Application of Hopfield Neural Network to the optimal chilled water supply temperature calculation of air-conditioning systems for saving energy

The values of chilled water supply temperatures of chillers indicate their load distributions due to the chilled water return temperatures of all chillers being the same in a decoupled air-conditioning system. This study employs Hopfield Neural Network (HNN) to find out the chilled water supply temperatures of chillers for solving Optimal Chiller Loading (OCL) problem. HNN overcomes the flaw that Lagrangian method is not adaptable for solving OCL as the power consumption models include non-convex functions. The chilled water supply temperatures are used as the variables to be solved for the decoupled air-conditioning system and solves the problem by using HNN method to improve this defect. After analysis and comparison of the case study, it has been concluded that this method not only solves the problem of Lagrangian method, but also produces results with high accuracy. It can be perfectly applied to the operation of air-conditioning systems.     

Application of genetic algorithm to the optimal‐chilled water supply temperature calculation of air‐conditioning systems for saving energy

The values of chilled water supply temperatures of chillers indicate their load distributions due to the chilled water return temperatures of all chillers being the same in a decoupled air‐conditioning system. This study employs genetic algorithm (GA) to find out the chilled water supply temperatures of chillers for solving optimal chiller loading (OCL) problem. GA overcomes the flaw that Lagrangian method is not adaptable for solving OCL as the power consumption models or the kW‐PLR (partial load ratio) curves include non‐convex functions. This study uses the chilled water supply temperature as the variable to binary code chromosomes, and execute reproduction, crossover and mutation operation. After analysis and comparison of the case study, it has been concluded that this method not only solves the problem of Lagrangian method, but also produces results with high accuracy within a rapid timeframe. It can be perfectly applied to the operation of air‐conditioning systems. Copyright © 2007 John Wiley & Sons, Ltd.     

大温差水系统运用于数据中心空调节能性分析

对大温差空调水系统应用于数据中心项目进行了节能性分析,基于假定的系统模型对不同冷冻水供回水温差条件下系统的制冷主机能耗、冷冻水泵能耗以及末端精密空调设备能耗进行了计算。计算结果表明,增大供回水温差对于数据中心空调系统能效提升具有积极意义。     

Economic dispatch of chiller plant by gradient method for saving energy

This study employs gradient method (GM) to solve economic dispatch of chiller plant (EDCP) problem. GM overcomes the flaw that with the Lagrangian multiplier (LM) method the system may not converge at low demand. In this study, the load balance constraint and the operating limit constraints of the chillers are fully accounted for. After analysis and comparison of the two cases studies, we are confident to say that this method not only solves the problem of convergence, but also produces results with high accuracy within a rapid timeframe. It can be perfectly applied to the operation of air-conditioning systems.     

Performance analysis of combined microgas turbines and gas fired water/LiBr absorption chillers with post-combustion

The integration of microgas turbines (MGT) and absorption chillers is an emerging technology that uses a wide range of fuels to produce electricity, cooling and heating simultaneously for small scale distributed generation in grid connected or isolated locations.This paper studies the performance of MGTs of different power capacities directly coupled to double-effect water–LiBr absorption chillers. In these systems the MGT exhaust gas is the heating medium to drive the chiller. Also post-combustion natural gas is used to increase the cooling capacity of the system. The paper analyses the effect of the post-combustion degree on the integrated system performance of four MGT power sizes. Two cases are considered. In the first, fresh air is added together with the post-combustion natural gas and in the second it is not added. In the latter case the oxygen necessary for the combustion reaction is extracted from the MGT exhaust gas stream. For the sake of comparison a study is also made of the performance of a more conventional system consisting of an MGT and a hot water heat exchanger to drive an absorption chiller. The main advantages of the new technology over this conventional system are that the COP of the chillers is higher because they are driven by higher temperatures, the production of electricity and chilled water is decoupled and there is a wider range of chilled water production capacity.     

大型超市室内环境及空调系统能耗测试分析

深入了解掌握建筑空调系统实际运行状况,有助于准确地分析建筑能耗及空调系统能耗。为此作者选择了上海某一大型超市,通过测试其夏季室内热环境、空调机组、冷水机组水流量等参数,得出超市室内温湿度的分布状况、空调水系统的平衡程度以及冷水机组的能效比,发现实际运行中存在的问题,提出改进超市空调系统运行的方案。     

An innovative approach for demand side management—optimal chiller loading by simulated annealing

This investigation attempts to solve the optimal chiller loading (OCL) problem by utilizing simulated annealing (SA). SA eliminates the limitation that the Lagrangian method cannot solve OCL because the kW-PLR curves simultaneously include convex functions and non-convex functions. This study fully addresses the load balance constraint and chiller operating limits. The case study analysis demonstrates that this method solves the Lagrangian problem and generates highly accurate results. The proposed approach can be applied perfectly to the operation of air conditioning systems.     

