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PDF | 554 KB - Australian Building Codes Board

E N E R G Y E F F I C I E N C Y P R O J E C T

C O M M E R C I A L B U I L D I N G S

DISCUSSION PAPER -

MODELLING THE BUILDING FABRIC INDEPENDENT

OF BUILDING CLASS

Ernest Donnelly PhD, FIEAust, consultant to the ABCB

Summary

Provisions in overseas energy codes 1 for commercial buildings are described independent of

the Building Class. The provisions for fabric and air conditioning are independent of the type

of use, but lighting levels and equipment power levels are related to the function carried out in

the space.

The consultant energy specialists engaged by the Australian Building Codes Board (ABCB)

Office propose that the Building Code Australia (BCA) Deemed-to-Satisfy energy provisions

for commercial buildings can be evaluated independently of Building Class. The consultants

have evaluated building class functions and associated parameters - occupancy, lighting and

equipment absorbed power levels, and hours of use - in respect to cooling and heating energy

use. The evaluation was carried out by modelling the energy use of a single perimeter zone of

a representative building or modelling the whole building, using the energy analysis program

DOE2.1E. The representative building had a 20m x 10m floor plan.

The analysis did not cover all combinations of parameters, but was limited to a set that

allowed the trend being examined to be established.

In summary, the results of the analysis showed that heating and cooling energy use depends

on the occupancy, lighting and power levels and on the hours of use of the air conditioning

system, but is independent of the BCA Class. This independence fits well with the reality that

a building’s use may change its Building Class many times during its life.

Background

Under the BCA, building construction requirements are related to an occupancy function.

The occupancy function is reflected in a building’s Class. The Class is usually related to

providing appropriate safety provisions for the occupants.

Building energy use is related to the occupancy function, lighting levels, equipment power

levels and the hours of use of the lighting, equipment, transportation systems, heating, air

conditioning and ventilation systems (HVAC), hot water services, etc. In particular, the

HVAC energy use is related to the hours of use, occupancy, lighting and power levels,

infiltration, outside air ventilation rates and heat transfer across the fabric.

1

2001 Energy Efficiency Standards for Residential and Nonresidential Buildings, California Energy

Commission

ASHRAE/IESNA Standard 90.1 - 1999, Energy Standard for Buildings Except Low-Rise Residential Buildings

Approved Document L Conservation of fuel and power, 1995 - (UK) Department of the Environment and The

Welsh Office

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This study is limited to an examination of the occupancy, lighting and equipment power levels

and hours of operation on the HVAC energy use. It is applicable to commercial buildings

only and not houses. Commercial buildings are described in the BCA as buildings in Classes

2 to 9.

Some typical ranges for occupancy, lighting and power levels for particular Classes of

buildings are listed in Table 1.

Class People 2

(m 2 /person)

Lights 3

(W/m 2 )

Power

(W/m 2 )

2 20 0 to 25 0 to 10

3 15 0 to 40 0 to 10

5 2 to 20 9 to 20 0 to 20

6 1 to 5 10 to 20 0 to 40

7 30 10 to 25 0 (excludes

process power)

8 5 to 50 0 to 20 0 (excludes

process power)

9 1 to 10 0 to 20 0 to 5

Table 1 - Ranges of occupancy, lighting and power levels for Building Classes

Ranges of hours of use for some of the above Classes are shown in the Table 2. They have

been derived from the Activity Profiles developed by the ABCB’s industry based Working

Groups (these Groups have been established to assist in developing the BCA energy

provisions for commercial buildings).

Class People Lights Power HVAC

2 To 8,760 To 5,000 To 5,000 To 8,760

3 To 8,760 To 7,000 To 8,760 To 8,760

5 2,000 to 4,000 2,500 to 5,000 2,500 to 5,000 2,500 to 3,500

6 2,000 to 5,000 2,000 to 5,000 2,000 to 5,000 0 to 5,000

Table 2 - Ranges of hours of use for Building Classes

2 BCA Table D1.13

3 AS1680.1 - 1990 - Interior lighting, Part 1: General principles and recommendations

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Methodology

To determine whether the BCA energy efficiency provisions can be described independent of

Building Class, the study examined the effects of internal flux levels (comprising occupancy,

lighting power density and equipment power density) and hours of operation, on cooling and

heating energy use.

