A new integrated design tool for naturally ventilated buildings part 1: ventilation model

In many cases natural ventilation may be sufficient to ensure acceptable comfort levels in occupied buildings. In these cases installation of energy-intensive active environmental control systems will not be necessary. This will result in considerable energy and cost savings and also indirectly in a reduced burden on the environment, since the use of energy is always associated with the production of waste materials.

This paper describes the development of a new model to predict natural ventilation flow rates in buildings. The model employs a flow network where openings are represented by non-linear flow resistances. It accounts for both wind-induced pressures and pressures due to thermal forces. The model draws on a healthy balance between purely theoretical equations and empirical data. Simplified equations are derived through a synthesis of measured data obtained in boundary layer wind tunnel tests as well as from the literature. Tracer gas measurements show a good comparison between measured and predicted ventilation rates.

The implementation of the new model into an integrated design tool for naturally ventilated buildings is discussed in Part 2 of this paper.     

A new integrated design tool for naturally ventilated buildings part 2: integration and application

A major problem in the design of naturally ventilated buildings is the complicated interaction between the flow rates and the indoor air temperatures. The natural ventilation flow rates are influenced by the indoor air temperatures while the indoor air temperatures are in turn influenced by the flow rates. A good design tool should therefore consist of a flow model to determine the flow rates and a thermal to determine the indoor air temperatures. These two should be solved simultaneously in an integrated manner. Existing design tools lack the ability to address this.

This paper describes the implementation and verification of the new flow model derived in Part 1 of this paper into such an integrated natural ventilation design tool. The thermal model is based on existing theory that has been verified extensively. An iterative solution algorithm is employed to ensure simultaneous solution of these two models.

Continuous tracer gas and temperature measurements show that the integrated tool can be used with confidence in the design of naturally ventilated buildings. A case study is also presented that illustrates how the new tool can be used successfully to optimize the design of a naturally ventilated factory building.     

Facade design optimization for naturally ventilated residential buildings in Singapore

Parametric studies of facade designs for naturally ventilated residential buildings in Singapore were carried out to optimize facade designs for better indoor thermal comfort and energy saving. Two criteria regarding indoor thermal comfort for naturally ventilated residential buildings are used in this study. To avoid the perception of thermal asymmetry, temperature difference between mean radiant temperature and indoor ambient air temperature should be less than 2 °C [F.A. Chrenko, Heated ceilings and comfort. J. Inst. Heat. Ventilating Eng. 20 (1953) 375–396; F.A. Chrenko, Heated ceilings and comfort. J. Inst. Heat. Ventilating Eng. 21 (1953) 145–154]. Thermal comfort regression model for naturally ventilated residential buildings in Singapore was used to evaluate various facade designs either. Facade design parameters: U-values, orientations, WWR (window to wall ratio) and shading device lengths are considered in the investigation. The building simulation results for a typical residential building in Singapore indicated that the U-value of facade materials for north and south orientations should be less than 2.5 W/m² K and the U-value of facade materials for north and south orientations should be less than 2 W/m² K. From the coupled simulation results, it was found that the optimum window to wall ratio is equal to 0.24. Optimum facade designs and thermal comfort indexes are summarized for naturally ventilated residential buildings in Singapore.     

Thermal analysis of naturally ventilated buildings

A simplified electric analogue method to analyse the thermal performance of naturally ventilated buildings is presented. One of the main features of the method is that empirical constants in some equations account for typical rates of natural ventilation in conventional buildings. Another feature is that a very high degree of lumping is attained by using a special calculation procedure to estimate effective capacity values of building elements. The method is therefore extremely easy to use. Predictions are compared with measurements. The comparison is acceptable for design purposes.     

Artificial neural networks and naturally ventilated buildings

The author found that the results obtained were reliable and indicates that neural networks can be used as a predictor for investigating window opening configurations to study the effects on interior air motion. Further study is needed in the development of the database to cover wider architectural parameters and the implementation of new types of network is also needed, as well as the need to consider variation spatial coefficients more fully.     

Thermal comfort for naturally ventilated residential buildings in Harbin

This field study was conducted during summer 2009 in Harbin, northeast of China in order to investigate human responses to the thermal conditions in naturally ventilated residential buildings in cold climate. We visited 257 families in six residential communities and collected 423 sets of physical data and subjective questionnaires. The neutral temperature is 23.7 °C, with the clothing insulation of 0.54 clo. The neutral temperature in Harbin is lower than neutral temperatures in warm climates by others, which is in accordance with the thermal adaptive model. 80% of the occupants can accept the air temperature range of 21.5-31.0 °C, which is wider than the summer comfort temperature limits by the adaptive model. The preferred temperature range fell between 24.0 °C and 28.0 °C. About 57.9% of the subjects voted “no change” with the humid range of 40% and 70%. 61.5% of the occupants voted “no change” with the air velocity within the range of 0.05-0.30 m/s. In summer, occupants preferred air velocity of lower than 0.25 m/s even at higher indoor temperature, which is different from the other field studies. The Harbin occupants in naturally ventilated dwellings can achieve thermal comfort by operable windows instead of running air-conditioners.     

