Dehumidifer inside vs. outside tent (with CO2)?

[jjng5]

Hello all --

I'm curious what everyone does to dehumidify during flower. SWIM has two dehumidifers that each can fit inside the flower tents, however they will take up valuable space. SWIM also is using co2 in both sealed tents with controllers and doesn't want to waste CO2 either -- because if humidity raises above the set point the controller will turn the output fans on to dump the room and then need to refill with CO2.

So SWIM is weighing the two options -- is it worth putting the dehumidifiers inside the tent or if one puts the dehumidifiers outside the flower tents, will it be effective to drop humidity inside the tent? For some context this is in a cool basement in the north eastern US. Also the lights are a combo of LED QB's and HPS with aircooled tubes with separate ventilation to the outside outside (not outside into the basement, but to the outside outside lol).

Looking for some input on this one... grrr
Thanks!

 

[rkymtnman]

how would a sealed tent be affected by the enviro outside the tent??

 

[jjng5]

how would a sealed tent be affected by the enviro outside the tent??

Because at some point the tent is going to dump it's internal atmosphere (probably around once every 2 hours during lights on) and pull in dry air (if the dehumidifiers are external to the tent). Obviously sooner if humidity spikes. I'm worried less about temp's as the HPS fixtures are aircooled with air run outside the basement window to the outdoors. What would you do rkymtnman? Sacrifice the space inside the tent it's about 1.5 sq foot of well lit grow space and unfortunately the height of the dehumidifiers are unable to grow over and build a canopy over top of it

 

[rkymtnman]

i have a really small dehuey that i just installed in my bloom room. 12 sq ft. drilled a hole in the res, glued in an elbow and ran some tubing into my drain. works fine for me.

for a bigger area, i'd have to rethink. as is with mine, it doesn't take up any space. it hangs right next to one of my waterfarms.

 

[jjng5]

i have a really small dehuey that i just installed in my bloom room. 12 sq ft. drilled a hole in the res, glued in an elbow and ran some tubing into my drain. works fine for me.

for a bigger area, i'd have to rethink. as is with mine, it doesn't take up any space. it hangs right next to one of my waterfarms.

What size dehumidifier do you use? Maybe I should purchase new dehumidifiers that are really little and can be hung with ratchet straps or put on top of a DWC container to allow plants to grow around it?

The two flower tents are 5x5 (well one is 4.54 x 4.54 but whatever).

 

[rkymtnman]

What size dehumidifier do you use?

this is what i went with:

https://www.amazon.com/Eva-dry-Edv-1100-Electric-Petite-Dehumidifier/dp/B000H0ZDD2/ref=sr_1_7?keywords=eva+dry+dehumidifier&qid=1551727032&s=gateway&sr=8-7

 

[jjng5]

this is what i went with:

https://www.amazon.com/Eva-dry-Edv-1100-Electric-Petite-Dehumidifier/dp/B000H0ZDD2/ref=sr_1_7?keywords=eva+dry+dehumidifier&qid=1551727032&s=gateway&sr=8-7

Okay, something like this may be the only good option. No one wants to consistently waste CO2 nor do you want to give up valued grow space if you don't have to. A full sized unit would cost SWIM between 2-3 ounces each grow -- ouch!

I looked at your unit and it says that it only pulls 8 ounces of moisture per day -- that isn't very much. Does that keep your humidity down enough? What size space do you use this unit in? It looks like there are other units that will pull a bit more for about the same size and cost. I appreciate the info!

 

[rkymtnman]

Does that keep your humidity down enough? What size space do you use this unit in?

i cant find my RH meter. it just felt moister in my room compared to normal. feels better now. in summertime, i run at night and suck in cool night air to keep temps down. can't do that now. and here in CO, RH is really low. 30% usuallly.

i'm only 3x4x8 room size.

don't you need to keep a pretty high RH% when supplementing with CO2? i thought it was high temps/high humidity as a rule?

