Part load performance of air-cooled centrifugal chillers with variable speed condenser fan control

Air-cooled centrifugal chillers are commonly used in commercial buildings but their performance analysis is lacking. This paper investigates the part load performance of the chillers via a thermodynamic model. The model was validated using a wide range of operating data from an existing chiller with specific settings of outdoor temperature and condensing pressure in controlling the condensing temperature. The validated model was developed specifically to ascertain the maximum coefficient of performance of chiller (COP) together with the strategy for optimizing the condensing temperature under various operating conditions. It is found that the highest COP occurs at a part load ratio (PLR) of 0.71–0.84, depending on the outdoor temperature and the control of condensing temperature, rather than at full load. Yet the chillers operating at such part load conditions will cause extra energy used for the early staging of chilled water pumps. To minimize the overall chiller plant energy consumption, it is still preferable to implement chiller sequencing based on the full load condition than on the aforementioned PLRs. The results of this paper present criteria for implementing low-energy strategies for operating air-cooled chillers satisfying a given building cooling load profile.     

An alternative approach for the performance rating of air-cooled chillers used in air-conditioned buildings

Air-cooled chillers are widely used to provide cooling energy for air-conditioned buildings at the expense of considerable electricity. The (Air-Conditioning & Refrigeration Institute) ARI standard 550/590 sets out a rating condition to specify the coefficient of performance (COP) of the chillers under part-load conditions. This condition was found to be insufficient to deal with diverse operating conditions under the multiple chiller arrangement. This paper proposes an alternative approach to specifying more precisely the chiller COP under part-load conditions. It is desirable to establish a set of part-load performance curves showing how the chiller COP varies with the condensing temperature at various combinations of chiller loads and outdoor temperatures. The results of this paper will give engineers and researchers a better idea about how to specify the upper limit of condensing temperature for more energy efficient chillers and how chiller COP curves help compare air-cooled chillers for buildings in any climate zone and to estimate the annual electricity consumption of chillers satisfying any given building cooling load profile.     

基于模型的离心式制冷机组系统优化控制策略研究

本文提出了基于模型的离心式制冷机组系统台数优化控制策略。该优化控制策略充分利用系统日常调试与机组自身提供的可靠数据,采用简化模型来评估单台机的最大制冷量、计算单台机的瞬时制冷量,并预测一定负荷下不同台数机组运行时的系统总电功率,寻求制冷机台数的优化组合,以使得制冷机组系统的性能系数最大化。     

离心式制冷机系统优化控制策略研究

提出了基于模型的离心式制冷机系统台数优化控制策略。该优化控制策略充分利用机组系统的日常调试与制冷机组自身提供的可靠数据,采用简化模型来评估单台机的最大制冷量、计算单台机的瞬时制冷量、并且预测在一定负荷下不同台数机组运行时系统的总电功率,从而寻求制冷机台数的优化组合使得制冷机组系统性能系数最大化。     

Strategy for designing more energy efficient chiller plants serving air-conditioned buildings

In cities located in the subtropical regions, air-cooled chillers are commonly used to cool commercial buildings almost year-round, which accounts for considerable electricity consumption in the long term. This paper explains how a chiller plant should be designed to enable the chillers to operate frequently with maximum performance. Four design options with respect to the number and size of chillers were studied for a chiller plant satisfying the year-round cooling demand of a hotel. For each design option, the annual electricity consumption of chillers and pumps was assessed using a sophisticated chiller model. The assessment showed that an electricity saving of 10.1% can be achieved by installing a chiller plant with six chillers of three different sizes instead of four equally sized chillers. The results of this paper will give engineers and researchers a better idea about how to select chillers of different sizes and how chiller part load performance curves can be used to evaluate improvements in the energy performance of a chiller plant with alternative designs.     

Low-energy design for air-cooled chiller plants in air-conditioned buildings

Chillers are widely used for cooling buildings in the subtropical regions at the expense of considerable energy. This paper discusses how the number and size of air-cooled chillers in a chiller plant should be designed to improve their energy performance. Using an experimentally verified chiller model, four design options were studied for a chiller plant handling the cooling load profile of an office building. Using chillers of different sizes is desirable to increase the number of steps of total cooling capacity. This enables the chillers to operate frequently at or near full load to save chiller power. Pumping energy can also be saved because of the improved control of chilled water flow whereby the chilled water supplied by the staged chillers can match with that required by air side equipment for most of the operating time. It is estimated that the annual electricity consumption of chiller plants could drop by 9.4% with the use of unequally sized chillers. The findings of this research will offer guidance on how to select chillers of different sizes for a low-energy chiller plant.     

Chiller sequencing control with enhanced robustness for energy efficient operation

This paper presents a strategy for improving the reliability and the energy efficiency of chiller sequencing control based on the total cooling load measurement of centralized multiple centrifugal chiller plants. The improvement is achieved as follows. Firstly, a fused measurement of building cooling load is used to replace the direct/indirect measurement. Secondly, the maximum cooling capacity of individual chillers is computed online using a simplified centrifugal chiller model. Thirdly, the online computed maximum cooling capacity is calibrated according to the quality of the fused measurement in order to deal with the possible misbehaviours in measurement instruments. A simplified model for computing the maximum cooling capacity is developed and validated using field data. The performance of the proposed chiller sequencing control strategy is tested and compared with a conventional chiller sequencing control algorithm. Test results are presented showing that the proposed strategy can effectively improve the reliability of chiller sequencing control and reduce the energy consumption of chiller plants.     

