Air Cooler UA when it rains

Hi PaulMinchin,

I agree the UA will change ,due an a change in the U value
which is approximately of 1/U = 1/hi +1/ho + t/k

hi = tubes-inside heat transfer coefficient
ho = tubes-outside heat transfer coefficient
t = tube wall thickness, k= tube metal thermal coductivity

And the main cause for the increase is the variation in (ho)
the main change,on a rainy day will be an increase in (ho) wich will improve the U value ,causing more vapors to condense.
A common practice by the industry,to overcome excessive condensation,is to have a bypass line with a pressure control valve (PCV) ,that is actuated by a Pressure Controller(PC) on the reflux drum..the valve can be sized to pass up to (20%) of the main flow to the condenser

Hysis dynamic simulation will give you the solution,provided you give it the appropriate input data.

Regards,

Whylie

I wonder whether an induced draft air cooler would suffer from rain or other precipitation.

To reduce the cooling in the air cooler, you can turn off some of the fan coolers. this will save some electric energy, and this is a usual practice in winter.