Dehumidify a building via enthalpy heat exchanger

[joth]

We're trying to lay bamboo flooring, glue down, but it's been delayed for weeks because the indoor humidity is too high. It's a bad time of year for this I know. Plaster and screed are dumping water constantly, and our 0.5 ACH airtightness doesn't help!

We turned on the mvhr to try and circulate air out a bit more, but as it's got an enthalpy exchanger I'm not dead sure what the correct settings should be. It's a zehnder Q350

 

The controls has "humidity protection" mode, "humidity comfort" mode, plus force bypass for 24hrs at a time.

I think complex calcs involving latent and sensible energy may be required to work out if bypass will help or hinder, as it's wetter but colder outside...

 

Outside relative humidity 90%, inside is 86%

Outside temperature 8°C, inside is about 17°C

 

 

Suggestions?

 

MIs https://www.zehnder.co.uk/download/22227/90547/en_uk-59051.pdf

 

 

Edited December 23, 2020 by joth

[MikeGrahamT21]

Why not just open some windows? Sure it will let heat out, but it'll get rid of humidity.

 

I don't think enthalpy heat exchangers are particularly suited to the UK from what i've read. I have a non-ethalpy MVHR and my humidity holds between 40-50%

[PeterW]

56 minutes ago, joth said:

Plaster and screed are dumping water constantly, and our 0.5 ACH airtightness doesn't help!

We turned on the mvhr to try and circulate air out a bit more, but as it's got an enthalpy exchanger I'm not dead sure what the correct settings should be. It's a zehnder Q350

MVHR won’t help here - you need big industrial dehumidifiers running as the outside air is probably at 80-90% humidity anyway. 

[joe90]

1 hour ago, MikeGrahamT21 said:

Why not just open some windows?

 

1 hour ago, joth said:

Outside relative humidity 90%, inside is 86%

Our relative humidity is about the same, I have an enthalpy unit and it won’t reduce indoor humidity (shame), as per @PeterW you need industrial units like I did after plastering to get it down.

[Iceverge]

Can you remove the enthalpy module? 

 

I had a similar issue with humidity, in fact one particularly cold morning I was worried we might have a leaking window there was so much condensation after running down the frames. IIRC indoor RH was about 90% and temp 14deg. 

 

I put the MVHR from 40% to boost for a couple of days and it made a big difference. The house is now at 16deg at 75% humidity buy feels bone dry.

 

Opening the windows periodically and allowing a complete airchange and closing them again will help as the outside air even at 90%RH once warmed up can absorb much more moisture than the already warmer but saturated air inside. 

 

It may not be enough though and you might have to resort to a dehumidifier. 

[Iceverge]

I've had quick scan of your manual. 

 

Turn on the enthalpy/exchanger bypass and crank the MVHR to its top setting.

 

With the heating on also you should see results in a day or two. 

 

[SteamyTea]

At those sort of levels you have about 5gm/m³ difference. 0.007 kg/m³ @ 8⁰C, 0.012 kg/m³ @ 17⁰C.

Just heat the place up with some fan heaters while ventilating though a relatively small apperture i.e. small window open, not a door.

Edited December 23, 2020 by SteamyTea

[joth]

2 hours ago, MikeGrahamT21 said:

Why not just open some windows? Sure it will let heat out, but it'll get rid of humidity.

 

I don't think enthalpy heat exchangers are particularly suited to the UK from what i've read. I have a non-ethalpy MVHR and my humidity holds between 40-50%

 

2 hours ago, PeterW said:

MVHR won’t help here - you need big industrial dehumidifiers running as the outside air is probably at 80-90% humidity anyway. 

 

Yes we've tried industrial dehumidifier for a month, and windows open whenever on site, but neither these have worked hence now attempting something else with mvhr.

It ran overnight, but this morning the inside of windows were still damp hence the query. Given it'll be unoccupied for a couple days now it'd be good to figure a system that actually is helping it dry. 

 

I have it set to "bypass active 24hours" yet the status menu is resolutely saying Bypass = 0% so not sure what's up with it. 

 

Thanks

 

 

[MikeGrahamT21]

Maybe its using a set point temperature for the bypass?

 

The fact there is condensation on the windows is good, as long as you remove it from the building, karcher window vac maybe? It'll get rid of a fair amount.

 

The air outside at this time of year is cold and moisture laden, but at say 4C and 90% RH if warmed up to 18C, will be more like 50-60%RH which will have a big drying effect, so if you can get some heat in and leave the windows on vent, given a week or two it will shift a lot

[Mr Punter]

We had a newly completed property flood a couple of years ago from a loose pipe on the first floor.  Overnight the water poured through the ceilings.  In the morning when I got to site it was like a rainforest down there.

 

The ceilings remained intact so we swept out the water, cranked up the heating, got 2 x industrial heaters and 2 x industrial dehumidifiers.  The place was bone dry in 2 weeks.  We must have got it up over 30 centigrade.

[joth]

Sounds good, it's really a case of more of the same as we've been doing.

Frustrating I've got a nice Ecodan ASHP sat here unused because the scaffold is still blocking where it needs to go. Else we could have all the heat we ever need. As it is the electrician has only commissioned a couple sockets on a 16A circuit which rather limits the amount of heat we can get in. Still I can crank up the setpoint temperature and see how we do

[Ferdinand]

How much water did you put on with the plaster - that's how much you need to get out roughly.

 

The last one I did was a 65 sqm bungalow and I was able to get that from new plaster -> paintable in about 4 days running a couple of big dehumidifiers at a temp of 30C.

 

TBH I would say get one good big dehumidifier and see. I would recommend a Broughton CR40, which is the smaller of the two I have.

 

F

[MikeGrahamT21]

Maybe patience is a better idea? Wood flooring and an unbalanced atmosphere aren't a good combination. Besides the slower the plaster dries, the more durable it will be long term.

[Iceverge]

@joth

 

Any update on the drying?

 

 

[joth]

59 minutes ago, Iceverge said:

@joth

 

Any update on the drying?

 

 

 

Yes! Down to 75% humidity and seems to have settled there. Left the MVHR going just to ensure all the air gets moved around a bit and manage some of the black mold spots building up. Left a couple windows open a crack to let air out, but after the humidity settled last week we've not bothered leaving them open.

It seems we need a 2kW heater running 24/7 just to maintain 18deg which is I guess nearish to what PHPP predicted (it has been fairly cold out)... it's a bit scary leaving that going when not there overnight, but necessary to keep the food flooring settle to correct temp & humidity to install.

The fitter seems happy with it all today, coming back Friday to install at last! Then we just need a kitchen install date, and we can start to dare to think about a move-in date. (I might move my laptop and monitor down there sooner, and "work from home" from site until we officially move back in)

 

[Iceverge]

Top stuff. Did the enthalpy/heat exchanger bypass make much difference?

 

Your situation sounds almost identical to ours. We have a 2kw heater running with the MVHR since November. 

 

It began at 13 Deg at 94% humidity. It's taken a while but humidity seems to have settled at 65% at 17 Deg. 

 

We did get some mold when the temperature rose initially when the humidity was still in the high 80's but that's since disappeared.