1. Objectives Cooling Cycles Cooling system components Refrigerants
Examples
Cooling system components
Refrigerants

2. Subcooling and Superheating
Refrigerant may be subcooled in condenser or in liquid line
Temperature goes below saturation temperature
Refrigerant may be superheated in evaporator or in vapor (suction) line
Temperature goes above saturation temperature

3. Two stage systems

4. Multistage Compression Cycles
Combine multiple cycles to improve efficiency
Prevents excessive compressor discharge temperature
Allows low evaporating temperatures (cryogenics)

5. Example 1 R-22 condensing temp of 30 °C and evaporating temp of 0°C
Determine
qcarnot wcarnot
COPcarnot ηR

6. Example 2 R-22 condensing temp of 60 °C and evaporating temp of 0°C
Determine the ηR

7. Example 3 Two stage compressor R-22 condensing temp of 60 °C
Evaporating temp of compressor A 30°C and for compressor B 0°C.
Determine the ηR
Assume that condenser temperature for compressor B is the same like evaporation temperature of compressor A

8. Systems: residential
Outdoor Air
Indoor Air

9. Large building cooling systems (chillers with cooling towers)
Weather
parameters
DBT=30oC
WBT=20oC
25oC
35oC
Water P
refrigerant
6oC
11oC

10. System components Large building system
Water to
cooling tower
Water form
cooling tower
25oC
35oC
Plate heat
exchanger
6oC
11oC
Water to
building
Water from
building

11. Chiller

12. Compressors

13. Reciprocating compressor

14. Scroll compressor

15. Screw compressor

16. Rotary Compressor

17. Refrigerants

18. What are desirable properties of refrigerants?
Pressure and boiling point
Critical temperature
Latent heat of vaporization
Heat transfer properties
Viscosity
Stability

19. In Addition…. Toxicity Flammability Ozone-depletion
Greenhouse potential
Cost
Leak detection
Oil solubility
Water solubility

20. Refrigerants What does R-12 mean? ASHRAE classifications
From right to left ←
# fluorine atoms
# hydrogen atoms +1
# C atoms – 1 (omit if zero)
# C=C double bonds (omit if zero)
B at end means bromine instead of chlorine
a or b at end means different isomer