Lab-Project B: AIR CONDITIONING
MECHENG 715 - Building Services
1. Introduction
An air-conditioning system comprises several thermodynamic processes. These processes are
arranged so that the temperature and relative humidity of the air can be controlled to provide the
desired “comfort level” in the air-conditioned space. Not only must the temperature be
“comfortable”, but also the relative humidity must be low enough so that an individual's body
can regulate its own temperature by perspiring, yet not too low as to cause dehydration.
In this laboratory class, each of the processes (i.e. heating, humidification, cooling, and
dehumidification) in the unit will be demonstrated and their effect on the air condition will be
studied with the help of a psychrometric chart.
2. Aims
The aims of the experiments are: (i) to understand the various air conditioning psychrometric
processes, and (ii) to study the working principles of an air heater, a steam humidifier and an air-
cooler (air conditioner).
3. Equipment
Figures 1, 2 and 3 show the schematics of the air-conditioning and refrigeration units. The
various components perform the following individual tasks:
Air Conditioning Unit
• Control Box: Contains the ON/OFF switch and controls the whole unit through a software.
• Duct: In which the conditioned air flows and is tested.
• Fan: Propels air to flow to the air conditioning unit at various speeds.
• Preheater and reheater heating coils: Used to preheat or reheat the air for various
experimental purposes. The preheater has a maximum heating power of 400 W.
• Sensors: Temperature and humidity sensors are located at points 1 to 4 (shown in Figure 1).
A speed sensor is located at point 4.
• Room: A room model that models the air-conditioned space.
• Humidifier / Boiler: Supplies moisture to the system for humidification purposes.
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Figure 1 Side view of the Air Conditioning Unit.
Figure 2 Top view of the Air Conditioning Unit.
Figure 3 Schematic of a simple vapour compression refrigeration unit.
Cooling System
Boiler System
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Refrigeration Unit (Cooler or Chiller)
• Compressor: Compresses the refrigerant and causes it to circulate.
• Condenser: Transfers heat from the refrigerant into the ambient.
• Expansion device: Throttles the refrigerant and reduces the temperature and pressure.
• Evaporator: Absorbs heat and acts to cool the air in the air conditioning unit.
4. Air Conditioning Psychrometric Processes
5. Heating and Humidification
Heating and humidification demonstration in the rig involves: 1) Sensible heating of the
incoming air by the preheater, and 2) Addition of moisture from a hot steam supply from the
humidifier/boiler. Note: φ symbolizes relative humidity in the figure below.
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The energy balance equations:
• For heating process (a-b):
̇ = ̇(ℎ − ℎ)
• For humidification process (b-c):
̇(ℎ − ℎ) ≈ ̇ℎ
6. Cooling and Dehumidification
For cooling and dehumidification (a-b), the energy balance comprises the sensible (air cooling)
and latent (moisture removal through condensation) components.
The energy balance equation can be written as:
̇ = ̇(ℎ − ℎ) − ̇ ℎ,@
The rate of moisture removal:
̇ = ̇( − )
<
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7. Test Cases
7.1. Scenario 1: Heating without humidification
This test simulates the heating process without humidification. The objective is to understand the
psychrometric processes involved. The procedure is as follows:
• Close the internal louvre; and open the inlet and outlet louvres fully.
• Set the fan setting to 50%.
• Test at preheater settings of 30% and 60%.
• The re-heater, cooler and boiler are turned off throughout the test.
7.2. Scenario 2: Heating with humidification followed by cooling with
dehumidification
This test simulates the heating with humidification process followed by that of cooling and
dehumidification. The objective is to understand the psychrometric processes involved. The
procedure is as follows:
• Close the internal louvre; and open the inlet and outlet louvres fully
• Set the fan setting to 30%.
• Test preheater setting of 30% to 60%.
• Turn on the cooler.
• Turn on the boiler at “full power”. Once steam is observed, set the boiler to 80%.
8. Data Analysis and Discussion
1. Populate the tables with the recorded data and perform the necessary calculations. Attach
the completed tables and a set of sample calculations for the 1st set of data for Scenario
1 only (i.e., Scenario 1 at Preheater 30%) to your submission.
Note: The mass flow rate calculations need to be up to four significant figures. Use this
formula to compute the mass flow rate:
̇ = 0.6 × × ×
where, ρ is the air density (kg/m3), A is the cross-sectional area of the duct (i.e., 0.04 m2
in this rig) and u is the air velocity (m/s).
