Low Carbon Buildings – Target Zero Carbon Construction
Low carbon buildings are frameworks created and constructed with reduced embodied carbon materials, which improves the energy efficiency of buildings in the UK.
Whatever the truth about the proportion of global warming caused by man and compared to natural causes, there is no doubt that we are burning more hydrocarbon fuels and causing more pollution than ever before.
This impacts climate change and causes environmental degradation. As more fossil fuels are extracted, the demand for them grows, which results in the price increasing. Most fossil fuels are now imported; leading to dependency,so there are very sensible economic and political cases for reducing hydrocarbon, or fossil fuel consumption.
Buildings account for about half of the total fuel burn in the country and half of that is accounted for by commercial buildings. The reduction of this figure is probably easiest on big buildings, which members of the BCSA construct and REIDsteel are one of those members.
Unless buildings become more efficient, there is no way the political target of an 80% carbon reduction by 2050 will be met.
There are five routes to reducing hydrocarbon fuel burn involved in buildings:
a. Reducing the amount of ’embodied carbon’ materials used in the original building constructions.
b. Making commercial buildings more efficient in use.
c. Recycling the materials at the end of a building’s life.
d. Getting energy from sources other than burning hydrocarbons.
e. Offsetting the carbon building content, by saving carbon elsewhere.
How to embody less carbon construction materials in your building:
Concrete and steel both emit carbon dioxide in their production. If all steel used in the building project were new and made from imported ore in a blast furnace, then the carbon content within the steel would be as high as concrete. Fortunately steel is nearly 100% recyclable, and the re-use embodies much less carbon.
Therefore, steel framed buildings and structures embody less carbon than their concrete cousins (40% of steel is deemed to be ‘new’, and 60% is recycled; yet almost all embedded steel will be recycled).
Steel buildings are often smaller and lighter than concrete structures. Suspended floors can be made with concrete slabs, or with precast hollow core planks and topping, or with thinner concrete poured on to steel decking. Research shows that the thinner the slab is on the steel decking will embody low carbon.
Using timber framing is an alternative and unlike steel and concrete, the production of timber absorbs carbon dioxide from the atmosphere. Apart from the energy spent, harvesting, transporting and processing it, the timber is therefore carbon-negative. If all the timber at the end of its life were to be burnt in a waste-to-power plant, the use of timber would be very positive; but timber has an Achilles heel.
Only a small proportion of a tree becomes structural timber. Wood that rots gives off part of its carbon content as methane, which is 25 times more dangerous as a greenhouse gas, than carbon dioxide. If only 4% of a tree rots in this way, its global warming potential is the same as the burning of a whole tree. Timber frame is also very expensive, and is best kept for those places where the aesthetic value is great.
Even there, it is more effective to clad steelwork rather than using pure timber or glulam. Thus steel buildings in practice usually embody low carbon. Naturally, the highly efficient REIDsteel designs are constructed to eliminate waste and are more sustainable than most.
How to make commercial buildings more efficient in use:
a. Reducing the amount of air leakage- Large uninterrupted areas of double skin sheeting or sandwich panel that are properly fixed and sealed, suffer very little air leakage. Eaves, corners, ridges and joints over masonry walls all have air gaps which need good detailing and good erection to minimise leakage.
Windows, doors, vents, structural penetrations through the envelope all have joints that allow leakage. Keeping the number of these to a minimum and improving the detail and erection of these will help to minimise air leaks. Good fillers and seals can very much reduce air leakage. Generally the joints of translucent sheets to metal sheets are harder to seal correctly.
b. Doors can have rapid opening and closing to minimise the time they are open.
c. Increasing the thermal insulation of the envelope- This can be done with thicker fibreglass or poly-isocyanurate foam although if there is an increase in thickness there can be a diminishing return.:.
d. Reducing thermal bridging- Again every door, window and vent will transfer heat through the envelope. In particular, structural steel which passes through the skin can transfer heat and needs a thermal break. The smaller the number of such thermal bridges, the better.
e. White or light coloured sheeting reflects more heat on summer days and gives out less heat in winter or at night. For example, in sunny climates white sheeting may reach 50 degrees C and dark sheeting may go to 100 degrees. If inside is to be 25 degrees, you get 3 times less solar gain with the white sheet.
