Task/ambient Air Conditioning Research Articles

Experimental study on the influence of environmental parameters on human multi-node warming sensitivity and demand

The thermal comfort of personnel can be improved by optimizing the thermal environmental parameters. And local temperature regulation can enhance the body's comfort in hotter or colder environments. This study systematically investigates the changes in skin temperature, local thermal sensation, and thermal comfort in eight parts before and after heating stimulation under four ambient temperatures and six air velocities, and develops multi-node physiological models of human warming sensitivity and demand. The results indicate that post-stimulation ambient temperature and air velocity have weaker effects on thermal sensation vote and thermal comfort vote than pre-stimulation. The warming demand of the face shows poorer sensitivity to ambient temperature, which is 66.88% lower compared to the abdomen. The air velocity strongly influences the warming demand of the neck, which is 75.01% higher than the lower legs. In addition, the warming sensitivity of the trunk is more influenced by ambient temperature than by air velocity, whereas the extremities' sensitivity is more susceptible to air velocity. The effect of air velocity on warming demand is 2.01–5.91 times greater than the ambient temperature. This study also presents the optimum comfortable temperature and the corresponding equilibrium velocity, providing a certain design basis for pulsating air supply, task-ambient air conditioning, and other variable air supply parameters methods.

Numerical investigation on the heat flux properties of a thermal manikin in sleeping environments applying task/ambient air conditioning

As an energy-saving equipment, task/ambient air conditioning (TAC) system was widely used in sleeping environment in recent years. The TAC can deliver cooling air directly to the sleeping person, resulting that the micro climate around the human body becomes very critical in the evaluation of human beings’ thermal comfort. Different from sitting and standing, sleeping human body is always at lying posture, and thus at a lower metabolic rate than at waking status. To understand the heat balance between a sleeping body and the surrounding environment, investigation on the heat loss of human body becomes necessary. Hence, a numerical study on the body heat loss characteristics of a thermal manikin at sleeping state in a bedroom utilizing a TAC system was carried out. The convective heat transfer, radiative heat transfer, evaporative heat loss from skin and respiratory heat loss and their ratios were quantitatively analyzed. The results indicate that the convective heat transfer took the first place, accounting for about 80% of the total heat loss, and Latent heat loss accounted for 15.9%–21% of the total heat loss. In addition, the heat loss at different supply conditions was numerically studied. Results showed that the supply air temperature, flowrate and humidity play different effects on body heat loss. Contributions of this study are meaningful for the accurate control of micro climate of human activities.

Effect of air supply mode on the airflow distribution inside soft sleeper compartments of air-conditioned trains

Trains are an important means of transportation for people to travel. The train's soft sleeper compartment space is relatively small, and the density of people is relatively large. Therefore, improving the thermal comfort and air quality of the compartment is of great significance for ensuring a healthy travel environment. To analyze the appropriate mode of conditioned air supply in train soft sleeper compartments, the airflow distribution inside soft sleeper compartments is simulated numerically at four different air supply modes, namely, sidewall air supply with slot diffusers, perforated ceiling air supply, bedside task–ambient air conditioning, and displacement ventilation. The reliability of the numerical simulation models is verified with the experimental data in the literature. Comparative analysis is made in terms of the compartment temperature, velocity, predicted mean vote and predicted percentage dissatisfied (PMV-PPD), and ventilation efficiency among various modes of air supply. The four air supply schemes are evaluated comprehensively by stochastic multicriteria acceptability analysis (SMAA-2). As the computational results show, bedside task–ambient air conditioning is the best air supply mode in terms of comprehensive performance indicators, followed by the sidewall slot air supply. The perforated ceiling air supply ranks third, and is superior to displacement ventilation.

