02750 Global optimization for overall HVAC systems — Part I problem formulation and analysis

02750 Global optimization for overall HVAC systems — Part I problem formulation and analysis

13 Space heating and cooling effects of evaporating temperature and outlet temperature of gas cooler on the optimal heat rejection pressure, the coeff...

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13 Space heating and cooling effects of evaporating temperature and outlet temperature of gas cooler on the optimal heat rejection pressure, the coefficients of performance (COP), the exergy losses, and the exergy efficiencies are investigated. In order to identify the amounts and locations of irreversibility within the two cycles, exergy analysis is employed to study the thermodynamics process in each component. It is found that in the throttling valve cycle, the largest exergy loss occurs in the throttling valve, about 38% of the total cycle irreversibility. In the expander cycle, the irreversibility mainly comes from the gas cooler and the compressor, approximately 38% and 35%, respectively. The COP and exergy efficiency of the expander cycle are on average 33% and 30% higher than those of the throttling valve cycle, respectively. It is also concluded that an optimal heat rejection pressure can be obtained for all the operating conditions to maximize the COP. The analysis results are of significance to provide theoretical basis for optimization design and operation control of the transcritical carbon dioxide cycle with an expander.

05•02744 Experimental development of an intelligent refrigeration system Buzelin, L. O. S. et al. International Journal of ReJ~igeration, 2005, 28, (2), 165-175. In this study, an alternative solution to reduce energy consumption in industrial refrigeration systems is proposed and introduced. A typical industrial refrigeration system was conceived, built and modified in the laboratory, receiving a novel power law control system, which utilizes a frequency inverter. The operation and energy consumption of the system operating either with the new control system or with the traditional on-off control were compared to realistically quantify the obtained gains. In this manner, the measured temperature data acquired from several points of both systems and the energy consumption in k W h during a 24 h experimental run period are compared. The closed-loop power law controlled system shows a much smaller variation of the cold chamber internal temperature and electrical energy consumption economy of 35.24% in comparison with the traditional on-off system, under the same operating conditions.

05/02745 Experimental evaluation of the internal heat exchanger influence on a vapour compression plant energy efficiency working with R22, R134a and R407C Navarro-Esbr/, J. et al. Energy, 2005, 30, (5), 621-636. Internal or liquid-suction heat exchangers are used in many refrigeration and air conditioning systems based on the vapour compression cycle, with the basic objective of assuring the entrance of refrigerant in liquid phase to the expansion device. This purpose is achieved by exchanging energy between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant exiting the condenser. These devices can have positive or negative influences on the plant overall energy efficiency, depending on the working fluid and the operating conditions. In this paper the experimental results obtained from a refrigeration test facility with and without the presence of an internal heat exchanger, using R22, R134a and R407C as working fluids, are presented and analysed, including the impact of pressure drops and variations of refrigerant mass flow rate. A comparison between experimental and theoretical results is also enclosed.

05/02746 Experimental investigations on the characteristics of melting processes of stearic acid in an annulus and its thermal conductivity enhancement by fins Liu, Z. et al. Energy Conversion and Management, 2005, 46, (6), 959969. An experimental rig was set up to study the performance of a thermal storage unit using stearie acid as the heat storage medium, The unit mainly consists of an electrical heating rod and an outer tube, and the space between is an annulus that is filled with stearic acid. The thermal performance of the unit is measured, and the heat transfer characteristics of the melting processes of stearic acid are studied under different heat flux conditions to determine the influence of heat flux on the melting processes. A new type of fin is designed and fixed to the electrical heating rod to enhance the thermal response of the stearic acid. The experimental results show that the fin can improve the heat transfer of the melting process of the thermal storage unit greatly. The equivalent thermal conductivity of the PCM can be augmented by a factor up to 3. The analysis of the experimental results shows that the enhancement mechanism of the fin is attributed to its ability to improve both heat conduction and natural convection very effectively. The influences of the fin size and pitch on the enhancement are also studied and analysed and it is found that these two parameters can both affect the thermal conductivity enhancement significantly.

