自然通风环境下办公建筑中庭空间热舒适性模糊优化研究

：随着绿色建筑设计理念深入人心,办 公建筑的中庭空间因其特有空间特质受到越来 越多的关注。通常办公中庭空间中的节能性与热 舒适性是一对矛盾体,而自然通风作为被动节能 技术之一,不仅能够促进中庭空间的内外空气 循环,改善室内空气质量,而且降低能耗和提升 热舒适性,较好地解决这一矛盾。以江雅园办公 楼中庭空间为案例进行研究,从中庭屋顶形态、 中庭高度及进风口开启方式三个变量因素出发, 引用模糊评估方法寻找出中庭空间自然通风热 舒适性最佳方案,结论显示在多个组合方案中 斜屋顶形态+进风口全部开启的方案热舒适性最 佳,同时也证明屋顶形态与通风方式的变化对自 然通风舒适性的影响较大,而中庭空间高度的变化对自然通风舒适性影响较小。本研究希望建立一套以风速和温度为评价指标的模糊体系,为自 然通风的热舒适性的评价提供一种客观的评估手段,从而为方案阶段的中庭空间设计提供一种 有效的优化方法。     

Dynamic evaluation of airflow rates for a variable air volume system serving an open-plan office

In a typical air-conditioned office, the thermal comfort and indoor air quality are sustained by delivering the amount of supply air with the correct proportion of outdoor air to the breathing zone. However, in a real office, it is not easy to measure these airflow rates supplied to space, especially when the space is served by a variable air volume (VAV) system. The most accurate method depends on what is being measured, the details of the building and types of ventilation system. The constant concentration tracer gas method as a means to determine ventilation system performance, however, this method becomes more complicated when the air, including the tracer gas is allowed to recirculate. An accurate measurement requires significant resource support in terms of instrumentation set up and also professional interpretation. This method deters regular monitoring of the performance of an airside systems by building managers, and hence the indoor environmental quality, in terms of thermal comfort and indoor air quality, may never be satisfactory. This paper proposes a space zone model for the calculation of all the airflow parameters based on tracer gas measurements, including flow rates of outdoor air, VAV supply, return space, return and exfiltration. Sulphur hexafluoride (SF6) and carbon dioxide (CO2) are used as tracer gases. After using both SF6 and CO2, the corresponding results provide a reference to justify the acceptability of using CO2 as the tracer gas. The validity of using CO2 has the significance that metabolic carbon dioxide can be used as a means to evaluate real time airflow rates. This approach provides a practical protocol for building managers to evaluate the performance of airside systems.     

Field Measurements of Ventilation and Ventilation Effectiveness in an Office/Library Building

Mechanical ventalation system performance involves the provision of adequate amuunts of outdoor air, uniform distribution of ventilation air within the occupied space, and the maintenance of thermal comfort. Standard measurement techniques exist to evaluate thermal comfort and air change rates in mechanically ventilated buildings; procedures to evaluate air distribution or ventilation effectiveness in the field are still being developed. This paper presents measuremetlts of air change rates and ventilation effectivenes in an office/library building in Washington, DC. The tracer gas decay technique was used to measure whole building air change rates. The air change rates during the measurement period were essentially constant at about 0.8 air changes per hour, somewhat below the design specification and above the minimum recmmmded in ASHRAE Standard 62-1989. Ventilation effectiveness was investigated at several locations within the building through the measurement of local tracer gas decay rate and mean local age of air. The ventilation effectiveness measurements serve as an investigation of the applicability of the m e a s u r r n procedures employed, providing insight into the measurement issue of establishing initial conditions, the spatial variation in test results within a building, and the repeatabildy between tests. The results of the ventilation effectiveness meusurements are consistent with good distrhtion of the outdoor air by the ventilation system and good mixing within the occupied space.     

Using spatial indicators to predict ventilation and energy performance-correlation analysis for an apartment building in five Chinese cities

In the early design stages, architects are in constant search of a design direction that can determine the success or failure of the final design. However, in real design practice, most of the prediction methods for building performances, in this paper energy and thermal comfort, are utilised in the later design stages. Spatial configuration is one of the most important issues for architectural design in the early design stage. This study investigates the correlations between the spatial indicators connected with architectural design and the building physics indicators ventilation performance and energy performance. The main objective is to explore the potential of applying spatial indicators using space syntax to predict ventilation performance and energy performance in order to support architects for the evaluation of their concepts and schemes in early design stages. The layout of a high-rise apartment in China in five different cities is chosen as a case study. The results show that the selected three indicators: connectivity value, air change rate and annual cooling saving ratio are linearly correlated, not just at building level but also at room level. R², the correlation coefficient of determination, is between 0.53 and 0.90 (except for the case of Chongqing at building level).     

