Vapor Compression Research Articles

Analysis of a refrigeration system using carbon nanotubes (CNTs) lubricant and a combination of R290/R600 refrigerants

A combination of R290/R600 refrigerants with low global warming and zero ozone-depleting potential refrigerant was tested with a based lubricant and CNTs nanolubricant in a refrigeration system to improve its performance efficiency and minimise the environmental impact of refrigerants and energy demand by refrigeration systems. CNTs-nanolubricant, an alternative lubricant for the refrigeration system, was made by dispersing CNTs in the based lubricant. By connecting measuring devices at each system component, temperatures and pressures were determined. The experiment’s measured outputs were used to determine the system’s performance. When compared to a 290/600 in the based lubricant, CNTs nanolubricant showed a reduction in work input ranging from 39.8%, a shorter pulldown time, a lower evaporator temperature, an increased coefficient of performance (COP), and a higher cooling capacity of 9.1%. Therefore, the lubricant made of carbon nanotubes (CNTs) presents a viable substitute for based lubricant in a vapour compression system.

Design and Construction of a Rapid Milk Chiller Using Cold Energy Storage System in the Context of Bangladesh

Milk is a highly sensitive product that must be collected and cooled within a few hours to reduce losses due to chemical spoilage and to preserve quality. As milk production is often remote from markets and processing facilities, milk chillers using thermal energy storage (TES) units provide the means for preserving quality through chilling during a power cut and hygienic storage before onward transportation to processing facilities and operation of the chiller at maximum thermal efficiency. This study gives an overview of thermal energy storage (TES) base rapid milk chiller. A review of TES for cold storage applications utilizing solid-liquid phase change materials has been done. Various perspectives were focused on the different stages of the work: phase change materials (PCMs), exemplification, improvement in exchange of heat, and the impact of the whole process on the quality of the milk Materials used as potential PCMs by specialists at low temperatures (less than 4 °C) are condensed and a portion of their thermo-physical properties are accounted for. The concept of planning and measuring procedures based on the determined load profile for structure day is introduced. In this design of a milk chilling unit using thermal energy storage, two cycles have been combined to get the desired cooling temperature. One is the vapor compression cycle, which can also be called the ice storage cycle. Another one is the milk chilling cycle. The main purpose of the milk chilling cycle is to keep the milk temperature between 2°C to 4°C. The comparison of using cold water with ethylene glycol (PCM) as a storage source of refrigeration for the milk cooling process based on the compressor capacity, ice storage box volume, and power consumed at the variable of cooling load is presented. Also, the effect of using cold storage to reduce the refrigeration capacity and energy saving is presented. The time duration of the milk chiller’s capacity to keep a specific amount (20 liters) of milk cool has been calculated to determine the variance and efficiency of the system compared to other milk chilling processes. Some suggestions concerning the planning of milk chiller hardware are given. Unique consideration was paid to the examination of explicit highlights of heat transfer phenomena in ice storage boxes including the appraisal of the length and the rate of ice arrangement and dissolution. The approach of estimating parts of the ice storage capacity framework incorporated into the milk chilling framework arranged in hot, wet, and dry atmospheres is exhibited. In light of the hourly cooling burden figuring that was completed utilizing Carrier’s Hourly Analysis Program, estimating the ice thermal capacity framework for various working procedures including full, chiller priority, and ice priority storage tasks for the design are displayed. At last, an examination of some operational qualities of the framework is broken down.

Optimizing R152a/R600 and R290/R600 mixtures for superior energy performance in vapor compression systems: Promising alternatives to Isobutane (R600a)

