Faults that develop in the heat exchanger subsystems in air-conditioning installations can lead to increased energy costs and jeopardise thermal comfort. The sensor and control signals associated with these systems contain potentially valuable information about the condition of the system, and energy management and control systems are able to monitor and store these signals. In practice, the only checks made are to verify set-points are being maintained and that certain critical variables remain within predetermined limits. This approach may allow the detection of certain abrupt or catastrophic faults, but degradation faults often remain undetected until their effects become quite severe. This thesis investigates the appropriateness of using mathematical models to track the development of degradation faults. An approach is developed, which is based on the use of analytical models in conjunction with a recursive parameter estimation algorithm. A subset of the parameters of the models, which are closely related to faults, is estimated recursively. Significant deviations in the values of the estimated parameters from nominal values, which represent `correct operation', are used as an indication that the system has developed a fault. The extent of the deviation from the nominal values is used as an estimate of the degree of fault. This thesis develops the theory and examines the robustness of the parameter estimator using simulation-based testing. Results are also presented from testing the fault detection and diagnosis scheme with data obtained from a simulated air-conditioning system and from a full size test installation.

Cooling and ventilation of office spaces by displacement ventilation and chilled ceiling panel systems is potentially more energy efficient than conventional air conditioning systems. Heat transfer in this type of system is characterised by the presence of vertical temperature gradients and significant radiant asymmetry. The room heat transfer models used in current building simulation methods do not allow adequate representation of this type of system due to their reliance on a single node to define the internal air temperature. The overall aim of the work described in the thesis has been to develop a model of this type of system that is suitable for use in annual building energy simulation. The model presented, is intermediate in complexity between a CFD numerical model and the current single air node models, having ten air nodes. The operating characteristics of displacement ventilation systems, used both with and without chilled ceiling panels, have been studied by making experimental measurements in a test chamber and by reference to published experimental data. Numerical calculations of the flow and temperature fields have been made with a coupled flow and radiant exchange CFD code. Steady state calculations have been made of displacement ventilation using a conjugate heat transfer method. Interesting oscillations in the flow and temperature field of displacement ventilation operating with a chilled ceiling have been found through adopting a fully transient calculation procedure. The thesis describes how the experimental and numerical data has been used to develop the structure and define the parameters of a simplified nodal model. The logical development of the model structure, from the most elementary model to one which is able to capture the effects of the temperature gradients and incomp1ete mixing of the air in the room is described. A method is also presented whereby the parameters of the model are found directly from the experimental data by solving the heat and mass balance equations of the nodal model. The parameters of the model have been generalised by analysing these calculations and by making use of established convection coefficient correlations. The performance of the model is demonstrated by firstly making comparisons of the experimental and numerical data under steady state conditions, and also by demonstrating that the model is able to reproduce the characteristics of displacement ventilation and chilled ceiling systems under different operating conditions.

No description available.

The conditions under which stable separate and coalesced multiple parallel arcs can be operated from a common power supply have been investigated and analysed. Results indicate that any number of stable parallel arcs can be maintained provided each arc is individually stabilised. Multiple electrode configurations relevant to industrial plasma processes have been investigated including coalesced discharges with multiple, individually stabilised, anodes and cathodes and discharges with multiple cathodes and a common anode. The results have been applied to a number of plasma processes including a horizontal multiple discharge system, capable of producing large volumes of ionised gas with a high degree of uniformity, a plasma furnace incorporating multiple de plasma torches operating from a single power supply, and a high-current, non-consumable, multiple cathode assembly for use in do arc furnaces. A horizontal multiple arc system and a plasma furnace incorporating three plasma torches have been designed at the University and are in use for processing material at Cambridge University and in industry respectively.

A numerical model has been developed for the dynamic simulation of heat and radiation transfer from lamps and ballasts in an enclosure. The model, named LITEAC1, calculates temperatures, cooling loads and illuminances at each simulation time step. LITEAC1 is an improvement upon existing models in the literature in the following aspects: it performs dynamic simulation for all nodes without assuming that some nodes are massless; it calculates illuminances on room surfaces; and it runs faster on a desktop computer. In order to refine the simulation of the two-way interaction between lighting and HVAC systems, a fluorescent lamp positive column discharge model, named LAMPPC, has been incorporated into LITEAC1 to improve calculation of the conversion of input electrical energy into light, thermal radiation and heat. LAMPPC employs established principles in plasma physics to quantify the energy conversion processes.

