A ventilated courtyard as a passive cooling strategy in the warm humid tropics

The paper investigates the potential of a courtyard for passive cooling in a single storey high mass building in a warm humid climate. The inclusion of an internal courtyard in building design is attributed to the optimization of natural ventilation in order to minimize indoor overheating conditions. However, the efficiency of this strategy greatly depends on the design details of the building composition in providing appropriate airflow pattern to the courtyard. From the results of thermal measurements, a significant correlation between wall surface temperatures and indoor air temperatures is evident. A reduction of indoor air temperature below the levels of ambient is seen as a function of heat exchange between the indoor air and high thermal mass of the building fabric. However, this behavior is affected by indoor airflow patterns, which are controlled through the composition between envelope openings and the courtyard of the building.From a computational analysis, several airflow patterns are identified. A relatively better indoor thermal modification is seen when the courtyard acts as an air funnel discharging indoor air into the sky, than the courtyard acts as a suction zone inducing air from its sky opening. The earlier pattern is promoted when the courtyard is ventilated through openings found in the building envelope. The computational simulation utilizing the standard k-ε turbulent model with isothermal condition agrees closely with the measurements taken from the field investigation.     

Measurement of ventilation and aerosol particles in buildings

The work described in the paper is concerned with the measurement of the flow of tracer gas and aerosol particles in rooms. Measurements were carried out in single- and two-zone systems using SF₆ tracer gas and oil-smoke particles. Initial tests were carried out in a single-zone system using different arrangements of window opening. Results indicated that tracer-gas exchange rates were generally higher than particle exchange rates. This was due to the fact that the ventilation air entering the zone contained a significant concentration of particles but a negligible quantity of tracer gas. The exchange rates of tracer gas and smoke particles through a doorway were also measured in a two-zone system. The doorway coefficients of discharge were calculated using a theory based on the Bernoulli equation. The coefficients of discharge for the opening were in the range 0.4–0.96 for tracer gas measurements and 0.15–0.42 for smoke-particle measurements.     

An energy benchmarking model for ventilation systems of air-conditioned offices in subtropical climates

Since the energy crisis in 1973, engineers have endeavoured to implement energy conservation in buildings. Unfortunately, the effort resulted in energy savings without the fundamental delivery of indoor satisfaction in many cases. In this study, a benchmarking model for the energy consumption of ventilation systems in air-conditioned offices was proposed. This model was developed from the fundamental psychrometric analysis under probable office design conditions in Hong Kong. The results showed that the annual energy-consumption of a ventilation system per unit floor area would be correlated closely with the carbon dioxide (CO₂) concentration in the space, but its correlation with the air temperature set-point would be less significant. In some offices, significant energy-savings potential was demonstrated to provide satisfactory indoor air quality (IAQ) without any comfort penalty to the occupants. This model would be useful for the energy performance evaluation and benchmarking of ventilation systems in air-conditioned offices.     

Effect of ventilation strategies on air contaminant concentrations and energy consumption in buildings

Considering the diversity of indoor contaminant characteristics and generation patterns, finding an appropriate ventilation strategy that can secure acceptable indoor air quality with minimum energy consumption is a challenging task for HVAC system designers and operators. This study theoretically models and investigates the impact of various ventilation strategies on contaminant concentration behaviour and corresponding ventilation cooling energy requirements for a single‐zone enclosure. Two types of contaminants are considered; carbon dioxide as an occupancy dependent and formaldehyde, which is independent of occupancy. An airflow model is used to predict space pressure and air leakage rates across the enclosure envelope, and an air quality model is used to predict time‐varying contaminant concentrations. In addition, a building energy simulation model is utilized to predict the corresponding ventilation cooling energy requirements under hot climatic conditions. Results from this study show that acceptable contaminant concentrations during occupied periods can be achieved by different ventilation strategies but at substantially different ventilation energy requirements. More than 50 per cent reduction in ventilation energy requirements can be obtained while maintaining acceptable IAQ if proper ventilation strategy is employed. Copyright © 2001 John Wiley & Sons, Ltd.     

