Conventional Vapor Compression Refrigeration System Research Articles

The Effect of Electric Load Profiles on the Performance of Off-Grid Residential Hybrid Renewable Energy Systems

This paper investigates the energy performance of off-grid residential hybrid renewable electric power systems, particularly the effect of electric load profiles on the ability to harvest available solar energy and avoid the consumption of auxiliary energy in the form of propane. The concepts are illustrated by an analysis of the energy performance of electric and propane-fired refrigerators. Off-grid electric power systems frequently incorporate a renewable source, such as wind or solar photovoltaic (PV), with a back-up power provided by a propane fueled motor/generator. Among other design decisions, residential consumers face the choice of employing an electric refrigerator with a conventional vapor compression refrigeration system, or a fuel-fired refrigerator operating as an absorption refrigeration system. One interesting question is whether it is more advantageous from an energy perspective to use electricity to run the refrigerator, which might be provided by some combination of the PV and propane motor/generator, thereby taking advantage of the relatively higher electric refrigerator Coefficient of Performance (COP) and free solar energy but having to accept a low electrical conversion efficiency of the motor/generator, or use thermal energy from the combustion of propane to produce the refrigeration effect via an absorption system, albeit with a much lower COP. The analysis is complicated by the fact that most off-grid renewable electrical power systems utilize a battery bank to provide electrical power when it is not available from the wind turbine or PV system, so the state of charge of the battery bank will have a noticeable impact on what energy source is available at any moment in time. Daily electric load profiles combined with variable solar energy input determine the state of charge of the battery bank, with the degree of synchronization between the two being a critical factor in determining performance. The annual energy usage and fuel input depend strongly on the ability to make use of the renewable sources in real time to avoid battery bank conversion losses and dumping of excess electrical power, as well as to have sufficient battery storage capacity to minimize the need for operation of the motor/generator to meet electric loads which occur during periods when the renewable energy is not available.

A Review on Working Pair Used in Adsorption Cooling System

Adsorption cooling system find its application in refrigeration, air conditioning, chiller, Ice making, etc. It uses thermal energy as driving force. Adsorption systems are environmental friendly (zero global warming potential and ozone depleting potential) and also eliminates use of compressor and minimize vibration problem. So it can be used as substitute for conventional vapor compression refrigeration system or vapor absorption system. The adsorption generally classified in two types as physical adsorption (due to weak van der waal forces) and chemical adsorption (chemical reaction between adsorbent and adsorbate form new molecules). The working pair of adsorber and adsorbate play vital role in the performance of adsorption system. Activated carbon, zeolite, silica gel are commonly used adsorber and water, ammonia, methanol and ethanol can be used as adsorbate. The poor heat and mass transfer performance of adsorption is major challenge for researchers. The heat transfer performance of adsorption system can be increased by increasing heat transfer area of adsorber bed i.e., design of new adsorber bed, while mass transfer performance is improved by use of new adsorbent with higher sorption rate. Composite adsorber solve the problem of heat and mass transfer performance of chemical adsorbents and adsorption quantity of physical adsorbents by combination of chemical and physical adsorbent but it can add some limitation with it. In this paper, various adsorption pair, their selection, design of adsorber bed, methods to improve thermal performance of adsorber bed is reviewed with their properties, advantages and limitations.

Investigation Analysis on the Performance Improvement of a Vapor Compression Refrigeration System

The principal objective of the paper is to modify the conventional vapor compression refrigeration system by connecting heat exchangers thereby heating and cooling of water is done simultaneously. The vapor refrigerant is supplied to the hermetic sealed compressor where the refrigerant gets compressed to a temperature of 100-120◦ C. The compressor is connected to a counter flow heat exchanger. Experimentation is carried out to design and manufacture a modified vapor compression refrigeration system. The main parameters considered during the design are connection of a compressor to a hermetically sealed compressor, keeping polyurethane foam as insulating material, adjusting the capillary tube and finned evaporators. The operations carried during the fabrication of equipment are bending, brazing and arc welding process. After the experimental setup has been fabricated the system is checked for the performance by using refrigerants R-22 and R-407.The results are plotted between heating temperatures, cooling temperatures with respect to time in minutes.

A proposed subcooling method for vapor compression refrigeration cycle based on expansion power recovery

This study proposes a new subcooling method for vapor compression refrigeration cycle based on expansion power recovery. In a main refrigeration cycle, expander output power is employed to drive a compressor of the auxiliary subcooling cycle, and refrigerant at the outlet of condenser is subcooled by the evaporative cooler, which makes the hybrid system get much higher COP. Various refrigerants, including R12, R134a, R22, R32, R404A, R41, R507A, R717, and R744, are considered. Thermodynamic analysis is made to discuss the effects of operation parameters (expander efficiency and inlet temperature of cooling water) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves much higher COP than the conventional vapor compression refrigeration system, conventional mechanical subcooling system and conventional expansion power recovery system, with maximum COP increments 67.76%, 19.27% and 17.73%, respectively when R744 works as the refrigerant in the main refrigeration cycle. It is most beneficial for R12 and R717 in the auxiliary subcooling cycle and R744, R404A and R507A in the main refrigeration cycle.