Artificial neural networks and naturally ventilated buildings

The author found that the results obtained were reliable and indicates that neural networks can be used as a predictor for investigating window opening configurations to study the effects on interior air motion. Further study is needed in the development of the database to cover wider architectural parameters and the implementation of new types of network is also needed, as well as the need to consider variation spatial coefficients more fully.     

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.     

Empiricism in the thermal analysis of naturally ventilated buildings

Three thermal analysis methods with different degrees of empiricism are quantitatively investigated regarding the ease of use, efficiency, accuracy and redundancy of generated information. From this investigation it is concluded that, for design purposes, a sensitive interplay between experiment and theory can often lead to an optimum method.     

Thermal comfort: use of controls in naturally ventilated buildings

A field study of the thermal comfort of workers in natural ventilated office buildings in Oxford and Aberdeen, UK, was carried out which included information about use of building controls. The data were analysed to explore that what effect the outdoor temperature has on the indoor temperature and how this is affected by occupants’ use of environmental controls during the peak summer (June–August). The proportion of subjects using a control was related to indoor and outdoor temperatures to demonstrate the size of the effect. The results suggest that the use of controls is also related to thermal sensation and their appropriate use is a significant part of adaptive behaviour to modify the indoor thermal conditions. The results make it possible to predict the effect of temperature on the ventilation rate in naturally ventilated buildings.     

Comparison of thermal comfort algorithms in naturally ventilated office buildings

With the actual environmental issues of energy savings in buildings, there are more efforts to prevent any increase in energy use associated with installing air-conditioning systems. The actual standard of thermal comfort in buildings ISO 7730 is based on static model that is acceptable in air-conditioned buildings, but unreliable for the case of naturally ventilated buildings. The different field studies have shown that occupants of naturally ventilated buildings accept and prefer a significantly wider range of temperatures compared to occupants of air-conditioned buildings. The results of these field studies have contributed to develop the adaptive approach. Adaptive comfort algorithms have been integrated in EN15251 and ASHRAE standards to take into account the adaptive approach in naturally ventilated buildings. These adaptive algorithms seem to be more efficient for naturally ventilated buildings, but need to be assessed in field studies. This paper evaluates different algorithms from both static and adaptive approach in naturally ventilated buildings across a field survey that has been conducted in France in five naturally ventilated office buildings. The paper presents the methodology guidelines, and the thermal comfort algorithms considered. The results of application of different algorithms are provided with a comparative analysis to assess the applied algorithms.     

Thermal comfort in naturally ventilated buildings in hot-humid area of China

Human responses to thermal environments in naturally ventilated (NV) buildings in hot-humid area of China were systematically investigated in the present study. Thirty local inhabitants long-time living in NV buildings participated in the study and reported their thermal sensations and perceptions and adaptive behaviors while all physical and personal variables were collected. Based on a year-long survey, a close match of indoor physical variables and occupants’ clothing insulation with outdoor climate was found as an important feature of NV buildings. Integrated indices can capture more thermal contexts in the NV buildings in hot-humid area of China than simple indices. Thermal sensation was found to be a good linear function of SET* with the thermal neutrality of 25.4 °C and the 90% (80%) acceptable range of 23.5–27.4 °C (22.1–28.7 °C) in SET*. The adaptive evidences were obtained for clothing adjustment, window opening and using fan respectively and the modified PMV model was validated to be applicable in NV buildings in hot-humid area of China with an expectancy factor of 0.822. Comparisons with other field studies indicate that people can develop various human-environment relationships through thermal adaptation to local climate, resulting in different thermal neutral temperatures in various climates. The subjects in hot-humid area of China are more acclimated and tolerable with hot and humid environments and more uncomfortable and intolerable with cold environments while compared with those in temperate climates.     

