Experimental and Theoretical Study on the Cooling Performance of a CO2 Mobile Air Conditioning System
Abstract
:1. Introduction
2. Experimental Setup
3. Experimental Results
4. Theoretical Analysis
4.1. Thermodynamic Calculation
4.2. Results Discussion
4.3. Further Discussion
5. Conclusions
- (1)
- Increasing the outdoor temperature results in a decline in the cooling capacity and COP for both systems. When the outdoor temperature increases from 27 °C to 45 °C, the cooling capacity of CO2 and R134a are decreased by 21% and 13%, respectively, and the COP of CO2 and R134a are reduced by 38% and 49%, respectively.
- (2)
- By comparison, the CO2 MAC system is able to provide a comparable cooling capacity with the R134a system regardless of outdoor temperature. The COP of CO2 MAC system is 10–26% lower than that of R134a system. The COP reduction narrows at high outdoor temperatures, which could be explained by the change of compressor efficiency and evaporator temperature. The evaporation temperature of CO2 is 0.3 °C–2.5 °C higher than that of R134a, and the compressor overall efficiency of CO2 is 11.8–47.4% higher than that of a R134a compressor.
- (3)
- Theoretical calculations demonstrate that a 5 °C evaporation temperature increase could improve the COP of CO2 by 11–18%, and decreasing the gas cooler approach temperature from 9.3 °C to 0 °C will enhance the COP by 23–59%. When the compressor overall efficiency increases from 0.60 to 0.80, the COP of CO2 is improved by 33% regardless of the outdoor temperature conditions. These impacts indicate that the COP of the CO2 system could be significantly enhanced by component optimization and has the potential to surpass that of R134a systems.
Author Contributions
Funding
Conflicts of Interest
Nomenclature
Roman | |
Cp | Specific heat [] |
EXV | Electrical expansion valve |
h | Enthalpy |
IHX | Internal heat exchanger |
m | Mass flow rate [] |
p | Pressure [MPa] |
Q | Cooling capacity [kW] |
R | Pressure ratio |
T | Temperature [°C] |
T′ | Fitting temperature |
TXV | Thermal expansion valve |
v | Specific volume [] |
V | Displacement [] |
W | Work [kW] |
ΔT | Temperature difference [°C] |
Greek letters | |
Efficiency | |
Effectiveness | |
Subscripts | |
1 | Suction point |
2 | Discharge point |
2s | Isentropic point |
a | Air |
ap | Approach |
c | Condenser |
cond | Condensing |
comp | Compressor |
diff | Difference |
e | Evaporation |
eva | Evaporator |
exp | Expectation |
g | Gas cooler |
in | Inlet |
is | Isentropic |
max | Maximum |
out | Outlet |
op | optimum |
r | Refrigerant |
vol | Volumetric |
Acronyms | |
COP | Coefficient of performance |
GWP | Global warming potential |
MAC | Mobile air conditioning |
OCR | Oil circulation ratio |
RPM | Revolutions per minute |
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Component | R134a | CO2 |
---|---|---|
Compressor | Scroll type, mobile compressor, horizontal configuration, 1000–7200 RPM, 27 ccm/rev, 7.0 kg | Rotary type, commercial compressor, vertically configuration, 1000–6000 RPM, 6 ccm/rev, 17 kg |
Condenser/gas cooler | Micro channel, parallel flow, aluminum, mass production component, 570W × 330H × 12D (mm), 1 slab, 3 passes, 20-14-10 | Micro channel, parallel flow, aluminum, prototype, 570W × 330H × 12D (mm), 1 slabs, 3 passes, 20-14-10 |
Evaporator | Micro channel, parallel flow, aluminum, mass production component, 230W × 200H × 38D; 2 slabs, 4 passes, 16-16-16-16 | Micro channel, parallel flow, aluminum, prototype, 230W × 200H × 38D, 2 slabs, 6 passes, 10-11-11-11-11-10 |
Throttling valve | TXV, aluminum, mass production component, 1.5 t of cooling | EXV, copper, driven by step motor, commercially available, valve port diameter 1.6 mm |
IHX | Without | Tube-in-tube, aluminum, prototype, 1.5 m |
Accumulator | Without | 600 mL, commercially available |
Items | Uncertainties |
---|---|
Temperature sensors (RTD-type, Yokogawa, Japan) | ±0.2 °C |
Pressure transducers (GE-Druck, USA) | ±0.5%, Max 4 MPa or 20 MPa |
Mass flow rate (Coriolis type, KROHNE, Germany) | ±0.15%, Max 600 |
Digital power meter (WT210, Yokogawa, Japan) | ±0.5% reading |
Data logger (34972A, Agilent, USA) | 0.004% dcV of full scale |
Heating capacity | Max 5.5% |
Heating COP | Max 6.3% |
1 | 0 °C | 0 °C | 9.3 °C | 17.7 °C | 0.6 | 0.6 | 0.5 | 5 °C | 0.95 |
2 | 0, 1, 2, 3, 4, 5 °C | 0 °C | 9.3 °C | 17.7 °C | 0.6 | 0.6 | 0.5 | 5 °C | 0.95 |
3 | 0 °C | 0 °C | 9.3, 6, 3, 0 °C | 17.7°C | 0.6 | 0.6 | 0.5 | 5 °C | 0.95 |
4 | 0 °C | 0 °C | 9.3 °C | 17.7 °C | 0.6, 0.65, 0.7, 0.75, 0.8 | 0.6 | 0.5 | 5 °C | 0.95 |
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Wang, D.; Yu, B.; Shi, J.; Chen, J. Experimental and Theoretical Study on the Cooling Performance of a CO2 Mobile Air Conditioning System. Energies 2018, 11, 1927. https://doi.org/10.3390/en11081927
Wang D, Yu B, Shi J, Chen J. Experimental and Theoretical Study on the Cooling Performance of a CO2 Mobile Air Conditioning System. Energies. 2018; 11(8):1927. https://doi.org/10.3390/en11081927
Chicago/Turabian StyleWang, Dandong, Binbin Yu, Junye Shi, and Jiangping Chen. 2018. "Experimental and Theoretical Study on the Cooling Performance of a CO2 Mobile Air Conditioning System" Energies 11, no. 8: 1927. https://doi.org/10.3390/en11081927