humidity spikes in grow tent

_EQ

Well-Known Member
Hey y’all, I’m running into very intermittent humidity spikes in my grow tent. About every 2-3 minutes my RH will spike about 15-20%. I’m running a portable ac with the exhaust running out of the yent into the room the tent is in. I’ve noticed that along with these spikes the ac exhaust goes from blowing hot air to cool air. Could this be playing a role in the problem?
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Jimski

Well-Known Member
Question
When this happens do you hear any change in compressor noise?
A few things come to mind but they are very model specific depending on what type. Some ac units clear the coils of moisture by reversing flow. Some open the suction valve to superheat low side to stop icing up air coils. Also cold exhaust means warm condenser which can be a sign that the unit is cycling off and on by design or low on refrigerant.
I have never even seen a portable ac. Does it have a condensate tank like a dehumidifier?
 
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Rocket Soul

Well-Known Member
Cold air holds less water than hot. As your cooling your tent temps drop but plants are still transpiring: the water from the plants saturates the cold air much easier: rh spike. Cool the lung room and balance the tent with extraction. If its a closed space and all air recirculating around for ever you need a long term plan for humidity removal if the ac wont do enough of it. Every time you water that water goes to the air, if no renewal of dehueying it just stays in the space.
 

JustBlazin

Well-Known Member
What temps are you hitting? Just wondering how high it's getting for you to be using ac unit. If you run led your temp can get into high 80s with no issue. But when your light goes out the humidity will spike, so you would probably need a dehumidifier for lights out.
That's how I run mine. As soon as lights go out humidity spikes 10-20% so I run a dehumidifier 20-30 minutes before lights go out until after they come back on.
 

_EQ

Well-Known Member
Question
When this happens do you hear any change in compressor noise?
A few things come to mind but they are very model specific depending on what type. Some ac units clear the coils of moisture by reversing flow. Some open the suction valve to superheat low side to stop icing up air coils. Also cold exhaust means warm condenser which can be a sign that the unit is cycling off and on by design or low on refrigerant.
I have never even seen a portable ac. Does it have a condensate tank like a dehumidifier?
Yeah so I can hear the compressor kick in and than it goes back to exhausting warm air. And it’s one of the basement or floor units that you run a exhaust vent out to either the outside or some other room.
 

_EQ

Well-Known Member
What temps are you hitting? Just wondering how high it's getting for you to be using ac unit. If you run led your temp can get into high 80s with no issue. But when your light goes out the humidity will spike, so you would probably need a dehumidifier for lights out.
That's how I run mine. As soon as lights go out humidity spikes 10-20% so I run a dehumidifier 20-30 minutes before lights go out until after they come back on.
They’ll hit anywhere from 78-81F depending on the temp of the day. We’re in the fall here so it’s getting cooler out but in the basement they tend to stick around 75-80 until the nights start to get under 40 consistently. And the spikes occur both lights on and off.
 

_EQ

Well-Known Member
Can you instead condition the air of the room the tent is in, rather than having the AC unit inside the tent itself?

If any piece of climate control equipment is cycling every few minutes, it might be oversized for the space, working on too small a volume of air.
So that was my first thought was to try and cool my basement temp and use the intake and exhaust fans to help cool the tent but with the type of unit I have I can’t run the exhaust out anywhere because there’s no place for me to run it out to. So I have it in the tent exhausting out into the basement
 

_EQ

Well-Known Member
Cold air holds less water than hot. As your cooling your tent temps drop but plants are still transpiring: the water from the plants saturates the cold air much easier: rh spike. Cool the lung room and balance the tent with extraction. If its a closed space and all air recirculating around for ever you need a long term plan for humidity removal if the ac wont do enough of it. Every time you water that water goes to the air, if no renewal of dehueying it just stays in the space.
So as of now I have a 6” intake fan and 4” exhaust with a few oscillating fans, both intake and exhaust run constantly on full power. On top of those I have the ac and a dehumidifier in the tent. And even when I run the dehumidifier the spikes lifespan is like 2-3 minutes than the humidity goes back down to around my target percentage. It doesn’t last long enough for the dehumidifier to even pick up on the spike. I’ve tried using a humidifier to get the humidity up at a constant level and supplement the dehumidifier to bring it down to target humidity consistently but even doing that it’ll spike at a higher percentage for a minute or two, then sink back to target.
 

weedstoner420

Well-Known Member
So that was my first thought was to try and cool my basement temp and use the intake and exhaust fans to help cool the tent but with the type of unit I have I can’t run the exhaust out anywhere because there’s no place for me to run it out to. So I have it in the tent exhausting out into the basement
I think you need to focus on getting the overall basement climate right, rather than treating the tent as an isolated space. I would start by asking what the typical temp and RH is in your basement (or whatever room the tent is in)?

For a tent grow in a room, the best approach is to get the temp and humidity of the room to a good spot, preferably a bit cooler and lower RH than you want in the tent, then increase air exchange to get the tent's temp and RH closer to that of the room.

