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NABERS Energy
Guide to Building Energy Estimation
1 Introduction
This document is to be used as a guide whenever a computer simulation is used to estimate base building or whole
building energy use under NABERS Energy.
A separate document, being the NABERS Guide to Tenancy Energy Estimation is available that deals specifically
with the modelling of energy use of tenancies. This latter document is also to be used when the tenancy for the
building is known.
This document supersedes the ABGR Validation Protocol for Computer Simulations. It has been renamed to avoid
confusion with the Validation Protocol for Performance Ratings.
1.1
ABGR and NABERS
ABGR is a world first initiative, developed for Australian conditions, that provides accredited assessments of the
greenhouse intensity of office buildings by awarding a star rating on a scale of one to five. ABGR now forms the
basis of the National Australian Built Environment Rating System (NABERS). NABERS uses the ABGR
methodology to provide star ratings for the broad environmental impacts of buildings – energy, water, waste,
indoor environment and site impacts. ABGR has now been renamed NABERS Energy. For more information see
www.nabers.com.au.
1.2
The Role of Simulation in the NABERS Energy Commitment Agreement
Developers of new and refurbished office premises can use NABERS Energy by signing an NABERS Energy
Commitment Agreement that commits their building to achieving a 4, 4.5, 5, 5.5 or 6 star NABERS Energy
Performance Rating in operation. They are then permitted to use the relevant NABERS Energy trademark in
publicity for the building prior to completing an accredited rating of the building’s actual operational performance.
Persons or organisations quoting NABERS Energy ratings that are not substantiated by an accredited NABERS
Energy Performance Rating or an NABERS Energy Commitment Agreement are in breach of trademark and may
be subject to legal proceedings.
Under the NABERS Energy Commitment Agreement, simulation is recommended for buildings aiming to achieve
NABERS Energy 4 stars for base or whole building ratings and is compulsory for 4.5, 5, 5.5 or 6 star NABERS
Energy ratings. Compliance with this document is required for all simulations submitted for base building and
whole building Commitment Agreements. In addition, for whole building Commitment Agreements, the modelling
of the operation of the tenancy must comply with the NABERS Energy Guide to Tenancy Energy Estimation.
The use of a simulation as one part of determining energy performance is secondary in importance and authority to
the recommendations of the NABERS Energy Independent Energy Efficiency Design Review. This is because any
realistic determination of energy performance involves a substantial amount of professional judgement about
factors that are either impractical or impossible to simulate.
Those using this document who are not engaged in a Commitment Agreement are advised to use the
NABERS Energy Independent Energy Efficiency Design Review process to provide a more complete
understanding of the likely performance of their building.
NSW Office of Environment and Heritage
59-61 Goulburn Street Sydney
PO Box A290 Sydney South NSW 1232
Phone:
Email:
Web:
02 9995 6334
[email protected]
www.nabers.com.au
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1.3
The Role of Simulation in Design
This document has been written for use in all applications where simulation is estimating the potential for a
building design to reach the nominated NABERS Energy score (4, 4.5, 5, 5.5 and 6 stars).
Simulation is not a definitive indicator of the performance of a building, and indeed the relationship between the
average performance of buildings and their simulations is very weak. Real buildings rarely reach the performance
potential indicated by simulation and the gap between theroretical and actual performance is often very substantial.
As a consequence, simulation should not be advanced to clients as a sole and uncaveated means of estimating
building performance in operation.
1.4
The role of this document
This document is aimed at ensuring that simulations provide useful and realistic assistance to the design process.
This document assists in:
 The production of a building energy use estimate that can help inform the design, commissioning
and operation of a new building; and
 The conversion of a simulated energy use estimate, together with other energy calculations, into
an NABERS Energy Whole Building or Base Building Rating.
This document is structured to allow its use in a prescriptive manner. A compliance checklist is provided to ensure
that the building energy estimate complies with key elements. It is the responsibility of the simulator to comply
with such requirements in as far as possible in any given project. Where an issue of technical interpretation cannot
be resolved between the simulator and any body requiring compliance, the NABERS National Administrator may
be approached to resolve the issue.
However, in all cases, simulators must satisfy themselves that any choice they make in the simulation of the
building is a realistic assessment of what will happen once the building is built. In some cases this will be guided
by this document and in others it must be guided by the simulator's professional judgement. It is strongly advised
that simulators be conservative in their assumptions, include appropriate margins, and subject their own results to
vigorous internal assessment rather than run the risk of producing an optimistic assessment of a building that
subsequently rates lower.
No party associated in any way with the production or distribution of this document accepts any liability for any
loss, financial or otherwise, caused directly or indirectly in association with the use of this document. In all cases,
the sole responsibility for the simulation lies with the simulator.
1.5 The role of the simulator
The role of the simulator in the assessment of building energy performance is to:
1. Use the simulation to assess and advise the building design to achieve a more efficient outcome,
particularly with respect (but not limited) to: window shading and glazing options; HVAC
performance and alternative design, sizing and system scenarios; and building envelope design
and insulation performance.
2. Ensure that any interpretation of simulation results in terms of actual energy performance is
balanced by a realistic assessment of the real-life factors that would or could degrade performance
from that predicted by the simulation;
3. Utilise the simulation to identify and investigate performance risks and problems in the energy
performance of the building, particularly in common areas of risk such as reheat operation; VSD
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operation of fans; out-of-hours operation of small loads; impact of internal load variations and
control of central plant; etc.
1.6 Specific Application Requirements
The following applications of this document make specific compulsory requirements.
1.6.1 NABERS ENERGY Commitment Agreement
The purpose of simulation under the NABERS Energy Commitment Agreement is to provide a quantitative basis
upon which the risks of the building’s performance can be assessed. This requires that the simulation is, as far as
possible, a good representation of how the potential range of modes in which building will or may operate over
time.
All the requirements of this document must be met for an NABERS Energy Commitment Agreement.
particular:
In

The building is to be modelled as it is expected to operate. If this is unknown, default figures may
be used.

