Vapor Compression Cycle Research Articles

Experimental study and performance analysis of a mobile autonomous atmospheric water generator designed for arid climatic conditions

To offer an alternative way of supplying potable water to people in desert climatic conditions, a prototype of a mobile autonomous atmospheric water generator was designed, constructed, and experimentally investigated. The dimensions of the prototype are 1 × 1.4 × 1 m. To ensure the efficient water extraction from the atmospheric vapour in the desert climatic conditions, a desiccant wheel was used to provide a water vapour mass transfer from one airflow to another. Cooling the air stream (120 m3/h) below the dew point temperature was realised by a vapour compression cycle. The influence of the climatic conditions (air temperature and humidity ratio) on the water production, energy consumption, and device performance was studied and analysed. The developed prototype can effectively harvest water in arid locations with a water harvesting rate (WHR) from 0.23 kg/h to 1.45 kg/h and a unit performance coefficient (UPC) from 1.00 kWh/kg to 4.65 kWh/kg. Subsequently, a whole year simulation analysis with different control strategies was conducted for the desert climatic conditions of Riyadh (Saudi Arabia) and Tamanrasset (Algeria). The results of the simulation showed that, in the fully autonomous mode, annual average daily water production rates of 7.9 kg/day and 8.1 kg/day were achieved for the Riyadh and Tamanrasset climatic conditions, respectively, proving it to be an efficient and valuable solution for potable water production in extremely dry and hot regions.

Penentuan ukuran pipa kapiler dengan program aplikasi CapSel Versi 1.0 pada AC trainer unit jenis ekspansi langsung dengan R-410A

The use of air conditioning system currently mostly uses the vapor compression cycle. One such air conditioning machine is a direct expansion type AC. In this type of air conditioner, the air is directly cooled by the refrigerant. Cold air is flowed through the air duct to be entered into the room to be cooled. The refrigerant used is R-410A which does not contain chlorine so it does not cause depletion of the ozone layer because it has an ODP = 0. This direct expansion unit trainer uses an expansion device in the form of a capillary tube and an external equalizer type TXV. To determine the size of the capillary tube on the trainer unit, the direct expansion type uses the CapSel version 1.0 application program. By using the input data for refrigerant type R-134A, refrigeration capacity 2,637.6 Watt (9000 BTU/hour), evaporation temperature 5 °C condensation temperature 47 °C, and return gas temperature 12 °C, the recommended capillary pipe size data is obtained, namely the length of the pipe. capillary 1.47 m with an inner diameter of 2.50 mm. The test was carried out by varying the velocity of the air leaving the airways at high speed (22.3 ft/s) and at low speed (7.9 ft/s). The refrigerant temperature and pressure data are measured at 4 measurement points and the measurement of the electric current entering the system. After processing the data and entering it into the Coolpack application program, the average COP and EER in the low speed position produce a higher price than the high speed position.

Controversial Analyzing of a Vapor-Compression Cycle in Various Climatic Conditions Using Various Refrigerants

Abstract This research is about “controversial analysis of a refrigeration vapor-compression cycle,” using R22, and environmentally friendly hydrofluorocarbon (HFC) refrigerants such as R134a, R407c, and R410a in various climatic conditions. For initiation, a complete database was provided for thermophysical properties of the refrigerants’ performances. Then, P–h, s–T, s–h equations are derived in matlab and Excel with the maximum R2. Meanwhile, five climatic conditions (from hot to cold state) are assumed. Consequently, temperature, pressure, enthalpy, and entropy of the cycle states are illustrated for aforesaid conditions as per working fluids properties in the form of quadripartite diagrams. Subsequently, the cycle was analyzed thermodynamically. The coeffcient of performance (COP) was performed for refrigeration (cooling procedure), heat pump (heating procedure), and both heating and cooling for both standard and actual conditions. Afterward, the calculation was performed for parameters like energy efficiency ratio (EER), heat rejected ratio (HRR), capacity, energy, exergy, irreversibility, and exergy destruction ratio (EDR) of each system component according to the first and second laws of thermodynamics, individually. Derived and calculated values in each session illustrated in 3D diagrams on which TEvap s, TCond s and working fluids for each assumed climatic condition can be distinguished easily. A concise analytic study was performed for the increasing and decreasing in values. Forecast for two steps upper and lower than all values derived for trending. Making a trend for indicating either positive or negative inclines of the values and proposing a development for all similar cycles can be considered as the novelty of this research.

