Vapor Compression System Research Articles

Energy consumption and feasibility study of a hybrid desiccant dehumidification air conditioning system in Beirut

In this work, the transient performance of a hybrid desiccant vapor compression air conditioning system is numerically simulated for the ambient conditions of Beirut. The main feature of this hybrid system is that the regenerative heat needed by the desiccant wheel is partly supplied by the condenser dissipated heat while the rest is supplied by an auxiliary gas heater. The hybrid air conditioning system of the present study replaces a 23 kW vapor compression unit for a typical office in Beirut characterized by a high latent load. The vapor compression subsystem size in the hybrid air conditioning system is reduced to 15 kW at the peak load when the regeneration temperature was fixed at 75 °C. Also the sensible heat ratio of the combined hybrid system increased from 0.47 to 0.73. Based on hour by hour simulation studies for a wide range of recorded ambient conditions of Beirut city, this paper predicts the annual energy consumption of the hybrid system in comparison with the conventional vapor compression system for the entire cooling season. The annual running costs savings for the hybrid system is 418.39 USD for a gas cost price of 0.141 USD/kg. The pay back period of the hybrid system is less than 5 years when the initial cost of the hybrid air conditioning system priced an additional 1712.00 USD. Hence, for a 20-year life cycle, the life cycle savings of the hybrid air conditioning system are 4295.19 USD.

Performance Evaluation of Cryogenic Liquefaction System Precooled by Combined Vapour Compression-Absorption Refrigeration System

Liquefaction is a high-energy-consuming process. One of the most efficient methods of lowering energy consumption use is to run a precooled cycle with a cascade refrigeration system. When compared with the vapour compression system, the merit of adopting a cascade system is that it consumes very less energy. Another advantage is that non-traditional energy sources such as geothermal and solar might be used to power these cycles. This paper examines a precooled Linde Hampson-liquefaction system using a double-stage cascade vapour compression-absorption refrigeration cycle that consists of an absorption system at the high-temperature stage and a compression system at the low-temperature stage to generate cooling at a small temperatures by using various refrigerants in the absorption and compression sections. The system's performance was evaluated by employing various combinations of natural refrigerants in the absorption section. Liquefaction of Nitrogen is carried out using a precooled Linde Hampson system and precooled liquefaction using a cascade refrigeration cycle. Nitrogen was liquefied using two methods in the current study. A thorough examination of the precooled system was conducted, and it was discovered that by employing a cascade refrigeration cycle, the input required per unit mass of gas liquefied is decreased. The performance metrics of the liquefaction system, such as Figure of Merit (FOM) and Liquid Yield, were discovered for both scenarios, and it is concluded that the usage of a cascade refrigeration system has more efficiency and consumes less energy than a system without an absorption chiller. The use of a precooled Linde Hampson system with cascade cycles improved liquefaction characteristics by 5-7%.

Feasibility of R1234yf/R13I1 mixture refrigerant as replacement of R134A refrigerant in vapor compression system

The performance of a new mixed refrigerant R1234yf/R13I1 with a mass ratio of 90/10 under basic refrigeration cycle and refrigeration cycle with internal heat exchanger is calculated in comparison with the performance of R134a under basic refrigeration cycle at different condensation temperature and evaporation temperature. The results show that R1234yf/R13I1 is virtually non-flammable with global warming potential of less than 4. Under basic refrigeration cycle, the compressor power consumption, cooling capacity and COP of R1234yf/R13I1 are lower than these of R134a by about 4.5%, 9.5%, and 7.5%, respectively. Under refrigeration cycle with internal heat exchanger, the compressor power consumption, cooling capacity, and COP of R1234yf/R13I1 are lower than these of R134a by about 2%, 4.5%, and 3%, respectively. The R1234yf/R13I1 is a beneficial refrigerant of replacing R134a in vapor compression system.

