Abstract
This study describes a quantitative method using thermography to measure the thermal properties of building fabrics that are subjected to non-steady state heat flow due to consistently changing meteorological conditions. The method includes two parts. First, the convection heat transfer coefficient is measured by thermography and heat flux meters on a small segment of the examined building fabric with uniform surface temperature. Then, thermal properties of large building fabrics are evaluated by thermography. The two parts are measured simultaneously. The method was tested on 140/160/190 mm thick massive laminated spruce timber walls of a test facility cabin located in Östersund, Sweden. The results varied by only a few percent in comparison to validation measurements performed with heat flux meters and in comparison, to values from the literature. Due to rapid changes in weather conditions the measured values had large disparity, but still a linear regression with low confidence interval was obtained. Obtaining an accurate value of convection heat transfer was important for achieving high measurement accuracy and, therefore, the value of this parameter should be measured. Other important factors to consider are solar radiation, reflected infrared (IR) radiation from nearby objects and the number of thermal images.
Highlights
In an age of increasing environmental awareness and a growing demand for energy efficient buildings, the construction industry is faced with the challenge of ensuring that the energy efficiency and thermal performance projected during the design stage is achieved once a building is in use [1]
Energy efficiency and thermal performance are rarely validated after construction or renovation
The aim of this study was to investigate a post-occupancy quantitative method to determine the thermal performance of building fabrics during continuously changing meteorological conditions
Summary
In an age of increasing environmental awareness and a growing demand for energy efficient buildings, the construction industry is faced with the challenge of ensuring that the energy efficiency and thermal performance projected during the design stage is achieved once a building is in use [1]. Energy efficiency and thermal performance are rarely validated after construction or renovation. Projected values of energy indicators, such as the specific final energy demand, seldom agree with monitored final energy use after a building is constructed [1]. Danielski [2] reported a 20% difference on average between projected and measured values among newly constructed buildings in 77 locations in Stockholm. Similar results were found by Torcellini et al [3] in six high energy-performance commercial buildings in the USA. According to Pettersen [4], it is impossible to predict the final energy demand with better accuracy than ±15–20%, if the behaviour of a building’s residents is unknown
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