26.5k views
2 votes
A classroom is provided with the summer air conditioning system. The outside air is at 320 C DBT and 220 C WBT. The air passes through the cooling and dehumidification coil and comes out 220C and 55% RH. The amount of air supplied is 30m3/min. Find out the following: a) Sensible heat gained or lost by the air. b) Latent heat gained or lost by the air. c) Sensible heat factor

User Illabout
by
8.6k points

1 Answer

3 votes

The air conditioning system in the classroom cools and dehumidifies the outside air. The outside air has a dry bulb temperature (DBT) of **32°C** and a wet bulb temperature (WBT) of **22°C** . After passing through the cooling and dehumidification coil, the air comes out at a temperature of **22°C** and a relative humidity (RH) of **55%** . The amount of air supplied is **30 m³/min** .

a) The sensible heat gained or lost by the air can be calculated using the formula:

Sensible Heat = Mass Flow Rate x Specific Heat x Temperature Change

Here, mass flow rate = volume flow rate x density, specific heat = 1.006 kJ/kg-K ², and temperature change = DBT_in - DBT_out.

Substituting the given values, we get:

Sensible Heat = 30 m³/min x 1.202 kg/m³ x 1.006 kJ/kg-K x (32°C - 22°C)

Therefore, the sensible heat gained or lost by the air is **361.08 kJ/min**.

b) The latent heat gained or lost by the air can be calculated using the formula:

Latent Heat = Mass Flow Rate x Latent Heat of Vaporization x Humidity Ratio Change

Here, mass flow rate = volume flow rate x density, latent heat of vaporization = 2454 kJ/kg ², and humidity ratio change = WBT_in - WBT_out.

Substituting the given values, we get:

Latent Heat = 30 m³/min x 1.202 kg/m³ x 2454 kJ/kg x (22°C - 17.6°C)

Therefore, the latent heat gained or lost by the air is **262.15 kJ/min**.

c) The sensible heat factor (SHF) is defined as the ratio of sensible heat to total heat in a cooling coil . It can be calculated using the formula:

SHF = Sensible Heat / Total Heat

Here, total heat = Sensible Heat + Latent Heat.

Substituting the values we obtained in parts a) and b), we get:

SHF = 361.08 kJ/min / (361.08 kJ/min + 262.15 kJ/min)

Therefore, the sensible heat factor is approximately **0.58**.

User General Redneck
by
8.9k points