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Charikleia Chelmi, student no: 12835450
Date: 14 November 2012
Subject: Energy demand and supply.
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 objectives of the project are to design a 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 potentials for low carbon buildings in the city of Brighton and issues of energy demand and supply for this type of buildings will also be mentioned taking into consideration that over 27 % of the UK's CO2 emissions come from the residential sector.
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.
1.1. 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 UK with mild winters and warm summers. The range of average monthly temperatures is 12.5 Â°C, the highest mean temperatures are observed in July and August (20Â°C) and the lowest in February (2Â°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 us to make 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 result 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 using wool and 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 panels and collectors will be placed on it. 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, 2012). Large south-facing windows will be preferably constructed and timber window frames will reduce thermal bridging.
A fine-control slot ventilator will also be established.
3. Monthly energy demand profiles
MacDonald (2012, p.45) defines 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 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 result in suitable energy consumption, as well.
To supply 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 7.500 kWh per year. The tenants are estimated to consume the highest amount of electricity, for powering 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, energy requirements are expected to be less due to the house's design, the good insulation and airtightness (0.86m3/hr.m2 @ 50 Pa) (ModCell, 2012).
4. Suitable renewable energy sources and their supply profiles
The house will be equipped with the following renewable technologies:
Solar thermal glazed flat-plate collectors for water heating.
The system will be placed on south facing roof mounted on a slope of between 30 and 40 degrees to the horizontal. It will approximately collect from 1000 to 1300 kWh per year meeting about 50% of annual domestic hot water demand. The average monthly output for the collector is estimated to be: 20kWh in December and January, 45kWh in February, 80kWh in March, 105 kWh in April, 125 kWh in May, 150 kWh in June, 160 kWh in July, 115 kWh in August, 95 kWh in September, 60 kWh in October and 30 kWh in November. There is a back-up boiler to support the solar thermal hot water system, during the periods of low solar radiation.
Roof mounted photovoltaic array
The southerly facing1.85 kWp PV array will be installed at an angle of 35â° and will generate around 1.700 kWh per year. Specifically, the average monthly electricity production of this system is expected to be: 40 kWh in December, in 50 kWh January, 80 kWh in February, 125 kWh in March, 180 kWh in April, 210 kWh in May and June, 220 kWh in July, 200 kWh in August, 150 kWh in September, 105 kWh in October and 65 kWh in November. 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 (Solar Trade Association, 2012).
14 k W floor mounted air source heat pump.
It will supply underfloor heating, with radiators elsewhere. The seasonal COP will be approximately 2.6. 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 (Welsh Government, 2012).
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 a necessary strategy that Brighton and Hove City Council must follow.
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