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A real-world study was undertaken of the indoor air quality in a recently-built single

family home in central Sweden, to establish whether demand controlled ventilation

provided superior interior conditions, when compared with other air supply strategies,

including the standard used by the Swedish buildings regulator.

The property was highly airtight, with ventilation achieved using a forced exhaust system.

Extraction was possible from all rooms of the house, and using a Renson Healthbox air

handling unit, the rates of air flow from each room could be adjusted either according to

a time schedule, or under demand control according to the unit’s sensing of the air quality

in individual rooms.

Five ventilation modes were evaluated, each for a period of 24 hours. Occupancy of the

house was standardised, with test participants. Two separate air quality monitors were

deployed to verify whether measurements made at the air handling unit were

representative of the conditions that occupants experienced. Key measurements were the

stable level of carbon dioxide overnight in an occupied double bedroom and the time

taken for that room to refresh to background CO2 level the following day. The time taken

for a kitchen/living room to similarly refresh was also examined.

The study found that demand controlled ventilation achieved indoor air quality – assessed

on carbon dioxide concentration – comparable with rates of fixed ventilation far greater

than the regulated standard. In doing so, the air volume exchanged over a representative

day was 33 % less than that standard, providing for significant energy savings.

The parallel monitoring of air quality inside the room and via the air exhaust duct showed

noticeable variation, but indicated the air handling unit under demand control would

never ventilate insufficiently, based on its internal CO2 sensors.