• Internal Flux Levels

The effect of different combinations of occupancy level, lighting level and equipment power

level, was evaluated using the Form E building. This building shape is one of five developed

from statistical information and consideration of the extent of building surface area exposed to

the external environment 4 . General information on the building is shown in Figure 1.

Although the building form is shown with a gabled roof, it was modelled as having a hip roof.

total FECA 5 200 m 2

total NLA 6 190 m 2

Floors 1

aspect ratio 2:1

NLA/floor 190 m 2

Length

20.0 m

Depth

10.0 m

floor-floor

2.7 m

Figure 1 - Form E building shape and details

Of the set of five building forms, the Form E building will probably be the form most likely to

be sensitive to environmental influences because it has a high envelope area to floor area

ratio. The building was modelled using DOE2.1E with weather data from each of the capital

cities. The air conditioning systems modelled were heat pump air conditioners; these were

selected by the ABCB Working Groups as simple systems that could be easily compared

across all climate zones.

As the analysis aimed to examine the effects of internal heat generation on the cooling and

heating plant energy use, no outside ventilation air or infiltration was included. The

occupancy, lighting and equipment power were modelled using the Activity Profiles for

Office buildings.

4 Discussion Paper - Definition of basic forms for Representative Buildings, ABCB Office, April 2001

5 FECA - fully enclosed covered area

6 NLA - net lettable area

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When the effects of a parameter were being considered for the whole building, the Form E

building was modelled with nine air conditioning zones: one in each corner, one for the

remainder of the perimeter and one for the centre zone. It was modelled as a complete

building where heat transfer across imaginary zone boundaries (zone interaction) was

considered to be important in the evaluation.

• DOE2.1E, along with a number of other energy modelling programs, does not allow air

movement to be modelled the way computational fluid dynamics (CFD) programs do. To

allow for heat transfer between zones, bounded by imaginary walls, a large heat transfer

coefficient is used (the U factor in other calculations).

In other modelling, specifically where only the perimeter effects were being evaluated, a

single perimeter zone section from the long (20m) side of the building was used (the zone

area was 12.8 x 3.6 = 46.1m 2 ). The analysis did not include the corner zones. The perimeter

zone orientation was changed when evaluating the various internal flux levels for the north,

east, south and west zones.

The roof and walls of the building zones were assumed to be insulated with 100mm of bulk

insulation.

When a single perimeter zone was modelled, the zone was assumed to have 40% wall area of

clear glazing on the exterior wall and the glass was assumed to have a solar heat gain factor

(SHGF) of 0.86. When the Form E building was modelled as a whole, it was orientated with

the long axis aligned east-west and was assumed to have 40% glazing on the two longer

facades and 10% glazing on the two shorter facades. The glazing was also assumed to have a

SHGF of 0.86.

The heat from lighting and office equipment results in sensible heat - heat that increases the

temperature of the air in the space. People, because of their body temperature, exchange heat

with the space air through sensible heat transfer. They also add moisture to the space. The

addition of moisture increases the space relative humidity.

Most comfort air conditioning systems do not control space relative humidity except as part of

the sensible cooling process. The moisture in the space will influence the HVAC cooling

energy use only if it is removed from the air conditioning supply air during the cooling

process. However, it does not reduce the heating energy use because it does not offset heat

losses from the air conditioned space in the same way as sensible heat generated by

occupants, lighting and equipment.

If the air conditioning plant is assumed to control temperature only and not relative humidity,

the generation of moisture can be ignored and the internal load can be represented by a single

measure that combines the lighting, equipment and occupant sensible heat flux levels. The

flux level for lighting is a lighting power density (LPD), W/m 2 , for equipment absorbed

power is equipment power density (EPD), W/m 2 , and occupancy level, W/m 2 .

The sum of the sensible heat resulting from lights, equipment and people provides a single

measure of internal sensible heat, as an internal flux level, for the HVAC system. Equivalent

flux levels resulting from possible combinations of LPD plus EPD and occupancy levels are

shown in Table 3 below.

A set of thirteen internal flux levels was selected as the basis to examine the effects of the

internal flux levels on the cooling and heating energy use (the flux level combinations are

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shown in bold font in Table 3). The selection was made to ensure varying flux levels with

both high and low occupancy levels. The effect of high or low levels of moisture generation

in the air conditioned space, resulting from the number of occupants, can thus be included in

the determination of the heating and cooling energy use.

