Extending the validity of co-heating tests to warmer and sunnier weather conditions using an equivalent exterior temperature

The energy consumption of buildings is usually different from that predicted at the design stage. To measure the performance gap between designed and as-built buildings, it is possible to measure the actual Heat Transfer Coefficient, which characterizes the thermal performance of the building envelope. The actual reference method for measuring this coefficient is the co-heating test, which consists in normalising the heat input into a building with respect to the indoor-outdoor air temperature difference. However, the use of this method is limited to a certain period of the year when weather conditions allow a sufficient temperature difference, while avoiding heating the building to temperatures that could damage it. This work proposes to extend the period of validity of co-heating tests by using an equivalent outdoor temperature. This equivalent outdoor temperature allows to account for the impact of solar radiation and sky radiation which have a larger impact in hotter periods. This paper explores and demonstrates the feasibility of this new method from an experimental campaign and numerical simulations run in a summer period. It extends the co-heating feasibility period, throughout the year for the coldest climates and between seasons for the warmest climates. The results from the experimental campaign agree with the simulated data results.