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For thousands of years, buildings were designed based on the climate of the area and the physical and social environment (Roaf, Fuentes and Thomas, 2007). The provision of comfort for the dwellers is one of the most important functions of a building; as a result, there is a range of building types and the demand of energy depends on the occupants' needs and the activities taking place there (Douglas, 2011).
This report is produced in order to present the design of a low carbon building inhabited by a couple. The aim of the project is to design the low carbon house in a central location of Brighton and Hove, considering the climate and the location, using low carbon construction materials and energy efficient technologies. The objectives of the report are the presentation of the options for low carbon buildings in the city of Brighton and the analysis of the energy demand and supply of this type of buildings.
The project is based on information provided by books, case studies, tutorials, television programs and websites. Visits to other low carbon houses and informal interviews with the residents also helped to follow the best practice for the project.
1.2. Climate and background information
The low carbon house project is located in the southeast side of the Grand Parade campus of the University of Brighton.
The project is about a two-storey house. Since the purpose of making an energy efficient house is its appropriate orientation, the windows of the most habitable room should be located at the south side of the house. A south facing roof will also receive the highest amount of solar radiation (Pitts and Lanchashire, 2011). The surrounding buildings, trees and other types of vegetation will minimize the effects of wind.
The weather in Brighton is warmer that in other cities of U.K. with mild winters and warm summers. The range of average monthly temperatures is 12.5 °C, the highest mean temperatures are observed in July and August (20°C) and the lowest in February (2°C). There are around 4.8 sunshine hours per day and 1766 sunshine hours per year. The monthly and annual mean precipitation appears to be 67 mm and 801 mm respectively (Climate and temperature, 2012).
2. Building design, construction and performance specifications
The construction of a low carbon building requires making a choice of natural, locally sourced, with low embodied energy materials.
The construction of the building will be carried out using local sources with timber to be the main construction material. According to Pitts and Lanchashire (2011), timber frame is a very good method for construction due to the low embodied energy of timber-products.
The house will be constructed using Modcell system (McCloud, 2008). The structure will consist of timber framed wall panels infilled with straw bales. The size of panels will be 3m high x 3.2m wide and 480 mm thick. The straw bales will be packed tightly inside the timber wall frames, plastered on both sides using lime render and finally dried (Tickle, 2010). The final product will be straw panels. The straw bales results in highly insulated walls and have low embodied energy. When plastered, they are airtight and fireproof; in addition lime plasters offer high thermal mass (Jones, 2009).
The thermal performance profiles are easily defined when knowing the insulation value of a material. This value is commonly known as the U-value. The lower the U-value, the better thermal performance the house displays (Shomera House Extensions, 2012). Modcell indicates that the U-value for a 480mm straw panel lies between 0.13 and 0.19 W/m2K and the U-value for solid timber frame is 0.134 W/m2K.
Pitts and Lanchashire (2011) describe the wooden floor as the ideal place to locate thermal mass because solar radiation strikes it. The structure will consist of timber suspended ground floor suitable for underfloor heating and high insulation.
A pitched roof consisting of a pair of rafters formed into a truss, covered then by oak shingles will complete the structure. The rafters will be around 225mm deep and the roof will be insulated by sheepswool using a breathable membrane below. Oak singles are natural materials that do not need a waterproof membrane under them; in addition they match well with straw bale walls (Jones, 2009). The U-value for a timber roof is from 0.15 to 0.10 W/m2K. The roof will slope towards the south and solar collectors will be placed on it (Pitts and Lanchashire, 2011). There will also be rooflights to take advantage of natural daylight.
Windows influence heat loss, ventilation heat loss, solar heat gain and natural light representing an additional component to think about. A view, expressed by Modcell is that U-values for both glazing and frame of windows should not exceed 0.8 W/m2K.The building will have double glazed windows with a high-solar gain low-emissivity glass with argon-gas fill. The estimated U-Value is 0.30 W/m2K (Efficient Windows Collaborative [no date]). Large south-facing windows will be preferably constructed and timber window frames will reduce thermal bridging.
