Yet there is limited research work relate to CLS strategies for chillers with multiple refrigeration circuits。 The benefits of using two separate refrigeration cycles to meet demands was investigated for both the freezer and fresh food compartments in domestic refrigerators [2]。 The load sharing strategies in a refrigeration system with two screw compressors were discussed [3]。 Based on empirically models, a comparison was presented for a single-circuited centrifugal and a twin-circuited twin-screw chiller [4]。 An air-cooled screw chiller model with four refrigeration circuits was developed to analyse the chiller performance, in which the tubes in the evaporator were treated as onepass arrangement [5]。 The performance of air-cooled twin-circuit screw chiller was investigated, based on the assumption that the two circuits shared the same cooling output [6]。 However, there is a lack of developed strategy for realizing optimal CLS control and variable condensing temperature control (CTC), which is involved in the potential energy saving when the chillers operate in various outdoor temperatures and load conditions。 The deficient performance of air-cooled chillers is mainly due to the traditional head pressure control (HPC) under which the condensing temperature floats around a high set point of 50˚C based on a design outdoor temperature of 35˚C, irrespective of different chiller loads and weather conditions [5]。 CTC enables the condensing temperature to approach its lower boundary and minimize the sum of compressor power and condenser fan power for all operating conditions, hence improving the chiller COP [7]。 

然而，有限的研究工作与CLS策略的制冷机与多个制冷电路。使用两个独立的制冷循环，以满足需求的好处进行了研究，为冰箱和新鲜食品车厢在国内冰箱[ 2 ]。双螺杆压缩机制冷系统负荷分配策略的探讨[ 3 ]。基于经验模型，比较了一个单电路的离心和双脉冲双螺杆制冷机[ 4 ]。四风冷螺杆式冷水机组制冷电路模型分析机组的性能，在蒸发器管被视为OnePass安排[ 5 ]。研究了风冷式双回路螺杆式制冷机的性能，并基于两个回路共享相同的冷却输出（6）。然而，有一个缺乏发展战略，实现最佳CLS控制和可变冷凝温度控制（CTC），这是涉及在潜在的节能冷水机组在各种室外温度和负载条件下运行。风冷冷水机组的性能不足主要是由于传统的压头控制（HPC）下，冷凝温度浮动的基础上设计的室外温度35 C 50 C˚˚高设置点，不论不同的机组负荷和天气条件[ 5 ]。CTC使冷凝温度接近其较低的边界，并尽量减少压缩机功率和冷凝器风扇功率的总和，为所有的操作条件，从而提高了冷水机组COP [ 7 ]。

The objective of this paper is to develop a novel method to improve chiller efficiency by optimizing the CLS in various operating conditions。 First, a thermodynamic chiller model for an air-cooled twin-circuit chiller, with two screw compressors per circuit, is developed。 With the sophisticated chiller model, the chiller performance is investigated with different control strategies of CLS and CTC。 In what follows, the potential electricity savings resulting from the novel control strategy are assessed with regard to a chiller plant serving a representative office building。 The results of this paper are useful in developing more efficiently chiller plants serving air-conditioned buildings。

本文的目的是开发一种新的方法，以提高制冷机的效率，通过优化CLS在各种操作条件下。首先，热力学制冷机模型的风冷双回路制冷机，与每个电路的两个螺杆压缩机，开发。采用先进的冷水机组模型，研究了不同控制策略下的空调系统性能。在接下来的情况下，潜在的节约电力，从新的控制策略进行评估方面的制冷厂服务的一个有代表性的办公楼。本文的结果是有用的发展更有效的冷水机组服务空调建筑。