PDF | 4 MB - Australian Building Codes Board


PDF | 4 MB - Australian Building Codes Board

Australian Building Codes Board





A Case Study

B u i l d i n g A u s t r a l i a ’ s F u t u r e

This document was first published in 2006. It was revised in 2010 as part of the

amendments to the increased stringency of the energy efficiency provisions in the Building

Code of Australia, as part of the National Strategy on Energy Efficiency.

© 2007 – 2010 Australian Government and the State and Territory Governments of Australia

A Case Study – Module Four: Understanding Energy Efficiency Provisions for Class 2 to 9

Buildings (BCA Awareness Resource Kit). Material contained in the publication may be

reproduced for educational purposes and for use as permitted under the Copyright Act 1968.

Otherwise, no part may be reproduced without prior permission. Requests and inquiries

concerning reproduction and rights should be directed in the first instance to:

The General Manager

Australian Building Codes Board

GPO Box 9839





A Case Study

1. Introduction

The energy efficiency Deemed-to-Satisfy (DTS) Provisions for Class 2 to 9 buildings

are relatively detailed because they provide for all major components of various

buildings in different climate zones. Given this level of complexity, it is important that

practitioners have a good understanding of how to apply appropriate energy

efficiency provisions to a building.

The purpose of this case study is to examine how the energy efficiency DTS

provisions apply to a pre-cast concrete office building. This type of building is fairly

typical in construction and may help to provide a good understanding of how the

provisions are applied. More complex buildings can be assessed using the same

basic principles.

Please note that there are many software packages available that can be configured

to assess a building for its compliance with relevant energy efficiency provisions.

However this study will focus on the DTS Provisions.

2. The project

A single-storey office building is proposed to be built in the suburbs of Brisbane. It

has pre-cast solid reinforced concrete walls 125 mm thick with internal plasterboard

lining on furring channels. The office is to be constructed on concrete slab-on-ground

and will have a ventilated 22º pitched galvanised metal roof behind a parapet wall. It

has a kitchen with a non-openable 600 mm x 800 mm roof light above. Internally it

will have a flat ceiling.

A floor plan and glazing schedule of the subject office building are shown on the next


2.1 Glazing

It is proposed that the external windows be of single pane clear glass in thermally

improved aluminium frames with a Solar Heat Gain Coefficient (SHGC) of 0.68 and a

Total U-Value of 6.0.

2.2 Air-conditioning and ventilation

The building will be heated and cooled by a low pressure air-cooled direct expansion

package unit air-conditioning system of 25 kW r capacity. The air-conditioning air-flow

rate is 1650 L/s and the sensible heat load is 120 W/m 2 .

The maximum occupancy level has been determined by the tenant to be 20 people.

The air-conditioning damper requires that minimum performance filters are to be

installed and as a consequence the entrance air supply rate would be 200 L/s.

Case Study – Typical Office Building



True North






G6 G7 G8 G9












2500 1500









3500 1500 2500 2500


G1 2100h x 2000w00w



G2 2100h x 2000w00w



G3 2100h x 2000w00w

Glazed S winging


G4 2100h x 2000w00w



G5 2100h x 2000w00w



G6 1200h x 3000w00w



G7 1200h x 3000w00w



G8 1200h x 3000w00w



G9 1200h x 3000w00w



G10 1800h x 2500w




Title Boundary

Roof Light

G11 1800h x 2500w



Case Study – Typical Office Building


The air-conditioning unit is on the roof. A maximum length of 2 m of flexible ductwork

will be used to connect the main ductwork to each service outlet. It is proposed to

use a membrane as a vapour barrier in the air-conditioning ductwork insulation.

Due to the size of the office and the extent of north, east and south glazing, it is

expected that the air-conditioning designer will provide four thermal zones; one for

each of the north, east and south facing areas and a fourth zone for the centre of the

building. This zoning will provide comfort conditions under varying external ambient


The mechanical ventilation system serving sanitary facilities has an air-flow rate of

approximately 60 L/s.

2.3 Lighting

The office will have recessed fluorescent lights installed throughout the building. The

design is proposed with an illumination power load of 1270 Watts.