Cooling performance and energy saving analysis of cascade refrigeration system powered by solar energy for Riyadh region (Saudi Arabia)

Energy saving and reduction in the green house gas emissions are key to the growth of the economy of a country. The study's objective is to develop a solar-powered cascade refrigeration system. The solar assisted cascade system is the combination of electricity-powered conventional vapour compression refrigeration system (VCRS) and solar-powered vapor absorption refrigeration system (VARS), connected in series. The system performance is analysed based on the solar thermal energy potential available at Riyadh region of the Kingdom of Saudi Arabia (KSA). NH3 − H2O mixture is used in VARS and three different refrigerants of highest performance are selected for VCRS. Thermal Energy Storage (TES) is used to store potential energy to keep the system operating round the clock continuously. The results indicate that the coefficient of performance (COP) of the proposed system is superior compared to the conventional VCRS and has a 44.7% saving in electrical energy consumption during peak load demands. It is notice...

Thermodynamic analysis of a novel energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation

A new energy-efficient refrigeration system subcooled by liquid desiccant dehumidification and evaporation was proposed in this paper. In the system, liquid desiccant system could produce very dry air for an indirect evaporative cooler, which would subcool the vapor compression refrigeration system to get higher COP than conventional refrigeration system. The desiccant cooling system can use the condensation heat for the desiccant regeneration. Thermodynamic analysis is made to discuss the effects of operation parameters (condensing temperature, liquid desiccant concentration, ambient air temperature and relative humidity) on the system performance. Results show that the proposed hybrid vapor compression refrigeration system achieves significantly higher COP than conventional vapor compression refrigeration system, and even higher than the reverse Carnot cycle at the same operation conditions. The maximum COPs of the hybrid systems using hot air and ambient air are 18.8% and 16.3% higher than that of the conventional vapor compression refrigeration system under varied conditions, respectively.

Thermodynamic performance analysis of a vapor compression–absorption cascaded refrigeration system

In the present study, a thermodynamic model for cascaded vapor compression–absorption system (CVCAS) has been developed which consists of a vapor compression refrigeration system (VCRS) coupled with single effect vapor absorption refrigeration system (VARS). Based on first and second laws, a comparative performance analysis of CVCAS and an independent VCRS has been carried out for a design capacity of 66.67kW. The results show that the electric power consumption in CVCAS is reduced by 61% and COP of compression section is improved by 155% with respect to the corresponding values pertaining to a conventional VCRS. However there is a trade-off between these parameters and the rational efficiency which is found to decrease to half of that for a VCRS. The effect of various operating parameters, i.e., superheating, subcooling, cooling capacity, inlet temperature and the product of effectiveness and heat capacitance of external fluids are extensively studied on the COP, total irreversibility and rational efficiency of the CVCAS. Besides, the performance of environment friendly refrigerants such as R410A, R407C and R134A is found to be almost at par with that of R22. Hence, all the alternative refrigerants selected herein can serve as potential substitutes for R22. Furthermore, it has been found that reducing the irreversibility rate of the condenser by one unit due to decrease in condenser temperature depicted approximately 3.8 times greater reduction in the total irreversibility rate of the CVCAS, whereas unit reduction in the evaporator’s irreversibility rate due to increase in evaporator temperature reduced total irreversibility rate by 3.4 times for the same system. Since the changes in the inlet temperatures of external fluid in the condenser and the evaporator contribute significant changes in system’s overall irreversibility, due consideration is required in condenser and evaporator temperatures to improve the system performance.

Performance Analysis of Solar-Assisted Refrigeration Cycle

Energy-conservation and environmental protection are keys to sustainable development of domestic economy. The solar-assisted cascade refrigeration cycle system is developed. The system consists of electricity-driven vapor compression refrigeration system and solar-driven vapor absorption refrigeration system. The vapor compression refrigeration system is connected in series with vapor absorption refrigeration system. Refrigerant and solution reservoirs are designed to store potential to keep the system operating continuously without sunlight. The results indicate that the system obtains pretty higher COP as compared with the conventional vapor compression refrigeration system. COP of the new-type vapor compression refrigeration system increases as sunlight becomes intense.

Study on Solar-Assisted Cascade Refrigeration System

Energy-conservation and environmental protection are keys to sustainable development of domestic economy. The solar-assisted cascade refrigeration system is developed. The system consists of electricity-driven vapor compression refrigeration system and solar-driven vapor absorption refrigeration system. The vapor compression refrigeration system is connected in series with vapor absorption refrigeration system. Refrigerant and solution reservoirs are designed to store potential to keep the system operating continuously without sunlight. The results indicate that the system obtains pretty higher COP as compared with the conventional vapor compression refrigeration system. COP of the new-type vapor compression refrigeration system increases as sunlight becomes intense.

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.

