Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid
Abstract
:1. Introduction
2. System Modeling
2.1. System Description
2.2. System Assumptions
- The system operates under steady conditions.
- Heat loss and pressure drop during the heat transfer process is ignored.
- The influence of gravity and kinetic energy is ignored.
- The refrigerant is saturated at the evaporator outlet.
2.3. Energy Analysis Method
2.4. Exergy Analysis Method
3. Results and Discussion
3.1. Effect of CO2-Based Mixture Fraction
3.2. Effect of Ambient Temperature
4. Case Study
5. Conclusions
- The maximum temperature glide of 14.20 °C and maximum critical pressure of 7.58 MPa can be observed with the R32 mass fractions of 0.6 and 0.2, respectively. The GWP and critical temperature of the CO2/R32 mixture are always increased with the larger R32 mass fraction.
- The COP and exergy efficiency variation show an “M” shape trend, and these two parameters are lower than that of the pure CO2 cycle if the R32 mass fraction is within the range 0.4–0.6. The optimal pressure reduction is increased and the irreversibility of the EEV is reduced from 0.031 to 0.009 kW⋅kW−1 in relation to the increased R32 mass fraction.
- With regard to flammability and efficiency, the optimal concentration of the CO2/R32 mixture is determined as 0.9/0.1. Over an ambient temperature range of −15 to 25 °C, the COP and exergy efficiency improvements are more notable in a cold climate, since the total irreversibility reduction is more remarkable.
- In the selected typical city, the case study results show that the annual performance factor and annual exergy efficiency can be increased by 5.39% and 3.11%, respectively, with the CO2/R32 mixture cycle, leading to a 1.64 tce reduction in primary energy consumption.
Author Contributions
Funding
Conflicts of Interest
Nomenclature
Latin symbols | |
Eh | domestic hot water load, kJ |
ECF | energy conversion factor, kgce·kg−1, kgce⋅(kW·h)−1 |
ir | irreversibility per unit heating capacity, kW·kW−1 |
Ik | irreversibility of each component, kW |
LHV | lower heating value, kJ·kg−1 |
m | mass flow rate, kg·s−1 |
P | pressure, MPa |
Q | heating capacity, kW |
T | temperature, °C |
W | power consumption, kW |
Greek symbols | |
η | efficiency, % |
Abbreviations | |
ASHP | air source heat pump |
CFB | coal-fired boiler |
COP | coefficient of performance |
DEH | direct electric heater |
GWP | global warming potential |
IHX | internal heat exchanger |
ODP | ozone depletion potential |
PEC | primary energy consumption |
TCHP | transcritical CO2 heat pump |
Subscripts | |
0 | ambient (dead state) |
a | air |
c | cooling |
coal | coal |
Comp | compressor |
d | discharge |
e | electrical efficiency |
ele | electricity |
Evap | evaporator |
GC | gas cooler |
h | heating |
i | inlet |
is | isentropic efficiency |
m | mechanical efficiency |
Mix | mixture refrigerant |
o | outlet |
r | refrigerant |
t | transmission |
Tot | total |
w | water |
References
- Chang, C.; Zhu, N.; Yang, K.; Yang, F. Data and analytics for heating energy consumption of residential buildings: The case of a severe cold climate region of China. Energy Build. 2018, 172, 104–115. [Google Scholar] [CrossRef]
- Wang, Y.K.; Ye, Z.L.; Song, Y.L.; Yin, X.; Cao, F. Experimental investigation on the hot gas bypass defrosting in air source transcritical CO2 heat pump water heater. Appl. Therm. Eng. 2020, 178, 115571. [Google Scholar] [CrossRef]
- Wang, F.; Zhao, R.; Xu, W.; Huang, D.; Qu, Z. A Heater-Assisted Air Source Heat Pump Air Conditioner to Improve Thermal Comfort with Frost-Retarded Heating and Heat-Uninterrupted Defrosting. Energies 2021, 14, 2646. [Google Scholar] [CrossRef]
- Xu, Y.; Mao, C.; Huang, Y.; Shen, X.; Xu, X.; Chen, G. Performance evaluation and multi-objective optimization of a low-temperature CO2 heat pump water heater based on artificial neural network and new economic analysis. Energy 2021, 216, 119232. [Google Scholar] [CrossRef]
