Application of radiant cooling as a passive cooling option in hot humid climate

In hot and humid region, air-conditioning is increasingly used to attain thermal comfort. Air-conditioning is highly energy intensive and it is desirable to develop alternative low-energy means to achieve comfort. In a previous experimental investigation using a room equipped with radiant cooling panel, it was found that cooling water kept to 25 °C could be used to attain thermal comfort under some situations, while water at such temperature would not cause condensation of moisture from air on the panel. This paper reports results of a series of whole-year simulations using TRNSYS computer code on applications of radiant cooling to a room model that represents the actual experimental room. Admitting the inability of radiant cooling to accept latent load, chilled water at 10 °C was supplied to cooling coil to precool ventilation air while water cooled by cooling tower was used for radiant cooling in daytime application. For night-time, cooling water from cooling tower supplied for radiant cooling was found to be sufficient to achieve thermal comfort. Such applications are considered to be more amenable to residential houses.     

Performance evaluation of misting fans in hot and humid climate

Singapore experiences a hot and humid climate throughout the year. This in turn results in heavy reliance on mechanical systems especially air-conditioning to achieve thermal comfort. An alternative would be the use of evaporative cooling which is less energy intensive. Objective and subjective measurements were conducted at an experimental setup at the National University of Singapore (NUS) to evaluate the thermal conditions and thermal sensations brought about by misting fans. Field measurements were also conducted at food centres in Singapore to determine if they are coherent with the objective and subjective measurements conducted. Analysis of objective and subjective data showed that the misting fan was able to significantly reduce the dry-bulb temperature and thermal sensation votes. This is consistent with field measurements taken, where regression analysis showed that with the misting fan, thermal neutrality can be obtained at a higher outdoor effective temperature (ET*). However, the reduction in temperature comes at the expense of higher relative humidity which results in consistently greater biological (bacterial and fungal) pollutants being enumerated from samples collected under the misting fan system. In some samples, the bacteria count is very much greater than samples collected under the non-misting fan, illustrating the potential for a substantial increase in biological pollutants due to the generation of mists.     

Experimental investigation of dehumidification process in cooling coil by utilizing air-to-air heat exchanger in humid climate of Iran

Energy recovery systems can be used in HVAC to reduce energy consumption by recovering wasted energy from the exhausted air to pre-cool inlet fresh air. In this paper, experimental study of utilizing cooling coil (CC) and cooling coil combined with heat exchanger (CCHE) has been developed. Considering the different climate zones in Iran, the experimental study has been done for the areas with high humidity content. In each case, the effects of air-to-air heat exchanger (HE) on the sensible and latent cooling load are investigated. The analysis gives the applicability of HE in Iran for various operational conditions to obtain air with lower moisture content. In CCHE systems more latent load quota is allocated in cooling coils and lower air humidity ratio can be obtained. Also in the cities with higher dew point depression (difference between dry-bulb and dew point temperature) more humidity reduction is achieved and the difference between latent load quotas of CCHE system is higher than CC system.     

夏季湿热地区置换通风和冷却顶板复合系统节能潜力研究

根据上海一办公楼置换通风和冷却顶板复合系统的设计及运行特点,应用EnergyPlus软件模拟了采用转轮除湿方式的复合系统的供冷季能耗,并分别模拟了采用冷却除湿方式的复合系统、带热回收装置的混合通风系统和置换通风系统的供冷季能耗以进行对比。结果表明,在湿热地区采用转轮除湿方式可比冷却除湿方式节约制冷机冷量,空调季总能源费用比混合通风系统节约30%左右。     

木板壁民居对湿热气候的适应性

为调查山地木板壁民居对重庆夏季湿热气候的适应性,选取当地典型木板壁民居作为研究对象,在夏季对其室内热环境进行实测。结合当地建筑特点及居民生活习惯,对实测数据进行分析,并利用APMV对室内热环境进行评价。结果表明,木板壁民居夏季依靠自然通风显著改善了室内热舒适度,夏季典型日APMV达Ⅱ级以上的约占65%。传统木夹壁民居在热环境营造上响应了当地气候特点,具有较好的气候适应性。     

湿热气候区建筑天井的优化设计策略

以三亚地区某多层天井式办公建筑为研究对象,采用数值模拟方法研究了天井的主要结构特性、底层架空方式和室外环境等因素对通风效果的影响。结果表明:当天井的长宽比为1∶1时,天井最佳设计高宽比宜取4∶1~5∶1;底层架空方式以单面架空为最佳;随室外风速的增加,室外环境对天井内温度的影响减弱。     