No specific restrictions on the simulation package are made. However, it is strongly
recommended that packages meeting the requirements identified for the Green Star Office Design
tool are considered.

Weather data shall be for a reference year data set for a local weather station representative of the
building. Weather data shall use actual recorded solar radiation, temperature and humidity data
from the local weather station and either be the ACADS-BSG/CSIRO Nominated Test Reference
Year for the nearest available climatic weather station, a Typical Meteorological Year (TMY) for
the location or other standard weather year. TRY formats are preferred where available.
Additional analysis is recommended to quantify the potential effect of ‘non average’ weather
conditions and climate change on future ratings.
1.6.2 Green Star Office Design Tool
The Green Star Office Design tool (“Green Star”) uses this document to endeavour to create a simulation
model that can be compared on an equitable basis against an absolute scale under standardised conditions.
As a result, the following specific compulsory requirements are made under Green Star when using this
document:
1. The default figures nominated in Section 5 of this document for occupant density, equipment
density, and operating schedules must be used.
2. Lighting density shall be modelled as per the design for base building lighting provided to NLA
and house areas with an extra allowance of 1 W/m² for tenants lighting to office floors. Lighting
shall be schedules as per the figures nominated in Section 5 for Lighting (limited control)
3. The building must be modelled with all lettable spaces fully occupied with diversity of occupation
as nominated in Section 5.
4. The simulation package must either:
o Have passed the BESTEST validation test; or
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o Be certified in accordance with ANSI/ASHRAE Standard 140-2001: “Standard Method of
Test for Evaluation of Building Energy Analysis Computer Programs”; or
o European Union draft standard EN13791 July 2000
5. Weather data must use ACADS-BSG/CSIRO Nominated Test Reference Year for the nearest
available climatic weather station.
These requirements override any contrary requirements within this document when conducting a
simulation for Green Star rating purposes.
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2 Guidelines for simulation input parameters
In this section, guidelines are provided as to how the simulator should set up the simulation.
In all cases, the key imperative is to ensure that the simulation is as accurate as possible a model of how the
building will be working when it is rated in operation. This operational rating will be the sole means by which the
success of the building design - and by implication, the simulation - will be judged.
Simulators are strongly advised to avoid idealization of operating parameters as this generally leads to underprediction of energy use. Suitable margins should be applied to simulation results to take account of the difference
between idealised performance and the real world systems. These include a significant control errors, hysteresis,
performance deterioration over time, fitout errors and ‘random’ activity of building occupants. Performance
optimism in manufacturers catalogue data and the differences between factory/lab test rigs and real world
installations need to be considered.
2.1 Preparatory information for the client
All simulation packages have limitations. The simulator is to provide the client with a full briefing with
respect to the ability of the proposed simulation package to model the building.
This briefing must include the following as a minimum:
 The simulation package: Is the simulation a full dynamic energy simulation? Has it passed any
external validations standards such as BESTEST? Does it model building performance on an
hourly basis for a full year?

Model limitations: How accurately can the simulation model represent:
 The air conditioning system. Can the model be configured to represent the proposed airconditioning system?
 The air-conditioning controls actually to be used in the building. Note that most models make
compromises in this area that can have quite a significant impact on the actual energy use of
the building.
 Glazing. Does the model represent glazing as a U-value and shading coefficient, or is a more
complete model used?
 Plant performance: Can performance curves and sizes for actual plant items be fed into the
simulation?
 Daylighting: Can the model calculate daylighting effects and model the operation of the type
of daylight control proposed for light fittings (if applicable).
 The building as modelled: are there any aspects of the building that have not been modelled
accurately or where compromises have been made.
It is critical that the client and the simulator understand the limitations of the simulations and any models
developed, in order to adequately interpret the validity of the final results. See Guidelines for the use of
Simulation in Commitment Agreements.
2.2 Weather data
The weather data used should comply with the following parameters:
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
To be from a weather station with a climate representative of the climate local to the building.
Caution is required in some cities, and particularly Sydney, which exhibit a range of quite distinct
weather patterns across the urban area.

The weather file must comply with the rules set out in section 1.6.
2.3 The Building Environment
 External shading. Account to be taken of external shade from buildings and trees. Deciduous trees to
be modelled as having time-varying transmissivity.

Horizon. In locations where hills cause the horizon to be substantially higher than a flat plane,
additional shading or horizon modelling to be included to represent the impact of this on building
performance.
2.4 The building envelope – Thermal Simulation
The simulation model is to be a good representation of the building's physical shape, and should be
modelled in zones that are sympathetic to the operational and thermal characteristics of the building.
 Form. The building form is to be modelled completely, with all floors represented (use of identical
floor multipliers to be restricted to cases where individual floors cannot be modelled because of
restrictions of the simulation model). Simplification of envelope shapes to be limited and to pay heed
to the potential impact of shading effects.

Glazing. Glazing must be modelled using a detailed glazing model rather than a simple shading
coefficient and U-value model. This is particularly important when the window wall ratio exceeds
25%. Better models take account of differences in optical and heat transmission, variation of
transmission with solar angle, and other such effects. If the standard simulation model does not take
account of such effects, the simulator is to be prepared to demonstrate to the client why representation
of glazing in detail is not important for the particular building. Impact of frame U-values shall be
considered if projected frame area is greater than 5% of the glazing system area, or if high
performance, low-E, double glazing is being used.

Insulation. Account to be made of thermal bridging effects for insulated walls and ceilings

Windows. The window wall ratio is to be accurately represented

Shading to be accurately represented, including modelling of overhangs and window insets.