- Kim, M.S.; Kang, D.H.; Kim, M.S.; Kim, M. Investigation on the optimal control of gas cooler pressure for a CO2 refrigeration system with an internal heat exchanger. Int. J. Refrig. 2017, 77, 48–59. [Google Scholar] [CrossRef]
- Taslimi Taleghani, S.; Sorin, M.; Poncet, S.; Nesreddine, H. Performance investigation of a two-phase transcritical CO2 ejector heat pump system. Energy Convers. Manag. 2019, 185, 442–454. [Google Scholar] [CrossRef]
- Yang, J.L.; Ma, Y.T.; Li, M.X.; Guan, H.Q. Exergy analysis of transcritical carbon dioxide refrigeration cycle with an expander. Energy 2005, 30, 1162–1175. [Google Scholar] [CrossRef]
- Dai, B.M.; Qi, H.F.; Liu, S.C.; Ma, M.Y.; Zhong, Z.F.; Li, H.L.; Song, M.J.; Sun, Z.L. Evaluation of transcritical CO2 heat pump system integrated with mechanical subcooling by utilizing energy, exergy and economic methodologies for residential heating. Energy Convers. Manag. 2019, 192, 202–220. [Google Scholar] [CrossRef]
- Elbel, S.; Hrnjak, P. Flash gas bypass for improving the performance of transcritical R744 systems that use microchannel evaporators. Int. J. Refrig. 2004, 27, 724–735. [Google Scholar] [CrossRef]
- Chesi, A.; Esposito, F.; Ferrara, G.; Ferrari, L. Experimental analysis of R744 parallel compression cycle. Appl. Eng. 2014, 135, 274–285. [Google Scholar] [CrossRef]
- Zhang, Z.; Wang, H.; Tian, L.; Huang, C. Thermodynamic analysis of double-compression flash intercooling transcritical CO2 refrigeration cycle. J. Supercrit. Fluids 2016, 109, 100–108. [Google Scholar] [CrossRef]
- De Antonellis, S.; Joppolo, C.M.; Liberati, P.; Milani, S.; Romano, F. Modeling and experimental study of an indirect evaporative cooler. Energy Build. 2017, 142, 147–157. [Google Scholar] [CrossRef]
- Yu, B.; Yang, J.; Wang, D.; Shi, J.; Chen, J. An updated review of recent advances on modified technologies in transcritical CO2 refrigeration cycle. Energy 2019, 189, 116147. [Google Scholar] [CrossRef]
- Wang, D.; Liu, Y.; Kou, Z.; Yao, L.; Lu, Y.; Tao, L.; Xia, P. Energy and exergy analysis of an air-source heat pump water heater system using CO2/R170 mixture as an azeotropy refrigerant for sustainable development. Int. J. Refrig. 2019, 106, 628–638. [Google Scholar] [CrossRef]
- de Paula, C.H.; Duarte, W.M.; Rocha, T.T.M.; de Oliveira, R.N.; Mendes, R.d.P.; Maia, A.A.T. Thermo-economic and environmental analysis of a small capacity vapor compression refrigeration system using R290, R1234yf, and R600a. Int. J. Refrig. 2020, 118, 250–260. [Google Scholar] [CrossRef]
- Niu, B.; Zhang, Y. Experimental study of the refrigeration cycle performance for the R744/R290 mixtures. Int. J. Refrig. 2007, 30, 37–42. [Google Scholar] [CrossRef]
- Zhang, X.P.; Wang, F.; Fan, X.W.; Wei, X.L.; Wang, F.K. Determination of the optimum heat rejection pressure in transcritical cycles working with R744/R290 mixture. Appl. Therm. Eng. 2013, 54, 176–184. [Google Scholar] [CrossRef]
- Ju, F.; Fan, X.; Chen, Y.; Ouyang, H.; Kuang, A.; Ma, S.; Wang, F. Experiment and simulation study on performances of heat pump water heater using blend of R744/R290. Energy Build. 2018, 169, 148–156. [Google Scholar] [CrossRef]
- Ju, F.; Fan, X.; Chen, Y.; Wang, T.; Tang, X.; Kuang, A.; Ma, S. Experimental investigation on a heat pump water heater using R744/R290 mixture for domestic hot water. Int. J. Therm. Sci. 2018, 132, 1–13. [Google Scholar] [CrossRef]
- Wang, D.; Lu, Y.; Tao, L. Thermodynamic analysis of CO2 blends with R41 as an azeotropy refrigerant applied in small refrigerated cabinet and heat pump water heater. Appl. Therm. Eng. 2017, 125, 1490–1500. [Google Scholar] [CrossRef]
- Dai, B.M.; Dang, C.B.; Li, M.X.; Tian, H.; Ma, Y.T. Thermodynamic performance assessment of carbon dioxide blends with low-global warming potential (GWP) working fluids for a heat pump water heater. Int. J. Refrig. 2015, 56, 1–14. [Google Scholar] [CrossRef]