Energy performance of a cooling plant system using the inverter chiller for industrial building

The purpose of this paper is to clarify energy performance of the cooling plant system in the industrial building using actual measured operating data and numerical simulation analysis. One aspect of industrial buildings is that they have large energy consumption for manufacturing and air-conditioning compared with office and commercial buildings. Some examples of high-efficiency technologies installed in this particular cooling plant system are inverter chillers, integrated cooling towers and a free-cooling system. The inverter chiller which has been put on the market recently is state-of-the-art technology. The maximum COP of the inverter chiller reaches about 18 under certain conditions and integrated cooling towers make lower temperature cooling water as the whole capacity is large. Actual operating data indicates satisfied values for chiller and system COP during the running period and the simulation results show that the cooling plant system can cut down annual electric power consumption by about 48% compared with conventional cooling system.     

基于冷水量变化的冷水机组性能测试与故障诊断

研究了定流量/变温差和变流量/定温差条件下冷水量变化对机组性能的影响。结果表明:大型冷水机组蒸发器侧冷水大范围变流量不会影响系统的稳定性;在一定范围内冷水机组制冷量与冷水流量呈线性变化,系统的性能系数COP基本保持稳定,这为冷水泵的节能运行提供了良好的依据;蒸发器盘管中冷水流量较大时,允许的冷水流速变化范围可以适当增加;冷水量调节的极限速度为10.1%/min,否则会造成冷水机组运行不安全;蒸发器冷水流量变化引起的冷水机组性能变化可作为故障诊断的判断依据。     

联合运行冷水机组负荷优化分配及仿真研究

根据冷水机组的性能系数与其部分负荷率相关的特性,提出一种基于最小能耗的联合运行冷水机组负荷优化分配方法,从而获得最佳的机组负荷分配率和性能系数。对该负荷优化分配方法进行了MATLAB仿真。仿真结果表明,该控制策略能够优化机组的运行,减少系统能耗。     

Fusion of redundant measurements for enhancing the reliability of total cooling load based chiller sequencing control

Total cooling load based chiller sequence in multiple-chiller plants is essentially the best approach to stage a chiller on or off in order to satisfy thermal comfort requirement and achieve energy efficiency simultaneously. In practice, however, this approach cannot be reliably implemented. The reason is the measurement of the cooling load of multiple-chiller plants is not always consistent enough for staging chillers on or off appropriately. Measurement uncertainties, including noises, outliers and biases, have a significant influence on the performance of the sequencing operation. This paper develops a strategy of fusing available redundant measurements to reduce the measurement uncertainties. With a moving window, the proposed strategy can (i) remove measurement outliers according to a calibrated Moffat distance between redundant measurements; (ii) reduce the influence of measurement noises by merging redundant measurements; and (iii) calibrate the bias of the merged measurements. Simulation studies are represented to show the merits of the proposed strategy for improving the reliability of the total cooling load based chiller sequencing control.     

海南某数据中心空调系统设计

结合项目当地具体气候条件,综合对比多种空调系统方案,从节能效果、初投资、运行费用等各方面计算分析,找到适合本项目的 空调系统节能设计.空调设计从系统架构特点出发,利用备用机组的制冷能力,结合磁悬浮机组部分负荷效率高的优点,实际运行时冷水机组全部运行,主机负载率为70％～80％,磁悬浮主机的COP可达15以上,配合冷却塔...     

Energy signatures for assessing the energy performance of chillers

This paper investigates how energy signatures can be used as an alternative to an energy use intensity (describing the annual electricity consumption of chillers in kWh per unit floor area of a building in m²) to assess the energy performance of chillers with various design options and operating strategies. An energy signature is a best-fit straight line relating chiller power to a climatic index when chillers operate for a building cooling load profile. Sixteen combinations of four design options and four operating strategies for chillers serving a hypothetical hotel are studied by simulation. For each combination, an energy signature for the chillers is determined. The slope and intercept of the energy signature can be used to accurately predict the annual electricity consumption of the chillers and to evaluate the extent to which this consumption can drop when chiller efficiency is improved. It is desirable to develop reference energy signatures in relation to different characteristics of building cooling load as a yardstick for the minimum requirement of chiller performance. With this yardstick, the effectiveness of energy efficient measures in the operation of chillers could be identified.     

