Vapor Compression System Research Articles

Theoretical performance study on R600/R170 auto-cascade refrigeration cycle with mechanical pre-cooling

A mechanical pre-cooling auto-cascade refrigeration (PACR) system was proposed, R600a single-stage vapor compression system was used to provide pre-cooling for R600/R170 auto-cascade refrigeration (ACR) system. Performance of PACR system under different operating conditions was discussed. The result showed that maintaining a constant outlet temperature of 30°C for the condenser and −45°C for the evaporator in a PACR system resulted in an optimal intermediate temperature that maximized coefficient of cooling performance (COP). At this time, the optimal intermediate temperature of R600/R170 was 0°C, the COP maximum value ( COPmax) was 0.693 and exergy efficiency ( ηEx) was 20.9%. And as the evaporator outlet temperature decreases to −70°C, the optimal intermediate temperature decreases to −10°C. The cooling capacity ( Qe) of the low-temperature grade circulating refrigerant in the PACR system using R600/R170 at different evaporation temperatures was increased by 86.3%–108% compared to that of R134a/R23. COPmax was increased by 7.1% compared to that of R134a/R23 at the evaporator outlet temperature of −60°C.

Numerical investigation of high temperature heat pump integrated hybrid cooling system

Over 67 % of the energy demand within the pharmaceutical and semiconductor industries is for their cleanrooms, driven by stringent temperature and humidity control requirements. Despite high energy usage, heating, ventilation, and air-conditioning (HVAC) units consisting of conventional vapor compression systems (CVCS) are favoured for their simplicity. Hybrid cooling systems (HCS) offer potential efficiency gains by separating latent and sensible loads. Still, reliance on fossil-fuel-fired or electric heaters to regenerate the desiccant makes it energy intensive and reduces CO2 mitigation benefits. This study explores high-temperature heat pumps to simultaneously cool process air and heat regeneration air, thereby using multiple benefits. Heat pumps with condensing temperatures of 80 °C, 90 °C, and 120 °C and an ejector-enhanced trans-critical CO2 heat pump were compared with CVCS and HCS. The 120-bu and CO2HP configurations demonstrated a system COP of 2.94 and 3.22, respectively, surpassing CVCS, which has a system COP of 1.44. These setups achieved CO2 emission reduction of 51 % and 55.2 %, compared to CVCS, respectively.

Energy and Exergy Performance Analysis of Solar-Assisted Thermo-Mechanical Vapor Compression Cooling System

Air conditioning is vital for indoor comfort but traditionally relies on vapor compression systems, which raise electricity demand and carbon emissions. This study presents a novel thermo-mechanical vapor compression system that integrates an ejector with a conventional vapor compression cycle, incorporating a thermally driven second-stage compressor powered by solar energy. The goal is to reduce electricity consumption and enhance sustainability by leveraging renewable energy. A MATLAB® model was developed to analyze the energy and exergy performance using R1234yf refrigerant under steady-state conditions. This study compares four solar collectors—evacuated flat plate (EFPC), evacuated tube (ETC), basic flat plate (FPC), and compound parabolic (CPC) collectors—to identify the optimal configuration based on the collector area and costs. The results show a 31% reduction in mechanical compressor energy use and up to a 44% improvement in the coefficient of performance (COP) compared to conventional systems, with a condenser temperature of 65 °C, a thermal compression ratio of 0.8, and a heat source temperature of 150 °C. The evacuated flat plate collectors performed best, requiring 2 m2/kW of cooling capacity with a maximum exergy efficiency of 15% at 170 °C, while compound parabolic collectors offered the lowest initial costs. Overall, the proposed system shows significant potential for reducing energy costs and carbon emissions, particularly in hot climates.

