Carcoon and relative humidity conundrum and advice wanted.

[Markvh]

Hi all, Hopefully you experts out there can help me with my latest conundrum.
I have a single integral garage that is constructed under the house so that 2 walls are underground and 2 walls are exposed to the outside. The construction is insulated cavity walls with an insulated sectional overhead door. There are no windows and the garage is unheated (there is a radiator but wife won’t let me turn it on). The lowest temperature I have ever seen in the garage is 11°C. Generally the RH in the garage is about 70-85%

For over winter, I have put the Stag in there and connected up a Maeco Zambezi desiccant dehumidifier plumbed to drain outside. This maintains the air RH at about 50%. Trouble is, it is looking like it is going to cost at least £25 a month to run.
I have now put the Stag in a bubble Carcoon that the previous owner gave me and put the dehumidifier inside the carcoon to maintain a RH of 50% which is OK but the garage is still at about 55-60%.
I understand that the bubble will be expelling dehumidified air out through the zips into the garage which will then get pulled back in to the bubble in due course. So in effect the whole garage is getting dehumidified all the time (and pulling untreated air in from outside as well).
I also understand that a carcoon on its own works on the principle of air movement therefore drying any moisture off the car surfaces. But at the end of the day if the garage wasn’t dehumidified it will be pulling air in at 75-85% RH.
Will air movement at say 70 – 85% RH in a carcoon be sufficient to prevent any deterioration of the Stag or will using a dehumidifier be better?
Or doesn’t the RH% matter as long as the vehicle temperature is kept a few degrees above dew point as per painting procedures?
So which is the best solution:-

1. Keep bubble Carcoon with fan only inflating the bubble and keeping air movement albeit at 70-85% RH?
2. Keep bubble Carcoon with fan inflating the bubble and keeping air movement AND putting the dehumidifier in the bubble with drain to outside. So get air movement and maintains RH at 50% (expensive as dehumidifies the air in the garage as well)
3. Buy a Carcoon Veloce framed car storage. Run the intake fans keeping air movement albeit at 70-85% RH?
4. Buy a Carcoon Veloce framed car storage. But don’t run the intake fans, put the dehumidifier inside with drain to outside. This may work out less expensive to run because not having to dehumidify fresh sucked in air all the time but may be less air movement inside the storage due to fans not running.

In short, which is more important to prevent car deterioration over winter. Air movement from the intake fans or maintaining the RH% at about 50%?
I have trawled the internet and on here but can’t really find anything definitive.

I have just read on the Carcoon Veloce web site “Air circulation is provided by Carcoon's patented Active Airflow Concept that comprises of two air treatment units which operate continuously to provide super-atmospheric, circulating airflow for 24-hours a day, 7-days a week. Importantly, the circulating air is taken from inside the storage unit itself, which effectively isolates the flow of air from the outside environment”.
If this is correct then it will probably be the solution in conjunction with a dehumidifier circulating the same air (except the times when the Carcoon is opened up to access the car). I shall check with Carcoon.
Thanks for your patience in reading, I might have asked the same question twice here! I look forward to reading members views.
Confused, Mark

[Seaking]

Mark drive it enjoy it clean it dry it . Put away in a ventilated garage.

Cheers Glenn

[Motorsport Micky]

