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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.
Page 2
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
Page 3
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.
Page 4
The energy balance equations:
• For heating process (a-b):
̇ = ̇(ℎ − ℎ)