Performance analysis of a conventional two-stage indirect evaporative cooler

With the aim of saving a portion of the high-quality energy consumed in mechanical vapor compression systems for air conditioning applications, the present work focuses on utilization of low-quality energy conversion processes due to fluid evaporation. The conventional indirect evaporative cooler is selected based on its preference for further modification compared to a regenerative indirect evaporative cooler. It is configured to be operated with two identical stages in series. This task is achieved by developing a thermodynamic model to analyze the performance of the cooling unit and to indicate the extent of its development compared to the cooler in one stage. Preliminary results show that the best operating condition is when the ratio of primary air to secondary air is 1. The cooling unit produces fairly comfortable air within limited climatic conditions. It delivers air at 26 °C and lower even at climatic temperatures as high as 48 °C, but within a very low relative humidity range. The relative humidity range extends to less than 58% as the outdoor air temperature decreases. At high humidity levels (64 to 80% depending on climate temperature), cool air cannot be obtained at 26 °C, and the cooling unit performance is limited only by what the first stage produces. The average performance of the cooling unit exceeds that of the first stage by 42.6%. Increasing air flow rate leads to an increase in cooling capacity, but it also has a negative impact on supply temperature and effectiveness.

Oil circulation ratio prediction in a vapor compression system using a discharge side oil separator and mass flow correction

Oil circulation ratio (OCR) is defined as the ratio of the mass flow rate of oil to the total mass flow rate of refrigerant-oil mixture in a vapor compression system. The standard method for measuring OCR uses liquid line sampling as described in ASHRAE Standard 41.4. Sampling is tedious, alters the steady state operation of the system, depends on different parameters, and only applies to miscible refrigerant-oil pairs. A potential method for measuring real-time OCR is by using an oil separator to separate the refrigerant flow from the oil flow and using the individual flow rates to calculate OCR. Neither a liquid line, nor refrigerant-oil miscibility are necessary for this separation-based method. No oil separator is perfect as some oil always escapes with the separated refrigerant, and some refrigerant, dissolved in oil, always escapes with the separated oil. This can significantly reduce the accuracy of the procedure. The present study investigates OCR measurements using an oil separator-based approach for a full vapor compression cycle working with R134a and PAG ISO 46 oil. A full cycle allows sampling to also be performed in parallel for validation. Mass flow corrections were performed to account for refrigerant dissolved in separated oil, and for oil entrained by separated refrigerant. OCR values from the oil separator-based approach, upon mass flow correction, were within 6% of the sampling results. The usefulness of the oil separation efficiencies at the oil and vapor outlet ports for the oil separator-based approach is discussed.

A Novel Characterization Methodology for Vapor-Injected Compressors: A Comparative Analysis with Existing Black-Box Models

In regions characterized by high temperature gradients, vapor compression systems often necessitate operation at very high-pressure ratios resulting in a reduction in system capacity. Economized vapor injection compressors are used to avoid these issues, yet a precise predictive map for various compressor technologies with minimal data and relatively better performance remains unclear. This paper establishes a black-box compressor model to accurately predict compressor power, injection mass ratio, and evaporator mass flow rate in compressors with a single vapor injection port. This model is compared against three legacy models from literature and the ANN model, for reference. All five models are evaluated based on their ability to predict the aforementioned metrics. The proposed black-box model can predict the relevant metrics all within 5% Mean Absolute Percentage Error (MAPE). Additionally, a refrigerant sensitivity analysis is performed with the black-box models. The model is trained using data from R410A and then used the coefficients to predict the performance of the same compressor when using R454B, and vice versa. It can estimate the evaporator mass flow rate with an accuracy within 3%, the power within 2%, and the injection mass ratio with MAPE less than 3%.

