Modelling of CO 2 trans-critical refrigeration system with IHX. • ANN vs physics-based model up t... more Modelling of CO 2 trans-critical refrigeration system with IHX. • ANN vs physics-based model up to warm climate condition of 45°C. • The mean relative error below ± 1% for ANN model. • Trained ANN employed to explore optimisation of two controllable parameters. • A possibility of 5.31% improvement in COP.
The use of air conditioning equipment is becoming more frequent, and new technologies are emergin... more The use of air conditioning equipment is becoming more frequent, and new technologies are emerging to increase the efficiency of the process and decrease the operating costs of air conditioning systems. In data centres, where electric power consumption is high and indoor cooling is a constant, the air conditioning systems are responsible for a large part of the building's energy consumption. In this work, a data centre with a twenty years old cooling system (with production of chilled water-CW), was analysed and is about to be replaced. In order to meet the thermal load of the building, two solutions were proposedwith a more efficient refrigeration system: one with production of chilled water (case 1) and another one with a direct expansion system (DX, case 2). It was also analysed the possibility to use free cooling in both of them. In both cases the results obtained shows a significant reduction on the energy consumption and consequently a reduction in the CO 2 emissions, regarding the old system. An economic analysis was also carried and the conclusions were that they are profitable. The final decision is due to the customer.
Effect of inter-stage pressure on the performance of a two stage refrigeration cycle using inter ... more Effect of inter-stage pressure on the performance of a two stage refrigeration cycle using inter cooler is studied based on thermodynamic modelling. Six common refrigerants are selected for the analyses. These are R134a, R22 and R143a as synthetic refrigerants and propane, carbon dioxide and nitrous oxide as natural refrigerants. The designed input range is-50 o C to-30 o C for evaporator temperature and 40 o C to 60 o C for heat rejection temperature. Three classical relations for estimating inter-stage pressure in a two stage refrigeration system are selected and the performance is evaluated against optimized inter-stage pressure corresponding to the best COP. Results show that for trans-critical cycles, the deviation of optimized inter-stage pressure with the classical ones is considerable, while for sub-critical cycles, COP is very less sensitive to inter-stage pressure. Further, comprehensive analysis of CO 2 based trans-critical refrigeration system is presented for a wider range covering-50 o C to 10 o C evaporation temperature and 35 o C to 60 o C gas cooler outlet temperature. A correlation for estimating optimum inter-stage and gas cooler pressure for the same is also formulated. With gradual increase in focus towards adoption of natural refrigerants like CO 2 , the effect of inter stage pressure is expected to be an important consideration in warmer climatic condition.
This paper presents the techno‐economic assessment of different selected and proposed, CO2 booste... more This paper presents the techno‐economic assessment of different selected and proposed, CO2 booster configurations for supermarket applications. The mathematical model has been developed for eight different configurations and, analyzed for year‐round operations in five selected major cities of India having different climatic conditions. The performance of the configurations is evaluated in terms of annual energy saving, seasonal energy efficiency ratio, life cycle cost, and additional investment recovery time(AIRT). Subsequently, the performance of the systems are compared with the Basic Booster System (BBS). The results show, 357.4 MWh of maximum AES, and 51.2% of enhancement in SEER, for BBS with both low and medium temperature‐flooded evaporator integrated with the modified evaporative cooler (BBSM‐LT + MT) configuration over BBS in Ahmedabad, India, compared to the selected cities in India. The economic analysis reveals that BBSM‐LT + MT configuration has minimum AIRT of 1.2 years for Ahmedabad, India compared to selected cities in India. Hence, the performance of BBSM‐LT + MT is better compared to other investigated configurations, for all the selected cities. The proposed configurations can be considered as suitable option for supermarket application in terms of energy, environment, and economy.
