Greenhouse condensation - school me!

Deezl · Aug 3, 2016

1st greenhouse.
20' x 24' frame with plywood end walls no plastic on it yet.
Internal light dep on wires bunched up on one end of the ceiling during the day.
24"x24" light trap intake.
10" outtake can fan shoved under side of tarp and set on medium speed because of noise.
Close at 8 open at 8.

I'm getting lots of condensation. Dripping ceiling.
If I open the tarp without getting some of the condensation off then it pours water onto the plants when I put it on at night (the tarp is bunched up and doesn't dry during the day) so each morning I hit it with a broom making it rain big drops like crazy on the plants. So much water drops that I can shake the plants off like it rained.

I'm a week from harvest so it's worrying.

So geniuses, what's the physics here?
Does the water build up in the evening, the morning, when? How would 6-6 or 9-9 be different?

I'm open to practical advice but what I'm really looking for is knowledge about the physics of what's going on. Then I can use that knowledge to figure out what advice makes sense!

Deezl · Aug 3, 2016

Ps I didn't have any circulating fans. I added one last night and the dripping is by far the worst yet this morning. Coincidence or ???

Noonin NorCal · Aug 4, 2016

Dehumidifier?

_tessarecting · Aug 4, 2016

Put a wooden box stuffed with foam over the inline fan, run it on max speed

Use gravel floors

Deezl · Aug 4, 2016

Inline fan can be submerged in foam? I once had someone suggest that I wrap an inline fan up with insulation and duct tape. Never tried it it sounded dangerous.

What's the science in the gravel floor aside from thermal mass? Or is it just for thermal mass?

Thanks

Limeygreen · Aug 4, 2016

Does your plastic have anti condensate in it? You need to be running more out take fan to remove your humidity or ventilation with some heat to dry it up. As suggested a de humidifier would help too. If you solve air flow problem then you solve air humidity problem you would be better off. I personally would get more airflow then set up a heat on the opposite end of the out take fan and set it on a humidity switch but limit the max temp to 50 degrees c. setting rh switch for the heater to 40-45 %. For simplicity, if your outside temperatures are not too low, I would just set it to run continuously.

Chimera · Aug 4, 2016

If you are only a week from harvest, you do not need to keep pulling tarp...

Deezl · Aug 4, 2016

Chimera said:
If you are only a week from harvest, you do not need to keep pulling tarp...

Well that's interesting I've never heard that please elaborate!

Ps thanks for the input y'all.

GoeRilla · Aug 5, 2016

My greenhouse door is open 24/7 in summer time, still gets wet but less than with the door closed.

Rilla.

corky1968 · Aug 5, 2016

Deezl said:
Well that's interesting I've never heard that please elaborate!

Ps thanks for the input y'all.

That's because once a plant goes past a certain point it will continue flowering.
If all you have is a week left your plants won't go back into vegetative mode fast
enough and will finish up like they should.

If there was a door at both ends of a green house and they were left open the humidity would drop.

Chimera · Aug 5, 2016

corky1968 said:
That's because once a plant goes past a certain point it will continue flowering.
If all you have is a week left your plants won't go back into vegetative mode fast enough and will finish up like they should.

Well that's not really true that plants past a certain point won't go back- of it were, re-vegging would not be possible.

Put another way, it takes plants in flower about 2 weeks or so (cultivar depending) to begin to reveg. That means you have about 2 weeks in which the plants will continue to flower without starting to change flower morphology.

~~

I also see that you are keeping your extractor fan on medium because noise is an issue? That's a major mistake; limiting airflow is contributing to your humidity issue- you need to prioritize the humidity issue over the noise issue if you want to avoid mold.

corky1968 · Aug 5, 2016

Let me explain better then. I think.

Since his plants are in late flowering mode his plants won't revegetate under that current photoperiod in time and the harvest will happen.

Deezl · Aug 5, 2016

Thanks. Well that makes me feel better about the door plastic coming loose last night and leaking light!