Exergy analysis of hybrid air-conditioning systems with different evaporative-cooling condensers under hot-humid climates

Evaporative cooling (EC) technology can effectively improve the energy efficiency of the mechanical vapor compression (MVC) system by enhancing the heat exchange capacity of its condenser. However, the current evaporative-cooling condenser system is usually only equipped with a single-stage evaporative cooler as the precooling unit, and these designs are mainly suitable for hot-dry conditions. In this study, three hybrid air-conditioning systems with different two-stage evaporative-cooling condenser configurations were proposed, one is single-condenser type and the other two are dual-condenser type, which are used to improve the exergy performance and adaptability of the evaporative condenser system under hot-humid climates. Then, the all systems were modeled via the distributed parametric method and analyzed comparatively based on the exergy method. A suitable exergy reference temperature at air saturation was discussed. Finally, the effect of four key parameters (ambient temperature and relative humidity, outdoor airflow rate and room heat load) was studied. The results showed that under the high temperature, relative humidity or room heat load conditions, the hybrid systems have a low exergy efficiency ratio (EXR) and high exergy efficiency (ηx,OEC). Among them, the newly countercurrent dual-condenser configuration (MVC-TSEC(C)) exhibits the best exergy performance under most hot-humid conditions. Compared to the conventional MVC system, the EXR and ηx,OEC of MVC-TSEC(C) increased by at most 35.0 % and 78.2 %, respectively. Moreover, its components like compressor, condenser and expansion valve have the maximum reduction rates of exergy destruction of 43.5 %, 17.2 % and 55.3 %, respectively.

Parametric Based Techno‐Economic Evaluation for a Solar Thermal‐PV Integrated Multi‐Commodity Storage Facility

ABSTRACTPostharvest losses and spoilage of agricultural products are a major problem for tropical countries, and it is even more challenging for countries encountering fluctuating power shortages, such as Pakistan. Therefore, this study focused on the energy and economic analysis of cold storage to store three products (potatoes, pomegranates, and potatoes) according to the season and storage span throughout the year. The cooling load of the cold store was supported by a LiBr‐H2O vapor absorption and vapor compression refrigeration system to maintain the desired temperature for each product during cold storage. A solar thermal PV system is installed to operate cold storage refrigeration systems. Cold storage performance was analyzed by developing thermal models of integrated systems using the ambient conditions of Lahore, Pakistan. A parametric study was also conducted to analyze the impact of various working parameters on integrated system performance, and it was found that the maximum peak cooling load of 91 kW inside cold storage is attributed to pomegranates owing to high ambient conditions during its loading month. The product loading rate significantly affects the cooling load of cold storage and varies directly with it, as observed for an increase in the product loading rate from 0 to 50 000 kg/day cooling load also increases from 34 to 87 kW. To meet the thermal demand of the generator of the vapor absorption system, parabolic troughs were installed to operate cold storage, and it was found that a minimum of four PTC were needed to support the peak cooling load at the maximum product loading rate and minimum DNI value. To meet the electrical demand of cold storage electrical equipment and the compressor of the vapor compression system, solar photovoltaic panels were installed, and it was found that a minimum of 618 panels was required at a minimum tilted radiation value. To validate the viability of proposed design system economic analysis was also conducted which revealed a payback period of 12 years for Kinnow and potatoes and 16 years for pomegranates.

Centrifugal Compressor Surge in Closed Loop Systems: Initial Modelling and Comparison with Experiments

Abstract Heat pumps are expected to play a primary role in electrification of thermal users in the residential and industrial sectors. Dynamic compressors are widely used in large size heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency and low acoustic emissions. The instability, which may occur in a compressor installed in closed loop cycle such as in a heat pump, is quite different from the classic open loop configuration involving dynamic compressors. This is mainly due to the complexity of the compressor instability mechanism coupled to a vapor compression system connected with two- phase heat exchangers, having different thermal and fluid dynamic capacitance properties, under a physical feedback loop. The aim of this paper is to investigate the behaviour of a dynamic compressor installed in an innovative heat pump prototype, of laboratory scale, under stable and unstable conditions. A preliminary simple dynamic model of the compression system consisting of a radial compressor, condenser and evaporator, is developed to represent the heat pump compression system, which can capture the unstable behaviour. The evaporator and condenser are modelled using empirical correlations. The preliminary validation of the dynamic model results is done through a dedicated experimental campaign, under different operating conditions. Results show the complexity of the interaction between the centrifugal compressor and the heat pump loop, discerning the different contributions to the time-dependent response of the system, prompting the necessity of a detailed model in the next step of the work.

