Passive House calculations are generally considered more detailed and rigorous than typical Australian First Rate 5 (NatHERS) energy ratings due to several factors. Based on the information provided in your previous write-ups, here are some key reasons for the differences:

Energy Efficiency Focus:

Passive House calculations are specifically designed to prioritize energy efficiency by achieving extremely low energy consumption. The standard aims to create highly insulated, airtight buildings with minimal thermal bridging, resulting in reduced energy demands for heating and cooling. In contrast, the Australian First Rate 5 energy rating focuses on assessing compliance with minimum energy efficiency requirements set by the National Construction Code (NCC), which may not be as stringent as the Passive House standard.

Performance-Based Approach:

Passive House calculations adopt a performance-based approach, using verified building physics principles and advanced energy modeling software to predict a building’s energy consumption accurately. The calculations consider various factors such as the building envelope, ventilation system, heating and cooling equipment, solar gains, and internal heat sources. On the other hand, the Australian First Rate 5 energy rating relies on a prescriptive assessment method, primarily based on assumptions and simplified calculations that estimate energy use without considering some of the finer details that Passive House calculations take into account.

Stringent Certification Criteria:

Passive House buildings must meet strict certification criteria to ensure high energy performance. The standard specifies specific limits for energy demand, airtightness, heat recovery efficiency, and thermal comfort. To achieve certification, a building must undergo detailed energy modeling, including hourly calculations of energy consumption, thermal comfort analysis, and other performance indicators. In contrast, the Australian First Rate 5 energy rating is primarily a compliance tool rather than a certification program, and it focuses on achieving a minimum level of energy efficiency rather than aiming for the highest performance.

International Consistency:

The Passive House standard is internationally recognized and applied across various countries, allowing for consistency in energy performance calculations and comparisons. This global recognition and consistency facilitate a more rigorous and detailed approach to energy calculations, ensuring that buildings designed to Passive House standards deliver on their promised energy efficiency. In contrast, the Australian First Rate 5 energy rating is specific to Australia and may not have the same level of detail and consistency as the international Passive House standard.

It’s worth noting that both approaches serve different purposes within their respective contexts. While the Passive House standard is focused on achieving exceptional energy efficiency, the Australian First Rate 5 energy rating aims to establish a minimum standard for compliance with energy efficiency regulations in Australia.