Operation of ventilation systems in times of Coronavirus and other viral contaminations
Regardless of the manufacturer of a ventilation or air conditioning system, ventilation systems pose a potential risk to human health if maintenance is unsuitable. To reduce the existing risks, operators are obliged to carry out a risk analysis and to set up the maintenance cycles in accordance with the manufacturer's minimum specifications and to implement accordingly.
It must be taken-into-account which type of ventilation system is operated. In a pure air circulation system, the air must be freed of dust etc. by filters. Adequate fresh air must be ensured through conscious window ventilation. Unfortunately, circulating air systems only pose a minor hurdle to the spread of viruses.
However, most systems are ventilation systems enriched with fresh air. Regardless of the energetic side, in times when viral infectious diseases spread, the fresh air percentage should be increased to 100% in order to reduce a mixture of exhaust air and supply air and to strengthen the defences of the people in the building. This should be decided on the basis of the risk assessment and the local assessment of the acute risk from viruses.
Energy-optimized ventilation systems today have energy recovery systems, which, depending on the version, have to be considered under the aspect of viral pollution.
Integrated Circuit Systems separate the supply and exhaust air, so that technically correct systems are the best at preventing the spread of viruses in the ventilation system. As in other systems, the fresh air is filtered, and the cleaned air is then available as supply air. Since the heat is recovered via heat exchangers and piping, the energy is transported from the dispensing side to the receiving side without the direct exchange of air.
The same applies to cross-flow plate heat exchangers, where the energy flow takes place through the metal plates of the heat exchanger. The technical tightness of today's systems suggests that contamination of the fresh air by contaminated exhaust air never or hardly ever occurs.
On the other hand, systems with heat exchange wheels behave differently because their rotation means that particles adhering to different air flows in the heat wheel can mix again in the supply air flow. It is important to ensure that the upstream exhaust air filters are well dimensioned and serviced. If maintenance is not carried out, filters can tear due to the excessive pressure, which leads to contamination of the fresh air and would result in additional contamination of the heat wheel.
Mixed air switching is also possible in the systems under consideration, with portions of the exhaust air being mixed with the fresh air. As can be easily understood, these modes of operation counteract the measures described above, since the operation of the mixed air circuit does not separate the air flows.
All systems have in common that the supply air is channelled into the corresponding areas. Failure to clean the air ducts would undermine all previous efforts by virus exposure.
The following ventilation and air conditioning measures should be followed:
- Check which measures can also be checked for "non" hygienic devices according to the hygiene directive (see VDI directive 6022)
- Timely replacement of the pre-filter (2-4 times a year, or depending on the load)
- Timely replacement of the filters (ISO16880; ISO ePM2.5 or better is recommended, or depending on the load)
- Cleaning the air ducts every 4 - 7 years (see ASR)
- Maintenance of the heat wheels including their disinfection
- Regular hygiene inspections by trained specialists
- Avoid recirculation mode
- Reduce / avoid mixed air operation
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