No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Domestic heating for the majority of the housing stock within the UK and Ireland use a fossil fuel boiler, oil or gas, within a central heating system distributing heat to the living space through hydronic radiators. Current trends show a rise in the price of fossil fuels (through an increasing global demand) which is having a direct impact on the individual and the economy, increasing the price of all commodities through increased transportation costs and increasing the cost of energy (heating and electricity). The increasing costs and the environmental impact associated with the burning of fossil fuels are therefore driving the need for more renewable/more energy efficient means of supplying heat. Utilising a reversed Rankine cycle heat pump is a proven, well established method of providing high energy efficient heat transfer from a low temperature source to a high temperature sink through the manipulation of a working fluid about a pressure differential. The temperature and pressure differential across the compressor, have a large impact on the system performance. The aim of this work was to develop an air to water heat pump as an alternative to the fossil fuel boiler whilst using the existing heat distribution system and comparable water temperatures. This system could therefore be retrofitted into the majority of the existing housing stock providing an affordable energy efficient solution to the majority of homeowners whilst reducing national greenhouse gas emissions. An advanced cycle Economised Vapour Injection heat pump was utilised to improve the system efficiency when compared with a conventional system for the high temperature and pressure lift retrofit application. The COP was improved for the EVI cycle across the range of conditions tested. Between the minimum and maximum pressure differentials, the EVI cycle provided a performance improvement of between 1% and 27%. An off-the-shelf inverter was coupled to the BVI compressor to provide capacity control. The inverter-motor combination was evaluated detailing the maximum and minimum frequency limits. The heat pump performance was then evaluated between these limits comparing both the EVI and conventional cycles. As the frequency/compressor RPM was reduced, the improvement for the EVI cycle with respect to the conventional increased. The transient characteristics and the control strategies of the systems were evaluated showing large reductions of the start-up time-frame and power consumption when using the EV} cycle at increased speeds. When compare:d with the conventional cycle at 50Hz (nominal frequency), the maximum energy and time sav ings were 45% and 64%, respectively. This work concludes that th is set-up, using a nominal single speed compressor with an off-theshelf inverter is not ideal and creates reliability issues; however, it also highlights the potential benefits achievable when utilising capacity control which can be optimised by maximising the load matching range with a dedicated variable speed compressor.

No description available.

The research described in this thesis is concerned with the analysis, design and development of a novel temperature insensitive Current Controlled Current Source (CCCS), in bipolar technology, in order to provide accurate amplification of a Proportional To Absolute Temperature (PTAT) reference current. The output current of the CCCS is intended for application as the bias current for a bipolar Low Noise Amplifier (LNA) in order to minimise gain variations with temperature across the industrial temperature range (-40·C to 8S·C). The thesis begins with an explanation of key parameters concerned with LNA design and a target specification is defined. In Chapter 2, a conventional LNA, with constant with temperature bias current, is developed following a methodical approach based on conventional techniques. This meets the previously defined specification at room temperature but exhibits large gain variations with changes in temperature. The analysis and simulation results of this conventional LNA serve as a benchmark for comparison with later designs. In order to minimise any gain variations with temperature of a bipolar amplifier it is well known that the applied bias current should be PT AT. Thus, a thorough analysis and comparative review of traditional and novel PTAT reference current generator circuits is conducted in Chapters 3 and 4. Based on these findings the PTAT generator exhibiting best performance in terms of output current accuracy and insensitivity to power supply variations is presented. However, this circuit cannot accurately produce large rnA level currents necessary for LNA bias applications so that sufficient linearity of the LNA is maintained. Thus, a need for some form of accurate CCCS or Voltage Controlled Current Source (VCCS), which should be temperature insensitive in order to preserve the desired temperature coefficient of the reference current/voltage, is highlighted.Traditional VCCS/CCCS designs are investigated in Chapter 5. Limitations of these approaches leads to the design and development ofa novel CCCS with built in PTAT reference. The presented CCCS utilises a new, previously unseen, architecture and has led to a patent application [1]. The author has reported the majority of this work in technical literature [2-4]. In Chapter 6, the output of the novel CCCS is adapted to include the conventional LNA circuit designed previously in Chapter 2. The results of the combined LNA and CCCS are compared with the conventional LNA. The combined LNA and CCCS offers a dramatic reduction in gain variation with temperature.

Previous methods for predicting the heat transfer and pressure drop performance of crossflow heat exchangers with finned tubes have concentrated on developing correlations. These correlations have been based on the researchers observations of what geometric parameters may affect the performance, and then dimensionless groups developed to allow a correlation to be developed. This work shows that many of these models are limited either by design or by their databases, and often are not general enough to cater for air-cooled heat exchangers as well as the generally larger scale heat recovery bundles. The most recent prediction methods have been developed as more aerodynamically based models, although these still encompass an element of empiricism to account for effects that are not readily understood. This new work develops from these physically based models. An improved method for the prediction of the pressure drop of staggered finned tube bundles is presented, based on high quality test data and the results of a CFD (Computational Fluid Dynamics) study. This is shown to perform better than previous models, and also correct a defect in the formulation of a previous method. A new prediction scheme for inline finned tube bundles is also presented. Experimental work was performed on nine inline air coolers to determine their performance characteristics and, along with open literature data, develop a reliable databank for prediction method development. The models incorporate a new approach to the pressure drop prediction using a sophisticated gap flow model, and a multiple term heat transfer model, that considers heat transfer and flow mixing between the main flow streams. This method is shown to significantly improve on previous methods. Experiments were conducted on an isothermal staggered air-cooler bundle that allowed differing wall sealing devices (corbels) to be used, or allow a bypassing lane. Flow visualization tests were performed on this bundle, and observations of the flow patterns compared with a simple two-dimensional CFD model. From the test results a new method of predicting the pressure drop performance of staggered bundles with various corbels was developed. Using the bypassing air-cooler data and new data taken from a heat recovery bundle an iterative method to predict the pressure drop when a bypassing lane is present is presented. This method is shown to be both simple and computationally cheap, and is used in conjunction with the new staggered bundle pressure drop method. The experimental inline air cooler results were used in conjunction with CFD to provide data to investigate the effect on heat transfer with an increasing number of rows through the bundle. It was found that the key factors in determining this are turbulence and the temperature difference between the tubeside and crossflow fluids, and also that the fin frequency plays a key role. A model is presented to predict the local heat transfer coefficient, which uses sub-models to express the two contributory factors. The results of this approach are shown to be very good, and promote better understanding of tube row heat transfer duty than previously developed models.