The effects of night ventilation technique on indoor thermal environment for residential buildings in hot-humid climate of Malaysia

This study investigates the effectiveness of night ventilation technique for residential buildings in hot-humid climate of Malaysia. This paper firstly presents the results of a survey on usage patterns of windows and air-conditioners in typical Malaysian residential areas. Secondly, the effects of different natural ventilation strategies on indoor thermal environment for Malaysian terraced houses are evaluated based on the results of a full-scale field experiment. The results show that the majority of occupants tend to apply not night ventilation but daytime ventilation in Malaysian residential areas. It can be seen from the field experiment that night ventilation would provide better thermal comfort for occupants in Malaysian terraced houses compared with the other ventilation strategies in terms of operative temperature. However, when the evaporative heat loss of occupants is taken into account by using SET*, the night ventilation would not be the superior technique to the others in providing daytime thermal comfort mainly due to the high humidity conditions. Therefore, the indoor humidity control during the daytime such as by dehumidification would be needed when the night ventilation technique is applied to Malaysian terraced houses. Otherwise, full-day ventilation would be a better option compared with night ventilation.     

A qualitative ventilation model for prototype cavity structure

Creating a physical model structure that is able to simulate different ventilation scenarios is essential for improving the understanding of passive designs that are both sustainable and environmentally acceptable. The purpose of this investigation was to build a physical prototype model that could be heated from both the outside and inside to duplicate an occupied structure during the morning hours. This model was then used to provide information for two Computational Fluid Dynamic (CFD) models to firstly compare and then validate results obtained from experimental data. A sample of computational findings was initially presented in Chawynski et al. (2003). This paper presents the experimental sections used to validate numerical simulation in Chawynski et al. (2003) and incorporates findings from Chawynski (2004). The experimental component consisted of approximately 80% of the overall investigation. The findings enabled a better scientific understanding of how a structure’s thermal performance can be improved by mechanically forcing air (to simulate outside wind) inside to both lower and create an overall uniform internal air temperature distribution in a cavity enclosure. A chart-based model is proposed to qualitatively gauge the temperature inside a cavity enclosure for different ventilation scenarios.     

A review on wind driven ventilation techniques

Natural ventilation has gained prominence in recent times as a bespoke method of ventilating buildings. The two fundamental principles of natural ventilation are stack effect and wind driven ventilation. This paper reviews miscellaneous wind driven ventilation designs with respect to traditional means such as wind towers and more modern techniques including turbine ventilators and wind catchers. A distinction is made between specific types of wind driven ventilation techniques depending on their operation and mode of engagement with the wind. For example, a static wind catcher is classified as passive; a rotating wind cowl as a directed passive technique and a rotating turbine ventilator is classified as outright active due to its constant rotation with the wind. A table summarising the review is presented at the end with corresponding references.     

Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings

Passive design responds to local climate and site conditions in order to maximise the comfort and health of building users while minimising energy use. The key to designing a passive building is to take best advantage of the local climate. Passive cooling refers to any technologies or design features adopted to reduce the temperature of buildings without the need for power consumption. Consequently, the aim of this study is to test the usefulness of applying selected passive cooling strategies to improve thermal performance and to reduce energy consumption of residential buildings in hot arid climate settings, namely Dubai, United Arab Emirates. One case building was selected and eight passive cooling strategies were applied. Energy simulation software – namely IES – was used to assess the performance of the building. Solar shading performance was also assessed using Sun Cast Analysis, as a part of the IES software. Energy reduction was achieved due to both the harnessing of natural ventilation and the minimising of heat gain in line with applying good shading devices alongside the use of double glazing. Additionally, green roofing proved its potential by acting as an effective roof insulation. The study revealed several significant findings including that the total annual energy consumption of a residential building in Dubai may be reduced by up to 23.6% when a building uses passive cooling strategies.     

Cooling load reduction by using thermal mass and night ventilation

We provide a quantitative understanding of the relationship between thermal mass and cooling load, i.e. the effect of thermal mass on energy consumption of air-conditioning in office buildings. A simple office-building model with air-conditioning at daytime and free cooling at nighttime is analyzed in detail to quantify the hourly and overall variation of cooling load of air-conditioning. As an important parameter, an increase of time constant can effectively reduce the cooling load, by as much as more than 60% when the time constant is more than 400 h. However, when the time constant is larger than 1000 h, a further increase may slightly increase the cooling load, as a too large time constant may also postpone the heat release of thermal mass until the daytime. For the most effective reduction of cooling load, the interior and exterior convective heat transfer numbers need to be matched.     

