冷水机组联合运行策略仿真与分析

在空调系统的能耗中,冷水机组运行产生的能耗占很大的比例。多台冷水机组联合运行时,存在多种运行策略。当根据负荷控制冷水机组的运行时,负荷控制点大小的确定及不同的运行策略会对总能耗造成影响。探讨了冷水机组性能系数和综合部分负荷性能系数分析在冷水机组联合运行策略中的不足,对某建筑空调冷冻水系统冷水机组提出不同运行策略,并采用TRNSYS仿真软件进行仿真,对仿真结果进行了对比分析,得出冷水机组全年优化运行策略,以降低运行能耗。     

多台冷水机组负荷分配优化策略仿真研究

以广州某商场冷水机组系统为研究对象,根据机组全年运行数据,采用最小二乘法对机组能效模型的参数进行辨识,建立了各台冷水机组运行能效模型,并根据空调系统全年冷负荷分布特性,以冷水机组总能耗最小为目标,探讨了基于遗传算法的多台冷水机组负荷优化分配策略。对该商场夏季和过渡季节多台冷水机组优化运行策略进行了仿真实验,结果表明:与原有运行方式相比,夏季负荷率为50%~75%时,冷水机组优化运行后的能耗比原运行方式降低25.75%;过渡季节负荷率为25%~50%时,冷水机组优化运行后的能耗比原运行方式降低5.35%。     

多台冷水机组的负荷最优化分配策略

本文针对多台冷水机组并联运行的空调系统,首先建立了最优负荷分配策略的数学模型。其次,由于机组部分负荷性能曲线的非线性、非凸性,采用动态规划算法给出了负荷分配的求解方法,并以2台冷水机组并联运行为例,阐述了具体的应用方法。计算结果表明,采用动态规划算法可实现实时负荷优化分配,减少系统的能耗,且计算简单,容易编程。     

多台冷水机组空调系统的优化控制

以两台容量相同并联运行的冷水机组空调系统为例,通过绘制负荷比与比功率关系曲线,确定了最优负荷分配策略。分析结果表明,应用该方法确定多台冷水机组空调系统负荷分配策略可以减少系统能耗。     

一种冷水机组季节性能评价新指标与多台机组联合运行性能评价

综合部分负荷性能系数IPLV是评价冷水机组季节运行性能的重要指标,但在对其合理性的评价上存在诸多争议。从季节性能评价指标的物理本质出发,构建了描述单台冷水机组性能的季节部分负荷性能系数SPLV指标;基于SPLV的评价思想,提出了描述多台冷水机组联合运行时的季节部分负荷性能系数SPLV(N)的计算方法和测试工况,并应用SPLV(N)对不同类型冷水机组进行了性能评价。结果表明,所构建的SPLV指标可以更为真实地反映冷水机组的季节运行性能;SPLV(N)的大小与冷水机组的性能曲线形状有很大关系,不同类型的机组各有其适宜的应用形式。     

基于COP曲线的冷水机组节能优化控制

本次研究对数据中心空调系统整体COP值与其冷水机组负载率LR(Load rate)之间的关系进行了分析,重点描述了基于空调系统冷水机组的COP值来对机房内的空调主机进行控制,建立了冷水机组能耗的数学模型,利用了PSO算法的简单易操作性对冷水机组之间的负荷分配进行了寻优计算,实现了空调系统能源利用的合理优化分配,使得空调机组在高效率下运行,取得了较为理想的节能效果。     

多台冷水机组的优化配置与节能运行研究

本文针对公共建筑中的空调能耗,尤其是冷水机组能耗过大的问题,建立了多台冷水机组配置模型及优化目标.以某办公建筑为例,分析了不同运行策略下多台冷水机组运行时的能耗,同时对不同策略和配置情况下的运行情况进行了经济性比较.分析可知,当选用多台机组时,平均分配负荷的运行策略比较节能,节能效果视组合方式的不同而不同,其中容量相同的组合方式采用该运行策略优势最为明显.     

南方某地铁站蒸发冷凝冷水机组能效测试分析

为检验蒸发冷凝冷水机组的运行性能,对南方某地铁站车站设备管理用房冷源进行了改造,将原有2台风冷机组中的1台替换为相同冷量的蒸发冷凝冷水机组。在相同负荷、相同环境条件下对两种机组的性能和能耗进行了测试分析,发现蒸发冷凝冷水机组运行效果较优,可以达到预期的节能运行目标。     

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。     

水源热泵机组的节能效果

建立了水源热泵机组的仿真模型,通过实验对该模型进行了验证。应用该模型,以能耗最小为原则,优化了满足建筑物冷负荷需求时水源热泵机组的组合方式。结果表明,水源热泵机组相对于普通冷水机组,在供冷季最多可以获得13.1%的节能效果。     

Optimum load sharing strategy for multiple-chiller systems serving air-conditioned buildings

Many central cooling systems in air-conditioned buildings have multiple chillers to meet various cooling load requirements. This paper further develops optimum load sharing strategies for the chillers in order to maximize their aggregate coefficient of performance (COP). Based on the part load performance curves of air-cooled screw chillers, it is ascertained that for two equally sized chillers operating, one should carry a full load and the other should be partially loaded to meet the system load. When two chillers of different sizes are running, the larger chiller should be fully loaded and the smaller chiller should operate at part load in order that their combined capacity satisfies the system load. Such an uneven load sharing strategy for achieving maximum COP is independent of ambient conditions and the control of condensing temperature. The variable primary flow of chilled water should be applied to chillers in order to implement the strategy. The results of this paper are useful in developing low-energy chiller plants.     

