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U-Value Calculations |
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DEA Lincolnshire 53 Wragby Road Sudbrooke Lincoln Lincolnshire LN2 2QU |
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Energy can not be created or destroyed but its form can be changed from one state to another. Energy is thought of as the ability to do work and is measured in Watts or Joules and is either, potential energy or kinetic energy. Potential energy comes in forms that are stored and include chemical, gravitational, mechanical and nuclear. Forms of kinetic energy are electrical, heat, light, motion and sound.
Thermal Energy, better known as heat, always travels from a warmer to a cooler environment by conduction, convection or radiation. The purpose of insulation is to reduce or stop this flow and the measure of insulative efficiency is a U-Value. The lower the U Value of a property the smaller the heating and cooling cost will be. As most forms of heating and electrical generation currently rely on the burning of fossil fuels, better insulation means lower carbon emissions.
The U-Value of a wall, roof, window, floor or any element or structure is determined by the Thermal Resistance of each individual layer within each element. Thermal Resistance (R-Value) is determined by the type of material, its conductance (Lambda value λ) and its thickness. Speed of thermal transmittance will also depend on the thermal gradient (difference between inside and outside temperatures).
R-Value of a material is : R = Thickness (m) Thermal Conductivity (W/m²K)
The higher the R Value of a material the slower it conducts heat and the better it’s insulating properties as the simplified wall below shows.
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The U Value is the reciprocal of the R-Value so the U-Value of this wall is:
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It can be seen that the U-Value is converse to the R-Value and that a lower U-Value signifies better thermal insulation.
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Domestic, Commercial, DEC and New Build Energy Assessors |
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Extensions to Existing Property Where extensions to existing property have large glazed areas such as in garden rooms, conservatories and atriums that are not thermally separated, Building Control will require that calculations are undertaken to show that the U-Value of the building is thermally no worse with the new extension than with the addition of a notional extension of the same dimensions.
To achieve compliance it may be necessary to improve the thermal efficiency of the existing building. DEA Lincolnshire is able to undertake this work and provide calculations required by Building Control. |
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The wall’s layers |
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R-Value |
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External surface resistance |
Rsi |
surface finish and climate affect this value |
= 0.040 |
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100mm thick brick |
R = |
0.100m 0.770 W/m²k |
= 0.129 |
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100mm fibreglass wall bat |
R = |
0.100m 0.034 W/m²k |
= 2.941 |
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100mm lightweight block |
R = |
0.100m 0.250 W/m²k |
= 0.400 |
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3mm plaster finish |
R = |
0.100m 0.400 W/m²k |
= 0.0075 |
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Internal surface resistance |
Rso= |
surface finish and climate affect this value |
= 0.130 |
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This wall has an R-Value of |
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Total R-Value |
3.6475 |
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U-Value of the wall is |
__1__ 3.6475 |
= 0.274 |