Easy one to answer.
Unless you have other equipment you wish to keep dry the Carcoon will sort out your condensation problem around the car WITHOUT a dehumidifier. I can put my Carcoon up inside my outside ventilated garage (no insulation, so effectively RH as per outside) and then put my car inside with it wet and within 24 hours the car is dry. It goes in next week and will come out end of March and it's discs will still be bright and shiny and the upholstery without any growths or nastiness. It's action works by the control of the plunging temperatures which cause the condensation to format on cold surfaces out of the warmer air, it does this by two 10" computer sized fans on one end of the Carcoon taking milliamps to run sucking in ambient air through Carbon filters and blowing it out of a control aperture (it has a zip) when it is drying mode. After the car has dried the zip is closed and the car then goes into sealed storage mode and maintains it's status quo. The cost of the Carcoon is very reasonable, I tried working it out but got bored and I'm confident the annual cost is about £30 per annum.
A desiccant dehumidifier of about the correct size for a double garage will have around a 700 watt hr requirement and the better ones have a timer inbuilt as well as a RH setting so it can turn itself off when it gets to RH required or time. This time of year is the worst for temperature changes, and in my sealed 10' x 12' workshop at the end of the garage ( it is single brick non insulated,) it has a 75mm Celotex insulated ceiling with a cold roof 3" above) I had the desiccant dehumidifier on for 8 hours from 8pm bringing it down to 50 RH which turned itself off on timer at 4am, the dehumidifier is piped in (pipe outside through the wall).. I've not had the dehumidifier on today and the RH has slowly increased to 60 but I reckon it will last until morning before making 65 now I'm not in and out like I've been all day. After March the temp fluctuation is much less and other than an odd day will remain within the range which will prevent condensation.
My dehumidifier is by Prem i Air from Maplins now gone through and it works fine.
Just found the model on e bay
https://www.ebay.co.uk/itm/Prem-i-Ai...sAAOSwdINcn3q3

Micky

[dasadrew]

I've got an Air Chamber 'carcoon' with a small circulation fan. It sits in a lock up made of metal, so you can imagine the temperature differences that it goes through. I've had the old Escort stored in it both in summer and winter, and the Aston sometimes also. At no time have I noticed any stale air smell, condensation, or anything else and, as regards the Escort, it has even reduced some of the "old carpet" smell over the years. Apart from that, it's kept out mice and other rodents which, in the past, have nested in the chassis rails and eaten rubber and upholstery.

Drew

[mjheathcote]

50%RH is at 20 degree C
At 11 degree C the max recommended RH rises to 85% for storage.
You are wasting energy trying to get down to 50%RH at 11 degree C
See attached.
This is from when I had a Permabag for the Stag storage in a concrete prefab.
Therefore, you don't need to do anything and a carcoon or Permabag is not necessary.

[Rod1883]

As others have said, I don't think you need do very much, or anything at all.
The main thing I would suggest is to ensure ventilation and air movement. With no windows, I imagine the only fresh air access is via the gap around the up and over door - therefore a small fan to keep the air moving might be an idea. I might also risk the wrath of your better half and crack the radiator open the smallest amount possible...

[Ritchie6]

Mark drive it enjoy it clean it dry it . Put away in a ventilated garage.

Cheers Glenn

My thoughts exactly. My garage is adjacent to the house but not actually connected to it. On nice crisp sunny days I always open the up and over door to ventilate the garage. Also several times during the winter I take off the car cover and bring it out onto the drive and then run it up to temperature for half an hour or so. I haven't had any damp or condensation problems by doing this.

Richard

[barkerwilliams]

Carcoons do not de-humidify the air, what they do is circulate the air and moving air evaporates off any drops. I have never seen any condensation on my car in the carcoon and there are no water marks on the panels or glass. A dehumidifier in a garage will be trying to dry the great outdoors.

Do not put a damp car into a carcoon and seal it in without turning the fans on, it is the moving, circulating then venting of the air that keeps the car in good condition. The electricity to drive the fans is minimal when compared to heating or de-humidifying.

Alan

[Motorsport Micky]

It's what you can't see that causes the problems.

It's 11 deg C here today and 97% RH in my single brick corrugated roof non insulated garage., if your garage is like mine kneel down and look on the UNDERNEATH of the car floor, mine has hundreds of beads of condensation on it. I was putting into the Carcoon next week but I will put it in tomorrow now after washing it, the fans of the Carcoon will dry it and prevent further condensation.

Micky

Edit: You've confused me now, I've looked but can't see anywhere where anybody had said the Carcoon dehumidifies the air ? Markvh mentioned he's put an air conditioner inside his that's all.