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.     

Optimal control strategies for multi-chiller system based on probability density distribution of cooling load ratio

Probability density distribution profile of cooling load ratio is obtained by Parzen window density estimation method, which is used to describe the building cooling load variation. Based on the analysis of this profile, the optimal sequence control strategies (AI, AII and AIII) are presented. In order to optimize the COP of total chillers, the optimal load allocation control strategy B is presented. The optimal load allocation control strategy BI is presented to improve the strategy B for simplifying the process of the optimal calculation and maintaining stability of the system operating. Simulation results show that these optimal control strategies presented can save more power consumption of chillers operating than the original sequence control strategy. Comparing the strategy B, the strategy BI can avoid unnecessary switch on/off actions of chillers and decrease computational costs.     

某大型空调系统能耗分析

能源问题是决定我国能否可持续发展的关键因素之一。对某大型空调系统能耗进行了测试和分析，表明冷机实际COP低于其额定COP，并且空调箱能耗占到30％-50％；另外，对系统的负荷分析表明，造成系统的供需比下降的主要原因是该系统设计本身所造成。因此，对空调系统优化运行是节能改造必不可少的一个环节；同时，如何优化空调系统各级的设定参数以及系统的划分，将会从根本上提高系统冷负荷的供需比，从而大大减少系统能耗，可为大型空调系统的运行人员、设计人员提供参考。     

Analysis on energy saving potential of integrated supermarket HVAC and refrigeration systems using multiple subcoolers

The paper presents a model-based analysis on the energy saving potential of supermarket HVAC (heating, ventilating, and air-conditioning) and refrigeration systems using multiple subcoolers among the high-temperature HVAC system, the medium-temperature refrigeration system, and the low-temperature refrigeration system. The principle of energy reduction is to have the higher COP (coefficient of performance) system generate more cooling capacity to increase the cooling capacity or reduce the power consumption of the lower COP system. The subcooler could be placed between the medium-temperature and low-temperature systems, between the high-temperature and medium-temperature systems, and between the high-temperature and low-temperature systems. All integration scenarios of adding one, two and three subcoolers have been investigated. The energy saving potential varies with the load ratio between high-, medium- and low-temperature systems, COP of three systems, and the “on-off” duty time of HVAC system. The optimal sequence of adding subcoolers is also proposed.     

Fundamental optimal relation of a generalised irreversible quantum Carnot heat pump with harmonic oscillators

An irreversible quantum Carnot heat pump model working with many non-interacting harmonic oscillator systems is established in this paper. The quantum heat pump cycle is composed of two isothermal processes and two irreversible adiabatic processes. The irreversibilities of heat resistance, internal friction and bypass heat leakage are considered in the model. Based on the quantum master equation, semi-group approach and finite time thermodynamics (FTT), the cycle period, heating load and coefficient of performance (COP) of the quantum Carnot heat pump are derived, and detailed numerical examples are provided. At high temperature limit, the fundamental optimal relations between the heating load and COP of the quantum heat pump are deduced and analysed by using numerical examples. The effects of internal friction and bypass heat leakage on the optimal performance of the quantum heat pump are discussed in detail. The endoreversible, frictionless and without bypass heat leakage cases are discussed. The obtained results are general to the performance optimisation of quantum Carnot heat pumps and can provide some guidelines for optimal design of real quantum heat pumps.     

Heating load and COP optimisations for a universal steady flow endoreversible heat pump model

The heating load and coefficient of performance (COP) of a class of universal steady flow endoreversible heat pump cycle model, which consists of one heating branch, two cooling branches and two adiabatic branches, are optimised using the theory of finite time thermodynamics. The analytical formulae for heating load and COP versus temperature ratio as well as COP versus heating load of the cycle model are derived. Effects of the total heat exchanger inventory on performances of heat pump cycles are shown by detailed numerical examples. The results obtained herein include the optimal performances of endoreversible Otto, Brayton, Atkinson, Diesel, Dual and Carnot heat pump cycles.     

Load prediction method for heat and electricity demand in buildings for the purpose of planning for mixed energy distribution systems

Energy planning for mixed energy distribution systems is important to increase the flexibility in the regional and national energy systems. Expected maximum loads, load profiles and yearly energy demands, all divided into heat and electricity purposes, are important input parameters to plan for the most economical, technical and environmental optimal energy distribution system for a planning area. First, this article presents a load prediction method which estimates heat and electricity load profiles for various building categories. The method is based on statistical analyses of hourly simultaneous measured district heat and electricity consumption in several buildings, as well as background information of the measured buildings. The heat load model is based on regression analyses, whereas the electricity load model is based on various statistical distributions. Second, a method for load aggregation based on the building categories’ load profiles is presented to estimate the maximum load demands, yearly load profiles, load duration profiles and yearly energy demands, all divided into heat and electricity purposes, for a planning area.