This study presents an experimental investigation into the optimal composition of R152a/R600 and R290/R600 mixtures as potential alternatives to isobutane (R600a) in a single-stage vapor compression cycle. The research involved testing eight different mass compositions for R152a/R600 and ten mass compositions for R290/R600, comparing their performance with that of R600a. After careful analysis, the “optimum” mass compositions were identified as (10/90)% for both R152a/R600 and R290/R600, achieving a balanced trade-off among coefficient of performance (COP), volumetric cooling capacity (VCC), and cooling output (Q̇o). Further tests were conducted on the “optimum” compositions at nine different secondary fluid temperature inlets. The results indicated an average COP increase of + 7.3 % for the R152a/R600 mixture, with decreases of −11.4 % in VCC and −9.7 % in Q̇o. Similarly, the R290/R600 (10/90)% mixture showed a COP increase of + 10.3 %, accompanied by VCC and Q̇o decreases of −8.8 % and −6.6 %, respectively. Notably, both mixtures exhibited superior energy performance compared to isobutane while maintaining similar thermodynamic properties, particularly the R290/R600 (10/90)% mixture. These findings suggest that the R152a/R600 and R290/R600 mixtures could serve as long-term, high-efficiency alternatives to R600a in vapor compression cycles.

Energy analysis of a simple PV/T system for heating using a variable speed vapor compressor system

The use of photovoltaic/thermal (PV/T) modules reduces the losses in the photovoltaic cells and, in addition, uses the waste heat in the panel. This paper presents the simulation results of a PV/T system for domestic hot water supply using a vapor compression system during the four seasons of the year in the conditions of Salamanca, Mexico. The results obtained from the simulation indicate that the cooling of the panel causes an increase of approximately 7% in PV efficiency. During the spring, when there is greater solar radiation and, therefore, greater electrical power generation, despite the average temperature of around 36 °C, the lowest efficiency is found. On the other hand, the highest efficiency is achieved in winter, reaching up to 22%. As for the performance coefficient, the highest value is observed during the spring, with a coefficient of performance (COP) of 6.63, while the lowest value is recorded in summer, with a COP of 5.11. It is concluded that this system can satisfy the domestic hot water demand for the conditions under study.

Influence of coupling air conditioner with hybrid PCMs on building interior conditions and consumed power: Experimental investigation

Air conditioning systems are vital for modern comfort but consume a substantial portion of global energy, contributing to environmental concerns and rising energy costs. PCMs can store and release energy during phase transitions, making them promise to reduce cooling loads. This study endeavors to empirically investigate the influence of integrating hybrid Phase Change Materials (PCMs), specifically PCMSP24E and PCMSP26E, with a real vapor compression refrigeration system. The primary focus is on assessing the consequential effects on the energy consumption of the refrigeration system and the interior environmental conditions within a building, including temperature and relative humidity. The energy usage of the split air conditioner wherein the outdoor unit is attached to PCMs tube heat exchanger for precooling the incoming air is investigated. Experiments reveal that PCM precooling effectively reduces the ambient air temperature entering the air conditioning condenser, leading to substantial energy savings. Increasing the PCM quantity enhances the system performance and refrigeration unit power saving. With 11 kg of PCMs, energy consumption by the air conditioning system decreases by 10.4 %, and indoor air temperature and relative humidity reduce by 0.5° and 5 %, respectively. Hence, PCM integration ensures a more consistent indoor temperature profile, enhancing occupant comfort and reducing temperature fluctuations.

Dynamic modeling of a centrifugal chiller with hybrid falling film evaporator including pressure drop computation

Over the last decade, the introduction of new technologies such as falling film evaporators and advanced control techniques has significantly enhanced chiller efficiency while reducing refrigerant charges. However, the complexity of the involved transport phenomena poses significant challenges in simulating the behavior of these devices, resulting in very few validated models that encompass such advances. This study introduces a novel dynamic model for centrifugal liquid chillers with a hybrid evaporator (one that combines features of falling film and flooded designs). Employing the moving boundary method, the model incorporates the intricacies of the transport phenomena, including the pressure drop across the tube bank, with relatively low computational requirements. Implemented in OpenModelica, the model was validated using performance data from a 550 TR centrifugal chiller, yielding normalized residual errors of less than 0.5% for values of supply water temperature and power consumption. This provides a comprehensive tool suitable for analyzing chiller performance as a function of the evaporator geometric characteristics and enabling optimal dynamic control of central cooling systems incorporating this kind of chillers, as long as contributes to the development of dynamic and steady state models of vapor compression centrifugal chillers with falling film evaporators.