3. Climate zone and building classification

The first fundamental matter that needs to be determined in addition to the

classification of the building before applying the DTS Provisions is the climate zone in

which the building is to be located. An Australian climate map showing

diagrammatically the extent of each zone and a table detailing the applicable climate

zone for common locations are included in Volume 1 Part A1 of the BCA.

For locations that are more difficult to determine, an enlargeable climate zones map

can be viewed on the ABCB website, www.abcb.gov.au.

In this case, the applicable climate zone for Brisbane is 6. As it is an office, the

proposed building will be a Class 5 building in accordance with BCA Volume 1 Part


4. Building fabric

Having determined the applicable climate zone and building classification, the next

logical step is to examine BCA Part J1 and determine whether the fabric of the

building requires any particular treatment to improve its thermal performance.

4.1 Roofs

A Class 5 building's roof in climate zone 6 is required to achieve a minimum Total R-

value of 3.7 in the downward direction if un-painted galvanising (refer Table J1.3a).

According to Figure 2 in Specification J1.3, a ventilated pitched metal roof with a flat

ceiling achieves a Total R-Value of 0.72. This means that additional insulation that

achieves a minimum R-Value of 2.08 (3.7 – 0.72) in the downward direction is

required to be installed in the roof. This can be achieved by installing bulk insulation

or a combination of bulk and reflective insulation.

4.2 Roof lights

The roof light serving the kitchen is approximately 4.6% of the room area served and

its shaft index being just over 1.0; it is required to achieve a solar heat gain

coefficient of 0.47 and a Total U-Value of not more than 2.9.

Calculations for the roof light shaft index are as follows.

Case Study – Typical Office Building


Determining roof light shaft index



(Elevation view)

Roof cladding


Roof light


Roof light



Shaft measurement:

Measured from centre of the

shaft at the roof to the centre of

the shaft at the ceiling level.

Ceiling level






Roof light

(Plan view) Shaft


Average internal opening = (800 + 600) / 2 = 700





Roof light shaft index = 707mm height / 700mm average opening dimension ≈ 1.0

4.3 External walls

Class 5 external walls are required to comply with one of the options for each part of

the external wall listed in Table J1.5b. For 125mm thick pre-cast concrete walls the

only space for insulation would be provided by a furring channel, therefore, they must

comply with Table J1.5a Item (b). The external walls would need to achieve a

minimum Total R-Value of 1.4 and satisfy glazing energy index option B of Table


Using the information from Specification J1.5 Figure 2(d), a 125mm thick solid

reinforced concrete wall with 10mm internal plaster on furring channels achieves a

Total R-Value of 0.48. This means that additional insulation with an R-Value of at

least 0.92 is required to be installed in the walls.

Case Study – Typical Office Building


4.4 Floors

The provisions do not require insulation to be installed underneath or around the

vertical edge of the concrete slab-on-ground as it is in climate zone 6 with no in-slab


5. Glazing

Part J2 details the formulae to be applied to the glazing in a building to determine

compliance. To simplify this process, the ABCB has developed a glazing calculator

which is simply a spreadsheet that automatically determines whether the glazing

performance targets have been achieved based on the input of the glazing


It is important to note that due to the building being of precast concrete construction,

the only space for insulation would be provided by the furring channels (please see

4.3 External Walls above) and therefore Glazing Energy Index option B was used

which is more demanding for the glazing.

Although no shading is shown on the North and East side of the building, the

calculation can take into account the setback of the glazing in the wall and a gutter

overhead if they provide shading.

In terms of the case study building, the results from using the glazing calculator are

shown on the following pages. The drawing says that the north glazing projection is

more than 0.5 m above the glazing so 2.6 m from the bottom of the glazing to the

projection height is assumed.

The above results are based on the use of the performance values of single clear

glass in aluminium frames.

Case Study – Typical Office Building


Please note the far right hand column entitled "Element share of % of allowance

used". The first percentage given is the percentage that the individual glazing

element contributes to the aggregate conductance for all glazing elements

associated with a particular storey. It allows users to quickly identify which glazing

elements are having the greatest impact on the aggregate result.

The second percentage shows how the aggregate performance compares to the

conductance allowance. As such, this second value must be not more than 100% for

complying designs.

