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20th Century Technology Series
The Twentieth Century Technology Series was planned as an opportunity to look back and reflect on the key developments in engineering and technology and their impact on society and the economy. The five speakers were asked to explain the basic principles behind their respective technology and describe how the technology evolved bringing it up to the present day, then speculate on technological prospects after the year 2000.
Victor Suchar, Series Organiser
ENGINEERING A `GREEN' BUILDING
Douglas King and Roderick McDonald, Buro Happold, on 25 May 1999
Douglas King started by providing some background as to why sustainable (`green') engineering is necessary now.
In the 1980s the Club of Rome report forecast that the world's resources would be used up quite soon unless changes were made in their use. In the UK, each person, including children, `consumes', each year, nearly 6 tonnes of virgin material resources, 120,000 litres of treated water and 3½ tonnes of fossil fuels. Each person also `produces' annually, 11½ tonnes of greenhouse gases, 40 kg of acid-rain creating gases, 2 tonnes of refuse for landfill and 4½ tonnes of waste dumped at sea. There is an imbalance between what we use in manufacturing and what we generate in terms of value-added goods of 10:1.
The construction industry quarries 300 million tonnes of aggregate a year and puts 60 - 70 million tonnes back as landfill, but 1% of all the 360 million tonnes of input materials is wasted before it gets into the construction process.
In a commercial building less than 1% of the treated water is consumed by people — the rest is flushed down the drain from toilets, wash basins and floor washing but still has to be treated by sewage plants.
Global warming is a headline issue nowadays. The measurable parameter is the carbon dioxide content of the atmosphere. 500 parts per million (ppm) is thought to be the critical level above which irreversible ecological damage will occur. At present the level is 370 ppm, up from 250 ppm in 1900: 500 will be reached in 25 - 30 years at the present rate of increase.
Over the period 1974 - 94 there was a marked improvement (7%) in energy efficiency in dwellings thanks to improved boilers and insulation _ but we are buying 30% more electrical fittings and building 25% more houses, with the overall effect of increasing the energy consumption by 15% over that period. Buildings contribute half the carbon dioxide emitted in the UK and a further 10% is due to the manufacture and transport of building materials.
To save energy, `green' buildings install air conditioning and re-circulate much of the air many times. This can cause `Sick Building Syndrome' because the air conditioning system is an ideal breeding ground for bacteria and fungi. Nearly two millennia ago in the Middle East the problems of heating, cooling and ventilating buildings were solved without such artificial processes. We are now applying these techniques again as Roderick Macdonald will now explain.
The design of green buildings is a rigorous process. It is not an exercise in style. I intend to illustrate that it is a technological engineering process which can be applied to an enormous variety of building types. The steps taken can be graded. There are those that require a change in lifestyle of the occupants, and there are those which can be achieved by good application of technology. So for example the use of photo-voltaic cells is technological, whereas composting of sewage involves a change of lifestyle. The development of new types of glass is technological, but the way we travel affects our lifestyle. More efficient heating and cooling machinery is technological, acceptance by occupants of wider variation in comfort temperature is a lifestyle matter.
The principle factors in green building design are:
• form and mass
• solar control
• water recycling
• the management of the building
• the control systems
• heating and cooling machinery
• solar heating
• ice storage
• geothermal energy
• wind generation
Location is about travel distance and method of travel. It is about ambient noise, noisy city centres or quiet rural areas, and it is about the reuse of existing building land.
Materials. Doug has indicated that the energy involved in producing the materials of a building is only about 10% of the energy which will be used to run the building during its lifetime. However, the reuse of materials is vital; refurbishing old buildings, reusing aggregates in concrete, reusing steel, aluminium and glass. It is not good enough to say this is a material which is new but can be reused. It is important to be using materials which have been used before.
Form and mass. The orientation of a building, the positioning of the windows, the effect the building has on local wind speeds, the exposure of the mass of the construction internally to take out the peak loads of heating and cooling are all significant.