Optimising the ventilation configuration of naturally ventilated livestock buildings for improved indoor environmental homogeneity

Due to the geometrical structure and ventilation configuration of naturally ventilated livestock buildings the animal occupied zone can experience large heterogeneities in ventilation efficiency. Ensuring a homogeneous indoor environment is important when designing naturally livestock buildings as producers should be confident that all animals are receiving the same environmental conditions, at least for the prevailing climate. Moreover, by including climate homogeneity in the building design process, the occurrence of high airspeeds in specific regions of a building can be reduced during windy outdoor conditions, thereby reducing the cold-stressing of animals in these regions. Therefore, it is desirable to know how to alter the geometrical features of a building in order to promote homogeneity in the indoor environment. In the present study, response surface methodology and computational fluid dynamics were used to develop predictive models that described the homogeneity of the indoor environment of a naturally ventilated livestock building as a function of its geometry and ventilation configuration. Three different eave opening conditions were chosen in order to improve the applicability of the developed response surfaces to practical situations encountered in Ireland. Results showed that for high to medium porosity eave opening conditions the environmental homogeneity was most sensitive to the building's roof pitch. However, when low porosity eave opening conditions were used the homogeneity was found to be highly sensitive to the sidewall height. Overall, this study found that modifying the building geometry has the greatest effect on environmental heterogeneity when the most restrictive eave opening condition was employed. It is also hoped that with the developed equations, a designer can subsequently select the best combination of design variables in order to achieve good uniformity in a naturally ventilated calf building.     

煤矿建筑中联合建筑的设计解析

阐述了煤炭工业矿井地面生产灯房、浴室、任务交代室联合建筑在实际设计中应注重考虑的重点功能,以及应该结合的规范、规定,做好联合建筑的设计,可在一定程度上提高矿井的生产效率,提高矿井的生产能力。     

Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55

Recently accepted revisions to ASHRAE Standard 55—thermal environmental conditions for human occupancy, include a new adaptive comfort standard (ACS) that allows warmer indoor temperatures for naturally ventilated buildings during summer and in warmer climate zones. The ACS is based on the analysis of 21,000 sets of raw data compiled from field studies in 160 buildings located on four continents in varied climatic zones. This paper summarizes this earlier adaptive comfort research, presents some of its findings for naturally ventilated buildings, and discusses the process of getting the ACS incorporated into Standard 55. We suggest ways the ACS could be used for the design, operation, or evaluation of buildings, and for research applications. We also use GIS mapping techniques to examine the energy-savings potential of the ACS on a regional scale across the US. Finally, we discuss related new directions for researchers and practitioners involved in the design of buildings and their environmental control systems.     

Architectural design of an advanced naturally ventilated building form

Advanced stack-ventilated buildings have the potential to consume much less energy for space conditioning than typical mechanically ventilated or air-conditioned buildings. This paper describes how environmental design considerations in general, and ventilation considerations in particular, shape the architecture of advanced naturally ventilated (ANV) buildings. The attributes of simple and advanced naturally ventilated buildings are described and a taxonomy of ANV buildings presented. Simple equations for use at the preliminary design stage are presented. These produce target structural cross section areas for the key components of ANV systems. The equations have been developed through practice-based research to design three large educational buildings: the Frederick Lanchester Library, Coventry, UK; the School of Slavonic and East European Studies, London, UK; the Harm A. Weber Library, Elgin, near Chicago, USA. These buildings are briefly described and the sizes of the as-built ANV features compared with the target values for use in preliminary design. The three buildings represent successive evolutionary stages: from advanced natural ventilation, to ANV with passive downdraught cooling, and finally ANV with HVAC support. Hopefully the guidance, simple calculation tools and case study examples will give architects and environmental design consultants confidence to embark on the design of ANV buildings.     

A study of the effectiveness of passive climate control in naturally ventilated residential buildings in Singapore

Singapore has the hot and humid climate throughout the year. Many passive climate control methods are adopted in the naturally ventilated residential buildings to help achieve thermal comfort and reduce the energy consumption of air-conditioning. A field measurement and computational energy simulations were conducted to examine the effectiveness of commonly used passive climate control methods for these buildings. The effect of building orientation, façade construction, special roof system and window shading device on indoor thermal environment and cooling load was studied. The surface temperature of external wall and indoor thermal environment was measured to analyze the façade thermal performance. The cooling load was simulated to evaluate the effectiveness of various passive climate methods. Using the special roof system as thermal buffer is the most efficient method to reduce the room cooling load.     

我国湿热地区自然通风建筑热舒适与热适应现场研究

在2008—2009年为期1年的广州某高校自然通风建筑现场调研的基础上,对23周共计921人次的调研数据在热环境、人体热反应及适应行为等方面进行了分析,得到了我国湿热地区典型自然通风建筑的室内热环境全年变化特征,获取了热感觉与标准有效温度的确定关系,验证了修正的PMV模型的适用性,分析得到我国湿热地区自然通风建筑的期望因子为0.8,同时获得了调整服装、开窗与使用风扇等适应行为的变化规律。