Air Conditioning Applications Research Articles

Design and analysis of a medium-temperature, concentrated solar thermal collector for air-conditioning applications

Solar thermal energy is considered as a promising source to drive air-conditioning applications due to the good correlation between supply and demand. The present work examines the feasibility of a novel, low-profile concentrated solar thermal collector to provide medium-temperature heat to commercial buildings for both heating and cooling purposes, aiming to reduce their non-renewable energy consumption levels. To the best of the authors’ knowledge, the semi-passive tracking/concentrating platform employed in this collector represents a significant improvement for ‘stationary’ (internal tracking, the module itself remains fixed) solar concentrating technology. To investigate the real-world viability of this collector design for solar heating and cooling, a system-level techno-economic performance analysis is conducted using a validated TRNSYS model. The solar heating and cooling (SHC) system includes the proposed solar thermal collectors, an auxiliary heater, and a double-effect absorption chiller. In this study, the proposed solar collectors are employed to supply thermal energy to the chiller to offset the building cooling demand or the thermal energy can also be used directly to satisfy the building’s heating demand. When sufficient solar energy is not available, the auxiliary heater provides the rest of the heating and cooling demand. The annual solar fraction and economic metrics (e.g. total levelized costs) were used as the selection criteria among design options. The simulation results demonstrate that a specific collector area of 2.4m2 per kW cooling and an optimal storage tank specific volume of 40L/m2 are sufficient to cover 50% of the load requirement of the building. The economic analysis indicates that a levelized cost of cooling energy (LCOC) of ∼0.6$/kW-h can be derived from this solar air-conditioning system.

Numerical Investigations of Indoor Air Quality inside Al-Haram Mosque in Makkah

The air conditioning applications in mosques are considered as one of the important HVAC applications, which indoor air quality depend on the behavior of the airflow, the distributions of temperatures and relative humidity and concentration of carbon dioxide due to high occupancy load of people. The paper is devoted to numerically investigate the influence of ventilation rate on indoor air quality. The example shown here is Al-Masa’a between Al-Safa and Al-Marwa hills inside Al-Haram mosque located at Makkah-Saudi Arabia. The work focuses on air flow, thermal behavior and carbon dioxide dispersion where large number of people. Five different cases for change in ACH are studied to reveal the impact of changing it on the all people. The performance of the air conditioning system is characterized by airflow patterns, temperature, relative humidity contours and CO2 concentration as well as the most commonly used comfort parameters PMV and PPD based on Fanger’s model. The study is carried out using computational fluid dynamics (CFD) simulation techniques as embedded in the commercially available CFD code (ANSYS 15). The CFD modeling techniques solved the continuity, momentum and energy conservation equations in addition to RNG k – ε model equations for turbulence closure. Mesh sizes used in present work exceeded 4.5 million approximately.

Propositions of improvement of the cross-flow M-Cycle heat exchangers in different air-conditioning applications

This paper presents results of mathematical simulation of the heat and mass transfer in the two different Maisotsenko Cycle (M-Cycle) heat and mass exchangers used for the indirect evaporative cooling in different air-conditioning systems. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process, thus quantifying the overall heat exchangers’ performance. The mathematical model was validated against the experimental data. Numerical simulations reveal many unique features of the considered units, enabling an accurate prediction of their performance. Results of the model allow for comparison of the two types of heat exchangers in different applications for air conditioning systems in order to obtain optimal efficiency.

Research Status of Ice-storage Air-conditioning System

In this paper, the concept and domestic application of ice-storage air-conditioning are briefly introduced. Especially, the characteristics and working principle of four kinds of widely used systems, ice-ball type, ice-on-coil type, ice debris sliding type and ice crystal type ice-storage air-conditioning system are expounded. By analyzing the advantages, disadvantages and the application status of different ice-storage air-conditioning systems, the application status of ice-storage air-conditioning technology is summarized.Finally, the applications of ice-storage air-conditioning system are summarized.It can provide reference for the research and application of ice-storage air-conditioning system in the future.