Experimental investigation on CO 2 trans-critical refrigeration system with IHX. • Evaluation of ... more Experimental investigation on CO 2 trans-critical refrigeration system with IHX. • Evaluation of energetic and exergetic parameters up to warm climate condition of 45°C. • Cycle performance considering effect of gas cooler side air velocity. • Maximum improvement in COP and exergetic efficiency of IHX cycle as 5.71% and 5.05% respectively. • IHX to have least contribution towards exergy loss in the cycle.
This article presents a thermodynamic analysis of a hypothetical trans-critical CO2 refrigeration... more This article presents a thermodynamic analysis of a hypothetical trans-critical CO2 refrigeration system with enhanced booster and parallel compression for supermarket application in warm climatic conditions (35-50°C). The proposed system simultaneously incorporates two medium temperature and three low temperature loads for five different cooling demands typically found in supermarket application. These are HVAC load at 5°C, storage of dairy products at O°C, frozen ice cream, vegetable and animal products at -10°C, -20°C and -30°C respectively. Some of the major parameters affecting performance like gas cooler operating pressure, inter-mediate vessel pressure, mass flow rate and gas cooler inlet temperature are investigated to reveal the practicality of the proposed system. The simulation results show that the new cycle configuration has a distinct advantage over a few other modified cycles proposed from time to time for supermarket refrigeration in warm climatic conditions. A few p...
Carbon dioxide is one of the rediscovered sustainable options, as CFCs and HFCs are now in the li... more Carbon dioxide is one of the rediscovered sustainable options, as CFCs and HFCs are now in the list of regulated substances, to be phased out in time bound way. There are however various challenges to the successful use of CO2 as refrigerant. Cost effective and widely acceptable technology is demand of the time. Performance of trans-critical CO2 refrigeration systems is found to be sensitive to the gas cooler design. In the present work a detailed mathematical model is developed for a finned tube air cooled gas cooler and the same is validated using published literature. Subsequently, to achieve the lowest possible approach temperature, the performance of the gas cooler is analyzed for various air velocity and alternate pipe arrangements. The effect of increase in size of gas cooler to its performance is also studied.
Modelling of CO 2 trans-critical refrigeration system with IHX. • ANN vs physics-based model up t... more Modelling of CO 2 trans-critical refrigeration system with IHX. • ANN vs physics-based model up to warm climate condition of 45°C. • The mean relative error below ± 1% for ANN model. • Trained ANN employed to explore optimisation of two controllable parameters. • A possibility of 5.31% improvement in COP.
The use of air conditioning equipment is becoming more frequent, and new technologies are emergin... more The use of air conditioning equipment is becoming more frequent, and new technologies are emerging to increase the efficiency of the process and decrease the operating costs of air conditioning systems. In data centres, where electric power consumption is high and indoor cooling is a constant, the air conditioning systems are responsible for a large part of the building's energy consumption. In this work, a data centre with a twenty years old cooling system (with production of chilled water-CW), was analysed and is about to be replaced. In order to meet the thermal load of the building, two solutions were proposedwith a more efficient refrigeration system: one with production of chilled water (case 1) and another one with a direct expansion system (DX, case 2). It was also analysed the possibility to use free cooling in both of them. In both cases the results obtained shows a significant reduction on the energy consumption and consequently a reduction in the CO 2 emissions, regarding the old system. An economic analysis was also carried and the conclusions were that they are profitable. The final decision is due to the customer.
Effect of inter-stage pressure on the performance of a two stage refrigeration cycle using inter ... more Effect of inter-stage pressure on the performance of a two stage refrigeration cycle using inter cooler is studied based on thermodynamic modelling. Six common refrigerants are selected for the analyses. These are R134a, R22 and R143a as synthetic refrigerants and propane, carbon dioxide and nitrous oxide as natural refrigerants. The designed input range is-50 o C to-30 o C for evaporator temperature and 40 o C to 60 o C for heat rejection temperature. Three classical relations for estimating inter-stage pressure in a two stage refrigeration system are selected and the performance is evaluated against optimized inter-stage pressure corresponding to the best COP. Results show that for trans-critical cycles, the deviation of optimized inter-stage pressure with the classical ones is considerable, while for sub-critical cycles, COP is very less sensitive to inter-stage pressure. Further, comprehensive analysis of CO 2 based trans-critical refrigeration system is presented for a wider range covering-50 o C to 10 o C evaporation temperature and 35 o C to 60 o C gas cooler outlet temperature. A correlation for estimating optimum inter-stage and gas cooler pressure for the same is also formulated. With gradual increase in focus towards adoption of natural refrigerants like CO 2 , the effect of inter stage pressure is expected to be an important consideration in warmer climatic condition.
