Preliminary results from the testing of an advanced passive solar still incorporating a shielded condenser

An advanced passive solar still with separate condenser has been studied theoretically and experimentally. The system has one basin in the evaporation chamber and two basins (middle and upper) in the condenser chamber, with a glass cover over the evaporator basin and an opaque condensing cover over the upper basin. The evaporator, middle and upper basins form the primary, secondary and tertiary effects respectively. The top part of the condensing cover is shielded from solar radiation and heat. Water vapor from the primary effect condenses under the glass cover while the remainder of it flows into the condenser, by purging and diffusion, and condenses under the liner of the middle basin. Outdoor tests of the present solar still and a conventional system were conducted at the University of Strathclyde. The two systems are also simulated under the same meteorological conditions. It is found that the solar shield effectively keeps the condenser cover relatively cool. Under favorable weather conditions the present solar still produced up to 34% more distillate than the conventional type. Experimental and estimated results are in close conformity. It appears that the new solar still can be exploited within and outside the tropical region

Urban wind energy conversion: the potential of ducted turbines

The prospects for urban wind power are discussed. A roof-mounted ducted wind turbine, which uses pressure differentials created by wind flow around a building, is proposed as an alternative to more conventional approaches. Outcomes from tests at model and prototype scale are described, and a simple mathematical model is presented. Predictions from the latter suggest that a ducted turbine can produce very high specific power outputs, going some way to offsetting its directional sensitivity. Further predictions using climate files are made to assess annual energy output and seasonal variations, with a conventional small wind turbine and a photovoltaic panel as comparators. It is concluded that ducted turbines have significant potential for retro-fitting to existing buildings, and have clear advantages where visual impact and safety are matters of concern

Unsteady wake modelling for tidal current turbines

The authors present a numerical model for three-dimensional unsteady wake calculations for tidal turbines. Since wakes are characterised by the shedding of a vortex sheet from the rotor blades, the model is based on the vorticity transport equations. A vortex sheet may be considered a jump contact discontinuity in tangential velocity with, in inviscid hydrodynamic terms, certain kinematic and dynamic conditions across the sheet. The kinematic condition is that the sheet is a stream surface with zero normal fluid velocity; the dynamic condition is that the pressure is equal on either side of the sheet. The dynamic condition is explicitly satisfied at the trailing edge only, via an approximation of the Kutta condition. The shed vorticity is the span-wise derivative of bound circulation, and the trailed vorticity is the time derivative of bound circulation, and is convected downstream from the rotors using a finite-volume solution of vorticity transport equations thus satisfying the kinematic conditions. Owing to an absence in the literature of pressure data for marine turbines, results from the code are presented for the NREL-UAE Phase IV turbine. Axial flow cases show a close match in pressure coefficients at various spanwise stations; however, yawed flow cases demonstrate the shortcomings of a modelling strategy lacking viscosity

Thermal mass, insulation and ventilation in sustainable housing - An investigation across climate and occupancy

Sustainable housing standards are reviewed including the UK 2005 building regulations, the UK Advanced Standard and EU Passive-house Standard. Conflicts between the standards are highlighted. The significance of insulation, orientation, ventilation, thermal mass, occupancy, gains, shading and climate on predicted energy performance is illustrated. An ESP-r model is then used to investigate these factors across a range of climates and occupancy / gains scenarios. The investigation covers both heating and cooling energy requirements. The relative importance of key factors is quantified and a matrix of results presented with conclusions. The role of simulation in informing design decisions is demonstrated as well as the importance of considering climate and occupancy/ gains patterns

Output characteristics of tidal current power stations

With increasing targets being set for renewable-derived electricity generation, wind power is currently the preferred technology. It is widely accepted that due to the stochastic nature of wind, there is an upper limit to the capacity that can be accommodated within the electricity network before power quality is impeded. This paper demonstrates the potential of tidal energy as a predictable renewable technologies that can be developed for base load power generation and thus minimise the risk of compromising future power quality

The implementation of discrete demand management algorithms within energy systems modelling

