Decoupling between heat loss indicators and heating demand in a high-mass dwelling: implications for interpreting building performance

Gabriel Harvey, Szende Szentesi-Nejur

This study examines the relationship between design-phase energy predictions and measured operational heating performance in a core-insulated rammed earth dwelling located in a cold climate in southern Ontario, Canada. Design-stage performance was evaluated using the Passive House Planning Package (PHPP), a quasi-steady-state model estimating heating demand from envelope properties, ventilation losses, and standardized solar and internal gains. Operational performance was assessed through post-occupancy monitoring combining heating-season electrical measurements, blower-door testing, in-situ thermal transmittance measurements, indoor–outdoor environmental monitoring, regression-based analysis of heating demand, and a controlled free-running temperature decay test. Results indicate that the as-built envelope underperforms relative to design assumptions, with higher measured air leakage and thermal transmittance consistent with increased transmission and infiltration losses. Regression analysis shows that delivered heating demand is primarily governed by the indoor–outdoor temperature difference, while solar radiation and internal gains act as secondary moderating factors. However, the comparison between measured and modeled performance also indicates that apparent heat-loss metrics alone do not fully explain cumulative heating demand in this high-mass dwelling. Dynamic testing further shows a delayed indoor temperature response following heating shutdown, indicating short-term thermal buffering associated with the rammed earth mass. These results highlight a distinction between envelope performance, apparent heat-loss indicators, and cumulative heating demand. While thermal mass moderates short-term thermal response and contributes to the timing of heat flows, it does not compensate for envelope underperformance in cumulative heating terms. The study underscores the importance of complementing quasi-steady-state design tools with post-occupancy monitoring and dynamic assessment when interpreting performance in high-mass dwellings.