Thermal Comfort Study of Wall Hanging Air-Conditioning Office in Summer

The purpose of this study is to evaluate the effect of air curtains on indoor environment and dehumidification energy consumption for different air supply angle and velocity. The numerical investigation is conducted in a low-humidity plant located in the atmospheric boundary layer. The standard k-epsilon turbulence model is used in the simulation study. The optimum air supply angle and velocity are evaluated based on temperature and humidity distribution. The simulation cases range in air supply angle from 0° to 20° and velocity from 6 m/s to 14 m/s, which is studied by means of orthogonal experiments. Simulation results show that air curtain can reduce the average indoor temperature of the plant by up to 3.9°C and reduce the average moisture content by up to 86.6%. The energy saving assessment of the dehumidification rotor system shows a parabolic variation in energy consumption with increasing air velocity at a certain air supply angle. The optimum energy consumption occurs in the range of 9–11 m/s for air supply velocity. When air supply velocity is over 11 m/s, the airflow exchange is enhanced by air curtain at the plant opening, resulting in higher energy consumption from air leakage for dehumidification.

The purpose of this study is to evaluate the effect of air curtains on indoor environment and dehumidification energy consumption for different air supply angle and velocity. The numerical investigation was conducted in a low-humidity plant located in the atmospheric boundary layer. The standard k-epsilon turbulence model was used in simulation study. The optimum air supply angle and velocity were evaluated based on temperature and humidity distribution. The simulation cases range in air supply angle from 0° to 20° and velocity from 6m/s to 14m/s, which were studied by means of orthogonal experiments. Simulation results show that air curtain can reduce the average indoor temperature of the plant by up to 3.9°C and reduce the average moisture content by up to 86.6% compared to the cases without air curtains. The energy saving assessment of the dehumidification rotor system shows a parabolic variation in energy consumption with increasing air velocity at a certain air supply angle. The optimum energy consumption occurs at the range of 9-11m/s for air supply velocity. When air supply velocity is over 11m/s, the airflow exchange is enhanced by air curtain at the plant opening, resulting the higher energy consumption from air leakage for dehumidification.

Energy-efficiently creating comfortable and healthy indoor environment is required as people spend the majority of their time indoors. As a novel air distribution method, stratum ventilation (SV) has been demonstrated to be potentials for winter heating. This study aimed to derive out the optimal ranges of supply air temperature and velocity so as to achieve both energy-efficient thermal comfort and stable operation of the environmental control system for the heating applications of SV. Experiments with six cases were firstly conducted in a field experimental chamber to examine the influence of warm supply air on indoor airflow pattern as well as indoor thermal environment. The results revealed that the supply air temperature and velocity affected thermal comfort and energy efficiency inconsistently, which were measured by predicted mean vote (PMV), vertical air temperature difference between head and ankle levels (ΔT), draft rate (DR), and energy utilization coefficient (EUC). Then, using numerical simulations validated through the experiments, 42 cases with combinations of six different supply air velocities and seven different supply air temperatures were analyzed. The supply air temperatures and velocities were optimized using Pareto-based multi-objective particle swarm optimization (MOPSO). The results revealed that the locations of the 25 Pareto optimal solutions got by MOPSO were isolated in their value spaces. Thus, cluster analysis was used to obtain the optimal ranges of the warm supply air. The optimal ranges of warm supply air temperature and velocity for SV were 28.2–28.5 °C and 1.54–1.66 m/s, respectively.

The CFD software was employed to simulate numerically the indoor airflow distribution in an air-conditioned room with different air supply temperature (20, 22, and 24 °C) and velocity (2, 3, 4, and 5 m/s). The results show that the simulation result is consistent with the experimental data, which shows the accuracy and reliability of CFD software for simulating indoor thermal environment. Specifically, the indicators including temperature, velocity, PMV-PPD, and mean air age are used in the analysis of the differences caused by the varied air supply velocity and temperature on the human thermal comfort. The comparisons show that the optimal air supply condition is the temperature 22 °C and the velocity of 3 m/s.

