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Health-relevant operating criteria

to reduce the spread of viruses, bacteria, etc.

In order to reduce the spread of viruses and bacteria etc., standards and recommendations have been published by the international communities ASHRAE, REHVA and AiCARR.

Recommendations according to ASHRAE


American Society of Heating, Refrigerating and Air-Conditioning Engineers

Ventilation recommendations

  • Supply of 100 % outside air if possible
  • Local control of the exhaust air source and/or the supply of 100 % outdoor air
  • Highly filtered or UV disinfected air directly in the occupied area can provide protection from exposure to airborne pollutants direkt im Aufenthaltsbereich kann Schutz vor Belastung durch Luftschadstoffe bieten.

Humidification recommendations

  • ... 40-60 % relative humidity ...
  • Most unfavourable conditions for the survival of microorganisms (viruses) when the relative humidity is between 40 % and 60 %.

Recommendations for heat recovery

Avoid ventilation systems with energy recovery that discharge potentially contaminated exhaust air into the outdoor supply air.

Recommendations according to REHVA

Federation of European Heating, Ventilation and Air Conditioning Association

Ventilation recommendations

  • Ensure ventilation with outside air
  • Set ventilation to continuous operation at least two hours before building occupation and reduce to night operation 2 hours after building closure
  • No recirculation (100 % outside air)

Humidification recommendations

  • ... 25-30 % relative humidity is fine if available ...
  • In buildings with central humidification it is not necessary to change the setpoint of the humidification systems (normally 25 % or 30 % relative humidity)

Recommendations for heat recovery

  • Safe use of heat recovery units
  • If leaks are suspected in the heat recovery sections, adjust the pressure or bypass the heat recovery section

Recommendations according to AICARR

Associazione Italiana Condizionamento dell’Aria Riscaldamento e Refrigerazione
Italian Air Conditioning, Heating and Refrigeration Association

Ventilation recommendations

  • Increased airflow rate
  • Forcibly controlled air dampers for outside air only
  • Continuous operation of outdoor air supply

Humidification recommendations

... keep the humidity between 40-60 % relative humidity ...

Recommendations for heat recovery

Rotating recovery units:
Algorithm for assessing safe operation
If not: measures to intervene and correct
If not possible, seal the two streams

Cross-flow heat recovery units: Bypass to increase external air supply