humidistatic dehumidifiers

[charlie-ia]

what do i need to know? tried googling, but got too much. tried "dehumidistatic dehumidifier" timber ,and ended up with a link to a place called "ppuk".

NT help me!

I guess (having never seen one) that we turn the dial down a bit each week.
how much, how fast; and what are the danger signs before its too late!

 

[NT]

What do you need to know? Not a lot tbh. If your house is large & soaked you may need a higher extraction capacity than the cheaper 200w £100 units, or better 2 smaller units.

Used dehumids are available at good prices if you can find them.

The issue with dhs is that if wood is dried out too fast, ie by achieving too low an ambient RH, then plank wood can cup and large timber pieces can crack along the outside. This is why a dehumididtatic unit is wise, so you get reasonable RH rather than ultra dry air.

The dh can have a 2nd use too:
http://wiki.diyfaq.org.uk/index.php?title=Clothes_Dryer


NT

 

[NT]

A bit more: some units, mainly used ones, lack a hose attachment for continuous drainage. Older units may also not have mouldproof water containers, and you may need to clean the water container from time to time to avoid mould growth.

And I'd not recommend Amcor machines.


NT

 

[charlie-ia]

too low an ambient RH

NT

So what kind of levels are we looking at? how low is too low? does it matter the speed you get there as long as you dont go past a certain point, or are we trying to creep up on this mythical beast you call RH?

will the ambiant humidity be roughly the same as the humidity actually in the timber?
and i understand we need to get it below 12% to stop the worms. is that right?
how long will it take? months&months, or a week or so? (i know you cant be specific)

 

[NT]

too low an ambient RH

So what kind of levels are we looking at? how low is too low?

Good question. I'm not a wood expert so may be best someone else answers that. I believe 60% RH is quite safe.

does it matter the speed you get there as long as you dont go past a certain point, or are we trying to creep up on this mythical beast you call RH?

A dehumidifier can often reach a healthy RH in one afternoon, thats not a problem.

will the ambiant humidity be roughly the same as the humidity actually in the timber?

no, not at all, the movement of moisture from wood to air is very slow, and thats partly why problems can occur. Wet wood swells, so if you take the ambient RH too low, the outside wood dries and shrinks while the core is still wet, leading to cracking.

and i understand we need to get it below 12% to stop the worms. is that right?

Wood is not my expertise, so I dont want to give exact figures

how long will it take? months&months, or a week or so? (i know you cant be specific)

I cant be specific It depends on timber sizes, air movement etc. But not quick, probably a month or months.


NT

 

[charlie-ia]

that seems fairly clear, thanks. How do we know when the jobs finished?
can we safely leave it unattended?(assuming it has a wastepipe of course!) perhaps get someone to check it once a week?

 

[Aidan]

will the ambiant humidity be roughly the same as the humidity actually in the timber?
and i understand we need to get it below 12% to stop the worms. is that right?

The 12% in wood is the moisture content, not the Rh.

The Rh measurement is only relevant to the moisture content of the air. It is the humidity/moisture content relative to the saturation moisture content (100% Rh) at a specific temperature.

The wood moisture content can only be measured by drying a sample in an oven & comparing the before and after weights. It's usually estimated from the wood's conductivity, since you usually want to avoid destroying the wood.

I think structural timbers will usually dry out to a state that won't encourage worms in a normal, dry building. Worm & rot problems generally occur as a result of a damp problem. There was some timber preservation expert who posted on here ocasionally, his website had details; someone must have it bookmarked.

My understanding is that you only need close control of the Rh if you have some Rh critical items, e.g., thin wood sections (flooring, wooden instruments), paper, hydroscopic materials.

So what kind of levels are we looking at? how low is too low?

50 or 55% is generally desirable. It only becomes a problem for people when you jig about with the air temperatures. Simple heating of cold winter air will result in excessively dry air; simple cooling of warm, summer air will cause ludicrously high Rh. http://en.wikipedia.org/wiki/Humidity#Recommendations_for_comfort


If you really want to achieve close control of Rh, it usually requires a large application of dosh, a ventilation system and a sealed building. The condensation produced as a result of vapour leaks into a modern, insulated building can be huge. You need to achieve close control of the temperature before you can control the Rh. Most budget Rh meters & humidistats are inaccurate.

DX dehumidifiers generally don't achieve close control of the Rh level since they're on/off devices Chilled water cooling with re-heat can achieve more accurate control. I really, really wouldn't bother with domestic installations.

how long will it take? months&months, or a week or so? (i know you cant be specific)

A year or more for a new building, but you might then need to evaporate a ton or so of water. You don't need humidity control for structural timbers in buildings, they stood up for a long time before dehumidification came along.

 

[worms]

Anyone have any experience of dessicant wheel dehumidifiers? My understanding is that the refrigerant type become increasingly inefficient as temperature drops and I would like to be able to use one in the 4-10 degree range in winter. I've not seen a dessicant wheel dehumidifier that also has a humidistatic switch, but it surely can't be too hard to rig up an external humidistat to control it?

 

[charlie-ia]

so do we have to sort the drainage etc first, or can we get one now, plug it into the dodgy electrics when we pick up the keys and get going?
hmm, now ive put that in writing it sounds like a really bad idea!

does the machine need to run for a year, or did you mean that if you get the house mended, the general overall drying in a happyhouse takes a year?

from what Ive read the project management is the trickiest bit of this fine mess we're getting ourselves into. Im looking for jobs that can do themselves before we can get there, and thought this might be one.

does anyone know the phone number for the sorcerers apprentice?

