St. James GP group practice : a success story

The following is a history of the conception and development of a successful GP group practice working in the south of Malta . Fundamental concepts and practical aspects of its function and dynamics are discussed hereunder. We believe that these may be of interest to many Maltese GPs for whom this may be a new concept of general practice.peer-reviewe

Steady-state analysis of a conceptual offshore wind turbine driven electricity and thermocline energy extraction plant

A system for using offshore wind energy to generate electricity and simultaneously extract thermal energy is proposed. This concept is based on an offshore wind turbine driven hydraulic pump supplying deep seawater under high pressure to a land based plant consisting of a hydroelectric power generation unit and heat exchanger. A steady-state system model is developed using empirical formulae. The mathematical model comprises the fundamental system sub-models that are categorised as the rotor, hydraulic pump, pipeline, hydroelectric turbine and heat exchanger. A means for modelling the seawater temperature field across a two-dimensional bathymetry is also discussed. These mathematical models are integrated into a computational tool and a brief parametric static analysis is undertaken. The results illustrate the effect of pipeline diameter, rotational speed of the grid connected hydroelectric turbine, and the turbine distance from shore on the overall performance of the system. Through adequate parameter selection, the total rate of energy output for such a system, consisting of both electricity and thermal energy, is shown to increase by as much as 84%, when compared to a conventional wind turbine having an identical rotor diameter but which supplies only electrical energy.peer-reviewe

Ground cooling potential in a Mediterranean climate : fieldwork and computational modelling

The aim of this paper was to explore the potential of exploiting ground source cooling, utilising the high thermal mass of the indigenous sedimentary rock, globigerina limestone, typical of Malta. Based on earlier studies of horizontal and vertical pipe configurations, it was established that the vertical U-tube pipe is more efficient. This demonstrated that at 20m depth ground temperatures were around 20C all year round. This prompted further studies with various refined parameters, this time moving from fieldwork to numerical simulations, facilitating a greater variety of trials. A mathematical model of the system was developed, implemented into a computational model to simulate the heat transfer processes. This model was calibrated using results from the field tests. This was also used to carry out a more elaborate parametric analysis of the system and to simulate its performance in a variety of configurations. Preliminary results already indicate the validity of the numerical model and the applicability of such a system. The same numerical model results and field tests were then used to estimate the potential of such a ground source heat pump system to curtail energy demand for cooling on running the standard HVAC systems.peer-reviewe

A parametric building energy simulation case study on the potential and limitations of passive design in the Mediterranean climate of Malta

The present case study sets out to investigate the potential and limitations of passive building design in a typical Mediterranean climate. The Maltese Islands were taken as the case study location. Assuming a fully detached, cuboid-shaped, generic multi-storey office building, one representative storey was modelled by means of the building energy simulation code WUFI®Plus. Thermal comfort was analysed based on the adaptive acceptable operative room temperature concept of EN 15251 for buildings without mechanical cooling systems. Assuming neither artificial heating nor cooling, the free-running operative room temperature was evaluated. By means of a parametric study, the robustness of the concept was analysed and the impact of orientation, window to wall area ratio, glazing, shading, thermal insulation, nighttime ventilation and thermal mass on the achievable level of thermal comfort is shown and discussed. It is concluded that in a well-designed building and by means of decent insulation (present case: Uwall = 0.54 W/(m2 · K)), double glazing, variable external shading devices and passive cooling by nighttime ventilation, a high level of thermal comfort is achievable in this climate using only very minor amounts of energy for artificial heating and cooling or possibly even none at all.peer-reviewe

Analysis of a stand-alone hydraulic offshore wind turbine coupled to a pumped water storage facility

