Learn2Grow Club CA3722 HVAC Engineering Mock Exam Paper 2025
Learn 2 Grow . Club
CA3722 HVAC Engineering
Mock Exam Paper with Solutions 2025
Duration
2 hours 30 minutes
Answer all 5 questions
Each with 20 marks
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, Learn2Grow Club CA3722 HVAC Engineering Mock Exam Paper 2025
Q1
An AHU takes in outdoor air at 5 OC and 20% relative humidity at a steady rate of 60
m3/min. The outdoor air is first heated to 22 OC in the heating section, and then in the
humidifying section it injects hot steam to condition the moist air to 25 OC and 60%
relative humidity.
a) Assuming the entire process takes place at a pressure of 100 kPa, determine
1. the heat rate to be supplied in the heating section; (5 marks)
2. the degree of saturation µ ; (4 marks)
3. the required steam mass flow rate in the humidifying section.
(5 marks)
b) The above conditioned air is then adiabatically mixed with 10 m3/min of
recirculated air at 20 OC dry-bulb temperature and 40% relative humidity.
Determine the dry-bulb temperature, humidity ratio, and relative humidity of
the resulting mixture. (6 marks)
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, Learn2Grow Club CA3722 HVAC Engineering Mock Exam Paper 2025
Q2
Consider a two-stage compression refrigeration system with a flash chamber, and the
working fluid is refrigerant-134a. The operation is between the high-pressure limit 0.7
MPa and low-pressure limit 0.18 MPa. The inter-stage pressure is set to be 0.5 MPa.
The refrigerant leaves the condenser as a saturated liquid, and is then throttled by a
high-pressure expansion valve to a flash chamber. In the flash chamber, there are
saturated liquid and saturated vapor only.
The saturated vapor in the flash chamber is then feedbacked to mix with the
superheated refrigerant leaving from the low-pressure compressor. This mixture then
enters the high-pressure compressor to be compressed to the condenser pressure.
On the other hand, the saturated liquid in the flash chamber is throttled by a low-
pressure expansion valve to the evaporator pressure.
Assuming the refrigerant leaves the evaporator as a saturated vapor. Both
compressors are isentropic and both expansion valves undergo adiabatic process.
a) Refer to the following schematic diagram illustrating this two-stage
refrigeration system, draw the corresponding P-h diagram. (4 marks)
b) Find the mass fraction of the saturated vapor refrigerant in flash chamber.
(4 marks)
c) Determine the amount of heat removed by the evaporator per unit mass of
refrigerant flowing through the condenser. (4 marks)
d) Determine the total compressor work of the 2 compressors per unit mass of
refrigerant flowing through the condenser. (6 marks)
e) Calculate the coefficient of performance COP. (2 marks)
www.Learn2Grow.Club
Learn 2 Grow . Club
CA3722 HVAC Engineering
Mock Exam Paper with Solutions 2025
Duration
2 hours 30 minutes
Answer all 5 questions
Each with 20 marks
www.Learn2Grow.Club
, Learn2Grow Club CA3722 HVAC Engineering Mock Exam Paper 2025
Q1
An AHU takes in outdoor air at 5 OC and 20% relative humidity at a steady rate of 60
m3/min. The outdoor air is first heated to 22 OC in the heating section, and then in the
humidifying section it injects hot steam to condition the moist air to 25 OC and 60%
relative humidity.
a) Assuming the entire process takes place at a pressure of 100 kPa, determine
1. the heat rate to be supplied in the heating section; (5 marks)
2. the degree of saturation µ ; (4 marks)
3. the required steam mass flow rate in the humidifying section.
(5 marks)
b) The above conditioned air is then adiabatically mixed with 10 m3/min of
recirculated air at 20 OC dry-bulb temperature and 40% relative humidity.
Determine the dry-bulb temperature, humidity ratio, and relative humidity of
the resulting mixture. (6 marks)
www.Learn2Grow.Club
, Learn2Grow Club CA3722 HVAC Engineering Mock Exam Paper 2025
Q2
Consider a two-stage compression refrigeration system with a flash chamber, and the
working fluid is refrigerant-134a. The operation is between the high-pressure limit 0.7
MPa and low-pressure limit 0.18 MPa. The inter-stage pressure is set to be 0.5 MPa.
The refrigerant leaves the condenser as a saturated liquid, and is then throttled by a
high-pressure expansion valve to a flash chamber. In the flash chamber, there are
saturated liquid and saturated vapor only.
The saturated vapor in the flash chamber is then feedbacked to mix with the
superheated refrigerant leaving from the low-pressure compressor. This mixture then
enters the high-pressure compressor to be compressed to the condenser pressure.
On the other hand, the saturated liquid in the flash chamber is throttled by a low-
pressure expansion valve to the evaporator pressure.
Assuming the refrigerant leaves the evaporator as a saturated vapor. Both
compressors are isentropic and both expansion valves undergo adiabatic process.
a) Refer to the following schematic diagram illustrating this two-stage
refrigeration system, draw the corresponding P-h diagram. (4 marks)
b) Find the mass fraction of the saturated vapor refrigerant in flash chamber.
(4 marks)
c) Determine the amount of heat removed by the evaporator per unit mass of
refrigerant flowing through the condenser. (4 marks)
d) Determine the total compressor work of the 2 compressors per unit mass of
refrigerant flowing through the condenser. (6 marks)
e) Calculate the coefficient of performance COP. (2 marks)
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