Night Purging

Night purging is a highly effective method of pre-cooling a building or room during the night, before it is occupied again the next day. It involves operable windows or louvres being opened for a pre-set period of time over night, allowing a natural air flow through the building.

Why should night purging be incorporated into your building?

Night purging can help reduce the building operating costs, with hot and stale air being replaced with fresh night time air. This reduces the need for the HVAC system to be activated as soon as the building is occupied in the morning. The thermal mass of the building will be cooled, providing a fresher and cooler environment for the occupants.

If hot and stale air is not removed, not only will the room feel stuffy, but air borne pollutants, such as carbon dioxide, may reach alarming levels. This can be potentially harmful for the occupants with symptoms such as headaches, dry and itchy eyes or a sore throat developing. In turn this can have a negative effect on both productivity and satisfaction levels with the internal environment.

In which climates is night purging most effective?

It is particularly effective in climates that have cool to cold night time temperatures as there will be a greater difference between internal and external temperatures. This is not to say that night purging cannot be effective in warmer climates. Even when internal and external temperatures are very similar night purging can still provide a means for air borne pollutants to be exhausted and allow fresh air to enter.

Night purging with Arens

The Arens Automatic Ventilation Controller (AVC) provides a great degree of flexibility, allowing the night purge strategy to be tailored to suit your project needs. It provides a fully automated night purge system, meaning there is no reliance on the occupants of the building.

The following factors can all be programmed:

  • Duration of the purge
  • Days on which night purging is to occur – purging will only occur in the early hours of the morning, on days when the building will be occupied.
  • Seasons in which night purging will occur – it is possible to set night purging to either occur during a specific season, multiple seasons or all year round.
  • Operational periods – night purging will only take place during periods of operation. This means that during periods when the building is not occupied, such as Easter, Christmas and Holidays, night purging will not occur.

Avoiding Common Concerns with Night Purging

Security is a somewhat common concern when night purging is considered. This concern is alleviated by the fact that the windows are not required to open completely during night purging. Therefore, the actuators will only open the windows or louvres a small amount, lowering the risk of intrusion.

It should also be noted that the Arens Automatic Ventilation Controller includes wind and rain sensors. This ensures that assets are protected from water damage as a signal will be sent to close the windows when rain or wind speed limits are exceeded.


Some projects that include a night purge system from Arens International are:

  • Parkdale Intergenerational Community Hub – Parkdale
  • Padua College, Tyabb Campus – Tyabb
  • Melton North West Primary School, Games Hall, East and West Buildings – Melton

For more information on night purging and how you can incorporate it into your next project, please feel free to contact us today.