UNIT-2 HVAC (HEATING,

VENTILATION & AIR

CONDITIONING)

VENTILATION - Natural
and Mechanical
Ventilation, Conditions
of comfort, Principle of
Refrigeration, comfort
conditions,
temperature control,
humidity control, air
filtration - Mechanical
ventilation in buildings
- Fans, blowers and air
filters.
NATURAL
NATURAL
NATURAL
NATURAL
MECHANICAL
MECHANICAL
MECHANICAL
MECHANICAL
 PRINCIPLE OF REFRIGERATION

The principle of refrigeration is to remove heat from one

area (i.e inside) and locate it to another area (i.e
outside).
COMFORT CONDITIONS
COMFORT CONDITIONS
COMFORT CONDITIONS
UNIT-2 HVAC (HEATING, VENTILATION & AIR CONDITIONING)

AIR CONDITIONING - refrigeration and air cycle - various systems of air conditioning - Unit, split, Package, Direct
Expansion, Chilled water System - Scope - Layout of Ducts - Fan Coil System - Window A.C. Unit - split Unit, Blowers
& Diffusers, Cooling Towers - air conditioning layout, fittings and fixtures.
 AIR CONDITIONING

Air conditioning is the process of altering the properties

of air (primarily temperature and humidity) to more favourable
conditions.

More generally, air conditioning can refer to any form of

technological cooling, heating, ventilation, or disinfection that
modifies the condition of air.

In construction, a complete system of heating, ventilation and air

conditioning is referred to as "HVAC".
 Types of AIR CONDITIONING

Windows AC
Split AC
Tower AC
Cassette AC
Cube Air Conditioner

CENTRAL AIR CONDITIONER PLANTS

Direct Expansion (DX) Type of Central Air Conditioning Plant or System

Chilled Water Central Air Conditioning Systems
Windows AC
These types of AC are designed to be fitted in window sills. A single
unit of Window Air Conditioner houses all the necessary
components, namely the compressor, condenser, expansion valve
or coil, evaporator and cooling coil enclosed in a single box. Since a
window AC is a single unit, it takes less effort to install as well as
for maintenance.

Advantages
Single unit air conditioner
Less effort needed for installation
Costs lesser in comparison to other varieties
Split AC
These are kits of 2 units, one internal and another external. The indoor unit installed
inside a room intakes warm air and throws in cold air. The outdoor unit on the other hand
is installed out of the house. It contains the compressor and is linked to the internal unit
via drain pipes and electric cables. This external unit throws out the warm air.

Advantages Internal unit takes up less space for installation

Usually more silent than window ACs
Minimally affect your home decor
Can be installed in room with no windows
Tower AC
These are also known as floor-standing air conditioners.
Like split ACs, a tower AC set consists of 2 units- one
internal and an external. However, the indoor unit doesn’t
need wall installation. It rather occupies some space on
the floor. Tower air conditioners usually have high cooling
capacity and suitable for very large rooms.

Advantages
Suitable for high capacity cooling
Ideal for large rooms at home and in offices
Doesn't need windows or wall installation
CASSETTE AC
These space-saving ACs are shaped like cassettes and
are designed to be installed on ceilings. The panel of
these air conditioners is designed to blend with all
kinds of home décor. They are stylish, and are known
to deliver fantastic performances. Most cassette type
air conditioners require no ducting. They are perfect
for large spaces where windows or split AC may not
reach out.

Advantages Best at saving space

Able to cool large areas where other ACs don’t reach
out
Blends with decor
CUBE AIR CONDITIONER
This fairly new design introduced by Panasonic can be mounted close to a
ceiling or at the window level. Basically, this is a smaller version of the split
type air conditioner and costs less than the former. The indoor unit features a
newly designed diagonal propeller fan for efficient and fast cooling. Improved
blade shape curvature and larger intake grill further aid for efficient
performance.
 CENTRAL AIR CONDITIONER PLANTS
There are two types of central air conditioning systems: Direct Expansion (DX)
type of central air condition plants and Chilled Water type of the central air
conditioning plants. In this series of articles both these plants and air handling
units have been described.

Direct Expansion (DX) Type of Central Air Conditioning Plant or System

Chilled Water Central Air Conditioning Systems

Air Handling Units or Fan Coil Units

Central Air Washer or Central Evaporative Air Cooling Plant
 CENTRAL AIR CONDITIONING PLANT ROOM
The plant room comprises of all the important components of the
chilled water air conditioning plant.

These include the compressor, condenser, thermostatic expansion

valve and the evaporator or the chiller.