I installed another 24x24 intake light trap and shoved an additional (8") inline fan under the tarp and it helped a lot.

So as far as the science of dew...

I get that the tarp gets cold in the evening and when the wet air hits the cold surface the inverse proportion of heat/humidity (colder=wetter) causes the air to reach 100% humidity and form water.
So does that mean that all of the dew on the tarp ceiling happens at night?
If someone were to cover at 4am and uncover at 8 would there be dew on the tarp ceiling?

I don't have anything in the green house to intentionally hold heat (like water containers) but I do have a cement slab under half of it.

How does thermal mass like cement or water effect things? Does it hold heat to keep the humidity down and/or make it rise more slowly allowing for air exchange?
Or if I covered at 4am till 8am would the thermal mass still be warm enough to cause a temp difference that causes dew?
Thanks y'all!
Like GI Joe says, knowing is half the battle!

corky1968 · Aug 5, 2016

Is your greenhouse roof flat?

If the tarp was more at an higher angle the water would run off of it easier.

Elmer Bud · Aug 6, 2016

G`day Deezl

You could try a regime of covering before sun down and uncovering after sun down .
eg Pull the tarp at 6 PM , uncover at 10 pm .

Only a 4 hour commitment . Rather than twice at either end of a day .

Once its dark you don`t need the tarp . After sun up the plants get early morning sun to kick start their metabolism .

Thanks for sharin

EB .

Noonin NorCal · Aug 6, 2016

A dehumidifier will not only get humidity down but will also heat it up at the same time. plants respirate/respiration in the dark?. they put of moisture. specially the day that you water. Maybe all the dew is from your plants respirating?

Deezl · Aug 6, 2016

Yes that is what happens. Without enough ventilation the humidity gets high. When the humid air hits the cold plastic it cools. When air cools it gets more humid, so the humid air that hits the plastic reaches 100% humidity and turns to water.

I think that's how it works anyway

DJM · Aug 6, 2016

get anti condensation plastic and run two layers of plastic with blower inside of the gh, blowing into dead space between plastic..this helps insulate temps and prevents condensation almost entirely

Deezl · Aug 8, 2016

I'm still not understanding the details of the physics.
For example, I now have two 24"x24" passive intakes and a 10" and 8" inline outtakes.
The first two days with the increased circulation the condensation was almost gone and they were foggy days. Then the third day it was foggy and lots of condensation. Today is clear and sunny and the condensation was ridiculous.
I have to knock the water off the roof (onto the plants) in the morning or else it'll stay in the blackout tarp and pour into the plants when I close it at night. I figure morning water is better.

Any idea what caused the variations?

It's pretty bad it pours big drops I can shake the plants off afterwards like it rains.
Big wet buds but they seem to dry over the day.
Thanks for the practical solutions, I'm pretty aware of my options, I'm really trying to understand the science behind them!

Tynehead Tom · Aug 8, 2016

DJM said:
get anti condensation plastic and run two layers of plastic with blower inside of the gh, blowing into dead space between plastic..this helps insulate temps and prevents condensation almost entirely

I've been thinking about this idea.

my greenhouse (plants have filled it now and hitting the 5 1/2 foot mark

)

I tried to do light dep inside with 1/2 the greenhouse but quickly realized how mickey mouse my plan was and abandoned the idea.
I open the side ventilation flaps in mornings and close at sundown. each end of the top of the greenhouse has a triangle opening that stays open.
I get a lot of condensation overnight and it takes a couple hours in morning for the sun to evaporate. hasn't been an issue so far. it does rain a little on the plants but they don't seem to mind.

now, what happens when it starts to get cold here at night in September? easily gonna be close to zero at night by mid sept and below that into October. I'm rigging up a propane RV heater built into a box and will be exhausted outside the greenhouse. gonna put a small fan in the top of the greenhouse blowing air slowly out both top vents. Hopefully this does away with internal condensation as the evenings , then days, start to get colder. I gotta have a plan in place by months end.

anyone care to critique my plan, I'm no pro at this LOL

Greenhouse condensation - school me!

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