Orientation. The building orientation is to be correctly modelled.

Car parks. Car parks intended for the sole use of tenants to be modelled, including both lighting and
ventilation
2.5 The building envelope - Daylight Simulation
The simulation model is to be a good representation of the building's physical shape and glazing/shading
characteristics.
 Glazing. Glazing is to be modelled using a detailed glazing model rather than a simple shading
coefficient model.
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
Shading is to be modelled in detail. For Greenstar, moveable shading must be represented as movable
or otherwise in the fixed position that is most disadvantageous to the building’s daylight performance.
2.6 Simulation of internal loads
The key internal loads are lighting and office equipment. Overnight energy use of these systems can
severely affect all rating types. It is essential to model this realistically rather than on the basis of
idealized habits. Refer to Section 5 for default figures to be used if no information on the proposed
internal loads is available and when simulating for the purposes of a Green Star rating. However, in all
cases, consideration is to be given to the factors below:
2.6.1 Lighting Power Density
The installed lighting power shall be assessed from the reverse ceiling plans for the tenancy. If the tenant fitout is
unknown, allowance should be made for the possible increase in lighting power density caused by the fitout.
The power consumption used for individual fittings shall include the power consumption of the lamp plus any
associated control gear and transformers. The total circuit watts of these components should be confirmed by
manufacturers’ data or by in-situ measurement.
Toilets, lift lobbies, plant rooms and foyers are to be represented with different lighting power density levels
(providing this is true in reality).
2.6.2 Lighting Hours of Use
Overnight lighting energy use can severely impact upon the total energy use of a building. The lighting schedule
should be chosen to represent the expected operating patterns for the tenancy. Such patterns may reasonably be
derived by enquiry into the operating patterns of the tenants in their previous tenancy, if the switching technologies
are similar. If such operating patterns are not known, then the default schedules provided with this document may
be used and/or the defaults provided below used to assist in developing a probable pattern. Modellers are advised
to give particular consideration of the after hours operation of lights.
Consideration of cleaner’s hours is recommended as these can have a strong effect on the lighting hours. Careful
consideration should be given to the likely interaction of the operation of cleaners with the proposed lighting
controls.
2.6.3 Lighting Controls
Lighting controls are to be modelled realistically. Most simulation models have the ability to model
daylighting controls; if this is not the case then either this function is not to be modelled, a different
simulation model is to be chosen or a detailed and separate assessment of daylighting effects undertaken
and incorporated into the model. Occupancy detector systems will require some judgement in their
modelling. A conservative assessment would make little allowance for savings during the day but would
still recognize the economies at the beginning and the end of the day. The default methodology provides
some additional methodologies which may be used to assist in this process.
2.6.4 Equipment Loads
If the tenant fitout is known, the loads should be modelled to represent the actual loads in the site.
Suggested load figures are available under the default methodologies of the NABERS Guide to Tenant
Energy Estimation. Loads based on tenant fitouts should be modelled on a zonal basis to ensure that the
variability of loads passed through to the air-conditioning is captured in the modelling.
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The design loadings must not be used as these are intended to be maximum loads rather than realistic
operational loads.
2.6.5 Equipment Hours of Operation
It is common for offices to leave over 50% of their equipment operating overnight. This represents a
major problem for the achievement of a good rating in practice. If tenants are already known, it is
worthwhile investigating what level of equipment turn-off they currently achieve, as this will probably be
carried over to the new location. The default value of 50% overnight load is to be used unless
demonstrable evidence to the contrary can be provided. Even in such a case, higher percentages of
overnight equipment operation is to be considered as a potential energy performance risk for the building.
2.6.6 Occupancy
The occupancy shall be modelled in a manner that reflects a realistic projection of the operating patterns of the site.
This can viably be based on the operating patterns of the tenant at their previous site is this data is available.
Occupant density can be based on the tenant fit-out if known; allowance should be made for less than one person
per desk actually in attendance, as this is normal. Design occupant densities should not be used as these are
normally overestimated, and are intended to be maximum loads rather than realistic operational loads.
The building should be modelled without vacant areas. If it is expected that the building may be only partially
occupied at the time of the performance rating, then this should be investigated as an off-axis scenario.
If the tenant is unknown, then the default should be used.
2.6.7 Tenant Supplementary Air Conditioning
Tenant condenser water loops can be significant energy uses within base buildings and supplementary airconditioning, particular for 24 hour loads such as computer room air-conditioning, can be very substantial energy
uses within tenancies and indeed may create significant loads for base buildings in terms of pumping and cooling
tower energy.
The electrical input into the supplementary units should be determined on the basis of realistic loads, bearing in
mind that computer rooms in particular tend to be considerably oversized relative to the actual cooling requirement.
If metered data from a previous tenancy is available, this should be used to determine probably loads. If such data
is not available, the default methodology should be used.
The impact on base building energy use should be assessed on the basis of the estimated incremental cooling tower
energy arising from the calculated tenant loads plus the electrical input to the tenant supplementary conditioners
plus the mechanical energy delivered to the condenser water by the pumps. Incremental cooling tower energy may
be estimated on the basis of the average cooling tower energy use per unit heat rejection. In addition, the pumping
energy must be counted.
2.7 Simulation of HVAC
The simulation of HVAC energy use is an area with a high probability of producing misleading or
inaccurate results. This likelihood will be reduced if the following factors are taken into account.
 System choice. The system modelled is to be a good representation of the system being installed in
each part of the building.

System design. The plant size, number of systems, airflows and zoning is to be as per the design.
Default efficiency curves for boilers and chillers are to be replaced by the actual known efficiency
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curves of the plant being installed. Note that chiller data must be specified under conditions that
reflect the intended condenser water temperature controls. Most chiller data is by default specified
under standard condenser water conditions which are not suitable for use in a simulation.