Lighting +

People occupancy (m 2 /person)

Power, W/m 2 20 15 10 5 2 1.5

0 3.75 5.0 7.5 15 37.5 50.0

2 5.75 7.0 9.5 17 39.5 52.0

4 7.75 9.0 11.5 19 41.5 54.0

6 9.75 11.0 13.5 21 43.5 56.0

8 11.75 13.0 15.5 23 45.5 58.0

10 13.75 15.0 17.5 25 47.5 60.0

12 15.75 17.0 19.5 27 49.5 62.0

14 17.75 19.0 21.5 29 51.5 64.0

16 19.75 21.0 23.5 31 53.5 66.0

18 21.75 23.0 25.5 33 55.5 68.0

20 23.75 25.0 27.5 35 57.5 70.0

22 25.75 27.0 29.5 37 59.5 72.0

24 27.75 29.0 31.5 39 61.5 74.0

25 28.75 30.0 32.5 40 62.5 75.0

26 29.75 31.0 33.5 41 63.5 76.0

Table 3 - Internal Sensible Heat Fluxes, W/m 2

The combinations of lighting and power fluxes and occupancy levels that make up the set are

summarised in Table 4. The selection also includes both low and high occupancy levels, so

moisture generation should show up on the cooling and heating energy use if it is significant.

Internal load, Lighting, W/m 2 Power, W/m 2 Occupancy, m 2

W/m 2 per person

9.75 6 0 20

19.75 12 4 20

19.5 10 2 10

29.5 12 10 10

29 10 4 5

32.5 15 10 10

39 18 6 5

37.5 0 0 2

47.5 10 0 2

50 0 0 1.5

56 6 0 1.5

57.5 20 0 2

66 16 0 1.5

Table 4 - Combinations for Internal Fluxes, W/m 2

The internal fluxes were initially examined on a zone by zone basis and then on a total

building basis.

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• Hours of Operation

The whole building was used in the evaluation of the hours of operation analysis. The impact

of hours of operation on energy use was examined by selecting a base activity profile with an

occupancy level of one person per 10m 2 , a lighting level of 15W/m 2 and a power level of

10W/m 2 . The HVAC hours of operation for the base activity profile is approximately 3,000

hours per annum.

The Activity Profiles were then adjusted by increasing and decreasing the time of use in two

and four hour steps during Monday to Friday operation. These changes provided HVAC

operating times of 4,000, 3,500, 3,000, 2,500 and 2,000 hours per annum.

Variations in the Internal Fluxes

The heating and cooling energy use resulting from modelling the perimeter zone of the four

orientations (north, south, east and west) with the various internal fluxes is considered in the

following sections.

• Cooling Energy

The results in Figures 2, 3, 4 and 5 below show that cooling energy use varies almost linearly

with increasing loads. The energy use is expressed in MJ/m 2 .annum: the total cooling energy

of the HVAC system divided by the floor area of the zone (46.1m 2 ). Lines of best fit have

been graphed for the Hobart and Darwin results and the corresponding equations of the

respective lines recorded on the graphs.

For Darwin, the gradient (the rate of change of energy use relative to the change in internal

flux) varies from a high of approximately 6.56 for the south to approximately 6.37 for the east

- a variation of 3%. This highlights that the internal fluxes have a uniform effect when

cooling is always required (there is no heating required in Darwin). Of course, the constant in

the equation (the expected energy use with no internal flux) varies from zone to zone

indicating the orientation effect on the zone cooling energy.

At the other extreme, a similar effect occurs in Hobart except that fabric losses in the colder

climate affect the amount of cooling required: that is, the need for cooling of the internal loads

is reduced by the heat loss through the external glazing, wall and roof. Consequently, the

south zone gradient is less than the gradients of the other three zones. The variation between

the north zone and south zone gradients is approximately 20%.

In general, the graphs show that the cooling energy use for given zone geometry and

construction varies linearly with changes in the internal loads. The variation is independent of

the composition of the internal load. If the zone geometry is changed, for example by

increasing the glazing area, then the cooling energy will be increased uniformly upward from

that shown by the present graphs. A new set of results would be derived with similar linear

lines of best fit.

