During operation, buildings consume a large amount of energy, around 40\% of global final energy use. A major challenge is to reduce the amount of energy used while still providing a comfortable environment for building occupants. The use of passive techniques, such as natural ventilation, is promoted in certain climates to provide low energy cooling and ventilation. However, controlling natural ventilation in an effective manner to maintain occupant comfort can be a difficult task, particularly during warm periods. One area which has been identified as having the potential for reducing energy consumption while maintaining occupant comfort is the use of more advanced control techniques. A technique which has been much explored in recent years for application in mechanically ventilated buildings is Model Predictive Control (MPC). MPC is a control technique which uses a model of the system dynamics and by solving an optimisation problem is able to determine the optimal control inputs. In this thesis the application of MPC to naturally-ventilated buildings is investigated. The essential component of an MPC strategy is the predictive model of the building's thermal dynamics. An empirical approach to modelling was taken using multilayer perceptron (MLP) neural network models. To use empirical data from a building to create a predictive model it is essential to ensure the quality of the data is appropriate. In order to assess the data available from buildings during normal operation four studies were carried out in different buildings. The data collected from these studies represent a range of natural ventilation scenarios and building types in different locations in the UK. To test the impact of identification procedures upon the resulting neural network models, an identification experiment was carried out using dynamic thermal simulation. Neural network models were trained using both the data from real buildings and the simulation data. Results showed that neural network models trained using data from real buildings were capable of good predictions. However, the lack of input excitation during normal operation resulted in models which did not capture the effect of the window opening control. The identification experiment demonstrated that by exciting the control input the resulting neural network models captured the effect of the control, making them suitable for MPC. The main focus of this thesis is the investigation of techniques to develop predictive models which can be utilised as part of an MPC strategy. However, to demonstrate the potential benefits of MPC a controller designed to maintain a suitable internal temperature is demonstrated. The controller utilised the neural network models developed using the data from the system identification experiment and a non-linear optimiser. The MPC method showed the potential to reduce overheating and improve upon the typical control used in the majority of buildings. Findings in this thesis demonstrate that empirical models capable of good predictions can be trained and could be successfully applied to the control of natural ventilation systems. Furthermore, the potential advantages of adopting an MPC approach to natural ventilation control are shown.

Since electricity was first harnessed, humanity has developed a lifestyle which can not exist without it. Traditionally, electricity has been created by burning fossil fuels which produces waste gases including carbon dioxide. These waste gases have accumulated in our atmosphere and are theorised to have contributed to a warming of the earth, causing a 0.4°C rise in average surface temperature since the 1970's (DECC 2013). A warming of the earth is thought to lead to increased frequency of catastrophic weather events such as droughts and heat waves, leading to many deaths (Met Office 2015). In recent years, there has been a drive to reduce our dependence on the burning of fossil fuels by making technologies more efficient, developing methods of electricity generation which do not involve the burning of fossil fuels as well as replacing techniques requiring high energy demands with low energy techniques. Natural ventilation is one such low energy technique which can replace more electricity intensive strategies such as mechanical ventilation and air conditioning whilst still ensuring a room which is neither too cold nor too warm and removes pollutants.

Natural ventilation is a low-energy design strategy that has the potential both to significantly reduce energy usage in buildings and to provide a healthy and comfortable indoor environment. It has particular potential for use in tall, multi-storey buildings. However, the integration of natural ventilation into these large building designs has seen mixed success. Furthermore, there is a gap between simple 'rule-of-thumb' design guidance and detailed, computational design tools. This research attempts to bridge the gap between the simple and detailed with the broad aim of providing rapid and intuitive guidance for use in preliminary design. We use a simple mathematical approach to develop a coherent and easy-to-use framework for modelling ventilating flows, which quantifies the interactions between a core set of design variables. We focus in particular on buoyancy-driven ventilation in buildings with atria, ventilation stacks and/or similar vertical spaces that span multiple floors. Simple methods centred around hand calculations and design charts are developed to inform the sizing of vents in an 'ideal design' scenario, in which the desired ventilation flow rates and air temperatures are delivered to all occupants within a building. We define a measure of the ventilation performance of an atrium and use this to provide an indication of when an atrium is beneficial to a ventilation system design and when it is detrimental. We also use a transient flow analysis to consider 'off-design' scenarios, in which undesirable flow regimes may occur, and to place design tolerances on the building envelope. It is hoped that this work will form a point of reference for further research and for future revisions of design guidance literature.

