Reducing the energy consumption of air-conditioning systems is becoming increasingly important. This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant cooling in China. In the large spaces of this airport terminal, a temperature and humidity independent control (THIC) system has been adopted instead of a conventional nozzle air supply method, which significantly reduces the energy consumption of the air supply. The radiant floor is the main mechanism for indoor temperature control, while a liquid desiccant outdoor air processor combined with displacement ventilation is responsible for humidity control. Ice storage is adopted to reduce operating costs, and the supplied chilled water temperature can be as low as 3 °C. This paper examines the performance of the THIC system in detail. The indoor environment is determined through measurements to be comfortable, and the on-site performances of key components in both the airport terminal and the cooling plant are investigated. The outdoor air processor supplies air of appropriate temperature and humidity ratio; two kinds of radiant floors are used for temperature control, both with measured cooling capacities of about 30–40 W/m2; and the energy efficiency ratio (EER) of the cooling plant is 2.62.
The basic task of an air-conditioning system is to provide a suitable indoor environment with respect to temperature, humidity, fresh air, etc. With rapid economic development, the energy consumption of air-conditioning systems has increased dramatically, now accounting for about 30–40% of the total energy consumption of non-residential buildings in China [1]. Therefore, reducing the energy consumption of air-conditioning systems is an important way to conserve building energy use. In large spaces such as the check-in halls in train stations and airport terminals, nozzle air supply is the most common air-conditioning solution. However, distributing the air in such an all-air system consumes quite a lot of energy [1]. Therefore, many researchers have focused on improving the energy performance of air-conditioning systems for large spaces, and several studies designed to improve system performance have been beneficial [2], [3] and [4].
Olesen [4] introduced a radiant floor application for cooling in an airport terminal in Thailand in which solar radiation entering through the building envelope could be extracted immediately by radiant cooling, thereby reducing the energy consumption of the air supply considerably. One of the challenges of adopting radiant panels is the issue of condensation [5], [6] and [7]. In the airport terminal in Thailand, condensing dehumidification was used to handle the air to a sufficiently dry state to extract indoor moisture and prevent condensation. However, the dehumidified air had to be reheated before being supplied indoors due to condensing dehumidification. Inspired by Olesen's research in Thailand, radiant floors and displacement ventilation were employed to facilitate temperature and humidity independent control (THIC) in the large spaces of Terminal 3 of Xi’an Xianyang International Airport, which is the subject of this paper.
THIC air-conditioning systems, consisting of a temperature control subsystem and a humidity control subsystem, were first introduced in China [8]. Humidity control is realized by supplying sufficiently dry outdoor air, and both desiccant and condensing methods can satisfy the dehumidification requirement. As for temperature control, in contrast to conventional systems, a high-temperature cooling source (15–20 °C) is adopted, and radiant panels are often employed for this purpose. Previous studies focusing on applications of THIC systems in office buildings have demonstrated their superior energy performance compared to conventional air-conditioning systems [9] and [10].
In addition, ice storage technology is regarded as a feasible approach for peak-load shifting in the cooling season, as the price of electricity during off-peak hours is much lower than during peak hours [11]. Although ice storage processes consume more power than conventional processes with the same cooling capacity, the operating costs of ice storage processes are much lower, and their applications in buildings have been on the rise in recent years [12], [13] and [14]. Thus, ice storage was adopted in the system described in this study.
This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant floors for cooling in China. The operating principles of the terminal devices, distribution system, and cooling plant in this THIC system are described, and the performances of key components of the system are measured.
The air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport has been in use since May 2012, and an advanced THIC system utilizing radiant floors has been adopted there. In this paper, the operating principle of the system is introduced, and its performance is investigated. The main conclusions can be summarized as follows:
(1)
In the large spaces of the airport terminal, a THIC air-conditioning system was adopted instead of a system based on the common nozzle air supply method, and the indoor environment in these areas was shown to be very comfortable for occupants. The performances of the terminal devices in this THIC system were measured: the liquid desiccant processor was able to dry the outdoor air sufficiently for humidity control, and the two kinds of radiant floors used for temperature control had measured cooling capacities of about 30–40 W/m2.
(2)
Two-stage terminal devices were designed to make use of the chilled water step-by-step; the measured operating Δt of the chilled water was about 10 °C, which was higher than the 5 °C in the conventional system. The large Δt helped to lower the flow rate and reduce the energy consumption of the water distribution system.
(3)
Chillers’ operating performances were investigated in both melting ice mode and ice storage mode. For the typical melting ice condition for cooling, the cooling capacity from the melting ice accounted for about 40% of the total cooling load, and the EER of the cooling plant was measured to be 2.62.
