Update - (bad) experience with a workshop dehumidifier....

[ondablade]

Some of you may remember my asking for feedback on your experience (it's not widely done, but does seem to be the accepted means) of using the above to control workshop relative humidty (RH) to about 45% as a means of conditioning wood to around the 8% moisture needed to go into a centrally heated house.

The essential difficulty is that our average RH outside all year round is about 70%, and this equates to around 16% moisture content - you can air dry for as long as you like but it won't go any dryer.

Achieving the required 45% RH at shop temperature requires heating in the winter (increasing the air temperature reduces the %RH), but air conditioning/de-humidification is required in Summer as there is little scope to raise the temperature further.

In absence of good information i took a flyer and bought a 21 litre/24hrs domestic de-humidifier made by a well know brand specialising in these. My workshop is about 8.5 x 5.5m with a loft area overhead, and is well insulated and has only a few small windows.

I'd love to be able to report a success, but it absolutely has not been the case. Despite a specification that suggests it should be fine (it's not too hard to work out from a chart how much water you need in 24 hrs to drop the %RH by the required amount) the unit in question simply is not man enough for the job. It seems to be working fine (but i can't be sure of this), but isn't shifting anything like 21 litres/24 hrs. More like 2 - 3 litres actually.

This with the doors left closed so it's not having to deal with fresh air being drawn in from outside.

At this stage it's going to be heading back to the maker under warranty in the next week or so. My best guess is that much like many DIY dust and other woodworking systems the problem is simply that the numbers claimed for it are not real world. For example maybe it can do them in highly selective conditions (at high air temperatures), but not at what we have even now.

If i had to guess it's maybe dropping the RH in the shop by 3 - 5% rather than the required 25% right now. Switch it off and the %RH eases up a few %, but it sure as hell is not that much affected.

What's a bit frustrating apart from the bum performance of the unit is that the beech for my bench have been conditioning away for five months now and cannot be as dry as i would like if whatever it's replaced with actually does the required job.

Ideas anybody?

Anyway - caveat emptor (buyer beware) if anybody was thinking of heading down that route. I'm calling the maker in the next few days to see if they can 'explain' what might be going on. Sounds like it's going to take some professional kit.

 

[9fingers]

I wonder if the problem is insufficient air circulation? Can you measure a lower humidity nearer the machine than further away after it has been running a while?

Bob

 

[devonwoody]

Interesting topic, and would like to hear what the manufacturer also replies.

Indoors we are always emptying our container so they do work in the domestic area.

(Could it be that you do not have a clear area of ventilation and extraction around your unit. )

 

[Eric The Viking]

In absence of good information i took a flyer and bought a 21 litre/24hrs domestic de-humidifier made by a well know brand specialising in these. My workshop is about 8.5 x 5.5m with a loft area overhead, and is well insulated and has only a few small windows.

I'd love to be able to report a success, but it absolutely has not been the case. Despite a specification that suggests it should be fine (it's not too hard to work out from a chart how much water you need in 24 hrs to drop the %RH by the required amount) the unit in question simply is not man enough for the job. It seems to be working fine (but i can't be sure of this), but isn't shifting anything like 21 litres/24 hrs. More like 2 - 3 litres actually.

(snip)

If i had to guess it's maybe dropping the RH in the shop by 3 - 5% rather than the required 25% right now. Switch it off and the %RH eases up a few %, but it sure as hell is not that much affected.

I have had a small pro- unit for many years. It's obsolete ("Trion Dryhome"), but is a commercial/small industrial model, similar in design to the black "Woods" unit here. We've used it for drying plaster and similar things, and in a basement storeroom.

From memory, the tank is about 10 litres. I've never known it do more than that in 24 hours. It does work, but it's far more sensitive to the environment than I hoped, and not good with large spaces. Two other things make a big difference: the amount of air movement (leaks) to outside the dried volume, and the ambient temp. It's far more successful in winter, with a colder environment, than in summer. In summer it pulls in a lot of water, but the RH doesn't drop much. In winter the heat it emits helps to drop the RH further (I think). I get the feeling it's just overwhelmed by the moisture content of the air in summer.

It's also expensive to run as it's well over 1kW (can't remember what as I can't get to it at the moment. It has a humidistat, which works, but I still wouldn't leave it on for long periods.

For my purposes (usually related to building work), it's fine, but I think if I wanted to use it for wood, I'd make some sort of polythene tent.

Incidentally, don't you want your bench to match the local RH, rather than reach a specific value?

 

[ondablade]

I moved my hygrometer to the other end of the shop, but didn't seem to see any very obvious difference in reading Bob. It's directly in the air flow coming from the unit now, so maybe that'll show some difference.