Experimental investigation on vapor pressure of desiccant for air conditioning application

Abstract: Recently, the rapid development of desiccant air conditioning technology, without using refrigerant fluids, energy saving and environmental protection, has expanded natural fluid to a broader niche applications. An experimental study is carried out to calculate the vapor pressure of CaCl 2 using regression dependent parameters and evaluate the mass transfer coefficient. The effect of relevant operating parameters, such as air temperature, humidity and air velocity on the mass transfer processes between the air and the desiccant CaCl 2 is analyzed. For a detailed study of the dehumidification process and desiccant regeneration, a ‘’DVS”, a ‘’Dryer” and ‘’climatic chamber” equipment are used. Several measurements were made in a relatively large range of operating conditions. It was found that the absorption mass rate increased linearly with increasing air humidity. After 6 hour of absorption the mass transfer becomes slow. The mass transfer coefficient is affected by the climatic condition variation. The decrease in mass transfer potential with time is mainly due to vapour pressure rise on the desiccant surface during absorption. The vapor pressure is significantly affected by the air humidity variation. At higher humidity, the concentration decreases while the vapor pressure increases. The mass transfer process duration decreased with increasing the air velocity during the desiccant regeneration. It can be pointed out that the CaCl 2 is able to absorb moisture and can be regenerated at low temperature then; solar collector can be used in liquid desiccant cooling system. This study allows selecting the best desiccant for use in LDAC system.

The characteristics of welded joints of stainless steel for air conditioning application

The characteristics of welded joints of stainless steel for air conditioning application

Performance characteristics of low global warming potential R134a alternative refrigerants in ejector-expansion refrigeration system

AbstractPerformance assessment of ejector-expansion vapor compression refrigeration system with eco-friendly R134a alternative refrigerants (R152a, R1234yf, R600a, R600, R290, R161, R32, and propylene) is presented for air-conditioning application. Ejector has been modeled by considering experimental data based correlations of component efficiencies to take care of all irreversibilities. Ejector area ratio has been optimized based on maximum coefficient of performance (COP) for typical air-conditioner operating temperatures. Selected refrigerants have been compared based on area ratio, pressure lift ratio, entrainment ratio, COP, COP improvement and volumetric cooling capacity. Effects of normal boiling point and critical point on the performances have been studied as well. Using ejector as an expansion device, maximum improvement in COP is noted in R1234yf (10.1%), which reduces the COP deviation with R134a (4.5% less in basic cycle and 2.5% less in ejector cycle). Hence, R1234yf seems to be best alternative for ejector expansion system due to its mild flammability and comparable volumetric capacity and cooling COP. refrigerant R161 is superior to R134a in terms of both COP and volumetric cooling capacity, although may be restricted for low capacity application due to its flammability.

Identification of NR and EPDM Samples by Means of Thermogravimetric Analysis and Multivariate Methods

Products based on ethylene-propylene-diene m-class (EPDM) and natural rubber (NR) are widely used in a different applications, including the automotive industry, heating, ventilation, and air conditioning applications, roofing systems, or the construction sector among others. The growing demand of these types of polymeric products has forced rubber industry to implement strict control schemes to ensure the specifications of the final products. The focus of this paper is the identification of different treatment types of NR and EPDM samples without any preceding analytical treatment to carry out a fast and reliable supervision of the vulcanization processes to improve the quality of the final rubber products. To this end, the thermogravimetric analysis (TGA) technique is applied in combination with the principal component analysis (PCA) and canonical variate analysis (CVA) multivariate feature extraction methods and the k-nearest neighbor (k-NN) classifier. Experimental results prove the suitability of the proposed approach and the potential of the TGA method for a fast supervision of the vulcanization processes. Using the information provided by the TGA technique in association with the PCA + CVA + k-NN approach, the system achieved 100% identification accuracy.

