Distribution of size in multi‐evaporator air conditioning systems

This paper reports the thermodynamic optimization of air conditioning systems with one or more evaporators, for one or more rooms. First, the paper shows that the minimization of the total power requirement leads to the same results as the minimization of entropy generation in the whole system, which includes the insulation between the cold space and the ambient. The results also show that there is a trade‐off between the power lost by fluid friction in the distribution network and the power required by the refrigerant. This trade‐off determines the optimal allocation of hardware in the installation. The optimum diameters of the refrigerant pipelines are independent of their lengths. Copyright © 2013 John Wiley & Sons, Ltd.     

A performance comparison between an air‐source and a ground‐source reversible heat pump

In this study, the performance of a reversible ground‐source heat pump coupled to a municipality water reticulation system, is compared experimentally and with simulations to a conventional air‐source heat pump for space cooling and heating. A typical municipality water reticulation system comprises hundreds of kilometres of pipes designed in loops that will ensure adequate circulation of water. This results in a substantial heat exchanger with great potential. Indirect heat transfer occurs between the refrigerant and ground via the municipality water reticulation system that acts as the water‐to‐ground heat exchanger. The experimental and simulated comparisons of the ground‐source system to the air‐source system are conducted in both the cooling and the heating cycles. Climatalogical statistics are used to calculate the capacities and coefficients of performance of the ground‐source and air‐source heat pumps. Results obtained from measurements and simulations indicate that the utilization of municipality water reticulation systems as a heat source/sink is a viable method of optimizing energy usage in the air conditioning industry, especially when used in the heating mode. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance evaluation of a triple‐effect evaporator with forward feed using exergy analysis

The present study evaluates the performance of a triple‐effect evaporator with forward feed (TEEFF) system by using exergy analysis based on actual operational data. The orange juice with a capacity of about 1.222 kg s^?1 is concentrated from a dry matter (DM) content of 12 to 65% in this TEEFF, which is situated in an orange juice concentrate line installed in a factory, located in Denizli, Turkey. A Visual Basic 6.0 program was also developed to show how the exergetic performance characteristics of the system vary with the feed flow rates ranging from 1.222 to 1.667 kg s^?1. The total exergy efficiency of the TEEEFF is found to be on average 0.85. The largest exergy destruction occurs in the first‐effect of the TEEFF system with 48.2% of total, followed by the third and second effects with 32.04 and 19.76% of that. Evaporator performance is also rated on the basis of steam economy, which is obtained to be in the range of 2.05–2.14 under the operation conditions. It is expected that the analysis presented here should provide a designer with a better, quantitative grasp of the inefficiencies and their relative magnitudes in the design, simulation and operation of multiple‐effect evaporators. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal modeling of a shell and tube type evaporator with R404A

In this study, the two‐phase heat‐transfer coefficient of R404A inside horizontal tubes is analyzed through the evaporator's overall heat‐transfer coefficient, obtained using the effectiveness—Number of Transfer Units thermal design approach. This method constitutes an approximation that can be used in the evaporator's thermal design with an attempt to break some of the initial assumptions established in the heat exchanger thermal design method development. For the analysis, an experimental refrigeration system that is commercially available is built up with a shell and tube evaporator. All the experiments are performed at different evaporator pressures (270, 570 kPa), evaporator temperatures (?20, 0°C) and cooling water temperatures (20, 40°C). For these parameters, overall heat‐transfer coefficient of the heat exchanger is found in the range of 0.05–0.35 kW °C^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermo‐economic‐environmental multiobjective optimization of a gas turbine power plant with preheater using evolutionary algorithm

In this study, the gas turbine power plant with preheater is modeled and the simulation results are compared with one of the gas turbine power plants in Iran namely Yazd Gas Turbine. Moreover, multiobjective optimization has been performed to find the best design variables. The design parameters of the present study are selected as: air compressor pressure ratio (r_AC), compressor isentropic efficiency (η_AC), gas turbine isentropic efficiency (η_GT), combustion chamber inlet temperature (T₃) and gas turbine inlet temperature. In the optimization approach, the exergetic, economic and environmental aspects have been considered. In multiobjective optimization, the three objective functions, including the gas turbine exergy efficiency, total cost rate of the system production including cost rate of environmental impact and CO₂ emission, have been considered. The thermoenvironomic objective function is minimized while power plant exergy efficiency is maximized using a genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost has been performed. In addition, the results showed that at the lower exergetic efficiency in which the weight of thermoenvironomic objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of Pareto Frontier with the lower weight of thermoenvironomic objective. Copyright © 2010 John Wiley & Sons, Ltd.     

