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VALIDATION There are minor differences between the theoretical model (based on Figure 1a) and the installation (Figure 2a), including separate expansion valve for each borehole and an oil circuit in the test bench but neither of which was water mass flow rate (ππΜ ) entering the gas cooler at 0.25 kg/s and constant inlet water temperature at 35 Β°C. As ππππππππππ considered by the model. A 17-hour experiment was performed in heating mode for model validation with constant shown in Figure 3, CO2 pressure value reaches 8300 kPa at the gas cooler inlet. Furthermore, intermediate pressure (Preceiver=3750 kPa) is very close to the low pressure (Pin_borehole=3540 kPa) level. Evaporating pressure (Pin_borehole) decreases slightly over time from 3540 kPa to 3412 kPa; this is caused by the expansion valves to maintain the superheat set point at the borehole outlet. Water temperature increases by 3.5 Β°C (from 35 Β°C to 38.5 Β°C) taking the heat from CO2 in the gas cooler (qh) and corresponding to nearly 3.6 kilowatts of heating. 40 38 36 34 32 5 10 15 20 Time (hr) Tin_water Tin_water - EXP Tout_water Tout_water - EXP Tout_CO2 Tout_CO2 - EXP 9000 8000 7000 6000 5000 4000 3000 5 10 15 20 Time (hr) High pressure Pdischarge_comp Pdischarge_comp - EXP Pin_borehole Pin_ borehole - EXP Preceiver Preceiver - EXP Intermediate pressure Low pressure Figure 3 Cycle pressure levels Figure 4 Gas cooler temperatures The model was modified to include the four control strategies implemented into the test bench. Figures 3 and 4 present predicted (line) and measured (symbols) pressure levels of the heat pump and gas cooler water and CO2 temperatures. The model shows a very good agreement with experimental data considering the measurement uncertainties (Error bars); except, discharge pressure that fluctuations beyond uncertainties mainly due to the superheat control strategy (last point of the control subsection). PARAMETRIC ANALYSIS For a better understanding of the system and at exploring the performance improvement actions, a parametric analysis was undertaken using the theoretical model. This analysis focuses on producing domestic hot water using the DX CO2 GSHP. Eight different cases are considered and compared against the base case. The ninth case is also considered combining the best two individual cases (#5). All system parameters of the base case which are different from that of the test bench are presented in Table 5. One parameter at a time is changed in each case (#1 to #8) to evaluate the effect of six different parameters including the degree of superheat at the compressor suction (ΞTsh_comp), inlet water temperature to the gas cooler (Tin_water), CO2 gas cooler outlet temperature (Tout_CO2), intermediate pressure (Preceiver), water mass flow rate (π¦π¦Μ ) and IHE efficiency (Ξ΅IHE). The optimum pressure π°π°π°π°π°π°π°π°π°π° Cycle pressures (kPa) Gas cooler temperatures (C)PDF Image | Direct expansion ground source heat pump using R744
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CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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