Influence of supply and return water temperatures on the energy consumption of a district cooling system

In a district heating and cooling system, for example, the Beijing combined heating, cooling and power (CHCP) system studied here, high temperature water generated by cogeneration plants circulates through a network between the plants and the heating substations. In heating substations, high temperature supply water from the network drives absorption chillers for air-conditioning in the summer, satisfies space heating demands in the winter and provides domestic hot water using heat exchangers throughout the year. This paper studies the significant effect of the parameters, i.e. the supply and return water temperatures in the network, on the CHCP system energy consumption for cooling and for domestic hot water.     

Solar hybrid air-conditioning system for high temperature cooling in subtropical city

Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5–7 °C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15–18 °C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city.     

Genetic algorithm based optimal chiller loading for energy conservation

This study employs genetic algorithm (GA) to solve optimal chiller loading (OCL) problem. GA overcomes the flaw that Lagrangian method is not suitable as there is non-convex kW-PLR function in a system. This study uses the part load ratios (PLR) of chiller units to binary code chromosomes, and execute reproduction, crossover and mutation operation. Since the semiconductor plant is the largest a/c load for power consumption, it is used as an example in this paper. After analysis and comparison of the case study, we are confident to say that this method not only solves the problem of Lagrangian method, but also produces results with high accuracy within a rapid timeframe. It can be perfectly applied to the operation of air conditioning systems.     

Chillers energy consumption, energy savings and emission analysis in an institutional buildings

Chillers consume more than 40% of the total energy used in the commercial and industrial buildings for space conditioning. In this paper, energy consumption by chillers and chilled water pumps, condenser pumps and fan motors has been estimated using data collected by a walkthrough energy audit for the 16 faculties of the University of Malaya. It has been estimated that chillers and motors and pumps used in chillers consume 10,737 MWh (i.e. 51% of total energy consumption) of electric energy for different percentage of loadings. As chillers are major energy users, variable speed drives are applied in chillers to reduce their energy consumption. It has been estimated that about 8368 MWh annual energy can be saved by using efficient chillers at different loadings. It has also been found that about 23,532 MWh annual energy can be saved for chilled water supply pumps, condenser pumps and cooling tower fan motors by matching required speeds using variable speed drives for 60% of speed reduction. About 1,274,692 kg of CO₂ emission could be avoided for using energy efficient chillers at 50% load. It has been also found that about 2,426,769 kg CO₂ emission can be reduced by using variable speed drives for 60% speed reductions. Payback periods found to be only few months for using variable speed drives in chilled water pumps, condensers and fan motors.     

Performance enhancement of a complex chilled water system using a check valve: Experimental validation

The large primary–secondary chilled water systems often suffer from the excess flow demand and low chilled water temperature difference, which is known as the low ΔT central plant syndrome, during operation. This paper presents an approach for experimental validation of the possible utility of a check valve (i.e., putting a one-direction check valve in the chilled water by-pass line) to solve this operational problem and enhance the overall system performance, prior to a check valve is really installed. The experimental tests were carried out on the complex central chiller plant in a super high-rise building using a simulated check valve through fully closing one of the butterfly valves in the by-pass line when the system operated with a significant excess flow demand and experienced the low ΔT syndrome. The results from the tests showed that the system operational performance can be improved when the simulated check valve was used. Compared to that without using the check valve, about 9.2% of the total energy of the chillers and secondary water pumps was saved in the test period when the simulated check valve was used.     

Optimal chiller sequencing by branch and bound method for saving energy

This paper proposes a method for using the branch and bound (B&B) method to solve the optimal chiller sequencing (OCS) problem and to eliminate the deficiencies of conventional methods. The coefficient of performance (COP) of the chiller is adopted as the objective function because it is concave. The Lagrangian method determines the optimal chiller loading (OCL) in each feasible state. The potential performance of the proposed method is examined with reference to an example system. The proposed method consumes much less power than the conventional method and is very appropriate for application in air conditioning systems.     