Evaluation and Design of Large-Scale Solar Adsorption Cooling Systems Based on Energetic, Economic and Environmental Performance

In hot and dry regions such as the Gulf Cooperation Council (GCC) countries, the cooling demand is often responsible for more than 70% of electricity consumption, which places a massive strain on the electricity grid and leads to significant emissions. Solar thermal driven Silica-Gel/Water adsorption chillers, used for space cooling, could provide low carbon emission cooling and reduce the reliance on grid electricity. However, a meticulous design is required to make this both economically and environmentally beneficial. This paper aims to evaluate the solar thermal adsorption chiller performance based on large-scale cooling demand through a TRNSYS simulation for 1 year of operation. The proposed system consists of two main parts: first, the solar loop with evacuated tube solar collectors; and second, the adsorption cooling system with a silica-gel/water adsorption chiller. A neighbourhood of 80 typical 197 m2 villas in Riyadh, the capital city of the Kingdom of Saudi Arabia (KSA), was taken as a case study. The solar adsorption cycle’s performance has been compared to the conventional vapour compression cycle in terms of energy, economic and environmental performance. In addition, a parametric study has been performed for the main design parameters. Results reveal that the system can reach a solar fraction of 96% with solar collector area of 5500 m2 and a storage tank volume between 350 and 400 m3. Furthermore, the annual energy cost can be reduced by 74% for the solar adsorption system compared to the conventional vapour compression cycle. Meanwhile, the CO2 saving percentage for the solar adsorption cycle was approximately 75% compared to the conventional vapour compression cycle. Carefully designed solar thermal cooling systems can reduce greenhouse gas emissions while covering a large scale of cooling demands. This can reduce the strain on the electricity grid as well as greenhouse gas emissions.

Performance analysis of an ejector-assisted two-stage evaporation single-stage vapor-compression cycle

• An ejector-assisted 2-stage evaporation 1-stage vapor-compression cycle is proposed. • New cycle works for different refrigerants, especially for CO 2 transcritical cycle. • Energy savings depend on reasonable design and variable operating conditions. For actual vapor-compression refrigeration or heat pump systems with variable-temperature heat reservoirs, two-stage evaporation cycle is an efficient way to improve the coefficient of performance (COP). However, its application is limited because the two-stage evaporation cycle requires two individual suction pressures carried out by two cylinders or two compressors. To solve this problem, a two-stage evaporation cycle with a common single-stage compressor is proposed. An ejector is applied to lift the lower evaporation pressure up to the higher evaporation pressure or the compressor suction pressure. A thermodynamic model is developed to analyze its performance. Numerical results indicate that the COP of the novel cycle is 12.1% higher than the ejector cycle, 6.9% higher than the two-stage evaporation cycle and 22.0% higher than the basic refrigeration cycle under rated operating conditions. The exergy analysis indicates that TSEC-E can reduce 49.6% exergy loss of expansion process and 21.5% exergy loss of heat transfer process in evaporators in comparison with the basic refrigeration cycle. Although TSEC-E is applicable with various refrigerants, particularly it is more effective for CO 2 transcritical cycle. Moreover, performance improvement of the novel cycle under variable operating conditions is numerically investigated.

