This thesis describes an investigation into the phenomenon of air entrainment in vertical dropshafts conveying water from a high level to a lower level. The study initially commenced with hydraulic tests on scale models of a vortex-entry dropshaft arrangement. This subsequently expanded into a more detailed analysis of the mechanisms involved in the air entrainment, rejection and transport processes evident in the early stages of the work. An attempt has been made to define the criteria controlling these three modes of operation in air/ water systems. The physical process of initial entrapment by the plunging water film was researched extensively. The inability to accurately reproduce the bubble sizes in scale models conclusively shows that this aspect is fundamental to the understanding of the problem. A dimensional analysis of the parameters controlling the rate of entrainment in the system was undertaken in the investigations. A number of dimensionless groups were obtained to describe the relationships between the parameters involved in the process. This enables the rate of air entrainment to be predicted in any.system of dropshafts under certain flow and geometrical conditions. The downward passage of air bubbles in water (just one mode of operation in two-phase flow systems) was investigated to establish the air transport capabilities of various flows and hence the air rejection process. An empirical relationship was derived which describes the air void ratio at various discharges and hence enables many aspects of the transport of air bubbles to be studied. A series of values defining the limits of operation of the phases invovled in air entrainment were also identified, e.g. onset of air entrapment and air transport.

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The global increase in demand for dwelling energy and implications of changing climatic conditions on buildings require the built environment to build sustainable dwellings. The aim of this thesis is to apply passive mitigation and adaptation design strategies to newly detached residential buildings in the UK with the view to identify the key building envelop and systems parameters to secure the right balance of energy consumption and thermal comfort in dwellings. In addition, currently, acceptable robust validation process for validating space temperatures is required, as existing simulation software validation is geared toward energy consumption. The thesis further aims to apply an effective validation method to the validation of building simulation indoor temperatures. This thesis comprised of six case studies. In the first study, Bland-Altman’s method of comparison is used as a validation technique in validating space temperatures in building simulation application. This is a newly developed knowledge in civil and construction engineering research in validating thermal analysis simulation software. The relevance of this approach is due to the emergent understanding that the goodness of fit measures used in current building simulation model validation are inadequate coupled with that fact that the current simulation software validation are geared toward energy consumption. In the second study, global Monte Carlo sensitivity analysis is performed on two differing weather patterns of UKCIP02 and UKCP09 weather data sets to compare their impact on future thermal performance of dwellings when use in thermal analysis simulation. The investigation seeks to ascertain the influential weather parameters which affect future dwelling indoor temperatures. The case study when compared to literature affirms the mean radiant temperature and the dry bulb air temperature as the key parameters which influence operative temperatures in dwellings. The third study, the extent of impact of climate change on key building performance parameters in a free running residential building is quantified. The key findings from this study were that the average percentage decrease for the annual energy consumption was predicted to be 2.80, 6.60 and 10.56 for 2020s, 2050s and 2080s time lines respectively. A similar declining trend in the case of annual natural gas consumption was 4.24, 9.98 and 16.1, and that for building emission rate and heating demand were 2.27, 5.49 and 8.72 and 7.82, 18.43 and 29.46 respectively. This decline is in consonance with the range of annual average temperature change predicted by the GCM based on the IPCC scenarios (IPCC, 2001) which generally shows an increase in temperature over stipulated timelines. The study further showed that future predicted temperature rise might necessitate the increasing use of cooling systems in residential buildings. The introduction of cooling to offset overheating risk, the trend of heating and cooling demand shows