Effect of solar radiation on thermal performance of external wall structures based on long-term measured data

Abstract

This paper discusses some of the factors affecting the energy consumption of different external wall structures in northern climate. The studies have been conducted at the Department of Civil Engineering at Tampere University of Technology (RTEK/TUT) during the past 16 years. As one of the outputs measured data from 6 test buildings (plus six-year data from additional 2 test buildings) has been built up. The level of detail (520 sensors in each building), amount (after each 20 seconds), long-term (measuring period of six and ten years) and coherency (measured at the same time at the same conditions) makes that data unique in Finland as well as in Europe. Up to 50% differences were found in the measured and calculated heat losses. Possible reasons for such a discrepancy are described and discussed. It has been focused on the effect of solar gains to thermal performance of massive exterior wall structure. Examples from massive external brick leaf (cladding) of the insulated brick wall are demonstrated. The thermal energy from solar radiation stored in the cladding during daytime warms the air in the ventilation gap and has a great momentary impact on the need to compensate heat losses. Due to the high thermal inertia of the brick leaf temperature of the inner surface of the leaf facing the air gap remains relatively high until early evening. This advantage is not available throughout the year, but its impact is much greater than usually believed. The knowledge from this study forms the base for the design and construction of sustainable external wall structural solutions. The location of the test buildings is showing a significant impact of solar radiation and thermal inertia to the thermal performance of external wall structures in Tampere, Finland. As the average solar radiation increases towards the south, the effect is expected to be greater in Baltic states.