properly sizing dehumidifier for large scale greenhouse grow - Growroom Designs & Equipment - International Cannagraphic Magazine Forums

914safbmx · 01-07-2018, 03:19 AM

hey guys. had my own small scale medical indoor grows going for a little while now. this year i've just become a caregiver and i'm gonna step it up big time. i'd like to think i'm a decently knowledgable grower at this point, but i'm worried that i'm gonna struggle with environmental controls on a large scale, mainly the humidity.

i'm building two 30x60 greenhouses side by side, 36 plants in each. I can have super gross cool and misty dank mountain nights here pretty consistently in the fall so i'm kind of bugging out in anticipation.

is there a rule of thumb for square footage, or gallons of soil/gallons watered daily that i can use while shopping for dehumidifiers? i've heard "you should be able to remove as much water from the air, as you will be giving the plants each day".... which doesnt seem realistic at all.... UNLESS i divide that amount of water up across the say 3-4 days in between waterings. but still leaves me with a pretty insane number that still seems unattainable.

i'm thinking maybe i should ditch the fabric pots and build wooden beds? i figured a lot more moisture can leave the soil more rapidly from smart pots but thats just a theory.

also trying to do research on laying some sort of vapor barrier across the entire floor of the greenhouse to reduce any humidity i might draw from the ground beneath me. think that would help me keep it under control??

have any other tips for things that can help me control the humidity? I'm almost positive that i wont be able to afford the IDEAL dehumidifier set up, so i wanna make sure i can do everything else possible to help

Speed of green · 01-08-2018, 05:59 AM

geo-textile is one route for ground cover its breathable and works well, although it can get expensive... my greenhouses have road base, it was inexpensive, compacts well and keeps dust down and it stays dry as a bone.

dehumidifiers are unrealistic in a greenhouse that size, you are going to spend a fortune on the fixtures and electricity.

Look into pellet stoves, they heat and dehumidify extremely well, dirt cheap. you need really good HAF and a partially sealed house to make them work right.

i think either smart pots or raised beds will give you about the same amount of humidity, id go with whatever you are accustomed to.

Limeygreen · 01-08-2018, 11:58 AM

Geo textile is great, get some big O drainage tile under the greenhouses to take away excess water, especially where you drain water will be, you can put drainage ditches or gutters in the greenhouses to direct the water to the tile. Exhaust fans to exchange air and remove humidity and a heater as well, heater dries it up exhaust fan or vents to allow air exchange.

914safbmx · 01-10-2018, 03:27 AM

the space i have cleared out for the greenhouse is pretty far back in the property so to do gravel i would have to drive bed after bed up the rough dirt road myself. nobody with a dump truck is making it up there, believe me. i think im limited to expensive geotextiles haha.

my theory about smart pots vs wooden beds comes from my own experience just with using fabric pots vs plastic pots. the more room you give the soil to breathe, the quicker it can dump the moisture out into the air around it. i know that with the in put being the same, they will both eventually release the same amount of humidity, but i figure if i can prolong the process i can control it easier.

well im interested in the idea of using a stove, but what if i wanna keep the temps down?

Speed of green · 01-10-2018, 07:47 AM

If you are in a hot humid environment then a pellet stove is probably a bad idea.

if you are trying to lower humidity when its warm and dry outside then exhaust fans are the ticket.

When temperatures drop humidity rises, if you have a hot humid day of say 80 degrees and 80% humidity the dew point is 74 degrees, keeping the temperature above this will stop dew from forming.

what size dehumidifier(s) were you thinking?

Lazyman · 01-12-2018, 11:01 AM

The formula is very easy actually. Plants transpire 99% of the water they intake daily, so your dehumidifier capacity has to match how much you're watering a day. If that's 200 gallons a day, you need 200 x 8(pints) per day at your temperature and RH, which is 1600 ppd.

Most dehuey manufacturers rate their dehueys at 85*F and 80% RH, which may apply to a few grows, but certainly not all of them year round. At night, or when it's cold, they will remove a fraction of their "rating." Unfortunately for you, that means you have to be able to remove half of that water in the dark, when it certainly won't be 85*F, so you'd need 3-4 times the capacity to be effective (5000-7000 ppd.)

Once you start looking at the prices and size of several 200gpd units (and the staggering amount of 3-phase electricity they require) you'll probably throw the idea out. If you can't control it at least 95%, it just isn't worth doing IMHO.

For giggles, check out gas-fired dessicant dehumidifiers. Very neat technology for large units, but the price tag will leave you weak in the knees.

