A study in the UK of 97 certified Passive House projects shows predicted heating demand was accurate in both flats and houses. Measurements were recorded for over a year of both heating demand and internal temperature. Results:
- average measured heating demand 10.8 kWh/m2/year
- predicted heating demand 11.7 kWh/m2/year.
The study’s authors considered this statistically identical. Several of the buildings in the study used zero heating but there were 5% of outliers that used >30 kWh/m2/year.
This shows no performance gap and is in marked contrast to other predictive modelling tools which, when tested against real life performance, are shown to often significantly under-predict actual heating demand. Certified Passive House buildings get it right because of the discipline of the methodology: a significant quality inspection process with a third-party independent review of the energy model, construction drawings and construction process. The blower door testing in particular focuses minds and hands on the building site: do things right or fail (the blower door test and certification).
Energy modeling on the other hand, even with very advanced tools like EnergyPlus, can’t be expected to match reality when it lacks a quality inspection of the energy model, plans and construction.
Read more about the study in Passive House Accelerator magazine (Fall/Winter, 2020).