建筑环境设计模拟分析软件DeST第9讲冷热源与水系统模拟分析(上)

冷热源系统是整个集中空调系统的核心，完全决定了系统能否保障用户的冷热需求，是投资和能源消耗的主要部分。因此冷热源的选择和运行方式直接关系到空调系统的运行效果，并影响到空调系统的运行能耗的大小。综述了目前模拟计算中的制冷设备的各种建模方法，并结合建筑能耗模拟计算的特点，详细阐述了DeST模拟软件中冷源和水系统模拟过程中所用到的制冷设备半经验模型以及冷源模拟分析方法，为冷热源和水系统的全工况优化运行设计计算奠定了基础。     

An integrated model for the design of air-cooled chiller plants for commercial buildings

Cooling load calculation is the first step in designing the air-conditioning system of a building. The calculated cooling capacity with appropriate buffer is then used to select the number and size of chillers in the system. N + 1 is a common formula used by designers to size the chiller plants in Hong Kong buildings, where N is the actual number of chillers required and 1 is a redundant chiller provided to ensure reliability. This paper reviews the problem of excess capacity and discusses the risk exposure of chiller systems without redundant chillers. The cooling load profiles of the chiller plants of four medium-sized commercial buildings in Hong Kong are reviewed. The risk exposure of chiller systems without redundant chillers can be minimized by applying risk-based preventive maintenance. The just-in-demand design reduces capital cost of the building and frees up funds for continuous energy measurement and improving the energy efficiency of chiller plant systems. This paper presents a model for designing chiller plants that improves the energy efficiency of the plant in a cost effective and thoughtful manner. It is designed with consideration of the life cycle of the plant and real-time continuous commissioning, monitoring, measurement, comparison and execution for better energy management.     

Analysis of district cooling system with chilled water thermal storage in hot summer and cold winter area of China

A typical district cooling system (DCS) with a chilled water storage system is analyzed in hot summer and cold winter area in China. An analysis method concerning operation modes is proposed based on measured data, which is obtained by long term monitoring and on-site measurements of cooling season. The DCS operates at partial load for a large proportion of the cooling time; in particular, the partial-load rate (PLR) can be less than 25% for more than 50% of the total cooling season. In the night, PLR reaches 5% of the peak load. Thus, it is critical to achieve efficient operation under partial-load conditions of the DCS. Installation of chilled water thermal storage presents a solution to improve the working condition of the DCS and chillers. From the beginning to the end of the cooling season, the DCS operation can be summarized by typical operation modes according to cooling demand and chiller operation. For each mode, the base-load chiller operated at a high-load rate, with an average value of 0.88, and the coefficient of performance (COP) remained in a small range, between 4.2 and 5.2. The average energy efficiency ratio (EER) of the DCS for the cooling season was 3.65 and 3.81 for Years A and B, respectively. With respect to the economics, chillers used 90.2% of off-peak electricity, at only half the price of peak electricity.

     

风冷机组与水冷机组耗电量大小的比较

本文从理论上对风冷及水冷系统的输入功率进行了分析。结论是在额定负荷时,风冷机组的输入功率是水冷系统总输入功率的1.35倍。考虑部分负荷时机组效率的变化及气温对机组效率的影响后,风冷机组的输入功率是水冷机组输入功率的1.26倍。     

Evaluation of alternative arrangements of a heat pump system for plume abatement in a large-scale chiller plant in a subtropical region

Heat pumps could be used to produce hot water for hybrid cooling towers for preventing the occurrence of plume in subtropical regions. The evaporative side of the heat pump system could be arranged either at the inlet side or at the outlet side of these cooling towers for cooling down the cooling water temperature. Alternatively, the evaporative side of the heat pump system could also be arranged at the evaporative side of chillers to reduce return chilled water temperature and therefore to reduce the cooling load of chillers. This study presents the evaluation of the impacts of these three arrangements of the heat pump system on the plume control performance and the energy performance in a large-scale chiller plant in Hong Kong. The performance prediction and evaluation of the chiller plant and the plume abatement system were conducted on a dynamic simulation platform. The results show that these three arrangements have almost the same plume control performance with sufficient plume control capability. The results also show that the arrangement of the evaporative side of the heat pump system for cooling down return chilled water temperature has much better performance that the other two arrangements for improving the overall energy efficiency.     

基于遗传算法的冷水机组运行优化策略研究

本文通过采用回归方法获得冷水机组性能系数(COP)与部分负荷率(PLR)的关系,并建立各台冷水机组能耗方程,利用遗传算法求解其最小值,从而获得各冷水机组所承担的最优负荷比率,同时根据某一实际建筑计算了其全年的冷负荷率时间分布情况,在此基础对系统冷水机组全年的运行情况进行了优化,从而达到5.7%的节能效果。     

冷水机组变流量综合节能分析与研究

为了更好地了解变流量对冷水机组节能的效果和性能的影响,将冷水机组在变流量工况下与正常工况下的热工性能进行了对比,通过建立冷水机组模型,对正常工况、变冷冻水流量工况、变冷冻水、冷却水流量工况和同时变冷冻水、冷却水、冷却风机流量工况等四种优化工况进行了对比分析与仿真计算,得出了在变冷冻水、冷却水流量工况下,在满足冷却塔正常运行前提下,系统最为节能,且在50%部分负荷率时,比正常工况节能45.54%,同时详细的分析了在变工况下,系统各参数的变化,为完善冷水机组部分负荷下变流量调节控制策略提供了依据和参考。