Comparison of annual energy performances with different ventilation methods for temperature and humidity control

Stratum ventilation has been proposed to accommodate elevated indoor temperatures recommended by governments in East Asia. TRNSYS is used for computation of the space cooling loads, sensible and latent, as well as system energy consumption. Typical configurations of an office, a classroom and a retail shop in Hong Kong are investigated. Desiccant dehumidification with and without solar assistance is utilized for the air treatment under displacement ventilation and stratum ventilation, while simple reheating is adopted under mixed ventilation. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following five factors: the reduction in ventilation, dehumidification and transmission loads, prolonged free cooling period and increased the COP of the chillers. For the office, the year-round energy saving is found to be substantial at 20% and 40% without the need for solar energy provision when compared with displacement ventilation and mixing ventilation respectively. For the classroom and retail shop, the year-round energy saving is at about 25% and at least 37% with the aid of solar energy provision when compared with displacement ventilation and mixing ventilation respectively.     

Evaluation of thermal comfort conditions in a classroom with three ventilation methods

Thermal sensation is studied experimentally under mixing ventilation, displacement ventilation, and stratum ventilation in an environmental chamber. Forty-eight subjects participated in all tests under the same boundary conditions but different ventilation methods in the classroom. Thermal comfort analysis was carried out according to the designated supply airflow rate, room temperature, and relative humidity for the three ventilation methods. The thermal neutral temperature under stratum ventilation is approximately 2.5 °C higher than that under mixing ventilation and 2.0 °C higher than that under displacement ventilation. This result indicates that stratum ventilation could provide satisfactory thermal comfort level to rooms of temperature up to 27 °C. The energy saving attributable to less ventilation load alone is around 12% compared with mixing ventilation and 9% compared with displacement ventilation. PRACTICAL IMPLICATIONS: The confirmation of the significantly elevated thermal neutral temperature can have a number of implications for both thermal comfort in an air-conditioned room and energy consumption of the associate air-conditioning system. With respect to the former, it provides scientific basis for the feasibility of elevated room temperatures, and with respect to the latter, it reveals considerable potentials for energy saving.     

Application potential of solar air-conditioning systems for displacement ventilation

Solar air-conditioning can have higher application potential for buildings through the strategy of high temperature cooling. In recent years, displacement ventilation (DV), which makes use of the indoor rising plumes from the internal heat gains, provides a more effective supply air option than the traditional mixing ventilation (MV) in terms of both thermal comfort and indoor air quality. As it is possible to raise the supply air temperature to 19 °C for DV, it would enhance the competitive edge of the solar air-conditioning against the conventional vapour compression refrigeration. Through dynamic simulation, a solar-desiccant-cooling displacement ventilation system (SDC_DV) was developed for full-fresh-air provision, while a solar-hybrid-desiccant-cooling displacement ventilation system (SHDC_DV) for return air arrangement. The latter was further hybridized with absorption chiller (AB) to become SHDC_AB_DV, or adsorption chiller (AD) to be SHDC_AD_DV, in order to be wholly energized by the solar thermal gain. Benchmarked with the conventional system using MV, the SDC_DV had 43.3% saving in year-round primary energy consumption for a typical office in the subtropical climate; the SHDC_AB_DV had 49.5% saving, and the SHDC_AD_DV had 18.3% saving. Compared with their MV counterparts, the SDC_DV, the SHDC_AB_DV and the SHDC_AD_DV could have 42.4%, 21.9% and 30.3% saving respectively.     

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。     

置换通风下的湿环境研究

利用CFD方法对一个典型置换通风办公室的湿环境进行了模拟研究，结果表明空间内的湿度呈分层梯度分布，明显区别于混合通风室内湿度一致的特点，与现有实验结果得出的规律一致。置换通风系统的这一特点，有利于对空调空间进行有效的湿度控制和空调系统的节能。     

置换通风与混合送风供冷季运行能耗比较

根据置换通风和混合送风设计及运行的特点，以DeST为模拟工具，分析了北京某写字楼分别采用置换通风和混合送风方式供冷季空调系统的运行情况，讨论了两种送风方式在定风量或变风量运行时系统的逐时能耗及在室外新风利用上的特点。结果表明，置换通风比混合送风节省10％以上的运行费用。     

Ceiling mounted personalized ventilation system in hot and humid climate—An energy analysis

This study is to evaluate energy saving potential of ceiling mounted personalized ventilation (PV) system in conjunction with background mixing ventilation compared with mixing ventilation system alone and with mixing ventilation system when occupants are provided with individually controlled desk fans for generating additional air movement at each desk. Control strategy applied includes different number of personalized ventilation air terminal devices used and different PV airflow rates supplied. Energy calculation is based on design conditions in Singapore, representing a hot and humid climate. The results reveal that increasing room temperature can save cooling energy when the combination of PV with ceiling mounted personalized ventilation nozzles and background mixing ventilation is used. In this case the energy for transport of air increases but the total energy decreases, i.e. energy can be saved due to elevated room temperature. Comparing with mixing ventilation plus desk fans, ceiling mounted personalized ventilation cannot only realize better cooling effect but also decrease the total energy consumption.     