I wouldn't put any climate control devices (AC or dehumidifier) inside the tent itself. For one, they take up valuable real estate, and for two, they're usually meant to operate on a larger volume of air than a grow tent.
 
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_EQ

Well-Known Member
I think you need to focus on getting the overall basement climate right, rather than treating the tent as an isolated space. I would start by asking what the typical temp and RH is in your basement (or whatever room the tent is in)?

For a tent grow in a room, the best approach is to get the temp and humidity of the room to a good spot, preferably a bit cooler and lower RH than you want in the tent, then increase air exchange to get the tent's temp and RH closer to that of the room.

I wouldn't put any climate control devices (AC or dehumidifier) inside the tent itself. For one, they take up valuable real estate, and for two, they're usually meant to operate on a larger volume of air than a grow tent.
The temps and humidity vary depending on season but late spring into summer it gets hot and humid down here 80F and 70RH, the colder seasons tend to be dryer so I can usually expect from late September into early November the temps and humidity to be around 70 and 30-40RH, and the winter it’ll get downwards of 55F and if we have snow or sleet/rain the RH will hit 60 but without that it stays around 30-40 also. My biggest problem is finding a space to exhaust the ac hot air. It’s not a window unit. It’s one of those big floor units that you need to run an exhaust pipe out to a separate room or outside, and unfortunately I don’t have the availability of doing so. My basement only has 3 small windows that only open at a 45 degree angle so I can’t fit the exhaust vent properly.
 

weedstoner420

Well-Known Member
The temps and humidity vary depending on season but late spring into summer it gets hot and humid down here 80F and 70RH, the colder seasons tend to be dryer so I can usually expect from late September into early November the temps and humidity to be around 70 and 30-40RH, and the winter it’ll get downwards of 55F and if we have snow or sleet/rain the RH will hit 60 but without that it stays around 30-40 also. My biggest problem is finding a space to exhaust the ac hot air. It’s not a window unit. It’s one of those big floor units that you need to run an exhaust pipe out to a separate room or outside, and unfortunately I don’t have the availability of doing so. My basement only has 3 small windows that only open at a 45 degree angle so I can’t fit the exhaust vent properly.
You can def use the dehumidifier to bring the RH of the room down (it'll work better and be easier to drain when it's outside the tent anyway) but not sure what the best way is to get the temps down in that case.

That sounds very similar to my unfinished basement. I have a dehumidifier but no central AC, and I've pretty much given up on flowering plants (or at least being in late flower) in the summer months. I've been trying to run two flower cycles from late summer/early fall through spring, then just veg and clone in the heat of summer
 
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_EQ

Well-Known Member
You can def use the dehumidifier to bring the RH of the room down (it'll work better and be easier to drain when it's outside the tent anyway) but not sure what the best way is to get the temps down in that case.

That sounds very similar to my unfinished basement. I have a dehumidifier but no central AC, and I've pretty much given up on flowering plants (or at least being in late flower) in the summer months. I've been trying to run two flower cycles from late summer/early fall through spring, then just veg and clone in the heat of summer
Yeah it’s an unfinished basement, the odd thing is that the ac worked fine in the heat of the summer I think the ambient humidity in the basement is so high that the spike the ac gives off is similar in percentage so the dehumidifier can actually take out the humidity. Also another variable is that I have young clones in it now and they don’t give off and perspire as much as the adult flowering plants I had during the summer. I first ran into it 2 weeks ago when I went to dry my outdoor harvest and I thought hmm that’s strange I didn’t encounter this issue during the summer. I was aiming to use it to help my dry environment get near 60-60. As well as help control the climate better in the tent year round. But I guess if I can’t figure this out it’s back to the drawing board…
 

Jimski

Well-Known Member
Yeah so I can hear the compressor kick in and than it goes back to exhausting warm air. And it’s one of the basement or floor units that you run a exhaust vent out to either the outside or some other room.
Ok so we know what is happening just not why. If the ac has temp setting and the calibration is off it may think work is done and shuts off. If it is a off low med hi setting prolly a cycling clutch tube type ac system and this is what ya got.
 

weedstoner420

Well-Known Member
Yeah it’s an unfinished basement, the odd thing is that the ac worked fine in the heat of the summer I think the ambient humidity in the basement is so high that the spike the ac gives off is similar in percentage so the dehumidifier can actually take out the humidity. Also another variable is that I have young clones in it now and they don’t give off and perspire as much as the adult flowering plants I had during the summer. I first ran into it 2 weeks ago when I went to dry my outdoor harvest and I thought hmm that’s strange I didn’t encounter this issue during the summer. I was aiming to use it to help my dry environment get near 60-60. As well as help control the climate better in the tent year round. But I guess if I can’t figure this out it’s back to the drawing board…
Huh...it might help to at least get the dehumidifier out of the tent and into the room. AC units also remove water from the air, and the dehumidifier exhausts hot air which you might want to spread out across the whole basement rather than having it concentrated inside the tent... Good luck!
 
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