大空间室内空气质量的空间流动影响因子分析

对兰州市某大型超市的热环境测试与空气质量问卷调查结果显示该超市存在严重空气质量问题。本文首先提出了在超市这样的大空间应采取传统通风与个性化通风相结合的措施,而后应用空间流动影响因子理论对个性化通风中气流组织形式进行了选择并对其除污效果作了定性分析。研究方法及结论对于大空间中点源污染问题的局部处理以及通风空调系统的设计、运行管理等有一定的指导意义。     

Numerical study of the influences of different patterns of the building and green space on micro-scale outdoor thermal comfort and indoor natural ventilation

Citizens could enjoy a healthy and comfortable living environment if outdoor thermal comfort and sufficient natural ventilation are available in their dwellings. In this paper, numerical studies were performed with the Simulation Platform for Outdoor Thermal Environment (SPOTE) to investigate: (1) the thermal environment and pedestrian thermal comfort of the occupants in the open space with different patterns of the building and green space; (2) the wind pressures on the building facades and the natural ventilation rate of these buildings. The conclusions are summarized as follows: (1) it has been observed that the long facades of building and green space, which are parallel to the prevailing wind direction, can accelerate horizontal vortex airflow at the edges where such airflow could strengthen the convective exchange efficiency of hot air in low altitude and cold air in high altitude, and can obtain thermal comfort and sufficient natural ventilation at the pedestrian level; (2) after a series of simulations and comparisons, the configuration in which buildings are grouped in staggered layout with a centralized green space can provide better ventilation conditions and suitable air movement as a result of attenuated revised standard effective temperature (SET*). This configuration is regarded as the optimum pattern of the building and green space.     

An investigation of naturally ventilated teaching spaces with windcathers in secondary school where site is constrained by noise and air pollution

Built environment consumes the bulk of the UK’s fossil fuel. Schools account for 15% of the public sector’s carbon emissions. Energy efficient building design can play a vital role in achieving the national carbon emission reduction target of 80% by 2050. Natural and mixed mode ventilation is at the forefront of suggested energy efficient strategies for reducing carbon emissions from schools while maintaining good indoor air quality and thermal comfort. However, it is challenging to naturally ventilate many urban school buildings through side openings because of high noise and particulate air pollution. An alternative strategy, such as multi floor operation of windcatchers was assessed in this research as a sole source of fresh air in teaching spaces. Dynamic thermal simulation (DTS) and computational fluid dynamics (CFD) simulations assessed the performance of the adopted natural ventilation (NV) strategy in meeting the approved requirements for fresh air, indoor air quality (IAQ) and summertime overheating. Simulation results show that it is challenging to meet approved guidelines on air quality and thermal comfort, only when windcatchers are employed for ventilation purpose. However, fan assisted ventilation in conjunction with windcatchers provided satisfactory results. Detailed performance assessments using CFD seem desirable to validate DTS based findings.     

Numerical and experimental study of velocity and temperature characteristics in a ventilated enclosure with underfloor ventilation systems

Airflow and temperature distributions in an enclosure with heat sources ventilated by floor supply jets with floor or ceiling air exit vents were investigated using experimental and numerical approaches. These ventilation configurations represent the floor return or the top return underfloor ventilation systems found in real applications. Experiments and numerical simulations were performed on a full-sized environmental chamber. The results reveal that the temperature stratification in the enclosure highly depended on the thermal length scale of the floor supply jets. When the thermal length scale of the supply jet was >1, temperature stratification was minor for all tested heat densities and air distribution methods. Significant vertical temperature gradients occurred when the jet thermal length scale was <1. Changes in air distribution methods also became significant for temperature stratification at small supply jet thermal length scales. Temperature stratification also affected the terminal height of the momentum-dominant region of the vertical buoyant supply jets. The applicability of these results to underfloor ventilation design was also discussed. PRACTICAL IMPLICATIONS: In designing underfloor ventilation systems, supply jet conditions and heat load density have to be considered to avoid thermal discomfort because of excessive temperature stratifications. This study demonstrated, by both numerical simulations and experiments, that thermal length scale can be used as a design indicator to predict thermal stratifications under a floor return and a top return underfloor ventilation setting.     

The influence of environmental and geometrical factors on air-ground tube heat exchanger energy efficiency

More and more efficient solutions of thermal insulation of buildings result in an increasing role of ventilation in the energy balance of buildings. This leads to a necessity for seeking unconventional heat sources, as well as development of the exhaust air heat recovery methods. The use of heat accumulating potential of the ground perfectly fits into this trend, allowing natural pre-heating and pre-cooling of the inlet air. There appears to be very limited research and published data on their thermal performance in Poland. This paper introduces a developed method of air-ground heat exchanger (AGHX) performance evaluation together with its validation and research results of conducted simulation. The AGHX model (based on a quasi 3D finite elements method) allows analysis of energy performance dependence on a wide range of parameters including AGHX geometrical configuration, mode of operation and environmental factors. The simulation results indicate that the analyzed parameters in various degrees affect the thermal efficiency of AGHX; various is also the nature of their impact. For some of them it is possible to set a value to maximize heat or cold yield (pipe diameter and placement depth, number of parallel pipes, bypass system, soil thermo-physical parameters, ground area shading and ground surface cover). In other cases, the influence of parameters has an asymptotic nature for which the maximum heating or cooling efficiency is achieved for parameter values tending to infinity (pipe length and distance between parallel pipes).     