毛细管网供冷室内环境对比实验研究

在18℃供水温度下,对重庆地区毛细管网辐射供冷系统进行实验测试,分析了毛细管网顶棚、墙面、地面3种敷设方式的室内热工参数。结果表明：毛细管网顶棚、墙面、地面3种敷设方式供冷稳定时,人员活动区的平均温度依次为26.27、27.22、26.57℃,辐射表面平均温度依次为20.96、21.14、22.76℃,PMV依次为-0.27、0.32、-0.2,PPD依次为7.06%、7.47%、6.34%。在实验条件下,3种敷设方式供冷时室内温度均能满足≤ 28℃的要求,PMV、PPD均能满足《民用建筑室内热湿环境评价标准》（GB/T50785-2012）Ⅰ级热舒适评价指标。     

Thermal performance of latent heat storage for free cooling of buildings in a dry and hot climate: An experimental study

Experimental studies on the Phase Change Material (PCM) storage unit for building ventilation in dry and hot climates were conducted to determine its thermal performance. The PCM unit stored the night time coolness and used it for cooling the hot ambient air during day time. The influence of air flow rate and the inlet air temperature on cold accumulation in PCM during charging process and cold extraction from the PCM during discharging process were analyzed. The air temperatures used for charging of PCM were 20^oC, 22^oC and 24^oC, while during the discharging process, it was at 36^oC, 38^oC and 40^oC. The air flow rates considered for charging of PCM were 4 and 5 m³/hr/kg of PCM. Experimental observations showed that solidification of PCM was more sensitive to the charging air temperature compared to the air flow rate. When the charging air temperature was reduced from 22^oC to 20^oC, ∼33% less time was needed to completely solidify the PCM. Moreover, when the charging temperature was increased from 22^oC to 24^oC, ∼52% more time was required by the PCM to complete the solidification process. Changing the air flow rate from 4 m³/hr to 5 m³/hr reduced the solidification time period up to ∼16%.     

Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

高温高湿环境下湿帘-风机温室降温特性及影响因素研究

通过对上海一栋采用湿帘-风机降温的温室内部温度、湿度的连续实测,验证了高温高湿气候下湿帘-风机在温室中的降温效果。对湿帘风机系统在该环境下的蒸发降温效率及温度梯度进行了测试分析,并应用测试数据对温室热环境模型进行了验证,讨论了空气温度、相对湿度、太阳辐射量等室外环境参数对温室降温能力的影响。     

Application of passive cooling systems in the hot and humid climate: The case study of solar chimney and wetted roof in Thailand

The thermal performance of two passive cooling systems under hot and humid climate condition is experimentally investigated. The experimental results were obtained from a test cell and a controlled cell with identical walls but different roof configurations. The passive cooling systems applied to the test cell are solar chimney and water spraying on roof. The experimental results obtained from the test cell are compared with the closed and no passive cooling controlled cell. In addition, the significant of solar-induced ventilation by using a solar chimney is realized by utilizing a wind shield to reduce the effect of wind-induced ventilation resulting in low measured air velocities to the solar chimney and low computed value of coefficient of discharge. The derived coefficient of discharge of 0.4 is used to compute Air Changes rates per Hour (ACH). The ACHs with application of solar chimney solely are found to be in the range of 0.16–1.98. The studies of air temperature differences between the room and the solar chimney suggest amount of air flow rates for different periods in a year. The derived relationships show that the air flow rate during February–March is higher than during June–October by 16.7–53.7%. The experimental results show that application of the solar chimney in the test cell could maintain the room temperature at 31.0–36.5 °C, accounting for 1.0–3.5 °C lower than the ambient air and 1.0–1.3 °C lower than the controlled cell. However, to make the test cell's room temperature much lower than the ambient temperature and increase the flow rate of air due to the buoyancy, the application of water spraying on roof is recommended together with solar chimney. The application of the two systems in the hot and humid climate are discovered to sustain the room temperature of the test cell to be lower than the ambient air by 2.0–6.2 °C and lower than the controlled cell by 1.4–3.0 °C.     

Study on simulation methods of atrium building cooling load in hot and humid regions

In recent years, highly glazed atria are popular because of their architectural aesthetics and advantage of introducing daylight into inside. However, cooling load estimation of such atrium buildings is difficult due to complex thermal phenomena that occur in the atrium space. The study aims to find out a simplified method of estimating cooling loads through simulations for various types of atria in hot and humid regions. Atrium buildings are divided into different types. For every type of atrium buildings, both CFD and energy models are developed. A standard method versus the simplified one is proposed to simulate cooling load of atria in EnergyPlus based on different room air temperature patterns as a result from CFD simulation. It incorporates CFD results as input into non-dimensional height room air models in EnergyPlus, and the simulation results are defined as a baseline model in order to compare with the results from the simplified method for every category of atrium buildings. In order to further validate the simplified method an actual atrium office building is tested on site in a typical summer day and measured results are compared with simulation results using the simplified methods. Finally, appropriate methods of simulating different types of atrium buildings are proposed.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.     

