Within a closed environment, (e.g. building, car, aircraft) that is thermally and hygrically isolated from the exterior climate, one approach that can help reduce the energy required for indoor mechanical climate control whilst increasing comfort levels for occupants is to use hygrothermal coatings on top of existing materials. Hygrothermal coatings can re-introduce both thermal and hygric buffering within the isolated envelope. Understanding of the behaviour of these coatings allows them to be optimized for different environments. The overall aim of the research is to design the functional properties of inorganic, nano structured surface coatings i.e. mesoporous silica (MS) to produce desired hygrothermal behavioural responses to climatic variables in a controlled environment. This can be achieved through correlation of the hygrothermal properties of desiccant materials with their microstructural characteristics and understanding the hygrothermal behaviour of the materials under representative psychrometric conditions. Stage 1 was to characterise the hygrothermal properties of the MS and other conventional desiccant materials i.e. Silica Gel, Molecular Sieve, Clinoptilolite and Bentonite to produce a ‘Template of functional properties’ and provide material input data for the numerical models. These tests included dynamic vapour sorption (DVS) techniques for moisture absorption including cyclic adsorption/desorption and sorption isotherms, wet-cup tests for vapour permeability, partial immersion tests for liquid water absorption, modified transient plane source (MTPS) tests for thermal conductivity and differential scanning calorimetry (DSC) for heat capacity. Stage 2 utilised techniques to classify the pore geometry of the desiccants, including helium pycnometry for solid density, gravimetric testing for bulk density, N2 physisorption for specific surface area, mesopore volume and mean pore diameter with small angle X-ray scattering and transmission electron microscopy used to corroborate the N2 results. Scanning electron microscopy (SEM) was used to confirm material composition and purity and to indicate macropore distribution. A correlation between the hygrothermal properties from Stage 1 with their microstructural characteristics was then sought. Stage 3 was a parametric analysis of the candidate materials hygrothermal behaviour using the validated 1D numerical simulation software WUFI Pro v5.1. Further analysis was carried out to assess how the numerical model could be used to tune the functional properties of the MS materials to suit differing psychrometric conditions in closed environments. A series of simulations using a representative climate (Nottingham) were also run to compare the hygrothermal behaviour of the MS materials to the conventional desiccants A series of energetic 3D physical and numerical models (WUFI Plus v 2.1) were designed to study the resultant relative humidity levels in both occupied and unoccupied spaces and under different air exchange rates due to the presence of the hygrothermal materials in a closed environment. The 3D model was also used to compare the operational energy usage of different retrofitting cases under the same representative climate used in Stage 3 with three different heating, cooling humidification and dehumidification (HCHD) control scenarios. The MS materials displayed significantly higher Moisture Buffer Values (MBV), equilibrium moisture contents (EMC) and faster response rates when compared to the conventional desiccants. It was shown that WUFI Pro can be used as a design tool for material functional properties, with the sorption isotherm, and in particular adjustment of the w50 – w80 gradient of the absorption branch isotherm being by far the most sensitive parameter. In the MS samples, the dynamic vapour sorption (DVS) response time has a significant and positive logarithmic relationship with both the mesopore diameter and the mesopore volume implying that mesopore geometry can be tuned in order to give the desired dynamic vapour sorption/ desorption response rate and storage capacity to suit a given set of interior psychrometric conditions. It is therefore possible to tune an MS material to suit a particular set of psychrometric conditions using WUFI Pro. The MS materials displayed outstanding passive buffering performance across a range of exterior climate conditions combined with numerous internal moisture and ventilation overloading scenarios, providing constant humidity buffering within the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) comfort limits. When compared against a retro-fitted gypsum-lined indoor environment there was a potential reduction in humidification/ dehumidification energy demand of up to 100% when using an MS material coating.