progressive increase variability with an average percentage increase of 0.53, 4.68 and 8.12 for 2020s, 2050s and 2080s timelines respectively. It is therefore observed that the introduction of cooling cancels out the energy gains related to heating due to future climatic variability. The fourth, fifth and sixth case studies consider the integrated passive mitigation strategies of varying future climatic conditions, variable occupant behaviour, building orientation, adequate provision of thermal mass, advance glazing, appropriate ventilation and sufficient level of external shading which influence the potential thermal performance of dwellings and a methodology that combines thermal analysis modelling and simulation coupled with the application of CIBSE TM52 adaptive overheating criteria to investigate the thermal comfort and energy balance of dwellings and habitable conservatories. In the fourth study, the impact of four standardized construction specifications on thermal comfort on detached dwellings in London, Birmingham and Glasgow are considered. The results revealed that the prime factor for the variation of indoor temperatures is the variability of climatic patterns. In addition, London is observed to experience more risk of thermal discomfort than Birmingham and Glasgow over the time period for the analysis. The total number of zones failing 2 or 3 CIBSE TM52 overheating criteria is more in London than in Birmingham and Glasgow. It was also observed that progressive increase in thermal mass of the standardized construction specifications decrease the indoor temperature swings but increase in future operative temperatures. The day ventilation scenario was seen not to be effective way of mitigating internal heat gains in London and Birmingham. The opposite was observed in Glasgow. Night ventilation coupled with shading offered the best mitigation strategy in reducing indoor temperatures in London and Birmingham. In the fifth study, Monte Carlo sensitivity analysis is used to determine the impact of standard construction specifications and UKCP09 London weather files on thermal comfort in residential buildings. Consideration of London urban heat island effect in the CIBSE TM49 weather files leading to the generation of three different weather data sets for London is analysed. The key findings of the study indicated that in the uncertainty analysis (box and whiskers plots), the medians for the day ventilation scenarios are generally higher than those of the night ventilation and further higher than the night ventilation with shading scenarios. This shows that applying mitigation scenarios of night ventilation and shading have a significant impact on reducing internal operative temperatures. In addition, the sensitivity analysis shows glazing as the most dominant parameter in enhancing thermal comfort. The sensitivity of glazing to thermal comfort increases from Gatwick, with London Weather Centre having the highest sensitivity index. This could be attributed to the urban heat island effect of central London, leading to higher internal operative temperatures. The study thus shows that more consideration should be given to glazing and internal heat gains than floor and wall construction when seeking to improve the thermal comfort of dwellings. Finally, the sixth study considers the use of passive solar design of conservatories as a viable solution of reducing energy consumption, enhancing thermal comfort and mitigating climate change. The results show that the judicious integration of the passive solar design strategies in conservatories with increasing conservatory size in elongated south facing orientation with an aspect ratio of at least 1.67 could progressively decrease annual energy consumption (by 5 kWh/m2), building emission rate (by 2.0 KgCO2/m2) and annual gas consumption (by 7 kWh/m2) when the conservatory is neither heated nor air-conditioned. Moreover, the CIBSE TM52 overheating analysis showed that the provision of optimum ventilation strategy depending on the period of the year coupled with the efficient design of awnings/overhangs and the provision of external adjustable shading on the east and west facades of the conservatory could significantly enhance the thermal comfort of conservatories. The findings from these case studies indicate that thermal comfort in dwellings can be enhanced by analysis of future climatic patterns, improved building fabric and provision of passive design consideration of improved ventilation and shading. They also confirm that the utilization of appropriate mitigation strategies to enhance thermal comfort could contribute to the reduction of the environmental implications to the built environment and facilitate the drive towards the attainment of future sustainability requirements.