Theoretical and experimental investigations on horizontal heat pipe heat exchangers using a composite wick structure for heat recovery in air-conditioning systems

The literature review indicates that, though water has a good figure of merit, very limited information is available on the use of water as the working fluid in a horizontal heat pipe heat exchanger for air conditioning applications. This article investigates theoretical and experimental analyses of horizontal heat pipe heat exchangers for air conditioning applications using distilled water as the working fluid. This heat pipe heat exchanger study consists of 20 copper tubes of 9.5 mm outside diameter arranged in two rows with a 0.3 m evaporator length, a 0.3 m condenser length, a 0.05 m adiabatic length, and 12 fins per inch of aluminum plate fins. A comparative analysis is studied for two configurations of heat pipe heat exchangers. The first configuration of heat pipe heat exchanger consists of a single wick structure with two layers of 180 mesh of phosphor bronze wire mesh, and, in the second configuration, the heat pipe heat exchanger consists of a composite wick structure (two layers of 180 mesh and two layers of 60 mesh of phosphor bronze wire mesh). The investigations are performed only for sensible heat recovery between outdoor and return air. The experimental investigations are performed by varying the outdoor air dry bulb temperature in the range of 24°C to 40°C and return air dry bulb temperature in the range of 20°C to 24°C. The present study reveals that the amount of heat recovered by a heat pipe heat exchanger with a composite wick structure is 56% better than a heat pipe heat exchanger with a single wick structure at a higher velocity of 2.4 m/s and further improves to 88% at a lower velocity of 0.6 m/s.

Experimental evaluation of system modifications to increase R1234ze(E) cooling capacity

The GWP limitations are being progressively introduced in Europe through Regulation EU No 517/201, phasing out R134a in most of its refrigeration and air conditioning applications. Pure hydrofluoroolefins are proposed to substitute this fluid, however generally system modifications are needed to achieve a good performance. In the case of R1234ze(E), the cooling capacity is always much below that of R134a in drop-in or light retrofit substitutions.This work performs an experimental comparison using R1234ze(E) and R134a under different refrigeration operating conditions. R1234ze(E) is tested considering the use or not of an internal heat exchanger, and R134a at the same or lower compressor rotation speed. Results show that the use of R1234ze(E) with an open-type compressor 43% larger and an internal heat exchanger of 25% effectiveness, leads to a cooling capacity augmentation, enough to reach R134a cooling capacity in the different conditions tested. For R450A, it is sufficient only with the IHX activation.

Prediction of solubility of ammonia in liquid electrolytes using Least Square Support Vector Machines

Abstract Liquid electrolytes or ionic liquids (ILs) are a new class of environmentally friendly solvents which is highly promising for refrigeration and air conditioning applications in chemical industrial processes. In this contribution, Least Square Support Vector Machine (LS-SVM) models have been utilized to predict the solubility of ammonia in ILs as a function of molecular weight (MW), critical temperature (Tc) and critical pressure (Pc) of pure ILs over wide ranges of temperature, pressure, and concentration. To this end, 352 experimental data points were collected from the published papers. Moreover, to verify the accuracy of the proposed models, statistical analyses such as regression coefficient, mean square error (MSE), average absolute deviation (AAD), standard deviation (STD) and root mean square error (RMSE) have been conducted on the calculated values. The results show the excellent performance of LSSVM models to predict the solubility of ammonia in different liquid electrolytes.

Design and Simulation of PFC Converter for Brushless SRM Drive

In most of the industrial applications, Switched Reluctance Motor (SRM) is mainly employed due to the reasons like having low maintenance and high efficiency. SRM consists of windings only on its stator, but would not have any windings on rotor thus having very simple construction. The available supply is AC. But AC cannot be directly supplied to SRM when used for air-conditioner application which is employed in this paper. Also power factor in the system needs to be corrected when using a SRM drive. Thus AC supply is fed to power factor correction (PFC) converter which is Buck-Boost converter here in this paper. The output of the PFC converter is fed to SRM through a simple asymmetrical converter. This PFC circuit consists of a simple diode bridge rectifier with Buck-Boost DC-DC converter. A suitable control circuit was proposed to control the input power factor under various loading conditions. This paper gives analysis of SRM drive for air-conditioner application with Buck-Boost converter based PFC circuit. A Matlab/simulink based model is developed and simulation results are presented. Simulation is carried out for different speed response.

