Performance assessment of a direct expansion air conditioner working with R407C as an R22 alternative

This paper presents an experimental investigation of a direct expansion air conditioner working with R407C as an R22 alternative. Experiments are conducted on a vapor compression refrigeration system using air as a secondary fluid through both the evaporator and the condenser. The influences of the evaporator air inlet temperature (20–32 °C), the evaporator air flow rate (250–700 m³/h) and the evaporator air humidity ratio (9 and 14.5 g_wv/kg_a) at the condenser air temperature and volume flow rate of 35 °C and 850 m³/h, respectively on the system performance are investigated. Experimental results revealed that the evaporator air inlet temperature has pronounced effects on the air exit temperatures, pressures of the evaporator and the condenser, cooling capacity, condenser heat load, compressor pressure ratio and the COP of both refrigerants at humidity ratios of 9 and 14.5 g_wv/kg_a. Significant effects of the evaporator air flow rate are also gathered on the preceding parameters at the same values of mentioned-humidity ratios. The best performance, in terms of operating parameters as well as COP, can be accomplished using R22 compared to R407C. The inlet humidity ratio affects dramatically the performance of vapor compression system using R22 and R407C. The raising up humidity ratio from 9 to 14.5 g_wv/kg_a leads to an augmentation in the average cooling capacity by 29.4% and 38.5% and an enhancement in the average COP by 30% and 24.1% for R22 and R407C, respectively.     

Experimental investigation of a vapor compression heat pump used for cooling and heating applications

The present work aims at evaluating the performance characteristics of a vapor compression heat pump (VCHP) for simultaneous space cooling (summer air conditioning) and hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of evaporator water inlet temperature (14:26 °C) and condenser water inlet temperature (22:34 °C). R134a was used as a primary working fluid whereas water was adopted as a secondary heat transfer fluid at both heat source (evaporator) and heat sink (condenser) of the heat pump. Performance characteristics of the considered heat pump were characterized by outlet water temperatures, water side capacities and coefficient of performance (COP) for various operating modes namely: cooling, heating and simultaneous cooling and heating. Results showed that COP increases with the evaporator water inlet temperature while decreases as the condenser water inlet temperature increases. However, the evaporator water inlet temperature has more effect on the performance characteristics of the heat pump than that of condenser water inlet temperature. Actual COP of cooling mode between 1.9 to 3.1 and that of heating mode from 2.9 to 3.3 were obtained. Actual simultaneous COP between 3.7 and 4.9 was achieved.     

Thermodynamic analysis of R422 series refrigerants as alternative refrigerants to HCFC22 in a vapour compression refrigeration system

In the present study, the first and second law analysis of R422 series refrigerants (R422A, R422B, R422C and R422D) is presented as an alternative to HCFC22. A computational model, developed in engineering equation solver software, is employed for comparing the performance of these refrigerants in vapour compression refrigeration cycle. The thermodynamic properties of the R422 series refrigerants are computed using Refprop version 7.0. The parameters computed are volumetric cooling capacity (VCC), compressor discharge temperature, coefficient of performance (COP), exergetic efficiency and efficiency defects in system components. The results indicate that VCC, COP and exergetic efficiency for HCFC22 are higher in comparison with R422A, R422B, R422C and R422D. The efficiency defects in the condenser are largest followed by throttle valve, compressor and evaporator. Thus, the design improvement of condenser is of utmost importance to reduce the overall irreversibility and improve the system performance. Copyright © 2009 John Wiley & Sons, Ltd.     

Study on a compact silica gel–water adsorption chiller without vacuum valves: Design and experimental study

A compact silica gel–water adsorption chiller without vacuum valves was manufactured and experimentally studied. This chiller contains two adsorption/desorption chambers and one chilled water tank. Each adsorption/desorption chamber consists of one adsorber, one condenser and one evaporator. The chilled water tank is adopted to mitigate the variation of the chilled water outlet temperature. A mass recovery-like process, which is a heat recovery process between the two evaporators, was carried out in this chiller. A novel heat recovery process was also fulfilled after the mass recovery-like process to improve the coefficient of performance (COP). The cooling power and COP were 9.60 kW and 0.49 respectively when the average hot water inlet temperature, cooling water inlet temperature, and chilled water outlet temperature were 82.0, 31.6 and 12.3 °C, respectively.     