The compressor is of open type and can be driven by the motor directly
or by the belt via pulley arrangement connected to the motor. It is
cooled by the water just like the automotive engine.
The condenser and the evaporator are of shell and tube type. The
condenser is cooled by the water, with water flowing along the shell
side and refrigerant along the tube side. The thermostatic expansion
valve is operated automatically by the solenoid valve.
The evaporator is also called as the chiller, because it chills the water.
If the water flows along the shell side and refrigerant on the tube side,
it is called as the dry expansion type of chiller. If the water flows along
tube side and the refrigerant along the shell side, it is called as the
flooded chiller.

The water chilled in the chiller is pumped to various parts of the building
that are to be air conditioned. It enters the air handling unit, cools the air in
cooling coil, absorbs the heat and returns back to the plant room to get
chilled again. The amount of water passing into the chiller is controlled by
the flow switch.
AIR HANDLING UNIT ROOMs
The air handling units are installed in the various parts of the building that are to be air
conditioned, in the place called air handling unit rooms.

The air handling units comprise of the cooling coil, air filter, the blower and the supply
and return air ducts. The chilled water flows through the cooling coil.

The blower absorbs the return hot air from the air conditioned space and blows it
over the cooling coil thus cooling the air.

This cooled air passes over the air filter and is passed by the supply air ducts into
the space which is to be air conditioned.

The air handling unit and the ducts passing through it are insulated to reduce the loss of
the cooling effect.
COOLING TOWER

The cooling tower is used to cool the water that absorbs heat from
the compressor and the condenser.

When water flows through these components some water gets

evaporated, to make up this loss some water is also added in the
cooling tower.

The cooling tower is of evaporative type. Here the water is cooled by

the atmospheric air and is re-circulated through the compressor
and the condenser.
http://www.brighthubengineering.com/hvac/
50548-central-air-washer-or-central-
evaporative-air-cooling-plant/

AIR HANDLING UNITS OR FAN COIL UNITS

COOLING COIL
The cooling coil is one of the most important parts of the air handling units. It
is made up of copper tubing of several turns and covered with the fins to
increase the heat transfer efficiency of the cooling coil.

In direct expansion (DX) type of the central air conditioning plants the refrigerant
flows though the cooling coil, which also acts as the evaporator of the plant.

In case of the chilled water system the chilled water from the chiller flows through
the cooling coil. In packaged and the split air conditioners also the refrigerant
flows directly through the cooling coil, thus acting as the evaporator of the system.

The hot return air from the room flows over the cooling coil and gets cooled. This
air is supplied to various rooms via the ducts..
DUCTS

The air handling is connected to the supply air and return air ducts.
The supply air duct supplies the cool air from the air handling unit to
various rooms, while the return air supplies hot return air from
various rooms back to the air handling unit.

There is one main supply duct that bifurcates into various small
ducting that are laid in all the rooms that are to be cooled. The return
ducts from all the rooms also end into one main duct.

All the supply and return air ducts are covered with the insulation
material to prevent the loss of the cooling effect. The ducts are
designed and laid such that there is even distribution of the cooled air to
the rooms as per their heat loads and there is least wastage of the cooling
effect.
FAN OR BLOWER

The fan or the blower sucks the hot return air from the room and blows it
over cooling coil, cools it and sends it to the room to be air conditioned.

There are two possible arrangements of the fans in air handling units: draw
though arrangement and blow through arrangement.

In the draw through arrangement the fan sucks the return air through the
filter and the cooling coil. As the air passes over the cooling coil its gets
chilled, it is then passed to the rooms to be cooled.

In case of the blow through arrangement the fan absorbs the return air and
blows it over the air filter and the cooling coil. The air then flows to the rooms
to be air conditioned. The draw through arrangement is used more commonly
due to its compactness. The fans are of centrifugal types.
AIR FILTER

Air filter is one the important parts of any air conditioning

system.

The air filter removes dirt, dust, smoke and other

impurities from the air and cleans.

The air filter is usually attached to the cooling air and before
it.

The air is first absorbed or pushed over the air filter and
then over the cooling coil.
INTRODUCTION TO CENTRAL EVAPORATIVE AIR COOLING
PLANT

In the previous articles of this series we saw DX and Chilled types of

central air conditioning plants.

In these plants the regular refrigeration cycle is used comprising of

components like compressor, condenser, expansion valve and the
cooling coil or evaporator.

The central air washer is nothing but an evaporative or desert

cooler. The small desert cooler is used for rooms and halls, just like
the window and split air conditioners.