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Highland Grow Tent AC + Humidity Issues

Hi All, I have recently set up a highland tent. I have a window mount AC cut into the side of the tent and a bucket humidifier with 8 single disc pond foggers circulating back and forth from the tent similar to Kyles basement setup.

The issue I am having is that whenever the AC unit kicks on it rapidly reduces the humidity in the tent. I can have it sitting at 95% with the humidifier working away then when the ac unit comes on it will drop to 70 within minutes further down the longer the AC unit needs to run to get to temp.

I have tried making the output from the AC untit cross paths with the output of the bucket humidifier to mix the air however it has made no difference.
I have temps set at 77 day 53 night and 95% humidity. I can acheive 53deg within minutes however by then the humidity has dropped rapidly to 70ish then as soon as the AC unit turns of it will quickly return to 95% with the AC cycling on again approx every 10 mins for a few mins will this constant rise and fall of humidity be damaging to the HL neps. I am aiming for hamata, eddy, vilosa etc so I need to get this sorted prior to getting them :)

thanks in advance if anyone can help me out.

Cheers, Dave
1st off Congratulations on your 1st post in 10 years :D
I am not the expert for those 3 popular neps yet have experience with HL & LL terrariums & can offer a few words. From your post I would assume that the cooled a/c air both condensates some moisture in the air & adds circulation. Do you have another source of circulation in the tent besides what you may be using from your buckets output? Good circulation would help stabilize the humidity. You say that the humidity rapidly rises back to 95% in under the 10 minute increments of your a/c cycle so either you have fast humidity output from your bucket or you may just be getting false overall humidity readings if your guage is getting direct cold air current every 10 mins. Humid air rises & cold air falls so another possibility that I can only take a guess at without pics is that maybe your a/c output is too low in the tent & your buckets outlet is too high making for a poor mix.
Those are just some thoughts that came to mind & I'm sure someone with better experience with those 3 plants or tent setups will drop some better advice.
Best of luck
Hi, thanks for your reply. I am hoping it is only false readings due to the cold air. Im going to go get a humidistat tomorrow to confirm if the sensor is reading correctly.
I forgot to mention that it is the zoo med hygrotherm that i am using.

The ac unit i have is mounted at the top of the tent and the bucket fogger output is also towards the top of the tent. I have also tried pointing both outputs in various directions to alter circulating altho it makes no difference to the sensor reading nor does moving the sensor.
I should also mention that the ac unit blows quite strong and there is a food strong breeze right round the tent from it alone. I will have to put some pics up tomorrow. :)
This sounds really cool, I would love to see pictures of this!
Anyways, If im reading this right, 70% humidity is perfect.
Highland nepenthes thrive in that area, but nothing below
I ran into this issue with my 8 x 8ft grow tent, unfortunately, there isnt a fix, because the AC compressor turns on, its going to blow air into the grow tent, thus blowing the air inside the tent out. I had this exact same problem, however, one the ac kicks off the humidifier should kick up the humidity again rather quickly. I grew plants this way for years with no problems. :)
Thanks for the replys guys, it wasnt so much the level it was dropping too that I was worried about, it was the large regular fluctuation that i was worried about, as in every 10 - 15 mins going from 95% down to 70% then back up again. I was worried that this drop of humidity repeating overnight would stress the plants So I went and got one of those weather stations and it tells a different story then the hygrotherm, weather station reports the humidity dropping much slower then the hygrotherm and not as far of a drop either. Same story once the ac turns off it rises back up much slower and not as far, hygrotherm will go straight back up to 94% while the weather station is still climbing the 80's. The Weather station only records a drop do around 79% as well whenever the ac comes on so better then i thought. I played around with it a bit more last night and get it running prety well.
Another problem with the Hygrotherm was that it takes 2 full minutes once the humidity levels drop before it decides to turn on your humidity devices, So the AC would kick in and start dropping the humidity and the foggers wouldnt turn on for another 2 mins and by then the ac had chewed a ton of humidity from the tent. So after a bit of testing I have ended up with 3 foggers hooked up to the humidity controller, 4 foggers hooked up to the AC controller to come on at same time as AC and 1 fogger to run 24/7 lol. This seems to be running prety well.
I have mounted the AC unit directly in the side of the tent too so this allows it to circulate the air in the tent rather then outside air. temps in my area can climb over 100 in summer so I cant be pulling in outside air, it wont get cold enough.

Ill have a go at uploading some pics I have taken along the way with the build.


The tent has a floor tray the size of the tent (which i found out is not waterproof the hard way) so I raised it with blocks under it and used some marine ply, cut a hole and made a drain which is connected to a hose to go out of the tent so now I can water in there and it will just drain itself, also keeps 1/4 inch of water as a pool so I chucked a bunch of expanded clay balls in to raise the pots off the water and adds as an extra source of humidity.

Using a bucket with foggers inside with a fan in the piping circulating air from the tent into the bucket then back to the tent again.

AC unit is a window mount which i put in the side of the shed then cut a hole in the side of the tent and put the tent in place so that it fits right in the side of the tent :)
by circulating the high humidity air through the AC unit i ran into another issue where once the ac turns of it may freeze up. So I had a friend re wire the AC unit. He took out the thermostat so It can go below its min settings and also ran 2 seperate power cords to the unit. 1 for the fan and another for the compressor. This allowed me to have the fan hooked up 24/7 and only the compressor connected to the temperature controller so now when it cools down to temp the compressor turns off but the fan keeps going which prevents it from freezing up and also provides great airflow through the tent :) win / win

I put some plants in there last night which should start taking off now and appreciating the new conditions.

Nice and foggy

And just for something I have found interesting, I have been playing with tissue culture for a couple of years now and below pic is of a cephalotus culture I have had in a chinase takeout container for over 2 years now without ever being opened or touched. they just keep multiplying in there and loving the 100% humidity altho I am amazed at how long they have survived in there with no media change. People always say you need to replate every 8 weeks or so however I find ceph do best in TC when left undisturbed for longer, 2 years is a stretch but I have just been letting this one go out of curiosity :)

Thats awesome nugget! Very nice design on your tent. As long as the media remains sterile then the plants will continue fine until nutrients or space is no longer available. I guess you accurately proved this point. lol very cool indeed
Nice setup! Went on a nice shopping trip at EP for the neps I'm guessing?
Lol yeh theyre all EP plants.
Not in one hit tho. Ive done a couple of orders the last few catalogue releases but they been out in the harsh weather so finally can put them in some higher humidity.
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Awesome, what plants do you have? Looks like some promising ones in there.
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The temperature of the AC's evaporator coil is lower than the dew point temperature, hence your humidity dropping because it is condensing on the coil.
If you were simply cooling the air without reaching dewpoint, the humidity would be rising not falling even with no additional humidification.
The capacity of your dehumidification exceeds that of your humidification

Only solutions are
1. Decrease the effects of the evaporator coil (by reducing cooling capacity), smaller ac but running longer. (best solution, most efficient and most stable RH and temperature) and reduce cooling requirements by removing sources of temperature rise.
2. Increase the capacity of your humidifier, but this will also become a problem when the ac cycles off
3. Add additional humidification that cycles only when the AC kicks on, but this will also become a problem when the ac cycles off
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