Potential role of post-harvest management in agribusiness

Agriculture plays a key role in deciding the economy of the country and agricultural marketing has become the potential driver of the agricultural sector. Green revolution and succeeding technologies made our farmers to succeed in the production front, but lagging appreciably in terms of price realization owing to their inability to stop post-harvest losses and inaccessibility to efficient and scientific marketing system. Post-harvest management includes storage, packaging, coating, disease management, extended shelf life, maintaining food quality. Foods and other products can be preserved by storage at low temperature, which retards the activities of microorganisms and preserve perishable foods in their natural state. Preservation depends on the storage time required whether short or long-term short and the type of product. A cold storage unit works on two principles: Vapour absorption system (VAS), and Vapour compression system (VCS). Although VAS is a bit costlier, but economical in operation. Food irradiation is another recent food preservation technology to address some of post-harvest losses. Food is exposed to ionizing radiation (i.e. radiowaves, microwaves, UV rays, X-rays, gamma rays etc.). Food irradiation can be applied to specific purposes as quarantine treatment of fruits and vegetables and as a method to ensure hygienic quality of foods. Food processing techniques like grading, sorting and packaging, etc add value and enhances shelf life of food. Agricultural productivity augmentation needs a concurrent development of post-harvest support mechanism and efficient and organized marketing system, which would ensure maximum price rrealization to the farmers.

Development of a Sustainable Nano-refrigerant using agro-waste (rice husk ash) as a base material for a domestic refrigeration system

Silica nanoparticles were synthesized from Rice husk ash (RHA) through the top-down approach production greyish coloured particles. The spectroscopical investigation showed a compositional analysis of 74.6% silicon, 20% oxygen and 5.4% carbon. Microstructural studies indicated an average particle area of 7.8nm2 and average particle size of 4nm. The nanoparticles were dispersed into the lubricant oil of the compressor such that when the refrigerant is dispersed over the compressor, the particles mix with the refrigerant giving the nano-refrigerant mixture. The nanoparticles were dispersed into the mineral oil at concentrations of 0.2wt%, 0.3 wt%, 0.5 wt% and 0.6 wt% and fed into the compressor to combine with the refrigerant in the vapour compression system. The refrigerator was run for 240 minutes for each sample as well as the control sample which was the refrigerant R600a. Performance evaluation was carried out to assess the viability of the developed nano-refrigerant. Generally, an increase in the refrigerating effect compared to the control sample by all concentrations apart from the 0.6wt% by 13, 7.5, and 12.5% and a corresponding increase in the COP by 31, 23 and 35% compared to the control sample for the 0.2 wt%, 0.3 wt% and 0.5 wt% concentrations respectively was recorded.

Optimizing Sustainability: Exergoenvironmental Analysis of a Multi-Effect Distillation with Thermal Vapor Compression System for Seawater Desalination

Optimizing Sustainability: Exergoenvironmental Analysis of a Multi-Effect Distillation with Thermal Vapor Compression System for Seawater Desalination

The impact of a balanced humidification-dehumidification desalination system driven by a vapor-compression heat-pump system

This study adopts a numerical thermo-economic investigation of a novel desalination system. In this system, a vapor compression (VC) heat pump is used to drive a balanced humidification-dehumidification (HDH) desalination unit with multiple extractions. The mathematical model of the proposed VC-HDH system is validated experimentally. The system is examined for water production under a condenser temperature of 45 °C, evaporator temperature of −5°C, feed saline water temperature of 30 °C, feed saline water flow rate of 1 kg/s, and an energy effectiveness value of 0.85 for the HDH unit’s components. The results show that without air extraction, the system can produce 6.62 kg/h of desalinated water for 0.011 $/l with a gained-output-ratio (GOR) value of 9.1. On the other hand, when a single air extraction is applied, about 20 kg/h of desalination water is produced by the system for 0.0042 $/l and 29 GOR. Increasing the number of air extractions to two yields a freshwater production rate of approximately 40 kg/h for 0.0026 $/l and a GOR value of 57. A considerable positive effect of the HDH unit’s performance is found on the system’s performance on both thermodynamic and economic scales. For better desalination performance, it is found that the feed water temperature should be maintained between 25 °C and 30 °C. Finally, the theoretical ceiling of the proposed system’s GOR is estimated.

