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F7+F7 filter set may increase the energy consumption of the ventilation unit even up to 30%

The vast majority of ventilation equipment manufacturers such as SALDA, Komfovent, Brink, Zehnder, etc. do not use a more efficient F7 class (ePM1) filter for the extracted air filtration. In general, 2 options are available:

  • Standard set (mostly intended for the protection of internal components): G3+G3, G4+G4 or M5+M5
  • Efficient one to supply of clean and healthy air to the premises: F7+G3, F7+G4, F7+M5.

Quite often analog filters suppliers offer only one set F7+F7. It is obvious that the second F7 filter on the extracted airside is excessive, it is almost the same as to clean wastewater to the level of the mountain spring. As pressure drops of F7 filter are much higher in relation to M5, G4 or G3 filter, more energy will be consumed. But how much?

Let’s take Komfovent Domekt R 400 V air handling unit with an electrical heater as an example. Komfovent selection software will be used for calculations and its standard settings (outdoor air temperature at winter -23C, RH – 90%). Initial airflow 250 m3/h and pressure drop 75 Pa on both channels. According to the software, we may find pressure drops of clean filters: F7 – 27 Pa, M5 – 11 Pa. In order to get the same pressure drops as F7+F7 set, we will add additional pressure drops on the extract airside. Thus, exhaust airflow dropped to the 244 m3/h.

Domekt R 400 V calculation with clean F7+M5 filter set

Domekt R 400 V calculation with clean F7+F7 filter set

It is because, that due to pressure increase, a fan may provide lower airflow consuming the same amount of energy. With clean filters, it led to the pressure drop in 1.3 percent points and drop air temperature after the heat exchanger in 0.6C. If an electrical heater is set to maintain 22C supply air temperature, it may require 0.05kW more power and may lead to an extra 1.2 kWh energy consumption per day or 36 kWh per month.

But filters will not be clean for a long, therefore pressure drops will increase in F7 and M5 filters differently. Let’s take that conditioned F7 filter pressure drop is 89 Pa and M5 – 31 Pa.

Domekt R 400 V calculation with conditioned F7+M5 filter set

Domekt R 400 V calculation with conditioned F7+F7 filter set

Therefore, supply airflow will decrease up to 220 m3/h. Exhaust airflow in case of M5 filter – up to 243 m3/h and 210 m3/h in case of F7 filter. Heat recovery rate accordingly 88.4% in the case of F7+M5 and 83% in the case of F7+F7, or even 5.3 percent points lower! Consequently, temperature difference after heat exchanger is 2.5C, and the electrical heater required capacity 0.18kW higher. It may lead to extra up 130kWh consumption per month.

There are very few manufacturers such as FLEXIT, that still uses F7+F7 filter set, but the air handling unit is designed for such an option. Therefore, why do they offer F7+F7 set? There is no clear answer, but usually, distributors tend to have lower variations for the lower stocking and working capital need.

CleanFilter filters for Komfovent, SALDA, Zehnder, Brink, and other AHU corresponds to the requirements of the manufacturers and several options allow to choose filters according to personal needs.

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