System control. This is the most problematic area. In particular, the simulator must consider how
well the simulated control system actually models the design control system.
Some key issues in this respect are as follows:
 The economy cycle for an air-based system
 Primary duct temperature control for air-based systems.
 The control of airflow for variable speed fans systems.
In all cases, there are often differences between how these are commonly controlled in reality and how these are
modelled. Extreme care is required in ensuring that there is good alignment between the two. In many cases, this
will be an opportunity to improve the control system of the real building.
System loads. Simulation models tend to assume that loads are uniform throughout a building. In practice, loads
are not evenly distributed. This immediately causes significant additional energy consumption. Consideration is to
be given to running some scenarios with different internal loads in different zones of individual HVAC systems, to
determine how robust results are to this factor. The default figures in Section 5 provide figures for use in this
respect.
2.8 Energy Efficiency Risk Assessment
A range of scenarios are to be modelled to identify the "weak points" in the simulation information. The
particular scenarios required will vary between buildings but generally are to deal with the parameters
that are least well defined for the building. Suggested parameters are:
 HVAC controls. As it is often extremely difficult to exactly align the simulation model with the real
control operation, it is worthwhile to model several HVAC control scenarios, covering the range from
"worse than expected control" to "better than expected control". This will also provide valuable
information into the controls design process. To achieve this, common flaws in control are to be
identified and attempts made to simulate these. In general, this will require some compromise, as few
if any HVAC models are able to represent the detail of real failure modes.

HVAC after-hours operation. It is particularly important to determine how efficiently the plant can
respond to the low loads generated by an after-hours call. This should be tested well beyond the ‘base
case’ after hours assumptions in this document.

Equipment hours of use. Given the unpredictability of overnight equipment loads, the sensitivity of
the model to this parameter is to be tested.

Lighting hours of use. If there are no specific technologies in place to prevent overruns of lighting
hours, the sensitivity of the model to this parameter are to also be tested.

HVAC loads. As noted earlier, it is a natural tendency in simulation modelling to assume uniform
internal loads across different zones. In practice there will almost always be rogue zones that cause,
for instance, cooling demand in the middle of winter. The effect of this on system performance is to
be investigated.
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
Multiple failures. Buildings are highly interactive systems and as a result the effect of multiple minor
failures can often vastly exceed the sum of the impacts of each failure taken individually. It is
essential to consider building failure issues in an integrated manner to avoid a gross underestimate of
the total potential impacts.
The purpose of modelling these scenarios is to assist in identifying the factors that pose a risk to building operation
in the inevitable situation that the building does not work perfectly. Thus for instance, a common issue with airbased reheat systems is that they use too much reheat. This can be demonstrated and enumerated via simulation. A
design team can then consider taking this information and using it to either reduce or eliminate reheat from the
design, or specify means of monitoring and managing reheat operation.
It is recommended that design assessment and energy performance assessments are based on a number of nonidealised scenarios rather than on an idealised case. This is because the idealised case will in general over estimate
the efficiency in the building.
2.8.1 Suggested Off-axis Factors for Common System Types
The following list is not comprehensive but is provided to assist in the compilation of off-axis scenarios
for particular projects.
System type
Off-axis factor
All
Increased overnight tenant equipment and lighting loads
Excessively tight control bands (e.g. no deadband and heating/cooling
proportional bands only 0.5°C each)
Increased running hours at no appreciable occupancy.
Impact of changes in shading from other buildings and/or trees.
Different operating schedules.
Impact of a small tenancy running 24 hours per day
Impact of the building operating at 75% occupancy
Variable air volume
VAV turndown limited to half of design figure (e.g. a turndown to 50%
becomes a turndown to 75%)
Supply air temperature control constant at minimum supply temperature
Linear fan energy turndown (representing poor fan speed control)
Air based systems
No economy cycle
Increased fan pressure (i.e. poor duct construction, dirty filters)
Baseboard
or
slab Conflict with air based systems
heating/cooling systems
Tenancies
Increased overnight tenant equipment and lighting loads
Changes in tenant equipment loads per person
Changes in server consumption
A minimum of one off-axis scenario simulation investigating the simultaneous impact of not less than
four key off-axis factors in combination is required for a compliant simulation. The simulator must select
off axis factors which are likely to have the greatest impact, depending upon the design of the HVAC
system, rather than selecting factors that are least likely to impact negatively on the results.
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3 Estimating a whole building or base building rating under NABERS ENERGY
3.1
The NABERS ENERGY Base Building and Whole Building Ratings
NABERS Energy awards stars based on the greenhouse performance of rated space, with a higher number of stars
for better performance. The number of stars is determined from the normalised emissions figure in kgCO2/m2,
which is calculated from the type and quantity of energy consumed and the rated area, normalised for hours of use,
equipment density and climate.
The NABERS Energy base building rating rates the greenhouse performance of the landlord operated services in an
office building. The NABERS Energy whole building rating rates the greenhouse performance of the combination
of landlord services and tenancies in an office building.
This section discusses the calculation of the NABERS Energy Whole Building and Base Building ratings only.
Details on the NABERS Energy tenancy rating are provided in the NABERS Guide to Tenancy Energy Estimation.
The key items of data required are:

The net lettable area of the office space being rated, less exclusions for non-office or otherwise
non-assessable items.

