1. AIR CYCLE
An integral part of air-conditioning system. Refrigeration cycle is part of air cycle.
Both Air cycle and Refrigeration cycle is not independent but inter dependent.
Indoor air can be too hot, too cold, too wet, too dry etc. These can be changed by treating the air.
The treatment of air includes cooling of hot air, heating of cool air, adding or removing moisture, creating air movement etc.
The treatment provided in the air cycle is part of the air-conditioning.
Major components of air cycle - Fan, Supply air Duct (SAD), Supply Air Grille (SAG), Space to be conditioned, Return Air Duct (RAD), Return Air Grille (RAG) with filter, heating or cooling coil.

4. COMPONENTS
FAN
Circulates, creates air movement & Forces air from supply duct to room
Can be regulated to prevent draft
SAD – Supply Air Duct
For uniform air distribution, Minimum turns & length
SAG – Supply Air Grille
Uniform distribution by jet or flow or combination of both
Number of outlets and their design is vital for comfort.
ROOM SPACE
Most important component, & a must for working of an air cycle
The material used for floor, wall, ceiling etc are very important to prevent heat loss or gain.

5. RAG – Return Air Grille
Allow used air to escape through outlets & best location is opposite SAG
RAD – Return Air Duct
From RAD the air passes through this duct & filter to the Cooling coil.
RAD can be eliminated if plenum is used.
FILTERS
To remove dust, dirt, pollutants, contaminants etc, location in RAD
Materials - spun glass, plastic etc,
Attract and capture dust particles with the help of electricity
COOLING COIL OR HEATING CHAMBER
Located only after the filter to prevent accumulation of dust and dirt over coil and before SAD
If the air is too dry, moisture is added with shallow pan of water, above heating chamber OR after the cooling coil in the SAD
Cooling coil can be used for cooling air or to reduce the humidity

6. REFRIGERANT CYCLE REFRIGERANT
Any liquid can be used for absorbing heat by evaporation. Water can also be used as a refrigerant but its boiling and freezing temperature is too high for ordinary cooling purposes.
A change of state of refrigerant from liquid to vapour and back to liquid helps to absorb or discharge large quantity of heat efficiently. This has been efficiently used in refrigeration cycle and Air-conditioning.
The selection of refrigerant depends on specific application and the context.
Any refrigerant must satisfy two main conditions.
1. It must readily absorb heat at the temperature required by the product load.
2. For economy and continuous cooling, the system must use the same refrigerant over & over again.

7. OTHER FEATURES OF REFRIGERANT
To absorb heat from a cooling coil by evaporating at low temp & Pr.
It gives up heat by condensation at a higher temp and pressure.
Ammonia (R-717) - earliest refrigerant. Boiling point –28 F but it is very corrosive and toxic.
R12 is Trichloride di fluro methane & its boiling point is F.
Some refrigerants boils at very low temp, as low as -40 deg C
A boiling refrigerant absorbs huge quantity of heat from surroundings hence are most suited for refrigeration purpose.
Some refrigerants cause damage to the ozone layer
Ozone friendly refrigerants - gradually replacing old types

8. Secondary Refrigerant
Large a/c areas
Cost of main refrigerant
pumping to AHU/FCU
Water or brine is chilled in the evaporator (chiller)
pumped to AHU or FCU at different places through insulated pipes
Secondary refrigerent runs in evaporator coil in AHU or FCU

9. REFRIGERATION
It is the process of producing and maintaining temperature below the surrounding atmosphere
it is nothing but the removal of heat from the substance to be cooled to reduce its temperature below atmosphere
Temperature and humidity is controlled by refrigeration process
One ton of refrigeration is equivalent to the amount of heat required to be removed from 1 ton of water (2100 Lb) at 32 F in 24 hours
One ton refrigeration (TR) = 1200 British thermal units (BTU)

10. REFRIGERATION CYCLE
Common refrigeration can be accomplished by several different processes. In the great majority of applications vapor compression system is adopted. However vapor absorption system and steam jet vacuum system is also successfully used in many applications.
Compressor, the main component in vapor compression system involves with two types of pressure. First, evaporating at low pressure and second, condensing at high pressure.

11. REFRIGERATION CYCLE

12. REFRIGERATION CYCLE

15. REFRIGERATION PROCESS
Liquid refrigerant evaporates in cooling coil (evaporator).
Refrigerant boils at very low temp like, R-22 at-40deg C
The cooling coil with refrigerant is in contact with air surrounding it. Chilled water (Secondary refrigerant) is distributed to AHU or FCU in coils.
Fins are used to get clear contact of all air that is passing through the cooling coil.
This air is distributed to the conditioned spaces through ducts
The hot refrigerant comes back to evaporator again in a cycle as cold refrigerant