Wet central heating systems account for a very large portion of energy consumption in the UK and recent figures indicate that its usage in households will be increasing even further. Under such circumstances, it is desirable to use these systems in the most efficient way possible. However, dissolved gases that penetrate into central heating systems are later released as bubbles due to local supersaturated conditions occurring on the primary heat exchanger wall of the boiler. This leads to a two-phase flow throughout the pipework, causing microbubbles to escape to the upper parts of the system and creating cold spots in the radiators, thus, reducing its efficiency. There is an increasing trend in building services to install devices that remove these unwanted gases. Therefore, investigation of two-phase structures throughout different pipe installations will facilitate companies in enhancing their deaerator designs. In this regard, extensive experimental and computational investigations of two-phase flow structures were conducted within this study. Two-phase flow structures were measured by a photographic technique and investigated in means of void fractions, bubble sizes, and velocities. Fluid velocities in the range of 0.5 to 1.1 m/s at typical wet central heating temperature (60 to 80 °C) and pressures (2.2 to 27 bar) were utilized. Results show that that bubble production increases as temperature, boiler heating load, and saturation ratio escalate. On the other hand, it reduces when the pressure and flow rate of the system gets higher. A clear relationship between bubble sizes and system parameters was non-existent, except for the system flow rate (where bubble diameters decrease as the flow rate increases). Moreover, bubbles were evenly distributed during vertical flow when compared to horizontal flow, where bubbles tend to flow at the upper parts of the pipe. Furthermore, it was shown that bubble distributions were highly affected by obstacles like the 90 degree bend, thermocouple or pressure sensors. In addition, it was observed that axial flow development of bubbly flow was a continuous process and void fraction at the upper part of the pipe increased as the flow travelled through horizontal pipeline. Regarding the bubble velocity measurements, it was concluded that, bubble velocity profiles show development along both vertical and horizontal flows and approach to profiles which can be expressed with the power-law. Moreover, coalescence of two bubbles during horizontal flow was captured, emphasizing that the effect of coalescences should not be neglected at low void fractions. It was also found that bubbly flow in central heating systems was in a coalescences dominant regime and maximum bubble diameter observed at most positions were higher than theoretically defined values. Moreover, bubble dissolution effect was not observed at any of the test rig conditions. The reasons were thought to be the variation saturation ratio and axial flow development of two-phase flow, which supress the effect of dissolution and favour coalescence phenomenon. Finally, after evaluating conclusions from the experimental results and computational study regarding the effect of the 90 degree bend on void fraction distributions, it was concluded that the employed physical model and solver settings in ANSYS Fluent 14.5, can be utilized to predict bubble distribution developments throughout the central heating systems’ pipework. Keywords: Central heating systems, two-phase flow, bubbly flow, bubble distributions, bubble sizes, bubble velocities, coalescence, image processing, experimental fluid easurements.

Most existing houses in the UK have a single thermostat, a timer and conventional thermostatic radiator valves to control the low pressure, hot water space heating system. A number of companies are now offering a solution for room-by-room temperature and time control in such older houses. These systems comprise of motorised radiator valves with inbuilt thermostats and time control. There is currently no evidence of any rigorous scientific study to support the energy saving claims of these zonal control systems. This thesis quantifies the potential savings of zonal control for a typical UK home. There were three components to the research. Firstly, full-scale experiments were undertaken in a matched pair of instrumented, three bedroom, un-furbished, 1930s, test houses that included equipment to replicate the impacts of an occupant family. Secondly, a dynamic thermal model of the same houses, with the same occupancy pattern, that was calibrated against the measured results. Thirdly, the experimental and model results were assessed to explore how the energy savings might vary in different UK climates or in houses with different levels of insulation. The results of the experiments indicated that over an 8-week winter period, the house with zonal control used 12% less gas for space heating compared with a conventionally controlled system. This was despite the zonal control system resulting in a 2 percentage point lower boiler efficiency. A calibrated dynamic thermal model was able to predict the energy use, indoor air temperatures and energy savings to a reasonable level of accuracy. Wider scale evaluation showed that the annual gas savings for similar houses in different regions of the UK would be between 10 and 14% but the energy savings in better insulated homes would be lower.

