Refrigeration Plant & Refrigeration Plant & ComponentsComponents

Type of Refrigeration System

Most common type: vapour compression refrigeration system– liquid refrigerant throttled from high to low pressure on

leaving the condenser and entering the evaporator– production of refrigeration effect in evaporator upon

vaporisation of refrigerant– compression of vapour refrigerant in the compressor

upon leaving the evaporator and entering the condenser– rejection of heat at the condenser through condensation

of vapour refrigerant to liquid phase

Types of Refrigerant

Classifications depending on composition of refrigerants, e.g. chlorine, hydrogen, halogen– chlorofluorocarbons (CFC): e.g. CFC-11 and CFC-12– halons (BFC): e.g. BFC-13B1– hydrochlorofluorocarbons (HCFC): e.g. HCFC-22– hydrofluorocarbons (HFC): e.g. HFC-134a– azeotropes: e.g. CFC/HFC-500– inorganic compounds: e.g. ammonia (R-717)

Effects on Environment Ozone depletion

– reduction of shielding layer against UV causing• increase in skin cancer and suppression of immune system• reduction in crop yield and affecting micro-organisms in sea• global warming

– increased chance of depletion with presence of chlorine as a catalyst and higher degree of stability of refrigerant, e.g. CFC-11 and CFC-12

Green house effect– long wave radiation emitted from surface being trapped and

absorbed by CFCs/CO2 in the troposphere leading to global warming

– affecting distribution of crops/animals and sea level

Effects on Environment

Refrigerant ODP GWP

HCFCs and HFCs:

HCFC-22

HCFC-123

HFC-134a

0.05

0.02

0

0.4

0.04

0.26

CFCs and BFCs:

CFC-11

CFC-12

1

1

1

3.2

Azeotropes or Blends:

CFC/HFC-500 0.74

Inorganic compounds:

R-717 0 0

Ozone Depletion and global warming potential

Phasing out/restricted use of CFC/BFC/HCFC

Types of Compressors

Positive displacement vs non-positive displacement– positive displacement type: increase of pressure by

reduction in volume of compression chamber, e.g. reciprocating, screw, rotary and scroll compressors

– non-positive displacement type: no reduction in volume of compression; mainly based on conversion of dynamic pressure to static pressure, e.g. centrifugal compressor

Types of Compressors

Types of construction: hermetic, semi-hermetic and open type

Types of Compressors Reciprocating compressors

– intake, compression and discharge strokes in cylinder– a no. of cylinders in a compressor with up to 200 TR

Types of Compressors Reciprocating compressors (cont’d)

– typical example of refrigeration plant

– total refrigeration capacity from 50 TR to 500 TR with use of multiple compressors in a chiller plant

Types of Compressors

Screw compressors– typical construction

Types of Compressors Screw compressors (cont’d)

– operation

– male rotor driven by a motor which enables the meshing female rotar to rotate with compression of trapped refrigerant

– 50 TR to 500 TR for a compressor

Types of Compressors Scroll compressors

– construction

Types of Compressors Scroll compressors (cont’d)

– operation

– 2 identical scroll: one stationary and one revolving eccentrically with compression of trapped refrigerant

– low noise and vibration– small refrigeration capacity (up to 60 TR)

Types of Compressors Rotary compressors

– 2 types: rotating piston and rotating blade; stationary cylinder and revolving piston/rotor

– up to 4 TR; quite and smooth in operationRotating piston Rotating blade

Types of Compressors Centrifugal compressors

– construction

Generally used for large installations (100 to 10,000 TR)

Compressor Comparison

Reciprocating vs other positive displacement compressors– more moving parts and maintenance– several cylinders implying balancing problem– less reliable and slightly lower efficiency– more noise and vibration problem– greater clearance volume lowering volumetric

efficiency– step control instead of stepless control

Single Stage Refrigeration Cycle p-h diagram

Constant temp line

Constant entropy (s) line

Constant pressure line

Constant enthalpy (h) line

Single Stage Refrigeration Cycle

Ideal and practical refrigeration cycle

– throttling process from 3 to 4: h3 = h4

– vaporisation process from 4 to 1• refrigeration effect: RE = h1 – h4, kJ/kg

1

23

4

P

h

Subcooling

Superheating

Single Stage Refrigeration Cycle Ideal and practical refrigeration cycle (cont’d)

– compression process from 1 to 2• ideal compression: no change in entropy (s1 = s2 )

• specific work input: w = h2 – h1, kJ/kg

– condensation process from 2 to 3• heating effect: HE = h3 – h2, kJ/kg

– coefficient of performance of cooling

– refrigeration capacity• RC = mr (RE), W

12

41c h - h

h - h

w

RECOP

Single Stage Refrigeration Cycle

Ideal and practical refrigeration cycle (cont’d)– coefficient of performance of heating

– superheating• prevent entry of liquid refrigerant to compressor to

affect lubrication and damage components• increase refrigeration effect• be kept to a min. because of reduction in COP

– subcooling• increase in refrigeration effect

12

23h h - h

h - h

w

HECOP

Single Stage Refrigeration Cycle Actual refrigeration cycle

– losses in system and compression process included

– entropy increase s2’’ > s1

– determination of 2’’ using isentropic efficiency(isen)

1

2

3

4

P

h

2’2’’

12

1' 2isen h - h

h - h

input work Actual

input work Ideal η

''

Ideal compression:s1 = s2’

Single Stage Refrigeration Cycle Plotting of single stage refrigeration cycle

2

4

Evaporator pressure: 0.2 MPa

Condenser pressure: 1 MPa

1

Suction temperature: 10 oC

Ideal compression

3

Subcooling: 5 oC

THE END