Hello everyone, I have a question about calculating Relative humidity. If I have a surrounding with 30 degrees Celsius and RH of 30%. I am cooling the surrounding with an air conditioner that works at 15 degrees Celcius. At the end of the process, the room reaches 25 degrees Celcius. In this situation, there is no condensation in the process. How can I calculate what is the RH at the end of the process? Thank you very much

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Hi, welcome to the Thermodynamics Forum :)

For this problem,

are you assuming that the air coming at 15 C from air conditioning does not add more moisture into the system?

If YES then,this problem can be easily solved as follows:

By using the given RH1 = 30% you can calculate the specific humidity w1.

w1=0.622 Pv/(P-Pv)

where,

P = atmospheric pressure = 101.325 kPa

Pv is calculated using RH1 = Pv/Psat (@T=30 C)

Pv = RH1 * Psat (@T=30 C)

since w1 = w2

Using the same formulae from above for cooled air, just that the Psat (@T=25 C) will change.

So,

RH2 = Pv/Psat(@T=25 C)

Pv = vapor pressure remains the same in both cases.

[This problem can also be solved using a psychrometric chart.]

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If NO then,You will have to provide more information like what is the relative humidity of the air at 15 degrees C. What are the mass flow rates of incoming streams and outgoing streams, etc