It's very possible that the fan is simply not circulating enough air - it's not very powerful. It could be a double edged sword deal in that case - if it's just creating a dehumidifed zone around itself then it can't take out more water. On the other hand despite the building being basically sealed apart from the small air gaps you get in a modern house with PVC windows etc. the hygrometer reacts easily within a day to changes in outside weather conditions.

Checking the brochure is telling. Lots of small print caveats about the spec not comprising a binding contract (?), no kW rating (5A fuse specified suggests it's maybe at most 1Kw?), different capacity numbers depending on where/who you look on the web. (but should still be OK - claims to do a large 5 bedroom house and my shop is only about 600ft2 including the loft. It claims to be intelligent - i wonder if there might not be something stopping it dropping the RH below a set number since it's never got the shop below 65% RH.

This one has not done more than maybe a litre or two, at least not back in Jan before i fitted a hose kit so it became self draining Eric. Matching %RH is the issue that's bothering me. My beech has been conditioning away for months in the shop at the above 65%RH, but if i get a dehumidification deal working properly it'll drop to something more like the 45% required to deliver 8% moisture content. But i'll be ready in a few weeks to start building the bench, and can't wait another six months. Maybe ripping the stock down to something safely oversize would speed it up enough....

Will call the maker E**C later...

 

[lurker]

IIRC "the Wicketkeeper" warned you that it was a folly.

Unless you have a totally sealed area then you are trying to dehumiify the world.

 

[jasonB]

As you are not getting below 65% whats the humidistat set at, you need to set it at your desired humidity level.

I been doing a lot of work for the same client over the last 18mths and they have a unit that will get down to 45% and it really sucks the water out, so much that I fitted a hose to the container so it does not need emptying several times a day. The default setting on this is 65%.

Jason

 

[Benchwayze]

If possible, just build your south facing wall of metal (Mine's a garage door) and probelm solved. Or am I just lucky where humidity is concerned?
:?:

John

Stage right :arrow:

 

[jasonB]

Don't know what Ebac you have, sounds like a domestic one but for the commercial ones the amount of water removed is based on 30degC and 80%RH as either drops so will the removal rate.

Jason

 

[ondablade]

There could be something in that, at least in Winter John as a very cold wall would cause condensation which would run down it, and maybe out through the leaks? Although raising the shop temp will do the business in Winter. But then a bit of sun on your wall should do that then too! Probably not so good in the Summer though when it would be baking hot and would just fry your a**!

It'd be great to to find a way around the need to pump in energy with a bit of lateral thinking though.

Not so sure about the folly part Lurker, as it's not exactly rocket science to air condition a room. (or indeed a whole factory) For sure it can't be left wide open to the weather, but as above my shop is far from that. In practice it comes down to air change rates vs. capacity - and the unit i have should have enough grunt to accommodate what's going on. I've spoken to a couple of people who say they do it successfully...

When i took my unit out of the box Jason i was surprised to find no obvious humidity setting, just a button that toggles between various consumer speak descriptions of settings. It could very well be that what you say is the problem. Ebac should be able to set me straight this afternoon on that.

Thanks all for the steer, will keep you posted...

 

[ondablade]

OK Well that's clarified the position anyway - if not in the way i'd have liked.

The lady at Ebac tech support says that the domestic units control to a non adjustable 55 - 60% RH, which if some allowance is made for outside air infiltration makes my typical 65% RH sound about right.

She can't quite say if that's to do with the particular automatic controls fitted, or if it's a specific limit of the type of refrigeration circuit (they say they use ozone friendly refrigerants, and it's quite possible that as a result of the type of refrigerant they simply can't get down to low enough temperatures to deliver 45% RH.

Next step is to talk to somebody in their industrial division, they do purpose units designed for kiln drying timber http://www.eipl.co.uk/Websites/UK/lumberproducts.htm which if reasonably priced might be an option.

i.e. If it's more expensive it might be practicable and more cost effective to air condition the shop to controlled conditions for timber in use, and at the same time start drying some timber in it - as to build the separate kiln i've been toying with. Make a virtue out of a necessity. Will ask the Ebac guy when i get to him and report what i'm told....

 

[jimi43]

Have you checked your electricity consumption recently?

I put quite a large unit in my shop last winter and you could actually smell the room was dryer but it ate kWh for breakfast! It filled up so much I was going to put in an outside drain it was such a pain.

Jim

 

[ondablade]

The unit i have has not had any very noticeable effect on our overall power consumption Jim, but then in dropping the air to only 60% RH and having a small fan it's probably not working all that hard either. It's very possible that an industrial unit which probably also has heating capability could be a very different story.

