Multi-Stage Vapour Compression Refrigeration Systems

Air-Conditioning SystemClassification of Air-Conditioning SystemsAccording to the purposeComfort air conditioning systemsIndustrial air conditioning systemsAccording to season of the yearWinter air conditioning systemsSummer air conditioning systemsYear air conditioning systemsAccording to the arrangement of equipmentUnitary/Package Unit air conditioning systemsCentral air conditioning systemsComfort air conditioning system(DBT=21, RH=50%)

Industrial air conditioning system(Constant DBT, RH)

Summer air conditioning system(Cooling with Dehumidification)

Winter air conditioning system(Heating with humidification)

Year around air conditioning system

Effective and Grand room sensible heat factor

Window type Package Unit(Unitary Systems)A package unit is a self-contained unit because the complete unit including evaporator and condensing unit is all incorporated in a common enclosure.Normal capacity is 1 and 1.15 tonnesCapable of cooling, heating, cleaning and circulating the air.Console type Package Unit(Unitary Systems)Units are packaged in decorative cabinets and are mounted on the floor directly.Water cooled condensers are employedCapacity is 3 to 20 tonnesShort length of Duct work is attached for proper conditioned air. Central UnitAir handling unit is generally separated from the condensing unit.Available in horizontal and vertical depending upon the position of filter

Infiltration :General DefinitionInfiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called ex-filtration. Infiltration is caused by wind, negative pressurization of the building.Requirements of Human comfort/ Factors affecting Human ComfortEffective temperatureHeat production and regulation in human bodyHeat and moisture losses from the human bodyMoisture content of airQuality and quantity of airAir motionHot and cold surfacesAir stratificationEffective temperature

Comfort Chart

Variation of effective temperature with air velocity

Modified Comfort Chart

Heat production and regulation in human body

Heat and moisture losses from the human body

Moisture content of air

Quality and quantity of air

Air motion

Hot and Cold surfaces

Air stratification

Factors effecting optimum effective temperature

Climate and seasonal differencesClothingAge and sexDuration of stayKind of activityDensity of occupants

EquipmentsCompressorsBlowers and FansFiltersCompressors, Blowers and FansCompressor:Compressor is a mechanical device that increases the pressure of a fluid, either gas or liquid by reducing its volume. The inlet diameter of the pipe will be more than the outlet diameter. This reduces the volume flow rate and thus the pressure of the fluid increases. Thermodynamically, low pressure high volume in the Inlet becomes high pressure low volume at the outlet. Compressor are mainly used for fluid flow at high pressures i.e, the inlet pressure will be low while inlet volume will be high and outlet pressure will be high while outlet volume will be low. There are many types of compressor based on the different principles of working such as

1. Rotary Compressor2. Reciprocatory Compressor3. Centrifugal Compressor4. Axial CompressorCompressors are extensively used in refrigerator, air conditioner, pipeline transport of natural gas, petrol refineries, pneumatic compressors are used in industries.

Blower:Blower is also known as "Centrifugal Fan". This fan increases the velocity of air or gas when it is passed into the impellers. The inlet pressure will be low and the outlet pressure will be high. At constant volume flow rate, the low pressure air becomes high pressure at the outlet. This is mainly due to the rotating blades in the impeller. The kinetic energy of the blades increases the pressure of the air at the outlet. Blowers are mainly used for industry purposes and in climatic control after fan due to its high pressure than fan.Fan:Fan is a machine used to create a fluid flow. The flow of fluid is increased with the fan. It produces high volume and low pressure than the ambient conditions. It is mainly used as cooling device in computer CPUs and other electronic gadgets apart from climatic condition control.

Main difference between Fan and Blower is blower can achieve more pressure ratio than fan. Blowers can produce more high pressured air than fan.

Difference between Compressor and Blower - Compressor produces high pressure at low volumes where as blower produces low pressure at high volumesFans

Types of FANCentrifugal or radial flow FanWhen the air enters the impeller axially and is discharged radially from the impeller, it is called a centrifugal or radial flow fan.Forward curvedBackward InclinedBackward curved

Axial Flow fan When the air flows parallel to the axis of impeller, it is called an axial flow fan. PropellerTube axialVane AxialCentrifugal fan

Axial Flow Fans

Propeller Fan:

Tube-Axial Fan

Vane Axial Fan

FiltersFunction of filter is to arrest the solid impurities such as soot, ash, lint, smoke and fumes and even living organisms such as virus, bacteria and fungus spores.Placed ahead of heating or cooling coils.

Classification is:Dry air filterViscous impingement filtersElectrostatic filtersDry air filtersFiltering medium consists of fabrics made out of wool felt, cotton batting, cellulose fibre etc.Wire frames or V-shaped plates used in order to increase the area of medium exposed to air.High dust arrestance including lint.Throw away filters have frame of card board of fibre; these must be replaced by a new one, after collection of full dust load.

Viscous FilterFiltering medium consists of coarse fibres (such as glass, steel wool, wire screen, animal hair, hemp fibres, metal stamping or shaving) packed between two panels of expanded metal screen enclosed in a frame.Three types of filters are:Throw away or replaceable type (contains fibrous materials such as glass wool and discarded after a period of use)Manually cleaned type (metal frame and must be cleaned periodically)Automatic or sell cleaning filter (consists of a continuous roll of material coated with oil and motor driven

Electrostatic filterUse of electrostatics principle.Dirty steam has to be passed through a series of charging plates.Collector is given an opposite charge.Dirt particles adhere to the collector plates and cleaned.