Analysis of the influence of the definition of the interior dwelling temperature on the characterization of the heat loss coefficient via on-board monitoring

Abstract

Over the years, several dedicated on-site measurement tests have been developed to assess the heat loss coefficient (HLC) of a building envelope. These tests, and their associated data analysis methods, take the single-zone heat balance as a starting point. This assumption is, however, challenged when the measurement data is no longer collected during dedicated heating experiments, but via on-board monitoring (OBM), as recent studies suggest. OBM is the collection of measurement data of the energy use and interior climate of occupied buildings, via sensors. Under normal, ‘in-use’ conditions, the interior temperature of a building is most probably not identical in the various rooms. Using the single-zone heat balance hence requires the definition of an ‘equivalent homogeneous building temperature’. This paper seeks to determine adequate approaches (sensor setups, default values) to assess this temperature. It specifically investigates the impact a certain approach has on the accuracy with which the HLC can be estimated. Hereto, a sensitivity analysis is performed based on six synthetic OBM data sets, generated from simulation models of residential buildings with different envelope performances and occupancy profiles. The results show how using monitoring data of the living room temperature to represent the equivalent homogeneous building temperature can lead to an underestimation of the HLC by up to 30%. This deviation can be limited to 12%, by adopting a default value suggested in a Dutch standard, and even to 6% by using temperature data collected in each individual room and volume weighting these signals. The HLC of uninsulated buildings with many unheated rooms proves to be the hardest to assess.