f. Carefully balance the need for windows and translucent sheeting- These let in somewhere between 1.5 to 3 W/degC/sqm. Compare this to 0.25W for roof sheeting. 10% translucent loses or lets in which is the same amount of heat as the rest of the roof. The same goes for windows. These figures exclude ‘solar gain’, the heating of the interior by sunlight that passes through the translucent or glass; can give intense heating. Various expensive coatings can reduce this; and sun shading (brise soleil) will also reduce direct sunlight. A careful calculation of the need for light, and for heat or cooling, will determine if natural light is a benefit or a cost. Natural light through the walls give less solar gain than through the roof, as the sun is hotter from overhead; and translucents in the roof lose more heat because the higher air in the building is hotter.
g. Efficient lighting and internal equipment will reduce energy use.
h. Hot air rises to the roof, and can be directed downwards using fans with socks or de-stratification nozzles.
i. Various wall finishes on south facing walls can trap heat which can be used for space heating. ‘Solar Wall’ is an example. Pinholes in a dark outer sheet can let air enter the gap behind it, and then heat it in sunshine; this hot air can then be pumped to heat buildings.
j. Buildings can be built with ‘green roofs’ with insulation and then a membrane, over which soil or other growing medium is placed. Then suitable plants are planted. This can absorb Carbon Dioxide (but here you need great care. Planting grass which is then mowed, and the mowing composted, changes CO2 to vegetation and then to methane which is25 times more damaging than Carbon Dioxide). ‘Green Roofs’ are expensive, and need maintenance; but they also reduce heat transmission through the roof so do have a value.
There are packages of measures available under the name of ‘Target Zero’ researched by Corus. Providing three steps for reducing carbon, at increasing expense and decreasing value; so one should stick to the first step. www.targetzero.info.
How to recycle construction materials at the end of the buildings life:
In the perfect world, timber structures would be taken to bits and the wood would be re-used or burnt in a waste to power plant. Though the majority of it can be burnt in situ or sent to landfill. Landfill is extremely damaging as the wood can rot over the years and produce large quantities of methane, 25 times more damaging than carbon dioxide.
Nothing much can be done with concrete except to break it up and use it for road-base and doing so takes up energy. Recovering the steel content can be difficult as concrete cannot be recycled to any advantage. A similar problem occurs with masonry walls as the product is of low value (down-cycling).
Steel buildings can be almost entirely recyclable. The purlins, rails and frames can be melted to make new steel, and this takes 3 times less energy than making new steel. Steel cladding can also be recycled; although foam filled sandwich panels are difficult because of their chemical content, The floors made of composite style decking and concrete are difficult to recycle, and are usually distributed to landfill, though at least they are thinner than regular concrete floors. The salvage rate for steel buildings is around 94%!
How to get power from sources other than hydrocarbons.:
a. Ground source heat pumps – Use pipes buried in the ground to circulate water over large areas. This can extract heat from the ground. Alternatively a heat pump consumed in a fridge can extract heat from the water and can be used for heating. . This is an efficient process, especially if there is a moving water table in the ground. Though the disadvantage to this is the initial cost and the need to plan the installation with the building programme. Some experts consider that this is the only energy saving system that will recoup its cost in a reasonable time.
b. Air source heat pumps – By extracting heat from the outside to heat buildings. This can be used by heat radiators, under floor heating systems or warm air convectors. They are less economical in operation as the calorific value of air is much less than soil or water.
c. Combined Heat and Power, CHP – Generating both electricity and useful heat with the appliance of a heat engine or power station. Most methods of generating power, produces heat, and this heat is usually wasted to the atmosphere. For instance, in cooling towers, diesel engine radiators, and turbine cooling systems etc.. This heat can be reused for industrial plants green-houses, and heating homes and buildings etc. If a site is properly planned to produce its own power, and to distribute the waste heat where it is needed, the combination of heat and power that produces carbon dioxide would be reduced, and this is done effectively in a few places.
d. Biomass Fuelled Power Stations – This renewable energy source is derived from various energy sources such as; wood, waste, landfill gases, alcohol fuels and rubbish. Wood energy or even wood grown for that purpose are both direct use for harvested wood by ‘coppicing’. This can be burnt to produce heat to form electricity. Farms can use manure and rotting vegetation to produce methane; this is then burnt to make power or etahnol. Biomass Boilers – Biomass can be classified as a renewable energy source that can be burnt for heating in special boilers. Biomass boilers can generally burn wood chip, wood pellet, cereals or a combination of fuels. This produces heat, rather than gas, coal or oil.