Solar control, in other words the use passively of natural light, or shading and absorbing solar energy makes the building work for itself.
High insulation values in the roofs and the walls and where possible insulation `outside' with mass `inside' is a low cost way of achieving large energy savings. The difficulty comes at the windows. Double and triple glazing show great savings in energy, but in life-cycle cost terms, because sealed double glazing has a short life span, these become questionable. New glass technologies and new frame designs are necessary.
Ventilation. Many of us here probably live in old Bath buildings where the ventilation comes from leakage from windows, doors, floors and roofs. In green buildings design this uncontrolled leakage is minimised and ventilation is controlled so that there is enough to keep the buildings fresh and cool, but avoiding unnecessary heat loss.
Water recycling. We are only tinkering at the edges of the process of water recycling. In reality we need only drinking water and a little top up water for our buildings. The rest can come from recycling and rainwater. This would result in a 90% reduction in water consumption and eliminate the need for municipal sewage systems. It is a large lifestyle change but a dramatic change for sustainability.
The new Royal Armouries Museum in Leeds demanded an environment with constant temperature and humidity levels. This could have been achieved simply through a well designed air conditioning system. We sought, however, to get the building fabric to do as much as possible for itself. There is minimal natural light in the galleries minimising solar gains. The spaces have high ceilings and high thermal mass exposed both in the undersides of the slabs and in the walls. There is very good insulation outside this mass. The air distributed in ducting around the building is limited to that needed to keep the building fresh. It provides both heating and cooling, and it works on a displacement principal.
Many air conditioning systems force air around buildings, but air has a natural buoyancy: if it is introduced cool at low levels it will remain there, rather like water in a tank, until it warms, when it will rise. When it rises it can be collected in ducting or it can be allowed to move up through an atrium or a stairway, or indeed it can be encouraged by a chimney which is heated naturally by solar energy. We will see such a chimney in a
later building example. This displacement principle is used in the Armouries Museum.
Exposing the thermal mass of the buildings to the air and the spaces takes out the peak heating and cooling loads by absorbing and emitting energy. Taking out these peaks not only reduces the energy demand but it reduces the capacity of the equipment required to heat and cool and it allows the equipment to run more efficiently.
We achieved a building which virtually controls its own temperature. The air conditioning systems are used to extract the energy and humidity resulting from the passage of visitors through the spaces.
The Thames Valley University Learning Resources Centre is a new style library containing 500 computers, each giving off heat. The College wanted to be able to let the building commercially in July and August, the hottest months of the year. The aim was to produce a naturally ventilated low energy building. The steps we took were to highly insulate the roof, to expose the mass of the concrete structure to the enclosed spaces and to use a `mix mode' ventilation system. The low level windows can be opened and closed by the occupants, some high level windows are opened and closed mechanically. The cost of mechanically operated windows and the maintenance of them is high, so the ventilation at the highest levels in the roof is through large very slow running extract fans. During most of the year this mixed mode ventilation provides sufficient cooling. Heating is required for only 3 months of the year and only during the hottest days of the year is the natural ventilation closed down; then an air conditioning system takes over recycling cooled air within the building. Computational fluid dynamics analysis was used to understand the way the building would perform throughout the year. The windows on the south, east and west sides of the building are shaded with fixed louvre systems which reflect light onto the ceilings and bring natural light deep into the building.
Along with Max Fordham we worked on the Building Research Establishment's new building at Garston. It was the aim of the BRE to include many sustainability features and then to monitor the effects of these after the construction. Photo-voltaic cells are used to produce electricity direct from the sun. The building is highly insulated, the glazing shaded and the space is naturally ventilated. Thermal chimneys are used to assist in the natural ventilation process. South facing glass block walls absorb solar energy, heating the air in the chimneys, and the buoyancy of the hot air assists the natural ventilation. The structure is built using recycled aggregates. Moulded pre-cast concrete elements form the exposed ceilings and floors and these elements are designed to allow the air entering the building to pass across the surface of the concrete, thereby moderating temperatures. The shade louvres are mechanically operated to maximise natural light gains and to minimise solar energy gains.
