Vapor Compression Refrigeration Unit Research Articles

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.

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.

Experimental Investigation of Energy and Exergy Assessment of Vapor Compression Refrigeration Unit Enhanced via Encapsulated Phase Change Material

Energy and exergy performance of simple vapor compression refrigeration unit is investigated experimentally with and without coupling heat exchanger of phase change material before the condenser. The hot outside air is cooled before entering the condenser throughout the day by flowing over the cooled phase change material structure that previously solidified during nighttime. Phase change material SP24 is employed because its melting/freezing range is suitable for most selected countries' climates. An experimental set‐up of an air‐phase change material heat exchanger coupled with the unit is constructed to examine its performance, including pressure–enthalpy curve, coefficient of performance, exergy performance, and power consumption including inflow air temperatures and flow rates impacts. Results affirm that the coefficient of performance, cooling capacity, power usage, and exergy destruction are improved by using phase change material. Compared to the unmodified unit, the maximum percentage of saved power and exergy destruction enhancement for the modified refrigeration unit with phase change material is about 8.8% and 10%, respectively. The maximum coefficient of performance and exergy efficiency rise is about 15.1% and 14.2%, respectively. Increasing the temperature differential across the phase change material heat exchanger, either by increasing inlet temperature or decreasing airflow, enhances the refrigeration unit power saving.

Experimental study of vapor compression refrigeration system enhanced via tubular heat exchanger incorporating single/dual phase change materials

Vapor compression refrigeration (VCR) systems operating in hot climates suffer from high condenser temperatures that reduce their performance. One interesting approach being investigated to improve VCR performance is incorporating phase change materials (PCMs) into VCR systems that have not yet been expanded experimentally. So, this work experimentally studies the effect of using tubular PCM heat exchanger to cool the VCR condenser. The impact of two PCMs types suitable for warm climate conditions: SP24 and SP26, and combination of them on the VCR energy and exergy performance is investigated for two inlet ambient air temperatures. The impact on the exit air and PCMs temperatures, and VCR unit's pressure-enthalpy curve, VCR coefficient of performance, and power consumption is also examined. The results show that PCM-equipped systems significantly enhance the VCR exergy efficiency and coefficient of performance, especially at higher ambient temperature. Compared to the system without PCM, the power consumption can be reduced by up to 10.4% with PCM, while the exergy efficiency and coefficient of performance can be improved by 13.7% and 13.4%, respectively. While PCM SP24 provides the best performance, PCM SP26 has longer effective cooling period. A combination of SP24 and SP26 balances the performance and effective cooling period.

Numerical Investigation of the Expansion Devices Applied in Modern Vapour Compression Refrigeration Unit Considering Specific Entropy and Entropy Generation Analyses

Numerical Investigation of the Expansion Devices Applied in Modern Vapour Compression Refrigeration Unit Considering Specific Entropy and Entropy Generation Analyses

Thermo-economic and environmental assessment of hybrid vapor compression-absorption refrigeration systems for district cooling

District cooling plants are predominantly based on vapor compression refrigeration cycles with detrimental environmental impacts due to fossil-based electricity. Vapor absorption refrigeration cycles promise operating improvements and emission reductions in vapor compression-absorption refrigeration system configurations. However, the use of conventional vapor absorption refrigeration working fluids and the limited studies of systems with capacities that are relevant to district cooling plants, prohibit their scaling-up. This work compares the thermodynamic, environmental, and economic performance of seven configurations of the vapor compression refrigeration cycle with a double-effect vapor absorption refrigeration cycle that employs either the conventional ammonia/water or the novel acetaldehyde-N,N-dimethylformamide working fluid. These three cycles are compared with the cascade and parallel vapor compression-absorption refrigeration system configurations, with ammonia/water or acetaldehyde-N,N-dimethylformamide in the vapor absorption refrigeration. The coefficient of performance of the vapor compression refrigeration unit in the cascade configurations is 252% higher than the stand-alone vapor compression refrigeration configuration. The stand-alone vapor absorption refrigeration coefficient of performance with the novel fluid acetaldehyde-N,N-dimethylformamide is 9.1% higher than that of the vapor absorption refrigeration with ammonia/water. The cost per ton of cooling and the total equivalent warming potential of the cascade vapor compression-absorption refrigeration system with acetaldehyde-N,N-dimethylformamide are 65% and 67.8% lower than those of the stand-alone vapor compression refrigeration. The electrical energy utilization factor is 30.5% lower for the acetaldehyde-N,N-dimethylformamide fluid compared to ammonia/water, in the cascade configuration.