Note also that in the far right column, there are values given in red with readings of

"20% of 157%". In these cases, the aggregate air-conditioning value is higher than

the allowance which is why the design does not comply. This only applies to the

glazing on the North and East; not on the South.

In order to achieve compliance, the North and East windows are changed to tinted

glass instead of the proposed clear glass. The new results are as shown below.

6. Building sealing

The next step is to examine Part J3 and to determine whether the subject building

needs to be sealed in order to control unwanted air movement throughout the


6.1 Chimneys and flues

There are no chimneys or flues installed in the proposed building, so Clause J3.2 is

not applicable.

Case Study – Typical Office Building


6.2 Roof lights

According to Clause J3.3, the roof light serving the kitchen is required to be sealed or

be capable of being sealed because it serves a conditioned space. The roof light is

not a roof window and cannot be opened and therefore it must be either constructed

with an imperforate diffuser installed at ceiling level or have a shutter system readily

operated manually, mechanically or electronically by its occupants.

6.3 External windows and doors

Clause J3.4 requires all external doors and openable external windows to

conditioned spaces or habitable rooms in climate zone 6 to be fitted with a seal to

restrict air filtration. There are no openable windows in the subject building, therefore

only external doors will require sealing by fitting foam or rubber compressible strips,

fibrous seals or the like.

The external doors which are the main entrance to a building must be self closing or

the like so that when doors are in use, the loss of conditioned air is minimised.

6.4 Exhaust fans

As required by F4.5 of Volume 1, each of the toilets in the office building is to be

provided with a mechanical exhaust ventilation system complying with AS 1668.2­

1991 and AS/NZS 3666.1-2002. Please note that as these fans are part of a system,

a sealing device such as a self closing damper or the like is not required in

accordance to J3.5.

6.5 Construction of roofs, walls and floors

The case study building's roofs, external walls, external floors and any opening

forming the external fabric of a conditioned space, habitable room or public area

must be sealed to minimise air leakage because it is proposed to be built in climate

zone 6.

Compliance with this part will be addressed by conventional internal fixing and lining

systems, provided the lining is close fitting or caulking, skirtings, architraves, cornices

or the like are used to seal any gaps at the ceiling, wall and floor junctions. Any

penetrations for wiring, piping, etc forming part of the building envelope must also be

sealed against air leakage.

6.6 Evaporative coolers

There are no evaporative coolers installed in the proposed office, therefore Clause

J3.7 does not apply.

7. Air-conditioning and ventilation systems

The next step is to analyse the air-conditioning and ventilation system proposed in

the case study building to ensure systems are installed that use energy in an efficient


This provision requires controls to deactivate the air-conditioning units or system

when the area served is not occupied.

Any motorised outside air and return air dampers on the air-conditioning units or

system must be closed when the system is inactive.

Case Study – Typical Office Building


All supply and return ductwork must be insulated and sealed in accordance with

Specification J5.2 in order to minimise amount of energy lost through the ductwork.

Low pressure ductwork (less than 500Pa) and its fittings in an air-conditioning system

that cools or must be sealed against air loss with a sealant and draw band encased

with adhesive tape.

Some of the insulation on the ductwork and fittings of the air-conditioning system is

exposed on the roof so in climate zone 2 it must achieve a Total R-Value of 3.0 while

the insulation on the ductwork and fittings in the roof space must achieve a Total R-

Value of 2.0 (refer to Specification J5.2, Table 3). Flexible ductwork of a maximum

length of 2m at each outlet must achieve a minimum Total R-Value of 1.0.

The air-conditioning system is used for cooling and therefore insulation on ductwork

must be protected by a vapour barrier on the outside of the insulation. As it is

proposed to use a membrane as the vapour barrier, the adjoining sheets must

overlap by a minimum of 50mm and be bonded or taped together.

The external ductwork insulation must also be protected against the effects of

weather and sunlight. It must be installed in such a manner to form a continuous

barrier with adjoining insulation, ensuring that it maintains its position and thickness,

other than at flanges and supports.

Please note that BCA Specification C1.10, Clause 8 requires flexible ductwork to

comply with fire hazard properties set out in AS 4254-1995.