The concept of wind turbines operating with hydraulic transmissions is gaining popularity. With the promise of improved energy density and lower maintenance costs, a number of manufacturers are evaluating such a novel concept. In the current study an offshore-specific hydraulic wind turbine design is proposed. This is based on the use seawater as the working fluid in a large scale, open-loop transmission system. The possibility of coupling such a system to an onshore pressurized water storage facility is also evaluated. Simulation results indicate the potential for such an energy storage system, to address a supply-demand mismatch without requiring intermediate conversion to electricity, as in current pumped storage facilities used in conjunction with wind turbines.Alternative Technologies Ltd., Energy Investment Ltd, JMV Vibro Blocks Ltd., Solar Engineering Ltd. and Solar Solutions Ltd.peer-reviewe

A preliminary computational study of flat roof convective thermal resistance in the presence of photovoltaic panels

The effect of roof mounted photovoltaics on the heat transfer performance of roofs has primarily been investigated in the context of the resulting shading effect. The convective heat transfer coefficient will change as a result of the blockage caused by the photovoltaic panels. In this work, a quantification is given of the differences between heat transfer coefficients on a bare roof and a roof with photovoltaic panels having a specified configuration. A computational fluid dynamics approach is used. The study is only preliminary and hence a standard k-e turbulence model is used. The presence of photovoltaics is found to increase the convective heat transfer coefficients by around 26% for a north wind. The influence on the U-Value depends on the type of roof construction but for summer conditions an increase in U-value is observed which has positive cooling effects.Bajada New Energy, Bitmac ltd., Econetique, Energy Investment, JMV Vibro Blocks, Solar Engineering.peer-reviewe

Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters

A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe

Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters

A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe

The effect of alloying elements on the properties of pressed and non-pressed biodegradable Fe–Mn–Ag powder metallurgy alloys

Current trends in the biodegradable scaffold industry call for powder metallurgy methods in which compression cannot be applied due to the nature of the scaffold template itself and the need to retain the shape of an underlying template throughout the fabrication process. Iron alloys have been shown to be good candidates for biomedical applications where load support is required. Fe–Mn alloys were researched extensively for this purpose. Current research shows that all metallurgical characterisation and corrosion test on Fe–Mn and Fe–Mn–Ag non pre-alloyed powder alloys are performed on alloys which are initially pressed into greens and subsequently sintered. In order to combine the cutting-edge field of biodegradable metallic alloys with scaffold production, metallurgical characterisation of pressed and non-pressed Fe, Fe–Mn and Fe–Mn–Ag sintered elemental powder compacts was carried out in this study. This was performed along with determination of the corrosion rate of the same alloys in in vitro mimicking solutions. These solutions were synthesised to mimic the osteo environment in which the final scaffolds are to be used. Both pressed and non-pressed alloys formed an austenite phase under the right sintering conditions. The corrosion rate of the non-pressed alloy was greater than that of its pressed counterpart. In a potentiodynamic testing scenario, addition of silver to the alloy formed a separate silver phase which galvanically increased the corrosion rate of the pressed alloy. This result wasn't replicated in the non-pressed alloys in which the corrosion rate was seen to remain similar to the non-silver-bearing alloy counterparts.peer-reviewe

Control of an open-loop hydraulic offshore wind turbine using a variable-area orifice

The research work disclosed in this publication is partly funded by the Malta Government Scholarship Scheme.The viability of offshore wind turbines is presently affected by a number of technical issues pertaining to the gearbox and power electronic components. Current work is considering the possibility of replacing the generator, gearbox and electrical transmission with a hydraulic system. Efficiency of the hydraulic transmission is around 90% for the selected geometries, which is comparable to the 94% expected for conventional wind turbines. A rotor-driven pump pressurises seawater that is transmitted across a large pipeline to a centralised generator platform. Hydroelectric energy conversion takes place in Pelton turbine. However, unlike conventional hydro-energy plants, the head available at the nozzle entry is highly unsteady. Adequate active control at the nozzle is therefore crucial in maintaining a fixed line pressure and an optimum Pelton turbine operation at synchronous speed. This paper presents a novel control scheme that is based on the combination of proportional feedback control and feed forward compensation on a variable area nozzle. Transient domain simulation results are presented for a Pelton wheel supplied by sea water from an offshore wind turbine-driven pump across a 10 km pipeline.peer-reviewe