Performance of heat pumps charged with R170/R290 mixture

In this study, thermodynamic performance of R170/R290 mixture is measured on a heat pump bench tester in an attempt to substitute R22. The bench tester is equipped with a commercial hermetic rotary compressor providing a nominal capacity of 3.5 kW. All tests are conducted under the summer cooling and winter heating conditions of 7/45 °C and −7/41 °C in the evaporator and condenser, respectively. During the tests, the composition in R170/R290 mixture is varied from 0% to 10% with an interval of 2%. Test results show that the coefficient of performance (COP) and capacity of R290 are up to 15.4% higher and 7.5% lower, respectively than those of R22 for two conditions. For R170/R290 mixture, the COP decreases and the capacity increases with an increase in the composition of R170. The mixture of R170/R290 mixture at 4%/96% composition shows the similar capacity and COP as those of R22. For the mixture, the compressor discharge temperature is 17–28 °C lower than that of R22. For R170/R290 mixture, there is no problem with mineral oil since the mixture is composed of hydrocarbons. The amount of charge is reduced up to 58% as compared to R22. Overall, R170/R290 mixture is a good long term ‘drop-in’ candidate from the view point of energy efficiency and greenhouse warming to replace R22 in residential air-conditioners and heat pumps.     

Experimental investigation of a natural zeolite–water adsorption cooling unit

In this study, a thermally driven adsorption cooling unit using natural zeolite–water as the adsorbent–refrigerant pair has been built and its performance investigated experimentally at various evaporator temperatures. The primary components of the cooling unit are a shell and tube adsorbent bed, an evaporator, a condenser, heating and cooling baths, measurement instruments and supplementary system components. The adsorbent bed is considered to enhance the bed’s heat and mass transfer characteristics; the bed consists of an inner vacuum tube filled with zeolite (zeolite tube) inserted into a larger tubular shell. Under the experimental conditions of 45 °C adsorption, 150 °C desorption, 30 °C condenser and 22.5 °C, 15 °C and 10 °C evaporator temperatures, the COP of the adsorption cooling unit is approximately 0.25 and the maximum average volumetric cooling power density (SCP_v) and mass specific cooling power density per kg adsorbent (SCP) of the cooling unit are 5.2 kW/m³ and 7 W/kg, respectively.     

Experimental study of gas engine driven air to water heat pump in cooling mode

Nowadays a sustainable development for more efficient use of energy and protection of the environment is of increasing importance. Gas engine heat pumps represent one of the most practicable solutions which offer high energy efficiency and environmentally friendly for heating and cooling applications. In this paper, the performance characteristics of gas engine driven heat pump used in water cooling were investigated experimentally without engine heat recovery. The effects of several important factors (evaporator water inlet temperature, evaporator water volume flow rate, ambient air temperature, and engine speed) on the performance of gas engine driven heat pump were studied in a wide range of operating conditions. The results showed that primary energy ratio of the system increased by 22.5% as evaporator water inlet temperature increased from 13 °C to 24 °C. On the other hand, varying of engine speed from 1300 rpm to 1750 rpm led to decrease in system primary energy ratio by 13%. Maximum primary energy ratio has been estimated with a value of two over a wide range of operating conditions.     

Theoretical analysis of LiBr/H2O absorption refrigeration systems

A computational model is developed for the parametric investigation of single‐effect and series flow double‐effect LiBr/H₂O absorption refrigeration systems. The effects of generator, absorber, condenser, evaporator and dead state temperatures are examined on the performance of these systems. The parameters computed are coefficient of performance (COP), exergy destruction rates, thermal exergy loss rates, irreversibility and exergetic efficiency. The results indicate that COP and exergetic efficiency of both the systems increase with increase in the generator temperature. There exist different optimum values of generator temperature for maximum COP and maximum exergetic efficiency. The optimum generator temperature is lower corresponding to maximum exergetic efficiency as compared to optimum generator temperature corresponding to maximum COP. The effect of increase in absorber, condenser and evaporator temperatures is to decrease the exergetic efficiency of both the systems. The irreversibility is highest in absorber in both systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Transcritical CO2 refrigerator and sub‐critical R134a refrigerator: A comparison of the experimental results

