Airflow and Thermal Comfort Assessment

An ESRU Consultancy Case Study

ESRU consultancy were commissioned to undertake a review of the thermal performance of the auditorium of the Theatre of Besançon, France. Thermodynamic assessments using ESP-r were carried out to study the thermal performance of the building and the airflow among all the rooms under different operational and climatic conditions to allow several design options to be tested. After this detailed CFD appraisals of airflow and thermal comfort were carried out using the parameters predicted bt ESP-r as boundary conditions.

The building is mainly stone structure (walls up to 1m thick) built in the fifteenth century.  The main auditorium can be broadly divided into four sections; ground level seats, low gallery, high gallery and stage. One of the main problems with the currently implemented ventilation system was overheating of the high gallery during summer time. A cutaway section of the theatre is shown below:

3D interior view of the theatre

The objectives of the study were as follows:

• Building summertime temperatures.

• Airflow and air temperature distributions within the main auditorium space.

• Assessment of the existing HVAC system for its plant capacity increased to account for overheating.

To accomplish these the following studies were carried outs:

• An initial thermal study of the current and HVAC system as the base case against which quantitative results may be compared.

• A typical summer overheating assessment.

• Further assessments using different airflow regimes e.g. air extraction from the roof as opposed to the stage, re-circulation instead of fresh air only.

The following figures show the models for thermal (left) and CFD (right) simulations. 

The study revealed shortcomings of the existing HVAC system and proposed a redistribution of air using the same HVAC plant and ducting. This resulted in lowering temperatures of the occupied space considerably. Temperatures from the existing and proposed ventilation schemes are shown below in side-by-side cross-sections (the stage is on the right of each image):

BEFORE

AFTER

It can be seen that with the new scheme the seating areas (middle-left portion of each cross section) are cooler and there are less radiant thermal gains from the ceiling. The scheme is cost effective to implement because the same plant and distribution system will be used.

The following figures show the animated airflow vectors within the theatre by which the velocity vectors are coloured by air temperature.