Good luck, most greenhouse growers use lots of fans (both oscillating and intake/exhaust) and sulfur burners, UV lights or disease-management sprays to keep PM and botrytis at bay.

MedResearcher · 01-13-2018, 06:40 AM

Little off topic, but find the right genetics that resist rot and pm. Then keep the plants as healthy as can be.

Genetics make such a difference. Skinny floppy stems typically good VS rot.

Mr^^

914safbmx · 01-17-2018, 11:28 AM

Quote:

Originally Posted by MedResearcher

Little off topic, but find the right genetics that resist rot and pm. Then keep the plants as healthy as can be.

Genetics make such a difference. Skinny floppy stems typically good VS rot.

Mr^^

i've been thinking on this lately. any suggestions?

914safbmx · 01-17-2018, 11:44 AM

i wish i could find more reports from people using pellet stoves online. any body here actually used one? i'm not sure how efficient they will be so its hard to make what i would call an informed decision about how i'm going to control the humidity.

late summer/fall up here tends to bring temps in the high 50s and low 60s with an average humidity of like 70%. pretty gross conditions. should i just crank the intake late afternoon when humidity is the lowest, then seal everything off and turn on the heat at night? in theory it sounds like it would work great, but again, without ever using one, i have no idea how efficient one of these pellet stoves will be. maybe it will get much to hot before it can effectively start reducing humidity? isnt humidity directly relative to temperature in a sealed space? so then it would all just depend on if the stoves can get the temp to where i want it?? so many questions. would really appreciate any input from anyone with experience or any knowledge of this at all!!!

914safbmx · 01-17-2018, 08:53 PM

ok so i just read a little blurb online that said a greenhouse will need about 4000 BTU per 1000sqft to raise the temperature about 20 degrees. from all the pellet stoves i've looked at, they seem to be rated at like 40-50 thousand BTU!!!

can i get away with running smaller electric heaters or something? is this little online statistic that i found totally wrong? to me 4000BTU just doesnt seem like enough per 1000sqft of greenhouse.....

01-07-2018, 03:19 AM	#1
914safbmx Newbie Join Date: Dec 2017 Posts: 14	properly sizing dehumidifier for large scale greenhouse grow hey guys. had my own small scale medical indoor grows going for a little while now. this year i've just become a caregiver and i'm gonna step it up big time. i'd like to think i'm a decently knowledgable grower at this point, but i'm worried that i'm gonna struggle with environmental controls on a large scale, mainly the humidity. i'm building two 30x60 greenhouses side by side, 36 plants in each. I can have super gross cool and misty dank mountain nights here pretty consistently in the fall so i'm kind of bugging out in anticipation. is there a rule of thumb for square footage, or gallons of soil/gallons watered daily that i can use while shopping for dehumidifiers? i've heard "you should be able to remove as much water from the air, as you will be giving the plants each day".... which doesnt seem realistic at all.... UNLESS i divide that amount of water up across the say 3-4 days in between waterings. but still leaves me with a pretty insane number that still seems unattainable. i'm thinking maybe i should ditch the fabric pots and build wooden beds? i figured a lot more moisture can leave the soil more rapidly from smart pots but thats just a theory. also trying to do research on laying some sort of vapor barrier across the entire floor of the greenhouse to reduce any humidity i might draw from the ground beneath me. think that would help me keep it under control?? have any other tips for things that can help me control the humidity? I'm almost positive that i wont be able to afford the IDEAL dehumidifier set up, so i wanna make sure i can do everything else possible to help
	Quote

01-08-2018, 11:58 AM	#3
Limeygreen Senior Member Join Date: Mar 2006 Posts: 1,750	Geo textile is great, get some big O drainage tile under the greenhouses to take away excess water, especially where you drain water will be, you can put drainage ditches or gutters in the greenhouses to direct the water to the tile. Exhaust fans to exchange air and remove humidity and a heater as well, heater dries it up exhaust fan or vents to allow air exchange. __________________ Your best you try, to harm I and I, Aiming to kill. But I love you still Cause you are here to make prophecy fulfill.
	Quote