Performance evaluation of locality-based compact solar refrigeration system

Cooling system with low capacity utilising solar power can be widely used for remote and rural cooling applications. This paper describes the trend of solar insolation for a period of one year at Tiruvannamalai town, a district capital in Tamil Nadu state, South India which is geographically located at latitude 12.229 N, longitude 79.076 E. The performance of a compact solar refrigeration system attached with micro spray nozzles in the evaporator chamber during specified period was studied. The analysis of the result shows that the coefficient of performance of the compact solar refrigeration system is consistent in the range between 0.3 and 0.5 during the period when the solar insolation was high and also performs well during low solar insolation days due to the fewer loads on the system. The trend signifies that the area of the solar collector can be reduced to 20 to 30 percentages for the required load during winter seasons. Also the cost analysis made for operating the system with conventional vapour compression refrigeration system of the same capacity was compared and the proposed system was found economical during operation.

Experimental investigation on a solid desiccant system integrated with a R407C compression air conditioner

In the present work, experimental performance data of a solid desiccant based hybrid air conditioning system are presented. The system consists of a packed bed solid desiccant integrated with a R407C conventional vapor compression refrigeration system. Experiments are carried out during dehumidification operation mode for various operating parameters such as; desiccant mass on shelves (5, 10 and 15 kg), air mass flow rate (7.4 and 10.2 kg/min), shelves number (1, 2 and 3) and three values of shelves span (7, 14 and 28 cm) at evaporator air inlet conditions of 28 °C DBT and 66% RH, condenser air inlet volume flow rate of 850 m 3/h and temperature of 35 °C. The reactivation of the desiccant at different regeneration temperatures and air flow rates as well as desiccant masses is also investigated. During the dehumidification mode, the average system coefficient of performance increases by 6.2% and 1.61% when the mass of desiccant increases from 5 to 10 kg and from 10 to 15 kg, respectively. The enhancement in the coefficient of performance is 6.2% due to increasing the air mass flow rate from 7.4 to 10.2 kg/min. Increasing both shelves number and span yields to a reduction in the adsorption rate that can be extracted by the desiccant material in the ranges of considered operating conditions. The regeneration temperature and the air flow rate of regeneration have significant effects on the reactivation process. It was found that, with increasing the mass flow rate of regenerated air from 7.4 to 10.2 kg/min produces a reduction in regeneration time by 87.5% and an augmentation in the desorption rate by 16% after 10 min of regeneration. In addition, with escalating the regeneration temperature from 45 to 55 °C, the reactivation time reduces by 25%. Reported results revealed that solid desiccant based hybrid air conditioning system reduces the compressor electric power and the number of electric unit (kW h) by 10.2%.

Simulation of absorption refrigeration system for automobile application

An automotive air-conditioning system based on absorption refrigeration cycle has been simulated. This waste heat driven vapor absorption refrigeration system is one alternate to the currently used vapour compression refrigeration system for automotive air-conditioning. Performance analysis of vapor absorption refrigeration system has been done by developing a steady-state simulation model to find the limitation of the proposed system. The water-lithium bromide pair is used as a working mixture for its favorable thermodynamic and transport properties compared to the conventional refrigerants utilized in vapor compression refrigeration applications. The pump power required for the proposed vapor absorption refrigeration system was found lesser than the power required to operate the compressor used in the conventional vapor compression refrigeration system. A possible arrangement of the absorption system for automobile application is proposed.

Performance analysis of activated carbon + HFC-134a adsorption coolers

The purpose of this paper is to present the results of performance analysis of a heat driven continuous vapor adsorption refrigerator with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC-134a) as the refrigerant. A set of four adsorption cells takes on the role of the mechanical compressor in the conventional vapor compression refrigeration (VCR) system. Three specimens of activated charcoal under various packing densities were investigated. A parametric analysis was carried out with several evaporating, condensing/adsorbing and desorbing temperatures which are typical operating conditions catered to by HFC-134a. A new integrated relative performance evaluation scheme is proposed. It uses the maximum cycle uptake difference as a factor against which the coefficient of performance (COP) and exergetic efficiency are evaluated. It is shown that there is an optimal set of operating conditions wherein the exergetic efficiency is the maximum. A major part of the thermal energy input is for sensible heating of the compressor body.

Vapor Absorption Refrigeration in Road Transport Vehicles

This study includes an experimental investigation into the use of vapor absorption refrigeration (VAR) systems in road transport vehicles using the waste heat in the exhaust gases of the main propulsion unit as the energy source. This would provide an alternative to the conventional vapor compression refrigeration system and its associated internal combustion engine. The performance of a VAR system fired by natural gas is compared with that of the same system driven by engine exhaust gases. This showed that the exhaust-gas-driven system produced the same performance characteristics as the gas-fired system. It also suggested that, with careful design, inserting the VAR system generator into the main engine exhaust system need not impair the performance of the vehicle propulsion unit. A comparison of the capital and running costs of the conventional and proposed alternative system is made. Suggestions are also made regarding operation of the VAR system during off-road/slow running conditions.