An exploration of the feasibility of converting the New Zealand commercial building stock to be Net Zero Energy
Authors:   , Cory Shaan 
Published: November 2021

This thesis explores the feasibility of converting the current New
Zealand commercial building stock to Net Zero Energy (NZE). The analysis
presented is grounded in real building performance and construction
information. The goal was to establish results that are as realistic as
possible to actual building performance. The Net Zero Energy Building
(Net ZEB) concept is one of many low energy building movements that
respond to the issues of climate change and energy security. The Net ZEB
concept strives to reduce demand for energy and then to offset any
residual energy consumption with non-CO2 emitting renewable energy
technologies. The (re-)design focus for Net ZEBs is to reduce annual
energy consumption to be equal to or less than any generated renewable
energy. This is an important concept since approximately 40 percent of
all energy and emissions worldwide are building related. If all
buildings were designed and operated to be NZE, the existing energy can
be used by other sectors which will increase energy security.
Conversely, reducing the fossil fuel CO2 producing component of the
energy consumed by buildings has the benefit of negating building’s
contribution to climate change. The Net ZEB concept assumes each
building is grid-connected, and balances the energy taken from the grid
against the energy put back into the grid over a year. This study
exploits the available synergies of the grid connection to achieve NZE
for the whole building stock. Thus each individual building does not
need to be NZE at the site, but they act as a community to reach NZE
collectively. Furthermore, any grid-tied renewable energy does not need
to be offset, only the non-renewable portion. A NZE target was
calculated to determine the percentage reduction in current energy
consumption needed before the current commercial building stock could be
considered NZE. It was found that a 45 percent reduction in primary
energy would offset all non-renewable CO2 emitting energy supply
currently consumed by the New Zealand commercial building stock.
Previous studies assessing whether converting an entire stock of
commercial buildings to NZE is possible used prototypical building
energy models. Prototypical models represent a hypothetical average
building and have many assumptions about the way a building is operated.
This thesis develops a method that takes a representative sample of
real commercial buildings and makes calibrated energy models that can be
aggregated to represent energy consumption for all commercial buildings
in New Zealand. The developed calibration method makes use of as-built
building information and a standardised procedure for identifying the
inaccurate model inputs which need to be corrected for a building energy
model to be calibrated. To further base the process in reality, a set
of Energy Conservation Measures (ECM) that had been implemented in real
Net ZEBs worldwide was adopted for the proposed retrofits. These ECMs
were combined into Net ZEB solution sets for retrofitting the aggregated
commercial building models. Optimisation of the Net ZEB solution sets
was performed on hundreds of models to maximise energy savings. It took
over six months for all of the optimisations to be completed. This
thesis demonstrates the estimated New Zealand commercial building
stock’s energy consumption based upon the calibrated energy models was
robust by comparing it to an external estimate. It shows that NZE can be
achieved by applying well understood Net ZEB solution sets to the New
Zealand commercial building stock. 96 percent of the NZE goal is
attainable just through demand reduction without the use of onsite
renewable energy generation. The additional four percent of reduction
required to meet NZE is easily attainable with onsite renewable
generation. Another benefit is that the retrofitted commercial buildings
will provide improved thermal comfort for the occupants. Having
established NZE was possible, this thesis concludes with an analysis of
the broader implications of achieving the NZE goal. It identifies the
next step would be to design a NZE commercial building stock that
reduces the stresses on the existing energy infrastructure. The Solution
Set adopted was not developed with the interaction of the building and
electrical grid in mind. To have a practical implementation of NZE will
require costing and community prioritisation. This would be the next
phase of work assessing nationwide NZE retrofit.