Evaporative cooling calculation

[WorknCrazy]

In a direct evaporative cooler how much water does it take to drop 1 cubic foot of 90 degree F 50% Rh air to 70 degree F?

A simple spreadsheet or software to calculate water consumption in evaporative coolers would be helpful.

Thanks

 

[quark]

WorknCrazy!

The rule is you cannot cool air below the wet bulb temperature. With 90 deg.F and 50% RH the WB is 74.5 deg.F

But in practical acheiving wet bulb temperature is also very difficult.So as a general rule evaporative coolers are considered to be operating at 80% efficiency. So now the outlet temperature you acheive is

DB_out= DB_in- [0.8(DB_in-WB_in)]
=90 - [0.8(90-74.5)] = 90-12.4 = 77.6 deg.F

Now the process of evaporative cooling is Isoenthalpic. (but the amount of sensible and latent heat capacities change before and after the process)

To check water content, take a psychrometric chart and plot the initial and final conditions. For the second point follow the enthalpy line and see where it cuts the 77.6 deg.F DB line. Now take the moisture content from the right side of the chart. The difference will give you howmuch water is being evaporated in the process.

For your process it is 0.1ml/cu.ft of air.

You can download good psychrometric chart from here.

http://www.heatpipe.com/ProductsServices/forengineers/heat_pipe_psychrometrics.htm

Regards,