condensation

Hello all, just wondering how you guys deal with poly tunnel condensation. Thank-you for your time.

 

At this time of year it's nigh on impossible to prevent condensation as even if the soil in the tunnel is dry; at night the warm and moist air in the tunnel condenses when the temperature falls and chills the polythene. If we have a sunny day I open both doors to help dry the skin of the tunnel and this does help a bit.

 

I do the same Dave W, but I was wondering if venting the top of the poly tunnel would be worthwhile. My idea is to cut into the polythene and with a clear silicone glue hit&miss vents. I'm sure this is possible, but will it work? The polythene on my tunnel will need replacing in a couple of seasons as it is getting tired. So even if this venting does not work, it isn't as though I will have ruined brand new polythene cover. Further thoughts? Thanks for your time.

 

i,m pleased someone else is having same problem. i,ve just put my new cover on my first polytunnel and thought it was my fault. checked cover was right way up.o,k. any help will do.

 

There's no way I'd cut the top of my tunnel as there's too great a risk of developing tears. Also vents in the roof, unless they can be closed properly, will vent warm air and at this time of year I'm trying to build up the soil temperature ready for sowing/planting. If I find condensation becomes too great I have in the past used a floor mop to mop it off the cover. The condensation won't do any real damage unless the overall humidity rises to the level that starts fungal growths on the soil.

 

I just knock the door frame a couple of times with the palm of my hand to shake it off.

I think the only way to get rid of it is to dry your soil out to dust, then you wont get any condensation at all.

If you cut vents in, you'll risk tears as Dave says, remember the polythene is under tension so more chance of tear spreading quickly!

Steve...

 

Won't be any help if you don't have electricity to the tunnel, but I have used an electric fan in my unheated conservatory this winter. The conservatory is STUFFED with over-wintering plants, and in previous winters the damp has been a problem and the cause of moulds and other problems. This year has been miserably wet, and cold enough to cause plenty of condensation, but touch-wood there doesn't seem to be any sign of consequential problems

I run the fan on a 15-minute segment timer set to run 30 mins off, 15 on, during the day and 15-15 at night (as I have economy-7 which is cheaper at night)

 

I don't think even bone-dry soil would help?? The temperature difference across the polythene, outside-to-inside, will cause condensation by the, relatively, cool inside surface coming into contact with the warmer air in the tunnel. Air that you let in on warm days will have enough moisture to then condense at the reduced dew-point that the lower temperatures will, regrettably :(, cause.

 

Thanks for your replies, I agree with Kristen, the problem of condensation is something that comes with poly tunnel territory regardless of soil condition. I should have mentioned that my concern is for later in the season and not at this very early stage. Over-wintering plants can suffer from moulds and in our presently bizarre climate of up and down temps, moulds could become even more of a problem. Last season was awful and my poly tunnel constantly gave me condensation regardless of what I tried to prevent it and that is why I wondered if venting the top of the tunnel would be helpful rather than hindering. As for causing tears in a poly tunnel when slicing the polythene...that does not worry me, due to the fact the polythene is becoming tired. I'm sure it can be controlled with a strong waterproof adhesive tape and a clear silicone seal around said vents I am considering. Will inform you of my findings on this, can't find out if I don't at least try.

 

My worry, when I read of your idea to add roof-vents, was of the wind getting "under" the Polythene and doing damage.

During Summer, and late season, I vent my glasshouses at night, as well as day. Even if the Vents are only open a crack. Perhaps you could similarly have the doors at each end open enough to create a gentle air flow?

I like the sort of tunnel which has a lift-up / roll-up side which then reveals a net "side" so that the tunnel can be fully vented, rather than just using the doors at each end.

Arranging the door-ends to face the prevailing wind may help, but I think that is then forced ventilation, which is a lot less kind to plants than convection and the like (i.e. forced airflow causes more transpiration)

 

If you go ahead and cut holes in your plastic sheet how then will you prevent rain from entering the tunnel? I'm just interested in what you had in mind.

 

A layer of condensation is not really a problem and will happen almost at any time of year, it can become a problem when tunnel beds are full of plants that are kept watered, more condensation will appear (due to plant transpiration) and dripping will occur.

What I meant above is the only way to reduce condensation from a problem to no problem is to probably let your soil dry out to avoid transpiration adding to the condenstaion..that is all. It's then and only then that condensation is a problem.

Manufacturers make tunnel covers that are supposedly non-drip to combat condensation, but none that I have seen make or sell venting for the top of the tunnels, if it was of value you can bet the opposite would be true.

Steve...

 

Just had a thought (a rare thing!). The water that drips from condensate is virtually distilled water. No chlorine or traces of lime and just about as clean as it comes, assuming of course that the polythene is reasonably clear of soluble bodies.

 

Take a look at northern polytunnels cantilevered roof vents for some diy vent inspiration

The best way to deal with condensation is to convince the humid air to condense somewhere it cant drip and cause problems. Better still, somewhere it`ll do a bit of good.
Drying out the soil is the last thing your plants would want, so why not give the condensate back to them along with the energy that created it to begin with?
(techy bit ..look away now )
It takes 234w of energy to convert a pound of water into vapour, the same energy has to be given up to change it back into liquid water (condensation). Every pound of condensation sitting on or dripping from the poly represents energy lost to the outside world.

The condensation issue ceases to be a major problem and can be turned into a plus for the plants. Its not the complete answer and you`ll still need to vent at times, to control excessive humidity >90%, extreme temps (unlikely judging by last summer) or simply to bring in fresh air to maintain reasonable co2 levels.