11 by Mike

[G and J]

5 hours ago, JohnMo said:

I have winter data for MVHR, but wouldn't you need to overlay on my external temp, external humidity, internal temp and ventilation rates?

 

On cold day I had internal humidity was as low as 36.5%, 14 days previously it was 45% and a couple of days later back to low 40s. House temp was pretty stable around 21 degs.

Are those humidity levels comfortable ?

[JohnMo]

8 hours ago, G and J said:

Are those humidity levels comfortable ?

Didn't notice, so must be. Also looked at our summer house with dMEV and that dropped to 32.5% humidity on the same day, the weather at that time had been a steady 3 days of sub zero temperature.

 

From the sleep foundation 

According to the Environmental Protection Agency, the best indoor relative humidity falls between 30% and 50%, and it should never exceed 60%. Other studies suggest 40% to 60% is a better range.

 

So at all times stayed within the recommended levels, most the time it's at 40 to 45 range, mid May we got up to about 55 to 58% but was hot and had cooling on and most likely the windows and door open after.  So no concerns, always in the recommended range. 

[G and J]

Thank you, one of the issues with building is that one has to make many, many decisions that are so hard to reverse later, but MVHR seems like a no brainier.  Where I’m less confident is whether we’ll need an enthalpy thingy which can be sorted later. 

 

We get used to nicer environments very easily - do you now notice when you go to houses that are more humid?

[JohnMo]

9 hours ago, Mike said:

Yes, it soon gets complicated like that, and I'm going to have to be very unscientific this time. However the methods included with WUFI look detached from reality for MVHR:

• The ISO 13788 option has 'humidity classes' to choose (i.e. guess), and one mean internal temperature to pick (constant for the entire year). To get relative humidity into the kind of range that I'd expect for a year (35% to 50% or so) requires that temperature to be around 30°C, which clearly isn't realistic.
• ASHRAE 160 takes the external climate file and generates the internal climate from that. It can take into account air changes, but assumes pulling in air at external temperature & RH, modified only by heating or aircon - no heat exchange option. That makes it very driven by building volume, and for a small volume like mine the internal climate generated is sub-tropical - in my case forecasting year-round RH at about 70%. Or from 35% in winter to 70% in summer if I plug in a moisture generation rate of 0.00003 kg/s (which has no link to anything).
• EN 15026, if I choose a 'low moisture load', comes closest to my expectations, but relative humidity is capped at 55% from mid-June until the end of September. It may peak at that, but to stay that way for a third of the year? Seems unlikely, but maybe.
• The external climate file (based on real data) can also be used as-is, but that's not helpful unless designing a building without walls or a roof (not even a tent).
• It looks like the paid version may have the option to input your own data, which is fine If you've been monitoring an existing building for a while, or you have some other software in which to model the internal environment (edit: looks like WUFI Plus can do that), but no good to me.

The only other option is to 'best guess' one sine curve for temperature and another for RH, ignoring the fine detail. As the results from WUFI are only used a long time scales - months or years - such generalisation should work, I imagine. So data to (literally) help shape these would be useful - or just comments & opinions.

 

At the cold end that looks about in line with my attempt, which is encouraging. I've picked low RH of 32% in mid-March, and a high of 48% in mid September (the peak and high have to be 6 months apart; I've put the high one month after peak August temperatures) - does that seem plausible?

 

Not sure what you are trying to get towards with all the data.

 

But currently outside it's 8 degs and 74% humidity.

House inside (MVHR) it's 19 degs and 48.5%. No heating on.

The summer house also has the heating off its 11.6 degs and 54% humidity (dMEV).

[JohnMo]

2 minutes ago, G and J said:

enthalpy thingy

Last week there was a thread and @ProDave and I listed our current and past humidity levels. Dave is North or West of Inverness in the Highlands and I am East of Inverness possibly 70 miles between us but different climates (we are not so extreme cold and if it is cold it's a shorter period).  Enthalpy is good for long cold spells and keeps the humidity to sensible levels. We had a week at or around -9 and the humidity stayed sensibly, but we didn't bother with a MVHR pre heater, so the MVHR is possibly in self protection mode (although no lights came to say that).

 

I would say if your not in a cold spot in the Highlands of Scotland, or need a higher humidity level for health reasons, the benefits of enthalpy heat exchanger are low, and also you possibly don't need a pre heater at all in the UK at all.

[G and J]

36 minutes ago, JohnMo said:

Last week there was a thread and @ProDave and I listed our current and past humidity levels. Dave is North or West of Inverness in the Highlands and I am East of Inverness possibly 70 miles between us but different climates (we are not so extreme cold and if it is cold it's a shorter period).  Enthalpy is good for long cold spells and keeps the humidity to sensible levels. We had a week at or around -9 and the humidity stayed sensibly, but we didn't bother with a MVHR pre heater, so the MVHR is possibly in self protection mode (although no lights came to say that).

