Human perception of indoor environment generated by chilled ceiling combined with mixing ventilation or localised chilled beam under cooling mode

Experiments with 24 subjects were performed to study and compare the human perception of the indoor environment under summer conditions generated by a chilled ceiling combined with overhead mixing ventilation and localised chilled beam. The experiments were performed in an experimental chamber (4.2 m x 5.4 m x 3.1 m) equipped as an office with two workstations.

One of the workstations (with a laptop) was by the window and the other in the opposite side of the room. Five heated radiant water panels were used to simulate direct solar gains from windows (404 W). Five electrical foils were used to simulate direct solar load on the floor (270 W). The total heat load in the room was 56 W/m2.

The air temperature around the workstation by the window was kept either 26 or 28 oC. The supplied air by the overhead mixing ventilation and the primary supply air of the localised chilled beam was kept at 13 L/s and 16 0C. The localised chilled beam was installed over the workstation placed by the simulated window.

During the experiment the subjects were delegated control over the primary flow rate supplied by the localised chilled beam. The whole exposure lasted 2 hours with 30 min of acclimatisation before the experiment. Every person spent in total 90 minutes at the workstation by the windows (three sets of 30 min), 10 min at the other workstation and 20 min away from the workstations performing office work at increased activity (1.4 Met).

The primary airflow rate supplied by the chilled beam was reduced to 6 L/s during the 20 min period of physical activity, when the occupant was not at the desk with the localised chilled beam, resulting in increase of the air temperature in the room. Subjects used questionnaires to answer on thermal sensation and acceptability, perceived air quality, air movement and SBS symptoms.

Under 26 oC the localised chilled beam provided more local cooling compared to the chilled ceiling. The opposite trend between the two systems was noticed at 28 oC. However the local thermal acceptability votes were similar for the two systems. Majority of the occupants did not wish change in the air movement at WS1 at 26 oC.

With the chilled ceiling more subjects complained of not sufficient air movement especially at 28 oC. Most of the subjects tended to use the localised chilled beam at the maximum flow rate available, i.e. 13 L/s.