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Mon 17 Mar 2008 04:00 AM

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Sunshine solutions

As the use of solar power gets set to increase in the region, Jelle Post and Giorgos Mixoudis outline possible future technology options and considerations for MEP professionals.

As the use of solar power gets set to increase in the region, Jelle Post and Giorgos Mixoudis outline possible future technology options and considerations for MEP professionals.

The sun is the most influential energy source for our planet. Therefore the sustainable development of future buildings can only be achieved when the sun and the solar energy it produces is considered as such by all the stakeholders involved over a building's lifetime.

Solar energy in the form of heat is a big concern for building design engineers.

On earth, the sun provides eight thousand times more energy annually than humans consume over this period of time. Although a substantial portion of that energy can and should be exploited, an even larger part can have negative implications for development.

The Middle East's climate is a clear example of the sun's contradictive influences: the potential of renewable energy systems is huge, but the sun also substantially affects the daily lives of the region's inhabitants.

The construction industry in general is also vastly influenced by the sun's extreme power. The operation and maintenance of buildings in the Middle East, for example, consume a vast portion of natural resources and energy - far larger than in other regions around the globe - due to the extreme climate conditions. While efforts must be made to exploit the sun for the supply of energy to buildings, ways to minimise demand by reducing the sun's influence must also be considered.

Harvesting the sun

Solar energy is found in various forms: light, heat, wind, wave energy, biomass and hydro-electricity all are alternative forms of solar energy. Various techniques to exploit this energy have been developed throughout the years. In building applications, the use of renewable energy systems is an active way of reducing fossil fuel consumption.

To date, technologies such as photovoltaic (PV) cells and solar flat plate thermal collectors have mainly been used as small-scale solutions, but other large-scale solutions are now available.

Parabolic trough power plants are the most successful and cost-effective concentrated solar power plant (CSP) systems currently available. These use a curved trough, which is tilted to continually follow the sun during the day, reflecting direct solar radiation onto a hollow tube running above the trough. A working fluid (thermal oil, water or molten salt) passes through the tube, being heated as it does so, this is then passed through a heat exchanger creating steam that drives a steam turbine.

A power tower is another example of a large-scale solar solution. This comprises a central collector consisting of an array of flat reflectors (heliostats) that concentrate light in a central receiver located on a tower. Molten salt flows through the receiver where it is heated to temperatures of up to 1000°C.

Storing and using solar energy

One advantage of using molten salt as a working fluid is that it enables energy storage. Energy storage of up to 12 hours is possible, enabling power supply for 24 hours per day.

Moreover, the heat that is gathered from solar collectors can also be used for powering absorption chillers and desiccant dehumidifiers in heating, ventilation and air conditioning (hvac) systems, or even for desalination systems.

Such installations can be coupled close to high-rise buildings or residential areas so that the production is carried out next to the place of consumption. These installations generally produce low noise levels and negligible by-products.

Coupling renewable energy systems with desalination and wastewater treatment installations is another concept that has excellent opportunities. Various techniques have been proposed and implemented in places with limited access to water but with high sun radiation, such as islands.

PVs, wind turbines coupled with reverse osmosis plants and distillation desalination systems coupled with solar thermal systems are among those concepts that have been successfully applied around the world.

Providing protection

Solar energy in the form of heat is a big concern for building design engineers. The external heat loads in the Middle East are vast, thus the energy needs for the cooling of building's can be double that needed in Europe.
Applying techniques to prevent these external loads from entering the building will provide a passive but effective way of reducing the building's energy demands.

Utilising outside shading is a simple and relatively efficient way to minimise the energy demand for the cooling of a building. Outside blinds will reduce heat gains from sunlight in summer, while verandas and courtyards provide extra shading. Furthermore, using the shading of nearby buildings and the intelligent orientation of a building are techniques that can also help to reduce heat loads.

In addition, well insulated buildings (Rc > 4m2K/W) with double-layer reflective glass and walls that are insulated from the outside are an excellent measure to reduce solar heat gains. Also, by raising the ratio volume versus the external surface of a structure, the external heat gains will be reduced.

Evaluating design

For the evaluation of solar related building performance, extensive use can be made of computational building performance simulation models. With these, digital models of varying scales and levels of detail are constructed for use in specialised software applications that have been previously proven to give reliabile results.

From the results of these software simulations a proposed building design can be tested against the requirements of daylight factor levels in sustainability standards systems such as the US Green Building Council's Leadership in Energy and Environmental Design (LEED) rating system.

The combination of these modelling technique has great potential, because they are capable of relating the opposing performance parameters to balance the wanted and unwanted aspects of solar heat and light. These simulations are also rapidly becoming more reliable.

Deerns' summarises its vision with the Trias Energetica concept, which focuses on limiting the initial demand for energy by using, for example, well-insulated buildings with active facades.

If all feasible measures in this step have been implemented, the next step would be to use as much renewable energy as possible. After implementing all feasible options, at the final step taken any further energy needs should ideally be satisfied by means of the highly efficient use of fossil fuels.

From the first until the last of those steps, MEP professionals must work alongside the building designer and offer knowledge and expertise through dedicated collaboration to reach the desired, optimum design result.

Towards sustainable development

All of the techniques described above will only be realised with close co-operation between MEP professionals and the building designers. Traditionally, the design, construction and operation phases of a building have been dealt with by different groups of individuals that may have different approaches. Even in the design phase, it is not uncommon that several approaches are implemented in the same building.

Sustainable buildings will only become a reality when it is considered as such by all of its stakeholders, starting at the design and continuing until the demolition phase.

Initiatives like LEED certification, issued by the US Green Building Council and now adopted in the UAE, monitor a building's lifetime from the design until the operational phase. This is a very positive step towards more sustainable buildings in the future.

Jelle Post is building physics specialist and Giorgos Mixoudis is sustainable energy consultant engineer with Deerns MEP Consulting Engineers.

Case study: New city of Deh Sabz, AfghanistanDeerns has recently collaborated in a conceptual study for the development of the New City of Deh Sabz, north of Kabul, Afghanistan, proposing solutions that maximise the use of renewable energy, while minimising overall energy use.

In the masterplan, the use of two central solar power plants has been proposed: a 300MWe parabolic trough collector plant and a 90MWe solar power tower. Both proposals are concentrated solar power (CSP) systems.

Buildings have been designed to collect heat from the sun during winter by placing all the tall buildings at the North side of the urban blocks and adding shading openings at optimum angles.

In order to further minimise energy demand, additional daylight systems have been proposed for the Deh Sabz City. Considering the broad depth of the building blocks that have been proposed for use in the city, the installation of light pipes to provide daylight inside buildings has been suggested.

Daylight systems will also provide a contribution if the light pipes can be combined with ventilation shafts and be positioned in the roof or the building facades. If an artificial lighting source is added inside the light pipe it can be used as a continuous light source day and night. By linking these to a small PV solar and battery system, they will function as a self-supporting basic lighting system.

Participants at this study were AS Architecture-Studio, Franor Conseil, Composante Urbaine, Eaux de Paris, SETEC Partenaires Développement , Deerns, le CERTU et Urbanistes du Monde.

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T Crowe Semler 11 years ago

What a great article, bravo! We can only hope all people read and grasp the potential for this ingenious system. The possibilities are only limited by the imagination. Nature offers us a path to a sustainable world if we are willing to follow. Matching the new architecture with the most sustainable principles insures the best possible solution..