上海市集合住宅气密性能实测及换气性能分析

对上海 13户居民住宅气密性能进行了实测调查 ,结果表明近年来随着建筑技术的发展 ,住宅的气密性能有了较大的提高。根据简易算法对住宅的自然通风量进行了预测 ,换气量根本无法达到相关的标准规定。如何采取主动式的通风措施来改善室内的空气环境已经是一个突出的问题     

Tracer gas technology for airflow measurements in HVAC systems

This paper describes the use of tracer gas techniques for airflow measurement in ducts. The author had carried out extensive work in both the laboratory and the field to test the accuracy and viability of these techniques. Preliminary measurements were carried out in the laboratory to examine the accuracy of these techniques. The mixing of tracer gas (e.g. sulphur hexafluoride, SF₆) in ducts of various shapes and sizes was examined using different types of tracer injectors. Measurements of airflow estimated using tracer gas techniques (e.g. constant-injection, pulse-injection) were compared with measurements made using traditional instrumentation such as pitot tubes. Field testing on a large-scale heating, ventilation and air-conditioning system was carried out and tracer gas techniques were used to determine airflow rates in air handling units serving a library building.     

Numerical study of a hybrid ventilation system for single family houses

The main objective of this study is to develop and test hybrid ventilation systems and control strategies that are suitable for residential buildings. Two ventilation systems were modelled: a mechanical extract ventilation system (called the reference system) and a hybrid low pressure ventilation system that can support two different types of demand control strategies (occupancy detection and CO₂ concentration). The newly developed models were assembled with the existing thermal models of the SIMBAD Building and HVAC Toolbox developed by the CSTB.A single family house located in Athens (Greece), Nice (France), Trappes (France) and finally Stockholm (Sweden) was considered as the case study. Yearly simulations were performed to assess the performance of the hybrid ventilation control strategies. The assessment criteria used are related to indoor air quality, thermal comfort, energy consumption and stability of control strategies. The results show that the low pressure ventilation system can improve the indoor air quality and reduce the fan energy consumption compared to the reference system while maintaining the same building energy consumption for heating.     

办公室场所自然通风状况模拟

建筑环境中的空气环境是人们生活和工作中最重要的环境之一。室内空气环境主要有热环境、湿环境和空气品质等部分组成。在CFD技术基础上,应用Fluent软件分析了办公室等场所在有热源自然通风条件下的温度场与速度场,初步得到了此种状态下室内温度速度分布图。     

被动式太阳房的降温研究

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,自然通风形成的室内热环境有利于人体舒适性.太阳能烟囱管能强化房间的自然通风,可以有效地改善室内的空气品质和室内热环境,但尚未达到舒适的温度.     

An investigation of passive ventilation cooling and control strategies for an educational building

Many non-domestic buildings, built recently in the UK, use natural means to provide ventilation for indoor air quality and thermal comfort. This paper presents monitoring results obtained from such a purpose built naturally ventilated educational building. Its performance during the summer is discussed based on monitored results. Using thermal and ventilation modelling, the paper also discusses the optimisation of the building’s summer performance. Recommendations on the selection of appropriate ventilation strategies in relation to the prevailing external conditions are derived and the appropriateness of the control methods is discussed.     

Integrated analysis of whole building heat,air and moisture transfer

There is a continuous dynamic heat, air and moisture (HAM) interaction between the indoor environment, building envelope and mechanical systems. In spite of these interdependences, the current indoor, building envelope and energy analysis tools are used independently. In this paper a holistic HAM model that integrates building envelope enclosures, indoor environment, HVAC systems, and indoor heat and moisture generation mechanisms, and solves simultaneously for the respective design parameters is developed. The model is benchmarked with internationally published test cases that require simultaneous prediction of indoor environmental conditions, building envelope moisture performance and energy efficiency of a building.     

Optimal decision making in ventilation control

In this paper, a two-mode ventilation control of a single facility is formulated as a scheduling model over multiple time horizons. Using the CO₂ concentration as the major indoor air quality index and expected room occupancy schedule, optimal solutions leading to reduced CO₂ concentration and energy costs are obtained by solving the multi-objective optimization model formulated in the paper. A modified evolutionary strategy algorithm is used to solve the model at different time horizons. The optimized ventilation schedules result in energy savings and maintain an acceptable level of indoor CO₂ concentration.     