A wall hanging air-conditioning office was simulated on three different air supply angle and three different air supply velocity by the AIRPAK .Based on the velocity fields, temperature fields, PMV-PPD obtained, analysis indoor thermal comfort. The result shows obvious difference of air distribution and great effect of indoor thermal under different air supply angle and different air supply velocity. By comprehensive comparison, the best air supply condition is the one of 75° downward, 3.0m/s.

Air curtains is promising in reducing the short-range infection risk in hospitals. To quantitatively evaluate its performance, this paper explores air curtains equipped on normal consulting desk to avoid doctor’s direct exposure to the patient exhaled pollutants. A numerical investigation is conducted to evaluate the effects of supply air velocity and angle on cutting off performance. Simulation results show that the average mass fraction of exhaled pollutants decreases significantly (70%–90%) in the consulting ward, indicating satisfying performance of air curtains. Increasing supply air velocity is demonstrated to be conducive in forming full air curtains, whereas an excessively high supply air velocity may be of adverse effects by entraining exhaled flow. Besides, the supply air angle is also critical due to its coupling with supply air velocity. It is found that larger angle (0°–40°) is better where velocity is less than 3 m/s, otherwise a small angle (20°) is preferable where velocity is larger than 3 m/s. Exhaled flow could be well suppressed at the supply air angle 20° but moves over air curtains at 40°. This study can provide effective and intuitive guidance in applying air curtains in consulting wards.Electronic Supplementary Material (ESM)Supplementary material is available in the online version of this article at 10.1007/s12273-020-0649-7. The ESM files include the animation of patient exhaled droplets from the droplet birth at 0 s to 5 s under the supply air angle 0°, 20°, 40°, at supply air velocity 3 m/s.

Underfloor Air Distribution (UFAD) systems have received increasing attention during the past decades due to thermal stratification and energy saving potential over conventional mixed air conditioning system. Different supply air parameters have significant impacts on the UFAD system performance. In this study, experimental study and energy simulation software EnergyPlus were used to investigate the UFAD performance in a full size experimental room. The distance between diffusers and human, supply air temperature and velocity were discussed. The orthogonal experiments were employed to discuss the effect of supply air parameters on the temperature distribution, thermal comfort and indoor air quality (IAQ). By the analysis, the most important factor is the distance between diffusers and human. Furthermore, the preferable supply air parameters are suggested by means of controlling parameters. The results show that better thermal stratification and thermal comfort can be achieved when the distance between the swirl diffusers and human is 0.7m, the Supply Air Temperature (SAT) is 18-20°C and the Supply Air Velocity (SAV) is 1.2-1.5m/s. Another contribution of this paper is that the energy consumption of UFAD system is calculated by EnergyPlus. The calculation shows that the satisfied thermal stratification and prominent energy saving can be achieved simultaneously by using reasonable supply air parameters, such as the SAT is 18°C and the SAV is 1.2m/s.

A new experimental methodology is presented to show the effect of water supply temperature, mass flow rate and thermal load distribution on the radiant ceiling capacity and thermal comfort conditions. Computerized fluid dynamics simulated vertical temperatures and velocities profiles were validated by a comparison with experimental results and the difference was within 10%. Uniform surface temperature distribution was achieved in a 45.6 m3 test room installed with capillary ceiling radiant cooling panels by an increase in water temperature and air supply velocity. When the ventilation system was turned off, the mean ceiling surface temperature rose from 16.9 ± 0.4°C to 21.5 ± 0.3°C with a rise in the inlet water temperature to 20.1°C. The temperature difference between the head and ankle of an occupant was 2.0°C, which complies with the Chinese standard, GB/T 18049-2017. At a height of 1–1.5 m, the maximum temperature fluctuation was 2°C in the horizontal direction. When the ventilation system was turned on, with the air supply temperature and velocity at 19.8°C and 1.11 m s−1, the ceiling surface temperature was increased by 0.5°C. The indoor air temperature has a positive correlation with the air supply temperature and internal heat load but a negative correlation with air supply velocity.

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