 

[jjng5]

i cant find my RH meter. it just felt moister in my room compared to normal. feels better now. in summertime, i run at night and suck in cool night air to keep temps down. can't do that now. and here in CO, RH is really low. 30% usuallly.

i'm only 3x4x8 room size.

don't you need to keep a pretty high RH% when supplementing with CO2? i thought it was high temps/high humidity as a rule?

I've read that plants like temps ~5 degree's F higher with CO2 injection. I've not heard that humidity should be higher, however I know that they are related to a degree. Everything I've read has said that humidity should be 45-55 %RH towards the end of flower. During early flower I think 55-65 % RH is okay. Here in the north eastern states those lower RH numbers can be a challenge, especially during summer months! No one wants moldy bud that's for sure! I know that the Titan / Saturn controller will just dump the entire room if humidity gets too high and then it will turn the co2 on to refill the room. Ugh...

 

[rkymtnman]

from reading @Dr. Who in another thread, this is what he recommended for CO2:

Best effective temp and RH range is about 89-91 deg and low 80's RH......That's right, high RH levels with gas on.

i'd have to read more about it to be honest.

 

[jjng5]

from reading @Dr. Who in another thread, this is what he recommended for CO2:

Best effective temp and RH range is about 89-91 deg and low 80's RH......That's right, high RH levels with gas on.

i'd have to read more about it to be honest.

Wow that humidity sounds crazy high -- seems like an invite to mold and bacteria to your bud. I've heard that temps upwards of 90 degree's is okay but you do not want temps or humidity levels too high or the stomata will close on your plant leaves (which is how the plant breathes in CO2 in the first place to utilize the molecule as carbon building blocks).

Irregardless the last 2-3 weeks you do not want high CO2 levels or you reduce your bud mass, so humidity is still an issue.

 

[Apalchen]

Buy a 30 pint (if that’s enough) and hang it from the roof of tent if it will support it, if not get creative hang some chains or something from hooks above the tent and cut a couple very small holes in the roof of tent for chains to hang thru (patch around after of course). Or if one side of your tent is against a wall you could attach brackets to the wall then you would just have a few screw holes to seal up. My 30 pint has hose attachment make sure you get one that does so you don’t have to change water buckets while it’s hanging above your plants.

 

[rkymtnman]

Irregardless the last 2-3 weeks you do not want high CO2 levels or you reduce your bud mass, so humidity is still an issue

that's true.

well good luck to ya! one of those smaller dehueys should do the trick i would think.

 

[Apalchen]

Buy a 30 pint (if that’s enough) and hang it from the roof of tent if it will support it, if not get creative hang some chains or something from hooks above the tent and cut a couple very small holes in the roof of tent for chains to hang thru (patch around after of course). Or if one side of your tent is against a wall you could attach brackets to the wall then you would just have a few screw holes to seal up. My 30 pint has hose attachment make sure you get one that does so you don’t have to change water buckets while it’s hanging above your plants.

EDIT: I have way heavier stuff than my 30 pint hung in my tent but it’s a strong ass tent the big green ones from hygiene supply that copy gorilla tents.

Sorry didn’t mean to double post was trying to edit original

 

[jjng5]

I don't think a 30 pint is needed though -- @rkymtnman does your small dehumidifer seem like it's running a lot -- it only pulls 8 oz per day it says. There are some on Amazon that do a bit more. A 30 pint unit is rated for a 1500 sq foot room. This is going in 25 sq foot tents.

 

[rkymtnman]

does your small dehumidifer seem like it's running a lot

i think it runs 24/7. it's nearly silent, hard to tell. and with the drain line i put in, it never needs to be shut off to drain the tank. i thought i read that it shuts off at 40% ?

 

[jjng5]

Picked up two units (one for each flower tent) -- 30 pint Haier compact compressor style dehumidifiers with drain hose connection on the rear. This should work well with the Saturn 6 controllers on the setting selection where you "unlink" temp and humidity so that it does not dump your CO2 atmosphere when RH % gooes outside the set range, it will only dump if temps raise outside the range.