Performance analyses of novel two-phase ejector enhanced multi-evaporator refrigeration systems

In the present study, four novel layouts (namely EECRS1, EECRS2, EECRS3 and EECRS4) of three-evaporator two-stage compression refrigeration system have been proposed using double two-phase ejectors. Thermodynamic analysis and ejector area ratio optimization have been done to study the effects of cycle operating temperature and evaporator load distribution on the cycle and ejector performance parameters. Performance comparisons with basic valve expansion two-stage compression, ejector enhanced single-stage compression and basic valve expansion single-stage compression three-evaporator refrigeration systems are presented as well. Study shows that for typical combination of air-conditioning (5°C), refrigeration (−20°C) and freezing (−40°C) applications, proposed refrigeration cycles yield the COP enhancement of about 20% compared to basic valve expansion two-stage compression, 67% compared to ejector enhanced single-stage compression and 117% compared to basic valve expansion single-stage compression system. Volumetric cooling capacity also improves significantly. Within proposed layouts, EECRS4 is most efficient; however, the operation is more challenging than others. Simulation results also reveal that the performance improvement is more sensitive with cooling load distribution compared to operating temperature. Present study may serve as a good guideline for promising use of ejector in three-evaporator system.

Analysis of a variable speed air conditioner considering the R-290/POE ISO 22 mixture effect

Air-conditioning applications using propane (R-290) have several environmental and thermodynamic advantages over more commonly used refrigerants, such as R-410A and R-22. This paper presents the development of a mathematical model for variable capacity air conditioning systems that use R-290/POE ISO 22 as refrigerant/lubricant. The thermodynamic performance of the refrigeration system is evaluated in terms of the SEER (Seasonal Energy Efficiency Ratio). The thermodynamic properties of the refrigerant/lubricant mixture were obtained from a departure-function approach using the Peng-Robinson equation of state. The effect of the oil on the condenser and evaporator heat transfer coefficients and pressure drops was also taken into account. Sub-models were developed for each component of the air conditioning system, including the connecting lines and the scroll compressor. Furthermore, an air conditioner experimental calorimeter was constructed and tested in order to validate the proposed model.

Characteristics of R718 refrigeration/heat pump systems with two-phase ejectors

The paper describes investigations of R718 refrigeration cycles with two-phase ejector as a compression device. The complex thermal and flow phenomena inside two-phase ejector flow field are analyzed and characteristics of two-phase ejectors are estimated. Results of investigations of numerous refrigeration systems with two-phase ejectors are analyzed and recommendations for optimal geometric parameters of two-phase ejectors are summarized. Novel R718 refrigeration/heat pump systems are proposed: simple two-phase ejector cooling cycle, two-phase ejector heat pump cycle applied in evaporators–concentrators, and combined compact R718 centrifugal compressor–two-phase ejector water chiller for air conditioning application, and their thermal and performance characteristics are estimated.

LCCP evaluation on various vapor compression cycle options and low GWP refrigerants

Reducing environmental impacts from the energy conversion systems has been an important research topic due to recent severe global climate changes. In residential buildings, the space heating and cooling are main energy consumers, which are mainly relying on a vapor compression cycle. In an effort to better understand the environmental impacts of these systems, life cycle climate performance (LCCP) evaluation method was developed, which considers the direct and indirect emissions of the system over the course of its lifetime from manufacturing to disposal. Based on the developed LCCP evaluation method, five cycle options and seven low GWP refrigerants are evaluated for air conditioning applications.

Thermo-Hydraulic Performance Evaluation Using W-Discrete Rib in Solar Air Heater

Background/Objective: This paper have more emphasis towards augmentation of solar air duct thermal efficiency. Flow of heat restricted by sub-layer of laminar flow is the major criterion to reduce the thermal efficiency of solar air duct. Methods/Statistical Analysis: For breaking laminar sub-layer artificial roughness with pattern of W-Discrete geometry has been developed. With all consideration of different previous geometries as a pattern of artificial roughness W-Discrete ribs have best thermo-hydraulic performance. During experimental investigation different parameter taken are Reynolds number of 14000-4000, duct aspect ratio of 8, angle of attack of 45° and relative roughness height of 0.03375. Findings: Maximum increment of Nusselt number along with friction factor found in order of 2.79 and 1.98 as compare to smooth plate. Increase in heat transfer enhancement rate is obtained to be 2.35 times for W-discrete up and 2.60 times for W-discrete down rib pattern. Simultaneously with the consideration of smooth plate data results have been evaluated. Application/Improvements: Now a day's various solar collection and conversion systems are used like air heaters for crop drying, solar air conditioning and industrial applications. Solar collector is most important component that accounts for major portion of system cost comprising and utilization as a whole.