As the building will be divided into four thermal zones the air-conditioner must have

facilities to provide zone temperature and comply with Clause J5.2a(v). Specifically,

for the system proposed, zone temperature control cannot be provided by cooling the

supply air and reheating it by more than 7.5 K.

The proposed air-conditioning system has a capacity of 25 kW r , so an outdoor air

economy cycle is not required. As such, the outside air damper will probably not be

motorised dampers.

As the air-flow rate in the proposed air-conditioning system is 1,650 L/s, the building

under 500 m 2 and the sensible heat load 120 W/m 2 , the power for the air-conditioning

fans in this system must not exceed 7.3 W/m 2 .

The fans for the mechanical ventilation in the sanitary facilities must be capable of

being inactivated when that part of the building is not occupied. Time switches are an

effective way of meeting this requirement as explained below in 7.1.

The outside air does not exceed the minimum requirements of AS1668.2-1991 and

therefore complies with J5.2(b)(ii)(A).

In the proposed building the total air-flow rate of the toilet exhaust is approximately

60 L/s and therefore does not need to comply with Clause J5.2(b)(ii)(B).

Case Study – Typical Office Building


7.1 Time Switches

As the air-conditioning/heating system is above 10 kW r capacity, a time switch

complying with Specification J6 is required. The time switch allows automatic control

of the system and deactivation when not required. The automatic nature of the switch

removes dependency on direct human initiation to turn equipment off.

7.2 Heating and chilling systems

As the air-conditioning system is only 25 kW r so is exempt from complying with

Clause J5.4(c). For such equipment, the performance requirements are part of the

government’s Minimum Energy Performance Standard program.

7.3 Miscellaneous exhaust systems

There are no exhaust systems that would exceed an air flow rate of 1000 L/s and

therefore compliance with Clause J5.5 is not required in this case.

8. Artificial lighting and power

The next step is to ensure the artificial lighting and power for the proposed office is

designed to curb unreasonable energy use.

8.1 Interior artificial lighting

A simple lighting design has been selected using 2 tube 36 W fluorescents with

Minimum Energy Performance Standard (MEPS) compliant magnetic ballasts. The

illumination power density is 11.8 W/m 2 .

The Illumination Power Density (IPD) allowances are shown in Table J6.2a. Further,

the allowance needs to have an adjustment factor applied for small rooms (termed

room aspect ration adjustment), specifically the reception, the enclosed office, the

toilets, the storeroom and the kitchen. The partition between the office and toilets is

low level and so the space is considered part of the office.

For the reception with a 20.16 m 2 area, 23.4 m perimeter and 2.7 m height, the Room

Aspect Ratio (RAR) is A/(H x C) (note 3 to Table J6.2a), i.e. 0.32. As this is less than

1.5, the adjustment factor for room aspect is 0.5 + (RAR/3), i.e. 0.61. This results in

an adjusted IPD of 14.8. The IPD values both unadjusted for area (from Table J6.2)

and adjusted for area are shown are shown.

Room aspect ratio adjustment

Location Unadjusted IPD RAR Adjustment Factor Adjusted IPD

Reception 9 0.32 0.61 14.8

Office 2 (to < 200 lx) 9 0.32 0.61 14.8

Male & Female Toilets 6 0.17 0.56 10.7

Toilet for people with disabilities 6 0.18 0.56 10.7

Kitchen 8 0.27 0.59 13.6

Store 8 0.20 0.57 14.0

The designer has also allowed for automatic daylight sensors on the east main office

(4 lights). The adjustment factor for the east lights from Table J6.2c is 0.5.

Case Study – Typical Office Building


Summing all of the effects the total allowable maximum illumination power level is as




(m 2 )

Adjusted IPD Controls Factor Maximum

(W/m 2) Power (W)

Reception 21.6 14.8 1.0 320

Office 2 13.1 14.8 1.0 193

General office

- With daylight sensors

- Without daylight sensors



Male toilet 3.0 10.7 1.0 32

Female toilet 3.0 10.7 1.0 32

Toilet for people with disabilities 3.4 10.7 1.0 37

Kitchen 8.9 13.6 1.0 121

Store 4.3 14.0 1.0 60







Total 1348

As the aggregate design illumination power load is 1270 Watts it complies with the

BCA as it is less than 1,348 W.

