3.7. Topic 15: The modelling method includes requirements that are unclear or outdated
Areas in the modelling method where current requirements and assumptions are unclear or unnecessary.
On this page
3.7.1. Reasons for the change
The modelling method is based on computer simulation of the thermal and energy performance of the proposed building, and of a theoretical reference building which acts as a compliance benchmark.
The simulations rely on several modelling inputs and assumptions that influence the modelling results and compliance outcomes. Verification Method H1/VM2 specifies modelling requirements and default assumptions that aim to achieve consistency in how buildings are simulated, and certainty that a building has enough insulation to comply.
Feedback from sector technical experts has helped MBIE identify some areas in the modelling method where current requirements and assumptions are unclear or unnecessary. This includes:
- Uncertainty about what climate data best represents the climate at a building site.
All building modelling software requires climate information for the location of the proposed building, usually in the form of weather files.
There is a wide range of weather files from various sources that either come with relevant modelling software or can be downloaded online. However, not all-weather files are robust and up to date. This can affect the accuracy of the modelling and how much insulation is required for a building to comply.
- An unnecessary requirement to model HVAC systems.
For commercial buildings, the H1/VM2 modelling method currently requires heating, ventilation and air-conditioning (HVAC) systems to be simulated, even though this part of the modelling has no impact on whether a building complies with the H1 energy efficiency insulation provisions.
Whilst Building Code clause H1.3.6 has energy efficiency requirements for HVAC systems in commercial buildings, H1/VM2 is not a compliance pathway for those requirements.[1]
- Deviations from default modelling assumptions are not always explained in building consent applications.
This makes it more difficult for Building Consent Authorities to check if the modelling method was used correctly, and if a building complies.
3.7.2. Proposed changes
The proposed changes involve amendments to Verification Method H1/VM2 Energy Efficiency for buildings greater than 300m2. They include:
- Prescribing the use of the most recent NIWA weather files.
NIWA have recently produced updated weather files for use with building energy modelling software. These files include information about the present climate of the different parts of Aotearoa New Zealand and can be freely downloaded from MBIE’s Building Performance website.
Weather files for Aotearoa New Zealand(external link) – Building.govt.nz
MBIE proposes to prescribe the use of the new NIWA weather files for the present climate when using the modelling method, either directly or as climate data that have been converted from these weather files into the format required by the modelling software.
- Removing the requirement to model HVAC systems.
Verification Method H1/VM3 Energy Efficiency of HVAC systems in commercial buildings provides a compliance pathway to demonstrate compliance with Building Code clause H1.3.6 (Energy efficiency of HVAC systems).
- Adding a new requirement for modellers to document and justify any deviations from default assumptions.
This is to improve transparency and make it easier for Building Consent Authorities to assess building consent applications that are based on the modelling method.
For more details of the proposed wording in H1/VM2, please refer to Appendix D.
Appendix D: Proposed changes to Verification Method H1/VM2 [PDF, 4 MB]
3.7.3. Analysis of the proposed changes
The primary objective of the proposed changes is to support consistency of how the modelling method is applied and provide certainty for designers, Building Consent Authorities and building users that buildings have sufficient insulation for achieving Objective H1.1 of the Building Code, Functional requirement H1.2(a) and Performance H1.3.1(a).
For this issue, MBIE considers that the proposed changes to the modelling method will best achieve this objective.
MBIE expects that the impacts of this proposal include:
- Improved accuracy of modelling results that better reflect how buildings perform from updated climate data as modelling inputs.
- Better consistency and certainty of compliance from clearer requirements.
- Fewer delays in the building consenting process from more transparent building consent documentation.
- Less work for building modellers from the removal of the requirement to model HVAC systems.
On balance, MBIE considers that the benefits of the proposed exemption outweigh the costs.
3.7.4. Other options MBIE considered
As part of the analysis, we also considered other options that were not further pursued on the basis that the proposed changes were considered to address the issue more effectively.
These discounted options included:
- Allowing the use of weather files with future-projected climate data in the modelling method.
Whilst MBIE has confidence in the robustness of the future-projected climate versions of NIWA’s weather files[2], there has not been enough time since completion of these files to assess the potential impacts of their use in the modelling method.
There is also great uncertainty about which climate change scenario may be most appropriate to use. MBIE may consider this option for a future update of H1/VM2.
- Making the H1/VM2 modelling method an additional compliance pathway for the H1 Energy Efficiency requirements for HVAC systems in commercial buildings.
Whilst MBIE considers that computer modelling of HVAC systems could form the basis of a compliance pathway for HVAC system energy efficiency in the future.[3]
The current H1/VM2 modelling method is currently not set up for the computer modelling of HVAC systems.
Significant analysis would be required to help develop a computer-modelling based compliance pathway for demonstrating compliance with Building Code clause H1.3.6.
MBIE have determined that the proposed approach of amending Verification Method H1/VM2 to clarify and simplify modelling method requirements is the most reasonable and effective option for achieving the objective.
3.7.5. Questions for the consultation Topic 15
15-1. Do you support amending Verification Method H1/VM2 as proposed to clarify and simplify requirements for the modelling method?
- Yes, I support it.
- Yes, with changes.
- No, I don’t support it.
- Not sure/no preference.
15-2. Please explain your views.
Footnotes
[1] Instead, designers can use Verification Method H1/VM3 Energy Efficiency of HVAC systems in commercial buildings to demonstrate compliance with Building Code clause H1.3.6.
[2]Also available on MBIE’s Building Performance website – Weather files for Aotearoa New Zealand(external link)
[3] In addition to the current Verification Method H1/VM3 Energy Efficiency of HVAC systems in commercial buildings.