PMV-based dynamic optimization of energy consumption for a residential task/ambient air conditioning system in different climate zones

Considering the effects of climate zones on building energy, a numerical study was conducted to investigate the energy consumption of a bedroom task/ambient air conditioning (TAC) in different climate zones. In this study, a PMV-based operating strategy of TAC was proposed to dynamically control energy consumption during night. According to this operating objective, the TAC was operated at two conventional operating modes: variable supply air temperature mode (VAT) and variable supply air flow rate mode (VAF). It's found that compared to VAF mode, VAT mode help reduce energy consumption by no less than 10% in Beijing, 19% in Shanghai and 18% in Guangzhou. To further reduce operating power, the variable air flow rate and air temperature mode based on lowest energy consumption (VFT-LowE) was adopted to optimize the operating of TAC, and the results show that compared to VAT, VFT-LowE mode can save energy by up to 6.5% in Guangzhou. Moreover, the highest energy saving potential was also evaluated showing a highest energy saving per night of 403 kJ in Beijing, and around 1100 kJ in Shanghai and Guangzhou. It's also indicated that the optimized operating mode has the largest energy saving potential in climate zones with higher air temperature.

Analysis of climate zones’ effects on energy consumption of a bedroom TAC system

To promote the application of bedroom TAC to a larger region, task/ambient air conditioning (TAC) system was applied to different climate zones in China. In this study, China as a typical country which has a very large area and significantly different climate zones, was selected as the investigated country. Firstly, five cities in different climate zones were selected. Secondly, the CFD study was carried out on the bedroom TAC using the environmental parameters. Thirdly, predictive models of energy consumption were established using RSM method. Afterwards, the energy performance of the TAC system in different cities were predicted and analyzed. The results showed that the energy consumption in the typical day was from 0 kJ in Kunming to 4588.30 kJ in Shanghai.

The Development of the Bed-Based Task/Ambient Air Conditioning System Applied to Sleeping Environments

Task/ambient air conditioning (TAC) system is an excellent air conditioning method due to good performance in thermal comfort, indoor air quality and energy saving. For a sleeping environment, since a sleeper is usually immobile and occupied a small space, TAC systems can be regarded as the best air conditioning method. Nowadays, some bed-based TAC systems have been proposed and its operation performances on energy use, thermal comfort and indoor air quality were experimentally and numerically studied. In this study, the previous studies on these bed-based TAC systems are reviewed and its advantages and disadvantages are summarized.

Reduction of energy consumption for a TAC system applied to sleeping environments with varying envelope thermal load

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. However, 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 models of the energy consumption and thermal comfort. Secondly, 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.

Energy performance of a bedroom task/ambient air conditioning (TAC) system applied in different climate zones of China

Task/ambient air conditioning (TAC) system applied to bedrooms has been investigated and its energy efficient performance reported. To promote the application of bedroom TAC to a larger region, a numerical study was carried out on a bedroom TAC system applied in five different climate zones. To simplify the numerical study, response surface methodology (RSM) was used to predict operating power of TAC based on CFD results. It's found that the daily energy consumption in the typical day was from 0 kWh in Kunming to 1.27 kWh in Shanghai, the averaged daily energy consumption varied from 0.47 kWh in June to 0.56 kWh in August for Guangzhou, and the total energy consumption in summer ranged from 0 kWh in Kunming to 58.33 kWh in Guangzhou. Meanwhile, the operating time of the TAC were also different between these five cities. In order to save energy, different set points of toz (average air temperature in the occupied zone) were investigated. It's found that increasing the toz from 24 to 25 °C can reduce energy consumption by about 23.42% in Shanghai to 36.23% in Beijing. Besides, the energy saving potential using two operating modes were compared: variable air flow rate and variable air temperature.

A simplified numerical study on the energy performance and thermal environment of a bedroom TAC system

In subtropics, the higher energy consumption of air conditioning system in summer period brought about the application of task/ambient air conditioning (TAC) systems, not only in commercial buildings, but also in residential buildings. To better assess the performance of the TAC system, a numerical study was carried out to predict the energy and thermal performance of a bedroom TAC system in a bedroom in subtropical area. To conveniently predict the indoor thermal environment, response surface methodology (RSM) was applied to simplify the procedure of numerical simulation. Firstly, CFD study was carried out to evaluate the thermal and energy performance of the TAC system. Secondly, RSM method was used to establish the predictive models of important index of indoor thermal environment to form the simplified numerical method. Thirdly, these two methods were used and the predicted values were compared. It was found that the energy consumption was reduced from 260 to 160 W when the ts was increased from 19 to 23 °C, and the averaged draft risk (DRoz) reached at 20% when the Qs was set at 110 l/s. The significant vertical non-uniformity of air temperature, air velocity and relative humidity were also reported. Besides, the CFD method was compared with the simplified numerical method (RSM method). It was found that the maximum deviation between using the RSM and CFD methods was less than 5% in predicting energy consumption, draft risk, thermal parameters in the occupied zone, stratified air temperature and stratified air relative humidity. Overall, the simplified numerical method (CFD based RSM method) can predict the indoor thermal environment accurately.