This paper describes experiments comparing a commercial available R134a refrigeration plant subjected to a cold store and a prototype R744 (carbon dioxide) system working as a classical ‘split‐systems’ to cool air in residential applications in a transcritical cycle. Both plants are able to develope a refrigeration power equal to 3000 W. The R744 system utilizes aluminium heat exchangers, a semi‐hermetic compressor, a back‐pressure valve and a thermostatic expansion valve. The R134a refrigeration plant operates using a semi‐hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a manifold with two expansion valves, a thermostatic one and a manual one mounted in parallel, and an air cooling evaporator inside the cold store. System performances are compared for two evaporation temperatures varying the temperature of the external air running over the gas‐cooler and over the condenser. The refrigeration load in the cold store is simulated by means of some electrical resistances, whereas the air evaporator of the R744 plant is placed in a very large ambient. The results of the comparison are discussed in terms of temperature of the refrigerants at the compressor discharge line, of refrigerants mass flow rate and of coefficient of performance (COP). The performances measured in terms of COPs show a decrease with respect to the R134a plant working at the same external and internal conditions. Further improvements regarding the components of the cycle are necessary to use in a large‐scale ‘split‐systems’ working with the carbon dioxide. Copyright © 2009 John Wiley & Sons, Ltd.     

Exergetic analysis and optimization of a solar-powered reformed methanol fuel cell micro-powerplant

The present study proposes a combination of solar-powered components (two heaters, an evaporator, and a steam reformer) with a proton exchange membrane fuel cell to form a powerplant that converts methanol to electricity. The solar radiation heats up the mass flows of methanol-water mixture and air and sustains the endothermic methanol steam reformer at a sufficient reaction temperature (typically between 220 and 300 °C). In order to compare the different types of energy (thermal, chemical, and electrical), an exergetic analysis is applied to the entire system, considering only the useful part of energy that can be converted to work. The effect of the solar radiation intensity and of different operational and geometrical parameters like the total inlet flow rate of methanol-water mixture, the size of the fuel cell, and the cell voltage on the performance of the entire system is investigated. The total exergetic efficiency comparing the electrical power output with the exergy input in form of chemical and solar exergy reaches values of up to 35%, while the exergetic efficiency only accounting for the conversion of chemical fuel to electricity (and neglecting the ‘cost-free’ solar input) is increased up to 59%. At the same time, an electrical power density per irradiated area of more than 920 W m⁻² is obtained for a solar heat flux of 1000 W m⁻².     

Exergetic performance assessment of a variable‐speed R404a refrigeration system

The goal of this study is to carry out exergy analyses for an experimental variable‐speed refrigeration system working with R404a in order to determine irreversibility rates and exergetic efficiencies of system components and the overall system. For this aim, an experimental refrigeration system was designed with a frequency inverter mounted on compressor electric motor. Controlling the rotational speed of the compressor with a frequency inverter is one of the best methods to vary the capacity of the refrigeration system. The experiments were made for different compressor electric motor frequencies. The results showed that at low‐frequency values, irreversibility rates of the system decreased and exergetic efficiencies were increased. In addition, the major irreversibility occurs in the compressor by 61.47–61.83% followed by condenser by 17.00–16.52%, evaporator by 12.39–13.73% and expansion valve by 6.24–6.76% for different compressor frequencies. Copyright © 2009 John Wiley & Sons, Ltd.     

Change in energy performance as a result of a R422D retrofit: An experimental analysis for a vapor compression refrigeration plant for a walk-in cooler

In this paper, the energy performance of a walk-in cooler working with R22 and its substitute R422D are experimentally studied. The experimental investigation was carried out considering three different operating conditions; in particular, the AHRI standard has been used as reference for operating conditions. All tests were run at steady state conditions and keeping the external air temperature at 35 °C. The experimental analysis allowed the determination of cooling capacity, the electrical power absorbed, the COP and other variables characterizing the working of the plant. The results demonstrated that the cooling capacity for R422D was lower than for R22, while the electrical power absorbed with R422D was higher than that with R22. As consequence, the COP of R422D was lower than that of R22. Furthermore, technical proposals are introduced with the aim of improving the overall performances of those plants, which could be retrofitted with R422D.     

