Abstract: This paper presents the experimental as well as the
simulated performance studies on the transcritical CO2 heat pumps
for simultaneous water cooling and heating; effects of water mass
flow rates and water inlet temperatures of both evaporator and gas
cooler on the cooling and heating capacities, system COP and water
outlets temperatures are investigated. Study shows that both the
water mass flow rate and inlet temperature have significant effect on
system performances. Test results show that the effect of evaporator
water mass flow rate on the system performances and water outlet
temperatures is more pronounced (COP increases 0.6 for 1 kg/min)
compared to the gas cooler water mass flow rate (COP increases 0.4
for 1 kg/min) and the effect of gas cooler water inlet temperature is
more significant (COP decreases 0.48 for given ranges) compared to
the evaporator water inlet temperature (COP increases 0.43 for given
ranges). Comparisons of experimental values with simulated results
show the maximum deviation of 5% for cooling capacity, 10% for
heating capacity, 16% for system COP. This study offers useful
guidelines for selecting appropriate water mass flow rate to obtain
required system performance.
Abstract: In the present study, a steady-state simulation model
has been developed to evaluate the system performance of a
transcritical carbon dioxide heat pump system for simultaneous water
cooling and heating. Both the evaporator (including both two-phase
and superheated zone) and gas cooler models consider the highly
variable heat transfer characteristics of CO2 and pressure drop. The
numerical simulation model of transcritical CO2 heat pump has been
validated by test data obtained from experiments on the heat pump
prototype. Comparison between the test results and the model
prediction for system COP variation with compressor discharge
pressure shows a modest agreement with a maximum deviation of
15% and the trends are fairly similar. Comparison for other operating
parameters also shows fairly similar deviation between the test
results and the model prediction. Finally, the simulation results are
presented to study the effects of operating parameters such as,
temperature of heat exchanger fluid at the inlet, discharge pressure,
compressor speed on system performance of CO2 heat pump, suitable
in a dairy plant where simultaneous cooling at 4oC and heating at
73oC are required. Results show that good heat transfer properties of
CO2 for both two-phase and supercritical region and efficient
compression process contribute a lot for high system COPs.