Experimental investigation of the influence of vapor compression refrigeration in a multistage reciprocating dehumidifier test rig

The present work focuses on constructing a multistage reciprocating dehumidification test rig integrated with the vapor compression refrigeration and desiccant regeneration units. Four Celdek 7090 pads located at four different positions, undergoes reciprocating motion based on the cam follower mechanism and will be dipped in an absorber tank containing calcium chloride desiccant. Experiments are conducted with and without a vapor compression refrigeration unit for varied air velocities and desiccant concentrations. Results indicated that the dehumidification efficiency, moisture removal rate, and mass transfer coefficient are increased by 8.3%, 7.3%, and 4.5% for the system with a vapor compression refrigeration cycle compared to the system without a vapor compression refrigeration cycle. Energy consumption details reveal that the vapor compression refrigeration integrated cycle requires slightly higher energy than without vapor compression refrigeration resulting in reduced system coefficient of performance. Integrating vapor compression refrigeration has lowered the energy requirement for regeneration of the desiccant by 53%. The study infers that the dehumidification unit with vapor compression refrigeration gave better dehumidification performance with a slightly lesser coefficient of performance than the system without a vapor compression refrigeration cycle.

Experimental assessment of a small scale hybrid liquid desiccant dehumidification incorporated vapor compression refrigeration system: An energy saving approach

This work investigates a small-scale hybrid experimental setup developed combining the two technologies of liquid desiccant dehumidification and vapour compression refrigeration. A hybrid system of 5 kW capacity is designed and developed for energy saving analysis. The experiments are designed with central-composite design scheme using three variables namely air mass flow rate, desiccant inlet temperature, and desiccant inlet concentration. Three responses namely specific humidity change in the dehumidifier, dehumidifier heat load and hybrid system performance coefficient are considered for the investigation. The regression correlations for all three responses are developed and presented. Further, the performance comparison of the hybrid system with the standalone vapour compression refrigeration unit is also carried out. The comparative results reveal that the maximum improvement of 27.54% is observed in the coefficient of performance at which 54.93% of the total latent heat load is being covered by the dehumidifier. Finally, the energy saving analysis reveals that the hybrid system is having payback duration of 4 years compared to the standalone vapour compression refrigeration system of same cooling capacity.

Research of an integrated cooling system consisted of compression refrigeration and pump-driven heat pipe for data centers

An integrated cooling system is developed for the environmental control of all-year-round running data centers with high heat load. The system is consisted of a vapor compression refrigeration unit connected with a separated heat pipe unit by an evaporative condenser. Based on the outdoor temperature, the system can operate on three modes: vapor compression mode, dual refrigeration mode and heat pipe mode. The cooling capacity of vapor compression unit is regulated via volume control of six paralleled scroll compressors, while that of heat pipe unit is adjusted by frequency conversion outdoor fan. The experimental results indicate that the cooling capacity of the system has a nearly constant value of 200 kW, and EER changes from 21.2 to 3.1 when the outdoor temperature increases from −5 °C to 45 °C. The theoretical calculation and analysis show that, compared with air cooling direct expansion unit and air cooling dual source chiller, the proposed system has the lowest annual energy consumption with highest energy efficiency. So it can be the preferred choice for all-year-round running data centers especially in regions with low average annual temperature.

