No description available.

This project looks at the production of electricity by the CEGB's power stations noting the vast quantities of water required for cooling purposes. The main types of cooling system and the problem of condenser scaling often associated with the use of cooling towers and the evaporative cooling process are described, together with the usual methods of scale prevention/ treatment. The Croydon B power station is entirely dependant on treated sewage effluent for cooling water. A combination of the high total dissolved solids content of sewage effluent and their concentration by evaporative cooling made condenser scaling a particular problem. A novel method was developed, whereby nitrification of ammonia in the cooling water was used to control pH and prevent scaling. The system has been in operation for some twenty years, and this project investigates the effect of the major physical and chemical factors in cooling towers on the nitrification process. Work was carried out on a laboratory scale in a 15 litre culture vessel, a 27000 litre pilot scale cooling tower rig system and in the power station itself. The site of nitrification and the effect of pH, temperature, substrate concentration, flow rates, retention time, packing area and organic loading were investigated Differences in the reactions to these factors in the different scales of experiment were found and explanations attempted. In a power station cooling system the most important factors governing nitrification were felt to be pH, flow rate and area of packing. The results of the tests were used to develop a simple model of the system which could be used as a rapid guide to the degree of nitrification posible in any cooling tower. Finally the feasibility of the use of different sources of ammonia was investigated.

This thesis reports an investigation into the design of converters for induction heating systems based upon resonant switch mode power converter techniques. The proposed three phase unity power factor induction heating system consists of two stages of power conversions. The important requirements for each stage of the power conversion of a typical induction heating system working from a three-phase supply are identified. A wide range of power converters which fulfil these requirements are compared and evaluated. From the evaluation, the most applicable converter topologies are selected. Each selected converter class is investigated in great detail to outline their advantages and disadvantages. The first stage consists of a push-pull buck converter connected to a unity power factor rectifier stage. This stage converts the three phase AC mains supply to a required DC value. The second stage, which converters the DC into AC is a single ended resonant inverter system. Analysis of the converters has been made and the design procedure has been formulated. The design procedure allows a strenuous design of each resonant converter for particular converter applications. The final converter design has been simulated using the circuit simulation software packages Design Architect and Accusim to verify the results of analysis. The most important design and construction achievements can be summarised as follows: I A novel push-pull buck quasi-resonant converter with a three-phase rectifier stage has been built and tested. At its maximum operating frequency of 40kHz, the prototype converter delivers an output power of 500W. The converter draws nearly sinusoidal currents from the three-phase mains supply and has an input power factor approaching unity. A secondary stage resonant converter provides AC for the induction heater coil. This AC current flowing in the induction coil creates an alternating electromagnetic field for the workpiece. An induction heating coil has been designed and built by using electrical equivalent coil design method. A novel control strategy was developed to provide output power control. Both converter and inverter stage of the system are operated in the zero-current switching condition. The use of this technique allows higher switching frequencies and provides low switching losses. The full design details are presented along with simulation and practical results. The simulation and practical performance results presented show good correlation with theoretical predictions.

The zone method for analysing radiative heat transfer has been widely applied for furnace modelling, and is extensively reported in the open literature. The main reason for the application of this method lies in the accuracy with which it solves the radiant transfer in hot enclosures. Thus, it is generally the preferred method when it is essential to predict accurately the temperature distribution in the furnace. Its application, however, has been limited in most cases by the need to over-simplify the furnace conditions. These simplifications include the need to modify the furnace shape and zoning arrangement, the load representation, and the simulation of convection. Another significant feature of most applications of the zone method is the restriction of the simulation to steady-state conditions. This Ph.D. project aims to eliminate some of these constraints and, therefore, improve application of the zone method to furnaces. Hence, full transient conditions were simulated for different zone models, which varied in complexity from a single gas zone model to a full 3D multi-zone version. The exchange factors required in the zone method were calculated by a Monte-Carlo method using RADEX, a suitable computer code which enabled the furnace geometry to be accurately represented as well as the load, which could be simulated by a series of individual components instead of a single big slab covering the entire hearth surface area. Two different furnaces were modelled, namely a steel reheating furnace and a heat treatment furnace. Experimental data from production were used to validate the heat treatment system mathematical model. Parametric studies were then performed for both furnaces. The predictions clearly demonstrate the need for multi-zone transient models since the load temperature-history was significantly different from that predicted by a simpler long-furnace model. Another aim of the project was to produce reliable data concerning the convective heat transfer in furnaces. This parameter is often ignored in furnace modelling, or if included has been restricted to a crude single empirical value (usually 5 - 10 W/m2K). This can produce erroneous results in applications where the flame and combustion products temperatures are low, as in heat treatment furnaces. In these cases convection may play a more important role than is currently assumed. A mass transfer technique was employed in order to determine heat transfer coefficients for the heat treatment furnace for a variety of load arrangements and firing conditions. These coefficients which were significantly higher (25 - 45 W/m2K) than the usually assumed crude values were subsequently used in the mathematical models of the furnace performance.

