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Objectives

Objectives. Cooling Cycles Examples Cooling system components Refrigerants. 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

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Objectives

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  1. Objectives • Cooling Cycles • 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) Cooling tower Weather parameters DBT=30oC WBT=20oC 25oC 35oC Water P refrigerant 6oC 11oC

  10. 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

  11. Chiller

  12. Compressors

  13. Reciprocating compressor

  14. Scroll compressor http://www.youtube.com/watch?v=f_6xolDoqs0

  15. Screw compressor http://www.youtube.com/watch?v=xO7IhhzImMU&feature=related

  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

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