The European standard EN15450 states that the Coefficient of Performance (COP) target range for a Ground Source Heat Pump (GSHP) installation should lie within the range of 3.5 to 4.5; when used for heating a building, and a typical Air-Source Heat Pump (ASHP) has a COP of 2.0 to 3.0 at the beginning of the heating season and then decrease gradually as the ambient air becomes cooler, whereas a typical GSHP is in the range of 3.5 –4.0, also at the beginning of the heating season and then decrease gradually as heat is drawn from the ground. For these reasons, in the middle of winter, when the COP drop, the heat pumps can generally only be considered as a ‘pre-heating’ method for producing higher temperature heat such as domestic hot water. In addition soil presents certain difficulties, due to the high cost of drilling to position coils in the ground compare to air source, although frost formation on the evaporator in winter limits also limit the use of air source. Though technology advances or are needed to overcome those issues. The aims of this project, therefore, were firstly to reduce the drilling length of the ground heat exchanger of the ground source heat pumps and to maintain high COPs of the air and ground source heat pumps from beginning to the end of the heating season; and secondly to develop a viable alternative evaporator for air source heat pumps to reduce frost formation during winter. These were achieved; the first aim through the combination of ground loops with solar-air panels or solar roof/collectors roof to ground heat exchangers loops to reduce the length of the boreholes, and to reduce the freezing effects around the boreholes, hence increase or maintain a constant temperature during heating season. The second aim was also achieved through development and validation of novel air source heat pump evaporator, using Direct Expansion (DX) black flat plate absorber or/and vacuum tubes for frost reduction. In this thesis, in order to achieve the above aims; four aspects of investigations have been independently investigated as following: 1- Preliminary investigation on Direct Expansion (DX) Solar Source Heat Pump system. 2- Investigation on the performance of the DX- PV/heat pipe heat pump system to reduce frost and enhance the COP of the air source heat pumps, 3- A small scale testing on the heat injection on energy piles for residential buildings for earth charging by means of solar roof/collectors 4- A field trial testing of the performance of the combination of solar-air thermal collectors with conventional GSHP with shorter ground heat exchangers (48m deep) to charge the ground and reduce freezing effects around the piles after heating cycle. From the simulation results, the novel PV/hp-HP system has a COP ranging from 4.65 to 6.16 with an average of 5.35. The condenser capacity ranging from 33 to 174 W would provide the heat source for space heating and domestic hot water. The energy performance of the novel PV/hp-heat pump was not as good as expected due to the low solar radiation. It should be much better in some low latitude locations with better solar radiation. The results of this thesis have shown that the length of ground source boreholes could be considerably reduce by about 60% compare to conventional boreholes using a combination of solar-air collectors with the GSHP and the average COP of 3.7 was achieved.

This study aims to improve the performance of existing indirect evaporative coolers. A new dew point indirect evaporative cooler with counter-current heat/mass exchanger was developed in this research by optimal design, material selection, numerical simulation, experimental investigations and economic, environmental, regional acceptance analysis. A new dew point heat/mass exchanger using a counter-current flow pattern was designed by numerical simulation in terms of material, structure, geometrical sizes and operating conditions. The numerical results indicate that under a typical cooling design condition, i.e., 35oC dry-bulb/24oC wet-bulb temperatures, the heat exchanger could achieve a wet-bulb effectiveness of approximately 1.4. The results of numerical simulation are consistent with some published test data. Based on the numeric results and the material selection determined from a set of related tests, a prototype dew point heat/mass exchanger and the associated air cooler was designed and constructed in laboratory. Testing was carried out to evaluate the performance of the experiment prototype. The results indicate that the wet-bulb effectiveness of the prototype ranged from 55% to 110% for all test conditions. The power consumption of the prototype ranged from 10 to 50 W with energy efficiency (or COP) rated from 3 to 12. It is also found that the water consumption of the prototype was very small which ranged from 0.2-1.3 litre/h. A comparison between the numerical and experimental results was carried out and the reasons for the discrepancy were analysed. This research also investigates the feasibility, economic and environmental potential of using a dew point cooler in buildings in Europe and China. From the related studies in this thesis, it is concluded that the dew point cooler can achieve a higher performance (in terms of effectiveness and energy efficiency) than the typical indirect evaporative coolers without adding too much cost. It is found that the effectiveness and energy efficiency of the heat/mass exchanger in the cooler are largely dependent upon channel geometries, the intake air velocity, temperature, humidity and the working-to-intake air ratio but less on the feed water temperature. To maximise effectiveness and energy efficiency, it is suggested that 1) the channel height and the length of exchanger should be set below 6 mm and 1-1.2 m respectively; 2) the intake channel air velocity should be controlled to 0.5-1 m/s; and 3) the working-to-intake air ratio should be adjusted to 0.4-0.5. It is also concluded that the dew point system is suitable for most regions with dry, mild and hot climate. It is, however, unsuitable for humid regions where the system is used as a stand-alone unit. Compared to the conventional mechanical compression cooling system, the dew point system has a significantly higher potential in saving energy bills and reducing carbon emission. A project to construct an 8 kW commercial dew point cooler is currently under development with the assistance of a Chinese company. By the optimisation of material, structure and geometries, the cooler is expected to achieve a cooling output of 8 kW at the inlet air of 38oC dry-bulb/ 21oC wet-bulb temperatures, with a wet-bulb effectiveness of 1.02 at 1530 m3/h of supply air flow and 1200 m3/h of discharge air flow, whereas the power input of the unit is about 450 W and the energy efficiency (or COP) at 18.5.