Sounds like a high priority on the list of must know information. Unusually for me i allowed myself to be taken in a little by people talking of just do XYZ in this case and just went out and bought a domestic unit. This time no way! Even if the industrial unit proves too expensive a chat with an applications engineer who knows about wood drying should prove very informative.

Complicating factors that need thinking about are the other bits of kit that may interact or even be a cost saver - for example the dust system, a possible sawdust/scrap stove, the option to fit more oil fired central heating radiators and the extraction for a paint booth. The stove and the rad would be for winter heating.....

....

 

[jimi43]

Don't forget...a wood burning stove will produce some moisture too.

Good luck mate...you may need to clear a space under the bed though for drying! :wink:

Jim

 

[DaveL]

Don't forget...a wood burning stove will produce some moisture too.

But the moisture should be going up the flue with the smoke, I save all of the shavings and saw dust to help fuel my wood burner.
I can see the humidity in the shop go down when the stove is running.

 

[Eric The Viking]

Don't forget...a wood burning stove will produce some moisture too.

But the moisture should be going up the flue with the smoke, I save all of the shavings and saw dust to help fuel my wood burner.
I can see the humidity in the shop go down when the stove is running.

Slightly off topic: I don't trust those humidity sensors. I've got an "Oregon Scientific" weather station given to me as a present a couple of years ago. It has a remote (radio) temp and humidity sensor, and one in the main unit, which also has a Rugby atomic clock receiver (or wherever it's now been moved to). Yesterday it was showing 45% RH in the porch, 43% in the house, and the symbol was showing heavy rain. It was scorching sunshine all day.

Today, we've just had a downpour. It's still only showing 80% RH outside, and the symbol is for cloudy sunshine. If you stand the two sensors together on a shelf they don't agree with each other either (neither temp nor humidity). I've looked, and there seems no way to adjust it either.

 

[ondablade]

Not only will the moisture go up the flue Dave, but raising the temperature of the shop as in winter significantly drops the % RH (relative humidity) anyway. 70% RH at about 50 deg F (10 deg C) becomes 45% RH by about 65 deg F (18.5 deg C) without removing any moisture from the air.

Luckily as it happens, this is why heating alone is enough to get the 45% RH required for 8% wood moisture content in winter, but air conditioning (moisture removal by chilling the air before reheating and returning it to the room) is needed in Summer.

The relationship is set out on these charts. They look a bit complex, but are simple enough in the end: psychrometric chart

More info from EBAC today, i spoke to their industrial and domestic tech support people. They say that while it's technically possible to run the 2650E microprocessor controlled unit i bought down to 45 % RH that it's very complex in that it'd require reprogramming the chip that controls the unit, and probably also some hardware changes - none of which they can support. So it's for sale tonight on the local website. Anybody need a little used domestic dehumidifier? :wink:

It's turned out (silver lining) that the EBAC industrial guys do specialist kiln drying units which incorporate both heating and dehumidification. They also do suitable and relatively cheap dehumidifiers. The deal is i'm to drop them a mail setting out the requirement and they will come back with comments.

They say they have a lot of 'how to' information on kiln drying available, and that their German guys have a lot of experience.

I've been thinking of installing a 20ft container to go cottage industry kiln drying (what little trust i had in 'kiln dried timber' is already shot) to ensure my wood is right - with a view to possibly getting into small volume high quality kiln drying and selling some wood later.

Lots of study of kiln drying cycles is needed to avoid another **** as all i know at this stage is that it entails both heating to quite high temperatures (to kill bugs as well as whatever drying requires) and dehumidification. (Woodweb and some of the USDA sites are very good sources, but EBAC say they have good manuals on both processes and how to build a DIY kiln too)

That said i'm wondering if i install dehumidification and heating in my shop will it enable a slower (some say better) but still acceptably fast air drying process that will do the same job.

Air drying can only get your wood down to 8% moisture content if you hold the ambient conditions down to 45% RH, but with proper heating in the shop in winter as well maybe it would still be a heck of a lot faster than it is in the open air....

Any thoughts anybody? Mad?

 

[jasonB]

If you are thinking of a container size unit then have a look at a small kiln.

http://www.koetterkiln.com/timber-tikekilns.php

Thats the sort of thing you would want for "cottage industry kiln drying" I would have said the Ebac stuff is more for "conditioning" than full drying. If you are doing proper kiln drying then you need to do a whole container at a time, no use putting 1m3 of wet oak in there and expecting all the other timber stored in there to stay usable while you dry the oak!

Arrowsmith also do (did) small kilns but I think they are nomore.

Jason

 

[ByronBlack]

Tell me if I am wrong, and missing something here, but if the beech is for a workbench that is going to exist in your current workshop, then surely you don't need to worry about the humidity or dryness as long as the wood is in equilibrium with the surroundings?