This paper presents the techno‐economic assessment of different selected and proposed, CO2 booste... more This paper presents the techno‐economic assessment of different selected and proposed, CO2 booster configurations for supermarket applications. The mathematical model has been developed for eight different configurations and, analyzed for year‐round operations in five selected major cities of India having different climatic conditions. The performance of the configurations is evaluated in terms of annual energy saving, seasonal energy efficiency ratio, life cycle cost, and additional investment recovery time(AIRT). Subsequently, the performance of the systems are compared with the Basic Booster System (BBS). The results show, 357.4 MWh of maximum AES, and 51.2% of enhancement in SEER, for BBS with both low and medium temperature‐flooded evaporator integrated with the modified evaporative cooler (BBSM‐LT + MT) configuration over BBS in Ahmedabad, India, compared to the selected cities in India. The economic analysis reveals that BBSM‐LT + MT configuration has minimum AIRT of 1.2 years for Ahmedabad, India compared to selected cities in India. Hence, the performance of BBSM‐LT + MT is better compared to other investigated configurations, for all the selected cities. The proposed configurations can be considered as suitable option for supermarket application in terms of energy, environment, and economy.
Experimental investigation on CO 2 trans-critical refrigeration system with IHX. • Evaluation of ... more Experimental investigation on CO 2 trans-critical refrigeration system with IHX. • Evaluation of energetic and exergetic parameters up to warm climate condition of 45°C. • Cycle performance considering effect of gas cooler side air velocity. • Maximum improvement in COP and exergetic efficiency of IHX cycle as 5.71% and 5.05% respectively. • IHX to have least contribution towards exergy loss in the cycle.
This article presents a thermodynamic analysis of a hypothetical trans-critical CO2 refrigeration... more This article presents a thermodynamic analysis of a hypothetical trans-critical CO2 refrigeration system with enhanced booster and parallel compression for supermarket application in warm climatic conditions (35-50°C). The proposed system simultaneously incorporates two medium temperature and three low temperature loads for five different cooling demands typically found in supermarket application. These are HVAC load at 5°C, storage of dairy products at O°C, frozen ice cream, vegetable and animal products at -10°C, -20°C and -30°C respectively. Some of the major parameters affecting performance like gas cooler operating pressure, inter-mediate vessel pressure, mass flow rate and gas cooler inlet temperature are investigated to reveal the practicality of the proposed system. The simulation results show that the new cycle configuration has a distinct advantage over a few other modified cycles proposed from time to time for supermarket refrigeration in warm climatic conditions. A few p...
Carbon dioxide is one of the rediscovered sustainable options, as CFCs and HFCs are now in the li... more Carbon dioxide is one of the rediscovered sustainable options, as CFCs and HFCs are now in the list of regulated substances, to be phased out in time bound way. There are however various challenges to the successful use of CO2 as refrigerant. Cost effective and widely acceptable technology is demand of the time. Performance of trans-critical CO2 refrigeration systems is found to be sensitive to the gas cooler design. In the present work a detailed mathematical model is developed for a finned tube air cooled gas cooler and the same is validated using published literature. Subsequently, to achieve the lowest possible approach temperature, the performance of the gas cooler is analyzed for various air velocity and alternate pipe arrangements. The effect of increase in size of gas cooler to its performance is also studied.
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Papers by Dileep Gupta