How to use Psychrometric chart to estimate the air conditioner capacity?

This note, I illustrate “How to estimate the air conditioning cacacity with Psychrometric chart?”.

Two important thinks to know for using Psychrometric chart:

1. We have to measure the two properties of air in order to specify the “air state point” in the Psychrometric chart. The other properties will be read after specify this point. (For this example, we measure dry bulb temperature and relative humidity of the room air (or return air)).
2. In order to estimate the capacity of the air-conditioner (FCU in chis example) we have to measure the other two:
   2.1 The supply air state (also two properties are required to plot in Psychrometric chart). Be careful when measure supply air condtion, it have to insert the measurement prob deep enought to the sense the actual supply air condition, otherwise what you get is just the mixing of supply air and room air condition. This will lead to wrong capacity estimation.
   2.2 The supply air flow. In this case the FCU is also act as a recirculation unit (no fresh air mixed with return air). So the FCU capacity will be estimated from these parameters.

FCU capacity (Watt) = 1.20 x L/s x dh
L/s = supply air flowrate in L/s
dh = enthalpy difference (kJ/kg)

Note:

the only one property don’t give you the actual, so

1. Measure two properties of air —> you will get the point in Psychrometric chart
2. Measure two conditions with air flowrate —> you will get the capacity of the air-conditioner.