Energy‐saving evaluation of a thermosyphon heat recovery unit for an air‐conditioning system

The energy‐saving effect and economic benefits of a thermosyphon heat recovery unit installed in a shopping mall are investigated. To evaluate the thermal performance of the heat recovery unit in a season, a seasonal temperature effectiveness is advanced, and its calculation formula is deduced referring to the calculation method of seasonal energy efficiency ratio (SEER) for an air conditioner. The annual operating energy‐saving effect of the unit is analyzed by using the seasonal temperature effectiveness while the static economic evaluation method is applied for the economic benefits analysis of the unit. The analysis results indicate the seasonal temperature effectiveness of the unit is 66.08% in the winter and 55.43% in the summer. The energy‐saving effect of the unit is quite remarkable, and the payback time is about 2.65 years. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21049     

管翅式换热器遗传算法优化

管翅式换热器作为一种高效的换热设备,提升其换热效率和降低投资成本显得至关重要.通过单目标遗传算法(GA)和多目标非支配排序遗传算法(NSGA-Ⅱ)对管翅式换热器进行优化设计,设置翅片高度、翅片间距、管长、横向管数和纵向管数5个自变量的合理设计范围,单目标优化选用换热器效率、压降熵产和最大收益3个目标函数,根据热力学第一...     

A feasibility study of using thermal energy storage in a conventional air‐conditioning system

An Erratum has been published for this article in International Journal of Energy Research 2004; 28 (13): 1213. This paper deals with the simulation of thermal energy storage (TES) system for HVAC applications. TES is considered to be one of the most preferred demand side management technologies for shifting cooling electrical demand from peak daytime hours to off peak night hours. TES is incorporated into the conventional HVAC system to store cooling capacity by chilling ethylene glycol, which is used as a storage medium. The thermodynamic performance is assessed using exergy and energy analyses. The effects of various parameters such as ambient temperature, cooling load, and mass of storage are studied on the performance of the TES. A full storage cycle, with charging, storing and discharging stages, is considered. In addition, energy and exergy analysis of the TES is carried out for system design and optimization. The temperature in the storage is found to be as low as 6.4°C after 1 day of charging without load for a mass of 250 000 kg. It is found that COP of the HVAC system increases with the decrease of storage temperature. Energy efficiency of the TES is found to be 80% for all the mass flow rate of the discharging fluid, whereas exergy efficiency varies from 14 to 0.5%. This is in fact due to the irreversibilities in a TES process destroy a significant amount of the input exergy, and the TES exergy efficiencies therefore become always lower than the corresponding energy efficiencies. Copyright © 2004 John Wiley & Sons, Ltd.     

An experimental study of a direct expansion ground‐coupled heat pump system in heating mode

In this paper, an experimental performance evaluation of a direct expansion ground‐coupled heat pump (DX‐GCHP) system in heating mode is presented. The DX‐GCHP uses R134a as the refrigerant, and consists of three single U‐tube copper ground heat exchangers (GHEs) placed in three 30 m vertical boreholes. During the on–off operations from December 25, 2007, to February 6, 2008, the heat pump supplied hot water to fan‐coil at around 50.4°C, and its heating capacity was about 6.43 kW. The energy‐based heating coefficient of performance (COP) values of the heat pump and the whole system were found to be on average 3.55 and 3.28 at an evaporating temperature of 3.14°C and a condensing temperature of 53.4°C, respectively. The second law efficiency on the DX‐GCHP unit basis was around 0.36. The exergetic COP values of the heat pump and the whole system were obtained to be 0.599 and 0.553 (the reference state temperature was set equal to the average outdoor temperature of ?1.66°C during the tests), respectively. The authors also discussed some practical points such as the heat extraction rate from the ground, refrigerant charge and two possible new configurations to simultaneously deal with maldistribution and instability of parallel GHE evaporators. This paper may reveal insights that will aid more efficient design and improvement for potential investigators, designers and operators of such DX‐GCHP systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Boiling heat transfer coefficient of R22 and an HFC/HC refrigerant mixture in a fin‐and‐tube evaporator of a window air conditioner

The commonly used refrigerant in unitary type air conditioners is R22 and its phase out schedule in developing countries is to commence from 2015. Many alternatives to R22 are found in published literature in which R407C has similar characteristics to those of R22 except for its zeotropic nature. However, R407C which is an HFC is made compatible with the mineral oil lubricant in the system compressor by the addition of 20% of HC. This HFC/HC mixture called the M20 refrigerant mixture is reported to be a retrofit refrigerant for R22. Though its latent heat value is greater than that of R22, its refrigerating capacity is lower when it is used to retrofit R22 window air conditioners. Hence, a heat transfer analysis was conducted in the evaporator of a room air conditioner, for practically realized heat flux conditions during standard performance testing. The tests were conducted as per the BIS and ASHRAE standards. Kattan–Thome–Favrat maps are used to confirm the flow patterns, which prevail inside the fin‐and‐tube evaporator in the tested operating conditions. It is revealed that the heat transfer coefficient/heat fluxes are poorer for M20 because of the lower mass flow rate and higher vapor fraction at the entry of the evaporator than that of R22 in the prevailing operating conditions. The heat transfer coefficients of the M20 refrigerant mixture under various test conditions are lower in the range of 14% to 56% than those of R22. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20299     

