creating an optimal environment with co2 enrichment (V.P.D)

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GuFF

V.P.D. (vapor pressure deficit) is a measure used that can give you a clear idea of what temperature and humidity is optimal for your grow room.

-Found this online a while ago bit not exactly sure where from;

"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. Once air becomes saturated water will condense out to form clouds, dew or films of water over leaves. It is this last instance that makes VPD important for greenhouse regulation. If a film of water forms on a plant leaf it becomes far more susceptible to rot. On the other hand, as the VPD increases the plant needs to draw more water from its roots (and if it is a cutting, dry out and die). For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 to 0.95 kPa
In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature. Unlike relative humidity, vapour pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation."

Here is a link to a VPD calculator. You will need your room temperature, your leaf temperature, and your humidity. The only way to accurately measure your leaf temp is with an infrared thermometer.
http://www.autogrow.com/vpd_calc.php

Now onto co2 enrichment and how it affects the temperature at which you should keep your room at. I recently purchased an ir thermometer to check my leaf temps and see how co2 affects the leaf temperature compared to the ambient temp in the grow room. I have not finished cleaning out from my last grow but I will soon be experimenting with the ir gun when everything is going and I will post my results here.

I have a thought on why plants may grow faster when you increase temps beyond the ideal 75 degrees with co2 enriched gardens. My guess is that when co2 levels are increased the difference between the leaf temp and the ambient room temp also increase. Perhaps when co2 levels are raised the amount of co2 that gathers around the leaf is also increased and may have a "cooling effect". Or maybe with increased co2 levels the increase in photosynthesis increases the transpirtation rate of the leaves and in affect, cools the leaf. Whatever the case when putting different numbers into the vpd calculator I noticed that when there is a greater than normal difference (>4 degrees f) in leaf and ambient temperature that the optimal VPD kpa (0.8-0.95) are more reachable at higher temps while still having humidity at an acceptable range (40-60%)

Any educated opinions on the matter would be appreciated. I will update this thread with what I find using my new ir thermometer.
 
leadsled

leadsled

GrowRU
You pretty much nailed it.

Basically, Each 18degree rise in air temp double the plants respiration rate. As plants warm there respiration increases.

A high vpd means the plants has little water to balance the water lost by transpiration.
The plant then becomes stressed and struggles to maintain the internal water pressure.

Above 86 plants experience transpiration problems, (time to reduce c02) above 90 the stomata that take in c02 are closed. (turn off c02)

Leaves regulate there stomata opening based on taking in enough c02 without losing too much water.

high temps give the stomata a "double close" first is a signal for excess VPD, then second is the signal of extreme difference between internal and external c02 concentrations.

80-85 is that fine line where you can get excellerated growth without going to far. (stomata close)

Without digging out a book, I recall that being the scientific explanation as why the higher temps help excellerate things.

Looking forward to your finding with the infa red thermometer. Planning on getting one.
 
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Badmf

Be aware that temps vary widely in different areas of your grow! And the height its measured. I can run 90f at top shelves while lowers are 10 degrees cooler. With good circulation you can "return" co2 that "rests" on the floor to "re-circulate" again and again! Peace! Bad...
 
G

GuFF

I also recall reading that the higher temperature means things are moving faster within the plant. Just like how heat effects atoms in that it makes them move faster and faster with more and more heat.

I did a lot of looking around online trying to find a good IR thermomter, i'll try to put a link up to the site i choose i believe the company was called thermoworks. The meter I got is mainly based for food and is accurate to within 0.6 degrees celcius (one of the most accurate i could find). And anything more than 1 degree celcius than can really throw off you VPD calculation. The meter was just a little over $100.


Be aware that temps vary widely in different areas of your grow! And the height its measured. I can run 90f at top shelves while lowers are 10 degrees cooler. With good circulation you can "return" co2 that "rests" on the floor to "re-circulate" again and again! Peace! Bad...
yes true co2 does sink to the floor because it is heavier than air, i have multiple fans set up to circulate the air within the sealed room in a big circle. On one end of the room i have fans near the ceiling pointing at the other side. On the other side i have fans on the floor pointing towards the opposite wall. Of course I do not have any of these fans blowing directly on the plants as to not dry them out. I have small oscillating fans on the ceiling gently blowing down on the plants, i was told not to blow air down from the ceiling over the lights on the plants but i have heat shields for my reflectors and an ice box on each reflector so they are always cool, also my fans for my lights are aimmed to help circulate my grow room air in the direction of my "circle".

Thanks for your thoughts
GuFF
 
3 balls

3 balls

Any further science since the 10 years past on this thread?

Is there a VPD chart that compensates for CO2 enrichment?

Reason to believe it shouldn't make a difference perhaps?
 
asdfasdfdasdf

asdfasdfdasdf

1
0
1
Any further science since the 10 years past on this thread?

Is there a VPD chart that compensates for CO2 enrichment?

Reason to believe it shouldn't make a difference perhaps?
Yeah a VPD chart with C02 referenced would be a good thing, havn't seen one yet.
 
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