The Garden's Cure - View Single Post - Optimum temp/humidity throughout a plants life?

knna · 10-14-2007, 08:50 AM

I continue quoting (my posts and Lucas related post):

"Thanks Knna

very good info links on the relationship between temperature and humidity..

I used a farenheit to celcius converter here Celcius and Fahrenheit Converter to calculate the celcius equivalent of 80 degrees farenheit, then used the calculator you linked to.. VPD Calculator thanks!

I reached a couple of preliminary baseline conclusions.. assuming the target Kpa is .9 and that leaf temp is 3Celcius degrees below air temp..

if the temperature is 85F, humidity should not be higher than 62%

if the temperature is 80F, humidity should not be higher than 58%

If the temperature is 75F, humidity should not be higher than 53%

If the temperature is 70F, humidity should not be higher than 47%

the rule of thumb seems to be a target temp of 80F should have just under 60% humidity.

An interesting observation is that as temperature drops by 5 degrees F, required humidity also drops by 5 %

so, 80F @ ~60%, or 70F @~50%, are good ballparks..

thanks!
Lucas

ps. leaf temp will be a function of how close the light is.. so if there is less than a 3Celcius degree difference, the light could be closer..

"Yes, the concept is at

higher ambient temp-higher RH
higher CO2 concentration-higher RH

And in general, at higher metabolism rate, higher RH. Always between limits. Both, excesive RH and low RH lead to transpiration become difficult.

Time ago, i did some calculations:

T(ºC)-T(F)-RH-VPD(3ºC)-VPD(2ºC)
18-64-35-0.98 1,1
20-68-35-1,12 1,25
23-73-35-1,35 1,5
26-79-35-1,63 1,81
30-86-35-2,08 2,29

18-64-40-0,88 0,99
20-68-40-1 1,13
23-73-40-1,21 1,36
26-79-40-1,46 1,64
30-86-40-1,87 2,08

18-64-45-0,78 0,89
20-68-45-0,89 1,01
23-73-45-1,07 1,22
26-79-45-1,3 1,47
30-86-45-1,66 1,87

18-64-50-0,67 0,79
20-68-50-0,77 0,89
23-73-50-0,93 1,08
26-79-50-1,13 1,3
30-86-50-1,44 1,66

18-64-55-0,57 0,68
20-68-55-0,65 0,78
23-73-55-0,79 0,94
26-79-55-0,96 1,14
30-86-55-1,23 1,45

18-64-60-0,47 0,58
20-68-60-0,53 0,66
23-73-60-0,65 0,8
26-79-60-0,79 0,97
30-86-60-1,02 1,23

18-64-65-0,36 0,48
20-68-65-0,42 0,54
23-73-65-0,51 0,66
26-79-65-0,62 0,8
30-86-65-0,81 1,02

18-64-70-0,26 0,37
20-68-70-0,3 0,43
23-73-70-0,37 0,52
26-79-70-0,46 0,63
30-86-70-0,6 0,81

I work within these ranges:

18ºC-64,4F - 35%RH. Max 55%
20ºC-68F- 35-45% RH. <60%
23ºC-73,4F- 45-50% RH. 34-64%
26ºC-78,8F- 50-55% RH. 42-67%
30ºC-86F- 60% RH. 50-70%

Range are computed between 0,55 (min) and 1,4 KPa.

Quote:

leaf temp will be a function of how close the light is.. so if there is less than a 3Celcius degree difference, the light could be closer..

Yes, but if you have leaf temp at canopy less than 3ºC below ambient, something is going wrong (bulb too far or some kind of lock, reducing metabolic activity).