G
GuFF
- 34
- 0
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.
-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.