If it's reached that level, then I can't see what the issue is with making dryer, because as soon as you stop using your dehumidifier, won't it start to take up the moisture again? Wood don't stay dry forever.

In Chris Schwarz book, he talks about MC of wood a fair bit, and for workbenches, you can build quite a lot of it with relatively wet wood, so that when it dries and shrinks, the joints become stronger.

If you are laminating the top, the pieces will be thinner (and easier to get to equilibrium) and once glued together, won't move that much.

I did that in my workshop, and nothing has moved for a coupe of years. I don't even have a moisture meter. I just left the wood a few weeks to acclimatise and started working on it.

 

[ondablade]

It's tied in (at least in my mind) ultimately with how best to condition and handle the wood that goes into projects Byron. (bear in mind that i'm getting set up, and trying to sort out a working regime as well as build a bench)

Yes, you can run with your shop at whatever humidity the ambient conditions dictate, and yes - if you properly condition the timber to those conditions before making your bench it seems it should be fine. (never mind that 2 inch boards take close to two years to fully equlibriate in the open air)

Chris Schwarz talks of starting with the timber for his Roubo bench design quite wet, but very specifically in the case of the joints and the yellow pine he was using. Having seen the frolics of the (expensive) beech i've bought (cupping and some light end splitting) that has to be a risky strategy with this wood. I'm not too keen on heading off on a wing and a prayer.

There's a bigger picture than the bench though:

If you are making furniture and fine stuff for centrally heated houses you really need to be using kiln dried wood down around 8% moisture content if the resulting items are to be (relatively) stable. (it doesn't mean that there are not ways around this if you don't mind losing a lot of time and using specific designs, but if this isn't broadly true then a lot of eminent people writing on the topic are smoking dope as the old saying goes) You have to kiln dry to get down to this, as air drying in our climate doesn't no matter how long you leave it get you much below about 16% moisture content.

Theoretically you buy kiln dried wood at 8% or a bit higher. Several basic problems may follow though:

1. If you bring that kiln dried and genuinely 8% wood into a shop that is at whatever (highish) humidity naturally arises it's going to take up moisture like mad. Meaning that every time you saw open a piece to expose a surface it'll move like billy oh. (some try to get around this by getting the piece finished and sealed in a few days - but i don't really want this sort of gun to my head)

2. The resulting increase in wood moisture content will also risk problems in finished pieces in centrally heated houses.

3. So far as my experience, gut and reading go kiln dried wood is often anyway only very approximately at the correct moisture content. e.g. No doubt it was fine when it left Germany, but my very nice clean beech (did i mention it was expensive? ;-)) for the bench came through Boddy's, and despite being supposedly kiln dried was at about 14% moisture content overall, at around 17% at one end of some boards, and 12% in a few other places. (maybe it got rained on) Not only that, most of the 2 in x 10in boards cupped by about 1/4 in within a week or two of bringing them into my shop.

That all brings several issues/questions into play:

1. It's possible to let the shop find it's own natural (high) humidity level, and to wait the very long time needed to let wood acclimatise to this before starting projects. (you could even roughly rip down the timber closer to the finished sections to speed the drying) This would be OK for the bench which will be staying in the shop, and would solve the movement while working on it issue - but i can't wait very long, and anyway the subsequent relatively wet furniture coming out of there would surely risk problems in heated houses.

2. Is it worth air conditioning the shop to control the humidity in it so that 8% wood will stay stable and at that moisture content while stored in it, and being worked on?

3. If kiln dried wood is often dodgy in terms of moisture content, then maybe it would be worth building some sort of small finishing kiln in the shop to ensure a rapidly available supply of wood at accurate, correct and controllable moisture content without waiting for ever?

4. Could functions 2. and 3. even be covered simultaneously simply by accurately controlling shop conditions? Wood drying would be a little slower than in a dedicated finishing kiln, but maybe still OK - and with the advantage of delivering a better working more like air dried material.

5. This maybe all sounds like overkill, and no doubt leaves some problems unanswered. But it's not that expensive or hard to do DIY, and maybe it's a necessary part of setting up to work to high standards. (lots of makers have certainly gone down this road)

A consequent issue on the bench is that the beech has by now more or less equilibriated to suit the naturally quite humid conditions in my shop. If i build the bench at that, and then subsequently control (drop) the humidity in the shop it seems likely to do harm to it. So maybe best to decide the environmental regime for the shop, dry the beech to suit and then make the bench.

So questions questions. The easy route is to say 'ah f**k it', but the above is what i'm hoping i can tease out with the EBAC industrial wood drying guys, but please anybody shout if i'm missing something obvious...