This thesis is concerned with an experimental and theoretical investigation of domestic heat pumps. The development of heat pumps in the 1970's did not meet the original expectations and this thesis examines the reasons why. The items considered included cycling and unsteady conditions created whilst matching the heat pump's output to meet a space heating load. A detailed study was made of the hermetically sealed refrigerant compressor, the heat exchangers, and the refrigerant pressure and temperature control systems. In addition to the conventional heat pump a study was made of the advantages gained from modular designed heat pumps. The application of heat pumps to U.K. dwellings and climatic conditions was studied together with the suitability of thermostatic control. Initial studies were made of the operation of a demonstration unit. This showed how intermittent operation would reduce a heat pump performance and was followed by the development of a computer model which simulated the complete refrigerant circulation system. This allowed a study to be made of a heat pump performance at part load conditions. A computer model of the complete refrigerant cycle was developed which aided in the design and construction of a heat pump which used refrigerant R12. This was followed by the construction of a second test rig using R 134(a). The completed R 134(a) test rig was installed in an environmental chamber which could simulate outdoor weather conditions. Results from the test rigs indicated that the performance was greatly affected by on/off cycling an item that was further investigated.

This thesis presents a new method developed to adapt existing hydronic systems in buildings to take advantage of low temperature district heating (LTDH). The work carried out was performed by extensive use of buildings’ energy modelling, validated through recorded data. Two different case studies were investigated and the dynamic heat demand profiles, simulated for each building, were used to evaluate plate radiators connected to single and double string heating loops. The method considered an optimisation procedure, based on supply and return temperatures, to obtain the required logarithmic mean temperature difference (LMTD). The results of the analysis are presented as the average reduction of LMTD over the heating season compared to the base case design conditions. The developed strategy was applied to a Danish single family house from the 1930s. Firstly it was hypothesised a heating system based on double string loop. Two scenarios were investigated based on the assumption of a likely cost reduction in the end users energy bills of 1% per each 1◦C reduction of return and average supply and return temperatures. The results showed possible discounts of 14% and 16% respectively, due to more efficient operation of the radiators. For the case of single loop system, the investigated scenario assumed a cost reduction in the end users energy bill of 1% per each 1◦C lower reduction of average supply and return temperature. Although low return temperatures could not be achieved, the implementation of the method illustrates how to efficiently operate these systems and for the given scenario a possible discount of 5% was quantified. The method was also applied to a UK small scale district heating (DH) network. The analysis began by assessing the buildings of the Estate having double string plate radiator systems. Assuming a likely cost reduction in the end users energy bills of 1% per each 1◦C reduction of return temperature, the optimisation led to obtain a possible discount in the end users energy bills of 14% with a possible yearly average return temperature of 41◦C, compared to the present 55◦C. Moreover, few improvements in the operation of the heat network were proposed. It was assumed to operate the buildings with underfloor heating systems (UFH) with average supply and return temperatures of 40/30◦C, whereas the ones with plate radiators with the optimised temperatures of 81/41◦C. The results shown that an overall average return temperature of 35.6◦C can be achieved operating the heat network as suggested. This corresponds to a decrease in the average return temperature of 18.6◦C compared to the present condition and to a reduction of 10% in the distribution heat losses. Finally, the lower average return temperature achievable would guarantee a better condensation of the flue gases, improving the overall efficiency of the biomass boiler. This was quantified as a possible reduction of fuel consumption of 9% compared to present conditions.

