Experimental investigation of cold draft induced by two different types of glazing panels in metal curtain walls

Abstract

Metal curtain walls typically have a large portion of continuous glazing area. In cold climate, the cold draft induced by the large cold glazing surface may cause discomfort to occupants seated in the perimeter zone. This paper presents the experimental investigation of the characteristics of the cold draft induced by two different types of glazing panels and its effect on the occupant's local thermal sensation. A large-scale (3.8 m×6.7 m) metal curtain wall specimen consisting of two different wall systems was tested in an Environmental Chamber. The effect of the thermal performance of glazing units, the frame projection, and the mechanical ventilator on the cold draft was studied. The measurements indicate that the better-insulated glazing unit reduces the cold draft considerably compared to the conventional glazing unit, thus increasing the comfort level of the occupants. The frame projection deflects the cold flow from the wall surface and causes mixing of the cold air with the room air thus elevating the temperature and decreasing the momentum of the cold air before it penetrates into the occupied zone. The mechanical ventilator, located at the end of the room side, simulates the design of moving the heating supply away from the exterior wall. The measurements show that the resultant air movement from the ventilator increases the draft risks at ankle level for the occupants, and the ASHRAE requirements cannot be met until the occupants seat 2 m away from the wall. The analysis shows that, for the test conditions of this study, the glazing surface temperature of both wall systems needs to be raised, through perimeter heating or ventilation system for example, in order to provide a comfortable indoor climate, the need for the better-insulated system being less than the conventional system.