Predicting integrated thermal and acoustic performance in naturally ventilated high-rise buildings using CFD and FEM simulation

The study of ventilation windows for both natural ventilation and noise mitigation has drawn significant attention recently. This paper presents the numerical approaches to analyse the integrated thermal and acoustical performance of ventilation windows, for a residential building in tropical climate which employs double-layer noise mitigation window for natural ventilation. Given a set of outdoor wind conditions, the distributions of indoor flow and temperature fields are simulated using Computational Fluid Dynamics (CFD) model. The thermal comfort is evaluated using statistical Predicted Mean Vote (PMV) method. For the acoustic performance, noise radiation from road traffic is assumed as the noise source, and the sound insulation of building façade is simulated using Finite Element Method (FEM). From the simulation results, it is found that the thermal satisfaction response is closely related to the inlet wind temperature and speed, and the window opening size greatly affects the ventilation performance. From the case study in Singapore, during certain season, day/night time and with sufficient wind flow, the ventilation window can provide enough fresh air, maintain adequate thermal comfort and quiet acoustic environment for the occupants. The numerical approaches presented in this paper are applicable to general window design studies, and the simulation findings can be incorporated into green building planning. The advantages of using simulation approaches are highlighted and their limitations are discussed.     

Ventilation and energy performance of partitioned indoor spaces under mixing and displacement ventilation

Large variation in indoor air quality (IAQ) and thermal comfort can occur in partitioned office spaces due to heterogeneous air mixing. However, few published studies examined IAQ, thermal comfort, and energy performance of partitioned occupied spaces, which are commonly found in today’s buildings. The objective of this study is to evaluate indoor environmental quality and air conditioning performance of a partitioned room under two typical ventilation modes: (1) mixing ventilation and (2) displacement ventilation. For a total of six representative air-conditioning scenarios, three-dimensional computational fluid dynamics (CFD) simulations are performed to examine temperature distribution, ventilation effectiveness, energy consumption, and local thermal comfort for two partitioned spaces. Simulation results indicate that temperature distribution in a partitioned room is a strong function of ventilation strategy (mixing vs. displacement), but marginally affected by diffuser arrangements. Local age-of-air (air freshness) significantly varies with both diffuser arrangement and ventilation strategy. Regarding energy consumption, displacement ventilation can achieve an indoor set-point temperature in the partitioned spaces about two times faster than mixing ventilation. Under mixing ventilation, the time to achieve a set-point temperature was notably reduced when each partitioned space is served by its own diffuser. For the same supply airflow rate, displacement ventilation can generate local draft risk at ankle level, while mixing ventilation may result in a draft sensation in wider areas around an occupant. Overall, the results suggest that mixing ventilation system can save energy if each partitioned zone is served by its own diffuser such as a multi-split air conditioning. However, when multiple partitioned zones are served by only one diffuser, displacement ventilation is more energy-efficient and can achieve higher ventilation effectiveness than mixing ventilation.     

Calculation of the thermal response of buildings by the total thermal time constant method

This paper describes the theoretical development and experimental proof of the total thermal time constant (TTTC) method for calculation of the thermal response of buildings. The output is obtained in the form of time sequences of temperature, under given time-variation of internal heating load, or in the form of time dependent heating (or cooling) loads, under given patterns of internal temperature variation in time.TTTC method considers ventilation conditions, internal heating, metabolic heat production, cooling, solar radiation absorption on, and longwave i.r. radiation loss from, the external surfaces, solar radiation penetration through windows and the external air temperature and humidity variations in time. The main feature of this method is that each component of the building is represented here, as a heat transfer path, only by two easy to calculate numbers: the thermal resistance and the TTTC (this includes thermal resistances and heat capacities and their relative position in the heat transfer path, including partitions and ceilings) [1–3]. The two parameters characterize the influence of the element on the thermal response of a building as a whole.Experimental demonstration of the accuracy of the TTTC method in computing the thermal response of buildings is presented and compared with measured temperature time patterns both in models and actual buildings under various external conditions. The method is useful not only for the thermal design of buildings and the selection of building materials, but also for the design of passive methods of climatization, e.g. by the use of solar radiation for heating, and conversely, the cooling of a structure by longwave radiation loss (to the outer space through the atmosphere) and by ventilation. Thermal storage and insulation properties are also considered.     