Working Fluid Selection for High-Temperature Heat Pumps: A Comprehensive Evaluation

Heat pumps have the potential for several applications across various industrial sectors, showcasing significant promise, especially in sectors such as pulp and paper, food and beverage, chemical, non-metallic minerals, and machinery. Envisioning the near future, there is confidence that heat pumps can achieve temperatures above 200 °C, offering substantial potential for utilization in these sectors. Nevertheless, a crucial aspect for the advancement of high-temperature heat pumps is the selection of the fluid. Fluid selection involves considerations of both thermodynamic efficiency and environmental impact, requiring fluids with zero ODP, negligible GWP, and no PFAS. Moreover, it is essential to consider the risks to human health associated with a specific fluid. Despite extensive research, particularly in the realm of vapour compression heat pumps, choosing the most suitable working fluid for these applications is a complex undertaking. Therefore, this paper conducts a theoretical analysis to evaluate potential fluids with suitable thermodynamic properties for high-temperature heat pumps (HTHPs). The comparative results gleaned from this study provide valuable insights for the comprehensive analysis of fluids, showing promise within temperature ranges dictated by specific applications. The metrics employed in the comparison emphasise the merits of fluids in terms of the overall performance, dimensions, and operating ranges of applicable compressor, heat exchange capacity, transport properties, and safety. One noteworthy finding from the analysis is that maintaining a constant HTHP lift (at 40 K) results in having the highest COP across all fluids when the condensing temperature ranges between 85% and 90% of their respective critical temperatures. According to the results of the analysis, natural fluids, including water and alcohols like ethanol or methanol, emerge as particularly compelling candidates.

LateSearching for the most energy-efficient composition of a mixture of dimethyl ether and carbon dioxide as an air conditioning system refrigerantr

BACKGROUND: Carbon dioxide can be an alternative refrigerant for vapor compression refrigeration systems, particularly air conditioning systems (ACSs). However, its use suffers from the increased pressure in the refrigeration circuit. To solve this, for its reduction, a mixture of CO2 with a substance that has significantly lower pressures under the same conditions can be developed, for example, dimethyl ether (DME), which has zero GWP and ODP, is inexpensive and readily available. The study of DME, in particular, was conducted by the Department E4 “Refrigeration and Cryogenic Engineering, Air Conditioning and Life Support Systems” of N.E. Bauman Moscow State Technical University. DME is moderately toxic and flammable.
 AIM: This study aims to investigate the possible use of a mixture of DME and carbon dioxide for energy-efficient application in ACSs using commercially available compressors for R410A.
 METHODS: Comparative calculation analysis of the characteristics of a simple one-stage vapor compression cycle was performed using R410A and a mixture of DME and CO2 using the calculation packages Mathcad 15, Aspen HYSYS v. 10, SOLKANE8, and REFPROP.
 RESULTS: 1. The cycle on pure DME is the most effective in terms of the coefficient of performance: ε = 5.63 at an ambient air temperature of 26°C, ε = 3.07 at 40°C. 2. It is necessary to consider the influence of temperature glides, the average value of which ranges from 10°C to 30°C depending on the concentration of components. 3. At DME/CO2 ratios of 40/60% and 60/40% (in mole fraction), the discharge pressure corresponds to the discharge pressure in the R410A cycle, with 39.62 bar at an ambient temperature of 26°C and 37 bar at 40°C, respectively.
 CONCLUSIONS: An environmentally friendly mixture of DME and CO2 with low GWP and zero ODP is developed. An increase in the percentage of DME in the mixture increases the coefficient of performance and reduces the pressure range, and at the same time, significant temperature glides arise, which affects the installation efficiency, namely, the transition to a cycle with a receiver tank, i.e., with a recuperative heat exchanger between the fluorinated refrigerant flow leaving the evaporator and the fluorinated refrigerant flow leaving the condenser. The developed mixture is less efficient than the R410A refrigerant in terms of the coefficient of performance and discharge pressure. However, it is possible to further consider a mixture of DME and CO2 with concentrations of 40% and 60%, respectively, as a replacement for the R410 refrigerant because there is a correspondence of discharge pressures for serial compressors (about 40 bar); however, it is necessary to keep in mind the flammability risk of the mixture.