Novel Design and Thermodynamic Analyses of Cascade Refrigeration System at Ultra-Low Temperature

In this study, a cascade refrigeration system comprising gas and vapor compression cycles operating at ultra-low temperature was designed. In the thermodynamic analyses, R744, R404A, and R410A refrigerants in the high temperature cycle (HTC), and R1150, R170, and R23 in the low temperature cycle (LTC) were used. Thermodynamic analyses were carried out using the Engineering Equation Solver package program. Outputs considered were: system performance(COP), compression ratio, mass flow ratio and HTC cascade outlet temperature. Results show that, at different LTC condenser temperature values, R404A/R23 has the highest COP value, in the LTC, R23 has the highest compression ratio, while R1150 has the lowest one, in the HTC, R404A has the highest compression ratio, while R744 has the lowest one, the performance of the system increased with the decrease of the mass flow ratio.

Energy impact of the Internal Heat Exchanger in a horizontal freezing cabinet. Experimental evaluation with the R404A low-GWP alternatives R454C, R455A, R468A, R290 and R1270

• It has been tested the IHX effect in the energy performance of a freezing cabinet. • Test has been carried out with R404A and its current low and ultra‐low GWP alternatives: R468A, R454C, R455A, R290 and R1270. • It has been measured Energy saving with all refrigerants and operating conditions tested. • Greater energy saving as greater the heat sink temperature is. • No significant increment in compressor discharge temperature. This work analyses the influence of the Internal Heat Exchan ger (IHX) on the energy performance of a vapor compression cycle associated with a freezing cabinet using different R404A low-GWP alternatives. Among them, the refrigerants R454C (GPW 100 =146), R455A (GPW 100 =146), R468A (GPW 100 =146), R290 (GPW 100 =5) and R1270 (GPW 100 =1.8) have been tested in a horizontal freezing cabinet maintaining a product target temperature of -20°C at the heat rejection temperatures of 20, 30 and 40°C. The results from tests show that the use of the IHX reduces energy consumption in all scenarios without significantly increasing the compressor's discharge temperature. For a test period of 16 h, the refrigerants that offer better reductions are R404A and R1270, followed by R455A, R290, R454C and R468A. The maximum energy saving is rated to 9.2% at the heat rejection temperature of 40°C, demonstrating that the enhancement of the IHX is better as higher the heat rejection conditions are.

Performance evaluation of a vapor-compression-cycle based heat pump system for a lunar habitat under the impact of dust deposits on the coupled radiators

Space exploration is gaining new momentum. A near-term goal set by NASA is to return humans to the Moon and establish a sustainable presence on the lunar surface to enable more repeatable and affordable deeper space expeditions. Lunar dust is one of the dangerous environmental hazards causing serious problems for exploration activities. In this paper, a dynamic model is developed and used to study the impact of lunar dust on the performance of a thermal management system for a lunar habitat that is comprised of a vapor-compression cycle heat pump and a radiator loop. A heat pump to lift the heat rejection temperature is required due to high lunar daytime surface temperatures. Parametric studies on radiator size, percentage of dust coverage on the radiator, and lunar habitat location are carried out. The results show that lunar deposits can significantly increase the power consumption of the thermal management system. The lunar dust contamination problem raises the requirement for redundant design of the radiator loop for fault tolerance. A synergetic design of a thermal management system, a power generation system and robotic maintenance system is proposed to achieve maximal mass reduction for a whole lunar habitat system.

Research progress on recent technologies of water harvesting from atmospheric air: A detailed review

The increasing of the world population without increasing the natural resources caused water shortage in many regions around the world. Herein is a review of a new freshwater resource depending on harvesting the moisture of the atmospheric air. There are two main methods for extracting water from the ambient air: including composite materials method and cooling the air to the dew point. In the first method, the composite materials absorb the atmospheric air’s moisture and regenerate it into drinking water under certain conditions. Researchers have worked on changing the composite material type, and its additives and parameters to improve the productivity of water with acceptable cost. The second method requires just cooling of the atmospheric air until its moisture gets condensed. Power sources based on renewable energy have been developed to drive various techniques, such as vapor-compression cycles, absorption cycles, and Peltier effect-based devices. Beside reviewing different methodologies, this paper focused on the factors that affect the process of extracting water from the air. The formulas for computing the efficiency and water productivity were also mentioned. On the other hand, the research trend of the current topic was analyzed by conducting a comprehensive bibliometric analysis using VOSviewer software based on the Scopus database in the period (1988 – 2021).