Experimental cycle air cooling system for gas microturbine unit

The article considers the Combustion Turbine Inlet Cooling (CTIC) system — an experimental system for cooling the cycle air entering the gas microturbine unit. This enables to save electrical power of the unit generated at the design level in the period of seasonal increase in air temperature. Cooling of the air at the inlet to the turbocharger of the unit occurs up to its design temperature (which is, according to the ISO standard, equal to 15˚С). The basis of the CTIC model is an industrial cooling system based on a vapor compression refrigeration unit with a cold accumulator. Water ice is used as a cold storage medium in the accumulator, while ice water is used as a medium cooling the cycle air (ice water is water at a temperature of 0.5˚С – 1˚С). The eff ect of cooling of cycle air is achieved by pumping ice water coming from the cold accumulator through an air-to-water heat exchanger installed at the inlet to the turbocharger. The purpose of the study was to determine the operating time of a cold accumulator, depending on the speed of the circulating water. The experiments were carried out on a model of a cooling system with a cold accumulator having a 200 kg ice storage and working with the Capstone C-30 microturbine. Maintaining the temperature of the cycle air at its design level is achieved using a frequency-controlled circulation pump and a digital measurement and control system with the LabVIEW software package. The results of the study show that the considered CTIC system, while discharging the cold accumulator, is able to maintain the required design temperature of the cycle air at 15°C for 6 hours, which is quite enough to cover the peak load of the working day. Technical and economic parameters of the plant are evaluated.

Fire and Explosion Safe Technology of Storage and Regasification of Liquefied Petroleum Gas

The technology of storage and regasification of liquefied petroleum gas that implies storage in an isothermal tank and overheating the gas with subsequent supply of the vapor phase to the consumer is offered. The necessary storage and regasification temperatures are achieved by means of utilizing a vapor-compression refrigeration unit in the technological process. The technology allows to improve energy efficiency of the processes, reduce fire-and-explosion hazard, minimize LPG losses, exclude conditions formation of a combustible environment, regulate the storage temperature of LPG of various composition and efficiency of the regasification process, and ensure the composition of volatilized LPG remains constant during regasification.

Study on Technical and Economical Solutions for Improving Air-conditioning Efficiency in Building Sector

Climate change is an increasingly important global concern at this moment. Fossil fuels meet a majority of world energy needs and because buildings are large energy consumers, they are also a major contributor to global carbon emissions and greenhouse gas (GHG) production. It's important for the European Union, including Romania to avoid these problems.Buildings are responsible for 40% of energy consumption and 36% of CO2emissions in the EU, according to United Nations Environment Programme (UNEP). The construction sector is developing since 2013 so in the future the energy consumption will increase very fast. As a result, renewable energy sources represent one of the main directions in reducing conventional energy consumption in buildings. In this paper the authors analyze solutions for decreasing the energy consumption required by the air-conditioning system in an office building of 6466m2, located in Bucharest. The current air conditioning solutions are the classical ones, based on either fan coils, supplied with chilled water of 12/7°C, or air-coolers, as part of an Air Handling Unit (AHU). In the latter case, the cooled water is prepared by a vapor compression refrigeration unit chiller of 190kW cooling capacity, working with R22. The solutions analyzed in this paper consider each of the following alternatives: a. Heat recovery from the exhausted air by using a heat exchanger integrated in the AHU; b. Replacement of the vapor compression refrigeration unit chiller with an one stage lithium bromide/water absorption refrigeration unit driven bysolar energy; c. Coupling the above mentioned solutions. All these solutions are discussed and analyzed from both technical and economical points of view.

Modelling, Simulation and Optimization of Small-Scale CCHP Energy Systems

The article defines and discusses techno-economic models of CCHP system based on a power system with an internal combustion engine or a gas turbine with electric power of 0, 2–1 MW including an absorption or vapour-compression refrigeration unit. The thermodynamic, ecological and economical features of the CCHP system under different load situations are analysed in relation to the basic model of energy generation with boiler and vapour-compression refrigeration unit. Based on the data of the equipment manufacturer, functional dependency curves of individual components are created in dependency to the load, which enables the construction of a system model composed of a power system (internal combustion engine or a gas turbine), single-stage or two-stage absorption refrigeration unit and boiler. A program solution has been developed applying the object-oriented programming language Modelica that enables the insight into the behaviour and techno-economic validity of usage of the analysed systems in transformable operating conditions. The article examines various energetic models, defining for the influential parameters (electric energy and fuel prices, investment costs and the level of heat recovery) the value of total energy efficiency, the return period on investment costs and the environmental impact concerns.