There are many sources of outdoor pollution in Kuwait which then makes natural ventilation a poor mechanism for good Indoor Air Quality (IAQ). Therefore, a mechanical or hybrid ventilation system is necessary. First of all, Kuwait is situated in the northeast of the Arabian Peninsula in Western Asia with a desert weather climate. The prevailing wind is north and northeast and that causes sand storms. Also most of the towns and cities are situated and constructed within the vicinity of many industrial sites, petroleum downstream/upstream facilities (including Kuwait's three refineries, petrochemical complexes, crude oil production points etcetera) and many small industries. Most housing construction projects, as well as schools, commercial and governmental buildings are built in the downwind of the polluted air emitted from such plants, therefore, there is the potential for consequential health effects related to the ambient air. As a result, there is a prevalence of asthma and rhinitis among the schoolchildren in Kuwait. The estimated prevalence of asthma among school children was 22.4% and that of rhinitis was 23% (Abal et al., 2010). It was evident from a preliminary study that indoor air quality (IAQ) in Kuwait housing is under-researched and there is a clear lack of awareness amongst building stakeholders (Architects and Designers, M&E Engineers, User, etc.) of the harmful effects of chemicals that exist inside buildings. The risk of poor Indoor Air Quality (IAQ) is increased by a lack of proficient knowledge of how numerous factors can contribute to poor IAQ, both during design, construction and after occupancy. As a result, the study set out to: research previous related research studies in the field of IAQ, identify the current status quo of IAQ in Kuwait, conduct a survey (questionnaires and interviews) with Kuwait construction professionals regarding IAQ issues and to find the barriers to implementing IAQ best practice in all stages of the project, and then finally, to develop a framework for achieving good IAQ in Kuwait housing projects. The findings revealed no documents written for Kuwait, that encompasses codes, standards, regulations and guidance for the implementation of good IAQ in Kuwait housing developments, or a framework for government enforcement of such. It was also revealed that there was a significant lack of awareness of indoor air pollutants and good IAQ both amongst occupants and construction professionals. The analysis also revealed that the status quo in the housing development process did not enable integration amongst the project team and stakeholders at the design stage, hence team member’s valuable input on achieving good IAQ at design stage is lost. Furthermore, the process did not emphasize the following at every stage of the project to ensure good IAQ: commissioning of the ventilation design and installation, which includes value engineering, proper sequencing and scheduling of activities to avoid dust or debris from contaminating the ventilation system, proper documentation and reporting to ensure the owner’s project objectives are documented, achieved, checked, and carried over to the next stage. The findings show that the barriers to achieving good IAQ in Kuwait housing developments are; cost and budget, government enthusiasm, lack of awareness, lack of enforceable codes and standards, lack of design integration, distrust of the competence level of local IAQ companies, habit and age, low level of IAQ education, and lack of training. While, the drivers of good IAQ in Kuwait housing are; the client/end-user, the government, architects, designers, IAQ consultants, construction professional societies, contractors and manufacturers. The developed and validated framework achieves the aim and objectives of the study by proposing strategies and actions for improving indoor air quality (IAQ) in Kuwaiti housing developments through increased integration, commissioning, proper and adequate sequencing and scheduling, and documentation at design, construction, and occupancy stages. Kuwait Environmental Protection Agency (KEPA), Kuwait Institute of Environmental Management (KIEM), Kuwait Municipality, and Kuwait Institute of Science and Research (KISR) were also suggested as the main bodies to drive the education, awareness, and training, of not only the construction industry but also the general population on good IAQ practices.

A low-energy ventilation system is often incorporated as one of the major energy saving measures in sustainable building design. These systems often employ a hybrid strategy in which mechanical equipment, governed by a computer controlled building management system, is used to assist or manage a naturally-driven airflow - the latter occurring due to the density difference between warm air inside and cooler air outside the room. Hybrid ventilation flows are poorly understood and the principal aim of the research was to enhance our understanding of the fluid mechanics through complementary theoretical and experimental modelling. The research begins by comparing solely natural and solely mechanical ventilation of a room. The hybrid ventilation of a room is then considered under the combined effect of naturally occurring and mechanically imposed pressure differences, in which a mechanical fan imposes a fixed airflow rate through one vent, thereby altering the natural pressure distribution. Simplified theoretical models, to describe the ventilation airflow rate through a room and the resulting mean air temperature, were developed for solely natural ventila- tion, solely mechanical ventilation and, finally, hybrid ventilation. At each stage the theoretical model was compared with results from small-scale experiments, and good agreement was demonstrated. From the theoretical investigation, the neutral pressure level emerged as a key pa- rameter in determining the characteristics of the ventilation airflow. Moreover, it was found that the airflow rate through an open vent can be controlled remotely by managing the position of the neutral pressure level, and that this can be achieved by varying the magnitude of the mechanically imposed airflow rate. Experimental investigations revealed that, as the neutral pressure level approached the plane of a vent, quasi-steady pulsing flows and bi-directional or exchange flows were observed. The complicated fluid dynamics involved in these flows provides inspiration for significant future work.

