Introduction to HVAC
HEATING : is process of increasing the
temperature of the substance or a body or
thermodynamic system heating system
are design for colder climates system
HEATING : Designing the system for cold
Cooling : is process of decreasing
temperature of the substance or body
Cooling : Designing the system for warmer
or Hot climate
Ventilation : is the process to maintains
the indoor air quality
Ventilation : extraction of air (exhaust +
Air conditioning :condition the air to
provide human comfort by maintaining
artificial temp, relative humidity, purifying
the air through filter, noise level & by
providing fresh air to improve indoor air
Air conditioning is the process of altering
PRINCIPAL OF AC SYSTEM
Purify of air
The goal is to keep it more comfortable
inside the house than it is outside
Human comfort conditions
Relative humidity 50%
Temp 24.4◦C /76*F
Dust filtration –fr
This human comfort is define by ASHRAE
American society for heating refrigeration
and air condition engineering
Vapour compression cycle
Most common refrigeration cycle in use
► There are four principal
control volumes involving
All energy transfers by work and heat are taken
as positive in the directions of the arrows on the
schematic and energy balances are written
Process 4-1: two-phase liquid-vapor
mixture of refrigerant is evaporated
through heat transfer from the
Process 1-2: vapor refrigerant is
compressed to a relatively high
temperature and pressure requiring
Process 2-3: vapor refrigerant
condenses to liquid through heat
transfer to the cooler surroundings.
Process 3-4: liquid refrigerant
Vapor Absorption cycle
The vapour absorption refrigeration system is one
of the method of producing refrigerating effect.
Uses heat energy instead of mechanical energy
as in vapour compression system.
In the vapour absorption system the compressor
is replaced by an absorber, a pump, a generator,
and a pressure reducing valve.
These componet in vapour absorption system
perform the same function as that of a
compressor in vapour compression system
It mainly consists of three parts
ANALYSER-When ammonia is vapourised in the
generator some water is also vapourised,and flow into
the condenser along with ammonia .
if these unwanted particle are not removed before
entering into the condenser,they will enter into the
expansion valve where they freeze and choke the pipe
line,so in order to remove the unwanted particle flowing
in the condeser the analyser is used.
The subject which deals with the behavior
of moist air is know as psychometric
Psychometric is the science dealing with
the physical laws of air-water mixtures.
Psychometric chart contains relation
between properties of air.
The properties of mixture of air and water
vapour are as follows
Properties of air
Dry air : it is the mixture nitrogen and
oxygen neglecting small percentage of
Dry bulb temperature :it is the temperature
of air measured by thermometer
Wet Bulb temperature : it is the
temperature of air measured by a
thermometer whose bulb is covered with a
wet wick or cloth and kept in current of
Dew point temperature (change of phase):
it is the temperature of the air when it is
fully saturated and the moisture
condenses on a surface.
Relative Humidity : it is the ratio of the
actual moisture present in the air to the
maximum moisture the air can hold.
Humidity ratio: describes the actual weight
of water in an air-water vapour mixture
also humidity ratio can be expressed as
grains of moisture per pound of dry air.
Types of A/C
Window air conditioners are one of the most commonly
used and cheapest type of air conditioners.
To install one of these units, you need the space to
make a slot in the wall, and there should also be some
open space behind the wall.
Window air-conditioner units are reliable and simple-to-
install solution to keep a room cool while avoiding the
costly construction of a central air system.
Better yet, when the summer heat dies down, these units
can be easily removed for storage, and you can use the
window sill for other purpose
The split air conditioner comprises of two parts: the
outdoor unit and the indoor unit.
The outdoor unit, fitted outside the room, houses
components like the compressor, condenser and
The indoor unit comprises the evaporator or cooling coil
and the cooling fan. For this unit you don’t have to make
any slot in the wall of the room.
Further, the present day split units have aesthetic looks
and add to the beauty of the room. The split air
conditioner can be used to cool one or two rooms
The window and split air conditioners are usually used
for the small air conditioning capacities up to 5 tons.
The central air conditioning systems are used for where
the cooling loads extend beyond 20 tons.
The packaged air conditioners are used for the cooling
capacities in between these two extremes.
The packaged air conditioners are available in the fixed
rated capacities of 3,5, 7, 10 and 15 tons.
These units are used commonly in places like
restaurants, telephone exchanges, homes, small halls,
The central air conditioning plants or the systems are
used when large buildings, hotels, theaters, airports,
shopping malls etc. are to be air conditioned completely.
The window and split air conditioners are used for single
rooms or small office spaces.
If the whole building is to be cooled it is not economically
viable to put window or split air conditioner in each and
Further, these small units cannot satisfactorily cool the
large halls, auditoriums, receptions areas etc.