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Task/ambient air condition system (TAC) is an excellent air conditioning method because of good performance in thermal comfort, indoor air quality and energy saving, and can be best applied to sleeping environments due to the immobility of a sleeping person. Previously, an R-TAC system for sleeping environments was proposed to deal with the cold-draft problem encountered in C-TAC systems for sleeping environments. However, the potential risk of condensation should not be ignored when using R-TAC systems due to the cold radiant panel. Therefore, a follow-up experimental study on indoor moisture distribution and a way of mitigating condensation in a bedroom when using R-TAC systems was carried out, and are presented in this paper. Firstly, two different settings of the R-TAC system are described. Secondly, moisture distributions in the bedroom, and condensation thresholds of moisture content of the supply air are analyzed and compared at two settings. The experimental results showed that vertical and horizontal moisture distributions in the bedroom were not greatly affected by the height of the supply vent, however, the R-TAC system at Setting 2 performed better in reducing condensation risk as compared with Setting 1.

Due to the increased expectations on human thermal comfort in sleeping environments at a low energy consumption, task/ambient air condition system (TAC) can be the best air conditioning method when considering the immobility of a sleeping person. Previously, convection-based TAC systems for sleeping environments were developed, with an obvious inadequacy of cold-draft problem. Therefore, a new radiation-based TAC system (R-TAC) was previously developed and experimentally studied at a set of fixed design parameter for its radiant panel. Therefore, a follow-up numerical study on the effects of varying design/operating parameters of the radiant panel on indoor thermal comfort and energy saving performances has been carried out, and the study results reported in this paper. Firstly, a geometry model based on the experimental bedroom used in the previous experimental study, boundary conditions and numerical study cases are detailed. Secondly, the results of validating the numerical method using the previous experimental data are reported. Thirdly, the numerical results on indoor thermal comfort, energy saving and draft risk at different surface temperature and emissivity, area of the radiant panel, and the distance between the radiant panel and a bed are presented. The numerical results demonstrated that all the four design/operating parameters of the radiant panel can significantly affect thermal comfort and energy saving performances in the bedroom when using the R-TAC system: increasing surface temperature can lead to a higher PMV value and a higher EUC value; increasing surface emissivity and area of the radiant panel a lower PMV value and a lower EUC value; reducing the distance between the bed and the panel a lower PMV value and a higher EUC value. Finally, the DR values were at a very low level in all the study cases, indicating the cold draft problem encountered when using a convective heat transfer based TAC system for a sleeping environment can be effectively resolved when using the R-TAC system.

The use of task/ambient conditioning (TAC) systems can help improve thermal comfort and indoor air quality, and reduce the energy consumption in bedrooms in residences or guestrooms in hotels at nighttime for sleeping. However, its operational and energy saving performances would be affected by a number of factors, such as supply air flow rate and temperature, and supply vane angles. This paper reports on optimizing numerically the operating performances of a novel bed-based TAC system. Firstly, the methods on a novel bed-based TAC system are introduced, including the experimental method and the computational method. Secondly, the numerical model is validated using the experimental results at the experimental operating conditions. Thirdly, the operating performances of the novel bed-based TAC systems at non-experimental operating conditions using the validated numerical model are optimized and the results reported. Finally, the conclusion and limitations of the study are given. The numerical study results showed that by suitably controlling its supply air flow velocity and temperature, and supply vane angle, the bed-based TAC system can be operated to maintain an acceptable level of thermal comfort without the cold draft in an occupied zone at a low energy consumption.

A sleeping person is naturally immobile in a relatively small space. Hence, task\ambient air conditioning (TAC) can be best applied to a sleeping environment because of its proven performances in energy saving. However, when using previously developed the TAC systems for sleeping environment applications, cold draft was a serious issue and could hardly be avoided due to a high air velocity and a low air temperature inside an occupied zone. Therefore, in the experimental study reported in this paper, a radiation-based TAC (R-TAC) system has been developed, and its performances experimentally evaluated. In this paper, firstly, an experimental setup for a prototype R-TAC system, and experimental conditions and methods are reported. This is followed by presenting experimental results on the thermal comfort and ventilation performance. Finally, the issues of condensation risk when using the proposed R-TAC system are discussed. The study results presented in this paper have shown that the use of the R-TAC system could not only result in better thermal comfort and ventilation performances, but also effectively resolve the cold draft problem. In addition, the potential problem of potential condensation on a surface may be resolved by raising the panel surface temperature, or using a lower fresh air supply humidity.