This thesis is an investigation into the implications that a warming climate has for the housing retrofit programme recently completed at Rushenden on the Isle of Sheppey that was the subject of the EU Interreg research project IFORE (Innovation for Renewal, 2010- 2014). The aim of this thesis is to inform UK public policy on social housing retrofit, as to whether we are pursuing the correct goal by retrofitting with insulation and air-tightness, a strategy to conserve heat, rather than one that would also combat summertime overheating. The community of Rushenden was used as a case study to develop a specific adaptation strategy for retrofitted social housing in the South-East of England. Gaps in knowledge were identified relating to the role that insulation and air-tightness has in reducing or increasing the overheating risk, and the analysis of a wider range of shading strategies. The measures were discussed with sixteen households during completion of the adaptations questionnaire and three focus groups. Six households completed daily a longitudinal comfort questionnaire, over a period of two months. Monitoring of internal and external temperatures was carried out as part of IFORE but in addition questions about overheating were included by the author within the three IFORE questionnaires that were submitted to one hundred households during the timescale of the project. Two models were built in ESP-r, a European standard building simulation tool: a singlestorey and a two-storey house type. Dynamic thermal modelling, incorporating future weather files, was used to evaluate different specifications of insulation and air-tightness and the climate change adaptation measures. Future heating and cooling loads were calculated and the overheating risk was assessed using the adaptive comfort algorithm. The first results from the simulations showed that the light type of retrofit installed by IFORE will reduce both the heating load and the cooling load in 2030s, 2050s and 2080s. On the other hand, a deeper type of retrofit that complies with the Passivhaus standard U-value for wall insulation, and air-tightness, will reduce the heating load but increase the cooling load. Despite reduction of overheating risk using the lighter type of retrofit, the living room of the single storey house will not meet the adaptive comfort set of criteria and should be classed as “overheating”. The installation of internal white, opaque roller blinds, will meet the adaptive comfort criteria and eliminate the need for cooling in both the single and two storey houses. The adaptation measures were discussed in terms of their practicality, affordability and the interaction between occupant and technology. The discussion arising from this work is to judge the wider application of its results as a guide to retrofit decision-making.

This thesis investigates the design of domestic glazed spaces in the United Kingdom, by studying the effect of a range of variables on the thermal properties of glazed spaces, in order to achieve a thermally comfortable environment while minimising the use of energy for heating and cooling. Earlier research work on domestic glazed spaces has concentrated on optimising the design of the space as a mechanism for reducing the space heating load of the parent house. Computer based dynamic thermal simulation is used in this study as the method of assessment and the variables tested are; glazing type, orientation and the degree of integration of the glazed space with the parent building. Unshaded, unventilated, and unheated, glazed spaces were found to be thermally comfortable for only a quarter to a third of the hours of possible use whatever the form, orientation or glazing type. Generally the higher the insulating value of the glazing the fewer the number of comfortable hours for all orientations and arrangements, due to discomfort being caused by high temperatures, even though the weather data used for the simulations only rose above 27'C for 25 hours during the course of the year. Further studies showed that significant reductions in the number of hours experiencing high temperatures could be achieved by the use of buoyancy driven ventilation. The studies indicated that glazed spaces integrated into the house plan tended to experience high temperatures for long periods but that the peak temperatures were much lower than those experienced for shorter periods in the exposed spaces. The effect of ventilation on overheating was therefore more marked in the integral than in the exposed glazed spaces. A study of the effects of roof shading blinds indicated that internal blinds had minimal effect in reducing high temperatures. External blinds had a greater effect than ventilation and a combination of external roof blinds and ventilation appears to provide the best strategy for the control of high temperatures. Studies on space heating loads for the houses and glazed spaces indicated wide variations in the heating loads of the glazed spaces depending predominantly on the insulating properties of the glazing. In terms of the reduction in the space heating load for the parent house, the thermal simulation results predict very little change due to the presence of the glazed space. A study on the effect of increasing the thermal storage properties of the floor construction of the glazed spaces, by substituting a clay tile finish for the original thin carpet layer, in order to reduce high temperatures proved inconclusive with minimal changes in the number of comfortable hours experienced. An investigation of thermal comfort during the Winter indicated that low surface temperatures did not reduce resultant temperatures below the lower limit of the comfortable range in the glazed spaces, during the heated period.