In recent years there has been an increasing trend in the provision of central heating and split vapour compression air conditioning systems to domestic dwellings in Cyprus. To minimise their economic and environmental impact, this study examines the feasibility and economic viability of energy conservation measures and the feasibility of the application of solar driven LiBr-water absorption system for space conditioning. Initially, the study compares through simulation, the heating and cooling requirements of domestic dwellings constructed in Cyprus during the last century. The simulations required values for the thermal conductivity of local building materials, like the hollow brick and mud and straw block. These were not available, and measurements were performed on a machine specifically purchased for the project to establish these values for the first time. These material properties will be of value to building services engineers in Cyprus and the Middle East for the more precise determination of building heating and cooling loads. Evaluation of the internal conditions resulting from the various types of constructions indicated that the traditional and insulated modem houses, could maintain indoor temperature in winter between 16°C and 20°C, but in the summer temperatures exceeded 36°C. The use of natural and mechanical ventilation could reduce slightly the maximum indoor summertime temperatures, but not to a level that could provide thermal comfort. Window gains are an important factor in domestic building energy requirements, and significant savings can result when extra measures are taken. The savings in cooling energy demand for a well-insulated house may be as high as 24% when low-emissivity double glazed windows are used compared to clear double glazed windows giving a pay-back period of 3.8 years. Other factors investigated are the effect of overhangs, shape and orientation of buildings and thermal mass. The results show that the roof is the most important structural element of domestic dwellings in the Cypriot environment. For good thermal performance, the roof must offer a discharge time of 6 hours or more and have a thermal conductivity of less than 0.48 W/m-K. Life cycle cost analysis has shown that measures that increase the roof insulation pay back in a short period of time, between 3.5 to 5 years. However, measures taken to increase wall insulation pay back in a longer period of time, approximately 10 years. The only natural energy resource abundantly available in Cyprus is solar energy, which could be used to power a low energy active cooling system based on the absorption cycle. To facilitate investigation of the feasibility of the application of solar driven absorption systems for domestic cooling, a 1 kW LiBr-water absorption-cooling unit was designed and constructed. The unit was used to determine experimentally the heat and mass transfer coefficients in the heat exchangers of absorption systems. In certain cases these were found to differ considerably from values obtained from heat and mass transfer correlations published by other investigators. The experimentally determined heat and mass transfer coefficients were employed in the design and costing of an 11 kW cooling capacity solar driven absorption cooling machine which, from simulations, was found to have sufficient capacity to satisfy the cooling needs of a well insulated domestic dwelling. Economic analysis has shown that for such a system to be economically competitive compared to conventional cooling systems its capital cost should be below C£ 2000. This drawback can be balanced by a lower total equivalent warming impact being 2.7 times smaller compared to conventional cooling systems.

The purpose of this study is to obtain an insight into the mechanisms by which a geosynthetic membrane influences the performance of a plane strain and an axisymmetric two-layer soil system, where the reinforcement is incorporated either into a layer of fill, or at the interface of a layer of fill overlying clay subgrade. New axisymmetric membrane and interface element formulations are developed and incorporated in to an existing large strain finite element code. A linear elastic model of behaviour is used for the membrane material and an elastic-perfectly frictional model, based on the Mohr-Coulomb yield function, is implemented for the interface. These new formulations both take account of large global displacement and rotation effects, although the interface element is constrained to small relative displacements, and are checked against small and large strain closed form test problems. The finite element equations are based on an Updated Lagrangian description of deformation. Plane strain finite element investigations into the significance of the resolution and relative size of the finite element mesh, and the differences between large and small strain analyses, are undertaken. For typical unreinforced and reinforced plane strain and axisymmetric two- layer soil systems a detailed analysis is presented of the soil displacements, strains, stresses, principal stress directions, mobilised fill friction angles and the stresses on the underside of the footing. A series of plane strain and some axisymmetric parametric studies of the various material properties is conducted, to assess the influences and relative importance of those variables to the performance of the two-layer soil system under monotonic loading. The study considers various reinforcement lengths and stiffnesses, fill depths and strengths, and different clay strengths. The mechanisms of reinforcement are identified through careful examination of the footing load-displacement response, the reinforcement tension and the stresses and displacements at the interfaces with the surrounding soil. A comparative study is also undertaken between the results obtained by the finite element model and those predicted by a plane strain and axisymmetric limit equilibrium design method. The effects of including a low friction membrane within an oil storage tank base, as secondary containment against oil leakage, are investigated by a series of axisymmetric finite element analyses.