深圳居住建筑夏季自然通风降温实验研究

以深圳市六种布局不同、楼层不同的居住建筑为对象,调查了夏季室内热环境,测试了不同通风工况下围护结构内表面以及室内外温湿度,分析了居住建筑在夏季采用自然通风降温的可行性,比较了持续自然通风与间歇自然通风的优劣以及不同遮阳方式的遮阳效果,提出了采用自然通风降温方式的条件及建筑设计中应改进之处。     

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.     

Energy efficiency optimization of combined ventilation systems in livestock buildings

Good ventilation system in livestock buildings is necessary for removing excess moisture and heat and for improving building environment in general. Natural ventilation does not require energy consumption and on the other hand, animals would not be affected by electrical power failures. Because natural ventilation depends largely on temperature difference between inside and outside air and wind velocity and direction it is very important in early stages of building design to provide orientation and accurate opening areas. Numerical simulation of natural ventilation and computation of fluid dynamics in livestock buildings can be usefully integrated in whole ventilation system optimization and related energy consumption decrease. Even in mechanical system ventilation, from flow field obtained in numerical simulation it is possible to optimize these systems. CFD analysis is generally restricted to the study of buildings’ environment flows and space study, and the designer must supply boundary conditions in the form of external and internal buildings’ envelope/wall surface conditions. Finally, the needs for further research and engineering development are outlined.     

The acoustics and ventilation design tool applied retrospectively to four 19th century buildings

The acoustic and ventilation simple sketch design tool is a spread-sheet. It was constructed to encourage designers to explore a proposed building's size and shape, the natural ventilation and simple acoustics, in order to promote sustainable architecture. A number of simple input parameters are necessary, the number of people the space must accommodate and the volume of air per person appropriate to the acoustic function. Allowing the internal air temperature to rise by some 10–15%, the building geometry, the natural ventilation and acoustics can be discussed via the volume of the space. This paper has two aims, firstly to demonstrate the acoustic and ventilation design tool generating the geometric features, the simple acoustic properties and the natural ventilation rates for buildings, ranging from a simple open-plan office to a multi-purpose space. Secondly, the design tool is applied retrospectively to the London Custom House Long Room, the Truro Methodist Church, the Vienna Court Theatre and the Royal Albert Hall, so that the validity of the design tool may be discussed, and its effectiveness demonstrated and evaluated. This is achieved by comparing the design tool output with real data from the literature on these four 19th century buildings.     

民用建筑柴油发电机房通风量的计算方法

结合工程实际,介绍了柴油发电机组的基本构造和发热量的构成。指出了采用换气次数法的弊端,并给出发电机房通风量的较合理计算方法。     

Primary energy implications of ventilation heat recovery in residential buildings

In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings.     

Introduction to integration of renewable energy in demand controlled hybrid ventilation systems for residential buildings

In the scope of the EU supported project RESidential buildings HYbrid VENTilation (RESHYVENT), the possible integration of renewable energy solutions (RES) into hybrid ventilation systems has been analysed. The focus has been on solar and wind applications to substitute the use of fossil fuel. The feasibility of the investigated options depends on the ventilation concept the RES is integrated into, the location of the building geographically, placement of the RES in the building and on the urban environment. This paper describes the different renewable technologies, options and constrains in connection with integration into hybrid ventilation systems.     

住宅建筑设计的常见问题

指出住宅设计应当贯彻“适用、经济、安全、美观”的建设方针和“以人为本”的指导思想,分析了住宅建筑设计中的常见问题,以更新住宅设计观念,提高住宅设计水平,设计出更适合消费者的住宅;     

Meeting residential ventilation standards through dynamic control of ventilation systems

Existing ventilation standards, including American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) Standard 62.2, specify continuous operation of a defined mechanical ventilation system to provide minimum ventilation, with time-based intermittent operation as an option. This requirement ignores several factors and concerns including: other equipment such as household exhaust fans that might incidentally provide ventilation, negative impacts of ventilation when outdoor pollutant levels are high, the importance of minimizing energy use particularly during times of peak electricity demand, and how the energy used to condition air as part of ventilation system operation changes with outdoor conditions. Dynamic control of ventilation systems can provide ventilation equivalent to or better than what is required by standards while minimizing energy costs and can also add value by shifting load during peak times and reducing intake of outdoor air contaminants. This article describes the logic that enables dynamic control of whole-house ventilation systems to meet the intent of ventilation standards and demonstrates the dynamic ventilation system control concept through simulations and field tests of the Residential Integrated Ventilation-Energy Controller (RIVEC).     