No description available.

This thesis presents the experimental investigation of stall in low hub tip ratio industrial fans. Detailed measurements were obtained i four fan configurations. The effects of blade setting angle, solidity, blade profile and OGVs on rotating stall were investigated. The purpose of this work has been to get a better understanding of stall i low hub tip ratio fans. A fan test rig was built specially for this investigation. A three hole pressure transducer probe was made to measure the velocity and pressure at rotating stall conditions. A data acquisition system was developed to ensure the results of better quality. Blade Vibration was also monitored at different flow conditions for two builds. From the results obtained, some important features of rotating stall were observed. For the fans with a low blade setting angle, there was no rotating stall. The overall characteristics were continuous. For the fans with high blade setting angle, rotating stall appeared within a limited flow range. The rotating stall cells i the fans were always a single stall cell, covering part of the rotor tip region. The characteristics were the abrupt type. V A Detailed traverse measurements show that rotating stall has a very strong influence on the flow upstream of the rotor and has little effect on the flow downstream. The effects of space chord ratio, blade profile and OGVs on the stall behaviour have also been investigated. The experimental results also indicate that hub tip ratio has a important effect on the rotating stall behaviour. It is therefore concluded that the stall models based on the observation of high hub tip ratio compressors are not applicable to low hub tip ratio fans. The time averaged measurements show that a large radial shift of streamlines exist i the low hub tip ratio fans. Reverse flow near the hub downstream of the rotor was found in many cases, but reverse flow near the hub does not trigger rotating stall. However, the large low velocity region near the hub will affect the fan steady state performance. A simple streamline curvature program has been used to analyse the endwall boundray layer effect on the fan performance. \ Axisymmetric stall is important i low hub tip ratio fans because it dominates most of the stalled flow conditions. Axisymmetric stall is preferred to rotatíng stall since it gives the continuous type characteristic and it causes less Vibration problem. A set of nonlinear equations is used to simulate axsiyrnmetric stall a well a rotating stall and surge.

An experimental and theoretical investigation has been undertaken into the performance of a small prototype, water-cooled, gas-fuelled engine designed for use as a domestic heat pump prime mover. In light of the application, fuel type and capacity, both experimental and theoretical study of similar engines is at best poorly documented in the literature. A comprehensive engine test facility has been set up, incorporating extensive calorimetry, a separate lubrication system, emissions monitoring and high speed data acquisition for in-cylinder pressure measurement and analysis. Two new experimental cylinder heads have been designed together with new induction and exhaust systems, both to improve performance and to enable further investigation of the combustion process. A preliminary parametric study of the combustion process established that the thermal efficiency and emission levels are strongly dependent on operational and design variables and that a lean, fast-burning combustion process in a slow speed engine coupled with careful control of other operating variables had the potential for improving efficiency, reducing emissions, and lowering frictional losses and noise levels with enhanced durability. Accordingly, new information has been obtained relating to rates of heat release, energy flows and emission levels over a wide range of design and operating conditions with utility for and consistent with an envelope of conditions appropriate to such a lean burn strategy. Modelling techniques have been developed and used as diagnostic tools in conjunction with the experimental data to investigate the influence of operating and design variables on rates of heat release and energy flows. The models have been validated using the experimental data over a wide range of operating conditions and incorporated into a thermodynamic engine model for use as a sub-model in an overall heat pump model. The experimental and theoretical programme has provided a valuable insight into the lean burn strategy and realised a considerable improvement in the performance of the prototype engine. The theoretical study benefits from a new approach to small gas engine design and development.