Hybrid Desiccant Cooling System Using Condensing Heat as the Regeneration Source. Part I: System Model

In this paper, a scheme of hybrid desiccant dehumidification system was proposed. This system can recovery the condensing heat from the vapor compression refrigeration unit to remove moisture from the air. But the trick of energy saving is the sensible heat exchanger after the desiccant rotary wheel. After analysis of its energy consumption characteristic, the system model was established.

Cooling performance and energy saving of a compression–absorption refrigeration system driven by a gas engine

The prototype of combined vapour compression–absorption refrigeration system was set up, where a gas engine drove directly an open screw compressor in a vapour compression refrigeration chiller and waste heat from the gas engine was used to operate absorption refrigeration cycle. The experimental procedure and results showed that the combined refrigeration system was feasible. The cooling capacity of the prototype reached about 589 kW at the Chinese rated conditions of air conditioning (the inlet and outlet temperatures of chilled water are 12 and 7°C, the inlet and outlet temperatures of cooling water are 30 and 35°C, respectively). Primary energy rate (PER) and comparative primary energy saving were used to evaluate energy utilization efficiency of the combined refrigeration system. The calculated results showed that the PER of the prototype was about 1.81 and the prototype saved more than 25% of primary energy compared to a conventional electrically driven vapour compression refrigeration unit. Error analysis showed that the total error of the combined cooling system measurement was about 4.2% in this work. Copyright © 2006 John Wiley & Sons, Ltd.

Study of a Cooling System for the Telecommunication Base Site (Performance Analysis of a Cooling System Using Natural-circulation Loop)

New cooling system with a natural-circulation loop has been developed to reduce energy consumption of a cooling system for the telecommunication base site. The cooling system consists of two refrigeration units ; vapor compression refrigeration unit and pre-cooling unit with a natural-circulation loop. A simulation which calculates pressure drop, heat transfer and refrigerant charge has been developed and the experiments were carried out to evaluate the cycle performance of the pre-cooling unit using HFC refrigerants. The measured cooling capacity and operating pressure agreed with the simulation results within ± 10% in the various experimental conditions. In addition, the experimental results indicated that the cooling capacity of R 410 A is approximately 30% larger than that of R 407 C at the temperature difference of 20 K. Also the cooling capacity took a maximum value at the range of refrigerant charge of 2.0-3.0 kg. Furthermore, the cooling capacity slightly increased as the height difference between the evaporator and the condenser increased. These experimental results were in good agreement with the simulation results.

A comparison of the operating performance of alternative refrigerants

This paper provides a comparison of the operating performance of three alternative refrigerants for use in a vapour compression refrigeration cycle. The refrigeration capacity and COP of R401A, R290 and R134A were compared with those of R12 when used in a propriety vapour compression refrigeration unit initially designed to operate with R12. The results indicate that the performance of R134a is very similar to that of R12 justifying the claim that it is a drop in replacement for R12 but of the refrigerants tested it gave the poorest performance. When viewed in terms of green house impact however R290 showed the best performance.

A hybrid solar desiccant cooling system

Alternative methods of providing cooling using lower-grade energy have been investigated. This paper considers a cycle which combines indirect evaporative cooling with a dehumidifier to meet latent loads and a vapour compression refrigeration unit to meet sensible load. The cycle has been studied for two climate types and two different loads representative of those likely to be met in commercial buildings. Also considered is the combination of this cycle with a solar energy system which regenerated the desiccant dehumidifier. The advantage of a desiccant system is the use of low-grade heat at temperatures between 60/sup 0/ and 100/sup 0/ which can be provided by a conventional solar energy system or from waste heat. Another significant advantage of these cycles is their ability to operate in an indirect evaporative cooling mode at times of low latent load and low relative humidity.