Vent Light Formula

[New Holland]

I just found a post that I printed out from Overgrow. It's a formula that you can use to calculate the amount of ventilation needed if you enter in the room dimension and the amount of Kw of light and ambient tempretures.

 

Or if you put in the room dimensions the amount of ventilation you have it will tell you the maximum amount of light you can have.

 

I thought it would be neat if you can put it in a spreadsheet, that way you can put in the figures and it will automatically calculate the blank field, if you know what I mean?.

[stonedstump]

Cross-post is to here then and someone might know how

[toasty]

I can use excel, but as OG is down, maybe post the formula here? I'll have a crack at it

[New Holland]

I can't cross post it. I have it printed out on a sheet of paper it's

 

Q=V x P x C x dT

 

Where:

 

Q= Amount of lighting in Kw

V= Volume air being ventilated m3/s

P= Density of air (assume 1.2kg/m3 (sea level))

C= Specific heat capacity of air (assume 1.02kJ/kgK)

dT= Tempreture Difference between ambient and and growroom air

 

Here's how you would use it for each question:

 

Q1. What is the most lighting I can put into my grow space?

 

Where Ventilation = 240m3/hr (0.067m3/s)

Tempreture of air entering grow room = 21degC

Tempreture of grow space is to be no more then 26degC

 

Q = V x P x C x dT

Q = 0.067 x 1.2 x 1.02 x (26-21)

Q = 0.41kW i.e 400 watts

 

Q2 What Tempreture am I likely to get in my growroom?

 

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)

=> 4.87degC. i.e 21+5= 26degC in grow room

[New Holland]

Q3 How much ventilation am I likely yo need?

 

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 240m3/hr

[Pa-uul]

I can use excel. Yeah, it could be put into excel.

 

Formula looks like what I've seen too. I've got one here but it's in litres:

 

where H = heat generation inside the space (Watts)

Q = ventilation rate (litres/second)

cp = specific heat capacity of air (J/kg/K) = 1006 J/kg/Kelvin

rho(p) = density of air (kg/m3) = 1.2kg/m3 (sea level)

Ti = indoor air temperature (K) (= oC + 273)

To = outdoor air temperature (K)

 

A small portion of the heat will escape directly through the walls by absorption. This will reduce the temperature. How the exhaust and inflow to the room will be situated relative to the “plume”, the stream of hot air rising from the hot elements, will have also an effect. The placement of the thermometer too. It will be interesting to know the difference between theory and results.

Edited March 28, 2006 by Pa-uul

[New Holland]

Holy Fuck Pa-uul, You're giving me a head ache making me think that hard . Any chance OS can make this into an online calculator? . Put yours up and mine (actually Podge posted it on OG)?.

[New Holland]

Just fond exactly the same formula in the archives. Podges entire post from OG has been posted there

 

https://cannabis.community.forums.ozstoners...?showtopic=6999

[Pa-uul]

Holy Fuck Pa-uul, You're giving me a head ache making me think that hard

Sorry. That was too much info. I should have stayed out of it.

Just fond exactly the same formula in the archives. Podges entire post from OG has been posted there

 

https://cannabis.community.forums.ozstoners...?showtopic=6999

That is a good treatment of it. Some things there I thought of but was too lazy to put up myself like not having the ballast in the room.

[New Holland]

No worrys Pa-uul. It's good to here your 10 cents worth. All that maths is just abit too much for me, but on the other hand we're not the only ones reading these posts. It might be right up someone's alley! .

 

I just wish I knew how to work MS Excel to set them up so you just fill in the blanks. Kinda like the power consumption calculators?.