Energy impact of indoor environmental policy for air-conditioned offices of Hong Kong

Air-conditioned office buildings are one of the biggest energy consumers of electricity in developed cities in the subtropical climate regions. A good energy policy for the indoor environment should respond to both the needs of energy conservation and the needs for a desirable indoor healthy environment with a reduction in carbon dioxide (CO₂) generation. This study evaluates energy implications and the corresponding CO₂ generation of some indoor environmental policies for air-conditioned office buildings in the subtropical climate. In particular, the thermal energy consumption in an air-conditioned office building was evaluated by the heat gains through the building fabric, the transport of outdoor fresh air for ventilation, and the heat generated by the occupant and equipment in the space. With the Monte-Carlo sampling technique and the parameters from the existing office building stocks of Hong Kong, the energy consumption profiles of air-conditioned office buildings in Hong Kong were evaluated. Energy consumption profiles were simulated for certain indoor environmental quality (IEQ) policies on indoor air temperature and CO₂ concentration settings in the offices, with other building parameters remaining unchanged. The impact assessment and the regression models described in this study may be useful for evaluation of energy performances of IEQ policies. They will also be useful for the promotion of energy-saving measures in air-conditioned office buildings in Hong Kong. This study presented a useful source of references for policymakers, building professionals and end users to quantify the energy and environmental impacts due to an IEQ policy for air-conditioned office buildings.     

Prediction of hybrid ventilation performance using two simulation tools

This paper describes the results of a collaboration between ENTPE-LASH and LEPTAB within the framework of the IEA Annex 35 “Hybrid Ventilation in New and Retrofitted Buildings”. The aim of the work is to carry out a cross-simulation study and to identify optimal control strategies for ventilation systems in order to provide a comfortable thermal indoor environment and a good indoor air quality with energy efficiency. Two models were developed by ENTPE-LASH and LEPTAB in order to carry out hybrid system simulations taking into account air flows, heat transfers and CO₂ concentrations, and numerical results are compared in this study. The models were first adjusted to an experimental cell, HYBCELL, created in the same project. The simulations were carried out using a fictive classroom. The test room was assumed to be in Copenhagen and to be equipped with a natural ventilation system (two inlet grilles and an exhaust chimney) or with mechanical ventilation systems (fans with or without heat recovery). This work also reveals what are the differences in results between the two tools and outlines some conclusions on relative performance of the specific control strategies chosen in this study.     

An experimental tool for research and educational applications on HVAC systems

This paper describes an experimental tool elaborated at the building sciences laboratory (LASH/DGCB). The objective of this tool is to develop control strategies for heating, cooling and ventilation, and test them on heating, ventilating and air conditioning equipment. The tests are conducted in a large room of the laboratory equipped with a double-flow ventilation system and a global control/data acquisition system. The tool is used for research and some experiments are led by engineering students. It enables the identification of optimal parameters for each developed control strategy, in order to reach good thermal comfort, acceptable indoor air quality and good stability of actuators at the least energy cost. In this paper we present an example of global control strategy for heating and cooling periods based on interior temperature control (fuzzy regulator). This strategy includes an indoor air quality controller (proportional integral or fuzzy regulator) based on indoor CO₂ level control. A measurements campaign during an occupied period is shown with an overview of the actuators’ behaviour. This tool also highlights the key role of advanced control techniques to manage heating, cooling and ventilation systems.     

Derivation of equivalent continuous dilution for cyclic,unsteady driving forces

This article uses an analytical approach to determine the dilution of an unsteadily-generated solute in an unsteady solvent stream, under cyclic temporal boundary conditions. The goal is to find a simplified way of showing equivalence of such a process to a reference case where equivalent dilution is defined as a weighted average concentration. This derivation has direct applications to the ventilation of indoor spaces where indoor air quality and energy consumption cannot in general be simultaneously optimized. By solving the equation we can specify how much air we need to use in one ventilation pattern compared to another to obtain same indoor air quality. Because energy consumption is related to the amount of air exchanged by a ventilation system, the equation can be used as a first step to evaluate different ventilation patterns effect on the energy consumption. The use of the derived equation is demonstrated by representative cases of interest in both residential and non-residential buildings.     