This research explores technological interventions to reduce energy use in the domestic sector, a notable contributor to the global energy footprint. In the UK elevated challenges associated with renovating an outdated, poorly performing housing stock render a search for alternatives to provide immediate energy saving at low cost. To solve this problem, this thesis takes a holistic design approach to designing and implementing a spatiotemporal heating solution, and aims to investigate experiences of comfort, thermal comfort concepts for automated home heating, users’ interactions and experiences of living with such a system in context, and the underlying utility of quasi-autonomous spatiotemporal home heating. The mixed-methods research process was employed to explore and answer four questions: 1) what is the context within which these home heating interfaces are used, 2) to what extent can spatiotemporal automated heating minimise energy use while providing thermal comfort, 3) how are different heating strategies experienced by users, and 4) How do visibility of feedback, and intelligibility affect the user experience related to understanding and control? Ideation techniques were used to explore the context within which the designs are used with regard to all factors and actors in play and resulted in a conceptual model of the context to be used as a UX design brief. This developed model used mismatches between users’ expectations and reality to indicate potential thermal comfort behaviour actions and mapped the factors within the home context that affected these mismatches. Potential user inclusion through participatory design provided stakeholder insight and interface designs concepts to be developed into prototypes. The results of a prototype probe study using these prototypes showed that intelligibility should not be an interface design goal in itself, but rather fit in with broader UX design agenda regarding data levels, context specificity, and timescales. Increased autonomy in the system was shown not to directly diminish the experience of control, but rather, control or the lack of originated from an alignment of expectations and reality. A quasi-autonomous spatiotemporal heating system design (including a novel heating control algorithm) was coupled with the design of a smartphone interface and the resultant system was deployed in a low-technology solution demonstrating the potential for academic studies to explore such automated systems in-situ in the intended environment over a long period of time. Assessment of the novel control algorithm in an emulated environment demonstrated its fitness for purpose in reducing the amount of energy required to provide adequate levels of thermal comfort (by a factor of seven compared with EnergyStar recommended settings for programmable thermostats), and that these savings can be increased by including occupants’ thermal preference as a variable in the control algorithm. Field deployment of that algorithm in a low-tech sensor-based heating system assessed the user experience of the automated heating system and its mobile application-based control interface, as well as demonstrated the user thermal comfort experience of two different heating strategies. The results highlighted the potential to utilise the lower energy-use “minimise discomfort” strategy without compromising user thermal comfort in comparison to a “maximise comfort” strategy. Diverse heating system use behaviours were also identified and conceptualised alongside users’ experiences in line with the developed conceptual model. A rich picture analysis of all previous findings was utilised to provide a model of the design space for home automated heating systems, and was used to draw interface design guidelines for a broader range of home automation control interfaces. The work presented here served as important first steps in demonstrating the importance of assessing UX of automated home heating systems in situ over elongated periods of time. Novel contributions of (i) conceptual model of automated systems’ domestic context and thermal comfort behaviours within, (ii) nudging this behaviour by selecting a “minimise discomfort” heating strategy over “maximise comfort”, (iii) using UX to influence user expectations and subsequently energy behaviour, and (iv) inclusion of thermal preference in domestic heating control algorithm were all resultant of examining naturally occurring behaviours in their natural setting. As such, they are important exploratory discoveries and require replication, but provide new research directions that would allow reduction of domestic energy use without compromise.

Although the terms "Human Thermal Comfort" and "Indoor Air Quality (IAQ)" can be highly subjective, they still dictate the indoor climate design (HVAC design) of a building. In order to evaluate human thermal comfort and IAQ, one of three main tools are used, a) direct questioning the subjects about their thermal and air quality sensation (voting, sampling etc.), b) measuring the human thermal comfort by recording the physical parameters such as relative humidity, air and radiation temperature, air velocities and concentration gradients of pollutants or c) by using numerical simulations either including or excluding detailed thermo-physiological models. The application of the first two approaches can only take place in post commissioning and/or testing phases of the building. Use of numerical techniques can however be employed at any stage of the building design. With the rapid development in computational hard- and software technology, the costs involved in numerical studies has reduced compared to detailed tests. Employing numerical modelling to investigate human thermal comfort and IAQ however demand thorough verification and validation studies. Such studies are used to understand the limitations and application of numerical modelling of human thermal comfort and IAQ in indoor climates. This PhD research is an endeavour to verify, validate and apply, numerical simulation for modelling heat transfer and respiration of occupants in indoor climates. Along with the investigations concerning convective and radiation heat transfer between the occupants and their surroundings, the work focuses on detailed respiration modelling of sedentary human occupants. The objectives of the work have been to: verify the convective and radiation numerical models; validate them for buoyancy-driven flows due to human occupants in indoor climates; and apply these validated models for investigating human thermal comfort and IAQ in a real classroom for which field study data was available. On the basis of the detailed verification, validation and application studies, the findings are summarized as a set of guidelines for simulating human thermal comfort and IAQ in indoor climates. This PhD research involves the use of detailed human body geometries and postures. Modelling radiation and investigating the effect of geometrical posture has shown that the effective radiation area varies significantly with posture. The simulation results have shown that by using an effective radiation area factor of 0.725, estimated previously (Fanger, 1972) for a standing person, can lead to an underestimation of effective radiation area by 13% for the postures considered. Numerical modelling of convective heat transfer and respiration processes for sedentary manikins have shown that the SST turbulence model (Menter, 1994) with appropriate resolution of near wall region can simulate the local air velocity, temperature and heat transfer coefficients to a level of detail required for prediction of thermal comfort and IAQ. The present PhD work has shown that in a convection dominated environment, the detailed seated manikins give rise to an asymmetrical thermal plume as compared to the thermal plumes generated by simplified manikins or point sources. Validated simulation results obtained during the present PhD work have shown that simplified manikins can be used without significant limitations while investigating IAQ of complete indoor spaces. The use of simplified manikins however does not seem appropriate when simulating detailed respiration effects in the immediate vicinity of seated humans because of the underestimation in the amount of re-inhaled CO2 and pollutants from the surroundings. Furthermore, the results have shown that due to the simplification in geometrical form of the nostrils, the CO2 concentration is much higher near the face region (direct jet along the nostrils) as compared to a detailed geometry (sideways jet). Simulating the complete respiration cycle has shown that a pause between exhalation and inhalation has a significant effect on the amount of re-inhaled CO2. Previous results have shown the amount of re-inhaled CO2 to range between 10 - 19%. The present study has shown that by considering the pause, this amount of re-inhaled CO2 falls down to values lower than 1%. A comparison between the simplified and detailed geometry has shown that a simplified geometry can cause an underestimation in the amount of re-inhaled CO2 by more than 37% as compared to a detailed geometry. The major contribution to knowledge delivered by this PhD work is the provision of a validated seated computational thermal manikin. This PhD work follows a structured verification and validation approach for conducting CFD simulations to predict human thermal comfort and indoor air quality. The work demonstrates the application of the validated model to a classroom case with multiple occupancy and compares the measured results with the simulation results. The comparison of CFD results with measured data advocates the use of CFD and visualizes the importance of modelling thermal manikins in indoor HVAC design rather than designing the HVAC by considering empty spaces as the occupancy has a strong influence on the indoor air flow. This PhD work enables the indoor climate researchers and building designers to employ simplified thermal manikin to correctly predict the mean flow characteristics in indoor surroundings. The present work clearly demonstrates the limitation of the PIV measurement technique, the importance of using detailed CFD manikin geometry when investigating the phenomena of respiration in detail and the effect of thermal plume around the seated manikin. This computational thermal manikin used in this work is valid for a seated adult female geometry.

