Demand Controlled Ventilation (DCV) Systems in Commercial Buildings. Functional Requirements on Systems and Components.
Doctoral thesis, 2009
Demand controlled ventilation (DCV) is considered as an energy efficient solution for
air-based cooling and indoor air quality control. Considerable energy savings can be
achieved when the airflow rate is continuously adapted to the actual load condition.
However, in order to assure the desired performance of the system, it is essential to
know the requirements that the DCV system and its components should fulfil. The
objective of this work has been to clarify the requirements for a well functioning DCV
system. This includes cooling performance as well as sensor based air quality control.
The work is based on theoretical analysis, field measurements of occupancy and system
performance as well as laboratory investigations of DCV supply air diffusers and
sensors for air quality control.
This thesis shows that it is possible to implement in existing as well as in new buildings
an uncomplicated DCV solution that requires no active control dampers in the duct
system. This, however, requires variable supply air diffusers with good airflow control
properties and with a low noise generation even at a high pressure drop over the device.
Also, in cooling applications the devices must provide a comfortable airflow pattern in
the room within the entire airflow range and with low supply air temperature. In
addition, the duct system must manage the wide airflow range, including the design
minimum supply air temperature for cooling, with negligible heat gains. Tests carried
out with such a DCV configuration show that high requirements set on the system
components can be fulfilled.
An additional focus in this thesis is the application of DCV systems for air quality
control. This requires sensors that can monitor the air quality and/or pollution to control
the hygienic ventilation rate. Quantitative requirements for such sensors have been
developed based on ventilation guidelines and standards. A detailed sensor study was
carried out with a number of CO2-sensors and mixed-gas sensors. Results show that,
depending on the requirement, several tested CO2-sensors could fulfil the established
requirements set on sensors. However, the application of the tested mixed-gas sensors
for ventilation control is undecided. It is not clear how the output of mixed-gas sensors
should be interpreted. Another limitation comes from the lack of available standards
describing acceptable concentrations for many common air contaminants for nonindustrial
Finally, this thesis also provides some information on the actual occupancy patterns in a
commercial building in operation. One year monitoring in an office building indicates
that during 90 % of the time the aggregated occupancy in the building is equal to or less
than about 53 %.
indoor climate control