大空间建筑室内气流组织数值模拟与舒适性分析

分别对采用百叶侧送侧回、喷口侧送侧回、散流器顶送下回、分层空调、置换通风方式的大空间建筑空调室内气流的速度场和温度场进行了数值模拟,并对其结果进行了实验验证。根据ADPI指标对这几种送回风方式进行了热舒适性评价.结果表明,分层空调和置换通风是大空间建筑中较好的气流组织方式。     

Energy conservation effect of new HVAC system for condominiums with solar collectors integrated with the balcony handrail

Energy consumption in Japan's houses has been increasing rapidly over the past decades. Furthermore, installation of 24-h ventilation systems in houses became mandatory last year, which will probably increase the heating, ventilation, and air conditioning (HVAC) energy consumption in Japan's houses. Regardless of these situations, natural energy utilization to reduce HVAC energy has not spread, especially in condominiums in Japan. In this study, we propose a new HVAC system for condominiums that makes use of solar heat, outdoor cool air by integrating elements in condominiums such as the balcony handrail, the 24-h ventilation system, and under-floor space. As a first step in the development of this system, we carried out experiments and computational fluid dynamics (CFD) studies on a solar heat collector integrated with the balcony handrail to determine its specification and to obtain information on its heat collection performance. As a second step, we calculated dynamic thermal load on a model condominium to evaluate the energy-saving performance and thermal comfort of the proposed system. The calculation results show that the proposed system has a high performance, both for energy saving and thermal comfort.     

室内环境与自然通风

通风的目的是保证室内良好的空气品质,采用自然通风方式是生态建筑设计的重要内容,通过良好的自然通风组织减少对空调的利用,并及时将污染物排出,改善室内空气品质。在热舒适方面,自然通风形成的室内热环境有利于人体舒适性。分析了生态建筑中自然通风对室内空气品质与室内热环境产生的影响,探讨了利用自然通风来改善建筑的室内环境的效果和策略,并提出了相应的设计方法。研究结果表明:组织合理的自然通风,可以有效地改善室内的空气品质和室内热环境。     

基于下送中回气流组织Block模型内壁面对流传热系数的讨论

以大空间缩尺模型实验室为研究对象,基于Block模型,采用2种常数法及3种温差法的表面对流传热系数取值方法,计算室内在下送中回气流组织下的空气垂直温度分布。通过与实验值的比较发现,对流传热系数温差法计算结果优于常数法。其中一种对流传热系数温差法得到的空气垂直温度与实测温度的误差最小。     

Multi-objective optimization of impinging jet ventilation systems: Taguchi-based CFD method

This paper presents a Taguchi method-based approach that can optimize the operating performance of impinging jet ventilation (IJV) systems with limited computational fluid dynamics (CFD) simulation results. The Taguchi optimization calculation finds the best operating design for the weighted overall objective function as a presenter of the multi-objective function problem. The method is used to optimize the operating characteristics of an IJV system considering the factors of supply air temperature, level of the return air vent and percentage of the air exhausted through the ceiling to achieve an overall best performance of thermal comfort, indoor air quality (IAQ) and system energy performance as the objective functions. The study indicates the contribution percentage for each factor in each objective function. The level of the return air vent, the supply air temperature, and the percentage of air exhausted through the ceiling have a contribution of 35.8%, 28.5%, and 35.8% in the objective functions, respectively. Based on the results, the best performance of the IJV system happens when the inlet air temperature is 18 °C, the height of the return air vent is 2 m above the floor, and the percentage of air exhausted through the ceiling is 22.5%.     

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.     

圭亚那国际会议中心通风空调设计

根据工程所在地的客观条件,确立了室内热舒适标准和“遮阳、围护结构隔热散热—自然通风—机械通风—单冷型空调”的热舒适设计原则,并采用了适应当地气候条件的技术,设置了内外庭院和灰空间在建筑周围形成生态微气候,通透的建筑形式使大部分房间可以采用自然通风满足人体热舒适要求,大幅度减少了空调应用范围和使用时间,降低了不可再生能源的消耗量。     

Hybrid ventilation for low energy building design in south China

Buildings and their related activities are responsible for a large portion of the energy consumed in China. It is therefore worthwhile to investigate methods for improving the energy efficiency of buildings. This paper describes a low energy building design in Hangzhou, south China. A hybrid ventilation system which employs both natural and mechanical ventilation was used for the building due to the severity of the climate. The passive ventilation system was tested using computational fluid dynamics (CFD) and the results showed that, in the mid-seasons, natural ventilation for the building is viable. The likely thermal performance of the building design throughout the year was evaluated using dynamic thermal simulation (DTS) with local hourly standard weather data. It is evident from the modelling results that the hybrid ventilation system is a feasible, low energy approach for building design, even in sub-tropical climates such as south China.