Discussion: Vapor Pressure Deficit/Differential (VPD) during drying & curing

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MacroLogos

MacroLogos

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I found 70f at 50% for 3 days then 60-63 at 60% until ready to jar. Depending on bud size anywhere from 10-20 days. Just what i found to work well for me.

Sensor placement is key. Air movement is key but never directly at the buds
70f @ 50% is ~1.45 kPa, and 60-63 @ 60% is ~0.8-0.9 kPa

I'd have to use at least 2 different temp/RH combos... one starting a bit after dawn, and the other, after sunset... to sustain that VPD...

Evaporative coolers have a hard limit: they max out at a 40f temp drop from outdoor ambient @ <10% humidity. Also, as humidity rises, this max temp drop goes down.

So I can't drop and hold a ~110f+ outdoor ambient temp to more than about 82-84f in the tent... but I can drive up humidity to bring it to those VPD targets by using a dual micro-climate (mc) approach and running the 2nd evap cooler in the shop's ambient (around 100f+ and 30% RH) and venting the tent's humidity back into the shop.

Then, fine tuning the tent's mc is achieved by adjusting the mc RH of the shop.
 
Perrin6363

Perrin6363

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I found 70f at 50% for 3 days then 60-63 at 60% until ready to jar. Depending on bud size anywhere from 10-20 days. Just what i found to work well for me.

Sensor placement is key. Air movement is key but never directly at the buds
I was planning on placing my 2 little fans on the floor feeding each other to kinda push the air around into a vortex but not face them up. Is that too much air? They're like 8 inch fans.
 
MacroLogos

MacroLogos

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Min Temp: 65°f RH: 16% VPD: 0.6 kPa
Max Temp: 85°f RH: 77% VPD: 1.7 kPa
Ave. Temp: 77.1°f RH: 63% VPD: 1.21 kPa

So the VPD average has been 1.21 for about a week (a bit to the dry side during the day 1.2-1.4 kPa, nights are on the moist side 0.9-1.0), and a nice frost has formed on the sugar leaves. No molds or funk happening.

Under a 480w MARS, these buds are a bit small due to some nutrient issues during flower, but for a summer crop in the heat of the Arizona, it'll smoke. ;-)
 
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