 

I would say if your not in a cold spot in the Highlands of Scotland, or need a higher humidity level for health reasons, the benefits of enthalpy heat exchanger are low, and also you possibly don't need a pre heater at all in the UK at all.

We’re softy Suffolk southerners in a sheltered location, so the general benefits of the enthalpy exchanger sound limited.  
 

The only possible factor is that I use a CPAP machine with a humidifier (sleep apnoea).  Might just mean I have to turn up the wick on that and fill it up a bit more.  Small price to pay for a comfortable, dry house. 

[JohnMo]

28 minutes ago, G and J said:

We’re softy Suffolk southerners in a sheltered location, so the general benefits of the enthalpy exchanger sound limited.  
 

The only possible factor is that I use a CPAP machine with a humidifier (sleep apnoea).  Might just mean I have to turn up the wick on that and fill it up a bit more.  Small price to pay for a comfortable, dry house. 

This post has the details on enthalpy and not enthalpy MVHR

In your case perhaps enthalpy may be the way to go 

[SteamyTea]

I think you are on a hiding for nothing trying to estimate internal RH from external data.

RH is based on empirical data, not a formula, so even the best models are not correct (though good enough).

 

Ask another question, i.e. what is an acceptable level of RH for a given temperature range.

[MikeSharp01]

19 hours ago, Mike said:

methods included with WUFI look detached from reality

WUFI is not for those with a faint heart!  I did a full analysis of our wall build up looking for condensation using it and was relatively happy, 'this isn't so hard' I thought, but in the back of my mind I was concerned I hadn't got it right as I had some odd results I could not explain away. So decided to pay a professional - they soon put me straight - it was quite an eye opener! It turns out that for our application you need to focus on worst case zones so, in our case, low down & high up on the eastern side of the north face and ignore everywhere else. (This because the wall build up here is / was subtly different to everywhere else and North facing - something you could work out I suppose and nothing really to do with the software.) So taking an average for each elevation was, could have turned out to be, fatal. We were able to sort the problem by adjusting the build up slightly and using the 'intello' breathable membrane to remove the problem. I have, none the less, installed interstitial Temperature & Humidity sensors in the critical places so I can keep an eye on it!

[Mike]

23 hours ago, MikeSharp01 said:

I did a full analysis of our wall build up looking for condensation using it and was relatively happy, 'this isn't so hard' I thought, but in the back of my mind I was concerned I hadn't got it right as I had some odd results I could not explain away. So decided to pay a professional - they soon put me straight - it was quite an eye opener!

I'm getting a pro involved too, partly for the same reason - I have an tricky unventilated ceiling to insulate with limited options (a renovation) - and partly because the the free version is too restrictive anyway. However the consultant has proposed using ASHRAE 160 for the internal environment which, from playing with the free version, seems entirely unrealistic - as do all the other options. Hence this thread.

 

The free version is useful for exploring some of the materials choices too - such as the impact of using Intello (more pronounced than I'd expected); choosing between hemp -v- Rockwool insulation batts (hemp results in lower peak moisture loads, which I'd expected) and the insulation thickness (adding more insulation also reduces peak moisture).

 

On 12/06/2024 at 20:05, MikeSharp01 said:

I have, none the less, installed interstitial Temperature & Humidity sensors in the critical places so I can keep an eye on it!

I've been thinking about that too - which ones do you select, and what are you monitoring them with?

 

On 12/06/2024 at 19:06, SteamyTea said:

I think you are on a hiding for nothing trying to estimate internal RH from external data.

RH is based on empirical data, not a formula, so even the best models are not correct (though good enough).

That's why I'm after something better. The more realist the input the more realistic the output, even if still only a guide.

 

On 12/06/2024 at 10:50, JohnMo said:

This post has the details on enthalpy and not enthalpy MVHR

An interesting couple of graphs there, thanks!

 

[SteamyTea]

5 minutes ago, Mike said:

That's why I'm after something better

Two things to research then:

 

Converting from Temp/RH to Absolute Humidity (AH)

Statistical Modelling

[JohnMo]

Are people over thinking things or an I missing something. You should be controlling the internal RH to 60% max, regardless of the ventilation system installed. It really doesn't matter too much what temperature you have the house at, you still control at a max of 60% RH. I just have auto boost set to 55% to keep me away from 60%. 

 

So you just plug in 60%? You keep you house at a min 16, but more likely 19 to 21 Deg.

[MikeSharp01]

1 hour ago, Mike said:

I've been thinking about that too - which ones do you select, and what are you monitoring them with?