Passive ventilation and cooling systems can offer energy savings when combined into a mechanical ventilation and cooling strategy for office buildings. At early design stages, it is difficult to predict actual energy savings as current design and calculation tools are limited and do not allow assessment for energy reductions when attempting to use typical passive options such as solar chimneys, rain screen facades, ventilated double facades, passive downdraught evaporative cooling and earth ducts. The only passive systems that are directly incumbent to dynamic thermal modelling software are natural ventilation and external solar shading. Currently, impacts of passive systems on annual building energy performance is unclear and lacks clarity. In hot climates, this is even more problematic as buildings need to endure higher external temperatures and solar irradiation. Understanding minimal energy performance reductions for each passive system can aid with design decisions regarding building ventilation and cooling strategies. The aim of this study is to investigate how existing passive ventilation and cooling system design and operational strategies can be improved to reduce mechanical ventilation and cooling energy consumption for commercial buildings in hot climates. Theoretical commercial building models are created using dynamic thermal simulation software to determine minimum mechanical ventilation and cooling energy values, which are verified against published bench marks, known as base case models. These base case models are simulated using weather data from four different hot climates (Egypt, Portugal, Kenya and Abu Dhabi). Impacts of passive system energy performance are afforded by using either dynamic thermal simulation or fundamental steady state analysis identifying approximate passive ventilation and cooling potentials for reducing mechanical energy. These percentage reductions are created based upon passive system parameters and weather data, using appropriate methodology. From these findings new simplified design guidelines, integration strategies and performance design tools are created including a new passive system energy assessment tool (PSEAT) using Microsoft Excel platform to ensure that a wider audience can be achieved in industry. The design guidance and integration strategies are developed and simplified to enable architects, building services engineers and alike, to apply with speed and accuracy influencing the design process and improve confidence in desired passive solution.

Within the UK, space heating accounts for 66% of the total domestic energy used. New heating controls may offer a means to reduce this figure and help meet the UK s target of reducing its greenhouse gas emissions by 2050. However these technologies will only save energy if occupants are able to use them effectively. Currently, little is known about how occupants interact with their heating systems, in particular how they use the heating within their home and the reasons behind why it is used a specific way. To investigate further, this thesis presents research which used both qualitative and quantitative methods over two separate studies to uncover why and how households heat their homes and how people use their heating system following the installation of new heating controls. The results identify key drivers which impact how people heat their homes and highlight numerous issues preventing them from using their heating how they wish to. A taxonomy of heating use is presented based on the factors influencing heating use in homes and how those factors impact the use and control of the heating system. Occupants use of new heating controls over a ten month period is presented. Manual interaction with controls is separated from programmed heating schedules showing increased manual use over winter and a reliance on heating schedules during shoulder months. The analysis of measured heating use showed similar findings to larger scale studies, however the demanded set-point temperatures were varied and occupants regularly changed heating schedules throughout winter, indicating some of this complexity may be lost by studies inferring heating use patterns from internal temperature measurements alone. The research presented within this thesis is novel, in developing heating characters based on the factors which influence occupants heating behaviours, by presenting measured heating use, which included measured set-point temperatures, heating schedules and heating use duration. The thesis also presented the complexity of heating use within homes uncovered through use of mixed methods.

This research concerns the in-use performance of light-gauge steel modular construction used for residential purposes. The aim was to investigate ways to reduce the in-use energy consumption of new buildings, while ensuring thermal comfort. Data were collected from two case study buildings in the UK, one in Loughborough and the other in London, using a variety of methods including building measurement, building monitoring, inspections, and a detailed review of the construction documentation. The case study buildings were monitored using EnOcean enabled wireless sensor networks and standalone temperature sensors. Monitoring data included electricity consumption in individual rooms, often by end use, space heating use, internal temperature and relative humidity, and external temperature. Building measurements included blower door tests to measure fabric air leakage rates, infrared thermal imaging to identify fabric defects and weaknesses, and ventilation system flowrate measurements. Inspections and the review of documentation allowed problems with design, manufacture and construction to be identified. A particular concern for thermally lightweight construction is the risk of overheating, therefore overheating analyses were undertaken. The research identified weaknesses in the design, construction and operation of the case study buildings resulting in increased energy use and poor thermal comfort, particularly overheating. The modular construction studied requires specific design changes to improve the fabric and building services, in order to reduce energy use. There are also specific recommendations for quality control on site to ensure critical stages are correctly completed, such as installing rigid insulation. There are also more general recommendations for how a company operates because this can influence performance; there ought to be greater attention to holistic design and greater collaboration with suppliers and contractors to determine robust solutions. Overheating was a problem in the London case study, and more research is required to understand the scale of the problem. Avoidance of overheating must be a focus in the design of new buildings. The findings suggest that once the problems with the design and quality control on site are rectified, offsite modular construction can be used to consistently and reliably provide low energy homes.