AIR-CONDITIONING
SYSTEM
LEARNING OUTCOME
At the end of the lecture the student will be able to:
Explain the important of Air-conditioning
Sketch and explain the process of cooling the air
Describe the function of compressor, condenser, expansion valve and evaporator
Distinguish between split unit and central unit of air-conditioning
Explain the function of AHU, Chiller and cooling tower
Show the heat transfer in air-conditioning system
INTRODUCTION
Air-conditioning is the process of cooling the air
in a building to provide a comfortable
temperature.
It is divided by two, forced air conditioning
system and hydronic (hydronic is the name for
the use of water as the heat-transfer medium in
heating and cooling systems) air conditioning
system.
Air-Conditioning
System
Forced Air
Conditioning System
Hydronic Air
Conditioning System
Air-Conditioner Chiller
Unit System/Package Unit
Central Plant System
Air Cooled Water CooledSplit Unit Window Unit
TYPES OF AN AIR CONDITIONING SYSTEM
ADVANTAGES OF AN AIR CONDITIONING SYSTEM
Improve working efficiency, reduce illness and absenteeism
(absenteeism is a habitual pattern of absence from a duty or obligation).
Increase sales, productivity and comfort ness.
Less cleaning, material and furniture last longer.
Suitable environments for plants grow process, electronic and lab areas.
Reduce internal and external pollution e.g. dust, noise and smoke
Less risk of fire or damage due to static electricity caused by dry air
FACTORS OF CHOOSING TYPES OF SYSTEM
Size – volume
Usage – people, process
Arrangement of rooms, buildings
Building materials – heat retained
Water or air for releasing heat from condenser
Noise level of system used
Reliability, installation, cost & maintenance
Flexibility or user friendly
SELF CONTAINED (LOCALISED)
SPLIT UNIT•Most central air conditioning units operate by
means of a split system because of
Low-cost
Results in reduced noise
inside the house. (at the
expense of increased noise
outside the house).
Are perfect for those that do not have central air conditioning & do not want to settle for the noise & inefficiency of window units.
Offer higher efficiency & reduced noise without a large hole in the wall/ an open window.
By separating the compressor & condenser coil from the fan & evaporator coil, the noisiest component is away from the room.
The indoor unit will usually have remote control capabilities and a timer to cycle the system only when needed. The indoor unit is called an air handler because it has the evaporator coil, blower & controls inside.
The outdoor unit is called the condenser.
They are connected together with refrigerant
piping & control wiring, similar to a central system.
Since mini splits have no ducts, they avoid the energy losses
associated with ductwork of central forced air systems.
Duct losses can account for a significant portion of energy
consumption for space conditioning, especially if the ducts are
in a unconditioned space such as an attic.
“hot” side( condensing unit): including condensing coil, compressor and fan- situated outside home.
Consists of a long, spiral coil cylinder shaped. Inside the coil – fan: blow air through the coil, along with a weather-resistant compressor and some control logic.
"cold" side : consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler.
Furnace blows air through an evaporator coil, which cools the air. This cool air is routed throughout your home by means of a series of air ducts.
WINDOW UNIT
Compressor, evaporator, condenser and
expansion valve are in a compact unit at the
wall.
Suitable for individual rooms or offices with at
least one external wall.
Only disadvantages of window units are
noisy, no fine control of temperature and
humidity and higher consumption of electricity
per ton.
Ideal when only a few rooms are to be
cooled and individual controls are required.
Initial cost is low.
There are basically two types of package system – air-
cooled or water-cooled
Generally used with ductwork.
Provide better control than window units - have more
than one compressor, cylinder unloading compressors,
split coils, time delay starters, etc.
CENTRAL PLANT PACKAGE
AIR-COOLED
Consist of multi stage blower like window unit.
It is located in one big room or outside the building.
Cooling capacities and volume of air delivered by the
units would depend on individual manufacturers.
Generally for air-cooled packed units the cooling
capacities are from about 2 tons to about 20 tons (2
HP to 30 HP).
The nominal delivery volume of air delivered is about
500 cfm per ton.
Split into the compressor condenser section and the
fan coil section - provides more flexibility in
equipment placement but the distance between these
two sections should not be too much or the refrigerant
piping sizes would have to be increased.
Overall efficiency of packages units 7 to 11 btu/hr per
watt for air cooled packaged units
WATER-COOLED
Consist of AHU and blower chilled.
Consist of compressor, condenser, expansion valve
and evaporator.
For water-cooled packed units, the cooling
capacities are from about 2 tons to about 50 tons (2
HP to 60 HP)
The overall efficiency of packages units range from
9 to 15 btu/hr per watt for water cooled equipment.
Refrigeration cycle
BASIC AIR-COND SYSTEM
AN AIR CYCLE An air cycle is the process of distributing
the clean air to the particular room to be cooled. The purpose of cycle is actually removes heat from that room.
Removed heat in this cycle occurs when the return supply air are absorb at the condenser. The heat condensing medium using either air or water. So, this cycle have supply distribution and return distribution.
The method of this distributing might be using air ducting or cooling water piping.
