Dehumidification Load: Day Vs. Night

[Minkus]

Hey guys,

So as we know, plant transpiration of water consumed during the grow process is what causes the majority of the resulting humidity in a grow space.

However, at night, the plants cease transpiring. However, as many have no doubt observed, there is still a need for dehumidification at night.

Basically, what I'm asking is, what would you say the difference in your dehumidification needs are between night and day? Rather than looking at it with anecdotal evidence (grows are all different in the problems they go through), does anyone have any plant-science insight into the differences in dehumidification needs due to the change of plant transpiration between night and day?

 

[fishwhistle]

During the day my mini takes care of it no dehuey needed,in fact the opposite (humidifier) most of the time,at lights out with a/c off on the other hand it spikes and dehuey comes on.This is sealed room of course.

 

[Minkus]

Definitely know that you need dehumidification separate from AC at night, the question is - what's the dehumidification needs at night vs. during the day? Like, say you need to dehumidify a certain amount during the day cycle - during the night cycle, you need to dehumidify, but do you need to dehumidify as much, or 10% less, 30% less, 60% less than during the day?

 

[Walter Stark]

Definitely know that you need dehumidification separate from AC at night, the question is - what's the dehumidification needs at night vs. during the day? Like, say you need to dehumidify a certain amount during the day cycle - during the night cycle, you need to dehumidify, but do you need to dehumidify as much, or 10% less, 30% less, 60% less than during the day?

 

[Walter Stark]

We use 10% of day transpiration RATE. There are indications this is higher and we are waiting for some real data to arrive before changing this formula.

 

[DemonTrich]

VDP

Follow that chart. I kinda do until day 50 of a 64 day run. Then it's 50% night/day.

 

[Walter Stark]

Dermon, where can I find the chart you refer to?

 

[DemonTrich]

Search or Google

VDP chart

 

[Walter Stark]

Oh! VPD or Vapor Pressure Difference, right?

 

[DemonTrich]

It was early, and before my.morning coffee

 

[Walter Stark]

No problem. Do you have a feel for the the day/night transpiration rate difference? 90%/10% or 80%/20% or etc...?

 

[DemonTrich]

I think your over thinking it a bit. I set my controller and forget it until 2 weeks before harvest. Then I drop day/night temps to 70/65 and 50%rh and co2 to 500ppm

 

[Herb Forester]

I think your over thinking it a bit. I set my controller and forget it until 2 weeks before harvest. Then I drop day/night temps to 70/65 and 50%rh and co2 to 500ppm

Did you even look at the dood's signature? Something tells me he knows more about this than you do.

 

[Walter Stark]

Herb, Thanks for the compliment but we are mechanical engineers who design Climate Control systems for Cannabis facilities, and not horticulturists. We are typically give irrigation rates in gallons/day and we then need to divide this between day and night use in order to properly size our dehumidifier. It appears that no one has recorded this data and we are in a constant search.

 

[Herb Forester]

Herb, Thanks for the compliment but we are mechanical engineers who design Climate Control systems for Cannabis facilities, and not horticulturists. We are typically give irrigation rates in gallons/day and we then need to divide this between day and night use in order to properly size our dehumidifier. It appears that no one has recorded this data and we are in a constant search.

I'm working on it too and will share what I discover. Will be in touch on your equipment, looks interesting.

 

[Walter Stark]

Thank you Herb

 

[HydroGuy]

I run a rdwc system so its pretty easy to measure water uptake day vs night. In my system i have found on average about 85% of my water uptake by plants occur during lights on. I also collect all my dehumidifier water in a reservoir and it appears the transpiration rates of day/night are about the same as water uptake rates. So to make an educated guess i would say 15% dehumidification needs during night time which seems to be close to what @Walter Stark is suggesting. He definitely seems like a far better source of information than me. I know i dont have the scientific research quality test results you are looking for but its the conclusion i have come to in my system which seems to be pretty close to what the Pro's are suggesting.

 

[rmoltis]

During the day period my rh% always reads under %1.

It's not until nighttime when the temperature cools that it returns to ambient rh%

 

[MIMedGrower]

This has gotten complicated.

Aren't we talking relative humidity? At lights out the temperature drops and that is why the humidity rises.

 

[Walter Stark]

Yes, I agree. But the transpiration rate also decreases at night. This is the value I am seeking. Looks like Hydro-Guy has done some real data gathering which reveals an 85%/15% split in day/night transpiration rates. Any other collaboration would be appreciated.
Thank you all