Energy performance enhancement of Hong Kong International Airport through chilled water system integration and control optimization

doi:10.1016/j.applthermaleng.2013.06.025

Applied Thermal Engineering

Volume 60, Issues 1–2, 2 October 2013, Pages 303-315

https://doi.org/10.1016/j.applthermaleng.2013.06.025 Get rights and content

Highlights

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Energy performance of Hong Kong International Airport was enhanced.
•
Chilled water system integration and control optimizations were performed.
•
Performance comparison using field data demonstrated 5.93% COP improvement.
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Performance comparison through simulation indicated 4.7 M kWh annual energy saving.

Abstract

Poor energy performances of building systems in practice are often observed, especially under off-design conditions (i.e. at low part load ratios). In order to overcome such problem, most of existing methods are developed merely considering single system or building. Unlike them, a method integrating the chilled water systems in the neighboring buildings is proposed to enhance the overall energy performance of the Hong Kong International Airport. The system integration allows the excessive cooling from one building to be delivered to the other. In addition, one 1000 RT chiller is relocated from Terminal 2 to Terminal 1. After the system integration and chiller relocation, three different sized chillers can be selected to satisfy the overall cooling load with higher part load ratios. Meanwhile, the control optimizations of chillers and seawater pumps also contribute to the system energy performance improvement. With limited investment cost and easy implementation, the proposed method and the control optimization significantly enhance the airport system energy performance. The direct field data comparison demonstrated the average chiller plant COP value is improved by 5.93%. The simulated case studies indicated an annual energy saving about 4.70 M kWh is achievable.

Introduction

Building energy consumption contributes a considerable part to the overall electricity consumption, e.g. 90% in Hong Kong [1]. More than 40% is consumed by air-conditioning system [2], [3]. Cooling demand of a building varies significantly from time to time and season to season. When taking the worst conditions into consideration, i.e. the possible largest cooling demands in buildings, the designed cooling capacities of the chiller plants are usually much larger than the demand needed in the off-design conditions which account for a major part of system lifetime [4]. Under these off-design conditions, the part load ratios of the chiller plants are usually low which result in poor system energy performance. The main reason is that chiller coefficient of performance (COP) is much lower at low part load ratios than the rated value which usually appears at high part load ratios, e.g. 80% [5], [6]. A large proportion of energy is wasted due to the poor energy performance of chillers at low part load ratios [7].

In order to improve system energy performance under off-design conditions, many studies were conducted. Generally speaking, most of these studies take single building/system into consideration. They can be grouped into the following two categories. The first one is on the energy performance improvement of single chiller at different part load ratios. The other is on the energy performance improvement of multi-chiller system with equal/different capacities. Application of variable speed drive (VSD) to chiller is an effective method to improve the energy performance of single chiller especially at low part load ratios. Qureshi and Tassou [8] made a review on the application of VSD to chillers. They concluded that the successful application of VSD in chiller resulted in a superior part load performance compared with chillers with single/multiple constant speed compressors. However, traditional designers have not fully implemented the idea of using all-variable speed chillers in a multi-chiller plant partly because the associated control complexity and stability of chilled water supply temperature when using the variable primary systems. In Ref. [9], modeling studies found all-variable speed chiller systems can reduce the total annual plant energy use by 2–5%. Similarly, Taylor [10] addressed that the application of variable speed chillers and/or variable primary-only pumping systems is an effective method to mitigate significant degradation in system performance at part load operation. Hartman firstly promoted that all-variable speed chiller plants where all the chillers, condenser pumps and tower fans are driven by VSD in order to achieve the highest overall plant performance at part load ratios [11]. Based on his simulation study, the annual energy using all-variable speed chiller plants with optimized controls would be on average 28% lower than that using conventional constant speed plants.

A multi-chiller system with equal/different sized chiller provides flexibilities in matching the cooling supply with the demand from end-users. For chiller systems with equal capacities, a commonly used approach is to switch on/off chillers sequentially according to actual demand changes. The switch-point can be optimized based on the energy performance of chillers (e.g. COP) at different part load ratios. Hackner et al. [5] developed a method using the designed chiller cooling capacity to optimize the switch-points. Due to the fact that cooling capacity of a chiller can vary significantly under different operating conditions [12], the switching points determined using the designed value may not be optimal. An online chiller maximum cooling capacity model introduced in Ref. [12] can help to solve such problem by accurately estimating the varying chiller capacity under different working conditions. For chiller systems with different capacities, the related optimal control strategies are relatively more complex. Optimal chiller loading control and optimal chiller sequencing control are two major considerations in the control strategy development. Recently, strategies have been proposed for optimizing chiller loading and sequencing. For instance, genetic algorithm methods are used to solve optimal chiller loading problems in Refs. [13], [14]. The study results demonstrated the accuracy of these methods within a rapid frame rate. Chang [15] proposed a simulated annealing approach for optimizing chiller loading. With regard to optimal chiller sequencing, a “branch and bound method” was developed in Ref. [16] while the method can also eliminate the deficiencies of the conventional methods. With regard to the long standing practical problem in the chiller sequencing control implementation (i.e. inaccurate cooling load direct measurement through temperature difference and flow), Huang et al. [17] developed a data fusion method to largely improve the accuracy of cooling load measurement. Meanwhile, the associated confidence degree was able to quickly detect the faults in cooling load measurements.