In many dry desert climates such as in Kuwait, the summer season is long with a mean daily maximum temperature of 45°C. A round 80% of total electricity generation is consumed by air-conditioning systems in domestic buildings. A hybrid cooling technique to reduce the domestic cooling demand would have both environmental and economic benefits for Kuwait. A passive cooling technique, which assists the situation, is ground cooling. In this thesis a thermal model of an earth air heat exchanger (EAHE) has been developed to calculate the pre-cooling of ventilation air that can be achieved for a building through use of a buried pipe below ground surface.

Computational studies of two- and three-dimensional, turbulent recirculating flows within mechanically-ventilated enclosures are reported. Two principal cases are examined: (i) two-dimensional offset jets: and (ii) three-dimensional flow induced in rooms by supply jets emanating from low or high side-wall registers. The calculations were undertaken using iterative finite-domain proceedures which solve the conservation equations for mass, momentum and enthalpy, together with additional transport equations for the turbulent kinetic energy and its dissipation rate . The effect of buoyancy waS. explicitly accounted for when modelling these equations, in order that they could be employed to simulate buoyant flow in ventilated rooms. Computations of the mean velocity, temperature and convective heat transfer distribution are reported, and compared with experimental data where available. A modified version of the two-dimensional elliptic code of Pun and Spalding (1977) was employed to simulate the offset jet case. These involve the discharge of a turbulent jet parallel to a flat surface and eventually attaching to it. The investigations covered a wide range of offset ratio (3.5-32.4). and the computed flow properties are compared with measurements from several sources. These comparisons show good agreement downstream of the reattachment point, while some discrepancies are evident upstream from this location. The differences therefore occur mainly in the recirculating flow region, and are believed to arise from shortcoming in the starting profiles, the turbulance model and the treatment of the near-wall flow. A three-dimensional elliptic finite-domain code was developed to simulate the complex, jet-induced flow within rectangular enclosures. The code was verified using both laminar and turbulent flow test cases on simpler geometries. Comparisons with the measurements and predictions reported by previous researchers were employed for this purpose. Subsequentlyr the ventilated room simulations were undertaken using three different ventilation arrangements with thermal conditions corresponding to isothermall non-buoyant (constant property) and buoyancy'affected flows. The computations were again compared with experimental and numerical predictions of previous researchers. This comparison displayed generally good agreement with these sources. A study of the flow and convective heat exchange within a warm-air heated rom, for which buoyancy effects are significant# is also reported in a bound paper (Alamdari, Hammonda nd Mohammad, 1986) for three different heat loads. Its aim to assess the balance between accuracy and economy provided by the present higher-level method compared with the intermediate-level convection model of Alamdari and Hammond (1982) when used to supply building thermal simulation programs with accurate convection heat transfer data. The computed results of both models were compared, and indicate that the intermediate-level is a valuable alternative source that can satisfy the needs of building thermal modellers. It provides resonable accuracy at a very modest cost in computing terms.