The wide uses of solar energy technology (solar thermal collector, photovoltaic and heat pump systems) have been known for centuries. These technologies are intended to supply domestic hot water and electricity. However, these technologies still face some barriers along with fast development. In this regards, the hybrid energy system combines two or more alternative technologies to help to increase the total efficiency of the system. Solar assisted heat pump systems (SAHP) and photovoltaic/thermal collector heat pump systems (PV/T-HP) are hybrid systems that convert solar radiation to thermal energy and electricity, respectively. Furthermore, they absorb heat first, and then release heat in the condenser for domestic heating and cooling. The research initially investigates the thermal performance of novel solar collector panels. The experimental results indicate an average daily efficiency ranging from 0.75 to 0.96 with an average of 0.83. Compared with other types of solar collectors, the average daily efficiency of novel solar thermal collectors is the highest. The research work further focuses on the integrated system which combines solar collector and air source heat pump (ASHP). The individual components, configurations and layout of the system are illustrated. Theoretical analysis is conducted to investigate thermodynamic cycle and heat transfer contained in the hybrid system. Laboratory tests are used to gauge the thermal performance of the novel SAHP. A comparison is made between the modelling and testing results, and the reasons for error formation are analysed. The research then considers the specially designed PV/T collector that employs the refrigerant R134a for cooling of PV modules and utilizes the glass vacuum tubes for reducing the heat loss to the ambient air. The PV/T collector consists of 6 glass vacuum tube-PV module-aluminium sheet-copper tube (GPAC) sandwiches which are connected in series. The theoretical analysis and experimental tests all give the satisfactory results of up to 2.9% improvement of electrical efficiency compared with those without cooling. The research finally focuses on the integrated heat pump system where the PV/T collector acts as evaporator. Based on the energy balance of the four main components of the heat pump system, a mathematical model of the heat pump system is presented. When the instantaneous ambient temperature and solar radiation are provided, results are obtained for the spatial distributions of refrigerant conditions, which include temperature, pressure, vapour quality and enthalpy. Detailed experimental studies are carried out in a laboratory. Three testing modes are proposed to investigate the effect of solar radiation, condenser water flow rate and condenser water supply temperature on energy performance. The testing results show that an average coefficient of performance (COP) reached 3.8,4.3 and 4.0 under the three testing modes with variable radiation, condenser water supply water temperature and water flow rate, respectively. However, this could be much higher for a large capacity heat pump system using large PV panels on building roofs. The COP increases with the increasing solar radiation, but decreases as the condenser water supply temperature and water flow rate increases.

The subject of this work is the flow inside an axial pump impeller, which is studied both numerically and experimentally. The aim of the work is to provide a numerical method to predict the three-dimensional flow field within an axial flow pump impeller. The numerical scheme is divided into three basic parts. The first part involves the matrix through flow method to obtain the mainstream flow profiles on various blade-to-blade stream surfaces distributed from hub to tip and for given boundary conditions. In addition these solutions w to obtain a detailed flow field in the region of the leading edge. Furthermore, the transport equations of vorticity are integrated along each streamline to obtain the normal and stream wise components of vorticity.

In the present work, the more important parameters of the heat pump system and of solar assisted heat pump systems were analysed in a quantitative way. Ideal and real Rankine cycles applied to the heat pump, with and without subcooling and superheating were studied using practical recommended values for their thermodynamics parameters. Comparative characteristics of refrigerants here analysed looking for their applicability in heat pumps for domestic heating and their effect in the performance of the system. Curves for the variation of the coefficient of performance as a function of condensing and evaporating temperatures were prepared for R12. Air, water and earth as low-grade heat sources and basic heat pump design factors for integrated heat pumps and thermal stores and for solar assisted heat pump-series, parallel and dual-systems were studied. The analysis of the relative performance of these systems demonstrated that the dual system presents advantages in domestic applications. An account of energy requirements for space and hater heating in the domestic sector in the O.K. is presented. The expected primary energy savings by using heat pumps to provide for the heating demand of the domestic sector was found to be of the order of 7%. The availability of solar energy in the U.K. climatic conditions and the characteristics of the solar radiation here studied. Tables and graphical representations in order to calculate the incident solar radiation over a tilted roof were prepared and are given in this study in section IV. In order to analyse and calculate the heating load for the system, new mathematical and graphical relations were developed in section V. A domestic space and water heating system is described and studied. It comprises three main components: a solar radiation absorber, the normal roof of a house, a split heat pump and a thermal store. A mathematical study of the heat exchange characteristics in the roof structure was done. This permits to evaluate the energy collected by the roof acting as a radiation absorber and its efficiency. An indication of the relative contributions from the three low-grade sources: ambient air, solar boost and heat loss from the house to the roof space during operation is given in section VI, together with the average seasonal performance and the energy saving for a prototype system tested at the University of Aston. The seasonal performance as found to be 2.6 and the energy savings by using the system studied 61%. A new store configuration to reduce wasted heat losses is also discussed in section VI.

No description available.