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482 ENGINEERING THERMODYNAMICS

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Example 10.19. It is required to design an air-conditioning system for an industrial proc-
ess for the following hot and wet summer conditions :
Outdoor conditions ...... 32ºC DBT and 65% R.H.
Required air inlet conditions ...... 25ºC DBT and 60% R.H.
Amount of free air circulated ...... 250 m^3 /min.
Coil dew temperature ...... 13ºC.
The required condition is achieved by first cooling and dehumidifying and then by heating.
Calculate the following :
(i)The cooling capacity of the cooling coil and its by-pass factor.
(ii)Heating capacity of the heating coil in kW and surface temperature of the heating coil if
the by-pass factor is 0.3.
(iii)The mass of water vapour removed per hour.
Solve this problem with the use of psychrometric chart.
Solution. Refer Fig. 10.23.

Fig. 10.23

l Locate the points ‘1’, ‘5’ and ‘3’ as shown on psychrometric chart.

l Join the line 1-5.

l Draw constant specific humidity line through ‘3’ which cuts the line 1-5 at point ‘2’.

The point ‘2’ is located in this way.

From psychrometric chart :

h 1 = 82.5 kJ/kg, h 2 = 47.5 kJ/kg

h 3 = 55.7 kJ/kg, h 5 = 36.6 kJ/kg