Aorangi House revitalisation

This is a part of the Commercial buildings feature

By Ben Masters - 1 August 2019, Build 173

An award-winning commercial building, once earmarked for demolition, is now a high-performing environment for tenants. It’s proof of how well an expertly upcycled building can perform, even surpassing new buildings.

LAST YEAR, an unassuming 1970s office building in Wellington achieved international recognition by winning the World Green Building Council’s Leadership in Sustainable Design and Performance Award.

From unloved to desirable

When the original refurbishment of the building took place in 2008, Aorangi House was in poor condition and untenantable. The revitalisation of the 12-storey, 5,000 m² commercial building sets a new benchmark for cost-effective upcycling of our existing building stock and meeting New Zealand’s net-zero carbon obligations.

For a start, by recycling the building rather than demolishing it, 3,000 tonnes of concrete was diverted from landfill.

The work has continued to evolve with optimisation of the building’s systems and now proves that you can regenerate an unloved building to create a fantastic building that tenants enjoy working in – and that has significantly lower energy bills.

Better than building from scratch

Aorangi House is proof that building regeneration can deliver better building performance outcomes than building anew. This is crucial, because the building industry generates a fifth of New Zealand’s carbon pollution and requires a dramatic change in approach if we are to achieve the government’s target of net-zero carbon by 2050.

As well as leading the environmental design of the refurbishment, Beca has been the building’s anchor tenant over the last 10 years, using the building as a living laboratory for building performance strategies.

Three key reasons for success

Looking back, the three key reasons this project has been such a success are:

effective use of passive solar design
continuous monitoring and building tuning
performance focus and measurement of building users’ perceptions.

Passive solar design tackles energy and emissions

Back in 2005, the building was vacated due to issues with heating, cooling and ventilation. The single-glazed windows leaked, and the absence of insulation made the building unbearable in winter.

The property was up for demolition when a design team of Beca building services engineers and Studio Pacific Architecture suggested a major refurbishment could solve the building’s issues more sustainably.

Using passive solar design

The key was using passive solar design to use the refurbished façade as the primary climate modifier. While still relatively novel for high-rise buildings, the aim was to maximise natural ventilation and lighting and use mixed-mode – natural and mechanical – ventilation and cooling.

Exposure of the concrete structure allowed thermal mass activation to manage high summer internal temperatures and assist with passive heating. New 100 mm (R2.8) polystyrene insulation was fixed externally to the existing concrete building envelope.

Glass fibre insulation (R3.2) was included in the roof, and polystyrene insulation (R2.0) was installed beneath the lower level exposed floor slab. The majority of concrete ceilings were also left exposed as an additional heat sink.

Existing clear single-glazed windows were replaced with new spectrally selective double glazing with solar control treatment and high visible light transmittance. The area of glazing is around 33% of the total wall area, significantly improving control of solar gain and limiting heat loss.

Twin horizontal louvre blades were installed to all windows on the north elevation, while the east and west elevations used inverted L shades to reduce summer solar gain. Open-plan office spaces are naturally ventilated via high and low-level manually controlled windows.

Building users need to be on board

Passive buildings require active building users. Beca has made a concerted effort to improve summer and winter performance by opening windows in the morning during warm weather and fully closing all windows at the end of each day to reduce heat loss.

Actuators linked to the building management system automatically open and close three pairs of high-level windows per floor dependent on internal temperature and carbon dioxide levels. A weather station on the roof monitors external conditions to assist in the most appropriate operation. Night flushing helps passively precool the building structure during periods of warm weather.

Natural ventilation working well

These passive solar design features have ensured natural ventilation alone has delivered acceptable temperatures and indoor air quality throughout the year.

A variable refrigerant flow (VRF) air-conditioning system installed in the open-plan areas has only been in operation during periods of extreme summer temperature when the internal temperature exceeds 25°C.

Continuous monitoring and tuning

While continuous monitoring of energy use had been regularly carried out, a comprehensive building-tuning project was undertaken by Beca during 2016 and 2017. This aimed to further optimise energy efficiency and reduce the use of the gas boiler plant.

Emissions have been further reduced by using the VRF heat pump system that had been installed for peak summer cooling to also provide heating. This supplemented the existing 1970s gas boiler and convector radiator heating system to provide space heating to the office floors. VRF systems typically reduce carbon emissions by a factor of six while delivering the same heat output as a gas boiler.

Combining energy efficiency and renewable energy from the grid

We think a methodology that combines energy efficiency and maximises use of our 85% renewable electricity grid offers a better pathway to achieving net-zero carbon buildings in New Zealand. This offers significantly more bang for buck than installing on-site renewable energy generation such as photovoltaic panels.

Building tuning reduced Aorangi House’s energy consumption by 23% (130,000 kW/h) and greenhouse gas emissions by 30% (29 tonnes CO2-e/year). The energy performance is now benchmarked as 64% better than a typical New Zealand office building. In 2017, Aorangi House achieved the country’s first NABERSNZ 5.5 star base building rating certification for a refurbished building (see Figure 1).

Figure 1: Rolling NABERSNZ base building rating.

Huge potential from building tuning

These outcomes are not unique to Aorangi House. Over a large number of different buildings, we have achieved reductions of 10–30% through cost-effective building tuning that avoids capital expenditure. There is huge potential for this in transitioning New Zealand’s existing building stock to net-zero carbon.

Following the Aorangi House project, Beca has developed a continuous monitoring and building tuning service called B-Tune, which uses big data analytics to identify anomalies in a building’s energy performance, benchmark use and control energy creep.

Users rate building very highly

Users’ perceptions are another important measure of a sustainable building’s performance. Having been the main tenant in the building over 10 years, we are proud of what has been achieved and really do love being in the building.

This was backed up by an internationally recognised building use studies post-occupancy evaluation carried out by Victoria University of Wellington to measure tenants’ perceptions of a range of factors, from temperature, air quality and lighting, to health and productivity.

The building received excellent ratings in terms of overall comfort and its perceived influence on users’ health and productivity, placing Aorangi House at the top overall of the New Zealand dataset.

Lighting in particular rated very highly, and the manual control of natural ventilation by being able to open windows was positively perceived by many occupants.

Many opportunities for regeneration

Our work at Aorangi House proves existing buildings can be upgraded using a pragmatic, cost-effective approach that saves significant carbon without sacrificing occupant amenity.

The performance-focused passive solar design approach adopted for Aorangi House will not suit all existing buildings and tenants, but it demonstrates this can successfully deliver cash savings and a meaningful contribution to a more sustainable future.

Our experience should encourage tenants to look to existing buildings as a means of reducing their overall carbon impact and spur developers to consider holistic upgrades for existing buildings.

New office tenancies and seismic upgrades are the perfect moment to turn properties into high-performing energy-efficient comfortable buildings for comparatively little money.