I have fitted a 22mm Plastic pipe into the wall, mounted at DHT22 on the end of a piece of 15mm pipe and put a RPi PICO on the other end to monitor temperature and Humidity, it is all behind a standard drylining socket box so I can access it and it is fed by a PoE CAT6 cable - power only data is by WiFi. Slide the 15mm pipe and DHT22 into the 22mm pipe, plug the Rpi into the Poe converter, close the wall box and job is done. 

[Mike]

2 hours ago, SteamyTea said:

Converting from Temp/RH to Absolute Humidity (AH)

Good idea. I've put together a minor Excel calculator, posted here in case anyone else finds it useful.

 

Still need to have a think about adding some allowance for internally generated humidity. While it will be removed via the MVHR system, there will be some additional moisture load.

MikeRelativeHumidityConverter_v1.0.xlsx

[Mike]

3 hours ago, JohnMo said:

Are people over thinking things or an I missing something.

It makes a difference in the context of WUFI modelling and, in real life in the structure being modelled. Simplistically, moisture builds up in the structure when internal RH goes up or external temperature drops, and is released when the opposite happens.

 

For example, at the top of the insulation in my unventilated ceiling, using the improbably 'ASHRAE 160' internal relative humidity proposed by my consultant, the insulation would stay at almost 100% relative humidity for more than half the year (the green line). Which would be seriously bad. This is modelled without adding an Intello membrane, but that's wouldn't save it.

 

 

Using an updated version of the sine curve I posted above for temperature & RH, it looks as below, with RH peaking below 80%, also without Intello. It's OK if it peaks above 80%, as long as it doesn't stay there for too long, but since I expect to be near that danger line and the internal environment is one of the biggest drivers of what happens, It's essential that the consultant uses sensible, realistic internal RH values.

 

 

3 hours ago, JohnMo said:

I just have auto boost set to 55% to keep me away from 60%.

Yes, that would certainly be useful to cap the upper limit!

 

Edited June 13 by Mike

[Mike]

2 hours ago, MikeSharp01 said:

I have fitted a 22mm Plastic pipe into the wall, mounted at DHT22 on the end of a piece of 15mm pipe and put a RPi PICO on the other end to monitor temperature and Humidity

Sounds good - I'll add it to my list, thanks!

[JohnMo]

8 hours ago, Mike said:

Yes, that would certainly be useful to cap the upper limit!

But even with an internal control limit set, it would still need to migrate through a vapour stop barrier. So you have zero migration of water vapour upwards into the roof structure.

 

8 hours ago, Mike said:

Simplistically, moisture builds up in the structure when internal RH goes up

So the vapour barrier stops this happening.

 

8 hours ago, Mike said:

realistic internal RH values.

Is that even relevant with a vapour barrier?

[Mike]

On 14/06/2024 at 08:58, JohnMo said:

But even with an internal control limit set, it would still need to migrate through a vapour stop barrier. So you have zero migration of water vapour upwards into the roof structure... ...So the vapour barrier stops this happening.

Yes, a perfect vapour barrier would result in no migration and would solve the problem, and save me having to pay a consultant too, which would be good!

 

Unfortunately perfect vapour barriers are not easy to achieve in new-build, and harder in retrofit (UK Government advice is not to use them in retrofit). I am sure that there will be some leakage through the partitions into the ceiling insulation, so have added an allowance for that in the WUFI model. In the best case the moisture escaping through the top of the structure to outside is enough to keep relative humidity below 80%, but in the worse it's above 80% for around 9 months of the year. To find the actual leakage level would need a blower door test, but that value may well worsen over time as the building ages.

 

Adding an smart vapour check, such as Intello (which lets vapour through in both directions at a variable rate depending on the temperature differential between the two sides) is likely to be a better option. Under 'worst-case' air leakage, the forecast maximum moisture content in the insulation during a year is reduced by about 13%, compared to having no vapour check. And, instead of the top of the insulation having the highest moisture content (75% peak relative humidity), it's the bottom of the insulation, next to the Intello that has the higher value (80% peak relative humidity). I suspect that I'll end up installing Intello to provide some extra safety, but it's not a panacea.

 

Either way, the more realistic the curve for relative humidity the better, so any ideas on that are still welcome.

[marshian]

I've been data logging the house internal Temps and Humidity as well as the Loft (cold loft relatively well ventilated) Temps and Humidity for the last 10 months but I've spit the data into day/night (based on daylight hours as solar gain has a big impact on loft temps - south facing roof)

 

I did this as I don't have MVHR and when I insulated under my suspended floors to reduce heat loss I saw a spike in humidity levels - I fitted a PIV unit to reduce humidity levels and I've been logging data since

 

It's still not as low as I'd like but it's definately improved the feel of the house.