This paper explores the concept of characterizing the as-built Heat Loss Coefficient (HLC)of buildings based on-board monitoring (OBM), via energy consumption and temperature sensors, and time series analysis. It is examined (1)how the coefficients of different Auto-Regressive with eXogenous inputs (ARX)models can be interpreted and (2)whether these conclusions are sensitive to the building envelope assembly or the applied indoor temperature profile. The paper presents a theoretical case study whereby detailed building energy simulations are used to accurately map the impact of physical phenomena on the characterization process. The simulation models and boundary conditions are composed to focus on the link between the estimated ARX-coefficients and the physical driving forces for transmission heat loss to the ground and the exterior environment. The results show how the various ARX model coefficients are linked to specific components of the HLC (e.g. heat transfer through the walls and roof or through the slab-on-ground floor)and to what extent they are affected by the selection of input variables. By monitoring the ground temperature, the transmission heat losses can rather accurately be assigned to either the slab-on-ground or the walls and roof. Without this measurement data, the uncertainty on the estimates increases (ranges of the 95% confidence interval of up to 35% of the mean estimate). Modeling the ground heat losses by a constant intercept term leads to underestimations of the reference HLC of up to 59%, whereas adding heat flux sensors to monitor the transmission heat losses to the ground to the measurement set-up allows to assess the transmission heat transfer coefficient to the exterior environment HLCe within 2%.
- Heat loss coefficient
- ARX model
- Physical parameter identifications
- Synthetic monitoring data