Complete system of an air conditioner need the refrigeration cycle and air cycle. In air cycle there is a few component to be use such as:
a)Air Handling Unit
b)Air Filter
c)Air Ducting
d)Clean air inlet
e)Humidification Equipment
f)Dehumidification Equipment.
AIR-CONDITIONING COMPONENTS
1. Air Handling Unit
2. Expansion Valve
3. Condenser
4. Compressor
5. Evaporator
6. Chiller
AIR CONDITIONING
COMPONENTS
COMPRESSOR
EXPANSION
VALVE
EVAPORATOR
CONDENSER
Air Handling Unit (AHU)
AHU is function for the process of heating, cooling,
humidification, dehumidification, air filtering and air
distribution.
Therefore, it is also reprocess the return air from
particular cooled room
AIR HANDLING UNIT
Refrigerant
A refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back.
The two main uses of refrigerants are refrigerators/freezers and air conditioners
the most widely used refrigerants were the halomethanes R-12 and R-22, with R-12 being more common in automotive air conditioning and small refrigerators, and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers.
EXPANSION VALVE
EXPANSION VALVE
Refrigerant enters the inlet & screen as a high-pressure liquid. Refrigerant flow is restricted by a metered orifice through which it must pass.
As the refrigerant passes through this orifice, it changes from high-pressure liquid to low-pressure liquid (passes from high side to low side of the system).
Expansion valve removes pressure from the liquid refrigerant to allow expansion/change of state from a liquid to a vapor in the evaporator.
High-pressure liquid refrigerant entering the expansion valve is quite warm. The liquid refrigerant leaving the expansion valve is quite cold. The orifice within the valve does not remove heat, but only reduces pressure.
CONDENSER
Is a heat exchanger that removes heat from high
pressure refrigerant vapor. High pressure refrigerant
vapor flows through the condenser and a condensing
medium passes across the outside of the condenser.
Heat flows from the hot refrigerant vapor to the cold
condensing medium.
A condensing medium is a fluid (air or water) that has a
lower temperature than the refrigerant, which causes
heat to flow to the medium.
A condensing medium removes heat from a
refrigerant because it has a lower
temperature than the refrigerant.
Air and water condensing mediums used in
refrigeration system.
As a refrigerant vapor gives up heat to the
condensing medium in a condenser, the
vapor condenses to a liquid.
COMPRESSOR
COMPRESSOR
Purpose of the compressor is to circulate therefrigerant in the system under pressure, thisconcentrates the heat it contains.
At the compressor, the low pressure gas ischanged to high pressure gas.
This pressure build up can only beaccomplished by having a restriction in thehigh pressure side of the system. This is asmall valve located in the expansion valve.
EVAPORATOR
EVAPORATOR
Evaporator coils of air conditioning systems aresometimes called cooling coils. They are alsoused in air-handling units.
They contain chilled water. They are completelydifferent from those used in direct expansionair-cond units. So cooling coils is not anaccurate word to use in small air-cond units.Evaporator coils should be used instead.
Evaporator tubes must contain refrigerant liquidthat can evaporate to become gas. In an airconditioning system, when the liquid refrigerantabsorbs heat, it turns to gas. The heat is thustransferred to the refrigerant.
That's how the heat is moved from one locationto another location. The evaporator coils arelocated in the low-pressure system of arefrigeration circuit.
CHILLER
Unit where chilled water is cooled by the evaporator.
The chilled water is circulated inside the cooling coil in the AHU, being warmed and to the chiller.
Inside the chiller, the low pressure liquid refrigerant inside the evaporator absorbs heat and flows to the condenser.
The condenser is either air-cooled or water-cooled.
This unit is usually installed for central plant system.
AIR-CONDITIONING OPERATE
An air conditioner is able to cool a building
because it removes heat from the indoor air
and transfers it outdoors.
A chemical refrigerant in the system absorbs
the unwanted heat and pumps it through a
system of piping to the outside coil. The fan,
located in the outside unit, blows outside air
over the hot coil, transferring heat from the
refrigerant to the outdoor air.