16. BASIC LAWS OF REFRIGARATION
Fluids absorb heat while changing from liquid to vapor.
Vapor releases heat while changing from vapor to liquid
Heat cannot be destroyed but can be transformed from one substance to another.
Heat flows from higher temperature to substance at lower temperature
Heat and other forms of energy are mutually convertible
Temp of a liquid can be raised by increasing pressure
Temp of a liquid can be lowered by reducing pressure
Boiling temperature of refrigerant is very low

17. A TYPICAL AC UNIT

18. COMPRESSOR DESIRED TEMP IS ACHIEVED IN EVAPORATOR BY THIS TYPES
It is similar to automotive engine making alternate suction and compression strokes in a cylinder equiped with suction and discharge valve. It is suitable for small displacement volumes. It is efficient at high condensing pressures and high compression ratios. Its adaptability to different refrigerant is also an advantage. The other advantages are it is durable, simple in design and economical.
Open type compressor:
Earlier version of compressor in which only the piston and cylinder alone were sealed. A crank shaft was extended around the body with seal around to prevent leakage of refrigerant as well as oil. It is very heavy, large in size, noisy and seal failure was common. Due to these reasons it is not used frequently.
Accessible type Hermetics (Semi Hermatics)
driven by electric motor mounted directly on the crank shaft - compact, efficient, maintenance free and economical. - capacity of 17.5kw to 35kw

19. Welded Hermetic motor compressor:
It is small in size and used for 17.5kw and below capacity. All the parts including the electric motor is housed in a shell and sealed by welding. Hence field repair is not possible. It is very widely used for unitary air-conditioning system.
In this there are three types are available as below.
Reciprocating compressor: Available from very small fractional capacitiy and upto 35kw.
Scroll compressor: Very efficient and saves power. Available upto 50kw. The plus points are, high efficiency, less noise, high reliability and low maintenance. Tandem scroll type is an advanced type and is very energy efficient type.
Rotary compressor: It is less noisy when compared with reciprocating type. Due to this they are widely used in Window AC units and to some extent in Split units.

20. CONDENSER
COMPRESSOR

21. COMPRESSOR IN REFRIGERATION CYCLE
The hot refrigerant vapour from cooling coil moves to compressor.
The compressor compresses the hot vapour in to a high-pressure vapour.
This increases the temperature of vapour further.
The compressor automatically maintains low-pressure condition in cooling coil and creates high-pressure condition in condenser.

22. CONDENSER
Heat exchange takes place between refrigerant (hot high pressure vapor) and air) or water
AIR COOLED CONDENSER
Very commonly adopted type, inexpensive, easy to install and maintain
Fan forces large quantity of air through compact condenser assembly.
Satisfactory in all climates.
WATER COOLED CONDENSER
Economical - water available in abundance or as recycled
Water has excellent heat transfer characteristics
Types - Shell and coil, Shell and tube, Tube with in tube
Requires a cooling tower
spray ponds – Water aerated and cooled in the form of fountain jets
Requires plumbing & pump due to cooling tower
Cold weather - freezing of water may create problem

24. CONDENSER IN REFRIGERATION CYCLE
High-pressure hot vapor refrigerant passes to condenser
The condenser motor drives a condenser fan
Blown air receives heat - refrigerant vapor turns to liquid
This liquid is collected in a receiver.
Remember this liquid is high-pressure and high temp
Refrigerant movement from condenser to evaporator is called as ‘liquid line’
To remove heat – air – Air cooled condenser - water - water cooled condenser

25. EXPANSION VALVE
Liquid refrigerant under high pressure flows through this
Release of pressure reduces temp of liquid - cold refrigerant
Capillary tube or Restrictor is an alternative to EV
Cold refrigerant pass through cooling coil & cycle continues
Expansion valve also controls proper flow of refrigerant
Other flow control devices equivalent to EV are
Automatic expansion valve, Hand expansion valve,
Thermal expansion valve, Low side floats,
High side floats, Capillary tube

26. EVAPORATOR EVAPORATOR OR COOLING COIL
Located at low pressure of the refrigeration cycle. Here refrigerant boils or evaporates, absorbing heat & changes into vapor.
TYPES OF EVAPORATORS
BLOWER COIL OR FORCED CONVECTION TYPE – Here the refrigerant evaporates in side the tube with fin or plate around, extracting heat from air blown through the coil / fin.
DIRECT EXPANSION TYPE –Refrigerant is fed directly into the coil through a metering device like expansion valve, capillary tube etc. The heat is absorbed directly through the walls of the evaporator.
CHILLER – In a cylinder the coils with refrigerant is placed and secondary refrigerant like water or brine is fed into it. This chilled water / brine and is pumped to AHU or FCU

27. FCU & CHILLER

29. EVAPORATOR OR COOLING COIL IN REFRIGERATION CYCLE
The cold refrigerant liquid moves through cooling coil and picks heat from the surrounding air.
Surrounding air looses heat & becomes cold. Refrigerant boils and turns to vapor.
Refrigerant from evaporator to compressor as vapor is called as ‘suction line’