Machine learning-based process design of a novel sustainable cooling system

An exponential rise in cooling requirements occurred in the last few years because of rising global surface temperatures, population growth, faster urbanization, and income growth. Developing countries are facing major issues because of the larger impact of these cooling drivers. Conventional vapor compression systems are energy-demanding and involve dangerous chemicals. The current paper proposed an innovative indirect evaporative cooling system with high energy performance, less emissions, and chemical-free operation. To map the full-scale performance, a prototype was developed,and tested in a variety of outside air conditions. Then artificial neural network (ANN)-based machine learning model was developed incorporating important input parameters including outdoor air temperature, air flow rate ratio, working air temperature, and working air wet bulb temperature to predict the supply air temperature. The ANN model having nine neurons in the hidden layer exhibits excellent modeling performance with a coefficient of determination (R2) value of ∼ 1 and root mean square error of 0.046 °C, 0.06 °C, and 0.06 °C in the training, testing, and validation phases respectively. The variable significance analysis carried out by one factor at a time (OFAT) technique reveals that working air inlet temperature is the most important parameter to predict supply temperature with a significance factor of 33 %. According to the combined experimental and ML model, the proposed system generated 130 W of cooling capacity and dropped the temperature by more than 20 °C at 48 °C of outdoor air. The corresponding coefficient of performance achieved (just for cooling) was 32. It is also shown that the enhanced IEC operates steadily in ambient temperatures ranging from 30 to 48 °C and maintains supply air temperatures within the comfort zone of ASHRAE-55 and ISO7730.

Kinetics of Water Adsorption in Metal-Organic Framework(MOF-303) for Adsorption Cooling Application

Adsorption cooling systems (ACS) powered by low-temperature heat offer an energy-efficient and environmentally friendly alternative to traditional vapor-compression systems. The effectiveness of ACS is significantly influenced by the alignment of the adsorbent properties with the operating conditions of the cycle. Metal-Organic Frameworks (MOFs) are considered the next generation of water harvesting and ACS. Many MOFs are synthesized and tested for water harvesting systems, one of these MOFs is MOF-303 which was reported to have very rapid water sorption dynamics under atmospheric conditions. However, MOF-303 has never been tested under the same conditions as ACS (under vacuum). In this study, the isotherms and kinetics of water adsorption on MOF-303, as an efficient adsorbent of water vapor, is experimentally investigated for the ACS using the linear driving force model. The diffusion coefficients across a wide range of relative pressures under two different temperatures were estimated. The study compares the adsorption process of MOF-303 with traditional silica gel (SG) in the context of diffusion kinetics relevant to ACS. Based on the output and at a constant temperature of 25 °C and across all relative pressure ranges, MOF-303 exhibited an average increase of approximately eight times in diffusion kinetics compared to SG. Specifically, within the relative pressure range of 10–30 %, which is optimal for ACS, MOF-303 demonstrated a seven-fold increase in diffusion kinetics over SG. The diffusion values for SG display a clear upward trend with increasing temperature. In contrast, the diffusion values for MOF-303 are subject to fluctuations with temperature changes under investigation. Notably, the isotherm for MOF-303 shows an inflection point at relative pressures between 10–15 %, causing a significant reduction in diffusion at these specific relative pressures compared to other relative pressure values. The findings in this study highlight the potential use of MOF-303 as a highly efficient water adsorbent for the ACS which will enable scientists and engineers to develop sustainable low-grade energy systems.

