HVAC Psychrometry, Air Handling Systems and
Duct Selection
For solution, email mikelo.academy@gmail.com
Psychrometry
1. Explain the physical phenomenon that causes the wet bulb temperature to be
lower than the dry bulb temperature.
2. During a rainy day, it is found that the dry bulb temperature of the air is 25°C
with a RH of 100%. What is the wet bulb temperature and dew point of the air?
How much more water vapour can the air contain?
3. A stream of air having a mass flow rate of 0.5 kg/s flows through a heat
exchanger and undergoes 10 kW of sensible cooling. Before the heat transfer,
the air has a TDB of 45°C and RH of 20%. What is the new TDB and RH of the air
after the cooling takes place? Find the change in specific enthalpy. (specific
heat capacity of air = 1.0 kJ/kg.K)
Property of Mike Academy, Copyright ©
Page 1
4. An air stream originally having a TDB of 30°C and TDew of 25°C flows through a
desiccant wheel and is being dehumidified. The mass flowrate of the air is 0.6
kg/s. If the air loses 6.8 kW of latent energy in the process, find the new
humidity ratio of the air. What is the change in enthalpy? (Latent heat of
vaporization of water = 2,260,000 J/kg)
Property of Mike Academy, Copyright ©
Page 2
5. A cold stream of air (0.8 kg/s) having TDB of 15°C and RH 80% of are mixed
with a warmer stream of air (1.2 kg/s) having TDB of 35°C and TWB of 25°C. Find
the TDB and relative humidity of the stream of mixed air.
Property of Mike Academy, Copyright ©
Page 3
6. In the AHU for an office space, the parameters for the return air, outdoor air
and supply air are measured and indicated in the diagram below. The mass
flow rates of the return air and outdoor air are 1.5 kg/s and 0.5 kg/s
respectively. Find the sensible load, latent load and sensible heat ratio of the
cooling coil. If the Delta T of the chilled water is to be maintained at 5.5 °C,
find the mass flow rate of the chilled water.
Property of Mike Academy, Copyright ©
Page 4
Property of Mike Academy, Copyright ©
Page 5