Experimental study of closed‐loop thermosyphon with a different evaporator geometry

In this study, the effect of evaporator geometry on the loop thermosyphon's heat transfer coefficient is experimentally verified by using water as a working fluid with three filling ratios (50%, 70%, 90%), constant heat input (185 W), and condenser cooling water flow rate remaining constant at 2 Lpm. Three evaporator pipes are used (I: straight; II: helical coil evaporator with a diameter of 100‐mm coil and two turns; III: helical coil evaporator with a diameter of 50‐mm coil and four turns). From the experimental results, it can be observed that the performance of evaporator III is higher than the two other forms. A greater heat transfer coefficient value is found in case of type III evaporator and is equivalent to 2456 W/m²·°C. The maximum thermal resistance reduction occurs in the type III evaporator (37.32%), and the highest effective thermal conductivity for the same type is 6.123e + 05 W/m·°C. The experimental results demonstrate good agreement with the empirical equations.     

Optimal geometry and flow arrangement for minimizing the cost of shell‐and‐tube condensers

This paper presents a model for estimating the total cost of shell‐and‐tube heat exchangers (HEs) with condensation in tubes or in the shell, as well as a designing strategy for minimizing this cost. The optimization process is based on a genetic algorithm. The global cost includes the energy cost (i.e. pumping power) and the initial purchase cost of the exchanger. The choice of the best exchanger is based on its annualized total cost. Eleven design variables are optimized. Ten are associated with the HE geometry: tube pitch, tube layout patterns, baffle spacing at the center, baffle spacing at the inlet and outlet, baffle cut, tube‐to‐baffle diametrical clearance, shell‐to‐baffle diametrical clearance, tube bundle outer diameter, shell diameter, and tube outer diameter. The last design variable indicates whether the condensing fluid should flow in the tubes or in the shell. Two case studies are presented and the results obtained show that the procedure can rapidly identify the best design for a given heat transfer process between two fluids, one of which is condensing. Copyright © 2008 John Wiley & Sons, Ltd.     

Development and validation of helical‐coil‐in‐fluted‐tube gas cooler for CO2 heat pump water heaters

A segmented approach [1] for the CO₂ helical‐coil‐in‐fluted‐tube gas cooler is developed. The CO₂ helical‐coil‐in‐fluted‐tube gas cooler consists of helically coiled tube and fluted tube. It is fabricated by twisting a straight copper tube to form helically coiled tube and embedded in the groove of the fluted tube. The available heat transfer and pressure drop correlations for the supercritical CO₂‐side and water‐side are provided to simulate the gas cooler. The simulation is compared with a detailed set of experimental data, for given the inlet conditions. The predicted data matches well with the experimental data with absolute average deviations of 1.15, 4.6 and 4.7% for the CO₂ pressure drop, gas cooler exit temperature and hot water temperature, respectively. Based on the good matches between measured data and predicted data, the detailed thermodynamic processes of gas cooler parameters are predicted and analyzed. Furthermore, different arrangements of the gas cooler within the original package dimensions are simulated and better performance of the gas cooler is obtained under the structural parameters of the 3‐row fluted tube with the inner diameter 12 mm. Copyright © 2010 John Wiley & Sons, Ltd.     

Minimizing shell‐and‐tube heat exchanger cost with genetic algorithms and considering maintenance

This paper presents a procedure for minimizing the cost of a shell‐and‐tube heat exchanger based on genetic algorithms (GA). The global cost includes the operating cost (pumping power) and the initial cost expressed in terms of annuities. Eleven design variables associated with shell‐and‐tube heat exchanger geometries are considered: tube pitch, tube layout patterns, number of tube passes, baffle spacing at the centre, baffle spacing at the inlet and outlet, baffle cut, tube‐to‐baffle diametrical clearance, shell‐to‐baffle diametrical clearance, tube bundle outer diameter, shell diameter, and tube outer diameter. Evaluations of the heat exchangers performances are based on an adapted version of the Bell–Delaware method. Pressure drops constraints are included in the procedure. Reliability and maintenance due to fouling are taken into account by restraining the coefficient of increase of surface into a given interval. Two case studies are presented. Results show that the procedure can properly and rapidly identify the optimal design for a specified heat transfer process. Copyright © 2006 John Wiley & Sons, Ltd.     

