FENESTRATION VOL.2
ZERO ENERGY
After we published our first issue of Fenestration New Zealand, two things usefully coincided. The Ministry of Business and Enterprise (MBIE) released its consultation document on major changes to New Zealand’s Building Code at the same time as we were preparing a second pass at the thermal modelling of FMI’s Zero Energy/Ready house. We opted to focus most of our new research on measuring how our home performed in MBIE’s proposed six new climate zones and against MBIE’s three options of increasing insulation in the building envelope. The insights from this exercise culminated in FMI making a submission to MBIE on the Building Code.
To recap briefly, a Zero Energy (ZE) home produces as much renewable energy from solar panels on its roof as its occupants consume over the course of a year. A Zero Energy Ready home (ZER) is a ZE home without the solar panels. Our original ZE build had only been modelled in Auckland. With revisions, chiefly to our building envelope for airtightness, we explored whether our new build could meet the ZE definition in all New Zealand climates. Despite colder parts of the country placing higher energy demands and offering less intense sunshine for fewer hours than Auckland, we found the ZE home roof could fit enough solar panels to cover the annual electricity demand in Christchurch and Invercargill. Comparing our ZE home to MBIE’s three Building Code options was bittersweet. Sweet - and gratifying - in how far ahead in energy savings our ZE home was of the best insulated MBIE option. FMI’s ZE energy use for heating was a fifth, or less, of MBIE’s. High-performance windows remain the single most important component for achieving these savings. The bitterness came from our perceiving a lack of scope and ambition in the proposals. Our research tells us that New Zealand can move further, faster and more straightforwardly to supporting our country’s health and climate change goals than MBIE is considering.
Contrasting FMI’s view against MBIE’s of the extra costs of energy-efficient building was also a cause for concern. Our latest ZER build estimate is a cost premium of about 4% for changes in the building envelope, water heating and appliances, and half as much again for ZE with its solar panels. MBIE’s bestinsulated option, in the coldest climate, carried a 12% cost premium and that was only for the building envelope. We worry that reports of high premiums will undermine both policy and popular appetites for improving buildings’ energy efficiency. For simplicity we advocate one set of standards across all climates. We prefer some regional redundancy in building cost to the more insidious complexity costs of multiple versions of the code on design and compliance. We also recommend that the revised Code focus on performance outputs such as energy use per m2, not inputs such as R-values or specific appliances. Technology is changing fast and industry needs flexibility to respond optimally. Finally, we acknowledge that our thermal model can only approximate reality. Kiwi habits for home heating mean that the average household uses under half the heating energy the model predicts, which reduces the potential savings and payback. We are determined to take the next step of building our ZE home and testing it in the real world.
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