All air system

1. The Basic Concepts of Air
Conditioning

2. Introduction
• Although man’s struggle to control the
climate about him begain long ago….

3. • And effectively began in 1902 when
Willis H Carrier introduced scientific air
conditioning to the world.

4. Five factors
Comfort air AC can be defined as the
maintenance of five atmospheric factors.
Dry Bulb Temperature
Relative Humidity
Air Cleanliness
Odor Level
Mean Radiant Temperature

5. We spend 8+ hours

6. Figure represents a typical
office space in which the
working man will spend 8
hours per day. Heat flows
into the space from people,
equipment, lights, and the
ambient environment

7. Controlling a conditioned
space demand
the use of an air
conditioning system. All air
conditioning systems (Figure
below) fall into one of four
major categories - each type
having certain functional and
economic advantages.

9. All Air System
During the cooling mode of
operation, this system
supplies cool dehumidified
air (Figure below) to the
space to absorb heat and
moisture. The space
temperature is usually
maintained
around 75°F and 50%-
Relative humidity.
• Air entering the space should
be typically drier (less
moisture content than the

11. • The supply air is made cool
and dry-
(relative to the conditioned
space) by
passing through a coil
(Figure below)
whose surface temperature is
colder
than the air.
• The coil both cools the air,
and removes moisture from the
air.

13. • The cold supply air is transmitted from the
coil to the conditioned space through a
supply air duct system.
• The duct system is insulated to prevent
ambient moisture from condensing on the
cold duct surfaces.
• Power required to move the air through the
duct system is provided by a supply air fan.
• Shown below are the details…

16. • The use of a .supply air terminal
(Figure above) is required to
provide good,air motion in the
conditioned space.
• Good air motion facilitates
absorbing the space cooling load,
and prevents drafts or dumping of
cold air on the occupant. Proper
selection and location of the
supply air terminal is therefore
essential in providing "comfort“

17. What will happen if supply air
continues for long time?
• Pressure increases in the conditioned space.
• Load on supply fan increases-and less CFM
is supplied in the space.
• Proper cooling does not take place as the
sufficient cool air is not received.
• How to reduce it ?
• Provide a return air grill.

19. • In order to return the air back to the coil
where it can be cooled once again , a return
air duct system is required as show below

21. • For systems having a very
long return air duct system,
a return air fan(Figure
below) is sometimes used.
• The return air fan helps the
supply air fan to move the
air around the system by
assisting in overcoming the
air frictional losses in the
ductwork.

23. • One cycle is completed.
• This cycle is called One Air Cycle.

24. Air Changes
One air change can be defined as the air coming
from outer atmosphere getting cooled at the
cooling coil, taking the away heat from the room
and passing away to outer atmosphere again.
So Number of air changes will differ as per the
application.
Example: For Apartments it can be 1(one).
For Bar and restaurants it can be 2- 3.
(Data to be taken from Hand book)

25. Dirt particles and pollen are removed from
the circulating air by installing filters
(Figure below) in the system.

26. Components in AHU
The filters, coil, and
supply air fan are typically
combined into a manufactured
product called an Air
Handling Unit (AHU).

27. How is Odor Controlled ?
• Odor removal is handled by
introducing fresh outdoor air
into the air handling
unit.This air is mixed with
return air before being
treated at the coil.

29. Where from you get cold water ?
The source of cooling for
the coil in the AHU is
usually some type of water
chiller (Figure below) that
operates on the refrigeration
cycle. The chiller provides
chilled water which is
circulated by a pump to the
coil in the air handling
unit. Heat thus flows from

31. How will AC reject the heat
removed from the space ?
• Reject the heat removed from
the space to the outdoor air.
• How?
• A cooling tower-with
condenser water piping and a
pump. The system could also
use an evaporative condenser
or an air cooled condenser.

33. • Thus the cycle is complete.
Heat flows into the space
from outdoors. Cool air picks
up the heat and transfers it
to the coil in the AHU. Cold
water transfers the heat to
the refrigeration equipment,
and heat rejection equipment
transfers the heat from the
refrigeration equipment back

34. What about heating then?
• To complete the All-Air
System we need to consider
the heating cycle. Although
there are several ways of
heating the space, one
typical means is to connect a
Boiler (Figure below) into
the water piping serving the
coil.Heat thus flows from the
water to the air, and from

36. By way of review then, an All-Air system consists
of the following typical
components:
1 - Central Air Handling Unit
a. Coil
b. Filter
c. Fan
d. Outside Air Dampers
e. Return Air Dampers
2 - Supply Air Ductwork
3 - Supply Air Terminal
4 - Return Air Grill
5 - Return Air Duct
6 - Possible Return Air Fan
7 - Refrigerant And/Or Water Piping
8 - Refrigerant Equipment
9 - Heat Rejection Equipment
10 - Boiler