Comprehensive test of ultra-efficient air conditioner with smart evaporative cooling ventilation and photovoltaic

Going by current usage trends, the use of room air conditioners will increase by three times by 2050. Therefore, it is necessary to investigate an ultra-efficient air conditioner with extremely low operating energy consumption to realize the goal of climate change, especially in the (sub) tropical area. In this paper, an ultra-efficient air conditioner with smart evaporative cooling ventilation and photovoltaic is proposed, which is composed of a highly efficient air conditioner, a fresh air ventilator with evaporative cooling, an evaporative condenser, and a photovoltaic. The mechanical vapor compression system adopts a gas-injected vapor compression cycle with relay cooling, which adapts to extremely high temperatures and harsh environments. Fresh air ventilation, water usage, and indoor temperature/humidity control strategies are also proposed. In the 31-day field test, the independent ventilator operation hours accounted for approximately 38.4% of the total test period. The electricity savings reached 89.8% as the indoor temperature and humidity satisfied all requirements. Through a typical 10-day lab-simulated year-round performance test, the calculated annual power consumption of the ultra-efficient air conditioner was 746.2 kWh, which was 82.8% lower than that of the baseline prototype. Based on the Indian Seasonal Energy Efficiency Ratio test, the calculated results revealed a consumption of 8.43 kWh/kWh, an improvement of approximately 140.7%. The comprehensive electricity-saving rate was 84.1%. The developed prototype won the global cooling prize since it will counterbalance the booming of residential cooling demand in the future, demonstrating a reliable route for energy savings for room air conditioners.

Vapor compression refrigeration testing on parabolic flights: Part 1 - cycle stability

Long duration manned space travel is projected to bring a need for large cooling capacities in microgravity for typical freezing and refrigeration temperatures. Among possible cooling technology alternatives, the vapor compression cycle has the highest coefficient of performance but the confidence for microgravity applications is very low. This research effort experimentally investigated the effects of hyper and microgravity on a vapor compression cycle during parabolic flights. A total of 122 parabolas were flown over four days with a repeating pattern of 5 sequential parabolas. Transient data of the evaporation temperature and cooling capacity for selected parabolas are presented as the test stand experienced alternating hyper and microgravity levels. Most measurements and performance indicators showed mild effects on the cycle operation during the varying g-forces. For example, the refrigerant side cooling capacity fluctuated on average within a band of 15% (+/-7.5%) through all sets of parabolas. A loss of superheat due to gravity changes was observed for one set of parabolas but the set was started with an unusually low superheat of only 3 K. For all other sets of parabolas, superheat and subcooling were maintained. Flight results were compared with inclination testing in a laboratory using the same test stand. Inclination changes from -90° to + 90° impacted both the liquid and suction line mass flow rate while varying the gravity level between 0 and 1.8 g affected the suction line mass flow rate but not the liquid line mass flow rate.

Energy, exergy and economic analysis of combined solar ORC-VCC power plant

Abstract A renewable energy source, especially solar energy, is one of the best alternatives for power generation in rural areas. Organic Rankine cycle (ORC) can be powered by a low-grade energy source, suitable for small-scale power production in rural areas. This study investigates the combined power generation and cooling system using the combination of ORC and vapor compression cycle (VCC), where ORC is powered by a parabolic trough solar collector. Thermodynamic and economic simulation of the system is conducted for four different working fluids, which are R245fa, R114, R600 and R142b. It can be concluded that the thermal efficiency of the power plant increases by using the combined ORC-VCC system. The effect of thermodynamic parameters such as turbine inlet temperature and pressure on the system performance is also discussed, and the optimal design values are provided. The results show that the power plant uses R245fa as the minimum exergy destruction rate. The study indicates that R114 gives minimum cost function (PCEU) for 137°C turbine inlet temperature while the minimum PCEU for R142b is obtained at a turbine inlet pressure of 2500 kPa. Finally, the study indicates that the inlet pressure of the turbine has a significant impact on the system cost and thermal efficiency.