Heat extraction from salinity-gradient solar ponds using heat pipe heat exchangers

This paper presents the results of experimental and theoretical analysis on the heat extraction process from solar pond by using the heat pipe heat exchanger. In order to conduct research work, a small scale experimental solar pond with an area of 7.0 m² and a depth of 1.5 m was built at Khon Kaen in North-Eastern Thailand (16°27′N102°E). Heat was successfully extracted from the lower convective zone (LCZ) of the solar pond by using a heat pipe heat exchanger made from 60 copper tubes with 21 mm inside diameter and 22 mm outside diameter. The length of the evaporator and condenser section was 800 mm and 200 mm respectively. R134a was used as the heat transfer fluid in the experiment. The theoretical model was formulated for the solar pond heat extraction on the basis of the energy conservation equations and by using the solar radiation data for the above location. Numerical methods were used to solve the modeling equations. In the analysis, the performance of heat exchanger is investigated by varying the velocity of inlet air used to extract heat from the condenser end of the heat pipe heat exchanger (HPHE). Air velocity was found to have a significant influence on the effectiveness of heat pipe heat exchanger. In the present investigation, there was an increase in effectiveness by 43% as the air velocity was decreased from 5 m/s to 1 m/s. The results obtained from the theoretical model showed good agreement with the experimental data.     

PERFORMANCE OF A HEAT PUMP USING DIRECT EXPANSION SOLAR COLLECTORS

Theoretical and experimental studies were made on the thermal performance of a heat pump that used a bare flat-plate collector as the evaporator. The analysis used empirical equations to express the electric power consumption of the compressor and coefficient of performance (COP), as functions of temperature of evaporation at the evaporator and that of the heat transfer medium (water) at the inlet of the condenser. The experimental heat pump had a compressor with a rated capacity of 350 W and collectors with the total area of 3.24 m². Around noon in winter the evaporator temperature was found to be about 17°C higher than the ambient air temperature of 8°C, and a COP of about 5.3 was obtained when the water temperature at the condenser inlet was 40°C. These measured evaporation temperatures and COPs were in good agreement with those predicted by the analysis. According to the analysis, the total area of the collectors in the experiment was appropriate for the heat pump system. Also, the 1-mm thickness of the collector's copper plate used in the experiment could be 0.5 mm with little reduction of COP. The pitch of the tube soldered to the copper plate for the refrigerant flow was 100 mm in the experiment, but the COP would only be reduced by about 4% if the pitch were changed to 190 mm.     

Performance of a gas engine heat pump (GEHP) using R410A for heating and cooling applications

A gas engine heat pump (GEHP) represents one of the most practicable systems which improve the overall energy utilization efficiency and reduce the operating cost for heating and cooling applications. The present work aimed at evaluating the performance of a GEHP for air-conditioning and hot water supply. In order to achieve this objective, a test facility was developed and experiments were performed over a wide range of engine speed (1200 rpm–1750 rpm), ambient air temperature (24.1 °C–34.8 °C), evaporator water flow rate (1.99 m³/h–3.6 m³/h) and evaporator water inlet temperature (12.2 °C–23 °C). Performance characteristics of the GEHP were characterized by water outlet temperatures, cooling capacity, heating capacity and primary energy ratio (PER). The results showed that the effect of evaporator water inlet temperature on the system performance is more significant than the effects of ambient air temperature and evaporator water flow rate. PER of the considered system at evaporator water inlet temperature of 23 °C is higher than that one at evaporator water inlet temperature of 12.2 °C by about 22%. PER of the system decreases by 16% when engine speed changes from 1200 rpm to 1750 rpm.     