The energy consumed by the base building (Base Building rating) or the whole building (Whole
Building rating)

Hours of occupancy; and

The number of computers (Whole Building rating only)
These are discussed in Section 0.
A simulation result does not constitute an accredited rating under NABERS Energy. This can only be provided by
an accredited performance rating conducted by an Accredited Assessor. The NABERS National Administrator
strongly recommends that an NABERS Accredited Assessor be used to advise on the application of the NABERS
Energy methodology to new or refurbished buildings entering into a Commitment Agreement.
If there is any doubt as to application of the NABERS Energy methodology for the inclusion or exclusion of a
particular item of information (eg the area of a particular space or the energy associated with another space), advice
should be sought from the NABERS National Administrator or an NABERS Accredited Assessor
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4 Identifying data to generate the rating
4.1
Floor area
4.1.1 Data required:
Base Building and Whole Building
The Net Lettable Floor Area less deductions for non-office space. The primary data is the Net
Lettable Area or NLA. This is defined as the net lettable area for the office tenancy based on the
Property Council of Australia publication "Method of Measurement for Lettable Area" March 1997.
The rating area is to be based on the NLA, excluding areas that are not offices or supporting the
office, or not reasonably comparable to typical office spaces.
Car parks are excluded from the area calculation.
4.1.2 Interpretation
The simulation is to be based on full occupancy (i.e. no vacant areas), and thus the full rateable floor area
with no reduction for vacant areas should be used. If it is likely that the building will not be fully
occupied, a lower occupancy (with a correspondingly reduced floor area) is to be investigated as an offaxis factor.
Note that energy calculations are treated separately to area calculations. Energy use associated with
spaces that are excluded from the area calculation may be included in the energy calculation.
Spaces to be INCLUDED in the rating area include:
- The “office space” in which business, clerical or professional activities are conducted.
-
Other areas that are not technically considered “office” spaces but support the people carrying out
those tasks. This includes meeting rooms, kitchenettes, storage spaces, computer rooms.
-
Non-office spaces for the exclusive use of tenants, if the space may be reasonably compared with
an office. To be included in the rating, non-office spaces must be included in the NLA, and fitted
out for occupancy with air conditioning and lighting to suit. This would include:
o Gymnasiums, child minding centres, treatment rooms and similar (if for the exclusive use
of tenants).
o Storage spaces within the office space (if for the exclusive use of tenants).
o Commercial cafeterias and cafés (if for the exclusive use of tenants).
-
Spaces open to general public access, up to 10% of the total rating area. Where the public access
is over 10% of the rated area, a maximum of 10% of the rated area is allowed to be included. The
remainder must be excluded
Spaces to be EXCLUDED from the rating area include:
- Non-office spaces not for the exclusive use of tenants. This would include gymnasiums, childminding facilities etc that are open to the public.
-
All car parks
-
All retail facilities
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-
Long term storage spaces, or temporary storage fitted out in non-office spaces
-
Toilets, showers and change rooms (whether installed by the tenant or landlord) are not
considered comparable to an office, and the area must be excluded.
It is common for simulation floor areas not to exactly reflect the actual building floor areas. In this
situation, it is preferable to evaluate the simulation model areas in terms of the PCA guidelines to produce
an estimate of the rated floor area, rather than working solely to the building plans. This is because the
key output required for the rating is an accurate picture of the energy density of the building.
4.2
Hours of occupancy
4.2.1 Data required:
Base Building
Whole
Hours per week for which services are required Hours per week in which the building occupancy
by tenants, excluding start-up times.
is 20% or more of normal peak occupancy.
4.2.2 Interpretation
The hours of occupancy used in assessing the rating are to be assessed as per the table above. The
NABERS Energy methodology has correction factors that normalise the actual occupancy hours to
standardised occupancy hours.
The rating hours are to be weighted by area:
 For each space, determine the hours per week according to the rules above.

For each space, multiply its hours per week by its area.

Add all of these together and then divide by the total rated area.
This calculation is expressed in the equation below:
N
H
h a
i 1
i
i
A
Where:
H = Rated Hours (hours/week)
A = Rated Area (m2)
i = each space within the rated area
hi = hours allocated to each space (hours/week)
ai = area of each space (m2)
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4.3
Number of occupants and computers
4.3.1 Data required
Base Building
Not required
Whole
Number of computers
4.3.2 Interpretation
The number of occupants field of the NABERS Energy rating calculator is not used directly in the
calculation unless it is required to assess the number of computers.
Modelling of the number of computers is covered in Section . The figure used in the NABERS Energy
rating calculator should represent the number of computers normally switched on during the day.
4.4
Energy consumption details
4.4.1 Data required:
Base Building
Whole
Energy consumed supplying building central Energy consumed in base building systems as
listed opposite plus tenant lighting, power and
services including;
supplementary air-conditioning units.
 common area lighting,

lifts

air-conditioning and ventilation

exterior lighting

car park ventilation and lighting where car
parks are for the exclusive use of tenants.
Does not include energy use associated
with car parks outside the building.

hydraulic systems and DHW systems to be
modelled, or budgeted as appropriate
(allowance for use and testing)

safety and emergency systems

miscellaneous fans (eg kitchens, toilets,
refuse etc)

supplementary services provided for
tenants, eg chilled water / condenser water
/ outside air.

on-site generators (allowance for use and
testing)
in a representative calendar year.
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4.4.2 Interpretation
The energy used in the building should include all sources of utility energy including electricity, natural gas, LPG,
coal, and oil.
The correct interpretation of energy use is essential. The key principles are:
1. The energy use included within the rating is always at least the minimum coverage specified in the
table above, but may include a number of items that are not properly part of the energy coverage of
the rating but cannot practically be excluded.
2. Whatever exclusions are made must be able to be replicated in the rating of the actual building once it
is built. In general this means that there must be an intention to install and monitor sub-metering that
would enable the excluded energy to be explicitly identified.
The following points are essential in this process:
 Coverage. It is essential to ensure that all relevant energy use is included in the rating. This implies
that energy use for items commonly not simulated, such as lifts and domestic hot water, plus often
ignored items such as common area and exterior lighting, control systems, electrical losses and system
losses must be included in the model where applicable. This can be achieved either by separate
calculation or within the model itself. Energy figures must cover one complete and continuous year.
‘Miscellaneous’ energy usage is often underestimated (particularly systems which operate after hours)
and must be carefully quantified based on a knowledge of actual data from existing buildings.

