Heat_Loss_Example_9.docx
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Heat Loss Example
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Example Calculate the total heat loss from the building shown below.
Blockwork ‘U’ value = 0.317 W/m o C.
Inside o C Outside -2 o C Pitched Roof ‘U’ value = 0.4 W/m o C.
Floor ‘U’ value = 0.45 W/m o C.
Windows ‘U’ value = 2.8 W/m o C.
Workshop
DATA:
Building dimensions : 15.0 metres long x 7.0 metres wide x 5.0 metres high to eaves.
Roof ridge height is 7.5 metres.
The four identical window sizes are 1.8 m long x 0.6 m high.
The air change rate due to mechanical and natural ventilation is 3 air changes per hour.
Note: The design internal temperature for the building in this example is 200C.
For a Workshop environment a temperature as low as 16oC is often satisfactory.
The building volume may be calculated from:
V = ( L x W x H to eaves ) + ( 0.5 x W x perpendicular height from eaves to ridge x L )
| V | = | ( 15 x 7 x 5 ) | + | ( 0.5 x 7 x 2.5 x 15 ) |
| V | = | 525 + 131.25 | = | 656.25 m3. |
Q = ‘U’ . A . t
1.Calculate the heat loss through the windows:
| Total window area | = | 4 (1.8 x 0.6 ) | = | 4.32 m2. |
| Q windows | = | 2.8 x 4.32 x ( 20 - - 2 ) | ||
| Q window | = | 266.1 Watts |
2. Calculate the heat loss through the blockwork.
| Total blockwork area | = ((15.0 x 5.0 ) - 4.32 ) + (15.0 x 5.0 ) + ( 2 ( 7.0 x 5.0 )) + ( 2 ( 3.5 x 2.5 )) | |
| Total blockwork area | = ( 75 - 4.32 ) + ( 75 ) + ( 70 ) + ( 17.5 ) | |
| Total blockwork area | = ( 75 - 4.32 ) + ( 75 ) + ( 70 ) + ( 17.5 ) | |
| Total blockwork area | = 233.18 m2 | |
| Q blockwork | = | 0.317 x 233.18 x ( 20 - - 2 ) |
| Q blockwork | = | 1626.2 Watts |
3. Calculate the heat loss through the floor.
| Q floor | = | 0.45 x 15.0 x 7.0 x 22 |
| Q floor | = | 1039.5 Watts |
4. Calculate the heat loss through the pitched roof.
| Roof area | = | 2 x building length x rafter length | ||
| Rafter length h = | ( 2.5 2 + 3.5 2 ) 1/ 2 = 4.30 metres | |||
| Therefore, Roof area | = | 2 x 15.0 x 4.30 | = | 129.0 m2 |
| Q roof | = | ‘U’ . A . t | ||
| Q roof | = | 0.4 x 129.0 x 22 | ||
| Q roof | = | 1135.2 Watts |
5. Calculate the heat loss by ventilation.
| Q | = | N . V . Sp.ht. . t |
| Q | = | 3.0 x 656.25 x 0.34 ( 20 - - 2) |
| Q | = | 14,726.3 Watts |
Finally calculate the total heat loss Q total = heat loss window + heat loss blockwork + heat loss floor + heat loss roof + ventilation heat loss
| Q total | = | 266.1 + 1626.2 + 1039.5 + 1135.2 + 14,726.3 |
| Q total | = | 18,793.3 Watts |
Heat Loss Calculation sheets help to tabularise the data.
It can be seen from the above calculations that the ventilation heat loss accounts for:
( 14,726.3 / 18,793.3) x 100 = 78% of the total heat loss for the building.
File details come from the government source that posted it. Updated .