Solar shading and preventing overheating
29 June 2017
With the UK recently experiencing a record breaking heatwave, the subject of overheating comes back into focus. Whilst traditionally in the UK it has been the colder climate conditions that we have focused our attention on, summer overheating is increasingly becoming an issue. This is exacerbated by hotter summers and improved insulation in our homes. It was reported in 2015 that at least 1,700 deaths in the UK can be attributed to summer overheating. In 2013 760 deaths were attributed to one summer heatwave alone. Clearly this is a rising problem.
One of the key ways to deal with overheating is to control ‘problematic’ solar gain. It shouldn’t be forgotten that solar gain can be an added benefit to realising a highly sustainable low energy passive building, as it can help to significantly reduce the heating demand of a building. However, it is important to be able to control the solar gain so that it does not lead to overheating. The knock-on effect of which can lead to the addition of air conditioning which inadvertently will increase the energy use of the home. Solar shading is an important and incredibly useful tool in combating overheating.
Solar shading has been a feature of vernacular architecture in warmer climates for centuries. From the Arabic Mashrabiya style carved wooden screens to louvered shutters in Mediterranean towns and cities, the addition of solar shading does not look out of place to buildings across the continent. Due to the comparatively cooler climate of the UK, solar shading has not been a feature of our architecture. However with rising temperatures and the risk of frequent and prolonged heat waves, it is likely that we will have to include solar shading in our new buildings more and more. At Super Green Architecture, effective solar shading is incorporated into the design process from day one.
Broadly speaking there are 3 types of solar shading:
Fixed solar shading
This is typically supplied in two forms; generic and optimised. Large overhangs to a roof, deep window recesses and fixed screens on the outside of a build are good examples of generic fixed solar shading. This type of shading will provide protection throughout the year, quite often preventing direct solar gain in the summer and winter months although if carefully designed the overhangs of a roof for example can be calculated to allow direct solar gain in the winter whilst preventing it in the summer by allowing for the change in the sun angle as the earth rotates on its axis. A brise soleil or louvre system is a good example of an optimised fixed solar shading system. The angle, size and spacing of louvres will be designed to allow for winter solar gain and prevent solar gain; and they can be designed to suit the different sizes and locations of glazing around the building. Perforated screens can be used as solar shading, provided that the spacing and pattern of the screens create sufficient protection.
Credit: Adria Goula
Dynamic solar shading
Examples of this would be openable shutters, retractable blinds and automated louvre systems. They can be opened and closed to suit the need for shading, which can help reduce their impact on the external façade of the building as they can fold out of the way or retract in size. Moveable shading systems are likely to be more costly than fixed systems, both from an initial capital outlay and an ongoing maintenance cost. Dynamic shading can be both manual and automatic. Manual shading relies on the user ‘closing the building down’ prior to the sun’s rays coming into contact with it. An automatic system reduces the reliance on the building user; however it is likely to be more costly.
Climbing plants and tall trees can be used to provide solar shading. Climbing plants will require a support system to enable it to grow against; this is often timber or steel. The use of deciduous vegetation is considered to be a natural dynamic way of shading, as the time at which you need solar protection coincides with leaf and flower cover. This provides solar shading at the right time of the year. As vegetation shading relies on plant growth, the amount of time it takes for the plants and trees to grow to the optimum height to provide cover needs to be factored in to the design of the scheme. This is particularly important in the case of tall trees which are not present before the building is constructed. The added benefit of vegetation shading is that they can aid in cooling the building through evaporative cooling, and they can significantly contribute to a cleaner air environment. Thought and care needs to be taken in order to provide sufficient water and nutrition to sustain the plants and the ongoing maintenance of the planting and irrigation. This can often significantly add to the costs of the system.
As with any part of the building, careful design and consideration needs to be taken to ensure the choice of solar shading is right for the long term user. However, when solar shading is incorporated from the outset of a scheme it can form a part of a unique aesthetic whilst contributing to controlling the heat gain and risk of overheating in a building.
21 May 2017
A small company in Scotland has started using plastic waste to add in to an asphalt mix to create a stronger, longer lasting pot hole free road. MacRebur are taking waste plastics and recycling them into small pellets, which are then added to rocks, limestone and sand to replace some of the oil based bitumen used in a traditional road construction. Plastics that would usually go to landfill and farm waste are used to create the plastic pellets.
The advantages to a recycled road include increased tensile strength, improved fuel resistance, increased resistance to cracking, deformation and rutting, and a longer lifespan of the road. Added to this, by utilising recycled plastics in place of Bitumen there will be a reduction in fossil fuel usage. Bitumen is derived from crude oil, which is extracted from the earth at a huge financial cost and with significant carbon emissions. By replacing bitumen with plastic pellets there will be a reduction in carbon emissions from the oil extraction and its transportation.
Last year MacRebur won the Virgin Media Business Voom competition, enabling the company to go from concept to a fully-fledged business. Two councils in England have already used recycled plastic roads.
For more information see www.MacRebur.com or the following article on the BBC
The Eden Project
We have been a bit held up with April’s blog, partly due to the office move but also because of a much-cherished holiday.
Whilst away, we visited the excellent Eden Project in Cornwall. The Eden Project is a centre for the display, education and conservation of plant species from across the planet, contained within a Rainforest and Mediterranean Biomes which are surrounded by outdoor gardens cut into the terraced landscape.
In its simplest description, it is a large green house in a former quarry. However, this does a great disservice to both the complex engineering and design of the project, to say the least for the impressive scale and beauty of it.
One of the biggest challenges that the design team faced was the irregular shape of the site that was constantly changing as it was still being quarried. Examples from biology helped to inform the shape and design of the Biomes. Soap bubbles helped to generate a building form that would work regardless of the final ground levels, whilst pollen grains and carbon molecules helped to devise the most efficient structural solution using hexagons and pentagons.