Finally, a fine-control slot ventilator should not be omitted.
3. Monthly Energy demand profiles
MacDonald (2012, p.45) defines the energy demand profile as "the pattern of energy use in a building, which varies during the day and over the year".
Energy is used in several ways in buildings. According to Douglas (2011), the greatest amount of energy used in British residencies is for space and water heating. Space heating covers more than the half of the energy consumption in a British house. Water heating reaches a percentage of 24% while the energy rate used for cooking and lighting is 3%.
A significant amount of the energy used in a house is in the form of electricity which powers electrical appliances and is finally converted into heat.
Low carbon buildings aim at low carbon emissions. MacDonald (2012) claims that the measures that occupants have to take in order to achieve the best energy performance specifications are the following:
To reduce the energy demand
That means that occupants should reduce the consumption of energy and carbon emissions. The house will be appropriately orientated in order to get the best thermal and energy achievements that passive solar heating and passive design features can provide.
To use the energy in an efficient way
The building fabric efficiency plays an important role as the house's components are made of materials of high thermal performance. Precise use and management of high efficiency building services results in suitable energy consumption as well.
To supply the energy needs establishing renewable energy sources
A great amount of the needed electricity will be provided by renewable energy technologies so that fossil fuels can be limited.
The couple, who is out of the house most of the day, is estimated to consume around 4.000 kWh per year. The tenants are estimated to consume the highest amount of electricity, for powering the appliances or for lighting early in the morning, during the evening and weekend. From November to February the demand for space and water heating is expected to be much higher than in spring and summer. However, the house has very good insulation and airtightness (0.86m3/hr.m2 @ 50 Pa) (Modcell, 2012) and the requirement for energy is expected to be less.
4. Suitable renewable energy sources and their supply profiles
Solar thermal glazed flat-plate collectors, southerly orientated.
The system will be placed on the roof providing more than 50% of the annual hot water requirement in winter doubling this percentage in summer (MacDonald, 2012). There is a back-up boiler to support the solar thermal hot water system, during the periods of low solar radiation.
Roof mounted photovoltaic arrays (3 kW).
The annual average electricity consumption in the house is estimated to be around 4,000 kWh. The southerly facing array will be installed at an angle of 30â° and will generate around 2,550 kWh per year producing more than the half of the annual electricity demand. During periods of low electricity demand, the overplus electricity generation will be exported to the grid. As a consequence, occupants will use grid electricity at night or on cloudy days, when the PV array cannot generate it.
14 k W 'air to water' floor mounted heat pump.
It will supply underfloor heating on the ground floor. The electricity that PV generates can be used to power and support the pump.
Mechanical ventilation with heat recovery system.
It will provide very good quality of indoor air and reach the greatest space heating efficiency.
5. Discussion and conclusion
The energy balance is based on the proportion of energy that enters the house and is stored and the proportion of energy that exits the house.
Feist (2009) states that: "the sum of the losses equals the sum of the gains". Heat losses are the fabric heat losses through walls, doors, windows and roof and the natural ventilation heat losses. Passive solar gains and heat from electrical supplies and activities are the heat gains. His calculation shows that the annual energy balance of a passive house is 130kWh / (m2a).
The low carbon building in the Grand Parade will be constructed with the use of local and environmental friendly materials and renewable energy systems. The suitable specifications of the components and the supply profiles of the selected technologies aim at an energy efficient house with low carbon emissions during its lifetime. However, weather conditions can be unpredictable; as a result, energy deficiency can be a problem which can be solved with the use of conventional forms of energy.
The U.K. government aims at a 60 per cent reduction in CO2 emissions by 2050. This goal makes the construction of low carbon buildings an appropriate strategy to follow by the Council of Brighton and Hove.
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