Traditionally, demand side management (DSM) programs have been driven by utilities. With the prospect of growth in the utilization of building-integrated micro-generation, DSM offers opportunities for additional energy savings and CO2 emission reductions through better utilisation of local renewable energy resources. This paper examines the feasibility of using discreet demand management (DDM) to improve the supply/demand match. For many combinations of micro-generation and DDM controls, it is necessary to know the environmental conditions (i.e. temperatures and lighting levels) within the buildings being modelled. One method would be to embed all the renewable energy technologies and DDM algorithms within a detailed simulation program. An alternative method, investigated in this study, involves coupling two existing tools: a dynamic building simulation program (ESP-r) and a demand/supply matching program (MERIT) that incorporates DDM algorithms and renewable energy system technologies. These two programs interact at the time-step level and exchange calculated parameters (relating to loads, supply potentials and prevailing environmental conditions) to enable an evaluation of DDM techniques in terms of energy saving and occupant impact. This paper describes the technique and presents simulation results relating to a number of building cases

Energy and carbon performance of housing : upgrade analysis, energy labelling and national policy development

The area of policy formulation for the energy/carbon performance of housing is coming under increasing focus. A major challenge is to account for the large variation within national housing stocks relative to factors such as location, climate, age, construction, previous upgrades, appliance use and heating/cooling system types. Existing policy oriented tools rely on static calculation models that have limited ability to represent building behaviour and the impact of future changes in climate and technology. The switch to detailed simulation tools to address these limitations in the context of policy development has hitherto been focussed on the modelling of a small number of representative designs rather than dealing with the spread inherent in large housing stocks. To address these challenges, the ESRU Domestic Energy Model (EDEM) has been developed as a Web based tool built on detailed simulation models that have been aligned with the outcomes of national house condition surveys. On the basis of pragmatic inputs, EDEM is able to determine energy use and carbon emissions at any scale – from an individual dwelling to national housing stocks. The model was used at the behest of the Scottish Building Standards Agency and South Ayrshire Council to determine the impact of upgrades and the deployment of new and renewable energy systems. EDEM was also used to rate the energy/carbon performance of individual dwellings as required by the EU Directive on the Energy Performance of Buildings (EU, 2002). This paper describes the EDEM methodology and presents the findings from applications at different scales

A contra-rotating marine current turbine on a flexible mooring : development of a scaled prototype

The contra-rotating marine current turbine concept developed by the Energy Systems Research Unit at the University of Strathclyde is aimed at extracting energy in a wide range of water depths by 'flying' a neutrally-buoyant device from a flexible, tensioned mooring. After successful proof of concept turbine trials, the development programme has moved on to investigate the performance of a scaled prototype of the complete system incorporating the turbine, submersible contra-rotating generator and mooring. The turbine/generator assembly has been tested in a towing tank, and the entire system is now undergoing sea trials. An investigation into turbine wake development (an area in which it is hoped that the contra-rotating turbine will have uniquely beneficial properties) has recently begun. Small single-rotor model turbines have been deployed in a flume. Trends observed so far are in accordance with those observed by other researchers

Contra-rotating marine current turbines : performance in field trials and power train developments

Development of a novel contra-rotating marine current turbine has been continuing at the University of Strathclyde. Continuous monitoring of blade bending loads during trials has enabled an investigation of blade-blade and blade-structure interactions. The former are a particular concern with a contra-rotating turbine, but there is now evidence to suggest that in normal operation these are relatively small. By contrast, blade-structure effects are clearly visible. A turbine complete with single-point mooring and submersible contra-rotating generator is presently being prepared for sea trials. Details of the machine and the test programme are described

Contra-rotating marine current turbines : single point tethered floating system - stabilty and performance

The Energy Systems Research Unit within the Department of Mechanical Engineering at the University of Strathclyde has developed a novel contra-rotating tidal turbine (CoRMaT). A series of tank and sea tests have led to the development and deployment of a small stand-alone next generation tidal turbine. Novel aspects of this turbine include its single point compliant mooring system, direct drive open to sea permanent magnet generator, and two contra-rotating sets of rotor blades. The sea testing of the turbine off the west coast of Scotland in the Sound of Islay is described; the resulting stability of a single-point tethered device and power quality from the direct drive generator is reported and evaluated. It is noted that reasonably good moored turbine stability within a real tidal stream can be achieved with careful design; however even quite small instabilities have an effect on the output electrical power quality. Finally, the power take-off and delivery options for a 250kW production prototype are described and assessed