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Heat Losses from Farm Buildings

Heat Losses from Farm Buildings. The U-value (W/m 2 K ) The U-Value of a building component is a measure of the flow of heat through an insulating or building material: the lower the U-value, the better the component’s insulating ability. The U-value (W/m 2 K)

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Heat Losses from Farm Buildings

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  1. Heat Losses from Farm Buildings

  2. The U-value (W/m2K) The U-Value of a building component is a measure of the flow of heat through an insulating or building material: the lower the U-value, the better the component’s insulating ability

  3. The U-value (W/m2K) When multiplied by the area, A, of the component and the temperature difference across it (T1-T2) K, the result is the heat flowing (Watts) through it

  4. Q = UA(T1-T2) Watts

  5. This is known as the Fabric Transmission Heat Loss through the component

  6. The building components are Masonry Windows Roof

  7. Typical U-Values Component U-value W/m2K Masonry 150mm Concrete 3.5 105mm Solid Brick 3.3 200mm Concrete 3.1 220mm Solid Brick 2.3 335mm Solid Brick 1.7 Insulated Solid Wall 0.5 250mm Cavity Brick 1.5 250mm Filled Cavity 0.8

  8. Typical U-Values Component U-value W/m2K Windows Single Glazing 5.6 Double Glazing 2.9 Triple Glazing 2.0

  9. Typical U-Values Component U-value W/m2K Roof 5mm Asbestos 6.5 Uninsulated Pitched 1.5 Uninsulated Flat 1.0 Insulated 0.5

  10. Ventilation Heat Loss When ventilating air from outside enters a building, it heats up from the outside air temperature to the inside air temperature before it is extracted from the building as “spent” ventilating air

  11. Ventilation Heat Loss (Watts) = m cp (T1-T2) where m = Rate of Ventilating Air (kg/s) cp= specific heat of air (J/kg K)

  12. The Rate of Ventilating Air is usually given in number of volume air changes per hour n V m3/hour where V (m3) is the enclosed volume of the building

  13. Then the number of volume air changes per second = n V /3600 m3/second

  14. If ρ (kg/m3) is the density of the air then the Rate of Ventilating Air, m (kg/s) = ρ x the number of volume air changes per second = ρn V/3600

  15. So, Ventilation Heat Loss (Watts) = m cp (T1-T2) Watts = (ρ n V/3600)cp (T1-T2) Watts The density of air ρ= 1.2 kg/m3 The specific heat of air cp = 1000J/kg K

  16. So, Ventilation Heat Loss (Watts) = m cp (T1-T2) = (1.2 n V/3600)1000 (T1-T2) = (nV/3) (T1-T2) Watts

  17. Total Heat Loss = Fabric Transmission Heat Losses +Ventilation Heat Losses

  18. Total Heat Loss (W) = U A (T1-T2) for Masonry, Windows and Roof + nV/3) (T1-T2)

  19. Fuel Burnt (W) = Total Heat Loss + Flue Gas Losses

  20. Annual Heat Loss from a Farm Building (kWh/annum) = Total heat loss x hours per annum/1000 where T1 is the Annual Mean inside air temperature and T2 is the Annual Mean outside air temperature

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