The scope of this thesis is to answer the question: "What influences the functionality and delivered
indoor thermal comfort of a diffuse ceiling ventilation system?" This endeavour is pursued by
means of two overall methodologies;
• through two field study experiments in classrooms during true operating conditions
• through 70 full-scale laboratory experiments quantifying how the supply opening area
influences the cooling capacity, thermal comfort and airflow pattern in rooms with DCV
Investigations show how high cooling capacities (above 130W/m2) can be achieved while still
complying with thermal comfort category B. DCV systems are capable of delivering high
ventilation rates (from 6-16 h−1) with minimal risk of draught due to the application of large
supply opening areas compared to conventional ventilation systems. The combination of
ventilation rate and inlet air temperature comprising the cooling capacity is given in terms
of a design chart for three different supply opening areas (18%, 50% and 100% diffuse ceiling
area).
Correlation of important parameters in DCV system design show how the airflow pattern is
mainly heat load dominated but also affected by ventilation inlet momentum for all typical
ventilation rates, hence airflow patterns are better described by Archimedes number than
Reynolds number. Furthermore, it is found that total mixing of room air is effectuated both
during true operation conditions and in experiments. This mixing, as well as the preheating
capabilities of the inlet air while passing through the plenum volume, is also found to be a
function of Archimedes number.
Numerical predictions using CFD is attempted applied for a broad parametric study investigating
the robustness of system critical parameters towards changes in the boundary conditions,
however, the numerical model proved invalid in describing the fluid mechanical system.