The above methods merely took single building/system into consideration. Direct applications of them in existing building systems (e.g. equipping VSD or adding different sized chillers) may result in large investment costs or/and major system configuration changes which lower down building owners' willingness to take actions. With single building/system being considered, these methods have not fully utilized different load features and diverse system configurations of buildings for enhancing overall system energy performance. The load profile of a single building may vary dramatically from time to time which could result in chillers (particularly equal sized ones) operating at low part load ratios for a long period. The sum of building cooling loads with different features could mitigate such dramatic variations and reduce the time of chillers operating at low part load ratios. Integration of chilled water systems in different buildings can realize such time reduction. Moreover, system integration in buildings provides opportunity in selecting different sized chiller to meet the overall cooling load with higher part load ratios.

This paper presents a case study of the Hong Kong International Airport in which the system energy performance is enhanced through chilled water system integration and control optimization. Both direct field data comparison and simulation studies have been conducted to demonstrate the gained benefits. For enhancing building system energy performance at low part load ratio, the practical project in HKIA provides new and helpful retrofitting experience with limited extra investment cost. With energy performance enhancement validated by both the operation data and the simulation studies, the project also advises system configuration with multiple sized chillers is more energy efficient than the equal sized one. The associated control is more complex. In order to solve the complexity of multi-sized chiller sequencing control, a priority-based optimal control strategy is developed and validated. Control optimization has also been made on seawater pumps.

Section snippets

Airport and chilled water system descriptions

The Hong Kong International Airport consists of five major buildings. Each building has its dedicated central air-conditioning system. Since the chilled water system integration in Terminal 1 and Ground Transportation Center is presented in this study, the chilled water system in these two buildings is described here in details.

Chilled water system integration In Terminal 1 and Ground Transportation Center

In order to improve the overall system energy performance at low part load ratio, a practical method with limited investment cost and easy implementation has been proposed. In the method, the chilled water connection loops linking Terminal 1 to Ground Transportation Center is constructed. The bi-directional loops integrate the chilled water systems in the two buildings and they allow the excessive cooling from either side to be delivered to the other one. In addition, one small sized chiller

Control optimizations

After the chilled water system integration and chiller relocation, three different sized chillers are available to be selected for chiller sequencing control. The original control for equal sized chillers is no longer suitable and a new optimal sequencing control is needed. Similarly, the relocation of 1000 RT chiller to Terminal 1 requires the change and optimizations of the seawater pump control in Terminal 1. In the following sections, the related optimizations are addressed.

Simulation platform construction

In addition to a direct site field data comparison, simulation studies have also been conducted to estimate the annual energy saving under same load conditions. The simulation platform has been constructed using TRNSYS 16 [19]. The major component models used in the study are addressed as below.

Chiller model (i.e. type 699) was selected to study the energy performance of chillers under different part load ratios. In order to make the simulation models close to the actual conditions, the

Validations through field data and simulation

Validations through field data and simulation were both conducted to study the energy performance enhancement after the system integration and control optimization. In Section 6.1, the field data of November from 2011 to 2012 were used to perform the direct performance comparison. Note that the actual cooling loads of these two months were different. The load difference imposed impact on the system energy consumption. In order to eliminate such impact, the developed simulation platform was used

Conclusions

In order to improve the energy performance of the Hong Kong International Airport particularly at low part load ratios, the chilled water systems in the Terminal 1 and the Ground Transportation Center were integrated. Meanwhile, the optimizations of chiller sequencing control and seawater pump control were performed.

The energy performance enhancement has been validated through both direct field data comparison and simulated studies. The field data comparison demonstrated the average chiller

Acknowledgements

The research work presented in this paper is financially supported by a grant (5276/12E) of the Research Grants Council (RGC) of the Hong Kong SAR and a grant of the Research Institute for Sustainable Urban Development of the University.

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Case studyEnergy performance enhancement of Hong Kong International Airport through chilled water system integration and control optimization

Highlights

Abstract

Introduction

Section snippets

Airport and chilled water system descriptions

Chilled water system integration In Terminal 1 and Ground Transportation Center

Control optimizations

Simulation platform construction

Validations through field data and simulation

Conclusions

Acknowledgements

Appl. Energy

Energy Build.

Appl. Energy

Appl. Energy

Appl. Therm. Eng.

Energy Build.

Appl. Therm. Eng.

Energy

Energy Convers. Manage.

Case study
Energy performance enhancement of Hong Kong International Airport through chilled water system integration and control optimization