Garage Condensation

Bought a dessicant type de humidifier for garage as getting fed up with the dripping off the roof, the corrugated fibre type, after 2 overnight sessions of 8hours each collected just under 8 pints of water, I am impressed with this even the roof panels have resumed their light grey colour instead of black. A quick calculation resulted in approx 35-40 p extra cost on electric per day have not used the heating facility as I want the area to be unheated. Will take a while to work out most economical settings but I am well pleased

Mick 🇬🇧

Hello Mike, I've been using a de humidifier( not the same as yours) in my shed for more than 25 years and cannot understand why folk think they use a lot of electricity. I have a KWH meter and I think mine used 200 watt in 24 hours, I leave mine on continuously through out the winter, much better than every thing going rusty, just remembered mine is an Ebac and it was second hand when bought it. Originally I made a de humidifier following an article in Model Engineer 1980/90 time which worked OK, then a much smarter and more effective one came my way.John

Hi John,

The low consumption of mine is rated at 350 watts and a high of 650 watts. I am happy with the cost but am using it just overnight and will try different settings. Mine is a Toyotomi model TD 280 which is as I understand it is a British Company although equip made in Thailand I think. There is a good review on utube

Mick 🇬🇧

Hmmm, that would be about a 30% increase on my daily electricity cost,

Andrew

Ok Andrew., I'll just buy one less packet of biscuits a day that should cover it, everything costs just depends how much you want it, my electric costs about £1-50 a day

Mick 🇬🇧

Best thing about dessicant dehumidifiers is that they work down to almost freezing unlike conventional ones.

Matt

Hi Mick,

Seems like similar to the sometimes dependable Meaco dd8l and a load of other similar offerings?

I have two meaco machines - only one is running at the moment - and cost is currently about 9p a night as I only run it for 3 hours. Workshop volume will make a difference.

The important thing is to seal any draughts - as any damp air, entering unnecessarily, will partly defeat your efforts.

The construction varies, but they likely all use the same, or similar, components. If, like mine, it is made in china, the lubrication was the let down - both required dismantling and lubing with proper stuff! Maybe they have improved since mine were made! I bought mine second hand as dead units from epay and very happy with what I have.

There are two major types of dehumidifier. One uses a compressor and uses a peak of about 250W while the compressor is actually running but less than 100W in th other half of its cycle. Once the humidity is reduced it only has to run sporadically to test the air. I find these tend to corrode on the condenser after a while.
The other type uses an absorber that has to be heated to release the water so it uses far more energy but that contributes to the heating of the space. I've never used one of these as I want to have independent control of heat input.

Both in theory recover some heat from the vapour they condense so produce more heat than the energy they consume.

The time you most need a dehumidifier in the workshop is not when you walk in there and start puffing moist air onto the cold machines or when it has been cold and a warm wet spell starts binging in damp air to condense on the machines before they warm up. I like to put a block heater under my mill as this starts and of course cover the machines with cotton cloths not plastic that will sweat.

Good comments from Matt and ndiy, I will drop my hours running there are 3 settings 2-4-8 hours, I have used the 8hr initially and expect the cost to drop, who knows 2hours may be sufficient,it was only watching you tube that I learn't that I needed a dessicant type so that saved a mistake. Some time ago I started switching tv-digi boxes etc off at the sockets when we were not using them instead of leaving on stand by, that alone more than covers cost of running the dehumidifier,

Mick 🇬🇧

You eat MORE than one packet of biscuits a day?

Just noticed a terrible blunder in this sentence. I was writing something else and only partially edited it. Obviously remove the "not" at the beginning.

Hi Mick,

You have made the right decision on compressor or desiccant type. Compressor types work progressively less well at temperatures less than about 20 degrees C.

I currently run mine on a timer. They do have a humidistat for the continuous settings (where the fan runs for 5 minutes every half hour to check whether the heater is needed to kick in), but I just set mine for the clothes-drying option - as drier is better and warmth output is the more important for my sealed up, well insulated workshop. I may change the mode of operation in warmer, but damp, weather.

I bought a temperature/hygrometer from epay. Seems to give a fair indication of the conditions.

Mine will collect about 8l per day, but currently it is collecting about 2 litres each week on 2 hours each night, and a bit more when running 3 hours per night. I have only used the low power setting as the problem with one purchase turned out to be a shorting heating element - so I removed that half of it. I intend reducing air changes come the spring.

Good luck with reliability. The cheaper ones do not have a good record on that score, hence quite a few ‘duds’ on epay. A pita to dismantle and repair, but after doing it a couple of times, it does get easier. Another mode of failure is the over-heat fuse, which is cheap to source (not from the machine suppliers), easy to replace but a pita with the dismantling and rebuilding!

The average hobbyist should be able to diagnose any faults and effect a repair - the first one I bought was in pieces as the seller had given up on it. It took me about 2 hours to sort it and have it running. I then had to dismantle again as the desiccant wheel drive gearbox seized up. At that point I relubed all the fans as well. It has been no trouble since. I may need a new heater on the other one, but I may well take a chance on another ‘dud’ from epay if I cannot sort it.

