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For thousands of years, buildings were designed based on the climate of the area, the physical and social environment and the time of dwelling (Roaf et al. 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 two persons. The aim of the project is to design the low carbon house in a central location of Brighton considering the climate and the manufacturing location, using low carbon construction materials and energy efficient technologies. The objective is to present the options for low carbon structures in the Brighton area and understand the energy demand and supply of this type of buildings.
The project is based on information provided by books, e-books, case studies, tutorials, websites, on-line magazine articles, video recordings of television program and visits in eco houses and interviews.
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. In order to adopt the best practice, the climate of the area and the site layout should be examined.
The project is about a two-storey house. The house should be located in that way so that energy efficiency can be achieved. South orientation of the main habitable room windows and south-facing roof angled at approximately 35° should be used in order to reach the highest amount of solar radiation (Pitts and Lanchashire, 2011). There is an open space vision for this side; as a result the desired orientation is achievable. The surrounded buildings, trees and other types of vegetation will help in minimizing the effects of wind.
The weather in Brighton is warmer that in other cities of UK with mild winters and warm summers. In Brighton, the range of average monthly temperatures is 12.5 °C, the highest temperatures are observed in July and August (20°C) and the lowest in February (2°C). On balance there are almost 4.8 sunshine hours per day and 1766 sunshine hours per year. The average monthly and annual precipitation appears to be 67 mm and 801 mm respectively (Climate and temperature, 2012).
2. Building design, construction and low energy specifications
MacDonald (2012) declares that 'best practice in building design states that interventions to mitigate carbon emissions from the use of energy in buildings should follow the energy hierarchy. The energy hierarchy provides a logical approach to design; to reduce the amount of energy required in the ï¬rst place, ensure that it is distributed and supplied in the most efï¬cient way possible in order to reduce demand and wastage, and ï¬nally supply the remaining demand with energy from renewable and low carbon sources'.
[[[Thermal performance of a building refers primarily to how well a building is insulated from the external weather conditions in order to achieve a comfortable temperature internally.]]]
The construction of the building will be carried out using local sources. Timber frame will be the main construction material. According to Pitts and Lanchashire (2011), timber frame is a method, appropriate for sustainable construction because of the low energy that is required during the production.
The house will be constructed using Modcell system (McCloud, 2008).
External and Internal Walls
The building's walls will be panel timber frame infilled with straw bales. The size of the panels will be 3m high x 3.2m wide and 480 mm thick. The straw bales will be packed tightly inside the wooden 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 pests' proof, airtight and incombustible (Andrews, 2009). Lime plasters also result in high thermal mass (Jones, 2009).
The insulation value of the material (U-value), used in the fabric of the house (walls,floors,roof) is very important to know as it helps to define the thermal performance profiles. The lower the U-value, the better thermal performance displays the house (Shomera House Extensions, 2012). 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 (Modcell, 2012).
The requirements of high insulation and the underfloor heating that are going to be used leads to the construction of timber suspended ground floor. Solar radiation strikes ground floor so floor is appeared to be an ideal place to locate thermal mass (Pitts and Lanchashire , 2011).
A pitched roof will be constructed of timber frame truss rafters which will be covered by oak shingles. The rafters will be around 225mm deep to get sheepswool insulation into the roof with a breathable membrane below Oak singles are natural materials that do not need a waterproof membrane under them. In addition, they are well-matched with straw bale walls; both of the materials are breathable and long for years (Jones, 2009). The U-value for a timber roof is 0.15-0.10 W/m2K. The roof slope will be southerly oriented with a suitable pitch for solar collectors (Pitts and Lanchashire, 2011).
Pitts and Lanchashire (2011) mention that doors, windows and rooflights influence conduction heat loss, solar heat gain, ventilation heat loss and natural light.
According to Modcell (2012), the U-values for both glazing and frame of windows should not exceed 0.8 W/m2K with solar gain rate about 50%. The building will have double glazed windows with high solar heat gain coefficient; low-emissivity glazes with argon-gas fill. The estimated U-Value is 0.30 (Efficient Windows Collaborative [no date]). The larger windows should face south elevations considering that the seasonal average solar gain must be balanced against heat loss. Timber frames will help to reduce thermal bridging. A unique façade element will also be placed in SW elevations of the ground floor. GLASSX®crystal optically reminds of glass but its characteristics are better than these of double or triple glazed windows. It will be applied floor-to-ceiling, representing the thermal specifications of a solid wall. It is a translucent, quadruple-glazed window accompanied by insulation glazing and incorporated shading which absorbs internal and external heat masses and stores solar heat (GLASSX, 2012; McCloud, 2008). Finally, thermal performance of windows is of high priority but a fine-control slot ventilator should be placed; natural light is essential as well, so that artificial lighting can be avoided.
Energy efficient appliances and eco-friendly light bulbs for artificial lighting can be used .
3. Monthly Energy demand profiles
MacDonald (2012) defines as energy demand profile '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 private, 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. As it has been already mentioned, the house will be appropriately oriented 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. Furthermore, precise use and management of high efficiency building services results in suitable energy consumption.
To supply the energy necessities 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 pair, both out to work during the day, will consume around 4.100 k Wh per year.
During the day, the picked hours of significant energy consumption are estimated to be early in the morning, during the evening and at weekend. During these hours, electrical appliances and artificial lighting will particularly be used. In addition, from November to February the demand of space and water heating will be much higher than in spring and summer. However, due to the very good insulation and airtightness (0.86m3/hr.m2 @ 50 Pa), the space heating for a low carbon dwelling is very low (Modcell, 2012).
4. Suitable renewable energy sources and their monthly supply profiles
Solar panels will be installed to provide the suitable power that hot water heating system need not only on a sunny day but on a cloudy and winter day, too. As a result, roof mounted solar thermal glazed collectors, southerly oriented, will be installed. It will provide more than 50% of annual hot water demand in the winter and 100% in the summer (MacDonald, 2012). There is a back-up boiler to support the solar thermal hot water system, during the periods of no solar radiation.
Roof mounted 4 k W monocrystalline solar photovoltaic array, facing southwest so that energy could be generated in early evening. The photovoltaic will theoretically generate the 100% yearly electricity usage of the house (MacDonald, 2012).
The average electricity consumption in the house is estimated to be 4,120 k W h.
A 4 k W h photovoltaic can convert daylight into electricity on cloudy days, too and it is estimated to supply the house with approximately 3,400 k W h per year (the Eco experts). 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, when the PV array cannot generate it.
The average supply per month of the PV is estimated to be:
140kwh during the winter months
430kwh in spring
520kwh during summer months
270kwh in autumn time
14 k W 'air to water' heat pump mounted at ground floor, supplies underfloor heating. The electricity that Solar PV tiles generate can be used to power and support the pump.
Mechanical ventilation with heat recovery system used in winter will provide very good quality of indoor air and reach the greatest space heating effectiveness.
5. Annual Energy Balance
The energy balance is based on the proportion of energy that enters the house and is stored and the proportion that leaves each room by the fabric losses, ventilation losses, and roof and floor losses.
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