Energy and economic performance analysis of an open cycle solar desiccant dehumidification air-conditioning system for application in Hong Kong

In this article, a transient simulation model and the EnergyPlus were used to study the energy performance and economical feasibility for integrating a solar liquid desiccant dehumidification system with a conventional vapor compression air-conditioning system for the weather condition of Hong Kong. The vapor compression system capacity in the solar assisted air-conditioning system can be reduced to 19 kW from original 28 kW of a conventional air-conditioning system as a case study due to the solar desiccant cooling. The economical performance of the solar desiccant dehumidification system is compared with that of the conventional air-conditioning system. The results show that the energy saving potentials due to incorporation of the solar desiccant dehumidification system in a traditional air-conditioning system is significant for the hot wet weather in Hong Kong due to higher COP resulted from higher supply chilled water temperature from chiller plants. The annual operation energy savings for the hybrid system is 6760 kWh and the payback period of the hybrid system is around 7 years. The study shows that the solar assisted air-conditioning is a viable technology for utilizations in subtropical areas.     

空调变水量冷冻水系统运行工况下的管网特性曲线

针对变水量空调冷冻水系统实际运行时管网特性曲线随末端负荷变化和水泵实际工作点难以确定的问题 ,分析了传统的绘制管网特性曲线的方法不适用的原因 ,从实际出发 ,根据曲线拟合原理 ,提出了一种切实可行的分析运行工况下管网特性曲线的方法 ,并应用到实践中     

An evaluation of empirically-based models for predicting energy performance of vapor-compression water chillers

This paper presents an evaluation of six empirically-based models for predicting water chiller energy performance using over 1000 chiller data sets from chiller manufacturers and field measurements. The data sets comprise three broad classifications, including (1) constant condenser and constant chilled water flow, (2) constant condenser and variable chilled water flow, and (3) variable condenser and variable chilled water flow. The regression parameters for each performance model are obtained using least squares method. The criteria for evaluating the predictive ability of models are based on the coefficient of variation of root-mean-square error (CV). Results show that among the six empirically-based performance models for water chillers in this study, the bi-quadratic regression model (CV = 2.2%) and the multivariate polynomial regression model (CV = 2.25%) have the best prediction accuracy for all kinds of data sets. The results of this study can be used as a reference for selecting empirically-based models for the purposes of energy analysis, performance prediction, evaluation of energy-efficiency improvements, and fault detection and diagnosis of water chillers.     

热(汽、水)冷联供及其效益分析

根据山东省的地理位置和气候特点,论述了一种在原冬季供热设备的基础上用大型供热锅炉或热电厂中的锅炉,结合溴化锂吸收式制冷机向用户供冷的方案,并从能耗水平、节能效益、节电效益、热电厂的增电效益、设备投资、运转费用和社会效益等几个方面阐述了这种热（汽、水）冷联供的优越性,认为这种热（汽、水）冷联供方式是协调大中城市热电厂和大型集中供热锅炉冬夏负荷不均、充分利用现有供热设备、为夏季空调提供冷源的一种有效方式。     

Optimization of energy plants including water/lithium bromide absorption chillers

In this paper a methodology for the optimal integration of water/lithium bromide absorption chillers in combined heat and power plants is proposed. This method is based on the economic optimization of an energy plant that interacts with a refrigeration cycle, by using a successive linear programming technique (SLP). The aim of this paper is to study the viability of the integration of already technologically available absorption chillers in CHP plants. The results of this alternative are compared with the results obtained using the conventional way of producing chilled water, that is, using mechanical vapour compression chillers in order to select the best refrigeration cycle alternative for a given refrigeration demand. This approach is implemented in the computer program XV, and tested using the data obtained in the water/LiBr absorption chiller of Bayer in Tarragona (Catalonia, Spain). The results clearly show that absorption chillers are not only a good option when low‐cost process heat is available, but also when a cogeneration system is present. In this latter case, the absorption chiller acts as a bottoming cycle by using steam generated in the heat recovery boiler. In this way, the cogeneration size can be increased producing higher benefits than those obtained with the use of compression chillers. Copyright © 2000 John Wiley & Sons, Ltd.     

水蓄冷系统中蓄水槽设计需注意的几个问题

针对水蓄冷系统工程蓄水槽的设计中出现的一些常见问题进行了描述和分析,并提出了相应的解决方法,其结果对水蓄冷空调系统的设计具有一定的参考价值。     

太阳能吸收式空调及供热系统的设计和性能

一套太阳能吸收式空调及供热综合系统已在山东省乳山市建成。该系统由热管式真空管集热器、溴化锂吸收式制冷机、储水箱、循环、冷却塔、空调箱、辅助燃油锅炉和自动控制系统等内部分组成,具有夏季制冷、冬季供热和全年提供生活用热水等功能。太阳能集热器总采光面积540m∧2,制冷、供热功率100kW,空调、采暖建筑面积1000m∧2供生活用热水量32m∧3／d。文中着重介绍了系统的设计特点和测试性能。