地板辐射热水采暖系统设计及应用

简述了地板辐射热水呆暖系统的特点，介绍了其设计要点，提出了系统材料选用的材质要求，探讨了地热采暖的安装与维护保养中的注意事项。     

Operational characteristics of residential and light-commercial air-conditioning systems in a hot and humid climate zone

Forced-air space-conditioning systems are ubiquitous in U.S. residential and light-commercial buildings, yet gaps exist in our knowledge of how they operate in real environments. This investigation strengthens the knowledge base of smaller air-conditioning systems by characterizing a variety of operational characteristics measured in 17 existing residential and light-commercial air-conditioning systems operating in the cooling mode in Austin, Texas. Some key findings include: measured airflow rates were outside of the range recommended by most manufacturers for almost every system; actual measured cooling capacities were less than two-thirds of rated cooling capacities on average; hourly fractional operation times increased approximately 6% for every °C increase in indoor–outdoor temperature difference; and lower mean indoor surrogate thermostat settings and higher supply duct leakage fractions were most associated with longer operation times. The operational characteristics and parameters detailed herein provide insight into the magnitude of the effects of HVAC systems on both energy consumption and indoor air quality (IAQ) in residential and light-commercial buildings.     

Thermal comfort assessment and application of radiant cooling: A case study

A field assessment of thermal comfort was conducted at Mehran University of Engineering and Technology, situated in the subtropical region of Pakistan. The results show that people of the area were feeling thermally comfortable at effective temperature of 29.85 °C (operative temperature 29.3 °C). A comparison of this neutral effective temperature was made with the neutral effective temperature determined from adaptive models. It is found that the neutral effective temperature determined during this study closely match that of the adaptive model based on either indoor temperature or both indoor and outdoor temperatures. The results of thermal acceptability assessment show that more than 80% of occupants were satisfied at an effective temperature of 32.5 °C, which is 6.5 °C above the upper boundary of ASHRAE thermal comfort zone. Naturally ventilated classrooms and air-conditioned offices of the University were simulated using TRNSYS system simulation program for two cases, once when conventional air-conditioning is used for providing thermal comfort, and when comfort is achieved through radiant cooling. In the simulation, cooling tower was used to regenerate cooling water for the radiant cooling system. Energy consumption was estimated from simulation of both cases. The results show that it is possible to achieve thermal comfort for most of the time of the year through the use of radiant cooling without a risk of condensation of moisture from air on the radiant cooling surfaces. A comparison of the energy consumption estimates show that savings of 80% is possible in case thermal comfort is achieved through radiant cooling instead of conventional air-conditioning.     

Radiational panel cooling system with continuous natural cross ventilation for hot and humid regions

This paper investigates a hybrid cooling system, utilizing wind-driven cross ventilation and radiational panel cooling in an office setting. The characteristics of the indoor environment are examined using computational fluid dynamics (CFD) simulation, which is coupled with a radiation heat transfer simulation, and HVAC control in which the PMV value for a human model in the center of the room is controlled to attain the target value. The system is devised with an energy-saving strategy, which utilizes stratified room air with a vertical temperature gradient. The cooled air settles down within the lower part of the room, while the hot and humid air passes through the upper region of the room, sweeping out the heat and contaminants generated indoors. This strategy is found to be quite energy-efficient in the intermediate seasons of spring and autumn in Japan. Even under hot and humid outdoor conditions, the hybrid system coupled with radiational cooling would bring significant energy savings are possible compared with a hybrid system coupled with underfloor air-conditioning.     

浅析太原市地板辐射供冷的应用

通过对太原市夏季室内空气温度和相对湿度的调查,结合地板辐射供冷系统的节能、舒适等特点,对太原市采用地板辐射供冷的可行性进行了分析,得出了地板辐射供冷用于太原市居住建筑夏季降温理论上可行的结论。     

An experimental investigation of the wind tower-assisted by the underground passive cooling system

Wind towers have been used for the buildings passive cooling, in warm and dry regions. The wind towers are employed to capture the wind from the external air stream and direct it into the buildings and facilitate the circulation of the air from ambient through the building. The wind towers are not able to decrease the air temperature. In some locations of Iran such as Bam, the wind tower outlet was first directed into an underground channel, before being introduced into the building. The channel was built under the garden to employ the humidly of soil to cool down the air. In this paper, a small scale model of underground air-earth heat exchanger is employed to assess the system performance. The paper reports the effect of the garden irrigation time, humidity and temperature diurnal variations of the ambient air on the channel performance. The results show that when the garden is irrigated, and soil moisture content is at the higher level, the maximum average cooling performance of the channel is achieved, 51.30%. The temperature drop of the air inside the channel is due both the evaporation of moisture from the channel wall and the lower temperature of the soil than air.