The Basics of HVAC systems.

1. Heat Ventilation and
Air Conditioning
Aroh Thombre

2. What Is HVAC?
HVAC (heating, ventilating/ventilation, and air conditioning) is the technology of indoor and vehicular
environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality.
Why do we need HVAC?
• In a well climatically designed building human comfort factors are controlled naturally, that is the best
solution.
• In big building/complexes it is difficult to design entire building comfortably by natural energy sources like
sun, wind, orientation etc. In such cases we have to take the help of mechanical mean for obtaining
comfortable conditions inside the building.
• Improvement of the air quality
• Moisture regulation
• Maintenance of the constant temperature throughout the year
• Energy conservation

3. Terminologies related to HVAC:
• Dry-bulb temperature: It is the temperature of air measured by a thermometer freely exposed to the air but
shielded from radiation and moisture. It is called "Dry Bulb“ because the air temperature is indicated by a
thermometer not affected by the moisture of the air.
• Wet-bulb temperature: It is a type of temperature measurement that reflects the physical properties of a
system with a mixture of a gas and a vapour , usually air and water vapour . This is the temperature indicated
by a moistened thermometer bulb exposed to the air flow.
• Dew point: The dew point is the temperature at which water vapour starts to condense out of the air (the
temperature at which air becomes completely saturated).
• Latent heat : Heat energy added or removed as a substance changes its state, whilst temperature remains
constant.
• Absolute humidity: Absolute humidity is the total amount of water vapour presentin a given volume of air. It
does not take temperature into consideration.
• Relative humidity: Relative humidity (RH) is the ratio of water contained in air at a given dry bulb
temperature, as a percentage of the maximum amount of water that could be held in air at that temperature.

4. Terminologies related to HVAC:
• Specific humidity: It is the mass of water vapour present in a unit mass of air. This is also called “moisture
content”.
• Sensible heat gain: Heat that causes a change in temperature in an object is called sensible heat.
• Evaporative cooling: Evaporative cooling produces effective cooling by combining a natural process -water
evaporation -with a simple, reliable air-moving system.
• Condensation : Condensation is the change of the physical state of matter from gaseous phase into liquid
phase, and is the reverse of evaporation.
• Entropy : Measure of total heat energy in a refrigerant for every degree of temperature (kj/kgƒc).

5. What is an Air Conditioner?
An Air Conditioner is like a refrigerator without the insulated box. It evaporates a refrigerant, like Freon, to
provide cooling. Most Air Conditioners Have:
• Compressor: Heart of the system, belt driven pump that fastened to engine. Responsible for compressing
and transferring refrigerant. Very high volumetric efficiency (almost 98%) Lesser Noise and lighter
compared to rotary compressor.
• Condenser: Responsible for heat dissipation. The condenser is designed to radiate heat. Located in front of
the radiator. Require good air flow when system is in operation. Plate fin type heat exchanger with micro
channels used. Hot compressed refrigerant vapour cools at constant pressure to liquid.
• Evaporator: Heat absorption component. Used remove heat from the inside of vehicle. Secondary benefit -
dehumidification. Unconditioned air passes through a filter before entering the evaporator.
Types of Air Conditioning Systems:
2. Non Ducted
• Split Type
• Window Type
1. Ducted
• Packed Type
• Centralized Type

6. Schematic Air Conditioning Layout

7. Schematic Refrigeration Cycle

8. Packed Air Conditioning Systems:
Package air conditioner is a bigger version of the window air
conditioner. However, unlike window air
conditioner or PTAC units, it has a higher cooling or heating
capacity and is usually able to cool an entire house or a
commercial building. The nominal capacities ranges from 3
tonne to 15 tonne.
The conditioned air are transferred to the space to be
conditioned through ducting which is usually hidden in the
ceiling and wall of the building. The unit is placed outside
the house, a special room in a building or even on top of a
roof. This unit is factory assembled and skilled technicians
are needed to install this type of unit.
There is an interlocking circuit with the evaporator fan
motor starter to ensure that the compressor can only start if
the fan motor is running.

9. Packed Air Conditioning Systems:
Components
This self contained unit is assembled in a casing where all the air conditioning components are housed. They
include:
•Compressor usually hermetic or semi-hermetic type for operation on 380/400 Volts 3 Phase is used.
•Water-cooled or Air-cooled condenser.
•Electrical Panel.
•Thermostatic Expansion Valve.
•Air Filter.
•Front Panel & Return Air Grill.
•Evaporator Coil.
•Evaporator Fan And Housing.
•Heating and Humidifying Components may be included in the unit. Dehumidification is needed for cooling
mode during summer and Humidification for heating mode during winter.