Metering. The simulator is to assess the intended metering of the building with some care. The
actual performance rating will be based on the meter readings, and thus the interpretation of the
simulation model is to mimic this as far as is possible. Any assumptions made about sub-metering are
to be made clear to the in the reporting of the simulation.

Treatment of non-office occupancies. Energy use associated with non-office occupancies that are
not for the exclusive use of tenants may be excluded from the rating. The most common situation here
is that the base building servicing includes occupancies for retail functions on the ground floor. If any
of the energy for the non-office area is intended to be separately metered then the metered energy of
this non-office space can be excluded. Any component of the energy that is not intended to be
separately metered is to be included within the scope of the rating. Note that non-office occupancies
for the exclusive use of tenants are to be included in energy calculations.

Treatment of car parks. The energy use of lighting and ventilation for internal car parks provided
for the exclusive use of tenants is automatically included within the scope of a base building or whole
building rating, and must be included whether separately metered or not. If tenants have use of part
but not all of the building's internal car park then the energy use associated with these car parks must
be included, following the rules for proportioning as follows.

Proportioning is only permitted in the circumstance where there is a separate utility meter or submeter that covers the entirety of energy use associated with the car park and no other aspect of the
building central services energy use that is required is to be included within the rating.

If the lease(s) assign a proportion of the relevant energy use, then this proportion shall be used in
the assessment of the rating.
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
If no specific allocation of the energy use is identified in lease documentation, the relevant
proportion shall be determined by the total number of tenant allocated spaces divided by the total
number of available car parks. Where pass cards or keys are provided, the number of tenant
allocated spaces is to be deemed to be the greater of the number of physically dedicated spaces
and the number of pass cards or keys issued (to a limit of the total number of available car parks).
Tenant car park, pass or key allocation information should be sourced from the lease
documentation.

If there is no documentation describing carpark use by tenants then all of the energy use must be
included.

The percentage of energy allocation must be documented as per the above; therefore the actual
percentage rate can be used in the allocation, up to a maximum of 100% of the relevant utility bill.

Treatment of on-site generation. On-site generation that is connected to the building-side of the
electricity meter can be counted against on-site energy use. No discount of on-site energy use is
available against energy exported from the site under any circumstances. Fuels used to generate onsite energy must be included within the energy assessment.

Treatment of GreenPower. Any planned or future purchase of GreenPower, the accredited zero
greenhouse emission renewable energy supply product provided by energy retailers, is to be treated as
normal (i.e. non-GreenPower) electricity for the purposes of the assessment of a new building’s
performance under this document. High greenhouse performance in the new building or tenancy is to
be achieved through good design focussed on energy efficiency, and / or the application of renewable
energy integrated into the building and used by the building to reduce its reliance on fossil fuel energy
sources.
5 Default Figures
Where no information is available, the following default occupancy information is to be used:
 Occupant Density*: 1 per 15 m²

Equipment loads*: 11 W/m², built up by the random distribution into zones of the following loads
figures:
5W/m²|7W/m²|11W/m²|15W/m²|19W/m² in the following proportions: 1:2:2:1:1
Simulators must check that the area-weighted average equipment load in their model is within
10% of 11W/m².

Lighting load in tenancies (for “shell and core” buildings)*: 12 W/m²

Lifts 8 kWh/m² based on NLA.

Domestic hot water demand*: 2 kWh/m² based on NLA, plus any system losses

Hourly profiles*: As per the default schedules below.

Base building energy for tenant condenser water loops (tenant unknown)*. The energy use shall
be derived on the basis of cooling loads at 50% of the supplementary condenser water system
capacity operating for 10 hours a day and at 20% of the supplementary condenser water loop
capacity for the balance of time. A COP of 2.4 shall be used for the tenant units.
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
Base building energy for tenant condenser water loops (tenant known). The energy use of the
tenant units shall be derived on the basis described in the NABERS Guide to Tenancy Energy
Estimation. This shall be used as an input to reasonable modelling of the cooling tower and pump
operation.