The question is how good is such a design. Is it worth all this complexity?
In the diagram above, four office types are compared with the BRE building. The first is a `prestige headquarters', the 2nd a `standard air-conditioned office', and the 3rd a `naturally ventilated office'. In each case `normal practice' and `good practice' are compared and it is significant to note the difference between these; the diagrams showing roughly 30% savings in each case. However, the most dramatic fact coming from this diagram is that the BRE building is using about 15% of the energy of a prestige headquarters. In other words 85% less energy and what's more it is using only about 30% of the energy of a normal naturally ventilated building.
In a building designed for the Open University we were not allowed the luxury of the very effective but high capital cost of the BRE building. We did not use photo-voltaic cells or solar heated vent chimneys. We used fixed shading and a simple in-situ beam and slab frame structure. This low capital cost building uses 25% more energy than the BRE building but is still 30% better than a normal good practice, naturally ventilated building and more than 60% better than a traditional naturally ventilated building.
Tennis centres are being built around the country. One at Eastleigh is roofed with fritted foil
cushions. The structure is highly efficient being almost entirely in tension minimising the use of materials. The cushions are three-layer giving good insulation. The foil, unlike glass, is transparent to sound giving the space an `outside' feel. Also unlike the `greenhouse' effect of glass, foil transmits long- wave radiation allowing radiation to escape in summer keeping temperatures down. The environment of the internal space throughout the year is controlled mainly by the fabric.
In green building design there is green and there is green. 80% of all the commercially grown timber is scrapped. The aim of the development at Hooke Park in Dorset was to see how we could put that 80% to good use. It was used in its green state for the structures of residential and educational buildings. It was demonstrated that quality buildings could be achieved from waste products. There are problems with the glues used in the connections and the plastics used in the waterproofing, but we are working to overcome these problems and the buildings demonstrate how building construction can be achieved with very little demand on world resources.
So how do we put all this in perspective? The BRE has an energy assessment method called BREEAM in which they take into account the management, the health and comfort, the energy use, the modes of transport, the water use, the materials, the land use, the ecology, and the pollution effects of a building. They categorise these scores, weight them and come up with a rating for the building which is poor, good, very good or excellent. The BRE building gets a `very good' rating. It would be excellent but for its location which demands the use of private car travel by the occupiers and visitors.
When Buro Happold needed a new office in London we decided that we should `practice what we preach' in terms of sustainability. We selected a building with excellent public transport links, provided no car parking spaces, but we provide facilities for cyclists. The building is located on a site protected from vehicle noise and the worst of pollution by the buildings around it. This allows natural ventilation. The audience were shown a drawing showing the section through the building illustrating the entrance, the terraced building at the front which is repeated with a similar terrace behind, the open deck and the high ceilings. The previous occupants had installed low false ceilings and partitioned the building into little office spaces creating a stuffy `rabbit warren' environment.
The steps we used were to reuse the primary fabric and features of the building structure, but to strip out the rest. We insulated the roof and installed new windows throughout. The windows minimise air leakage but have opening vents at high level to allow night cooling in the hotter months of the year. The windows are single glazed with laminated low-e glass and are shaded with fixed louvres on the south side. Blinds are provided to all the windows to allow control of glare and solar gain and to reduce heat loss in the winter. Lighting is in general low energy and heating is by condensing boilers and radiators. The outside deck is put to use for both recreation and meetings. Whereas the BRE building achieved a `very good' rating we are able on this design, making allowance for the way we manage the building, to achieve an `excellent' BREEAM rating.
Doug and I hope that we have illustrated that green building is necessary, but that it does not have to be cranky. We hope that we have illustrated that dramatic energy reductions are achievable without enormous capital cost and that the buildings can feel good, be enjoyable and be delightful to the occupants. The message is to keep it simple and avoid the expensive gizmos unless you particularly wish to use them.
Doug King and Rod Macdonald