Comparative evaluation of experimental ejector refrigeration system for different operating configurations

In this study, a comparative performance evaluation of an experimental ejector refrigeration system was conducted for various operating modes. The experimental setup was operated in different modes: conventional vapour compression refrigeration (CVCR), conventional dual-evaporator system (CDES), and dual-evaporator ejector system (DEES). The system was tested under different operating conditions, including varying condenser temperatures and mass flow rates. The results of the evaluation showed that the highest total cooling capacity and coefficient of performance (COP) were achieved in the DEES mode, while the lowest total cooling capacity was observed in the CDES mode. The lowest compressor power was calculated when the system was operated in DEES mode. When the condenser temperature was 33°C, the compressor power obtained in the DEES was 22.7%, 5.4%, and 17.7% lower than that of the CVCRA, CVCRB, and CDES modes, respectively. In conclusion, the performance of the ejector-operated system was found to be superior to the other configurations, and the ejector contributed positively to the system performance.

Evaluation of three suction pretreatment systems for the air compressor

Air compressor, as the power source of pneumatic tools, suffers the problems of low efficiency and high failure rate in summer. In this paper, three suction air pretreatment systems are presented, which are characterized by the cold sources: a vapor compression refrigeration unit, a water chilling unit and a combination of water chilling unit with cooling tower. Models for the thermodynamic and economic performance evaluation of the three systems are established and solved. The moisture diffusion coefficient is applied to consider the influence of the moisture condensation and the Marshall and Swift coefficients is introduced to consider the capital change over time. Formula to calculate the efficiency of refrigeration compressor is adopted. Besides, the system total efficiency, percentage of power saving (PPS) and payback period (PBP) are defined as performance indexes. A comparative study with typical meteorological data of hot-dry regions and hot-humid regions is conducted to analyze the superiority of each system under the operation conditions of varied suction air temperature and volume flow. According to the results, optimal spray water flowrate exists for each operation condition and an air–water ratio of 0.8 is recommended. When the suction air temperature decreases, the PBP of each system increases and a sharp increase occurs when the temperature is lower than the air dew point temperature. A suction air temperature of 26 ℃ is suggested. Direct air cooling with an evaporator is preferred when the suction air volume flowrate is smaller than 60 m3/min for hot-humidity regions. The combined system is significantly superior in hot-dry regions. The PBP of the three systems is all longer than 10 months. How to guarantee the usage rate is the key for enterprises to consider the use of suction air pretreatment systems.

Colossal barocaloric effect of the spin-crossover compound {Fe(pz)2(BH3CN)2} near room temperature

As one of the most likely alternatives to traditional vapor compression refrigeration technology, solid refrigeration technology based on the barocaloric effect (BCE) has attracted extensive attention in recent years. Spin-crossover (SCO) compounds are considered suitable for working at low driving pressures due to high-pressure sensitivity and small hysteresis width. However, the entropy change (ΔSSCO) of the SCO compound is smaller than that of other excellent barocaloric materials (plastic crystals and two-dimensional perovskites). Here, we report the BCE of the SCO compound {Fe(pz)2(BH3CN)2} (pz = pyrazine) with a smaller molar mass and a third source of entropy change besides electron and vibrational entropy changes. Compound {Fe(pz)2(BH3CN)2} exhibits high pressure sensitivity (dT1/2dP= 20.2 K kbar−1) as well as entropy change (ΔSSCO= 202 J kg−1 K−1). The maximum values of reversible isothermal entropy change (ΔSit,rev,max) and adiabatic temperature change (ΔTad,rev,max) at 1 kbar are only 103 J kg−1 K−1 and ∼0 K, respectively, due to the hysteresis behavior. However, at sufficiently high driving pressures, ΔSit,rev,max exceeds 200 J kg−1 K−1, and ΔTad,rev,max can reach ∼47 K, which exceeds all SCO compounds reported in BCE studies and is comparable to some plastic-crystalline and two-dimensional perovskite barocaloric materials. The excellent BCE of the SCO compound {Fe(pz)2(BH3CN)2} is mainly due to its small molar mass, which makes the unit mass compound exhibit higher ΔSSCO, while the introduction of the third source of entropy change—the reorientation entropy change (ΔSreo), only plays a small role. This is expected to promote the practical application of SCO compounds as barocaloric refrigerants.

