Objectives

1
Objectives

• Finish cooling cycles
• Learn about and cooling system components and
  refrigerants

2
Multistage Compression Cycles

• Combine multiple cycles to improve efficiency
• Prevents excessive compressor discharge
  temperature
• Allows low evaporating temperatures (cryogenics)

3
Systems residential
Outdoor Air
Indoor Air
4
System componentsLarge building system
Water to cooling tower
Water form cooling tower
25oC
35oC
Plate heat exchanger
6oC
11oC
Water to building
Water from building
5
Chiller
6
Compressors
7
Reciprocating compressor
8
Scroll compressor
http//www.youtube.com/watch?vf_6xolDoqs0
9
Screw compressor
http//www.youtube.com/watch?vxO7IhhzImMUfeature
related
10
Rotary Compressor
11
Summary

• Many compressors available
• ASHRAE Handbook is good source of more detailed
  information
• Very large industry

12
Refrigerants
13
What are desirable properties of refrigerants?

• Pressure and boiling point
• Critical temperature
• Latent heat of vaporization
• Heat transfer properties
• Viscosity
• Stability

14
In Addition.

• Toxicity
• Flammability
• Ozone-depletion
• Greenhouse potential
• Cost
• Leak detection
• Oil solubility
• Water solubility

15
Refrigerants

• What does R-12 mean?
• ASHRAE classifications
• From right to left ?
• fluorine atoms
• hydrogen atoms 1
• C atoms 1 (omit if zero)
• CC double bonds (omit if zero)
• B at end means bromine instead of chlorine
• a or b at end means different isomer

16
Expansion Valves

• Throttles the refrigerant from condenser
  temperature to evaporator temperature
• Connected to evaporator superheat
• Increased compressor power consumption
• Decreased pumping capacity
• Increased discharge temperature
• Can do it with a fixed orifice (pressure reducing
  device), but does not guarantee evaporator
  pressure

17
Thermostatic Expansion Valve (TXV)

• Variable refrigerant flow to maintain desired
  superheat

18
AEV

• Maintains constant evaporator pressure by
  increasing flow as load decreases