住宅房间通风气流模型试验相似理论研究

根据相似理论的基本原理,从流体动力学相似和传热相似两方面导出了住宅房间通风气流模型试验的相似准则以及相似比例尺之间的关系,为搭建试验台打下理论基础,更好地模拟真实房间的气流流动情况。     

Full scale experimental study of single-sided ventilation: Analysis of stack and wind effects

Natural ventilation can contribute to the reduction of the air conditioning demand and to the improvement of thermal comfort in buildings. In this paper, the flow field and the air change rate generated by a simple configuration of natural ventilation, namely single-sided ventilation, are examined experimentally. The experiments are realized in a full scale building exposed to outdoor conditions, using several measurement techniques. The main features of the flow generated by stack and wind effect are examined for different outdoor conditions (temperature difference, wind speed and direction). Finally, measured air change rates are compared to those calculated by existing correlations in order to analyze their applicability to the experimental configuration. Results show that the wind generates turbulence diffusion at the opening, counteracting the stack effect. Moreover, in the case of windward opening, there is an additional effect, namely the effect of mixing layer, which tends to increase the airflow rate. Existing correlations give reasonably good results in the case of windward opening, while in the case of leeward opening they overestimate the airflow rate.     

On the cooling potential of night ventilation techniques in the urban environment

The present paper aims to examine the application of night ventilation techniques to 10 urban canyons, situated in the extended region of Athens, Greece. As the climatic conditions in the urban environment frequently present important variation in different locations of the same urban area, the outdoor air temperature and the wind profile have been measured inside and outside the experimental canyons. The present work determines the impact of the urban environment on night ventilation energy performance, by studying a typical room located in the urban domain, under air-conditioned and free-floating operation, when single-sided and cross-ventilation are considered, during the night period. The influence of the urban microclimate on the efficiency of the technique has been examined by considering the typical zone inside the canyons and under undistributed conditions. The comparison of the results permits to evaluate the impact of the urban environment on the effectiveness of night ventilation techniques. The performed analysis shows that due to the increase in air temperature and the decrease in wind velocity inside the canyons, the efficiency of the studied techniques is significantly reduced compared with the situation that considers the undistributed conditions, dominating outside the urban canyons.     

潮汕民居对现代住宅的启示

通过介绍潮汕民居的相关文献资料,对潮汕地区民居的建筑布局、功能特征和装饰文化进行了分析,从中探讨民居建筑对现代住宅的启示,以求为住宅建设积累经验,从而创造优美的居住空间。     

The night purging of a two-storey atrium building

We examine the fluid mechanics of night purging in a two-storey naturally ventilated atrium building. We develop a mathematical model of a simplified atrium building and focus on the rate at which warm air purges from each storey and the atrium by displacement ventilation into a still cool night environment of a constant temperature. To develop a first insight into how the geometry of the building influences the rate at which warm air purges from each storey via the atrium we neglect heat exchange with the fabric (so there is no thermal buffering) and furthermore assume that the warm air layers in each storey and the atrium are of uniform temperature.     

Estimation of passive cooling efficiency for environmental design in Brazil

An estimation of passive cooling techniques was conducted for 14 cities in Brazil, using a fairly accurate algorithm that accounts for heat conduction, convection, radiation, and evaporation; this was done to determine the amount of heat gain/loss of room air, defined as a particular quantitative index for passive techniques. Heat gains and losses were calculated for four envelope conditions - namely, insulated, high-albedo, wet surface, and a combination of the previous two - and compared to a case assumed to be the standard condition. A conclusion drawn was that a passive design is efficient in decreasing the need for cooling in typical dwellings in Brazil; solutions should differ with regional climate characteristics. In semi-arid areas, evaporative cooling showed the best results. Reduced heat gain was found during the warm seasons for all cities, along with increased heat gain during the cool seasons for mid-latitude cities. In particular, a combination of high-albedo enveloping and evaporation can greatly decrease heat gain in building walls. High-albedo surfaces in the sub-tropical areas found in southern Brazil are more efficient. It is suggested that passive techniques should be conceived in such a way so as to work during the cooling season and be disabled during mild ones.