In-situ U-value-measurements of wood frame roofs: analysis of deviations between measured and design performance

The hygrothermal performance of various lightweight sloped roof designs was monitored in the KULeuven VLIET testbuilding for 2 years (Janssens et al. 1998). One of the aims of the investigation was to evaluate whether the design U-value of 0.18 W/m²K was effectively met in practice. For this reason 3 heatflux transducers were installed at the inside surface of each component together with a number of thermocouples at the surfaces of the composing material layers. The U-value was derived from the measurements by averageing the collected data on a daily basis. The observed deviations between the measured and design U-values are analysed and explained by quantifying the inconsistencies between the assumptions for the calculation of the design thermal performance and the conditions of the in-situ measurement. The following causes of deviations are analysed in detail, and related to the position of the heat flux transducer on the test components: (1) heat transport affected by wind-washing in the roofs, (2) 2-dimensional heat flow through framing elements in the roof

Primitive Central Idempotents of Rational Group Algebras

We give a description of the primitive central idempotents of the rational group algebra QG of a finite group G. Such a description is already investigated by Jespers, Olteanu and del R\'io, but some unknown scalars are involved. Our description also gives answers to their questions

Bedroom indoor air comfort : a critical analysis

The criteria that are currently used for the assessment of Indoor Air Quality in a residential context were developed in the ‘80s and relate to comfort during occupancy. More than half the time at home however, is spent in the bedroom. There is no strong indication that the criteria that are traditionally used to assess Indoor Air Quality also relate to the level of comfort while asleep. Moreover, analysis of the results of a performance assessment of frequently used residential ventilation systems based on these traditional criteria, shows that they are dominated by the pollution level in the bedrooms