Energy saving of vacuum-based membrane dehumidification with indirect evaporative cooling in a low sensible-heat-ratio building

In hot and humid climates, dehumidification generally consumes more energy than cooling, and conventional mechanical vapor compression system is not efficient for dehumidification. Vacuum-based membrane dehumidification system have been developed as a more environmentally friendly alternative for dehumidification due to non-refrigerant system and isothermal dehumidification process. In this study, a novel hybrid air conditioning system that combines vacuum-based membrane dehumidification with an indirect evaporative cooler for pre-cooling is proposed to achieve efficient air conditioning in building with low sensible heat ratio. The energy performance of the proposed system is investigated by detailed thermodynamic simulations and compared with conventional variable air volume (VAV) system and indirect evaporative pre-coolers combined VAV system. The simulation results show that when the average sensible heat ratio of the space is 0.73 and the COP of the vacuum-based membrane dehumidifier is 1.0, the proposed system can reduce energy consumption by 16.1 % compared to conventional VAV system and by 6.4 % compared to indirect evaporative pre-cooler combined VAV system during the cooling season. The energy performance of the proposed system is significantly affected by the sensible heat ratio of the building and the energy efficiency of the vacuum-based membrane dehumidifier. When the COP of the vacuum-based membrane dehumidifier reaches 2.0, the proposed system can achieve an energy savings of 48.2 % compared to conventional VAV system.

Thermo-economic analysis and comparison of novel desiccant air conditioning systems

Desiccant air conditioning (DAC) systems are considered an effective alternative to traditional vapor compression systems due to their ability to independently control temperature and humidity, coupled with their environmentally friendly design. Consequently, this paper deals with experimental and simulation study on DAC systems. The experiments were conducted on a reference system (RS) equipped with all necessary control and measurement devices. This reference system includes a traditional desiccant evaporative air-conditioning system with an additional heat exchanger placed after the desiccant wheel, functioning as an after-cooler. In addition, steady state and transient simulation models were developed using TRNSYS software to predict the performance of four different configurations of DAC systems and the reference system, under hot and humid climatic conditions.The experimental data verify the precision and relevance of the simulation results, with an average error of 2.57 % for the air temperatures. The steady state findings showed that Config-4 exhibited the best thermal performance compared to the other configurations. Also, Config-4 demonstrates a stable thermal cooling capacity despite fluctuations in outdoor air dry-bulb temperature. Transient results revealed that, Config-4 has levelized costs of CO2 emissions that are 64.2 % lower than RS, followed by Config-3, Config-2, and Config-1. Lower CO2 emissions result in a positive impact on mitigating climate change and improving air quality. Economic analysis revealed that the total levelized cost of cooling (LCOC) for Config-4 is 70.5 % lower than RS, demonstrating the most significant cost reduction. Configurations 3, 2, and 1 also showed lower LCOC compared to the reference system.

Electrifying Chemistry: Characterizing TEMPO-Based Electrocatalysts for Isopropanol to Acetone Conversion in Novel Heat Pumps

Heating, ventilation, and air conditioning (HVAC) systems account for more than 40% of the U.S. electricity usage, primarily utilizing vapor compression system (VCS) heat pumps, raising environmental concerns. The phase down of high GWP refrigerants, targeting an 85% reduction by 2035, prompts the exploration of novel heat pump technologies. Electrochemical looping heat pumps (ELHP) show promise by employing redox reactions for fluid compression to replace conventional compression technologies. However, energy-intensive redox interconversion necessitates catalysts to lower activation energy. Inspired by electrosynthesis principles, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) emerged as a successful homogeneous electrocatalyst for selective isopropanol oxidation to acetone for use in ELHP. HPLC and 13C NMR confirmed remarkable selectivity (~100%) at practical isopropanol concentrations.To enhance TEMPO's catalytic activity, various electron-withdrawing and donating groups were explored. TEMPO-OCH3, among seven derivatives, exhibited superior efficiency with a notable rate constant (6 M-1s-1) and turnover frequency (3.1 s-1). This study innovatively applies concepts from molecular catalysis for the development of efficient catalyst materials.

