Ventilation Basics

Ventilation

Ventilation is the process of exchanging indoor air with outdoor air. Not air from roof spaces, or other dubious sources.

Ventilation air exchange

Air exchange in reference to the ventilation volume of the occupied space, usually measured in m3(or l/s) per hour per m3 (total volume of occupied/ventilated space). The typical value used in Passive House is 0.3 and in G4, AS1 is 0.35. This means that if the internal volume is 100m3 we exchange 30m3(Passive House), or 35m5 (G4) of that volume with fresh incoming air and dispose the same volume of old air (in theory).

Effective ventilation is a critical aspect of maintaining a healthy and comfortable living environment for a number of reasons;

Removal of pollutants, odour and CO2 control

Indoor spaces can harbor various pollutants, including accumulating levels of CO2, volatile organic compounds (VOCs), allergens, dust, pet dander, and cooking fumes.

Moisture Management

High humidity levels can foster mold and mildew growth, leading to respiratory problems and damaging building materials. Ventilation helps control moisture levels, preventing condensation and dampness that contribute to mold growth and its health-related health issues and potential structural damage (although that requires significant and long term decay).

The crucial link between ventilation and moisture control

According to DIN 1946-6:2009-08, a person generates approximately 30 grams of water vapour per hour, which is equivalent to about 0.72 litres of water vapour per day.

For example, if a family consists of 4 occupants:

Total water vapour generated per day = 4 occupants * 0.72 litres/person/day = 2.88 litres/day

The actual amount of water vapour generated can vary. Cooking, showering, laundry, and other activities that involve water can significantly contribute to indoor humidity levels.

Assuming the family lives in an apartment, or house of 100m2, with 3m high ceilings - creating an indoor volume of 300m3. At 20ºC and 50% relative humidity the absolute water content is at 2.59l. Adding 2.88 litres of water vapour to the mix the relative humidity increases to above 100%.

That's in theory, or course, because we always have some windows and doors open during the day, not everyone is at home all of the time and the generation happens over the course of several hours. However, adding only half of the amount of moisture is creating critical humidity in the air.

The other critical issue in New Zealand is the lack of heating. These humidity values above are for a comfortable 20ºC indoor temperature but what if the temperature remains around 10 -12 degrees?

The results of insufficient ventilation are well known.

Older buildings usually manage this issue by being air leaky but the increasing airtightness of buildings calls for more effective methods of ventilation. Natural ventilation and extract fans as suggested in G4, AS1 rarely work, due to the occupant having to actively manage opening doors and windows regularly. Mechanical ventilation with continuous flow rates provide an alternative that can be effective not just for air quality and moisture control but also highly energy efficient and comfortable.