Modeling and multi-objective optimization of polymer desiccant cooling system

The polymer desiccant cooling system (PDCS) efficiently reduces energy consumption compared to the vapor compression system (VCS). In this paper, a PDCS integrated heat pump is proposed. Experimental and simulation are used to analyze the performance of the PDCS. The control strategy is optimized with the NSGA Ⅱ algorithm. A case study in Shanghai illustrates the practical application of the PDCS optimization strategy. The calculation results based on the thermal comfort requirement show the maximum energy consumption of optimized PDCS, routine PDCS, and VCS are 549.9 kW, 597.7 kW, and 1327.7 kW. About 62.7 % and 72.3 % of energy can be saved in routine PDCS and optimized PDCS compared to VCS. Moreover, the maximum moisture removal efficiency of the above scenarios is 10.67 kW/(g·s), 11.56 kW/(g·s), and 25.42 kW/(g·s), separately. Additionally, the maximum coefficient of performance is 0.530, 0.457, and 0.182, respectively.

Generalization of second law efficiency for next-generation cooling and dehumidification systems

Dehumidification plays a significant role in space conditioning energy use. Conventional vapor compression cooling systems employ dewpoint condensation to deal with latent loads. In contrast, separate sensible latent cooling (SSLC) and other advanced alternative dehumidification systems can significantly reduce the electricity usage for dehumidification. The second law efficiency can be used as a benchmark to evaluate thermodynamic performance of alternative dehumidification systems. However, limitations exist in previous studies that define the thermodynamic reversible limits and second law efficiency for cooling and dehumidification systems. This work presents a new physics-based definition for the reversible limit and the second law efficiencies for cooling and dehumidification systems with air recirculation. The new framework is then extended to define a novel performance metric, the seasonal second law efficiency, to form a universal benchmark for assessing various cooling and dehumidification systems. Five cooling and dehumidification systems including magnetocaloric cooling, solid desiccant dehumidification, and membrane dehumidification are evaluated using this benchmark. Steady-state thermodynamic models are constructed for each system. Second law efficiency for each system under various outdoor temperatures and indoor sensible heat ratios (SHR) are calculated. The annual electricity usage of the five systems is used to justify the seasonal second law efficiency definition. The results show that compared to conventional vapor compression systems with mechanical dehumidification, the membrane-based AMX-R cycle can reduce annual electricity use by 12.2%–22.2% and increase the seasonal second law efficiency by up to 36%.

A novel approach combining thermosiphon and phase change materials (PCM) for cold energy storage in cooling systems: A proof of concept

A novel approach combining thermal energy storage (TES) and a thermosiphon was investigated for cold storage. The use of TES units for cooling systems has been studied for many years, as they are well suited for short-term energy storage. A cold latent heat accumulator was designed to replace the function of any vapour compression cycle in the event of electrical failure without using any electrical device but rather the thermosiphon principle. A laboratory prototype of a thermosiphon combined with the cold accumulator was developed using a paraffin mixture as a phase change material (PCM). The accumulator was connected to the vapour compression system of a closed display cabinet. An experimental study was carried out by simulating 1.5 h compressor shutdowns with and without the accumulator. The thermosiphon loop effectively transferred 97 % of the stored energy to the display cabinet. The air and product temperatures in the cabinet, the behaviour of the compressor during restart, and the charging and discharging processes of the accumulator were analysed. The results showed that shutting down the compressor with the cold accumulator significantly reduces the increase of air and product temperatures compared to shutting down without the accumulator. The air temperature in the rear duct was maintained within the acceptable temperature range for 72 min with the accumulator, compared to 3 min without. A default in the design of the accumulator was observed during the charging phase, as some areas of the accumulator never reached 80 % of charge. This new approach extends demand-side management and renewable energies to all end users of vapour compression machines.

