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COMMERCIAL
BUILDINGS
RETROFIT NET ZERO-ENERGY
COMMERCIAL BUILDINGS
Net zero energy building design is increasingly being demonstrated as an achievable
goal in many countries.
By Shaan Cory, PhD candidate in Architecture (Building Science), Victoria University of Wellington, [email protected]
T
he basic principle of net zero-energy
building is that the energy consumed
by appliances and space-conditioning
equipment is lowered by efficient
technologies and offset by clean renewableenergy generation sources, with the overall
result of at least zeroing the energy consumption
(see Figure 1).
Examples of net zero energy
Net energy consumption
At least 50 completed buildings around the
globe are being monitored in an International
Energy Agency (IEA) net zero research project.
These are all new building designs.
Far more challenging, and yet potentially
far more rewarding, is the application of this
principle to existing buildings. The potential to
negate one of the main global energy consumers
– buildings – is what makes net zero-energy
building an attractive concept. Refurbishing
existing buildings to net zero-energy buildings
means addressing the immediate need for
energy efficiency.
Over the past year, research has been done
at Victoria University to develop a methodology
to analyse the potential for refurbishing the
entire commercial building stock in New
Zealand to be net zero energy. The methodology
tests whether it is possible to achieve a net zeroDemand lowered by:
❚❚ improved envelope
❚❚ advanced daylighting
❚❚ heat recovery
❚❚ efficient equipment
❚❚ efficient lighting.
energy commercial building stock regardless of
the various building locations, ages, uses, sizes
and surrounding site contexts.
Thermal simulation and BEES
To carry out the research, the existing building
stock is modelled using thermal simulation
building models. There are approximately
50,000 non-residential buildings within New
Zealand, with a total floor area of 48.3 million m².
Templates of typical non-residential buildings
have been developed based on generic New
Zealand building information and will be refined
using information and data gathered in the
Building Energy End-use Study (BEES). BEES
is collecting information from and monitoring a
wide range of non-residential buildings to gain
a better understanding of energy use in New
Zealand buildings (see page 54).
The template models are a simplified version
of real New Zealand commercial buildings
where there are preloaded building sizes,
constructions, internal equipment, occupancy,
equipment, people schedules and heating and
cooling equipment. Figure 2 shows the template
models applied to a real city block.
This model was developed in order to test
the modelling and simulation issues in an
understandable situation. The model shown at
Demand offset
by:renewable energies,
such as wind power, solar
power and co-generation.
Resulting energy use the
overall energy consumed
by the building is equal
to the overall energy
generated by renewable
technologies.
the bottom of Figure 2 is a representation of
the EnergyPlus thermal performance simulation
software model where roof materials are red,
walls are yellow, glazed surfaces are blue and
external shading purple.
The research will model typical buildings in
typical city blocks rather than actual buildings,
but the template models are calibrated using
real energy consumption data from buildings
that were monitored in the BEES study.
Figure 3 compares a template thermal
simulation model of a real building against
actual energy data monitored in the real
building. The template model has results that
are within a recommended range of acceptable
tolerance for accuracy. The acceptable range is
+/-10% of the real monthly energy consumption.
Energy
producer
Energy
neutral
Consumed by:
❚❚ electrical equipment
❚❚ heating
❚❚ cooling
❚❚ lighting
❚❚ water heating.
Energy
consumed
+
Energy
produced
=
Figure 1: The net zero-energy principle (adapted from Commonwealth of Australia, 2009).
56 BUILD 125 August/September 2011
Net zeroenergy
building
Energy
consumer
Figure 2: Two models of the same city block of commercial
buildings using typical building templates.
Net zero-energy refurbishment
Passive design solutions
Efficiency/conservation
Renewable
energy
generation
As well as using the BEES information, this
research is also part of an IEA research project
on net zero-energy buildings. By participating
in the IEA project, the research gains access
to measured data and design descriptions for
50 existing net zero-energy buildings. These
buildings use state-of-the-art design and
technological approaches.
Figure 4 is an initial look at possible net zeroenergy building techniques that could be used
in the New Zealand refurbishment project. The
graph displays the design approaches used
in the 50 existing net zero-energy buildings in
three basic climate types around the world and
highlights the main passive design solutions,
energy-efficient technologies and renewable
energy generation approaches in these buildings.
Most of these net zero-energy buildings use
on-site generation, efficient space-conditioning,
advanced glazing and advanced envelope
measures. Advanced glazing systems are not
merely insulating glazing units, but window
systems that balance winter heating by sun and
summer shading to protect against potential
To accomplish this, the net zero-energy
definition needs to be for net zero-energy cities
and communities. This allows buildings to use
the synergies of the electricity grid balance times
of oversupply and undersupply of electricity in
each individual building.
It will require the analysis to examine not just
the energy performance of typical buildings but
all the aspects of building placement within a
city or community – connection to an electricity
grid that is partially renewable, overshadowing
in city centres and the relative importance of
big energy-intensive buildings versus multiple
small buildings.
glare from daylight. Advanced envelope
measures are typically opaque elements that
are super-insulated, such as vacuum insulation
panels or walls that incorporate substantial
amounts of thermal storage and insulation.
The future of net zero energy
A trial on a single building in Wellington has
demonstrated that it is feasible to convert
at least some existing buildings to net zero
energy in Wellington. To take this example and
generalise about converting all New Zealand’s
commercial buildings to net zero energy
requires a broadening of focus beyond the
building boundary.
4,000
3,500
3,000
Energy consumption (kWh)
With the existing commercial building models
made and calibrated, the next stage is to
refurbish them to be net zero energy.
2,500
2,000
Real
1,500
Template
Acceptable tolerance
1,000
500
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Figure 3: Comparison of template simulation results against real energy data (from Cory, Gates and Donn, 2011).
Off-site energy generation
Combined heat and power
On-site energy generation
Water conservation and efficiency measures
Efficient space-conditioning
Energy-efficient internal equipment
Integrated monitoring/advanced lighting controls
Cooling dominated
Heat/energy recovery ventilation (high-efficiency ventilation)
Heating and cooling dominated
Heating dominated
Natural ventilation/advanced ventilation/cooling
Maximise passive solar heat gain/thermal zoning/earth tube
heat exchanger/thermal chimney
Advanced daylighting measures/advanced glazing/solar shading
Improved/advanced envelope
Optimised floor plan
Figure 4: Net zero-energy lowering and producing techniques.
0
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6
8
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12
14
16
18
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BUILD 125 August/September 2011 57