Comparative study of mechanical and chemical methods for surface cleaning of a marine shell‐and‐tube heat exchanger

In this article, experimental analysis is done on shell‐and‐tube heat exchanger of a marine vessel for removal of fouling using optimum surface‐cleaning techniques. The main objective is to compare the performance of the heat exchanger before and after maintenance. Two identical deteriorated systems of heat exchangers are taken and real‐time analysis is conducted. The log data are taken before and after undergoing maintenance for the two systems. Two different cleaning techniques are used, namely, chemical cleaning and mechanical cleaning. Detailed calculations are made for the shell‐and‐tube heat exchanger. From the obtained data, comparisons are made for different parameters on the tube side such as friction factor, heat transfer coefficient and pressure drop, as well as total heat transfer rate on the shell side. From the analysis and comparison, it was found that greater heat transfer takes place for the tubes cleaned using the chemical cleaning method than for tubes cleaned by the mechanical cleaning method. Pressure drop is found to be less for chemical cleaning method than mechanical cleaning method. This indicates that the fouling effect is reduced for tubes cleaned by the chemical cleaning method, and furthermore these tubes remain corrosion‐resistant for longer periods of time.     

Performance analysis on a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation

In China, because of the emergence of a large number of high‐rise buildings, the solar hot water heater system often uses the balcony wall‐mounted method for installation. The thermoelectric energy converter is proposed as one of the possible technologies to incorporate solar water heater to produce electricity for building application. In this paper, the conceptual development and theoretical analysis of a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation are all proposed. The new system takes into account many advantages, including the high heat transfer, low convective heat loss, and low contact thermal resistance. The exergy analysis method based on the second law of thermodynamics is also introduced to evaluate the performance of this system. The results show that a novel micro‐channel heat pipe evacuated tube solar collector‐incorporated thermoelectric generation has a high thermal performance with addition of electricity production. Copyright © 2016 John Wiley & Sons, Ltd.     

Exergy analysis of direct expansion solar‐assisted heat pumps using artificial neural networks

Artificial neural network (ANN) is applied for exergy analysis of a direct expansion solar‐assisted heat pump (DXSAHP) in the present study. The experiments were conducted in a DXSAHP under the meteorological conditions of Calicut city in India. An ANN model was developed based on backpropagation learning algorithm for predicting the exergy destruction and exergy efficiency of each component of the system at different ambient conditions (ambient temperature and solar intensity). The experimental data acquired are used for training the network. The results showed that the network yields a maximum correlation coefficient with minimum coefficient of variance and root mean square values. The results confirmed that the use of an ANN analysis for the exergy evolution of DXSAHP is quite suitable. Copyright © 2009 John Wiley & Sons, Ltd.     

An experimental and theoretical investigation of refrigerant charge on a secondary loop air‐conditioning heat pump system in electric vehicles

Automotive air‐conditioning heat pump systems are particular interest worldwide in energy conservation and emission reduction for electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles. Refrigerant charge amount is a key factor for the air‐conditioning heat pump system optimization affecting the condensing pressure and subcooling in both heating and cooling modes. In this paper, the influence of the refrigerant charge on system performances was investigated using the experiment method on a secondary loop air‐conditioning heat pump system. The typical heat transfer and flow parameters were recorded, and both cooling and heating performances of the system were investigated and illustrated by pressure‐enthalpy diagrams. The critical refrigerant charges were determined in both heating and cooling modes. Three typical void fraction correlation models were also applied for the refrigerant charge determination modeling as a system off‐design method. Results show that the Hughmark void fraction correlation method has the best prediction of the critical refrigerant charge in both cooling and heating modes.     

Multi‐objective genetic algorithm optimization of thermoelectric heat exchanger for waste heat recovery

A model is developed to simulate a cross‐flow heat exchanger, including fins, in the wall of which thermoelectric generators are sandwiched. Such a system could be used for waste heat recovery. The model is used to optimize the device based on several objective functions: total volume, total number of thermoelectric modules, power output, and pumping power. The design variables are the local distribution of modules and of current, the shape of the fins, and the division of the heat exchanger in sub‐channels. Pareto fronts are achieved with a multi‐objective genetic algorithm, and are presented here. The results show that the number of sub‐channels in the heat exchanger has a larger impact on the overall performance than the fin geometry for this particular problem. Also, the net power output is mostly correlated to the number of thermoelectric modules, and less to the heat exchanger volume. Various relations between the different competing objectives are shown and analyzed. Copyright © 2011 John Wiley & Sons, Ltd.