Air-cooled chillers are generally the major electricity consumers in air-conditioned buildings in the subtropical climate。 To improve the energy efficiency of the air-cooled chillers at part load conditions, two or more refrigeration circuits are designed。 This paper considers how the use of optimal circuit loading sequence (CLS) enables these chillers to operate more efficiently。 A thermodynamic model for the air-cooled chillers with twin refrigeration circuits was developed using TRNSYS and validated using a wide range of operating data。 Based on the sophisticated chiller model, an analysis was carried out on how the chiller COP varied with different CLS and variable condensing temperature control (CTC)。 A chiller plant designed for a representative office building in Hong Kong was investigated to assess the potential electricity savings by use of CLS。 4。2% of the annual electricity consumption by chillers could be achieved with optimal CLS compared with the base case。 Under CTC, the coefficient of performance (COP) was improved further, and CTC coupling with optimal CLS would reduce the annual total electricity consumption for cooling by 72607

9。6%。 

风冷式冷水机组通常是亚热带气候条件下空调建筑的主要电力用户。为了提高风冷冷水机组在部分负荷条件下的能效，设计了两个或两个以上的制冷回路。本文认为，如何使用最佳的电路加载顺序（CLS）使这些冷水机组更有效地运作。采用双制冷回路的风冷冷水机组的热力学模型，利用TRNSYS和验证，使用范围广，操作数据。基于复杂的冷水机组模型，进行了分析，对冷水机组COP变化的不同CLS和可变冷凝温度控制（CTC）。冷水机组设计为代表的办公楼在香港进行调查，利用CLS评估潜在的节省电力。4。2%的年度用冷水机组的电力消耗，可以实现最佳CLS的基础情况相比。CTC下，性能系数（COP）进一步提高，CTC耦合与最佳CLS将减少年度总用电量冷却9。6%

Peer-review under responsibility of the organizing committee of ISHVAC-COBEE 2015

Keywords: Air-Cooled Chiller; Twin Refrigeration Circuits; Circuit Loading Sequence; Condensing Temperature Control 

1。 Introduction  介绍

Air-cooled chiller systems are commonly used in commercial buildings due to their flexibility, especially for the cities that have water shortage problem [1]。 Comparing to water-cooled chillers, air-cooled chillers are regarded as 

Energy inefficient。 The chiller efficiency decreases significantly under part load conditions。 To improve the chiller performance, many water chillers are designed with multiple refrigeration circuits connected by parallel, and each refrigeration circuit has one or more compressors。 This design of multiple refrigerant circuits is to enhance the reliability and standby capacity, decrease in-rush current at system start-up。 Such design also can reduce the power consumption at part load condition, and it gives an opportunity to improve the overall chiller performance。 As one of the circuits or both circuits in a chiller may be operated at any given conditions, the chiller performance will be different under different operating schemes。 This means that proper control strategy is critical, which is used to share the cooling load between the refrigeration circuits and sequence the compressors in each circuit。 For this reason, it is desirable to identify operating strategies on proper refrigeration circuit loading sequence (CLS) that improve the efficiency of the chiller with multiple refrigeration circuits。 

能源效率低下。冷效率明显负载条件下，提高性能的冷，多水是电路设计和多设备并行连接城市和电路，每个设备有一个或多个压缩机。本设计的多个电路的冰质两个增强的可靠性和备用容量，降低冲流在系统启动。这样的设计也可以减少功率消耗的空调负荷的地方，它提供的机会，提高整体性能的冷。作为一个电路的电路在一个或两个可能是挂在任何给定的操作条件下，将冷性能不同，在不同的操作方案。这意味这冰的适当的控制策略的关键，这是用来分享的冷却负载之间的电路和制冷压缩机在每个序列的电路。因为这个原因，它是两个可取的在线识别策略的正确操作设备电路负荷序列（CLS），提高效率的多设备电路。