Experimental research and operation optimization of an air-source heat pump water heater

In order to optimize design and operation strategy of air-source heat pump water heater, an experimental set-up and simulation model were constructed. Also, a methodology of optimizing operation, which takes into account thermostatic and timing control patterns, was presented and applied. Experimental results indicated that the average COP ranged from 2.82 to 5.51 under typical conditions. The recommended outside area ratio of condenser coil to evaporator is 0.14−0.31 when the evaporator outside area is between 6.0 and 6.5 m² for this set-up. The optimal start-up time was between 12:00 and 14:00 if there was no electricity price difference between day and night, or it was near 22:00. The optimal setting water temperature should be adjusted according to the variation of seasonal ambient temperature. It was suggested that, based on this set-up, setting water temperature should be set higher than 46 °C in summer and 50 °C in other seasons.     

A solar ejector cooling system using refrigerant R134a in the Athens area

This paper describes the performance of an ejector cooling system driven by solar energy and R134a as working fluid. The system operating in conjunction with intermediate temperature solar collector in Athens, is predicted along the 5 months (May–September). The operation of the system and the related thermodynamics are simulated by suitable computer codes and the required local climatologically data are determined by statistical processing over a considerable number of years. It was fount that the COP of ejector cooling system varied from 0.035 to 0.199 when the operation conditions were: generator temperature (82–92 °C), condenser temperature (32–40 °C) and evaporator temperature (−10–0 °C). For solar cooling application the COP of overall system varied from 0.014 to 0.101 with the same operation conditions and total solar radiation (536–838 W/m²) in July.     

Neural networks—a new approach to model vapour‐compression heat pumps

The aim of this paper is to model the steady‐state performance of a vapour‐compression liquid heat pump with the use of neural networks. The model uses a generalized radial basis function (GRBF) neural network. Its input vector consists only of parameters that are easily measurable, i.e. the chilled water outlet temperature from the evaporator, the cooling water inlet temperature to the condenser and the evaporator capacity. The model then predicts relevant performance parameters of the heat pump, especially the coefficient of performance (COP). Models are developed for three different refrigerants, namely LPG, R22 and R290. It is found that not every model achieves the same accuracy. Predicted COP values, when LPG or R22 are used as refrigerant, are usually accurate to within 2 per cent, whereas many predictions for R290 deviate more than ±10 per cent. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance simulation of refrigerated display cabinets operating with refrigerants R22 and R404A

This paper describes the analysis and performance comparison of a display cabinet system using refrigerant R404A and its substitute refrigerant R22. The model of the display cabinet is developed at steady state and integrated from three main component sub-models, air-cooling finned-tube evaporator, air curtain and display cabinet body. The evaporator model is built up based on the distributed method, which can simulate the heat exchangers with different circuit structures. The frost effect on the performance of the evaporator is included in the model. The correlations for the heat transfer and pressure drop calculations of both air and refrigerant sides are purposely selected in the evaporator model. In addition, the evaporator model has been validated with experimental results at steady states from published literature. Several correlated functions from the detailed numerical solution are used for the model of the air curtain. Some simplifications are also utilized for the model of display cabinet body. The performance simulation and comparison of the display cabinet using refrigerants R404A and R22 are carried out at different indoor ambient conditions especially at varied ambient air humidity to mimic the actual indoor space conditions in super stores. Some significant results such as the comparison of cooling load requirement for different refrigerant display cases have been obtained from the simulation, which can significantly contribute to the optimal cabinet design and operating analysis.     

Shell-and-tube evaporator model performance with different two-phase flow heat transfer correlations. Experimental analysis using R134a and R1234yf

This work presents a model of a shell-and-tube evaporator using R1234yf and R134a as working fluids. The model uses the effectiveness-NTU method to predict the evaporation pressure and the refrigerant and secondary fluid temperatures at the evaporator outlet, using as inputs the geometry of the evaporator, the refrigerant mass flow rate and evaporator inlet enthalpy, and the secondary fluid volumetric flow rate and evaporator inlet temperature. The model performance is evaluated using different two-phase flow heat transfer correlations through model outputs, comparing predicted and experimental data. The output parameter with maximum deviations between the predicted and experimental data is the evaporating pressure, being the deviations in outlet temperatures less than 3%. The evaporator model using Kandlikar's correlation obtains the highest precision and the lowest absolute mean error, with 4.87% in the evaporating pressure, 0.45% in the refrigerant outlet temperature and 0.03% in the secondary fluid outlet temperature.