Dehumidifier output

[Erin]

Bit of a 'how long is a piece of warp' question really, but I could do with knowing roughly how many pints a domestic dehumidifier would draw out of the air per day in an unheated, unoccupied 1 bedroom flat of say 800sq ft.

I realise there are many variables such as humidity, temperature, airtightness of building, quality of machine etc. The question relates to a flat with a suspected damp problem that a colleague is trying to investigate, but we have no gauge on how much water a dehume would pull out in a 'dry' flat. Any thoughts oh wise ones?

[martini]

3.142



:d

[Erin]

Thank you for your extremely helpful post . I see a certain resemblance to a well known theorum, and I'm not entirely sure it fits this particular application

[martini]

It rang a bell but I could be getting mixed up with something else...

Difficult one to answer, as you know much better than me, there is no "damp" or "dry", just an infinite number of degrees of damp/dryness.

I used to live in an old brick house, no d/g or c/h etc. My bedroom had damp problems, mould on the walls etc, my dehum. could get up to about 500ml just from that average sized room as a starting point for you.

Might be worth putting the dehum in one room at a time with the door shut, might give you a better picture of whats going on.

[willk]

Originally Posted by Erin

Thank you for your extremely helpful post .

Well, you can't have your Pi and eat it

[Erin]

Originally Posted by martini

could get up to about 500ml just from that average sized room as a starting point for you.

That's the kind of info I was hoping for . Apparently this particular property has some evidence of rising damp and some penetrating, and to confound matters there was a plumbing leak a month or so ago.

I gather 2 dehumidifiers had been set up and are collecting about 2 pints per day (not sure if that is each or total) but the problem was, we didn't know if that was normal for a dehume to produce, or indicative of a serious damp/humidity problem. Obviously the ideal would be to set them up in a known dry property and see what they collect, but that won't be possible due to time constraints. So if you collected 1 pint from a single occupied room, then 2 pints from a flat may not be particularly exceptional given that it is unoccupied/unheated and we are in winter and outside humidity levels are currently 85%.

[C-NUMB]

Regarding how it moves inside a wall its generally considered that it goes inside a wall
typically from warm surface towards cold surface, unless something is restricting the passage. Thats why in summertime it might be a worse issue than in winter.

Regarding damp in the air, I don't have the tables any more but it's pretty straight forward how much water air can hold in a certain temperature

here is a calculator, Vaisala is pretty pro so it should be ok. Its a downloadable file that need to be installed:

"http://www.vaisala.com/humiditycalculator/Vaisala%20Humidity%20Calculator.msi

Its important, when tracing the issue, to measure simultaneously the humidity both inside and outside, as then you can see if there is a source for topping on the humidity in the air inside( leak, but also normal activities like a shower will do the same).

Typically You should have less relative humidity inside than outside as the warmer air can hold more moisture. Difficult to say how much water the dehumidifier will collect as so many moving parts.

Accurate measurement of the air moisture content might tell plenty about the situation and potential issues.

Good luck!

[Erin]

Thanks for the help C-Numb. I am in fact a Chartered Building Surveyor and understand the technical aspects quite well. We have damp meters, wet and dry bulb thermometers and hygrometers along with the psychometric chart you are referring to for establishing dew-point etc and interstitial condensation, although at this stage we've just been asked for some basic advice so don't want to get too technical.

We know that there is dampness in the structure, but my colleague wasn't sure if the dehumidifiers were extracting anything more than just typical airborne moisture. I was hoping there'd be some ribnetters who would have some experience of basic dehumdifiers and be able to say whether 2 pints per day was either alot or not very much.

[Mollers]

We sell the big industrial dehumes. Ebac BD150, Rhino RD4S,Dantherm CDT50, Andrews Sykes HD500 etc, etc. These knock out around 40-50Ltrs per day depending on air temp and humidity.
Domestic dehumes are ok for cloakrooms etc. You need building dryers as mentioned above for decent results. Give me a shout if your in the market.

[Erin]

Originally Posted by Mollers

Give me a shout if your in the market.

Thanks, but luckily it ain't my problem and I suspect it will be a hire shop visit if anything.

Originally Posted by Mollers

We sell the big industrial dehumes. Ebac BD150, Rhino RD4S,Dantherm CDT50, Andrews Sykes HD500 etc, etc. These knock out around 40-50Ltrs per day depending on air temp and humidity.

I think if they had one of these running it'd start sucking the water table up through the concrete floor . Goes to show that 2 pints from a domestic is pretty much naff all.

Cheers

[Mollers]

Originally Posted by Erin

Goes to show that 2 pints from a domestic is pretty much naff all.

Cheers

Open and shut the door and and a couple of pints will sneak back in.

[C-NUMB]

Originally Posted by Erin

Thanks for the help C-Numb. I am in fact a Chartered Building Surveyor and understand the technical aspects quite well. We have damp meters, wet and dry bulb thermometers and hygrometers along with the psychometric chart you are referring to for establishing dew-point etc and interstitial condensation, although at this stage we've just been asked for some basic advice so don't want to get too technical.

We know that there is dampness in the structure, but my colleague wasn't sure if the dehumidifiers were extracting anything more than just typical airborne moisture. I was hoping there'd be some ribnetters who would have some experience of basic dehumdifiers and be able to say whether 2 pints per day was either alot or not very much.

Autch.. did not know, then you more than enough(and me )! But anyway its a interesting and challenging subject, water do sometimes travels in unbelievable ways.