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Carbon Challenge seminar - optimisation strategies


Part of the Carbon Challenge seminar includes a session on optimisation strategies for lower-carbon homes.

The presented optimisation strategies were derived from analysis of a parametric simulation exercise that considered both embodied and operational carbon. The operational carbon assessment was based on energy simulations carried out in the EnergyPlus thermal simulation tool.

The raw outputs of the parametric simulation exercise are graphs that summarise how the dependent variable on the y-axis – embodied carbon (kg CO₂eq), operational energy (kWh), operational carbon (kg CO₂eq) or total carbon (kg CO₂eq) – changes with different settings for the independent variable on the x-axis.

Parameters investigated

  • Construction R-values – compares current H1 settings (4th Edition of H1, pre-November 2021) to medium proposals for construction R-values in Thermal, financial and carbon review of NZBC energy efficiency clause H1/AS1 thermal envelope requirements for residential and small buildings.
  • Floor area – investigates how floor area affects results.
  • Orientation – investigates how orientation of the house with different glazing distributions affects the results.
  • Window-to-wall ratio – investigates how the amount of glazing for different glazing distributions affects results.
  • Window-to-wall ratio and orientation (deopt) – investigates the effects of glazing distribution and orientation of the house on results.
  • Shape – investigates how more-complex shapes (expressed as a decreasing area/perimeter ratio) affect results.
  • Shade – investigates how simple shading decisions can affect results.
  • Number of storeys – investigates how 1 or 2 storeys affects results.
  • Optimal – looks at the effect of cumulatively applying optimal design decisions from investigations above to understand potential greenhouse gas reduction relative to a Code-compliant 156 m2 stand-alone house.

Each section also features some accompanying graphs with supporting information that may show results in other ways, for example:

  • electricity used for cooling, heating and both
  • total electricity use (including plug loads and lighting)
  • greenhouse gas emissions associated with heating, cooling and ventilation.

Results are shown for each of the six climate zones.

Note, it is important to read the supporting report to understand the background, assumptions dependent variables and approach to modelling behind these scenarios – see Carbon Challenge Seminar supporting report - parametric simulation.

Naming conventions

Most of the graphs are presented as jpeg files with a consistent naming convention, for example:

areaMaterial (kg co2eq50yr (SusT, higherC, w.out D)).jpeg

  • “area” – the parameter being tested. For a comparison of construction R-values, this reads “RvalueComp”, and for shading, this reads “shade”.
  • “Material” –the dependent parameter being calculated. In this example, the graph solely focuses on embodied carbon. When the graph considers embodied and operational carbon, this is labelled as “Total”.
  • “kg co2eq50yr” – the units and timeframe for the simulation. Calculation of greenhouse gas emissions are in units of kg CO₂eq with the building service life over which the simulation is calculated being either 50 years or 90 years.
  • “SusT” – whether the simulation includes or excludes biogenic carbon sequestration in timbers and engineered woods. In this example, the simulation includes biogenic carbon sequestration. If it excludes biogenic carbon sequestration, it is labelled as “UnsusT”.
  • “higherC” – whether the simulation is based on use of higher or lower carbon concrete. In this example, higher carbon concrete assumes use of ordinary Portland cement (OPC) whereas lower carbon concrete assumes a proportion of OPC is replaced with supplementary cementitious materials (SCMs) in the concrete and is labelled as “lowerC”.
  • “w.out D” – whether the simulation includes or excludes potential benefits/loads beyond the system boundary (known as module D), arising from reuse, recycling or recovery of materials during the building life cycle. Inclusion is labelled as “with D” and exclusion is labelled as “w.out D”.

Raw tables of results are also provided in the Filtered Summary – GHG results.