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Simulation of transcritical CO2 heat pumps with expander for simultaneous cooling and heating.

Author(s) : SARKAR J., BHATTACHARYYA S.

Summary

A steady-state simulation model has been developed to evaluate the performance of a transcritical carbon dioxide heat pump system with expansion turbine for simultaneous water cooling and heating. Both the evaporator and gas cooler models consider the highly variable heat transfer characteristics of CO2 and pressure drop. Evaporator and gas cooler models have been validated individually with test data obtained from experiments on a heat pump prototype. Comparison between test results and model prediction for evaporator and gas cooler capacities with compressor discharge pressure shows a modest agreement with a maximum deviation of 20% and the trends are fairly similar. Correlations for compressor volumetric and isentropic efficiencies, developed based on manufacturer test data, have been employed. Validation of the developed system model with expansion valve (instead of turbine) also shows modest deviation. The simulation results are presented to study the effects of operating parameters such as, temperature of heat exchanger fluid at the inlet, discharge pressure and compressor speed, on system performance of the CO2 heat pump, suitable in a dairy plant application where simultaneous cooling at 4°C and heating at 73°C are required. Optimization of compressor discharge pressure is presented as well. Finally, the results are compared with an expansion valve based system. The comparison exhibits a maximum COP improvement of 20% and optimum discharge pressure reduction of nearly 10% through the use of an expansion turbine instead of a valve in the CO2 heat pump system.

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Pages: 2008-2

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Details

  • Original title: Simulation of transcritical CO2 heat pumps with expander for simultaneous cooling and heating.
  • Record ID : 2009-0364
  • Languages: English
  • Source: 8th IIR-Gustav Lorentzen Conference on Natural Working Fluids (GL2008)
  • Publication date: 2008/09/07

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