A hybrid piecewise FDD strategy for refrigeration charge fault of airborne vapor-compression cycle system

Many researchers have carried out study on refrigerant charge fault for variable refrigerant flow (VRF) air-conditioning system, while few pay attention to refrigerant charge fault for vapor-compression refrigerant cycle system (VCS) of enhanced vapor injection (EVI) with a flash tank onboard. To develop a strategy for refrigerant charge fault of the above system, the optimization methods have been implemented to predict the refrigerant charge level (RCL) based on virtual refrigerant charge (VRC) models. Firstly, Pearson correlation coefficient analysis is employed to obtain the characteristic parameters. Secondly, a piecewise modified VRC model with the different characteristic parameters from VRC models is obtained for two cases of RCL < 75% and RCL > 75%. Meanwhile, combined with the principal component analysis (PCA) and the support vector machine (SVM) algorithm, a PCA-SVM model is developed to improve the prediction accuracy, and the average root mean squared error (RMSE) is only 7.8 compared to 14.9 of the modified VRC model when RCL > 75%, meanwhile, the correctly detected ratio is improved from 62.8% to 84.5%. Then, for solving the difficulty of fault detection and diagnosis (FDD) when RCL > 160%, the moving time window average (MA) algorithm is introduced and an online PCA-MA-SVM model is developed. Finally, a hybrid piecewise FDD strategy combined with three models for refrigeration charge fault in airborne VCS of EVI with a flash tank is obtained.

Thermodynamic analysis of refrigerants used in ORC-VCC combined power systems for low temperature heat sources

Fossil resources are largely used for energy supply. This situation causes environ?mental pollution. In recent years, studies in the field of more environmentally friend?ly and sustainable energy conversion technologies have increased. In this context, organic Rankine cycle (ORC) technology is combined with RES. In this study, combined ORC and vapor compression cycle (VCC) were investigated. The electricity produced in the combined ORC-VCC system was used both in the compressor of the VCC system and in the plant. The main factor affecting the efficiency of the combined ORC-VCC system is the refrigerant. Therefore, it is necessary to examine the selection of the most suitable refrigerant for an ORC-VCC based system. Fifteen different refrigerants were optimized with the enginering equation solver program, and energy and exergy analyzes of the systems were made separately. According to the results, the best energy efficiency and COP values among the refrigerants was found to be R40 (?ORC = 0.1206) for the ORC system and R113 (COP = 4.405) for the VCC system. For all system components in the VCC, the most exergy destruction occurs in the evaporator, followed by the compressor, condenser, and throttle, respectively. In ORC, the most exergy destruction is in the evaporator, followed by the condenser, tube and pump, respectively. The total efficiency was found to be (? = 0.53) for the combined ORC-VCC system. The total exergetic efficiency was found to be (?glob = 0.26) for the combined ORC-VCC system.

Modeling nonlinear heat exchanger dynamics with convolutional recurrent networks

Deep learning for system identification has enabled fast and accurate predictions in applications where physics-informed models are either absent or are too complex to be used efficiently for analysis and control. In this paper, we propose a deep state-space modeling framework that combines the feature extraction capabilities of convolutional neural networks (CNNs) with the efficient sequence prediction properties of gated recurrent units (GRUs); we refer to the neural state-space model as CNN-GRU SSM. We compare this model to other state-of-the-art deep state-space modeling tools and demonstrate that our proposed method often outperforms contemporary algorithms on benchmark dynamical system data. We validate the CNN-GRU SSM on a real-world application of predicting multi-input, multi-output, coupled, and nonlinear heat-exchanger dynamics observed in vapor compression cycles.

