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The operating parameters of task/ambient air conditioning (TAC) systems including supply air temperature (ts) and air flow rate (Qs) were reported to have critical effects on energy savings and thermally comfortable environment. Due to the existing contradictions between these two aspects, a multi-objective study should be carried out to realize consuming minimum energy and at the same time to guarantee the thermal comfort level at suitable range. Two optimization methods were adopted in this study, one is the response surface methodology (RSM), and the other is the technique for order preferences by similarity to an ideal solution (TOPSIS) method. The objective of this study was to compare the pros and cons of these two methods. It was found that the optimum operating parameters obtained using RSM method were 26 °C (ts) and 28.94 l/s (Qs), corresponding to energy consumption (Qc) of 46.89 W and PMV of 0.11; while that obtained using TOPSIS method were 26 °C (ts) and 30 l/s (Qs), corresponding to energy consumption (Qc) of 49.64 W and PMV of 0.09. Furthermore, compared with TOPSIS method, there were only 9 cases used in RSM method saving 74% of computation cost.

Due to the variation of outdoor environment, the building envelope thermal load undergoes obviously corresponding variation. Therefore, it's previously reported that building envelope had a deep effect on the indoor thermal environment at daytime and nighttime. In subtropics, the higher energy consumption of air conditioning system makes it necessary to study the task/ambient air conditioning system, not only in commercial buildings, but also in residential buildings. At the same time, the effects of the envelope thermal load on these task/ambient air conditioning systems should also be investigated. In this study, a bedroom with a task air conditioning (TAC) system was established and the influences of the building envelope thermal load on indoor thermal comfort level and the energy utilization potential of the TAC system were numerically investigated. Firstly, EUC (energy utilization coefficient) was used to evaluate the energy utilization potential. The EUC values were found growing from 1.0 to around 1.2 with an obvious increase, indicating higher energy utilization potential. Secondly, PMV was used to evaluate the thermal comfort. It was found that the PMV values were increased with a growth rate of 0.051 per W/m 2 at t s of 20 °C, 0.036 per W/m 2 at t s of 23 °C, and 0.027 per W/m 2 at t s of 26 °C. Thirdly, the air temperature non-uniformity in three directions was evaluated. It was found that the increase in envelope thermal load enhanced the air temperature non-uniformity.

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.

Task/ambient air conditioning (TAC) system is reported to be an energy efficient technology with available methods to control thermal comfortable level for sleeping environments. Better performance in energy saving for TAC systems in sleeping environment has been demonstrated in previous studies. However, it should be noticed that the building envelope thermal load affects the indoor thermal environment and operation of the air conditioning system due to the heat transfer through the envelope. The variation of indoor thermal environment will directly affect the performance of the TAC system, especially the set of operation parameters. Therefore, an optimization study on the TAC system operation considering the effects of envelope thermal load was carried out in this paper. Firstly, a full factorial design method was used to construct the simulation case matrix. Secondly, the models of the energy consumption and thermal comfort were established using operating parameters and envelope thermal load. Thirdly, comfort surface and comfort lines were obtained to calculate the optimum operating parameters at which the energy consumption was at the lowest. Finally, the energy consumption at the optimum status was calculated. The results show that the TAC system at the optimum status can save 1.4 to 1.7 kWh each night.

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.

Task/ambient air conditioning (TAC) systems have been introduced to solve the problem of thermal comfort in bedrooms during night. The key point of this problem is the thermal environment or heat transfer between a sleeping human body and the surrounding environment. Therefore, a numerical study on the convective heat transfer between a thermal manikin and the surrounding environment was carried out in a bedroom equipped with a TAC system. Firstly, the influence of supply conditions on indoor environment was investigated. Based on this section and previous studies on the convective heat transfer coefficients (hconv) between the human body and surrounding environment, equations depending on temperature difference between the thermal manikin and the environment or the air velocity in the surrounding environment were respectively established. Considering the effects of temperature difference and air velocity on the hconv, the equations were modified to be a function of both temperature difference and air velocity. The further analysis of the new equation indicated that this modified equation can tackle with variations of both temperature difference and air velocity, and can also give a good prediction. Besides, the hconv distributions on the 16 body segments were presented. Higher hconv values can be obviously found at body segments of heat, neck, hand and trunk. Due to the importance of clothes to thermal comfort level, the influence of coverage (blanket) was studied. When the thermal manikin was covered with blanket, the hconv values were about 0.5–1.0 W/(m2 K) higher than the naked ones and the temperature differences were much lower than the naked ones.

There has been an increasing concern on thermal comfort in sleeping environments and its associated energy use in the past few years. To improve the thermal environment and to reduce energy use of air conditioning in bedrooms, applications of task/ambient air conditioning (TAC) systems were proposed and studied previously. It’s indicated that the TAC system can be well integrated with a bed. Due to the variation of the envelope heat gain in a bedroom during night, it is necessary to study the thermal environment inside a bedroom and the energy use of a TAC system for the bedroom at varying envelope thermal loads. Therefore, this paper reports on a numerical study on a TAC system applied to a bedroom with different envelope heat gains. The influences of envelope heat gain on energy consumption of the TAC system and the indoor thermal comfort were studied in this paper. The research results show that at supply air flow rate ( Q s ) of 50 l/s, energy consumption was increased from 47.78 W to 213.11 W, and the PMV value was increased from −1.69 to −1.29 with the increase in envelope heat gain from 3.11 W to 155.6 W. To make PMV equal to zero under different envelope heat gains, linear regression models between supply air parameters and PMV were built and solved. The obtained values form curves where PMV = 0 and give a guide for operation of the TAC system. It was found that the calculation of energy consumption on these curves depends only on envelope heat gain.

Because of the increased expectations on thermal comfort and indoor air quality in sleeping environments at a low energy consumption, it is necessary to develop new air conditioning systems applied to sleeping environments. In recent years, a large number of studies on task/ambient air conditioning (TAC) have been carried out due to its excellent ventilation and energy saving performance. However, compared to full volume air conditioning (FAC), there exists an inadequacy on thermal control for TAC because cooled air is directly delivered to the space around a human body. Hence, the TAC and FAC systems have their own pros and cons in aspects of thermal, ventilation and energy saving performances, and the position of a supply outlet in an air conditioning (A/C) system significantly influences its operating performances. Therefore, a study on the performance evaluations of an A/C system installed in an experimental bedroom with its supply outlet positioned at five different heights has been carried out, and the study results are presented in this paper. The study results suggested that overall speaking, the A/C system performed the best at a supply air temperature of 23 °C, an air flow rate of 50 L/s and a fresh air flow rate of 13 L/s at H1100 setting, among all study cases. On the other hand, the A/C system performed the best at H800 setting among the five height settings.

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.

Because of their excellent performance in local thermal environmental control, task/ambient conditioning (TAC) systems have attracted increasingly more research attention. However, the current applications of TAC systems are mainly for daytime activities, but seldom for nighttime. In fact, TAC systems may be best applied to a sleeping environment, since the subjects to be served by a TAC system are immobile during sleep. Therefore, there is a strong need for studying the operational and energy saving performance of TAC systems when applied to sleeping environments. This paper reports on an experimental study on evaluating the operational and energy saving performance of a novel bed-based TAC system. The experimental results and their analysis demonstrated that the use of the novel bed-based TAC system can help achieve energy saving, compared with the use of a full volume air conditioning (FAC) system. Considering the experimental limitations, the energy saving potential of the novel bed-based TAC system if used in an actual bedroom was studied through a theoretical analysis. It demonstrated that the novel bed-based TAC system would help achieve significant energy saving when used in real buildings.