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Lecture 30

Lecture 30. Heat Pump Systems. Tons of Refrigeration. One ton of refrigeration is the heat transfer rate required to melt 1 ton (2000 lbf ) of ice at 32°F in 1 day (24 hr ). What heat transfer rate can accomplish this?. Latent heat of fusion of ice ( h f – h s ) at 1 atm. Then:.

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Lecture 30

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  1. Lecture 30 Heat Pump Systems

  2. Tons of Refrigeration One ton of refrigeration is the heat transfer rate required to melt 1 ton (2000 lbf) of ice at 32°F in 1 day (24 hr). What heat transfer rate can accomplish this? Latent heat of fusion of ice (hf – hs) at 1 atm Then:

  3. The Heat Pump Cycle The heat pump cycle IS a refrigeration cycle! Performance

  4. Heat Pumps How can the high temperature heat transfer be utilized? It all happens at the condenser. A few possibilities are … Heating Air Heating Water Hot air out Cold water in Hot water out Hot condensed refrigerant Hot refrigerant vapor Hot condensed refrigerant Hot refrigerant vapor Cold air in

  5. Heat Pumps Application: Residential heating

  6. Air-Source Heat Pump Sink Source The heat pump is not able to meet the house heating load. An auxiliary heat source is needed. The heat pump is able to meet the house heating load.

  7. Isothermal Source Heat Pump Sink In principle, this is a great idea! However it is cost prohibitive to circulate refrigerant through the isothermal source. No auxiliary heat source needed. The heat pump can always meet the house load! Source

  8. Isothermal Source Heat Pump Evaporator Secondary heat transfer loop (Some type of glycol mixture)

  9. Possible Isothermal Sources • The Earth • In-ground secondary loop needed • Horizontal loop • Vertical loop • Ground water from a geothermal well • Environmental issues? • A contained mass of water • Ice-making heat pump • Others?

  10. Example Heat Pump used for Heating and Domestic Hot Water

  11. Example Given: A heat pump used for domestic hot water heating and space heating as shown below. Find: The heat transfer rate available for hot water heating The power requirement of the compressor The heat transfer rate from the source The coefficient of performance for the heat pump

  12. Example Draw the P-h diagram for the cycle ...

  13. Example

  14. Example

  15. Example

  16. Example Energy sought =

  17. Example Solution (Key Variables):

  18. Heat pumps Application: Providing both heating and cooling with a heat pump

  19. Heating and Air Conditioning The reversing valve reverses the roles of the heat exchangers.

  20. Reversing (4-way) Valve Expansion Valve Qout Qin Condenser Evaporator Condenser Evaporator Qin Qout Compressor Refrigeration (Air-Conditioning) Mode Heat Pump Mode

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