05102747 Experimental study of the characteristics of solidification of stearic acid in an annulus and its thermal conductivity enhancement Liu, Z. et al. Energy Conversion and Management, 2005, 46, (6), 971984.

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Fuel and Energy Abstracts

November 2005

The thermal and heat transfer characteristics of stearic acid during the solidification processes were investigated experimentally in a vertical annulus energy storage system. The temperature distribution and temperature variations with time at different radial positions during the freezing processes were obtained. The thermal characteristics of the stearic acid, including movement of the solid-liquid interface in the radial direction, and the effects of Reynolds number on the heat transfer parameters were studied. The heat flux was estimated by using a simple approximate model. A new copper fin was designed and fixed to the electrical heating rod to enhance the thermal conductivity of the stearic acid. The results show that the new fin can enhance both the conduction and the natural convection heat transfer of the PCM, and the enhancement factor during solidification is estimated to be as high as 250%. The effect of the fin width on the enhancement was also examined experimentally, and it is found that the fine fin usually produce more effective enhancement.

05•02748 Experimental study on locomotive driver cabin adsorption air conditioning prototype machine Jiangzhou, S. et al. Energy Conversion and Management, 2005, 46, (910), 1655-1665. Locomotive drivers can feel uncomfortable in a torrid working environment, especially in the hot summer. The current locomotive driver cabin air conditioning system cannot meet the demands of operating conditions and environmental protection. A locomotive driver cabin adsorption air conditioning system has been developed. This new type of system employs zeolite-water as the working pair and is powered by waste heat from the exhaust gas of the internal combustion engine. Operating experiments of a prototype machine showed that this system has a lot of unique advantages compared to a traditional air conditioning system. It is feasible and practical to apply this system for locomotive driver cabin space cooling. The working principle of the system is introduced. Some experimental results are present. The characteristics of the system are discussed as well.

05102749 Flow and heat-transfer in an internally-heated, naturally-ventilated space Barrow, H. and Pope, C. W. Applied Energy, 2005, 80, (4), 427-434. This paper presents the findings of a theoretical and experimental investigation of the thermodynamics of an internally-heated control volume (CV), ventilated by natural convection. A simple bench-type experiment has been used to determine the temperature history of the air, in support of a global calculation by numerical methods. Good agreement has been achieved between the experimental results and the mathematical prediction, which has wide ranging applications in practical situations.

05•02750 Global optimization for overall HVAC systems Part I problem formulation and analysis Lu, L. et al. Energy Conversion and Management, 2005, 46, (7-8), 9991014. This paper presents the global optimization technologies for overall heating, ventilating and air conditioning (HVAC) systems. The objective function of global optimization and constraints are formulated based on mathematical models of the major components. All these models are associated with power consumption components and heat exchangers for transferring cooling load. The characteristics of all the major components are briefly introduced by models, and the interactions between them are analysed and discussed to show the complications of the problem. According to the characteristics of the operating components, the complicated original optimization problem for overall HVAC systems is transformed and simplified into a compact form ready for optimization.

05•02751 Global optimization for overall HVAC systems Part II problem solution and simulations Lu, L. et al. Energy Conversion and Management, 2005, 46, (7-8), 10151028. This paper presents the solution for the global optimization problem for overall heating, ventilating and air conditioning (HVAC) systems using a modified genetic algorithm. The whole implementation procedure of the proposed optimal method is provided. Simulation studies for a pilot scale centralized HVAC plant by the proposed optimal method show that the proposed method indeed improves the system performance significantly compared with traditional control strategies,

05102752 Lauric and palmitic acids eutectic mixture as latent heat storage material for low temperature heating applications Tunqbileka, K. et al. Energy, 2005, 30, (5), 677-692. Palmitic acid (PA, 59.8°C) and lauric acid (LA, 42.6°C) are phase change materials (PCM) having quite high melting temperatures which can limit their use in low temperature solar applications such as solar space heating and greenhouse heating. However, their melting