(probably copyright disney)

 

[Aidan]

so do we have to sort the drainage etc first, or can we get one now, plug it into the dodgy electrics when we pick up the keys and get going?
hmm, now ive put that in writing it sounds like a really bad idea!

does the machine need to run for a year, or did you mean that if you get the house mended, the general overall drying in a happyhouse takes a year?

from what Ive read the project management is the trickiest bit of this fine mess we're getting ourselves into. Im looking for jobs that can do themselves before we can get there, and thought this might be one.

A year or more for a newly built house to dry out once occupied, without any dedicated drying.

Have a search for condensate pumps. They're much used for DX ceiling cassette cooling systems, where gravity condensate drainage is impractical. They usually have a small reservoir with on/off float switches; the condensate is pumped through a hose in the ceiling void, up & over any obstacles and into a remote drain.

There was a thread about dessicant dehumidifiers on uk-diy some time ago. The informed opinion was that they were less efficient than an inefficient refrigerant dehumidifier. They're generally not used in industry except on compressed air systems where really dry air is required.

 

[charlie-ia]

a "severly damp" old house is going to be wetter than any new house isnt it?
Im thinking about the woodworm. it looks like its going to be a long time before we've killed them off then.
any hints on speeding this job up? (within reason of course) or is all you can do is sort the drains, fit windows, put the fire on, get a dh & wait patiently?

 

[NT]

> that seems fairly clear, thanks. How do we know when the jobs finished?

when RH stays healthy by itself, the dh wont come on, or will come on very little.


> can we safely leave it unattended?(assuming it has a wastepipe of course!) perhaps get someone to check it once a week?

no reason for a weekly check that I can think of. If youre leaving it unattended, a metal cased machine is slightly more fire safe than a plastic one - though not much in a soaked house could burn


Aiden talks about a lot of tech & options that I dont see as useful for your case. You can plug a dehumidifier in, route the drain hose somewhere, prop the internal doors open, and thats it, you've got RH control, and a lot of the wood will slowly dry out.


> You don't need humidity control for structural timbers in buildings, they stood up for a long time before dehumidification came along.

This is true for buildings that are in good health, with sound roofcoverings, good drainage and so on. But for a sodden building, if you dont dry it out it will continue to rot. £100 to stop the structure deteriorating further is a bargain.


> so do we have to sort the drainage etc first, or can we get one now, plug it into the dodgy electrics when we pick up the keys and get going?

Plugging the dh in would be one of the things I'd do on the first day. It isnt going to solve all damp problems, but it certainly will make a real difference and shift at least most of the wood from rotting to no further damage. It isnt going to stop rot in any wood the water is pouring on to of course.


> hmm, now ive put that in writing it sounds like a really bad idea!

If the wiring is poor, it may be worth just leaving one fuse in the fusebox to power the dh, and pulling all the others. Be aware that pulling fuses on old fuseboards can fry you, always switch the power off first.

Using bad electrics can affect your insurance. Thankfully its easy to leave all fuses but one out & disconnect the old circuit from that one fuse, then add a new cable to a 2/3/4/6 way new socket. The cable can be taped to the wall, it takes all of an hour to set it up. In your house a rain cover over the socket might be a good idea too.


NT

 

[NT]

Anyone have any experience of dessicant wheel dehumidifiers? My understanding is that the refrigerant type become increasingly inefficient as temperature drops and I would like to be able to use one in the 4-10 degree range in winter. I've not seen a dessicant wheel dehumidifier that also has a humidistatic switch, but it surely can't be too hard to rig up an external humidistat to control it?

Right on all points aiui. My attempts to use refrigeration below 10C have been almost totally ineffective.


NT

 

[charlie-ia]

http://www.novelaire.com/DessicantDehumidifier.htm

is this page any use worms?

 

[charlie-ia]

"Plugging the dh in would be one of the things I'd do on the first day"

one of the things? are you about to drop me another gem of information?
go on, do tell, what else what else?

(wheres the icon for bouncing up and down like a small child waiting for christmas?)

 

[Craig]

I use an EBAC condensing dehumidifier with a continuous drain to keep my lathe and motorcycles happy and rust free. 60% Rh is pretty much where bare metal corrosion stops - its plenty dry enough and I wouldn’t try to go any lower than that as you will simply accelerate the rate at which moisture penetrates from the outside.

The workshop is unheated and faces north. The dehumidifier is on all the time with humidistat switch. It maintains 60% all year round despite its increasing inefficiency in the cold.

I looked at the desiccant types - the idea of background heating was quite appealing but they had limited drying capacity compared to the EBAC unit.

 

[charlie-ia]

http://www.ebacdirect.com/guide-wizard.php

 

[Craig]

All a bit domestic for what i was after - I got one of these things:

http://www.ebacusa.com/cs60.htm

 

[charlie-ia]

blimery! that looks like a beast! is that what you'd reccomend for me?

 

[NT]

"Plugging the dh in would be one of the things I'd do on the first day"

one of the things? are you about to drop me another gem of information?
go on, do tell, what else what else?

(wheres the icon for bouncing up and down like a small child waiting for christmas?)

I see. Well, I dont know what your plans are, but some things are best done at the start. Examples:

switching off electrics if theyre evil
removing plugs of vegetation from hoppers
clearing external debris from against the wall
putting bits of felt into the roof to plug the holes
putting clear polythene on the broken windows, and/or boarding, etc
securing the site if possible

Depends on what youre doing really, I forget if its a month visit, a days visit or youre moving in on day 1.

Oh, and in your case fitting foam pipe insulation to any low beams


NT