夏热冬暖地区某开敞式大空间建筑的节能改造技术分析

为了探讨夏热冬暖地区开敞式大空间建筑的节能改造措施,以广州市某实际工程为例,应用Fluent软件,对自然通风、置换通风、遮阳、屋顶淋水降温的节能效果进行了定性分析,并应用DeST软件模拟了全年能耗。分析了自然通风与空调系统联合工作时的室内温度和速度场,并给出了室内温湿度的实测数据。结果表明:在该工程中,自然通风、置换通风、遮阳挡板和屋面淋水技术可明显改善室内热环境,同时降低建筑能耗;下沉式地面有利于增强室内置换通风效果;通过采用被动节能技术合理设计后,建筑节能率达61.9%。     

Experimental investigation of heat transfer during night-time ventilation

Night-time ventilation is seen as a promising approach for energy efficient cooling of buildings. However, uncertainties in the prediction of thermal comfort restrain architects and engineers from applying this technique. One parameter essentially affecting the performance of night-time ventilation is the heat transfer at the internal room surfaces. Increased convection is expected due to high air flow rates and the possibility of a cold air jet flowing along the ceiling, but the magnitude of these effects is hard to predict. In order to improve the predictability, heat transfer during night-time ventilation in case of mixing and displacement ventilation has been investigated in a full scale test room. The results show that for low air flow rates displacement ventilation is more efficient than mixing ventilation. For higher air flow rates the air jet flowing along the ceiling has a significant effect, and mixing ventilation becomes more efficient. A design chart to estimate the performance of night-time cooling during an early stage of building design is proposed.     

置换通风的发展及研究现状

基于置换通风舒适、健康和节能的显著特点,本文回顾了置换通风的发展历程,从室内空气品质和节能等方面阐述了国内外置换通风的研究现状。气流组织、热舒适性和污染物分布是影响置换通风室内空气品质的主要因素,因而论文主要从置换通风的两个显著特性：热力分层和垂直温度梯度的角度讨论了室内热舒适性影响因素和研究现状,从颗粒和气体污染物的分布情况论述污染物对室内空气品质的影响,根据置换通风的气流特性,提出可以把室内污染物分为热源和冷源污染物进行研究;最后简要介绍了置换通风节能的情况和优势。     

Energy-saving strategies with personalized ventilation in cold climates

In this study the influence of the personalized supply air temperature control strategy on energy consumption and the energy-saving potentials of a personalized ventilation system have been investigated by means of simulations with IDA-ICE software. GenOpt software was used to determine the optimal supply air temperature. The simulated office room was located in a cold climate. The results reveal that the supply air temperature control strategy has a marked influence on energy consumption. The energy consumption with personalized ventilation may increase substantially (in the range: 61-268%) compared to mixing ventilation alone if energy-saving strategies are not applied. The results show that the best supply air temperature control strategy is to provide air constantly at 20 °C. The most effective way of saving energy with personalized ventilation is to extend the upper room operative temperature limit (saving up to 60% compared to the reference case). However, this energy-saving strategy can be recommended only in a working environment where the occupants spend most of their time at their workstation. Reducing the airflow rate does not always imply a reduction of energy consumption. Supplying the personalized air only when the occupant is at the desk is not an effective energy-saving strategy.     

置换通风的热压驱动增益模式可行性研究

通过对传统下置置换通风系统特点的研究,提出了一种新的下置置换通风空调系统——由太阳能烟囱为新系统中送风提供热压动力,使送风具有传统下置置换通风系统的送风特点,室内工作区具有良好的空气品质。同时通过数值模拟的方法分析并比较了传统下置置换通风系统与新系统。结果表明:该系统能解决传统置换通风不舒适的吹风感和竖直温差大的问题;相对于传统下置置换通风,新系统还具备节能和环保特性;烟囱具有良好的自我调节性能。     

Air flow rates and energy saving potential in schools with demand-controlled displacement ventilation

Demand control is particularly energy efficient and reliable when combined with displacement ventilation (DCDV). In order to investigate how much DCDV in practice reduce the ventilation air volumes and the energy demand, two Norwegian schools with CO₂-sensor based demand controlled displacement ventilation (DCDV-CO₂), Jaer School and Mediå School, are analysed and compared with traditional constant air volume (CAV) mixing ventilation. During daytime operation with normal school activity, DCDV-CO₂ reduces the ventilation air volume by 65–75% in both schools compared to CAV. For Mediå School, both the airflow rates and the energy performance were analysed through measurements and use of a detailed, calibrated simulation model. The analysis period was 11–17 November, 2002. It was found that during this week, DCDV-CO₂ daytime operation weekdays reduce the total heating energy demand by 21%, the amount of unrecovered heat in the exhaust ventilation air by 54%, and the average airflow rate by 50%. Presuming constant fan efficiency it was also found that DCDV-CO₂ daytime operation weekdays reduce the fan energy consumption by 87% the analysed week.     