01-12-2018, 11:01 AM	#6
Lazyman Overkill is under-rated. Join Date: Jun 2009 Location: Norcal Posts: 5,186	The formula is very easy actually. Plants transpire 99% of the water they intake daily, so your dehumidifier capacity has to match how much you're watering a day. If that's 200 gallons a day, you need 200 x 8(pints) per day at your temperature and RH, which is 1600 ppd. Most dehuey manufacturers rate their dehueys at 85F and 80% RH, which may apply to a few grows, but certainly not all of them year round. At night, or when it's cold, they will remove a fraction of their "rating." Unfortunately for you, that means you have to be able to remove half of that water in the dark, when it certainly won't be 85F, so you'd need 3-4 times the capacity to be effective (5000-7000 ppd.) Once you start looking at the prices and size of several 200gpd units (and the staggering amount of 3-phase electricity they require) you'll probably throw the idea out. If you can't control it at least 95%, it just isn't worth doing IMHO. For giggles, check out gas-fired dessicant dehumidifiers. Very neat technology for large units, but the price tag will leave you weak in the knees. Good luck, most greenhouse growers use lots of fans (both oscillating and intake/exhaust) and sulfur burners, UV lights or disease-management sprays to keep PM and botrytis at bay. __________________ I'm fairly busy so please excuse my absence or slow responses to PM's! All about Growroom cooling:* Keepin' it cool man (my 1st published article) How to automate reservoir top offs or most anything water-related The only UV-B lighting thread worth a damn CO2 for dummies Big grow: The 36KW medical/perpetual basement
	Quote

01-13-2018, 06:40 AM	#7
MedResearcher Member Join Date: Dec 2007 Posts: 561	Little off topic, but find the right genetics that resist rot and pm. Then keep the plants as healthy as can be. Genetics make such a difference. Skinny floppy stems typically good VS rot. Mr^^
	Quote 1 members found this post helpful.

01-08-2018, 05:59 AM	#2
Speed of green Member Join Date: Feb 2015 Location: SoCal Posts: 627	geo-textile is one route for ground cover its breathable and works well, although it can get expensive... my greenhouses have road base, it was inexpensive, compacts well and keeps dust down and it stays dry as a bone. dehumidifiers are unrealistic in a greenhouse that size, you are going to spend a fortune on the fixtures and electricity. Look into pellet stoves, they heat and dehumidify extremely well, dirt cheap. you need really good HAF and a partially sealed house to make them work right. i think either smart pots or raised beds will give you about the same amount of humidity, id go with whatever you are accustomed to.
	Quote

01-10-2018, 03:27 AM	#4
914safbmx Newbie Join Date: Dec 2017 Posts: 14	the space i have cleared out for the greenhouse is pretty far back in the property so to do gravel i would have to drive bed after bed up the rough dirt road myself. nobody with a dump truck is making it up there, believe me. i think im limited to expensive geotextiles haha. my theory about smart pots vs wooden beds comes from my own experience just with using fabric pots vs plastic pots. the more room you give the soil to breathe, the quicker it can dump the moisture out into the air around it. i know that with the in put being the same, they will both eventually release the same amount of humidity, but i figure if i can prolong the process i can control it easier. well im interested in the idea of using a stove, but what if i wanna keep the temps down?
	Quote

01-10-2018, 07:47 AM	#5
Speed of green Member Join Date: Feb 2015 Location: SoCal Posts: 627	If you are in a hot humid environment then a pellet stove is probably a bad idea. if you are trying to lower humidity when its warm and dry outside then exhaust fans are the ticket. When temperatures drop humidity rises, if you have a hot humid day of say 80 degrees and 80% humidity the dew point is 74 degrees, keeping the temperature above this will stop dew from forming. what size dehumidifier(s) were you thinking?
	Quote

01-17-2018, 11:44 AM	#9
914safbmx Newbie Join Date: Dec 2017 Posts: 14	i wish i could find more reports from people using pellet stoves online. any body here actually used one? i'm not sure how efficient they will be so its hard to make what i would call an informed decision about how i'm going to control the humidity. late summer/fall up here tends to bring temps in the high 50s and low 60s with an average humidity of like 70%. pretty gross conditions. should i just crank the intake late afternoon when humidity is the lowest, then seal everything off and turn on the heat at night? in theory it sounds like it would work great, but again, without ever using one, i have no idea how efficient one of these pellet stoves will be. maybe it will get much to hot before it can effectively start reducing humidity? isnt humidity directly relative to temperature in a sealed space? so then it would all just depend on if the stoves can get the temp to where i want it?? so many questions. would really appreciate any input from anyone with experience or any knowledge of this at all!!!
	Quote

01-17-2018, 08:53 PM	#10
914safbmx Newbie Join Date: Dec 2017 Posts: 14	ok so i just read a little blurb online that said a greenhouse will need about 4000 BTU per 1000sqft to raise the temperature about 20 degrees. from all the pellet stoves i've looked at, they seem to be rated at like 40-50 thousand BTU!!! can i get away with running smaller electric heaters or something? is this little online statistic that i found totally wrong? to me 4000BTU just doesnt seem like enough per 1000sqft of greenhouse.....
	Quote