What happen when the heat/cool the
air without adding moisture
50% 25%
10oC 20oC
Suitable heating i.e no moisture added
If the air heated from 10oC to 20oC the RH = 25% (too low)
30oC25oC
95% 70%
Suitable cooling i.e no moisture added
If the air is cooled from 30oC to 25oC the RH = 95% (too high)
Cooling of air without adding moisture/dehumidification
Human comfort level
70% 60%
5oC 20oC
Washing & cooling
preheating
Fine heating
Cooling to 9oC in the washer
Human comfort level;Temp = 20ocRelative humidity= 60% -70%
If the air enters the plant at 5oC and with a RH of 70% and the room air is required at 20oc with RH of 60% the air will require preheating to 18.5oc, cooled to 9oc dew point temperature and then finally heated to 20oC
Figure shows cooling air by preheating, washing and final heating
CASE STUDY
Location: University
Technology MARA Pulau
Pinang
Topic: Air-Conditioning
Air-Conditioning Location: Kolej
Baiduri and Zamrud
Type of Air-Conditioning: Ceiling
exposed split type
Name of brand: Fujitsu (Japan)
Location: University Technology MARA Pulau Pinang
Topic: Air-Conditioning
Air-Conditioning Location: Laman Perdana
Type of Air-Conditioning: Floor Standing Split type
Name of brand: Yonan (China)
Dimensions for indoor units: 600 x 350 x 1900mm
Net weight for indoor units: 55kg
Cooling capacity:42000btu
Heating capacity: 45000btu
Voltage: 220V/50Hz, 240V/60Hz
Location: Pangsapuri Idaman
Topic: Air-Conditioning
Air-Conditioning Location: House
Type of Air-Conditioning: Wall mounted
split type
Name of brand: Toshiba (Japan)
Dimensions for indoor units: 1070 x 295 x 370mm
Dimensions for outdoor units: 850 x 290 x 610mm
Net weight for indoor units: 14kg
Net weight for outdoor units: 47kg
Cooling capacity: 22000btu
Heating capacity: 22000btu
Voltage: 220V/50Hz, 240V/60Hz
CONDENSER
The condenser is a heat
exchanger that removes
heat from high pressure
refrigerant vapor.
As the refrigerant passes
through the condenser
coil and the cooler
outside air passes across
the coil, the air absorbs
heat from the refrigerant,
which causes the
refrigerant to condense
from a gas to a liquid
state.
The high-pressure, high-temperature liquid then reaches the expansion valve.
EXPANSION VALVE
The expansion valve is the "brain" of the system.
By sensing the temperature of the evaporator, or
cooling coil, it allows liquid to pass through a very
small orifice, which causes the refrigerant to expand to
a low-pressure, low-temperature gas.
This "cold" refrigerant flows to the evaporator.
EVAPORATOR
• is a heat exchanger that adds
heat to low pressure refrigerants liquid flows through the evaporator an evaporating medium passes across the outside of the evaporator.
• An evaporating medium is a fluid that is cooled when heat is transferred from medium to the cold refrigerant.
•An evaporating medium adds heat to a refrigerant because it has a higher temperature than refrigerant.
•As the liquid refrigerant absorb heat from the evaporating medium the refrigerant boils and vaporizes.
COMPRESSOR
-The compressor is the "heart" of the system.
-It acts as the pump, causing the refrigerant to flow through the system.
- Its job is to draw in a low-pressure, low-temperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant.
- This high-pressure, high-temperature gas then flows to the condenser coil.
Pump
AIR HANDLING UNIT (AHU)
The AHU is box-like equipment with a fan and a
cooling coil inside. Some units also contain air
filters. The whole fan and motor assembly,
comprising shaft, bearings, pulley, belting is usually
put inside the AHU.
to suck air from the rooms, let it pass through
chilled water cooling coils and then discharging the
cooled air back to the rooms.
A certain amount of fresh air may be introduced at
the suction duct so that air in the rooms may be
gradually replaced.
The cold air is transfer to the
next room.
If humidity of the air has to be controlled, steam coils, or other heating coils may be installed
Moisture in the air is condensed out when it comes into contact with the chilled water coils. At the bottom of the AHU, a pipe is installed so that water that is collected can be drained out.
Removable panels are installed so that personnel can enter into the AHU for maintenance. Maintenance is mostly changing or washing of air filters, greasing of bearings, changing of belts, and general inspection and cleaning work.
Fan (tangential type) of the
air handling unit
Hole of the flow of the fresh
air
CHILLED WATER SYSTEM
Chiller - heart of the central air conditioning system.
Better - To cool down a large building.
Chilled water is easily pumped and it is able to reach all floors in the building.
Chillers make use of the refrigeration
principles to work.
The flow of the heat in central air conditioning system:
• Heat is transferred from the air in the rooms to chilled
water at the air handling units.
• The chilled water is pumped through the chiller and the
heat is transferred to the refrigerant.
• The refrigerant is cooled by cooling water circulating in the
condenser of the chiller.
• The heated cooling water is passed through cooling towers
where the heat is dissipated to the atmosphere by fans.
A pipe connecting the compressor to cooling tower. CWP at the pipe bring means cooling water.
A pipe connecting the compressor to AHU room. CHW at the pipe means chilled water.
COOLING TOWER
used in central air conditioning systems.
function - to cool the warm water from the chiller
condenser.
heat from the rooms in a building is transferred
to chilled water, then transferred into the
refrigerant, and finally to the cooling water. The
cooling tower is at the final point of the heat
transfer. The heat is transferred to the
atmosphere.
heat in the cooling water is removed
by letting moving air come into
contact with it.
Water is normally spread out and
allowed to drop down by gravity from
a height.
Plastic fillings are arranged so as to
increase the wetted surface of the
water while it is dropping, while at the
same time provide better contact
between the air passages and the
water.
Cooling Tower
Big fan for cooling tower
CONCLUSION
The design objective of air-conditioning system is to control
indoor parameters within required thermal comfort and indoor
air quality overall. The air conditioning system is the one most
important devices to give the fresh air especially in house and
room.