Note: velocities near the walls and at the corners are lower than at the centre due to wall
frictions. The setup measures the flow rate at the centre of the duct. Therefore, a correction
factor is applied to calculate the average flow, which is 0.6 in this setup.
2. For each setting in Scenarios 1 and 2, using the average values, show the processes from
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points 1 to 4 on the psychrometric chart provided.
Note: use one (1) psychrometric chart for each setting in each scenario (i.e., prepare 4
charts in total) to show the processes from points 1 to 4).
3. For each setting in Scenarios 1 and 2, plot the average values of:
a. Relative humidity vs humidity ratio at points 1, 2, and 3
b. Temperature vs humidity ratio at points 1, 2 and 3
Use humidity ratio as the y-axis in your graphs and attach the graphs to your submission.
Describe the general relations between temperature, relative humidity and humidity ratio
according to your measurements.
4. Scenario 1: How did the temperature and humidity vary between points 1 to 2 and 2 to 3?
Do they agree with the theories? Discuss.
5. Scenario 2: How did the temperature and humidity vary between points 1 to 2 and 2 to 3?
Do they agree with the theories? Discuss.
6. Project: Refer to a separate document for the details of the project exercise, which are
to be supplied by the Tuesday 4pm lecture in Week 10, S2. Complete the project part of
this assessment and attach your analysis in no more than 3 pages, to the Lab Report.
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9. Useful Formulae
• Humidity ratio:
ω =
=
• Humidity ratiReport.so be calculated from:
ω = 0.622
−
where, ϕ is the relative humidity and = @
• Enthalpy of moist air:
ℎ [/] = 1.005 + (1.82 + 2501.3)
where, T is the temperature of moist air in °C.
• Mass flow rate of air:
̇ = 0.6 × × ×
where, ρ is the air density (kg/m3), A is the cross-sectional area of the duct (i.e., 0.04 m2
in this rig) and u is the air velocity (m/s).
• Rate of heating (with or without humidification):
ℎ = ̇ × (ℎ2 − ℎ1)
where subscripts 1 and 2 refer to the air entering and leaving the heating &
humidification zone (see Figures 1 and 2).
• Rate of cooling (with dehumidification):
= ̇ × (ℎ3 − ℎ2)
where subscripts 2 and 3 refer to the air entering and leaving the cooling &
dehumidification zone (see Figures 1 and 2).
• Coefficient of performance (cooling mode):
= ℎ, − ℎ,
ℎ, − ℎ,
SCENARIO 1: Boiler setting 0%, Fan setting 50%, Closed internal louvre, Fully open inlet and outlet louvre, Cooler off
Preheater
settings
[%]
Temp.
T1
[°C]
Rel.
Humid.
ϕ1
[%]
Temp.
T2
[°C]
Rel.
Humid.
ϕ2
[%]
Temp.
T3
[°C]
Rel.
Humid.
ϕ3
[%]
Temp.
T4
[°C]
Rel.
Humid.
ϕ4
[%]
Air
Velocity
u
[m/s]
Humid.
Ratio
x2
[gw/kga]
Enthalpy
h2
[kJ/kg]
Humid.
Ratio
x3
[gw/kga]
Enthalpy
h3
[kJ/kg]
Humid.
Ratio
x4
[gw/kga]
Density
ρ4
[kg/m3]
Mass
Flow
Rate
[kg/s]
Heating
Power
[kW]
30
Only calculate the average values
Average
60
SCENARIO 2: Boiler setting 80%, Fan setting 30%, Cooler on, Closed internal louvre, Fully open inlet and outlet louvre
Preheater
settings
[%]
Temp.
T1
[°C]
Rel.
Humid.
ϕ1
[%]
Temp.
T2
[°C]
Rel.
Humid.
ϕ2
[%]
Temp.
T3
[°C]
Rel.
Humid.
ϕ3
[%]
Temp.
T4
[°C]
Rel.
Humid.
ϕ4
[%]
Air
Velocity
u
[m/s]
Humid.
Ratio
x2
[gw/kga]
Enthalpy
h2
[kJ/kg]
Humid.
Ratio
x3
[gw/kga]
Enthalpy
h3
[kJ/kg]
Density
ρ4
[kg/m3]
Humid.
Ratio
x4
[gw/kga]
Mass
Flow
Rate
[kg/s]
Heating
Power
[kW]
Cooling
Power
[kW]
30
Only calculate the average values
Average
60
Only calculate the average values
Average