# [Equest-users] Evapotranspiration Rate - Greenhouse

Erik Kolderup erik at kolderupconsulting.com
Fri May 29 14:47:57 PDT 2015

```I can answer part of your question. The ET rate is provided in mm/day
because it's used by farmers to determine how much water to apply to their
crops. That's the depth of water required to offset the consumption by the
plants. A typical value is 0.25 inch/day in hot weather, so a farmer would
need to apply 1 inch of water if irrigating every four days.

For your purposes, you could multiply the ET rate by the the "footprint"
area of the plants to get a rough water consumption rate. Of course the ET
rate varies with the plant's environment: drybulb, wetbulb, airspeed, etc.

Seems reasonable that using that calculation would get you in the ballpark
of the latent load from the plants.

-Erik

*Erik Kolderup, PE, LEED AP*
erik at kolderupconsulting.com | 415.531.5198 | www.kolderupconsulting.com

On Fri, May 29, 2015 at 11:04 AM, Singhal, Harshul <
HSinghal at thorntontomasetti.com> wrote:

>  Hi everyone,
>
>
>
> I am modeling one greenhouse for which I need to manually calculate latent
> load through evapotranspiration rate through plants in the space. I came
> across with some research where they talked about calculating
> evapotranspiration rate in mm/day or mm/hr.
>
>
>
> http://edis.ifas.ufl.edu/pdffiles/ae/ae45900.pdf
>
>
>
> also, I got this software on “land & water division” website to calculate
> ET rate: http://www.fao.org/nr/water/eto.html
>
>
>
> Can someone please explain it to me if it makes sense to use this
> calculation for ET rate through crops in glass chamber? Why this unit is in
> mm/day (length/time unit)? Tried to look around but haven’t got the
> explanation. Why it’s not some volume/time unit? Is it mm/day for every sq
> ft or every sq metre?
>
>
>
> Some inputs will be very helpful here. Thanks
>
>
>
> *Harshul Singhal, LEED AP BD+C*
> Project Consultant
> Thornton Tomasetti
> 386 Fore Street, Suite 401
> Portland, ME  04101
> *T* +1.207.245.6060  *F* +1.207.245.6061
> *D* +1.207.245.6074
> HSinghal at ThorntonTomasetti.com
> www.ThorntonTomasetti.com
>
>
>
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