Evaluating Floor Losses in the Context of QUB Measurements of a Passivhaus Dwelling

Measuring the performance of building fabric is increasingly important as stakeholders wish to compare as-built performance with design expectations. When measuring whole house performance (Heat Transfer Coefficient) heat losses through the floor in slab-on-ground type constructions are intractable and introduce uncertainty into measurements. As such efforts are often made to isolate them from measurements. The QUB method is a practical method of measuring whole house building performance. Previous work has shown floor losses can successfully be isolated from measurement through use of heat flux measurements and additional calculation steps. To further test this isolation procedure, three QUB tests were performed on a slab-on-ground Passivhaus dwelling. Whilst the whole house performance measurements agree with the design performance (all results within 11% of the design) the floor losses measured appear unrealistically high. The conditions of the tests, conducted in late summer and in a highly insulated property, are likely causing the heat flux measurements to capture heat being stored in the floor construction rather than heat being lost from the property. Follow up measurements in more preferable conditions are planned which will assist in determining the cause of these observations.