How to size a dehumidifier

[grow nerd]

IME, two "45 pint" units will not come anywhere close to equaling the capacity of a "100 pint" unit... at least not at typical face value, simply because of the nature of the different markets that the differently sized (and spec'd) units are sold in. You will probably not find a >70 ppd unit in a retail store model (sub-$300), and those units' ratings are based at saturation levels whereas the commercial / home-owner models (typically > $1000) are at AHAM ratings.

For instance, a Santa Fe Classic dehumidifier is rated 100ppd @ AHAM, but 180ppd @ saturation. Through a decent amount of testing under various configurations and environments, the Santa Fe pulls more water than two 70ppd (@ saturation) retail store model, while drawing about half the power and throwing out about half (or less) the heat.

The point? Compare apples to apples; but as always, YMMV.

(Because there are certain measures you can take to reduce humidity in the room, as well.)

 

[sparkjumper]

I use a 45 pint unit for my 8 by 8 by 8 flower room,it works sufficiently well.The larger room will nedd a much larger one of course.I normally only run my dehumid during lights off in my sealed room during lights on with the AC it keeps around a 50-55 %RH which is cool.Its really nevessary though when the lights go out in a sealed room.

 

[NOYB]

For instance, a Santa Fe Classic dehumidifier is rated 100ppd @ AHAM, but 180ppd @ saturation. Through a decent amount of testing under various configurations and environments, the Santa Fe pulls more water than two 70ppd (@ saturation) retail store model, while drawing about half the power and throwing out about half (or less) the heat.

The point? Compare apples to apples; but as always, YMMV.

That's basically what I've heard when dealing with off-the-shelf units and something like Sante Fe in a comparo. If I had a large space to deal with I'd probably invest in a commercial grade unit and not mess around.

 

[Guest 18340]

Yeah, i tried using the 45 pint unit in the bigger room, what a joke. Definitely need 2 for the big room.

 

[jugdishe]

--possible dumb question--

--possible dumb question--

I have been trying with real success to get my rh down
I have 10x6x7 sealed room
18 plants in ebb and gro buckets
1600 watts
window ac unit
and 60 pint dehumidifier that cant seem to get rh below 60 during the day, better at night

The stupid part is that i have the dh mounted in the wall with the back side out of the room so the heat stays out
Is this why i have rh troubles or what
am i better to move it in the room and let the ac reduce temps
the ac doesnt seem to lower rh at all
from what some of you have said a 60 pint should be fine for my needs, yet it is not

any help would be great
j~

 

[Che]

You can move to a more commercial unit... a 100ppd Santa Fe would be more appropriate for what you're doing. Buckets create 100% RH output...

 

[grow nerd]

Another thing that I've learned while messing around with different dehumidifier configurations is that location is important... much more so than I thought. I once had the Santa Fe Classic located under a wall-mount fan, where the oscillating wall-mount fan was basically blowing air away from the top intake of the SFC. That didn't perform well at all, and simply moving the SFC a few feet away dropped the RH some ridiculous number I didn't expect (I forget, something like 10%-ish).

 

[njayjay]

IME dehumidifiers are only of value in an open system during lights off if you stop ventilation during this time. If you keep the fans running then a dehumidifier is useless in an open system.

how about dehumidifying the whole room where a vented growtent is, how well would that work to keep the RH low inside the tent? peace

 

[Philosophelon]

Jugdishe -- Your problem is likely that you are venting the dehumidified air out of your grow. The hot air coming out of your dehuey needs to stay in the room, because the hot air coming out is the dehumidified air. So if you are exhausting the hot air, you have essentially turned your dehuey into a very expensive and inefficient exhaust fan. Put it in the room and let your A/C cool the hot air that comes out. Also, adding heat will make your A/C run more, which should help pull even more water out of the atmosphere.

 

[NOYB]

how about dehumidifying the whole room where a vented growtent is, how well would that work to keep the RH low inside the tent? peace

It will be effective depending on the size of the tent (canopy area), growing method, air flow through the tent, size of the room, size of the dehumidifier and general geographic location (climate). The thing you're dealing with here is if you have a tent inside a sealed room eventually you'll use up your available CO2 and need to introduce it with fresh air exchange, which will introduce more humidity...so as your humidity levels are reduced by the dehumidifier and get low you'll also have to reintroduce fresh air for CO2 replenishment thus driving your humidity back up (obviously if the external humidity is higher than inside the room but also depends on the temp differential between outside and inside)...it's not really an effective way to deal with humidity.

For sure a lot of humidity issues I've seen inside a grow space is due to inadequate ventilation.

 

[hardseed]

with lights off get the biggest u can get

night time lower the better