# Choosing the right blower and filter

When we had the choice between a vertical and a horizontal air flow we decided to use a horizontal air flow. Before we started building the hood we had to choose the right filters and blower.

# Choosing the filters

To prefilter the air the company Luftfilterbau recommended us the filter pad HS-E/360. To choose the HEPA filte you have to keep in mind the following things:

- the HEPA filter has to remove all (99,9 %) airborne material (filterclass H 14 according to EN 1822)
- the HEPA filter should be big enough to have enough space available in the flasking area

We ordered the HEPA Filter HS-Mikro SF (30,5cm width, 61cm height and 7,8cm depth).

On the website of Luftfilterbau at "Info" you can find a very good guideline how to choose the right filter and how filters function.

# Choosing the blower

When choosing the blower we have to make sure that it is able to transport the required quantity of air through the filter pad and the HEPA filter. We know the dimension of the HEPA filter and the required air speed in the working area (0,5 m/s) so we then can calculate the airflow per hour.

width of the HEPA filter: | 0,305 m |

height of the HEPA filter: | 0,61 m |

required air speed: | 0,5 m/s |

airflow = width * height * air speed = 0,305 m * 0,61 m * 0,5 m/s = 0,093025 m³/s |

When we multiply this result by 3600 seconds (60 * 60) we get the airflow in m³/h.

airflow = 0,093025 m³/s * 3600 = 334,89 m³/h |

On many english websites you´ll find the airflow in Cubic Foot per Minute (CFM) and not in cubic meters per hour (m³/h). One ft (foot) is 0.figcaptionso one cubic foot is 0,0283 m³ (figcaption* figcaption* 0,3048 m).

1 m³/s | = | 0,5886 CFM |

1 CFM | = | 1,6990 m³/s |

In the next step we have to read from the diagram below how much pressure is necessary to transport 334,89 m³/s air through the HEPA Filter. An airflow of 334,89 m³/s is about 60% of the nominal airflow so the required pressure is 150 Pa.

# Diagram of the HEPA filter

Now we have all necessary data to choose a blower (334,89 m³/s3;/h at 150 Pa). In the picture below you can see the diagram of our blower (centrifugal blower G2E140-AI28-01) which we bought from Ziehl-ebm GmbH.

# Diagram of the blower

As you can see, the blower is a little bit stronger than required because of the following reasons.

- the filter pad slows down the airflow slightly
- after a while the filters become dirty and we need more power to transport the same quantity of air through them
- it is easier to regulate and reduce the blower slightly than buying a stronger one

Author: Thomas Ederer