Experimental analysis of an ejector assisted dual-evaporator vapor compression system

Condenser split dual-evaporator vapor compression systems (C-DEVCS) have been used to maintain the two evaporators of a single refrigeration system at different temperatures for long. The throttling process occurring in the expansion valve of these systems is irreversible in nature and thus responsible for a part of energy loss. It has been found that the isenthalpic expansion loss can be reduced using ejector as a throttling device which provides isentropic expansion. Moreover, it recovers some of the energy lost in expansion and reduces compressor work. In the current work, an experimental test facility of ejector assisted dual-evaporator vapor compression system (EA-DEVCS) is developed for R-134a working fluid and analyzed for different condenser temperature. The overall COP of EA-DEVCS is found to increase from 1.982 to 2.925 and 9.8 % decrease in compressor power consumption when the water temperature at the inlet of condenser is decreased from 35 °C to 27 °C. The entrainment ratio of the ejector gets increased from 0.396 to 0.701 with the decrease in condenser temperature.

Numerical verification of the condenser finite volume model

Numerical modelling of vapour compression systems is very useful for performance optimization through the implementation of suitable model-based control applications; in this context the heat exchangers are the most challenging component to devise, due to phase transition and ensuing discontinuities of the physical properties, and one tool which has proven itself suitable for the task is the finite volume method. A numerical verification of a finite volume model of a brazed plate condenser in counterflow arrangement is carried out, employing a fixed timestep solver; some useful guidelines are suggested to properly choose the solver order, the integration step size and the number of grid elements, balancing the accuracy of the predictions with computational time and model stability and flexibility during the transients, with the ultimate goal to provide a model suited for real-time simulations and control-oriented applications.

Comparative study of three hybrid air-conditioning systems based on multiple evaporative coolers and run-around reheating coils

Existing evaporative-cooling hybrid air conditioning systems cannot fully utilize the synergistic energy-saving potential of multiple evaporative-cooling technologies. Moreover, they cannot meet simultaneously the energy-saving requirements of standard mechanical vapor compression (MVC) systems in the terms of fresh air pre-treatment, condenser pre-cooling and supply air reheating. Therefore, in this paper, integrating MVC system with the indirect evaporative cooler, outdoor-air evaporative-cooling unit, and run-around reheating coils, three alternative hybrid systems were proposed to meet the aforementioned three requirements. The three hybrid systems have different outdoor-air unit configurations (single condenser with direct evaporative cooler, dual condenser with direct evaporative cooler, and dual condenser with two-stage evaporative-cooling configuration) and reheat sources (exhaust, outdoor, and mixed air of fresh and return air). Then, the parameter effects and application potentials of the three hybrid systems were analyzed comparatively based on detailed numerical models. The results showed that the third proposed hybrid system (HAC-R3) exhibits the best energy-saving advantages in almost the range of ambient temperature, relative humidity and fresh airflow rate studied. The first proposed hybrid system (HAC-R1) has the simplest outdoor-air side configuration, which is also a good choice in medium–low humidity conditions. In hot-humid summer in southern China, HAC-R3 has the highest average energy-saving rate and seasonal COP of 16.0 % and 7.0 respectively. In addition, HAC-R1 has the lowest static equipment payback period of 3.3 years, slightly lower than that of HAC-R3 (3.4 years).

Novel marine ejector-compression waste heat-driven refrigeration system: Technical possibilities and environmental advantages

A novel combined ejector-compression refrigeration system for provision rooms of merchant ships was conceptualized and analyzed. The principle possibility of recovery of onboard low-grade heat (85–95 °С) of jacket cooling water was confirmed. Two ejectors of different geometries to ensure the ejector stage operation when the seawater temperature varies in a wide range were designed and proposed to install in parallel. The performance of the combined system was compared to a vapor-compression one and the choice of the rational temperatures in the condenser-evaporator tC/Ev was performed. The combined system COPtotal is considerably higher than the vapor-compression system, and it weakly depends on heat source temperature. At condensing temperature tC = 34 °С the decreasing in tC/Ev from 20/15 to 10/5 °С results in increasing of COPtotal up to 13.5 % at generation temperature tG = 80 °С and up to 15.6 % at tG = 90 °С. Utilizing the combined system for the onboard cold production will contribute to fuel savings of 25 to 33 % per voyage (operation and transport) vs. vapor-compression system. The combined system inherent the lower specific CO2 emission per 1 kW h of cooling energy emrefr than the standard system for all considered operation modes. The value of emrefr for combined system at tC/Ev = 10/5 °C, tG = 80 °C and tC = 36 °C or tC = 42 °C is 23.1% or 18.3%, respectively, less than for the vapor-compression one. The approach to analysis proposed can be used for assessment of the feasibility of utilization of low-grade heat and the retrofit of ship refrigeration systems.