Optimization of a three-stage cascade refrigeration system operating with natural refrigerants to produce low temperatures by applying a bio-inspired method

With the growing global energy consumption, on the first hand, and the need to produce low temperatures on the second hand, therefore the technological challenges consist in minimizing greenhouse gas emissions by reducing the energy consumption. In fact, in refrigeration, this consists of the use of environmentally friendly refrigerants (GWP < 150) with the optimization of cold production processes. In this context, several optimization methods have been tested, and the objective of this work to seek the most reliable method to optimize a three-stage cascade vapor compression refrigeration system. Regarding refrigerants, hydrocarbons can be a solution, the R50/R1150/R290 and R50/R1150/R1270 groups are selected and used here to produce temperatures ranging from −160 °C to −120 °C. After comparing seven (7) nature-inspired optimization methods, the JSOA bio-inspired optimization method is applied. Energetic, exergetic and environmental analyzes are also applied to determine the optimal operating point that allows both the minimization of energy consumption and TEWI (Total Equivalent Warming Impact). A pragmatic comparison between the two considered groups provides insights into the choice of high-temperature sub-cycle fluid, and it is found that R290 shows better results compared to R1270.

Energy and exergy analysis with environment benefit of the underground cooling system of the chiller plant

Using an underground heat exchanger as an alternative to a wet cooling tower can offer several benefits, particularly in terms of energy efficiency and environmental impact. Heat exchangers and cooling towers are chosen depending on various factors, such as the application size, local climate conditions, and economics. The purpose of this study is to compare the use of an underground heat exchanger with a wet cooling tower for cooling purposes. The underground heat exchanger and wet cooling tower provide cooled water for vapor compression chillers. The comparison is conducted on technical, economic, and environmental grounds. Research has been conducted in the Mashhad region, where water resources are limited and cooling demands are high during the summer. In this context, Ferdowsi University of Mashhad is selected as a case study. Energy and water consumption are calculated and compared by simulating and modeling both methods of producing cooled water and the refrigeration cycle. However, improving the alternative mode's exergy efficiency was discussed for all system components. The findings reveal that using the underground heat exchanger results in a 14% reduction in energy consumption and eliminates water consumption. The current water-cooled compression chillers consume approximately 1.95 cubic meters of water per square meter of the building daily.

Sustainable off-grid residential heating and desalination: Integration of biomass boiler and solar energy with environmental impact analysis

As global energy demand rises and the environmental impact of fossil fuel-based heating systems becomes increasingly evident, transitioning to renewable energy sources like solar and biomass for residential use is imperative. This is further underscored by the growing scarcity of freshwater resources, especially in arid urban environments. This study introduces an innovative off-grid system that effectively integrates a floor heating system with a vapor compression desalination unit. The novelty of this study lies in its approach to combining solar and biomass energies for both heating and desalination in a single off-grid system. The system's electrical and thermal energy needs are met by combining photovoltaic thermal collectors and a biomass boiler. Using TRNSYS software, the system's performance was evaluated in varying design configurations across Riyadh, Doha, and Abu Dhabi, targeting optimal thermal comfort for a standard residence with four occupants. Results show Riyadh leading in solar fraction at 48.43%, followed by Abu Dhabi (47.23%) and Doha (44.85%). The optimal equivalent heat transfer coefficient for the floor heating system varied notably between these cities, with Abu Dhabi requiring a lower coefficient to achieve thermal comfort. Additionally, a life cycle analysis revealed that the biomass boiler is the predominant source of CO2 emissions, contributing over 70% of the total in each city. Riyadh exhibited the lowest CO2 emissions, attributed to its higher solar fraction. This study demonstrates the system's versatility across different urban climates and its potential to lessen dependence on traditional energy sources, positioning it as a promising solution for future off-grid applications.

