Stretchtastic
Well-Known Member
This isn't my equation I found it looking for the proper cfm to suit my new tent and lights. Worked well enough to keep my temps 75 and lower the whole flower period.
Q = V x P x C x dT
where:
Q = Amount of lighting (kW)
V = Volume of air being ventilated (m3/s)
P = Density of air (assume 1.2 kg/m3)
C = Specific heat capacity of air (assume 1.02 kJ/kgK)
dT = Temperature difference between ambient and growspace air in degC
You can use this to determine what the temperature rise in your space will be (dT), or given a desired temperature rise you can use it to work out how much ventilation you will require (V)
To get from CFM to m3/s divide the CFM by 2119.
Examples
Here are some examples of how you could use the formula in three different ways, each using the same basic figures for clarity.
What temperature am I likely to get in my growspace?
Assume: Lighting = 400W (0.4kW), ventilation = 240m3/hr (0.067m3/s) and temperature of air entering room = 21degC
Q = V x P x C x dT
=> dT = Q / (V x P x C)
=> dT = 0.4 / (0.067 x 1.2 x 1.02)
=> dT = 4.87, i.e. 21 + 5 = 26degC in growspace
How much ventilation am I likely to need?
Assume: Lighting = 400W (0.4kW), temperature of air entering room = 21degC and temperature of growspace to be no more that 26degC
Q = V x P x C x dT
=> V = Q / (P x C x dT)
=> V = 0.4 / (1.2 x 1.02 x (26-21))
=> V = 0.065 m3/s i.e. 240 m3/hr
What is the most lighting I can put into my growspace?
Assume: Ventilation = 240m3/hr (0.067m3/s), temperature of air entering room = 21degC, temperature of growspace to be no more that 26degC
Q = V x P x C x dT
Q = 0.067 x 1.2 x 1.02 x (26-21)
Q = 0.41 kW i.e. 400 W
So that's it, once you get used to using it its very simple really, Just stuff the formula and figures in a spreadsheet and let it do the work.
Q = V x P x C x dT
where:
Q = Amount of lighting (kW)
V = Volume of air being ventilated (m3/s)
P = Density of air (assume 1.2 kg/m3)
C = Specific heat capacity of air (assume 1.02 kJ/kgK)
dT = Temperature difference between ambient and growspace air in degC
You can use this to determine what the temperature rise in your space will be (dT), or given a desired temperature rise you can use it to work out how much ventilation you will require (V)
To get from CFM to m3/s divide the CFM by 2119.
Examples
Here are some examples of how you could use the formula in three different ways, each using the same basic figures for clarity.
What temperature am I likely to get in my growspace?
Assume: Lighting = 400W (0.4kW), ventilation = 240m3/hr (0.067m3/s) and temperature of air entering room = 21degC
Q = V x P x C x dT
=> dT = Q / (V x P x C)
=> dT = 0.4 / (0.067 x 1.2 x 1.02)
=> dT = 4.87, i.e. 21 + 5 = 26degC in growspace
How much ventilation am I likely to need?
Assume: Lighting = 400W (0.4kW), temperature of air entering room = 21degC and temperature of growspace to be no more that 26degC
Q = V x P x C x dT
=> V = Q / (P x C x dT)
=> V = 0.4 / (1.2 x 1.02 x (26-21))
=> V = 0.065 m3/s i.e. 240 m3/hr
What is the most lighting I can put into my growspace?
Assume: Ventilation = 240m3/hr (0.067m3/s), temperature of air entering room = 21degC, temperature of growspace to be no more that 26degC
Q = V x P x C x dT
Q = 0.067 x 1.2 x 1.02 x (26-21)
Q = 0.41 kW i.e. 400 W
So that's it, once you get used to using it its very simple really, Just stuff the formula and figures in a spreadsheet and let it do the work.
Spread sheets are very helpful for breaking everything down before you even start, because you want to protect yourself from as many obsticles as possible. I have a little trouble dealing with the spread sheets, i definately make it more defficult for myself. There's definately a way to assign collums into equations without the pain staking steps, I just haven't found it yet. But anyways Thanks for the info ^^
