Greenhouse evaporative cooler design question

[Clymber]

We are renovating an existing greenhouse. The researchers moving into this renovated space require evaporative cooling. This greenhouse, which is divided into two 20' x 33' sections, will have a very short pad-to-fan distance (side wall to opposite side wall). Both ASHRAE and the Nat Greenhouse Mfr Assn (NGMA) recommend a baseline 8 CFM/SF for evaporative cooling airflow. However, the NGMA ventilation white paper requires an additional "velocity adjustment factor" when the pad-to-fan distance is below 100'. In this case that factor is 2.24, which is a significant increase in airflow required.

Which is correct? The pad design is the critical airflow piece. I don't want to over-ventilate such a small space, and pad selection hinges on airflow requirements.

Any ideas or recommendations here?

Thanks in advance.
-Brad

 

[rogzog]

Consider going with the recommended CFM requirement but calculate the pad areas in relation to the CFM and keep the air velocity across the pads low enough to not create carry over of the water on the pads. If remember it should be below 500 FPM velocity but you should check that number, it has been a while for me.

 

[lukaiENG]

I would agree with Rogzog. (over)size your pads to keep the velocity low, thus reducing velocity adjustment factor.
What do the psychrometrics tell you? how close to saturation are you coming off the adiabatic cooler?