Dynamics of water adsorption on SAPO-34: Comparison of three adsorbent bed configurations of adsorption chillers

Intensification of the adsorption dynamics is a strategic way to make adsorption chillers and heat pumps more competitive with conventional vapour compression systems. This can be achieved by consolidating the adsorbent bed with a heat exchanger to enhance heat transfer. This work investigates the dynamics of water adsorption on a commercial adsorbent SAPO-34 for three bed configurations, namely, a reference bed consisting of a monolayer of loose beads located on an aluminium plate, and two consolidated beds – a monolayer of beads glued to the plate, and a homogeneous coating of the plate prepared with binder. The morphology and texture of the prepared beds were studied by optical and scanning electron microscope techniques as well as by low temperature nitrogen adsorption. Six binders involved, both organic (hydroxyethyl cellulose, polyvinylpyrrolidone, polyaniline) and inorganic (heat-conductive compound CPTD, bentonite clay, colloidal silica sol), produced varying effects. It was found that the most preferred configuration involves SAPO beads glued to the plate with bentonite for which the heat transfer was enhanced by a factor of 1.2–1.7 while maintaining sufficient mass transfer. The effective heat transfer coefficient was measured for the most promising binders and selected configurations, and varied between 120 and 248 W/(m2 K). The heat transfer acceleration permitted the specific cooling power (at a conversion of 0.8) to increase from 2.7 kW/kg for loose beads of 0.8–0.9 mm size to 3.5 kW/kg for the same beads bound with bentonite. Thus, gluing pre-made commercial adsorbent beads with heat-exchanger with suitable binders presents a simple and promising method to enhance the adsorption dynamics, resulting in a more compact design of adsorption chillers.

Model development and validation of a vapor-compression system integrating water-based thermal energy storage using a three-fluid heat exchanger (TriCoil™)

This paper presents a comprehensive simulation suite for a residential heating and cooling system that combines a vapor-compression system (VCS) with a water-based thermal energy storage (TES) using a three-fluid heat exchanger (TriCoil™). The VCS configuration includes the TriCoil™ as the indoor coil, a fin-and-tube heat exchanger as the outdoor coil, a variable-speed compressor, and an isenthalpic expansion device. To minimize computational cost for annual simulations, an artificial neural network (ANN) was employed to develop a data-driven model for the TriCoil™. The suite integrates models of the VCS, TES, and control systems, factoring in utility rates, building load profiles, and weather data. Validation against experimental data demonstrated accurate predictions, with TES temperature profiles having a root mean square error of 0.3 K and VCS heating capacity predictions showing mean absolute errors of 4.3% for the R410A side, 5.0% for the water side, 4.9% for the air side, and 4.3% for the air-sensible side.Simulations for a cooling season in Stillwater, OK, demonstrated significant electricity cost reductions by shifting cooling loads from peak to off-peak hours. The proposed system minimizes expenses using time-of-use rates and optimized load scheduling, showcasing substantial benefits even with a small TES unit.

DESIGN OF A NOVEL DEW POINT INDERECT EVAPORATVE COOLER: PRELIMINARY EXPERIMENTAL INVESTIGATIONS

Evaporative coolers may represent a promising alternative to conventional cooling technologies based on vapor compression systems. Indeed, they present lower production and operative costs, as well as lower environmental impact. The present study aims to develop a novel Dew Point Indirect Evaporative Cooler (DPIEC), by combining simplicity, hence low production costs, and higher cooling performance. The design proposed has mixed flow configuration and is made of polycarbonate plate covered with cotton cloth as wicking material. Two prototypes with different length are experimentally tested for two different water distributors. The performance of the novel DPIEC is evaluated and compared in terms of temperature drop, dew-point effectiveness, cooling capacity and compactness. The results show that the long prototype performs better in terms of temperature drop and dew point effectiveness, but yields lower cooling capacity and is less compact. In addition, it is observed that the distributor that supplies water over the system performs better, independently on the prototype. These results can serve as reference for future designs of mixed-flow DPIEC.