Take a peak -- $100 each including shipping:




It has handles it says -- going to try and use ratchet straps to hang this thing up-right from the tent, it's only 25 lb's empty.

 

[Apalchen]

Looks very similar to mine and mine works great for 32 sq ft. You said above you thought maybe it was over kill but they kick off and on if it’s too big, and you can drop it RH as low as you want toward the end of flower. I always feel like when buying equipment oversizing is better because most people eventually expand and even if not if you buy too small first time just means you gotta buy it again.

Also look up vapor pressure deficit that will explain more about high humidity during flower.

 

[Dr. Who]

Wow that humidity sounds crazy high -- seems like an invite to mold and bacteria to your bud. I've heard that temps upwards of 90 degree's is okay but you do not want temps or humidity levels too high or the stomata will close on your plant leaves (which is how the plant breathes in CO2 in the first place to utilize the molecule as carbon building blocks).

Irregardless the last 2-3 weeks you do not want high CO2 levels or you reduce your bud mass, so humidity is still an issue.

Never heard of the Vapor Pressure Deficit?
How about the Light Saturation Point in C3 plants?
Do you know the correct lighting requirements that actually limit Co2 ppm values?
How about that just about NO ONE can deliver enough light energy to actually use 1500 ppm of Co2?

The VPD chart is something that for most indoor plants.. you should at least keep an eye on....Especially for things that are needing a fairly consistent RH..Like say Orchid's.
Now for the most part. I ignore the VPD for growing Cannabis. I like a lower (45%) RH in bloom. I control that very accurately. And your right, I do it to help put off fungal spore germination.

Now when gassing cannabis. YOU MUST FOLLOW the VPD for actual effective use of increased Co2 levels! This whole thing has to do with how the plant can effectively use that increased gas level.
The relationship between the amount of;
Light energy delivered.
ppm's of Co2 maintained
RH and Temps maintained during lights on
Is absolutely critical to effective use by the plant of the available Co2!

Lets cover lighting first
Light needs to be delivered at certain intensity amounts to allow the plant to use the increased Co2 at all.
800 to 1200 ppm is basically the range that we can actually employ and get useful, effective results

This light intensity is increased on a Bell curve... Generally meaning that small increases of light energy can handle small increases of Co2.
The thing is that once you hit 1K ppm. The increase in lighting energy moves towards the point where your not going to effectively be able to employ the increased Co2.
Even basic 1k HPS lighting, is limited to about 900 - 1100 ppm of of actual Co2 concentration.... To go beyond that and to even be effective in using the available gas concentration,,,,you need to be delivering about 1400 watts of HPS to get to 1300 ppm... Beyond that is effectively not a viable option in terms of cost effectiveness in the yield increase!

Next in line to effectively use increased Co2??? Temps and RH!
In comes the Vapour-pressure deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated. ... In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature.

What does VPD have to do with growing?

VPD helps a grower identify healthy air moisture conditions over the full range of growing temperatures. Vapor pressure deficit correlates directly to plant transpiration rates. ... High VPD can cause wilting when the root water intake can't keep up with the leaf evaporation loss.

Ok, first I'll point out that we, growing our chosen plant. Hate fungus spores and mold spores growing on our plants.... We have far more Mold problems but, the point being. We do what we can to keep RH down to levels that inhibit mold spores from growing....Generally 50% is the industry standard.....Actual premium Temp and RH levels to grow cannabis....Under 75 F and 65% RH.

Now because we don't really follow that. Our feeding is adjusted to compensate for the lower RH we run at. Commercial fertilizer charting is basically charted for our used RH levels....We further got to the feeding rates we want by dialing in our feeding to our strains and their environment. What I'm saying is that savvy growers know to adjust feeding to their strains for optimal growth. This IS directly effected by the environment....Temps and RH are a part of the enviro.

Below is a VPD growing chart. I employed these constantly in greenhouse operations.

Take a look at where that RH and the 90 F TEMP intersect.... You accepted the temp given above as effective. Yet your RH is too low to actually effectively use all of your increased Co2.. That is waste and waste costs money!