The purpose of this paper is to optimize the operating parameters such as: supply air temperature, supply air flow rate and supply air humidity, for a bed-based task/ambient air conditioning (TAC) system installed in an experimental bedroom with two total insulation values of beddings and bed to obtain a thermally neutral sleeping environment with minimum energy use. A computational fluid dynamics (CFD) method was applied to calculate the values of predicted mean vote (PMV) and energy utilization coefficient (EUC) based on conditions of 16 simulation cases. From the simulation results, the design of experiment method was applied to identify operating parameters, individually or combined, that could significantly affect thermal neutrality and energy use for the bedroom environment to establish linear regression models for PMV and EUC. These models were used to obtain the optimum operating parameters of the bed-based TAC system. These models were validated by comparing the obtained optimization results using the models with the predicted results given by the CFD method. The results suggested that for a bed-based TAC system at a specified total insulation value of beddings and bed, a lower energy use can be achieved through adjusting operating parameters while the thermal comfort is maintained.

In the subtropics, air conditioning (A/C) for a bedroom in residential buildings commonly serves to provide an appropriate indoor thermal environment at nighttime for sleeping. During daytime when A/C is not provided, a large amount of thermal energy can be stored in the thermal mass in its envelope components, in particularly its external walls. The energy stored would be gradually released, contributing significantly to the total space cooling load in the bedroom at nighttime. Therefore, this paper reports a simulation study on the impacts of daytime external envelope heat gain/storage on the nighttime cooling load in a hypothetic west-facing bedroom and the related mitigation measures in the subtropical Hong Kong. The study results showed that, among all envelope components, the west-facing external wall contributed most significantly to the total nighttime cooling load, because of its direct exposure to solar radiation, thus the heat gain and storage in its thermal mass. In addition, adding an air gap in the west-facing external wall can reduce remarkably the hourly total nighttime cooling load for the first hour (21:00–22:00) and the total cooling load for the 10-h A/C period. However, while varying the width of either the air gap or inside/outside concrete layers would not reduce cooling load further, ventilating mechanically the air gap can further increase the cooling load reduction and improve the flatness of load variation profile at the expense of consuming additional electrical energy. Finally, adhering aluminum foil to both sides of the air gap can further remarkably reduce nighttime cooling load, and improve the flatness of the load variation profile.

To provide better indoor thermal comfort and indoor air quality in sleeping environments and to achieve greater energy saving, it is necessary to develop new air conditioning systems applied to sleeping environments. In recent years, a large number of studies have been carried out on the task/ambient air conditioning (TAC). To address a number of the inadequacies in a previous related study for a novel bed-based TAC system for sleeping environments, a ductless bed-based TAC system has been developed and its thermal, ventilation and energy saving performances have been experimentally evaluated, by comparing them with those of a full volume air conditioning (FAC) system. Firstly, an experimental setup at two different settings, a ductless bed-based TAC setting and a FAC setting, is presented. Secondly, the methods for measuring air dry-bulb and wet-bulb temperatures, air velocity and CO2 concentrations are reported and six groups of experimental conditions detailed. Finally, experimental results of thermal, ventilation and energy saving performances at the two settings are presented and analyzed. The experimental results demonstrated that using the ductless bed-based TAC could lead to a better ventilation performance and energy saving performance, but a poor thermal performance in terms of a higher draft risk than using the FAC system. It was possible to reduce the draft risk, while still maintaining an acceptable energy saving performance, by selecting a proper supply air temperature and air flow rate as well as a proper supply vane angle.

The summer in Hong Kong is hot and humid with temperatures over 30°C and relative humidity over 70%. Air-conditioned buses were first introduced in the early 1990s and have become more and more popular. Everyday, millions of passenger-trips are taken in such buses and the air quality and thermal environment in them has become a public health issue. One major source of pollution is the passengers themselves but re-entry of engine emission is also a concern. People have always complained about the thermal environment of the buses especially during rush hours saying they are stuffy, smelly and have inadequate fresh air. We measured conditions in air-conditioned buses and non air-conditioned buses, running on 12 different bus routes in the Hong Kong Special Administrative Region (HKSAR), in both urban and rural areas. Two trips were made for each route. Portable gas analysers measured carbon monoxide (CO), carbon dioxide (CO2), temperature and relative humidity. The measurements showed there was no evidence that CO and CO2 levels in the air-conditioned buses were statistically higher than in non air-conditioned buses ( p 0.05). For the rural commutes, the in-vehicle levels of CO and CO2 were not significantly higher than for urban commutes (p 0.05). The Environmental Protection Department (EPD), HKSAR had published a guidance note for airconditioned public transport facilities and most of the exposures found, including the thermal environment, were acceptable with regard to the recommendations in the note. Momentary high levels of CO2 were found, but this lasted for a short period only.