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.     

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.     

Life cycle analysis of enhanced condenser features for air-cooled chillers serving air-conditioned buildings

Air-cooled chillers are commonly used to provide cooling energy for air-conditioned buildings at the expense of considerable electricity. This paper examines the life cycle electricity cost of these chillers with the improved condenser features of condensing temperature control (CTC), evaporative pre-coolers (EC) and variable speed condenser fans (VSF). A validated model for an air-cooled screw chiller was used to ascertain how the individual and mixed features influence the annual electricity consumption of chillers in various operating conditions. It is estimated that the life cycle electricity cost savings range from HK$ 2,099,742 with EC to HK$ 6,399,564 with all the three features, with regard to a chiller plant serving an office building for 15 yr. The life cycle analysis reported here provides important insights into how to reap the benefits of energy efficient technologies for air-cooled chillers.     

Modelling of the coefficient of performance of an air-cooled screw chiller with variable speed condenser fans

Air-cooled chillers are generally recognized as energy intensive equipment in air-conditioned buildings in the subtropical climate. This paper considers how the use of variable speed condenser fans enables these chillers to operate more efficiently. The thermodynamic model of an air-cooled screw chiller was developed using the simulation program TRNSYS and validated using the field data and specifications of the chiller. The staging of condenser fans and the control of their speed in various operating conditions were described. A comparison was made on the coefficient of performance of the chiller in the steady state with various control strategies: head pressure control with constant or variable speed condenser fans; condensing temperature control (CTC) with constant or variable speed condenser fans. Potential improvements in the chiller COP due to the use of CTC with variable speed condenser fans were discussed. The findings of this paper are useful in developing more energy efficient air-cooled chillers.     

我国城镇住宅节能空调器适用性研究

对节能空调器在我国主要城市城镇住宅中应用的寿命周期能耗状况进行了定量分析,并分析了住户空调运行模式的差异对空调器寿命周期能耗的影响。研究结果表明,对于夏季气候炎热、经济发达的地区和空调能耗较高的住户,采用节能空调器的节能效果显著;但对于北方地区的许多住户和其他气候区空调能耗较低的住户,采用节能空调器会使空调器寿命周期能耗增加,同时使材料资源消耗增加,因此应针对不同的气候条件、不同经济发展水平和不同建筑类型,制定不同的空调器能效标准。     

窗墙比对居住建筑的冷热耗量指标及节能率的影响

以高层公寓式居住建筑为对象,利用特征温度法研究了对建筑采取相同改进措施时窗墙面积比对建筑冷热耗量和能耗相对变化率的影响,并分析了当建筑体形系数不同时,窗墙面积比对全年空调与供暖冷热耗量指标以及采取相同节能措施建筑的全年空调与供暖节能量及节能率的影响。     

A Round Robin Test for buildings energy performance in Italy

The energy policy in Europe regarding buildings and the energy efficiency sector are regulated by two directives: 2002/91/CE - EPBD and 2006/32/CE - EEESD [1] and [2].The CEN has elaborated a standard to revise all European normatives about building energy performance and HVAC plants. The “CEN Umbrella” CEN/TR 15615 [3] includes a new version of EN ISO 13790:2008 [4] and a new standard about heating plant, use and contributions of renewable energy sources. Furthermore, the CEN Standard provides a software version for technicians.In this paper we present a Round Robin Test between a selection of softwares applied to an Italian case study. The selected calculation methodologies, range from research packages to extra-simplified software. Furthermore, the Italian procedure described in UNI TS 11300 [5] has been analyzed and considered as the reference for all other calculation methodologies.The results of the Round Robin Test show the relationship between thoroughness of data input and energy evaluation accurancy. The more the input data is affected by uncertainty, the less precise is the energy efficiency calculation. On the other hand the energy performance of building evaluation accurancy depends on the aim of the simulation: the energy audit, the energy design or the energy labeling (certification).