A prototype centreless grinding machine was modified extensively to operate satisfactorily at high grinding wheel speeds and in the high rate centreless grinding regime. The principal modifications included the provision of a 75 k. W. d. c., variable speed, main drive motor which enables grinding wheel speeds up to 120 m/s to be employed and a coolant supply manifold was designed and manufactured-which was capable of delivering a high velocity coolant stream to the grinding zone. In addition, a measurement system was developed-which-allowed the grinding forces to be monitored and recorded in process. Two solutions for the accepted kinematic model of plunge feed cylindrical grinding are proposed. The general and more accurate solution takes account of the variable grit height and separation of the grinding wheel, whilst the particular and approximate analytical solution makes provision for variable grit separation only. The particular solution enabled parametric studies to be undertaken and allowed comparisons with the solutions proposed by other workers. The trends of theoretical grinding forces were predicted from analysis of the undeformed chip dimensions. The trends indicated two methods of achieving high stock removal rates, firstly, for a constant force value, higher stock removal rates are possible by increasing the grinding wheel speed and infeed-rate. Secondly, at a constant grinding wheel speed, and force level, reducing the workpiece speed and increasing the infeed-rate will yield higher stock removal rates. Experimental results were in agreement with these predictions. An extensive experimental programme investigating plunge feed centreless grinding of ferrous components was undertaken. Results from approximately 300 grinding experiments were used to establish a data bank of grinding parameters for a range of grinding conditions. High-rate centreless grinding has been shown to be a feasible first machining process. It has also been shown that the choice of kinematic conditions is important in achieving high stock removal rate grinding. Incorrect choice of kinematic conditions can cause problems of, workpiece burn, grinding vibrations and excessive power demands. Limit charts have been constructed which outline the boundaries to the process in terms of burn, grinding vibration and power limit. Operation between the boundaries is best achieved if the ratio of grinding wheel to workpiece speeds is in the range 90 - 200. The results enable a data based control strategy to be formulated and it is proposed that in process variable kinematics will allow a single cycle roughing and finishing operation on a suitably adapted centreless grinding machine.

No description available.

The work presented in this thesis investigates design, computer modelling and testing a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The context of this evaporative cooling technology design is specifically targeted at locations with a hot and dry climate such as that prevailing in most regions of Middle East countries. The focus of this technology is to address the ever-escalating energy consumption in buildings for space cooling using mechanical vapour compression air conditioning systems. In this work, two evaporative cooling configurations both based on sub-wet bulb temperature principle have been studied. Furthermore, in these designs, it was sought to adopt porous ceramic materials as wet media for the evaporative cooler and as building element and use of heat pipes as heat transfer devices. In the first test rig, the prototype system uses porous ceramic materials as part of a functioning building wall element. Experimental and modelling results were obtained for ambient inlet air dry bulb temperature of 30 and 35oC, relative humidity ranging from 35% to 55% and intake air velocity less than 2 (m/s). It was found that the design achieved sub-wet bulb air temperature conditions and a maximum cooling capacity approaching 242 W/m2 of exposed ceramic material wet surface area. The wet bulb effectiveness of the system was higher than unity. The second design exploits the high thermal conductivity of heat pipes to be integrated as an effective heat transfer device with wet porous ceramic flat panels for evaporative cooling. The thermal performance of the prototype was presented and the computer model was validated using laboratory tests at temperatures of 30 and 35oC and relative humidity ranging from 35% to 55%. It was found that at airflow rates of 0.0031kg/s, inlet dry-bulb temperature of 35oC and relative humidity of 35%, the supply air could be cooled to below the inlet air wet bulb temperature and achieve a maximum cooling capacity of about 206 W/m2 of wet ceramic surface area. It was shown that the computer model and experimental tests are largely in good agreement. Finally, a brief case study on direct evaporative cooling thermal performance and environmental impact was conducted as part of a field trip study conducted on an existing large scale installation in Mina Valley, Saudi Arabia. It was found that the evaporative cooling systems used for space cooling in pilgrims’ accommodations and in train stations could reduce energy consumption by as much as 75% and cut carbon dioxide emission by 78% compared to traditional vapour compression systems. This demonstrates strongly that in a region with a hot and dry climate such as Mina Valley, evaporative cooling systems can be an environmentally friendly and energy-efficient cooling system compared to conventional vapour compression systems.