Due to the complicated flow phenomenon in urban areas, the assessment of wind pressure forces as well as the rates of natural ventilation for groups of low rise buildings is complex. As a result, the current design methods for the prediction of these forces are oversimplified and lead to inaccurate estimates of wind forces and ventilation rates in buildings. A survey of previous studies regarding wind properties and their influence on pressure forces along with work related to natural ventilation, wind loading and air flow round buildings was carried out. The survey revealed that no general relationship exists which defines the interaction between the various aspects of flow. This thesis, therefore, attempts to enhance our knowledge about the flow around groups of buildings and suggests a means of quantifying the interaction between building shape, group geometry, flow properties and the resulting pressure forces. The present study has been carried out in a simulated urban terrain atmospheric boundary layer flow. A series of model scale experiments were performed for different building shapes. The study starts with the investigation of the influence of upstream fetch on the central model drag before going on to the detailed measurements on various models covering a wide range of building shapes, group form and plan area density. The detailed measurements of mean pressure forces on model buildings situated within a variety of groups of similar form indicated three different trends in the behaviour of these forces, corresponding to the three flow regimes known to exist for flow over general roughness elements. The existence of these flow regimes was confirmed by velocity profile measurements. A general correlation between group geometry, flow properties and the resulting pressure forces has been suggested. In order to apply the foregoing results to full scale building arrays, a method has been proposed to yield the pressure difference across low rise buildings for the prediction of natural ventilation rates in an urban built form. This method takes into account the relevant built form and flow parameters which are ignored in the current IHVE design guide method (1970), (applicable to high rise buildings only). The suggested method includes the prediction of ventilation rates from the openings in the walls as well as in the roof. Suggestions have also been made to revise the British Standard Code of Practice for wind loading to incorporate the trends which have been found to be different to those currently recommended.

No description available.

This thesis is an investigation into improving natural ventilation in low rise hospital wards in Northern Nigeria. The climate of this region is semi-arid, during the dry season, sub-Saharan fine dust (Harmattan dust) is blown into the region from the North East and during the wet season, Mosquitos are prevalent. The energy infrastructure in the whole of Nigeria is under resourced; hence ventilation strategies’ based on mechanical extraction are not possible. Five wards within low rise hospital buildings were studied; these were purpose designed hospital buildings, not converted buildings. Questionnaire surveys of health care workers in the hospitals was conducted and revealed dissatisfaction with the buildings’ ventilation and Indoor Air Quality. The questionnaires were then followed up by Tracer Gas measurements and during the period of measurement there was only one occasion when a ward achieved an air change rate of 6-ach-1, the ASHREA Standard requirement for hospital buildings. To investigate methods of improving natural ventilation in these wards, a CFD model was developed of a representative ward, the model was validated against the Tracer Gas measurements; with an acceptable agreement of ≤ 15%. Using the CFD model, achievable ventilation strategies within the context of the location, were investigated, and a combination of cross ventilation utilizing windows on the windward and leeward sides of the ward together with a roof ventilator on the leeward side proved the most successful. All openings were screened to prevent the entry of mosquitos. This best case was further investigated with the wind direction at an oblique angle to the ward side. The oblique angle of wind attack reduced the air change rates but improved air circulation/mixing within the ward. With the exception when the wind direction was parallel to the ward side. To reduce the ingress of Harmattan Dust, was problematic given the energy restrictions, a low energy solution of introducing screened plenums on both the windward and leeward sides of the building proved successful. Larger dust particles were detained within the windward plenum and the smaller dust particles were exhausted into the leeward plenum. With the mosquito screens located on the large surface area of the plenum, the window screens were removed resulting in higher air change rates. Thus, it is recommended that, openings should be provided on the windward and leeward walls and on the roof toward the leeward side for efficient ventilation and airflow circulation at the occupancy level. The longer sides of the wards should be oriented toward the North-South to capture the North-East trade winds and South-West monsoon winds with oblique angle of attack. Plenums should be incorporated to the windward and leeward facades and Insect screen should be installed on the plenums instead of the wards’ openings to increase ventilation rates while excluding mosquitoes and decreasing dust particle concentration in the hospital wards. Openings should be at the middle of the windward and leeward walls and on the roof toward the leeward to avoid airflow short-circuiting. It is recommended to use insect screen with the porosity of 0.2 and when the outdoor local wind speed is ≤ 1.26 m/s (2 m/s: airport value), the ventilation should be supplemented with fan.