Comparative studies on using RSM and TOPSIS methods to optimize residential air conditioning systems

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.

A multi-objective study on the operation of task/ambient air conditioning systems in subtropics

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. However, for real application the varied envelope thermal load should be considered. To determine the optimum operation under different envelope thermal load, an optimization of the TAC system operation was carried out in this study. A multi-objective optimization approach named TOPSIS method was used to evaluate the integrated performance of the TAC system. Finally, the ranking of the selected study cases was obtained and the optimum operation was achieved.

Operating optimization for improved energy consumption of a TAC system affected by nighttime thermal loads of building envelopes

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.

Evaluating Effects of Building Envelope Thermal Loads on Energy use and Thermal Comfort for a Bedroom TAC System

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 reduce energy use of air conditioning in bedrooms, task/ambient air conditioning (TAC) can be applied and was studied previously. Due to the variation of the envelope thermal loads in a bedroom during night, it is necessary to study the thermal environment inside the 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. PMV and EUC (energy utilization coefficient) values were evaluated, respectively. The study results indicated that when envelope thermal loads was higher, the advantage of the TAC system in energy saving was greater for the same thermal comfort level. However, it should be noted that a higher envelope thermal load could also resulted in the non-uniformity in air flow and air temperature distributions, leading to a possible uncomfortable micro environment.

A numerical study on influences of building envelope heat gain on operating performances of a bed-based task/ambient air conditioning (TAC) system in energy saving and thermal comfort

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 (Qs) of 50 l/s, energy consumption was increased from 47.78W to 213.11W, and the PMV value was increased from −1.69 to −1.29 with the increase in envelope heat gain from 3.11W to 155.6W. 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.

Computational fluid dynamics analysis of convective heat transfer coefficients for a sleeping human body

Abstract 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.

Experimental and numerical study on air flow and moisture transport in sleeping environments with a task/ambient air conditioning (TAC) system

An experimental and numerical study on indoor air flow and moisture transport was performed in a bedroom with a task/ambient air conditioning (TAC) system. To better evaluate the characteristics of the TAC system, a traditional full volume (FAC) air conditioning system was also investigated. In the experimental study, the horizontal stratification of temperature distribution created by the air conditioning (A/C) system and the skin (surface) temperature of thermal manikin were reported, and the results suggested an acceptable thermal stratification and a higher nonuniformity of skin temperatures at the TAC system. In the numerical study, the air temperature and velocity fields demonstrated the effect of supply air and buoyancy driven flow inside the bedroom, and the removal of moisture near the thermal manikin.

Parameter optimization for operation of a bed-based task/ambient air conditioning (TAC) system to achieve a thermally neutral environment with minimum energy use

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.

Experimental and numerical studies on the performance evaluation of a bed-based task/ambient air conditioning (TAC) system

A bed-based TAC system applied to sleeping environments has been developed and its performances experimentally and numerically studied, and the study results are reported in this paper. Firstly, a detailed description of an experimental rig for the bed-based TAC system at two settings is presented with a return air inlet on the wall (Setting 1) and with a return air plenum and inlet placed under the bed (Setting 2). Secondly, the experimental results on the operating performances of the bed-based TAC system at the two settings in terms of thermal environmental control and energy saving are analyzed and reported. Thirdly, to supplement the experimental study for a more detailed analysis on air temperature and flow fields, a follow-up numerical study was carried out and is reported. Both the experimental and numerical study results suggested that the bed-based TAC system at Setting 2 performed better in controlling thermal environment in an occupied zone but with a relatively poorer energy saving performance, as compared to that at Setting 1.

Performance evaluation of an air conditioning system with different heights of supply outlet applied to a sleeping environment

Abstract 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.

Thermal, ventilation and energy saving performance evaluations of a ductless bed-based task/ambient air conditioning (TAC) system

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.