To effectively utilize a Co2 ppm of 800 or above. Temps of 90 F and an RH of 80% is needed in the grow area!

VPD chart

The easiest way to control your grow room for gassing?

An environmental control unit! This unit will turn on and off the gas at night.

You also set the temp and RH value for the unit to shut off the gas and turn on the exhaust/cooling. This then rides down to a set point you choose and it repeat's the process over and over.....till shut down.

https://4hydroponics.com/autopilot-digital-environmental-controller.html

The Autopilot Digital Environmental Controller (DEC) is designed to control the humidity and temperature levels in your grow room while coordinating the use of supplemental CO2 injection within the temperature function.

It has four (4) receptacles and a remote combination probe with highly accurate temperature, humidity and light sensors.

The 15' remote sensor on the Autopilot DEC is designed to quickly react to changes in the growing area and to resist EMI / EFI from electronic ballasts.

Easy to use push button functions are identified on a large digital display. It has a built-in data logger that records minimum and maximum temperature and humidity levels.

Specifications:

Temperature control range: 41° to 113° F
Temperature accuracy: +/- 2°F
Temperature dead-band (hysteresis): adjustable
Humidity control range: 5% to 95% rH
Humidity accuracy: +/- 3% rH
Humidity dead-band (hysteresis): adjustable
CO2 ON timer setting range: 1 second to 12 hours
CO2 OFF timer setting range: 1 second to 96 hours
Input voltage 120 Volts AC
Maximum amperage: 14.5 amps @ 120 VAC
Weight: 5 lbs
Dimensions 9" tall x 7" wide x 4" deep



NOTE: This APCETHD controller has a 14.5A maximum load. For higher amperage units, such as A/C units, it is recommended to use a power expander.

Covered by a 3-year warranty.


I see somebody mentioned that you MUST turn OFF the gas for last cpl of weeks of bloom.... From past experience, I did it at week 7 (stop gassing) and let them finish out.
High Co2 levels inhibit Ethylene production by the plant. Ethylene gas does the actual ripening of the plant....Same as fruits..

If you do not follow the VPD when using gas.....Your shooting yourself in the foot!

All of this information. Can be verified in Ed Rosenthal's books!

I made it simple and understandable....

I could give you pages of technical answers.....Including why the plant decreases growth by over 30% everyday and that by gassing you can get almost all of that lost growth back...

The thing is.....Cost to return ratio's.... At my size. I have to employ Co2 generator's. They simply do not return enough in the long run to use for the size area's I grow in..

What is gassing good for then? Tent growers.....You can use big 75 lb tanks over the limited 40's and deal direct with the gas company for them. Cheaper and last longer...

Be sure your math is correct for your size area (volume)....

I don't gas anymore. Not worth the cost to yield....


Lastly. NEVER gas in veg...Talk about no cost effectiveness!

 

[Dr. Who]

Hello all --

I'm curious what everyone does to dehumidify during flower. SWIM has two dehumidifers that each can fit inside the flower tents, however they will take up valuable space. SWIM also is using co2 in both sealed tents with controllers and doesn't want to waste CO2 either -- because if humidity raises above the set point the controller will turn the output fans on to dump the room and then need to refill with CO2.

So SWIM is weighing the two options -- is it worth putting the dehumidifiers inside the tent or if one puts the dehumidifiers outside the flower tents, will it be effective to drop humidity inside the tent? For some context this is in a cool basement in the north eastern US. Also the lights are a combo of LED QB's and HPS with aircooled tubes with separate ventilation to the outside outside (not outside into the basement, but to the outside outside lol).

Looking for some input on this one... grrr
Thanks!

Answer is to effectively control the room temps/RH outside the tents, to "normal" grow area averages.
The environmental controller will shut off the gas....Turn on the exhaust (have that go out of the room with the tents)
as the exhaust pulls the hot/Humid air out.. New, cool and drier air fills the tents to the set pint and does it over...

I am hoping you read the above answer first.