Investigation of smart thermostat fault detection and diagnosis potential for air-conditioning systems using a Modelica/EnergyPlus co-simulation approach

Smart thermostats offer low-cost alternative for fault detection and diagnosis (FDD) in residential air-conditioning (AC) systems. However, smart thermostats do not directly measure AC performance, but measures indoor air conditions which reflect the indoor air responses to both AC operations and other factors like weather and building gains. Estimating uncontrollable building gain disturbances is essential to differentiate them from AC impacts. Since the uncontrollable disturbances are difficult to monitor using smart thermostat data, there is need to investigate the actual capability of smart thermostats for FDD. In this study, an integrated building and Vapor Compression cycle-based AC model was developed and simulated using EnergyPlus/Spawn and Dymola. The simulation was performed under ten scenarios covering relevant gains, low charge, and low indoor airflow faults. The sensitivity of the time-to-cool feature under these scenarios was studied. The results show about 10% time-to-cool increase from varied internal gains and infiltration. Meanwhile, low charge at 10%, 20% and 30% severity increased time-to-cool by about 3%, 6%, and 20%, respectively, suggesting that if these gains are neglected in an FDD method, it might not be possible to detect low charge below 30% using smart thermostat data since even without a fault, the combined impact of those gains already exceeded that for 20% low charge. For low indoor airflow at 10%, 20% and 30% severity, the increase in time-to-cool was about 3%, 9% and 12%, meaning that only low indoor airflow fault above 30% can be confidently detected if those gains are not captured. Thus, this study demonstrates the need to consider some of these gains in developing smart thermostat based FDD algorithms.

Performance improvement of vapor compression heat pump with superhydrophobic finned-tube evaporator

Residential buildings frequently employ vapor compression heat pump for winter heating. Its advantages over electric and coal-fired heating include great energy effectiveness and low emissions. However, the outside evaporator's frosting negatively impacts the performance of heat pump systems in low-temperature and high-humidity environments. To ameliorate the frosting problem, a finned-tube heat exchanger with superhydrophobic surface wettability prepared by the wet chemical etching method was applied to a vapor compression heat pump in this study. The performance of a commercial evaporator unit and the superhydrophobic evaporator unit under five frosting conditions was investigated through experiments. The maximum heat transfer rate of the superhydrophobic heat exchanger unit was increased by 17%–44% compared with that of the commercial unit. The COP improvement of the superhydrophobic unit reached 11.2%, 14.3%, 18.8%, 20.9% and 31.9%, respectively. The total mass of frost formation of the superhydrophobic unit experienced a 59.2%–76.3% decrease. The operation time of the superhydrophobic evaporator unit before defrosting determination was significantly extended, reducing the number of defrosting times during a long-time operation. This study proves the advantages of superhydrophobic finned-tube evaporators used in heat pumps in terms of heat transfer performance and frost suppression performance, promoting the application of superhydrophobic finned-tube evaporators in heat pump air-conditioning systems.

Prototype isochoric preservation device for large organs.

This paper presents the design and prototype of a constant volume (isochoric) vessel that can be used for the preservation of large organs in a supercooled state. This prototype is a preliminary version of a more advanced design. The device consists of a cooling bath operated by a mechanical vapor compression refrigeration unit and an isochoric chamber made of stainless steel. The preservation of organs using supercooling technology in an isochoric chamber requires a continuous temperature and pressure monitoring. While the device was initially designed for pig liver experiments, its innovative design and preservation capabilities suggest potential applications for preserving other organs as well. The isochoric reactor may be used to accommodate a variety of organ types, opening the door for further research into its multi-organ preservation capabilities. All the design details are presented in this study with the purpose of encouraging researchers in the field to build their own devices, and by this to improve the design. We chose to design the device for isochoric supercooling as the method of preservation to avoid the ice formation.