For whole building ratings where the tenancy is known, the tenancy defaults described in the
NABERS Guide to Tenancy Energy Estimation shall be used.
Items marked * are compulsory when a simulation is being used for a Green Star Design rating.
The default schedules are as listed in the schedules below. The “after-hours zones” schedule (which
operates the HVAC from 9.00am –midday on Saturday) must be applied to a single after-hours zone of
the building.
The schedules correspond notionally to a 50 hour a week schedule. However, this is sensitive to the
relative size of the after hours zones. When calculating the impact of the after hours zone on the hours
for the rating, it is required that the floor area included with the additional hours is limited to the smaller
of 10% of the building, 1 storey, or an individual and distinct tenancy with area greater than 5% of the
total building.
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Weekdays (All zones)
Time Period
Occupancy
0000-0100
0100-0200
0200-0300
0300-0400
0400-0500
0500-0600
0600-0700
0700-0800
0800-0900
0900-1000
1000-1100
1100-1200
1200-1300
1300-1400
1400-1500
1500-1600
1600-1700
1700-1800
1800-1900
1900-2000
2000-2100
2100-2200
2200-2300
0%
0%
0%
0%
0%
0%
0%
15%
60%
100%
100%
100%
100%
100%
100%
100%
100%
50%
15%
5%
5%
0%
0%
Lighting
(Automated
time of use
control)
5%
5%
5%
5%
5%
5%
5%
30%
75%
100%
100%
100%
100%
100%
100%
100%
100%
75%
25%
15%
15%
5%
5%
2300-2400
0%
5%
Page 18 of 26
Lighting
(limited
control)
Equipment
HVAC
Operation
15%
15%
15%
15%
15%
15%
15%
40%
90%
100%
100%
100%
100%
100%
100%
100%
100%
80%
60%
60%
50%
15%
15%
50%
50%
50%
50%
50%
50%
50%
65%
80%
100%
100%
100%
100%
100%
100%
100%
100%
80%
65%
55%
55%
50%
50%
off
off
off
off
off
off
off
on
on
on
on
on
on
on
on
on
on
on
off
off
off
off
off
15%
50%
off
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NABERS Energy Guide to Building Energy Estimation
Weekends and holidays (Non-after-hours zones)
Sundays and Holidays (After hours zones)
Time Period
Occupancy
Lighting
Lighting
(Automated
(limited
time of use control)
control)
0000-0100
0%
5%
15%
0100-0200
0%
5%
15%
0200-0300
0%
5%
15%
0300-0400
0%
5%
15%
0400-0500
0%
5%
15%
0500-0600
0%
5%
15%
0600-0700
0%
5%
15%
0700-0800
0%
5%
15%
0800-0900
5%
15%
25%
0900-1000
5%
15%
25%
1000-1100
5%
15%
25%
1100-1200
5%
15%
25%
1200-1300
5%
15%
25%
1300-1400
5%
15%
25%
1400-1500
5%
15%
25%
1500-1600
5%
15%
25%
15%
1600-1700
5%
25%
Equipment
HVAC
Operation
50%
50%
50%
50%
50%
50%
50%
50%
55%
55%
55%
55%
55%
55%
55%
55%
55%
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
1700-1800
1800-1900
1900-2000
2000-2100
2100-2200
2200-2300
2300-2400
50%
50%
50%
50%
50%
50%
50%
off
off
off
off
off
off
off
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0%
0%
0%
0%
0%
0%
0%
5%
5%
5%
5%
5%
5%
5%
15%
15%
15%
15%
15%
15%
15%
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NABERS Energy Guide to Building Energy Estimation
Saturdays (After-hours zones)
Time Period
Occupancy
Lighting
(Automated
time of use
control)
0000-0100
0%
5%
0100-0200
0%
5%
0200-0300
0%
5%
0300-0400
0%
5%
0400-0500
0%
5%
0500-0600
0%
5%
0600-0700
0%
5%
0700-0800
0%
5%
0800-0900
5%
15%
0900-1000
5%
15%
1000-1100
5%
15%
1100-1200
5%
15%
1200-1300
5%
15%
1300-1400
5%
15%
1400-1500
5%
15%
1500-1600
5%
15%
15%
1600-1700
5%
Lighting
(limited
control)
Equipment
HVAC
Operation
15%
15%
15%
15%
15%
15%
15%
15%
25%
25%
25%
25%
25%
25%
25%
25%
25%
50%
50%
50%
50%
50%
50%
50%
50%
55%
55%
55%
55%
55%
55%
55%
55%
55%
off
off
off
off
off
off
off
off
off
on
on
on
off
off
off
off
off
1700-1800
1800-1900
1900-2000
2000-2100
2100-2200
2200-2300
2300-2400
15%
15%
15%
15%
15%
15%
15%
50%
50%
50%
50%
50%
50%
50%
off
off
off
off
off
off
off
Page 20 of 26
0%
0%
0%
0%
0%
0%
0%
5%
5%
5%
5%
5%
5%
5%
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NABERS Energy Guide to Building Energy Estimation
6 Documentation Requirements
Where a simulation is being submitted in compliance with this document, it must be accompanied by the
documentation listed in this section.
 Input data validation form;

Metering requirement description;

Simulation Results, including scenario listing, building operation summary, energy end use summary,
floor area calculation and figures used in rating estimates;

Interpretation of the Results, including Estimated NABERS Energy Performance Based on the
Simulations, Risk Assessment and Disclaimer;