A comparison of winter pre-heating requirements for natural displacement and natural mixing ventilation

In winter, natural ventilation can be achieved either through mixing ventilation or upward displacement ventilation (P.F. Linden, The fluid mechanics of natural ventilation, Annual Review of Fluid Mechanics 31 (1999) pp. 201-238). We show there is a significant energy saving possible by using mixing ventilation, in the case that the internal heat gains are significant, and illustrate these savings using an idealized model, which predicts that with internal heat gains of order 0.1 kW per person, mixing ventilation uses of a fraction of order 0.2-0.4 of the heat load of displacement ventilation assuming a well-insulated building. We then describe a strategy for such mixing natural ventilation in an atrium style building in which the rooms surrounding the atrium are able to vent directly to the exterior and also through the atrium to the exterior. The results are motivated by the desire to reduce the energy burden in large public buildings such as hospitals, schools or office buildings centred on atria. We illustrate a strategy for the natural mixing ventilation in order that the rooms surrounding the atrium receive both pre-heated but also sufficiently fresh air, while the central atrium zone remains warm. We test the principles with some laboratory experiments in which a model air chamber is ventilated using both mixing and displacement ventilation, and compare the energy loads in each case. We conclude with a discussion of the potential applications of the approach within the context of open plan atria type office buildings.     

排除人员活动区内人体释放污染物的有效通风方式--置换通风

分析了置换通风和混合通风的原理。基于气流分布特性和双层模型理论，比较了这两种通风方式的排污能力。对办公室、会议室及体育馆置换通风系统的通风效率进行了实测。结合人体释放污染物的气流运动特性，指出以排除人员活动区内人体释放污染物为目的时，置换通风较混合通风更为有效。     

置换通风的通风效率及其微热环境评价

讨论了通风有效性与空气分布特性的相关性，分析了混合通风（上送下回）通风效率低于置换通风效率的原因。根据大量的实验资料，分析提出了影响通风效率的若干复合因素，得出了预测置换通风效率的经验式。经综合人体舒适性实验，说明置换通风微热环境能提供居住者整体舒适感，而在肢体下部风感不满意率小于１５％     

某报告厅空调系统的设计及其能耗分析

介绍了西安某办公楼报告厅空调系统的设计。分别应用置换通风与混合通风两种通风方式，在室外和室内设计参数相同的情况下，充分比较了它们在送风量、新风量、能耗以及室内空气品质的不同。结果表明在某些应用场合，置换通风在空气品质提高和能耗降低上有明显的优势，同时这种优势不以牺牲热舒适性为代价，因此建议使用置换通风系统。     

通风对住宅夏季空调能耗的影响

采用数值模拟方法,对一栋住宅分别位于北京、上海和广州时,不同通风量和不同通风模式下的夏季空调能耗进行了计算分析.结果表明,位于北京时,1.0h-1是最节能的通风换气次数,位于上海时,0.4h-1是最节能的通风换气次数,位于广州时,空调能耗随着换气次数的增加而线性增大,在这三个地区,间歇机械通风都有利于减少空调能耗.     

过饱和置换通风在纺织厂布机车间的应用探讨

针对纺织厂布机车间高湿度要求的特点,提出了过饱和置换通风的通风方式,经空调室处理过的空气携带充足的雾滴,从车间地面下以较小的速度送入室内,送风量小、相对湿度大、起尘量少,较适合于纺织厂布机车间,能达到较好的节能效果。     

Evaluating the commercial airliner cabin environment with different air distribution systems

Ventilation systems for commercial airliner cabins are important in reducing contaminant transport and maintaining thermal comfort. To evaluate the performance of a personalized displacement ventilation system, a conventional displacement ventilation system, and a mixing ventilation system, this study first used the Wells‐Riley equation integrated with CFD to obtain the SARS quanta value based on a specific SARS outbreak on a flight. This investigation then compared the three ventilation systems in a seven‐row section of a fully occupied, economy‐class cabin in Boeing 737 and Boeing 767 airplanes. The SARS quanta generation rate obtained for the index patient could be used in future studies. For all the assumed source locations, the passengers’ infection risk by air in the two planes was the highest with the mixing ventilation system, while the conventional displacement ventilation system produced the lowest risk. The personalized ventilation system performed the best in maintaining cabin thermal comfort and can also reduce the infection risk. This system is recommended for airplane cabins.