One-way oscillating flow cycle cooler: A promising technology for cooling and heating

Tens of cooling technologies have been proposed as alternatives to vapor compression systems for cooling and heating. But developing a cooling technology with technologically meaningful performance is still a challenge. We have developed a machine for gas cooling cycle consisting of two isochoric and adiabatic processes, which is called One-way Oscillating Flow Cycle (OOFC) in this work. 76.3% of Carnot efficiency is obtained at room temperature based on one-dimensional computational fluid dynamic model with considering various losses and thus should have high accuracy. The cooling capacity are dependent on the size and can be scaled up to megawattpowerratings. Furthermore, OOFC cooler can achieve a large temperature glide absorption and rejection. Thus, OOFC cooler could be a promising alternative to vapor compression systems.

Self-Optimizing Vapor Compression Cycles Online With Bayesian Optimization Under Local Search Region Constraints

Abstract Self-optimizing efficiency of vapor compression cycles (VCCs) involves assigning multiple decision variables simultaneously in order to minimize power consumption while maintaining safe operating conditions. Due to the modeling complexity associated with cycle dynamics (and other smart building energy systems), online self-optimization requires algorithms that can safely and efficiently explore the search space in a derivative-free and model-agnostic manner. This makes Bayesian optimization (BO) a strong candidate for self-optimization. Unfortunately, classical BO algorithms ignore the relationship between consecutive optimizer candidates, resulting in jumps in the search space that can lead to fail-safe mechanisms being triggered, or undesired transient dynamics that violate operational constraints. To this end, we propose safe LSR-BO, a global optimization methodology that builds on the BO framework while enforcing two types of safety constraints including black-box constraints on the output and local search region (LSR) constraints on the input. We provide theoretical guarantees that under standard assumptions on the performance and constraint functions, LSR-BO guarantees constraints will be satisfied at all iterations with high probability. Furthermore, in the presence of only input LSR constraints, we show the method will converge to the true (unknown) globally optimal solution. We demonstrate the potential of our proposed LSR-BO method on a high-fidelity simulation model of a commercial vapor compression system with both LSR constraints on expansion valve positions and fan speeds, in addition to other safety constraints on discharge and evaporator temperatures.

Experimental investigation of effect of extent and position of bypass openings on performance of a single unit liquid desiccant based indirect evaporative cooler

In high temperature and high humidity zones, evaporative cooling is ineffective and vapour compression systems are less energy efficient. Therefore, an alternative system is highly desirable which is effective, energy efficient and enables the use of cheap and sustainable energy sources. Indirect evaporative cooling helps in retaining humidity level of air, but is less effective in attaining lower air temperatures. To mitigate this challenge, M-cycle indirect evaporative cooling system helps in achieving sub-wet bulb temperatures. In this work, performance of a novel modified indirect evaporative M-cycle cooling system assisted by 40% aqueous Li-Cl liquid desiccant is experimentally investigated against various parameters. The cooling system used in this study is a single unit system which can perform indirect evaporative cooling, liquid desiccant dehumidification and internal cooling to the liquid desiccant. With an air velocity of 1 m/s at the inlet, the introduction of openings in between inlet and exit of the cooling system has shown a maximum improvement of 19.2% in its dew point effectiveness, with unaffected dehumidification effectiveness. Furthermore, it is observed that the dew point effectiveness is decreased with the increasing distance of openings from the inlet. The investigated cooling and dehumidification system is useful as a pre-air-conditioner to conventional air-conditioning systems and also as a stand-alone air-conditioning system.

