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renovation
Retrofitting commercial
buildings
Requests for tours and information have inundated Beca’s new Wellington office in
the refurbished Aorangi House – proof that green retrofits of commercial buildings
are a hot topic.
By Alan Barbour, Technical Director, Beca Buildings
B
uilt in 1970, Aorangi House was a relatively unremarkable
example of a commercial office building of its time and had been
unoccupied since 2005.
In 2008, owners Prime Property Group commissioned Studio
Pacific Architects and Beca to design a complete upgrade of the building.
They used an integrated green building approach and several major design
interventions to give the building a new lease of life as a highly functional
office.
Beca structural and building services engineers also compared notes
with their colleagues in Singapore who were working on South-east
Asia’s first zero-energy retrofit at the time for Singapore’s Building and
Construction Authority.
The team made extensive use of 3D computer simulation analysis at
the design stage. This provided valuable data for determining the right
balance between project costs and key performance attributes, such as
energy efficiency, occupant comfort, use of daylight, natural ventilation
and glare control.
Full insulation reduces heating and air-con needs
Well tested energy-saving improvements such as thermal insulation and
double glazing were top of the refurbishment list. The aim was to add value
by significantly reducing heating and air-conditioning needs.
The building was stripped of its existing windows, over-clad with
100 mm of high-density polystyrene insulation on the external façade and
replastered with a high-quality proprietary system to provide a waterproof
and well insulated building thermal envelope.
It was a New Zealand first for a commercial office building to be
externally insulated and reclad to a full 12-storey height as a green retrofit.
Aorangi House in Wellington, one of the first retrofitted commercial buildings to receive a five-star
Green Star rating.
Working with the sun
The sun has the largest impact on a building’s thermal load. To minimise
these effects, Aorangi House features external solar shading. The solar
shades are positioned to allow useful solar gains in winter while limiting
heat gains and cooling requirements in summer. The fixed elements were
designed to suit the differing solar impacts on each face, without the need
to change their position.
Double glazing with a high visible light transmittance was used, providing
good levels of daylight.
Internally, unlined walls and exposed concrete act as heat sinks to
reduce temperature fluctuations.
46 BUILD 122 February/March 2011
Inside the retrofitted Aorangi House.
Natural ventilation provides a comfortable environment
The refurbished Aorangi House uses natural ventilation to take advantage
of the Wellington climate. The desk layout on the office floors provides
occupants with excellent views and natural light. People have control
over the perimeter opening windows, which are manually operated to suit
individual preferences.
A roof-mounted weather station constantly measures wind speed
and direction, rain and outside air temperature. Although the windows
are intended to be user-operated, temperature and air quality sensors
continuously monitor conditions on each floor. These sensors and weather
station automatically control selected windows as required to achieve the
target conditions.
A night flushing feature passively pre-cools the exposed building
structure ready for the day ahead. If the target temperature cannot be
achieved (or if wind speeds are too high to have windows open), an exhaust
fan provides assisted ventilation.
A variable refrigerant flow (VRF) comfort cooling system is installed
to serve high tenant-load areas and provide a level of future-proofing.
This only operates for the open plan office spaces to manage comfort in
extreme conditions.
Although you’re unlikely to please all of the people all of the time,
feedback from Beca’s staff indicates that the retrofitted passively
designed system is providing a more comfortable working environment
than previously experienced in air-conditioned offices. Staff report feeling
healthier and more energised, particularly during the afternoon.
Measurements gathered to date indicate that the thermal performance
of the building is in line with design predictions.
One-size green option doesn’t fit all
Key to the Aorangi House retrofit was the building owner’s commitment to
investing in long-term outcomes. While most pragmatic commercial retrofit
projects can expect a positive financial return over the long term, high
upfront capital costs can present barriers to green building investment
in this sector. Beca uses a project-specific framework to assist owners to
evaluate appropriate options to retrofit their properties.
Other considerations include the building’s suitability for different
retrofit options. Not all commercial buildings would lend themselves to
the approach adopted for Aorangi House, where the relatively narrow floor
plates aligned well with a passive design approach. However, the roof to
floor-area ratio of Aorangi House meant rainwater collection and reuse was
not a favourable option.
Five-star accommodation
Aorangi House was one of the first retrofitted commercial buildings to be
awarded a five-star Green Star rating by the New Zealand Green Building
Council. Mike Kerr, Beca’s Wellington Regional Manager, believes the
benefits for the business have been numerous, including savings in energy
costs, reduced water usage and increased staff satisfaction with the new
workplace environment.
BUILD 122 February/March 2011 47