e. Wind turbines – This is a device that extracts energy from the wind and is used to generate electricity. On a bigger scale, this can cost twice as much per watt as regular generation, and need a 100% backup because the wind does not always blow on cold or hot days.
f. Solar Heating – These systems are a popular way of using renewable energy technology. This can work effectively for heating water, but probably not for space heating or cooling. This is most popular in hot climate countries and can easily be used for heating water and cooking. See also 6h above.
g. Solar Power Generation – This source of electricity is produced from the sun and pushes it into existing electrical grids. In hot climate countries, solar power can be concentrated by mirrors to heat water. Water can then be boiled to make steam to drive turbines to generate electricity. These can be very thermally efficient and be made to store heat to generate at night.
h. Photo Voltaic Cells – This is a direct conversion from light to electricity. These are expensive to make and require sunlight to work, therefore needing 100% backup. They are created to save carbon and designed to absorb electromagnetic energy to produce heat, although they only turn 10% of this into usable electric power. The rest of it becomes heat, radiated out in infra-red. Exactly the frequency which is trapped by the CO2 and CH4 in the upper atmosphere, so cause global warming.
i. Hydro Electric – A good clean method of generating electricity assuming there is a good head of water. It can be done on a small scale if there is a supply of high pressured water. Unfortunately we do not have enough of it in the UK and low head hydro-electric rarely works cost effectively (see h. Below).
j. Wave Power – This is an almost inexhaustible source of energy but it is still in its infancy. There is as yet no proven method of generating the energy and transmitting it economically to the users.
k. Tidal Power – Uses the power of the tides to convert energy into electricity or other forms of power. This works in some parts of the world but has a huge rise and fall of tide as this is needed and low head generation is very expensive Nuclear Fission- By producing energy for nuclear power, this is the only feasible way currently to generate the amount of electricity that we need, without burning hydrocarbons. It has the drawback of producing radioactive waste that will last for 10s of thousands of years. With costing a little more than fossil-fuel electricity at present, especially when de-commissioning costs and waste disposal, funds are added in. Though there is a political objection to this, as London receives their electricity from Electricte De France (EDF) which generates 75% of its electricity from Nuclear. The problems of waste are not insuperable, as are none of the other problems, except that by years of inaction we have lost expertise.
l. Purchasing ‘Green’ Energy – By producing your own energy and using natural resources, this electricity or heat can be described as zero or low carbon energy. Most users will not be able to do micro generation cost-effectively; but already it is possible to purchase energy from ‘green’ suppliers, usually at a premium cost. An undertaking to do so could offset the carbon content of the building operation.
How to Offset Carbon Dioxide produced in the construction or the utilisation of a building:
The government’s plan is to achieve Zero Carbon constructions using embodied materials, like ours, within a short period. It is extremely expensive and difficult to make a building using construction methods which embodies or emits zero carbon, although reasonable methods exist to get about halfway there. Construction will never-the-less take place, and the device used to allow this will be ‘Offsetting Carbon Dioxide Production’ elsewhere. The idea will be that the client will ‘Offset’ the remaining 50% of the building’s Carbon by reducing Carbon utilisation elsewhere.
See paragraph 8.
Most of our energy comes from burning fossil fuels. This produces Carbon Dioxide and pollution, and uses up a valuable and diminishing resource. Buildings of the type made by steelwork contractors use about a quarter of the Nation’s energy. Savings should be made in the ‘Embedded Carbon’ used in the building construction, and steel framed buildings are the most ‘Carbon Efficient’ way of doing so.
There are a series of relatively cheap things that can be done to improve normal construction buildings, then a diminishing return from further expenditure. Buildings should be re-cycled at the end of life to give the correct full life cycle carbon cost, and steel buildings are good for re-cycling. The government would like our constructions to be low carbon buildings by 2020, but is not practical to achieve 100% carbon reduction; this can be remedied by buying ‘green energy’ or by ‘offsetting’, making carbon savings elsewhere.
REIDsteel buildings are the most efficiently designed, to minimise ‘carbon content materials’ and help sustainability.