I can find a model Z80. Is that the one?

Also a good idea to check where the moisture is coming from! Is it condensation? Fibre cement roofs go porous with age and let water through. This can be cured with a couple of good coats of bitumen paint on a hot summer day when the sheets are bone dry. Always use crawling boards, or a long handled brush!!. Damp floor, damp walls ? usually caused by leaking gutters or drains, and to get that amount out of the air, it must be coming from somwhere! The cycle develops when moist warmer air hits a cold surface, cools to the dew point, , and releases its water onto the surface it is in contact with. The easiest way to get rid of condensation, is ventilation. If you insulate the underside of the roof, you eliminate the cold surface, and stop the condensation, then remove the damp air with a bathroom style extractor fan on a time switch. I have a 1000 sq ft workshop, unheated, but well insulated on walls and ceiling. ventilation is via some roller shutter doors which the wind blows over the top of. It was built in the seventies, and is by no means bone dry, as some of it is built into a bank. I have zero condensation, but I did rip up both floors, and re-lay them with a DPM under them. I like those cheap chinese dehumidifiers, you can buy them when the electronics quits, junk it and fit a couple of relays!

To David S 1, no its the wife and grandkids who eat the biscuits

To ndiy thats the one - model TD-Z80

Going to try it on 4 hours for a couple of nights then try on 2hrs

Thanks for all the comments gents

Mick 🇬🇧

Two comments:

1. with thin sheet roof coverings (especially metal sheet) the surface temperature of the roof gets much lower than the air temperature due to radiant heat losses to 'upper atmosphere air temperature' on a clear night (same process as causes ground frost when there is no air frost). When trying to avoid drips and reduce condensation in the workshop it is really good to avoid this by insulating the roof . When I put photovoltaic panels on my shed roof I immediately noticed a reduction in condensation on the underside of the roof sheeting so this was due to the photovoltaics interrupting radiant heat loss and bringing the roof sheet at ambient air temperature or maybe a shade higher at night due to warmth held in the fabric of the shed during the day.

2.Condensate water from the dehumidifier is really useful around the house - our steam irons now use this and so don't scale up like they used to with tap water. Also better than chlorinated water for houseplants.

I have a well insulated shop. I heat it in winter and cool & dehumidify in the warm months. I am too damned old to put up with wide swings in temperature.

Although compressor types cease to be effective at low temperatures the risk of condensation seems to be low. I find that although my dehumidifier collects plenty of water the lack of air circulation still allows large objects in sheltered corners to get rusty. I feel a dehumidifier needs an air mover to improve its effectiveness.

Mike

I used to have problems every winter but since insulating the roof and my double up and over metal door, stopping water run-off getting under the door bottoms and using a compressor type dehumidifier, rusted tools and machines have become a thing of the past (touch wood!) I run the dehumidifier through a temperature controlled switch to avoid it running at air temperatures below 5 degrees and maintain below 70% RH on my cheap hygrometer.

Not sure which type of dehumidifier I bought when I had to dry the house out after an incoming water main leak. I was not impressed with it and gave it away then just ran a fan, things dried out over a few months and the fan now does duty in the garage if I am going to leave things unused for a few days.

Historically, dehumidifier manufactures have had a ‘standard’temperature, on which they base their sales pitch.

That standard temperature used to be as high as 30 Celsius, where compressor types (the only type made) were really most effective, so gave advantageous collection rates. They rarely stated the testing temperature, of course!

However, testing temperatures have, more recently, been reduced to 27 degrees and even more recently to 21 degrees by which?. The compressor faction do not like that and have complained to Which?. They reckon dehumidifiers are left running for long periods and that desiccant types waste power, compared to theirs.

The industry admit that compressor types lose efficiency as the temperature falls and are effectively inoperative at around 5 degrees Celsius, while the desiccant type continue to work at the same afficiency down to about 1 degree Celsius.

Dehumidifiers UK **LINK** compare the real running costs and reckon compressor types have an approx 20% running cost advantage at 21 degrees on water removed from the room. This running cost difference obviously reduces as the temperature falls and at some temperature below 20 degrees there is parity, then desiccant types are cheaper to run, per amount of water extracted.

My workshop needs a dehumidifier in the winter, almost universally, when the temperatures drop lower than 10 degrees. Clearly, for me, a desiccant type dehumidifier is king for my situation. I need the heat to warm the workshop slightly while the humidity is controlled at an adequate level. The workshop machinery must be maintained above freezing point, or condensation of moisture in the air will condense on it.

I also disregard the idiot desiccant proponents on u-toob that are not clever enough to realise that simply raising the temperature will lower the RH! That means that each situation needs due consideration. For proection from condensation at lower winter workshop temperatures, I think the desiccant type are the best - as long as the workshop is completely draught-proof. Mine costs me no more than about 80p per week and less than 70p on average in the winter months. I may use supplementary heating while I am in residence, mind - the machines may be cold, but the air temperature rises quite quickly, with a minimum of 100mm insulation on nearly all wall and ceiling surfaces.