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What size fan do I need?
What is air change and how do I calculate it?
An air change is simply the number of times air enters and exits a particular area per hour. The air change rate can therefore be calculated by measuring the air flow volume added or removed from a space, divided by the volume of space itself.
For example: an engine room which is 3 metres high, 22 metres long and 8 metres wide requires ventilation due to the build-up of heat and fumes. By consulting the chart below, we know that the recommended air change is between 15 and 30 depending on the application’s intensity.
For argument’s sake, we’ll say this particular engineering facility is operating at full capacity – thus requiring 30 changes per hour.
So 3m x 8m x 22m = 528m³ x 30 changes = 15,840m³. Therefore, in this situation, a single FV900 unit would be perfect because it has a capacity of 16,500m³ per hour.
In the case of extraction, it is vitally important that sufficient air supply openings are present in the area in which fans are located. Our units are regularly used for a broad range of activities, including tank cleaning, sewer work, welding, excavation, demolition and even painting. However, in order to know how many fans – and what type – are required for your particular application, it is imperative that you accurately calculate the correct ventilation rate.
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Use the table below as a guideline:
| Location | Room Air Changes / Hour | Location | Room Air Changes / Hour |
|---|---|---|---|
| Assembly halls | 4–8 | Factory & workshop | 8–10 |
| Bakeries | 20–30 | Foundry | 8–15 |
| Banks | 4–8 | Fume cupboards | 40–50 |
| Boiler room | 15–30 | Garages (showrooms) | 6–8 |
| Bathrooms & shower rooms | 3–8 | Gymnasiums | 6+ |
| Canteens | 8–12 | Hospital – sterilising | 15–20 |
| Cellars | 3–10 | Hospital – wards | 6–8 |
| Commercial kitchens | 30+ | Hospital – x-ray | 10–15 |
| Compressor rooms | 10–20 | Laboratories | 6–15 |
| Conference rooms | 8–12 | Lavatories – public | 6–15 |
| Dairies | 8–12 | Offices | 6–10 |
| Electroplating | 10–12 | Stores & warehouses | 3–6 |
| Engine rooms | 15–30 | Swimming pools | 10–15 |
| Entrance halls & corridors | 3–5 | Welding workshops | 15–30 |
The selection of the most suitable fan can be gauged via the following:
- Calculate the volume of the room which needs to be ventilated (L x W x H)
- Select the recommended number of air changes per hour
- Multiply the results of the previous two steps – this will provide you with the required volume of air
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