- Yu, B.; Yang, J.; Wang, D.; Shi, J.; Guo, Z.; Chen, J. Experimental energetic analysis of CO2/R41 blends in automobile air-conditioning and heat pump systems. Appl. Eng. 2019, 239, 1142–1153. [Google Scholar] [CrossRef]
- Sun, Z.; Cui, Q.; Wang, Q.; Ning, J.; Guo, J.; Dai, B.; Liu, Y.; Xu, Y. Experimental study on CO2/R32 blends in a water-to-water heat pump system. Appl. Therm. Eng. 2019, 162, 114303. [Google Scholar] [CrossRef]
- Lemmon, E.W.; Huber, M.L.; McLinden, M.O. NIST Standard Reference Database 23, Reference Fluid Thermodynamic and Transport Properties (REFPROP), Version 9.1; National Institute of Standards and Technology: Gaithersburg, MD, USA, 2013. [Google Scholar]
- GB/T21362-2008. Heat Pump Water Heater for Commercial & Industrial and Similar Application. General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China. In Standardization Administration of the People's Republic of China; General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China: Beijing, China, 2008; Volume 1. [Google Scholar]
- Brown, J.S.; Zilio, C.; Akasaka, R.; Higashi, Y. Low-GWP refrigerants. Sci. Technol. Built Environ. 2016, 22, 1075–1076. [Google Scholar] [CrossRef] [Green Version]
- Heberle, F.; Preißinger, M.; Brüggemann, D. Zeotropic mixtures as working fluids in Organic Rankine Cycles for low-enthalpy geothermal resources. Renew. Energy 2012, 37, 364–370. [Google Scholar] [CrossRef]
- Zabetakis, M.G. Flammability Characteristics of Combustible Gases and Vapors; Bureau of Mines: Washington, DC, USA, 1965. [Google Scholar]
- GB/T50178-93. Standard of climatic regionalization for architecture. In Standardization Administration of the People's Republic of China; State Bureau of Technical Supervision Ministry of Construction of the People’s Republic of China: Beijing, China, 1994; Volume 1. [Google Scholar]
- Wang, Y.K.; Ye, Z.L.; Song, Y.L.; Yin, X.; Cao, F. Energy, economic and environmental assessment of transcritical carbon dioxide heat pump water heater in a typical Chinese city considering the defrosting. Energy Convers. Manag. 2021, 233, 113920. [Google Scholar] [CrossRef]
Fluid | Molecular Mass | Boiling Temperature | Critical Temperature | Critical Pressure | ODP | GWP | ASHRAE 34 Safety Group |
---|---|---|---|---|---|---|---|
R32 | 52.02 | −51.7 °C | 78.1 °C | 5.78 MPa | 0 | 675 | A2 |
Symbol | Meaning | Unit | Value |
---|---|---|---|
ηm | Compressor mechanical efficiency | - | 0.9 |
ηe | Compressor electrical efficiency | - | 0.9 |
ηis | Compressor isentropic efficiency | - | 0.8 |
Refrigerant mass flow rate | kg⋅s−1 | 1 | |
ΔTa | Temperature difference between the air inlet and outlet | °C | 5 |
ΔTGC,pinch | Pinch point temperature difference in the gas cooler | °C | 5 |
ΔTEvap,pinch | Pinch point temperature difference in the evaporator | °C | 5 |
Item | Interpretation | Unit | Coal | Electricity |
---|---|---|---|---|
ECF | energy conversion factor | kgce⋅kg−1; kgce⋅(kW⋅h)−1 | 1 | 0.4 |
ηh | heating efficiency | % | 0.75 | 0.99 |
ηt | transmission efficiency | % | 0.8 | 0.92 |
LHV | lower heating value | kJ kg−1 | 29307 | - |
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. |
© 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Share and Cite
Wang, Y.; He, Y.; Song, Y.; Yin, X.; Cao, F.; Wang, X. Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid. Energies 2021, 14, 4470. https://doi.org/10.3390/en14154470
Wang Y, He Y, Song Y, Yin X, Cao F, Wang X. Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid. Energies. 2021; 14(15):4470. https://doi.org/10.3390/en14154470
Chicago/Turabian StyleWang, Yikai, Yifan He, Yulong Song, Xiang Yin, Feng Cao, and Xiaolin Wang. 2021. "Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid" Energies 14, no. 15: 4470. https://doi.org/10.3390/en14154470