Temperature and Humidity Independent Control (THIC) of Air-conditioning System focuses on temperature and humidity independent control (THIC) systems, which represents a new concept and new approach for indoor environmental control. This book presents the main components of the THIC systems, including dehumidification devices, high-temperature cooling devices and indoor terminal devices. Other relevant issues, such as operation and control strategy and case studies, are also included.

This book is intended for air-conditioning system designers and engineers as well as researchers working with indoor environments.

The sensible load consisted of solar radiation, indoor devices, and so on varies completely different from the moisture load generated from occupants or other sources. If all the loads are undertaken by the air circulation, the supply air state (temperature and humidity) has to be changed all the time to accommodate to the variances of the sensible and moisture loads in order to maintain both the temperature and humidity for the conditioned space. This is quite a hard task. However, if the air circulation system is only used for humidity control and a radiant cooling system (or other cooling system) is adopted for removing the sensible load, things would be much easier. A radiant cooling system can remove sensible load only with little influence on humidity ratio if temperature of the cold water flowing through the radiant cooling device is higher than the indoor air dew-point temperature. In this way, both indoor temperature and humidity can be maintained well regardless of how the sensible and moisture loads change. Furthermore, as the sensible load could be removed by the cold water with a temperature higher than the indoor dew point, e.g., 16–18
C, which is also higher than the chilled water temperature in most conventional air-conditioning systems (e.g., 7
C), chiller’s efficiency will be much higher than that of conventional chiller if the chiller is specially designed to produce high-temperature chilled water for removing only sensible cooling load and regulating indoor temperature.

This is a new concept for HVAC system, which can provide more comfort thermal environment with less operation energy. This should be the principle and basic design guideline for the air-conditioning system in future. Although the key devices for the THIC system seem to be similar to those for the conventional air-conditioning system, the operating conditions and performances of devices we need in the THIC system are quite different: the air handling processor should be able to dehumidify air to a drier state for removing indoor moisture load but without a too low temperature to be supplied to the conditioned space; the chiller should provide chilled water with a higher temperature (16–18
C) and higher coefficient of performance (COP); if FCU is adopted for indoor temperature control, the FCU should work efficiently with a smaller temperature difference between circulating water and air but without the worry of condensing water; etc. These indicate that the THIC systems do need a complete set of new types of devices, a new generation of HVAC devices! We need different design approaches, we need different system components, we need different control devices with different logics, and we need different ways to operate and manage the THIC systems.

Xiaohua Liu is an associate professor at the Building Energy Research Center, Tsinghua University, China. Yi Jiang is a member of the Chinese Academy of Engineering, the director of the Building Energy Research Center, Tsinghua University, China and the director of the China-USA Joint Research Center on Clean Energy. Tao Zhang is a Ph.D. candidate at the Building Energy Research Center, Tsinghua University, China.

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