Analysis of the Vapor Compression Refrigeration Cycle Measures with and without Using a Heat Exchanger for Alternative Refrigerants

One of the most commonly refrigeration systems is the vapor compression refrigeration system. Since energy saving and environmental friendliness remain a challenge, researchers are working hard to find an effective solution to improve the performance of vapor compression refrigeration systems while committing to environmental standards. The main goal of this paper is to identify the best and closest alternative refrigerant to R22 among the alternative cooling fluids taken into consideration in terms of thermodynamic and mechanical properties, environmental protection, and safety of handling. This work presents an analysis and comparison of the various performance measures for a vapor compression refrigeration cycle operating without using and using a heat exchanger for environmentally friendly alternative refrigerants, namely R410A, R407A, R407C, R438, RS-44b, and R417A, and compares them with the refrigerant R22, which has direct environmental impacts on the ozone layer (ODP) and global warming (GWP). The computer simulation program Chemours Refrigerant Expert 1 was used to conduct the analyses. The performance parameters analyzed are coefficient of performance, compressor work, cooling capacity, temperature of condensation, intake and exhaust pressure, volumetric capacity, theoretical displacement, intake, exhaust, condensation and evaporation temperature without and with a heat exchanger, and super heating temperature with a heat exchanger. It was concluded from this study that the best alternative to R22 refrigerant among the alternative refrigerants taken into consideration in the study is the RS-44b refrigerant in terms of all performance measures and environmentally friendly. Keywords: Refrigerant; Vapor compression; Performance measures; Evaporation; Heat exchanger.

Impact of Ambient Temperature and Humidity on the Performance of Vapour Compression Air Conditioning System - Experimental and Numerical Investigation

Due to global warming, population growth, and urbanisation, demands for space cooling in buildings have significantly increased. Mechanical vapour compression cooling technology is relatively mature, well-understood and most commonly used globally. However, they suffer from high energy consumption and adverse environmental impact due to the refrigerants used. As ambient temperature and humidity have significant effects on the performance of vapour compression systems, this paper experimentally and numerically investigates their impact on the performance of vapour compression air conditioning system in terms of power consumption and cooling capacity. It was concluded that at ambient humidity of 55%, as the ambient temperature increases from 22 °C to 40 °C, the compressor temperature has increased from 46 °C to 59 °C which increased its power consumption from 751.2 to 935.52 Watts, giving an increase of 10.24 Watts for every one degree of ambient temperature increase. Also, as ambient humidity in-creased from 32% to 88%, the power consumption increased from 739.2 Watts to 853.2 Watts, an increase of 114 Watts. A validated CFD (Computational Fluid Dynamics) model was developed and predicted a loss in the enthalpy change from 11.7kJ/kg.d.a to 3.6kJ/kg.d.a. due to ambient temperature increasing from 22 °C to 40 °C and a loss of enthalpy change from 12.857kJ/kg.d.a to 5.524kJ/kg.d.a. due to increasing the ambient air humidity from 32% to 88%. This work high-lighted the impacts of ambient conditions on the performance of vapour compression cooling system in terms of increased power consumption and loss of cooling capacity.

Thermodynamic analysis of novel mixtures including siloxanes and cyclic hydrocarbons for high-temperature heat pumps

This paper presents the investigation of zeotropic binary fluid mixtures containing cyclohexane (critical temperature above 200 °C) as the base fluid with R600, R600a, R601, R601a, R1336mzz(Z), R1234ze(Z), R1233zd(E) and cyclopropane (critical temperatures between 100 °C and 200 °C). For pure components and their mixtures, the performance of the vapor compression system with an internal heat exchanger was analysed at 50 °C and 80 °C heat source and sink inlet, respectively. Variation of the heat source temperature difference and the internal heat exchanger pinch point temperature difference at supply temperatures (140–170 °C) were also investigated. A pinch point temperature difference of 5 K was maintained for the evaporator and condenser. An increase of 6.59 % in COP was obtained with the zeotropic mixture of cyclohexane/cyclopropane compared to that of pure cyclopropane. The design point analysis showed that increasing the heat source temperature difference and internal heat exchanger pinch point temperature difference reduces the COP. The adopted mixture criteria increased the performance between 3.23 % and 3.91 % with respect to standard working fluids like R1233zd(E) and R601, for a 170 °C supply temperature. With this promising thermodynamic analysis in a subcritical operation, the cyclohexane/cyclopropane mixture has prospect of full integration heat pump design.