Design of liquid desiccant dehumidifier to enhance the indoor air quality

LDAC (Liquid Desiccant Air Conditioning) system has become a more promising substitute for conventional air conditioning systems working on Vapour Compression Cycle (VCC). This research paper emphasizes on the design of LDAC system for a given confined space of the room and effects of heating sources on the dimensions of the LDAC system. The effect of vital heating sources on the design of the LDAC system has been presented by mathematical modeling. The solar heat gain factor is seen more dominating factor in the design of the LDAC system, as the solar heat gain factor increased by 50% (from winter to summer), the diameter of the dehumidifier increased by 18%, whereas other sources such as ventilation air, infiltration, the lightning load increases the diameter of the dehumidifier by 2–3% only, to maintain required indoor conditions such as dry bulb temperature 24 °C, and specific humidity 0.013 kg/kg da.

Analysis of methods for assessing the energy efficiency of data centers using the power usage effectiveness method

The article deals with the analysis of methods for assessing the energy efficiency of data centers according to the Power Usage Effectiveness method. The demand for data centers which consumes a large amount of electricity is growing with the growth of digitalization and the accumulation of big data in the network. The energy consumption of the cooling system for the machine room accounts for a significant part of the operating costs of the building. Free cooling in a refrigeration system reduces energy consumption much more than operating systems with a vapor-compression cycle. In 2006 according to The Green Grid, the assessment method of Power Usage Effectiveness has become an international standard for measuring energy efficiency and is widely used in the design and operation of data centers. In this regard, the operation principles of free-cooling chillers are considered. The calculation example of the system payback in free-cooling is also given.

Parametric exergy analysis of a two-stage vapour compression cycle for freeze desalination comparing eco-friendly refrigerants

The current work aims to analyse a two-stage vapour compression refrigeration (TSVCR) cycle for freeze desalination. In this system, a low-pressure reversible subsystem (LPS) performs simultaneous freezing-thawing. The high-pressure subsystem (HPS) ensures cycle thermal stability. A mathematical model is developed to evaluate energy and exergy performance. Three eco-friendly refrigerants [R1234ze(E), R1234yf and R1243zf] are considered and compared with R22. The results show COP ranging from 6.5 to 12.7, with a specific energy consumption of 8.2 to 14.8 kWh/m3 of freshwater. The highest exergy efficiency of 38.4% is reported for R1243zf, which is higher by 1-3%, compared to R22 and R1234ze(E). However, R1234yf exhibits 11.14% and 7.8% lower energy and exergy performance. The maximum exergy destruction arises from the low pressure compressor (29%) followed by the latent heat condenser (23%). The uncondensed refrigerant significantly affects the performance and thermal stability. The study shows R1243zf and R1234ze are good alternatives to R22 due to their better energy and exergy performance.

Dynamic Modeling of a Vapor Compression Cycle

This paper presents three alternative dynamic models and a corresponding comparison by simulations for a vapor compression cycle. The first model is derived by first principles and uses both the mass and energy balances in finite-volume models of the evaporator and the condenser, whereas the compressor and the expansion-valve are modeled by means of algebraic equations. Assuming vanishing pressure losses along the evaporator and the condenser, a second model description is established. Additionally, a further simplification concerning the inner mass flows, which can be often found in the literature, leads to a third model. Both model variations are compared in simulations with the original model regarding model accuracy and simulation time. It becomes obvious that the second simplification leads to a significantly larger error. Moreover, the achievable increase in simulation speed of the simplified models is shown. Finally, the impact of a varying spatial resolution is discussed.

Parametric exergy analysis of a two-stage vapour compression cycle for freeze desalination comparing eco-friendly refrigerants

Parametric exergy analysis of a two-stage vapour compression cycle for freeze desalination comparing eco-friendly refrigerants