Enhancement of Condenser Performance in Vapor Absorption Refrigeration Systems Operating in Arid Climatic Zones—Selection of Best Option

Generators and condensers are the two vital equipment items that determine the output of vapor absorption refrigeration systems. Arid weather conditions produce a significant reduction in the performance of the vapor absorption refrigeration cycle due to low condenser heat dissipation despite high generator temperatures. Although numerous studies on condenser cooling methods in vapor compression systems have been reported in the literature, solar-operated vapor absorption systems have not been studied. Limitations in generator temperatures of solar-operated vapor absorption systems necessitate a focused study in this area. This study makes the selection of the best choice for condenser cooling from among four different condenser cooling methods which have an impact on the performance of the vapor absorption refrigeration system for effective cooling using solar energy. A solar vapor absorption refrigeration system working with low-grade heat using a compound parabolic collector is considered in this study. Analysis of a vapor absorption refrigeration system for cooling in arid weather conditions is carried out using different condenser cooling methods with Engineering Equation Solver. Initially, the model used in the study is compared with a similar study reported in the literature. Techniques considered are air, water, evaporative, and hybrid cooling techniques. The performance of the vapor absorption cooling system was analyzed using experimental values of a solar compound parabolic collector obtained from real-time measurements for simulating the model. Results show that water cooling can provide suitable condenser cooling and improve the coefficient of performance of the solar vapor absorption refrigeration system using the solar collector. The water-cooled condenser has 1.9%, 3.3%, and 2.1% higher COP when compared to air-cooled condensers for spring, summer, and autumn seasons respectively, whereas the water-cooled condenser cooling recorded 6%, 14%, and 8% higher COP relative to the evaporative cooling method. Cost comparison showed maximum cost for water-cooled condensers and minimum cost for hybrid-cooled condensers. The effect of each cooling method on the environment is discussed.

Applicability of a heat-pump-driven liquid-desiccant air-conditioning system in energy-efficient buildings

Building trend is toward energy-efficiency by reducing building sensible load, while neglecting latent load. A heat-pump-driven liquid-desiccant (HPLD) air-conditioning system has emerged for effectively handling building latent load in energy-efficient buildings with low indoor sensible heat ratio. However, previous studies only investigated one building type, failing to account for the increase in building energy-efficiency. This study estimates building thermal loads of four different energy-efficient high latent load buildings, simulating building trend. Then, as energy-efficiency of buildings increases, the changes in indoor thermal comfort and energy consumption of the HPLD air-conditioning system and reference vapour compression system are compared. Simulation results show that in building with the highest energy-efficiency, the reference system can only maintain thermal comfort for 43.3% and 24% of summer operating hours when primarily meeting supply-air target temperature and humidity, respectively. Contrastingly, the proposed system can maintain thermal comfort in all building types for almost 100% of summer operating hours due to decoupled control of air temperature and humidity. Additionally, the proposed system saves up to 33.2% of operating energy when both systems achieve the same thermal comfort satisfaction. In conclusion, the HPLD air-conditioning system with decoupled control is more applicable as energy-efficiency of buildings increases.

How highly efficient power electronics transfers high electrocaloric material performance to heat pump systems

Electrocaloric heat pumps for cooling or heating are an emerging emission-free technology, which could replace vapor-compression systems, harmful refrigerants, and mechanical compressors by a solid-state solution with theoretically even higher coefficient of performance. Existing electrocaloric ceramics could reach around 85% of the Carnot-limit, and existing electrocaloric polymers could enable a compact and high power density system. However, the performance of published system demonstrators stays significantly below this performance, partly because of the external electronic charging loss (cyclic charging/discharging of electrocaloric capacitors). This work analyzes how the latest 99.74% ultra-efficient power electronics enables to maintain a high performance even at the system level. A first-principle analysis on material and system parameters also shows the effect of significantly different material properties of ceramics (PMN, PST) and PVDF-based polymers on system parameters. A system benchmark provides insight into system characteristics not covered by material analysis.Graphical abstract