Comparative analysis of promising adsorbent/adsorbate pairs for adsorptive heat pumping, air conditioning and refrigeration

In this study, the most promising working pairs are evaluated for utilization in thermal driven adsorptive heat pumping, air conditioning and refrigeration applications employing water, ethanol and methanol as refrigerant. With this aim, a comparative study was carried out for different currently available (silica gels, zeolites, aluminophosphates, activated carbons) and recently developed materials (composite adsorbents). A simple mathematical model was developed in order to evaluate the performance of various working pairs for different sorption cycles. Among the considered adsorbents, the Mitsubishi product AQSOA®-FAM-Z02, the composite adsorbents LiBr–silica and CaCl2–silica appeared the best water adsorbents for air conditioning and heat pumping purpose, providing heating/cooling COP up to 1.62/0.71 and heating/cooling enthalpy up to 1080/570kJkg−1. Also the LiCl–silica/methanol working pair showed high performance for air conditioning cycles, especially in terms of cooling enthalpy (Qev=640kJkg−1).The composite LiBr–silica showed to be the most promising methanol and ethanol sorbent for refrigeration purpose, permitting cooling COP in the range 0.53–0.59 and cooling enthalpy in the range 180–360kJkg−1.The noticeable influence of the metal-to-adsorbent mass ratio on the sorption cycle performance was also demonstrated, showing that utilization of compact finned tube aluminum heat exchanger types (typical mmet/mads=0.9–1.6) allows a 15–30% cooling COP higher than a traditional stainless steel tube-and-shell exchanger (mmet/mads=2.4–3.1). Additionally, some brief dynamic considerations are done for most interesting working pairs.

DESIGN OF WASTE HEAT DRIVEN VAPOUR ADSORPTION COOLING SYSTEM FOR VEHICLE AIR-CONDITIONING AND REFRIGERATION

In this present era more & more focus is to be given on energy conservation. Refrigeration & air conditioning is one of the growing field of engineering, the existing system are hampering the environment as they are suffering from various environmental problems such as depletion of ozone layer & global warming due to emission of harmful gases such as HFC’s ,CFC’s & CO2 as they were using traditional refrigerants. Waste heat driven Vapour adsorption cooling system is eco-friendly, efficient, & reliable in nature. But on the other hand this system having lowers COP as compare to existing systems which is Due to the lack of research and advancement in the system. By considering the environmental aspects & need of energy conservation it is necessary to design and developed the VAR’s system which will successfully compete the existing systems. This paper will give the idea about the Design of waste heat driven vapour adsorption system of 2KW capacity for vehicle air-conditioning & refrigeration application. The adsorber bed is the heart of the cooling system and it can affect the performance of the system to the greater extent. So that while designing the VAR cooling system more focused is given on design and selection of adsorber bed. This article mainly focused on the various and important design parameters of the vapour adsorption cooling system Such as Adsorber bed design, adsorber and adsorbate mass, design of evaporator & condenser, Coefficient of performance(COP), Specific cooling power (SCP) and the other performance affecting parameters.

Controlled falling film heat and mass exchange modules for liquid desiccant air conditioners

Academic and commercial research and development of liquid desiccant air conditioning technology has been pursued for several decades. Liquid desiccant air conditioning technology can provide significant benefits in terms of energy consumption and humidity control, particularly in applications where the latent load, energy cost, and operating hours are high. Common problems associated with the heat and mass exchange modules, incorporated into liquid desiccant air conditioners developed to date, include desiccant carryover into the air stream, large size, high cost, lack of scalability, and poor reliability. In addition, useful predictive modeling of latent and sensible heat transfer performance for a given module design is needed to enable equipment designers to properly incorporate the modules into an air conditioning system. These problems have prevented the technology from being more widely adopted at a commercial scale. A novel controlled falling film heat and mass exchange module, which also incorporates low pressure drop particle filtration, has been developed and tested at the laboratory scale and addresses these problems. Further development of the design will enable a broader range of liquid desiccant air conditioning system architectures and applications to be realized with the resultant benefits of improved humidity control, reduced energy consumption, and improved indoor air quality.