Garage dehumidification

my double garage is 6.2x6 and all materials to insulate (50mm insulation, osb, batons, fixings etc) were just under £1k to give you some perspective (inc ceiling)
 
Your prices were extremely good, I can't even get foiled insulation at that price trade round here.

Indeed. Prices of Kingspan etc went up 15 - 30 % last month along with other building materials due to America throwing an extra million or two to buy materials so a ship that was docked in England didn't offload the stuff bound for here.
 
It’s that time of year again. Earlier in the week my tools and motorbikes were dripping with condensation so I took the plunge and bought a dehumidifier. It’s this one: https://ecor-pro.com/product/dh1200-dryfan-12-litre-desiccant-dehumidifier/

It seems to be designed for this sort of application so fingers crossed.

Part way through the install:
NFl6YuS.jpg

Can you guess when it was turned on?
LOy9rql.png

The ambient RH is sitting at around 80% outdoors. My shed which is attached to the garage is showing around 88% RH and the garage was trending very similarly to the shed at night time before the install. So the conclusion from day 1 is that it is knocking the RH down by about 10-15%. Is it enough to keep the garage condensation free? I’ll see how it goes over the coming weeks. The real test will be on the warm damp days after a very cold spell where the temperature of the garage contents is very low but warmer humid air comes in.

I’m going to experiment with various levels of external ventilation and ducting of the inlet and dry outlet to see if it makes much difference.

You may ask why I didn’t go down the route of insulating the garage. In short, too expensive, too many compromises with space, and little guarantee it would actually solve the problem without continuously heating the garage throughout winter.
 
Why does it suddenly stop reducing the RH? Does it switch off? Is the garage well sealed?

45-50% is the target to apparently stop all corrosion. Below 60% seems essential.

It looks like a neat setup.
 
Why does it suddenly stop reducing the RH? Does it switch off? Is the garage well sealed?

45-50% is the target to apparently stop all corrosion. Below 60% seems essential.

It looks like a neat setup.
Good question. The humidistat was set to target 50% so I’m not yet sure. The obvious reasons would be either the dehumidifier is operating at its maximum capability or the influx of the external air mass through leaks is levelling it out. Or both. Or maybe the contents of the garage (cardboard boxes etc.) are still drying out? Having spoken to the manufacturer before buying they suggested the unit should be more than capable of bringing the RH lower so I’m leaning towards the air leaks. I’ll plug it up and see if that has any effect.

This morning the shed contents were soaking in condensation but the garage contents seemed completely dry in comparison. The indicated humidity level seems high but, acknowledging it is early days, it seems to have done the job last night.
 
If it’s anything like my dehumidifier you’ll find that the built in humidistat isn’t as accurate as it could be. It might be switching itself off too soon. Even with a few leaks into the room I’m sure it’ll be able to bring the humidity down more, although like you say, if it’s already eliminated the condensation then it’s doing/done it’s job.
 
I've found that dehumidifiers' effects can be surprisingly localised. i.e. in my basement I left a hygrometer on top of the unit and humidity improved, but if I placed the hygrometer 10 feet away, it bounced back up within a hour of turning the unit off.

Next step was to place a fan on top of the dehumidifier to move some air around the basement. I'm guessing yours does this itself!

Point being - stick a hygrometer somewhere neutral in the room and track the "average" or general humidity. You could even find the worst spot or the spot nearest something sensitive to rust. I expect humidity will change more slowly but should represent the state of the room/contents better.
 
You just need to make sure the garage is well sealed if you want to bring it down well below the outside humidity otherwise the moist air will just be drawn in from outside.

Most garage doors are about as useful as a sieve for that sort of thing. But also you need to check the roof and soffits for spots are can leak in. You’d probably need to board and insulate the rafters to get It sealed up properly.
 
Last night and this morning have provided the perfect test conditions. The garage started off cold and a warm front of heavy rain came through significantly raising the outside relative humidity to 96%. The RH in the garage increased markedly overnight despite a slight increase in temperature but it managed to stay below 80%. The contents are condensation free which is the main objective, however I’ll be looking to seal it up better as it has to be leaking quite a lot based on the data.

Garage:
YFM1Xj4.png
You can see from the trend graph at the bottom where the dehumidifier was turned on. There is a step decrease in humidity but I’d still like it to be less volatile to weather events like we have just had.

For comparison, here is the shed:
cM0NXUd.png

Next steps:
- Get up into the roof and look for air leaks. If necessary, board it up.
- Look at roller shutter garage doors. I have a standard cheap up and over which despite lots of plugging, still has gaps everywhere.
- Ventilate the shed.
 
So far so good. The dehumidifier has consistently dropped the RH by 10-15% throughout, so even on the warm days of 99% RH after a really cold spell it has lowered the garage to the mid-80s which has been sufficient to prevent condensation. Because it is doing the job I haven’t really bothered doing much else.

The built-in humidistat is terrible so I have been manually switching it on and off using a smart plug. I might look at smart hygrometers to act as a humidistat with the smart plug but that’s quite low on the priority list.

I’m happy with the outcome. My bikes and tools are dry!
 
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