[mjheathcote]

The posters garage is very similar to mine, which is built under the house, with an insulated garage door. Mine never gets cold and is sealed (almost, no draughty up and over doors) , like a room in the house. Never suffers from condensation, never falls out the chart I posted for storage temp/humidity. Quite simply don't need a Permabag or Carcoon.
I don't think the poster needs to do anything and is trying to achieve 50%RH when it just isn't necessary at lower temperatures.

[Markvh]

The posters garage is very similar to mine, which is built under the house, with an insulated garage door. Mine never gets cold and is sealed (almost, no draughty up and over doors) , like a room in the house. Never suffers from condensation, never falls out the chart I posted for storage temp/humidity. Quite simply don't need a Permabag or Carcoon.
I don't think the poster needs to do anything and is trying to achieve 50%RH when it just isn't necessary at lower temperatures.

Yes, that is pretty much my garage situation exactly, also the door is an overhead insulated sectional door with rubber seals around the perimeter so no air movement. The only air movement takes palce in the carcoon bubble with the single fan.
I still can't get my head around the RH% thing. Everywhere I read, it says to keep RH% below 60% (or lower) to slow steel corrosion right down. Ive also read that the rate of steel corrosion increases massively where air with high relative humidity gets into crevices (seams etc).
We hear all the time that Classic cars from the states near desert regions stay in really good condition because of the very low humidity levels, not because they have a draught blowing over the body.
I don't understand the RH% chart above. Isn't a RH% above 60% bad for steel corrosion whatever the temperature? I also think that dew point might have something to do with it. Looking at numbers, it appears that with a RH% of less than 60% the dew point of the ambient steel will be about 7degrees lower than the ambient air temperature so that condensation will not take place. The lower the RH% and the higher the ambient air temperature = a bigger difference between ambient temperature and the dew point temperature.
I don't have a condensation problem in either of my garages. I have never seen any damp on any of the metal surfaces.
I can see that a Carcoon will be a great help in preserving the overall condition of the car and that too low a RH% can be bad for leather, wood, rubber and other materials.

Thanks very much for your views and comments, please keep them coming because although I still don't fully understand all this I find it very interesting.
I hope there isn't a negative confrontational tone to this post, I don't mean there to be. I'm not very diplomatic!
Incidently I've just been out to the garage and noted some readings.
Garage and bubble air temp = 16 degrees C (temperature partly due to the warmer air emitted by a desiccant dehumidfier)
Garage RH% = 60%
Bubble RH% = 55% (50% reading on Dessicant dehumidifier?)
Outside air temperature = 7 to 8 degrees C
Outside RH% = 93%.
Best regards, Mark.

[Goldstar]

Dew point is the important consideration - as I understand it (did my meteorology exams 30 years ago) keep the temp above the dew point and condensation will not occur on an otherwise dry car assuming the surface is warmer than the dew point. If I put my car away wet I leave the garage door cracked open to encourage airflow to dry it. There will always be humidity in our air but it will stay in the air if the temp > dew point and your car is at the ambient temperature. I’d still have a cartoon though if it helped me sleep better

[Kithmo]

Wouldn't it be easier and cheaper to just put the radiator on a low setting and heat the garage ?

[dasadrew]

Wouldn't it be easier and cheaper to just put the radiator on a low setting and heat the garage ?

..... but don't tell Greta Thunberg!

[Motorsport Micky]

This is a handy calculator for Dew point, saves us remembering how to use formulas.

https://www.omnicalculator.com/physics/dew-point

Using Marks figures above with an garage temp of 16 deg and a RH of 60% the calculator gives a dew point of 8.2 degree so if Mark thinks his garage will get down to that or the humidity varies that's the area he may become concerned at.
Try entering 11 deg and 93% RH and you'll see the garage temp only has to drop by 1 deg and you are into dew and condensation, that's why at 11 deg and 97% RH my garage was dripping, ventilated or not !
At this time of year with swinging temp variations possible and high wet levels outside (we've had rain for every day over 3 weeks, even if not constant) owners who think their circumstance make them immune still need to check their garages carefully.

Micky