10. Centralized Air Conditioning Systems:
• The typical central air conditioning system is a split system, with
an outdoor air conditioning, or "compressor-bearing unit" and an
indoor coil, which is usually installed on top of the furnace in the
home.
• Using electricity as its power source, the compressor pumps
refrigerant through the system to gather heat and moisture from
indoors and remove it from the home.
• Heat and moisture are removed from the home when warm air
from inside the home is blown over the cooled indoor coil. The
heat in the air transfers to the coil, thereby "cooling" the air.
• The heat that has transferred to the coil is then "pumped" to the
exterior of the home, while the cooled air is pumped back inside,
helping to maintain a comfortable indoor temperature.
• Central air conditioning can also be provided through a package
unit or a heat pump.
Centralized System

11. Centralized Air Conditioning Systems:
Most Important Component of Central system:
Air Handling Unit:
An Air Handling Unit (most of the times abbreviated to AHU), or Air Handler, is a central air conditioner station
that handles the air that, usually, will be supplied into the buildings by the ventilation ductwork (connected to
the AHU). Handling the air means that the air will be delivered into the building spaces with thermo-hygrometric
and IAQ (Indoor Air Quality) treatment. The accuracy of the treatment will depend from the specificity of each
project (offices, schools, swimming-pools, laboratories, factories with industrial processes, etc). This means, the
Air Handling Unit treat the air by filtering,
cooling and/or heating, humidifying and/or
dehumidifying. There are several types of Air
Handling Units: Compact, Modular, Residential,
DX integrated, Low Profile (ceiling), Packaged,
Rooftop mounted .
Schematic Section of AHU

12. Centralized Air Conditioning Systems:
Air Handling Unit:
Components
To be considered as an Air Handling Unit a minimum of components must considered, to know: at least 1
filtration section, 1 heat transfer component (cooling/heating coil or heat recovery system) and 1 fan.
The Air Handling Units can have several components, depending on the complexity and requirements, such as
energy efficiency, of each specific building and application. Some of the most known components are:
- Fans (Plug Fans, Double Inlet, Single Inlet, Axial, etc)
- Filters (Plate Filters, Bag Filters, Compact Filters, EPA Filters, HEPA Filters, ULPA Filters, Carbon Filters)
- Cooling/Heating Coils (water/steam/Direct Expansion DX/electric/gas fired)
- Heat recovery systems (cross flow plate heat exchangers, cross flow plate heat exchangers, )
- Humidifiers (Adiabatic/Evaporative Pad, non-pressurized Steam, pressurized steam)
- Ultraviolet UV disinfection lamps
- Photocatalytic oxidation (PCO) air cleaners
- Mist/Droplet eliminators
- Dampers

13. Split Air Conditioning Systems:
A split air conditioner is made up of two primary parts that a very familiar: the evaporator and the compressor.
The difference with a mini-split system is that they are separated into two different, distant components, one
being outdoors and one being indoors. The outdoor section is a compressor that initiates the cooling process,
while the indoor component consists of an evaporator and fan.
The two sections are connected with a set of electrical wires and tubing, also called lines, used to transport air
between the two sections. It's these lines that allow the split AC to be considered ductless, and the fact that the
wires and tubing are so small and discreet compared to large ducts is where the "mini" split name comes from.
Function
The compressor is controlled by an internal thermostat. As the thermostat detects warm air, it activates the
outdoor compressor. The compressor circulates a refrigerant gas, increasing the pressure and temperature of the
refrigerant as it compresses it through a series of pipes. The refrigerant then moves to the condenser for further
processing.
In the condenser, a cooling system removes heat from the high-pressure gas and the gas changes phase and
becomes a liquid. This chilled liquid is pushed through tubing indoors until it reaches the evaporator system .

14. Split Air Conditioning Systems:
Inside the home, the evaporator fan collects warm air and passes it through a chamber containing the chilled
liquid refrigerant. The fan system blows this air, which has now been cooled, back into the room, lowering the
overall temperature of the space. If the thermostat still detects air that is warmer than desirable, the process
continues, and the refrigerant and any excess heat that remains in the system are passed back outdoors to the
compressor in order to begin the cycle again.

15. Window Air Conditioning Systems:
Window air conditioners are comprised of components like the compressor, condenser, expansion valve or
expansion coil, and the evaporator or the cooling coil, all housed in a single box. There is also a motor which
has shafts on both sides. On one side of the shaft the blower is connected, which sucks hot air from the room
and blows it over the cooling coil, thus cooling it and sending it to the room. On the other shaft the fan is
connected, which blows the air over Freon gas passing through the condenser.
Window Type System