夏季自然通风教室室内环境与学习效率的调查研究

通过环境参数测量与问卷调查结合的方式探索夏季教室室内环境与学生学习效率间的关系。主要分析同济大学两种典型教室正常上课期间室内热环境、空气品质和光环境状况,结果表明教室室内环境存在的主要问题是新风量不足,二氧化碳浓度长期维持在较高的水平,从而导致室内人员学习效率不高。     

Integration of variable refrigerant flow and heat pump desiccant systems for the cooling season

Energy saving and indoor air condition enhancing potentials by integrating the variable refrigerant flow (VRF) and heat pump desiccant (HPD) systems were investigated in a field performance test during a cooling season. Three different operating modes: non-ventilated, HPD ventilation assisted and HPD ventilation–dehumidification assisted VRF systems were investigated. The HPD systems operated in the ventilation–dehumidification mode dehumidify the outdoor air and supply it to the indoor air during the ventilation. It was found that the VRF systems provided an average of 97.6% of the total cooling energy for the HPD ventilation assisted mode. The remainder was the recovered cool by the HPD systems during ventilation. The VRF systems provided an average of 78.9% of the total cooling energy for the HPD ventilation–dehumidification assisted mode. The remainder was covered by the HPD systems which provided additional sensible and latent cooling. Overall, among the three operating modes, it is concluded that the HPD ventilation–dehumidification assisted VRF outdoor units consume less energy than the HPD ventilation assisted ones, but more than the non-ventilated ones, while providing the best indoor thermal comfort and indoor air quality conditions. For the total system, the HPD ventilation–dehumidification assisted VRF systems consume less energy than the HPD ventilation assisted ones.     

Application of ANN to explore the potential use of natural ventilation in buildings in Turkey

Indoor natural ventilation provides both the circulation of clear air and the decrease of indoor temperature, especially, during hot summer days. In addition to openings, building dimensions and position play a significant role to obtain a uniform indoor air velocity distribution. In this study, the potential use of natural ventilation as a passive cooling system in new building designs in Kayseri, a midsize city in Turkey, was investigated. First, indoor air velocity distributions with respect to changing wind direction, magnitude and door openings were simulated by the FLUENT package program, which employs finite element methods. Using the simulated data an artificial neural network (ANN) model was developed to predict indoor average and maximum air velocities. The simulations produced by FLUENT show that the average indoor air velocity is generally below 1.0 m/s for the local prevailing wind directions. The simulations results suggest that, in addition to the orientation of buildings in accordance with prevailing wind directions, a proper indoor design of buildings in the area can significantly increase the capability of air ventilation during warm summer days. It was found that a high correlation exists between the simulated and the ANN predicted data indicating a successful learning by the proposed ANN model. Overall, the evaluation of the network results indicated that the ANN approach can be utilized as an efficient tool for learning, training and predicting indoor air velocity distributions for natural ventilation.     

Energy and exergy performance of residential heating systems with separate mechanical ventilation

The paper brings new evidence on the impact of separate mechanical ventilation system on the annual energy and exergy performance of several design alternatives of residential heating systems, when they are designed for a house in Montreal. Mathematical models of residential heating, ventilation and domestic hot water (HVAC–DHW) systems, which are needed for this purpose, are developed and furthermore implemented in the Engineering Equation Solver (EES) environment. The Coefficient of Performance and the exergy efficiency are estimated as well as the entropy generation and exergy destruction of the overall system. The equivalent greenhouse gas emissions due to the on-site and off-site use of primary energy sources are also estimated. The addition of a mechanical ventilation system with heat recovery to any HVAC–DHW system discussed in the paper increases the energy efficiency; however, it decreases the exergy efficiency, which indicates a potential long-term damaging impact on the natural environment. Therefore, the use of a separate mechanical ventilation system in a house should be considered with caution, and recommended only when other means for controlling the indoor air quality cannot be applied.