Compliance Checklist
The format for each of these items is provided in the sections below. While exact use of the formats
provided is not essential, the documentation is to cover the information requirements laid out within the
formats in a clear and concise manner.
The documentation requirements have been designed to provide a degree of error checking in the process.
The forms also provide an opportunity to list all the potential issues with the simulation model and the
associated results. Simulators are strongly advised to be full and frank in identifying problems and
compromises in the simulation.
6.1 Input data validation form
Descriptions provided in this form must describe the simulation treatment of each item and highlight any
compromises and assumptions that have been made in putting together the simulation.
Item
Description
Climate Data
Type of data, weather station locations. Note: see section 1.6.
Building Form
Describe how this has been represented. Any simplifications
must be identified
External Shade
Describe how this has been represented
Glazing
Describe the type of glazing and how it has been represented in
the model
Insulation
Describe insulation levels modelled
Car parks
Describe what has been modelled for car parks
Floor Area
Describe the modelled floor area. This may not be the same as
the rated floor area.
Lighting Power Density
Identify different levels in different areas if applicable
Lighting hours
Provide a full description of the schedule. Include assumptions
about the operation of cleaners on site
Lighting Controls
Describe controls that have been modelled, including notes on
how control effects were modelled.
Equipment Density
Include assumptions made for equipment load per person.
Equipment Hours
Identify the pattern of equipment use assumed and the
consequent effective equipment operating hours.
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Occupant density
HVAC system type
HVAC Hours
HVAC After hours
HVAC plant
HVAC Zoning
HVAC Control
Energy Coverage
Document Referencing
Identify the basis upon which this figure was derived.
Describe the systems modelled and any differences between the
design and the modelled systems
Describe the hours of operation of the HVAC plant
Describe the representation of after-hours operation used.
Describe the plant sizes used, and specifically note any areas
where the simulation was allowed to default rather than use
data from the design. Describe chiller and boiler efficiencies.
Describe the zoning of the HVAC systems and identify any
differences between the design and the model.
Assess the differences between the known or likely control
methodologies of the actual building and those modelled.
Describe energy covered within the scope of the rating.
Identify any exclusions or any items outside the scope of the
NABERS Energy rating that have had to be included in the
energy coverage because of lack of metering.
List drawing and specification versions and dates used to
source information.
6.2 Metering requirements description
This table must provide a full description of the metering arrangements required or assumed to allow the
NABERS Energy rating to be conducted
Metering Requirements
Energy Coverage
Meter Description and Location
Describe the energy items covered by this meter.
Repeat as necessary for additional meters. Include any submetering required to exclude non-rated energy from the
assessment.
6.3 Simulation Results
This section must list each scenario, identifying:
 Any changes between this scenario and the reference case;
 The purpose of the scenario
 Results for the scenario in the format presented in the following subsections
An absolute minimum of two scenarios, being a reference scenario and one off-axis scenario representing
a minimum of four off-axis factors is required for compliance with this document.
6.3.1 Building operation summary
This section must identify any issues noted with the building design, including but not limited to the
issues listed in the table below:
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Issue
HVAC system performance
Comments
Are any of the systems failing to meet peak demands? How
well are temperature control targets met?
Plant performance
Do boilers and chillers meet the demand? Conversely, do they
appear oversized?
Are systems sized and staged to perform efficiently over the
full range of loads?
Improvements – Building Envelope Are there any aspects of the building envelope performance that
appear capable of being improved?
Improvements – HVAC
Are there any aspects of the HVAC design and control that
immediately appear capable of being improved?
It is required that the following information is provided for each simulation scenario.
 A quantitative identification of the percentage of occupied hours that any conditioned spaces lie
outside the nominated control range for the building.

A quantitative indication of the percentage of plant operation hours that the HVAC plant fails to
meet the system load demands.
6.3.2 Energy End-use Summary
The following information is to be provided for each of the nominated design and off-axis scenarios.
Energy End Use Total Electricity Total Fuel Use
Electricity
Fuel included in
Use
Fuel
included
in Rating
Type:________
Rating
Tenancy Lighting
Common
Area
Lighting
Car Park Lighting
Exterior Lighting
Tenancy
Equipment
Lifts/Escalators
Domestic
Hot
Water
Miscellaneous
Non-Tenant
Loads
Space Heating
Space Cooling
Heat Rejection
HVAC
fans
(Occupied areas)
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Ventilation fans
(toilets,
plant
rooms)
HVAC fans (Car
parks)
Tenant condenser
water loop energy
use
Tenancy
Supplementary
Air-conditioning
energy use
Total Energy Use
6.3.3 Floor Area Calculation
The following information must be listed in description of the modelled floor area:
 For each floor of the building as modelled: Gross floor area, net lettable area, and brief
description of spaces.

Total net lettable area of the building as modelled.

Total net lettable area of the building in reality.
6.3.4 Figures for use in NABERS ENERGY ratings
The following information must be listed for all scenarios for which an estimate of the performance under
NABERS Energy has been completed.
Item
Post Code
Rated Floor Area (as modelled)
Hours of Use
Number of Computers
Electricity Use
Fuel Use
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Figure for use in Rating
Notes
Describe rated area and any
exclusions made.
Relate to input data
Relate to input data
Describe how this figure was derived
from the figures in the other tables.
Describe how this figure was derived
from the figures in the other tables.
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6.4
INTERPRETATION OF RESULTS
6.4.1 Estimated NABERS Energy Performance Based on the Simulations
The estimated building performance must be discussed in the context of the Scenarios Results. It is not
compulsory under this document to present a single result figure. However, where external requirements
dictate that such a single figure is provided, it is compulsory to present the following:
 The nominated performance level in MJ/m², kg/m², and NABERS Energy stars

The kg/m² figure for the nearest NABERS Energy half star performance level

The scenario(s) that represent the nominated performance

Any caveats on the interpretation of the performance level.
6.4.2 Risk Assessment
In this table, the simulator must summarize the risk factors that might impinge upon the achievement of
the nominated estimated performance, the potential impact of these risks as derived from the energy risk
assessment simulations and suggestions as to how these risks might be abated.
Risk
Describe the area of risk. For
instance "Equipment hours of
use sensitivity"
Potential Impact
Describe the potential impact.
For
instance
"Changing
equipment
hours
of
use
changed the rating from four
stars to three stars."
Abatement approach
Describe how the problem
might be approached.
For
instance “Incorporate lease
clauses to place obligations on
tenants."
Repeat as necessary
6.4.3 Disclaimer
It is required to include, as a minimum, the following disclaimer:
Computer building simulation provides an estimate of building performance. This estimate is based on a
necessarily simplified and idealised version of the building that does not and cannot fully represent all of
the intricacies of the building once built. As a result, simulation results only represent an interpretation of
the potential performance of the building. No guarantee or warrantee of building performance in practice
can be based on simulation results alone.
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6.5
COMPLIANCE CHECKLIST
This table must be completed for a complying simulation.
Item
Input Data Validation Form
Metering
Requirements
Description
Scenarios Listing
Off-axis Scenarios
Building Operation Summary
Energy End-use Summary
Figures for use in NABERS
Energy Rating
Risk Assessment
Interpretation of results
Disclaimer
Included?
Notes
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
Yes/no
A complying simulation must include all the items listed in the compliance table.
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