Please note these provisions do not apply to emergency lighting, signage lighting or

lighting within display cabinets.

8.2 Interior artificial lighting and control

Artificial lighting switches must be located in a visible position, in the room or space

being switched or in an adjacent room or space from where the lighting being

switched is visible.

The proposed office building area is 150m 2 and therefore does not need to be

controlled by a time switch or occupant sensing devices. Due to area size of less

than 250m 2 , there is also no requirement to zone artificially lit areas adjacent to

windows separately from the rest of the office.

As in section 9.1 above, note that the emergency lighting does not need to comply

with the above provided that the lighting conforms to Part E4 of the BCA Volume 1.

8.3 Interior decorative and display lighting

Clause J6.4a requires the display cabinet lighting to operate from a separate switch

to other artificial lighting in the office. As lighting will be less than 7kW, a time switch

will not be required.

8.4 Artificial lighting around a building

There is no external artificial lighting provided around the perimeter of the proposed

office building.

8.5 Boiling water and chilled water storage units

This provision specifies that the power supply to boiling water and chilled water

storage units in the kitchen are to be controlled by a time switch which must be

Case Study – Typical Office Building


capable of switching on and off electric power at variable pre-programmed times and

on variable pre-programmed days and limiting the period the systems are switched

on to 2 hours beyond the time for which the building is occupied. In addition, the time

switches provided to the boiling water and chilled water storage units must be

capable of being overridden by a manual switch for a period of up to 2 hours, after

which the time switch must resume control.

9. Hot water supply

The aim of Part J7 is to ensure the amount of energy used in providing sanitary hot

water to the building is minimised. This does not include for hot water circulated for


The office must comply with the hot water supply provisions contained in Section 8 of

AS/NZS 3500.4 – 2003.

10. Maintenance of energy efficiency installations

The final step is to ensure that all plant, equipment and components that require

maintenance must be accessible. The extent of accessibility will depend on the type

of equipment and the associated maintenance requirements.

Where replacement of major parts is required, adequate access must be provided to

allow these parts to be easily installed, including any necessary plant replacement.

Please note that there are corresponding requirements in Occupational Health and

Safety legislation.

As the building is less than 500 m 2 there is no requirement for annual energy


11. Summary

This case study provides a detailed analysis of application of the energy efficiency

DTS provisions of the BCA to a typical precast concrete office building, proposed to

be constructed in the Brisbane suburbs.

The DTS provisions are based on the eight climate zones that classify Australia into

broad regional areas with similar climatic conditions.

After the applicable climate zone is established and the building class has been

determined, Part J1 for the building fabric is to be consulted to determine the

minimum acceptable levels of thermal efficiency for roof and ceiling constructions,

roof lights, walls and floors.

Then the external glazing provisions detailed in Part J2 must be examined to

establish the treatment of glazing to control the amount of heat entering or exiting the

office through glazing. The glazing calculators developed by the ABCB assist with

calculations required under this part of the BCA.

Part J3 for building sealing addresses unwanted air movement through the building

and must be examined to verify sealing provisions for chimneys and flues, roof lights,

external windows and doors, exhaust fans and evaporative coolers and general

construction requirements for roof, walls and floors.

Case Study – Typical Office Building


The next step is to examine requirements relating to the beneficial air movement

within the building contained in Part J4, which clarifies the applicable provisions for

air movement, borrowed ventilation, ventilation openings and installation

requirements for ceiling fans and evaporative coolers. Due to the classification of the

proposed building, this part is not applicable to the case study building.

Part J5 has provisions for air-conditioning and ventilation systems designs. This part

requires systems to be designed and installed so that they are comparable to

demands of the actual location and to operate in an energy efficient manner.

Artificial lighting and power must then be considered in accordance with Part J6 of

the BCA to provide minimum energy efficiency requirements for the lighting systems

in the proposed building.

Part J7 refers to AS/NZS 3500.4-2003 and aims to minimise the energy required to

provide hot water to the building.

Then finally, the last step is to ensure that the building is designed in order to

maintain all plant, equipment and components. Accessibility to these parts is crucial

to ensure that the building is capable of continuing to perform in an energy efficient


Case Study – Typical Office Building


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