Transient analysis of an efficient solar assisted air-conditioning system for subtropical climate with various solar thermal collectors

The air conditioning demand of the world is largely fulfilled by vapor compression systems; however, these systems are also responsible for depleting ozone layer due to the nature of refrigerants. Desiccant cooling systems integrated with solar thermal energy technologies could be an attractive alternative with some performance enhancement techniques. In this study, transient seasonal performance investigation is performed for an innovative solar integrated desiccant cooling system that uses regenerative evaporative cooler known as solar assisted desiccant integrated Maisotsenko cycle cooler for better cooling performance. Furthermore, transient annual performance analysis of solar system for meeting thermal energy requirement for regenerating the desiccant wheel in summer season and handling heating load of the building in winter season is also carried out with three different solar thermal collector technologies for finding out more efficient technology. The key performance indicators in this study are useful energy gain, solar source efficiency, auxiliary energy sharing, coefficient of performance, and solar fraction. The results of the key performance parameters are reported as monthly average values. The proposed integrated system resulted to be very efficient with a maximum COP value of 1.13 in April when latent cooling loads are low and 0.78 in August when latent cooling loads are higher. The system’s maximum cooling capacity is 24 kW in April corresponding to a sensible heat factor of 0.720. Furthermore, the regeneration temperature requirements ranged from 50 °C to 78 °C, respectively that makes it favorable to use low grade thermal energy through non concentrating solar thermal collectors. The regeneration thermal energy requirement for desiccant wheel fluctuates throughout the year, maximizing in August due to higher dehumidification requirements. The study also revealed that the evacuated tube collector technology is most suitable with average annual efficiency of around 36 %.

Investigation of the energetic and exergetic performance of hybrid rotary desiccant-vapor compression cooling systems using different refrigerants

In this study, a desiccant-based hybrid cooling system supported by a vapor compression system and a heat recovery unit (rotary heat wheel) was analyzed from energetic and exergetic perspectives during the daily working hours of an office building in Istanbul to meet the desired comfort conditions. We focus on the impact of different refrigerants; namely R32, R1234yf, R290, R134a, R600a, R245fa, and R717, on hybrid rotary desiccant-vapor compression systems. While the highest electricity consumption was obtained in the system using R1234yf, the lowest electricity consumption was achieved with R717. However, with the effectiveness of the desiccant wheel, the best results were obtained for R1234yf with those pertinent to R717 at the other extreme. Considering the total electricity consumption of the system, the highest energetic and exergetic performance parameters were achieved with the use of R717 as the refrigerant. Compared to R1234yf, the daily average energetic performance parameters obtained with R717 increased by 22.3 % for COPr, 21.8 % for COPel, and 4.7 % for COPth. Similarly, compared to R1234yf, the daily average exergetic performance parameters in R717 presented increases of 13.6 % for COPx,el, 7.5 % for COPx,th, and 8.1 % for ηx.

State of the art of micro vapour-compression systems

Thermal management is becoming more challenging due to the increasing compactness and computational power of appliances. Affordable and efficient solutions include active liquid cooling methods, thermoelectric cooling, and the use of heat pipes. From these, vapour-compression technologies achieve the highest power density. However, the downscaling of vapour-compression for cooling of personal computers or workstations is rather problematic from several different reasons. The first problem concerns the low second law efficiency of miniature vapour-compression systems. The second problem concerns the available space occupation of such a cooling system. Moreover, miniature and high-power density condensers and evaporators have not yet been adequately researched and developed to date. In this review, we present several vapour-compression refrigeration systems that are based in some way on the miniaturisation of systems or individual components – evaporators, condensers, and compressors. These are presented and compared in terms of cooling power, COP, and the second law efficiency. At the end of the manuscript, guidelines for future improvements and the implementation of miniature vapour-compression systems are presented.