Control strategies for demand controlled ventilation in dwellings

Ventilation of Danish and many other European dwellings has in the past mainly been achieved by natural ventilation or mechanical exhaust systems. Requirements for energy efficiency is changing this picture and mechanical ventilation with balanced exhaust and supply, efficient heat recovery and efficient fans is becoming the standard solution.

The building regulation requirement for air change in dwellings is often a constant value that has been chosen to avoid moisture related problems in the indoor environment. This required air change is sometimes sufficient, sometimes too low and sometimes too high. Too low ventilation rate results in poor air quality for the occupants and moisture risk.

Too high ventilation rate results in unnecessary energy consumption. This paper presents results from a study where demand controlled ventilation was installed in an existing single family house. In the studied house two control strategies were tested. A simple strategy where all sensors and controls were located in the air handling unit and only the speed of the fans can be controlled, and a complex strategy where sensors were placed in each room and where individual control of air flow in each room was possible.

The results showed that the ventilation rate in periods can be reduced significantly without significant increase in moisture or CO2-concentration.