Maximising the size of the hexagons was the next challenge; to do that the designers had to find an alternative to glass as it is limited in terms of its maximum unit size. ETFE was utilised as it could be manufactured in panels up to 7m in length and was only 1% the weight of a double-glazed panel. With such large lightweight panels they found that they needed less steel, this allowed more sunlight to get it. The increase in passive solar heating helped to reduce the artificial heating requirements in the cooler months. With less weight in the super structure there was a large reduction in the amount of foundations required. At the end of the project, the designers calculated that the weight of the superstructure was less that the weight of the air inside the building!
We couldn’t recommend a visit highly enough to this incredible and disarming feat of sustainable architecture and engineering.
Passive Power - the future for UK energy?
31 March 2017
A significant milestone has been reached toward making passive power a reality for Britain with the tidal lagoon proposal in Swansea Bay.
The UK government is currently considering the findings of former energy minister Charles Hendry's independent study into the viability of tidal lagoon power. The intention is to make the Swansea tidal lagoon a pilot scheme for our renewable energy future.
(Credit: Tidal Lagoon Power)
The process involves 6 metre high and 18 metre long underwater turbines which are capable of generating 16 megawatts of electricity per hour. As the tide comes in, wicket gates prevent the water from entering a large enclosed lagoon. At peak tide the gates are opened, allowing the water to drive the turbines whilst filling up the lagoon. At low tide, the process is reversed. Two daily tides provide four opportunities to generate power over a 24 hour period. This makes it a reliable and constant source of clean energy.
(Credit: Tidal Lagoon Power)
Imagine filling your bath twice a day, with the water rushing in through a giant water wheel and then emptying it out through another one. Only the water isn't wasted, it is simply re-used to fill the bath again. A simple premise, and one that harnesses the natural energy available from tides without generating carbon emissions.
The impact on marine life is one of the key details to be established. Provided that this is not detrimental to the habitat of marine wildlife, tidal lagoons could be a real answer to our long term energy needs. All of this, without the need to threaten our water table through fracking or to import carbon heavy electricity from abroad.
The science behind climate change
28 February 2017
Human aggravated climate change is real; at least we believe it is. But what do you say to those that believe it is a hoax, a Chinese conspiracy or simply a cyclical factor of nature? The argument usually goes along the following lines; "There is no clear evidence to show that the earth is warming up", "The planet has always warmed up and cooled, its cyclical", and "How can the earth be warming up when the sun's energy is constant".
Ignoring the complexity behind the sun’s lifespan and eventual collapse, if we take it simply that the amount of heat coming from the sun is constant, how could this regular heat output accumulate to cause the Earth’s temperature to gradually rise?
The answer lies in the amount of greenhouse gasses in the atmosphere. Methane and carbon dioxide allow visible light to pass through the Earth’s atmosphere but absorb infra-red light. Heat that would otherwise bounce off the Earth’s surface is absorbed by the greenhouse gasses. An increase in greenhouse gas emissions arising from the burning of fossil fuels increases the absorption of heat in the atmosphere and reduces the amount of heat that would usually bounce back into space. Therefore the overall temperature of the Earth rises.
But where is the evidence? The earth’s temperature has always fluctuated. Putting rising global temperatures, warmer oceans, shrinking ice sheets, declining arctic sea ice, diminishing glacial ice and ocean acidification to one side; this graph clearly demonstrates that whilst carbon dioxide levels have fluctuated throughout the earth’s history, there is a clear and rapid increase in the amount of carbon dioxide in the atmosphere in the post industrial age.
(Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.)
If you needed any more evidence, as reported in Environmental Research Letters 97% of scientists concur that man-made climate change is real. We would recommend the excellent documentary ‘An inconvenient truth’ by Al Gore, Leonardo DiCaprio’s polemic ‘Before the Flood’, The Met Office or NASA.
Christopher Hitchens may have put it best when he borrowed Jonathan Schell’s view on the nuclear experiment; “we don’t have another planet on which to run the experiment. We can’t find out but one way... We have no right to run an experiment in warming on the planet”.
To those who believe it is a hoax by NASA or a Chinese conspiracy you can leave the room; you’ve already left the conversation.
What is Passive Solar?
31 January 2017
Many people ask us what passive energy and in particular what passive solar design is. As it is a core principle of our design philosophy at Super Green, we have put together a brief explanation using our shortlisted design for the AJ Barratt 2020 House of the Future competition.
A passive solar design relies upon allowing the suns energy to warm the building’s interior. The building must have an efficient fabric to prevent this energy being lost too quickly. There is a risk of overheating when a building is super insulated and there are no measures in place to prevent overheating.
The summer sun angle in Britain is approximately 60 degrees. Louvres are fixed on the external facade of the building at an angle and spaced apart. This allows natural daylight to enter the home and enables the occupants to see out, whilst preventing direct solar gain during the summer which would lead to overheating.
The winter sun angle in Britain is approximately 15 degrees. The angle of the louvres allows direct solar gain during the winter, helping to heat the home during the winter months when overheating is less of a concern. This form of free clean energy will lower energy bills and reduce the buildings impact on the environment.
Intrinsic to this design was the inclusion of a vaulted stairway and entrance hall. Roof lights supplying the light well over the staircase are unprotected to allow heat to build up in the high space throughout the year. By using the principle of heat rising, air is drawn through the building and out at high level. Opening windows at lower levels allows fresh cooler air to enter the home. By encouraging air movement in this way, cool air can be brought into the building to replace the hot air leaving it. This is known as stack effect ventilation and provides purge ventilation for summer months.