This research concerns the mathematical and physical modelling of the buoyancy-driven flow of warm air at night from a multi-storey atrium building by displacement ventilation. The process of clearing warm air from a building at night is known as 'night-purging'. The primary aim of this research was to enhance understanding of these flows to thereby facilitate efficient design of passively night-purged buildings. The thesis begins with a review of research on natural ventilation and night-purging. Particular focus is given to the conditions for achieving classical displacement flow, in which there is an absence of mixing between warm and cool air, as this has been shown to be the most efficient means of removing warm air from a space. We identify that the dynamics of the plumes of warm air discharged from the storeys into the atrium play a crucial role in the development of the thermal stratification in the atrium. The majority of research on turbulent plumes has concerned plumes from horizontal sources, while ventilation openings are often oriented at some angle off-horizontal. We therefore investigate how varying the angle of orientation of the plume source (or ventilation opening) affects the dynamics of the plume to determine the implications for buildings ventilated via wall-mounted windows. This modelling reveals that, for a significant proportion of a typical night-purge in a single storey, a plume from a vertically oriented opening will not project away from the opening. Thus the simple plume model we have developed will not apply during the late stages of a night-purge. In order to develop a model of plumes which do not project away from the source, we investigate the limiting case of a plume from a vertically distributed source (such as a vent) with zero source momentum flux, such that the motion is entirely parallel to the source. To investigate the overall flow in the building, guided by the results of the plume modelling, we develop a simplified mathematical model to predict the purging of warm air in a generic two-storey atrium building. The pre-dictions of the model enable the classification of night-purging behaviours into three distinct classes of flow, based on the chronology of a number of key events in the progression of a night-purge. Interrogation of the predictions suggests that two transitional behaviours which fall between the three classes of flow provide 'optimal' purging behaviour: one for purging just the storeys in a minimum time and the other for purging the entire building in a minimum time. Adaptation of the mathematical model facilitates the development of design curves for building designers to appropriately size ventilation openings in order to achieve the optimal night-purges. Complementary physical modelling in water-filled visualisation tanks enabled testing of the mathematical model predictions and optimal nightpurging behaviours. Whilst demonstrating the suitability of a simplified mathematical approach to predicting what are complex patterns of airflow, the physical modelling highlighted the complexity of the developing stratification in the atrium and raises a number of new questions for future research.

The prevailing paradigm in indoor environment control of office buildings often excludes natural ventilation, due to the fact that its dynamic nature may not be compatible with the close control of mechanical conditioning systems. The challenges will be greater in terms of the potential high magnitudes of wind and buoyancy forces at high levels of tall buildings. This research is concerned with the prospect of tall office buildings that are purely naturally ventilated. It is proposed that “segmentation” might offer the least risky approach for natural ventilation design of non-domestic tall buildings. Accordingly, the generic design procedure are proposed for investigating the influence of segmentation on ventilation air flows: firstly, the single-cell envelope flow model is adopted to evaluate the steady-state bulk flows through openings under a specified design condition; secondly, dynamic thermal modelling with an air flow network module is used, because of the particular importance of the coupling between the airflow and thermal process for evaluating the year-round ventilated cooling potential of targeted spaces. The chosen thermal model utilizes a multi-cell airflow network model (AFN) since the targeted buildings can no longer be described by a single-cell model; thirdly, computational fluid dynamics (CFD) simulation is suggested in the later design stage to cope with insufficient resolution of local airflow distribution in previous modelling stages; finally, the overall performance of comfort ventilation is then interpreted in relation to adaptive thermal comfort theory by the use of Building Bioclimatic Charts, which offers a way of rapidly testing whether or not natural ventilation is likely to produce comfortable conditions. The novelty of this work lies not in the methodology, which uses available modelling tools, but in the evaluation of naturally ventilated tall buildings with reference to segmentation in the climatic context of Taiwan. The effect of segmentation is evaluated by comparing the overall ventilation performance under three different building configurations, namely the isolated, segmented and non-segmented tall buildings. The overall objectives are to determine whether the magnitudes of air flow rates and the resultant flow velocity can achieve the desired comfort ventilation over a range of specified conditions. Potential scenarios where the design goals may not be ensured are identified. The feasibility for naturally ventilated tall office buildings in hot and humid climates is clarified accordingly.