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Fig. 2 - NORTH ZONE COOLING

Fig. 3 - EAST ZONE COOLING

900.0

900.0

800.0

y = 6.5332x + 385.39

800.0

y = 6.3686x + 410.06

Energy Use, MJ/m².a

700.0

600.0

500.0

400.0

300.0

200.0

y = 3.5427x + 107.64

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Darwin)

Linear (Hobart)

Energy Use, MJ/m².a

700.0

600.0

500.0

400.0

300.0

200.0

y = 3.3844x + 96.211

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

Linear (Darwin)

100.0

100.0

0.0

0 10 20 30 40 50 60 70

0.0

0 10 20 30 40 50 60 70

Internal Load, W/m²

Internal Load, W/m²

Fig. 4 - SOUTH ZONE COOLING

Fig. 5 - WEST ZONE COOLING

800.0

900.0

700.0

y = 6.5576x + 265.67

800.0

y = 6.5199x + 407.86

Energy Use, MJ/m².a

600.0

500.0

400.0

300.0

200.0

100.0

0.0

y = 2.8208x - 9.1117

0 10 20 30 40 50 60 70

Internal Load, W/m²

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

Linear (Darwin)

Energy Use, MJ/m².a

700.0

600.0

500.0

400.0

300.0

200.0

100.0

0.0

y = 3.1059x + 52.968

0 10 20 30 40 50 60 70

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

Linear (Darwin)

Internal Load, W/m²

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In the following graph (Fig. 6), three internal fluxes with changes to the glazing area of the

north zone are examined. The solar aperture is the glass area, as a percentage of the wall area,

multiplied by the SHGF. For example, 40% glass area with a SHGF of 0.86 gives a solar

aperture of 0.344.

Fig. 6 - NORTH ZONE COOLING

900.0

800.0

700.0

Energy Use, MJ/m².a

600.0

500.0

400.0

300.0

200.0

100.0

0.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Solar aperture

Hobart(19.5)

Hobart(47.5)

Melbourne(19.5)

Melbourne(47.5)

Brisbane(19.5)

Brisbane(47.5)

Darwin(19.5)

Darwin(47.5)

The graph shows that that the variation of cooling energy use with solar aperture for a specific

internal flux level (19.5 or 47.5W/m 2 ) can be approximated by a linear relationship.

• For example, based on the earlier zone graphs, the solar aperture was 40% x 0.86 =

.344, and the energy use varied linearly with changes in load. For Darwin with an

internal flux level of 19.5W/m 2 the cooling energy use is approximately

510MJ/m 2 .annum. If the glazing area is increased to 50%, a solar aperture of 0.43, the

cooling energy use increases to approximately 580MJ/m 2 .annum. This linear

relationship allows the cooling energy use to be estimated for different apertures if the

internal energy use is either 19.5W/m 2 or 47.5W/m 2 .

However, as the 19.5 and 47.5W/m 2 lines are approximately parallel, the energy use for

internal loads between 19.5 and 47.5W/m 2 would also be expected to vary linearly

across varying solar apertures. The result would be a suite of parallel lines for varying

internal fluxes.

When the internal fluxes are modelled for the Form E building as a whole, the cooling energy

use also demonstrates a linear variation. This is shown in Fig. 7 below.

Accordingly, the linear relationship for the variation in internal flux levels for a particular

zone/building geometry and orientation can be used to estimate the effects of other flux levels

on that same geometry and orientation. This has particular advantages in that it can reduce

the amount of modelling required to examine the effect of internal flux levels on the fabric

energy saving measures.

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Fig. 7 - COOLING ENERGY USE

FORM E BUILDING

Energy Use, MJ/m².a

700.0

600.0

500.0

400.0

300.0

200.0

100.0

0.0

0 10 20 30 40 50 60 70

Internal Load, W/m²

Hobart

Canberrra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Darwin)

Linear (Brisbane)

Linear (Perth)

Linear (Sydney)

Linear (Adelaide)

Linear (Canberrra)

Linear (Melbourne)

Linear (Hobart)

• Heating Energy

The effect of variations in internal flux levels for single zone systems are shown in Figures 8,

9, 10 and 11 below. There are wide variations in heating energy use for the different internal

flux levels.

Linear lines of best fit have been fitted to the Hobart results for each of the perimeter zones.

The correlation coefficients (R 2 ) for north and east zones show almost no correlation between

the heating energy use and the internal flux level (the correlation coefficient is the measure of

error between the value predicted by the line of best fit and the actual value). However, the

heating energy use is less than 20% of the cooling energy use in these zones for the particular

zone geometry.

For the Hobart south and west zones, the correlation is slightly better. For the south zone the

heating energy use is higher than the cooling energy use, until the internal flux level reaches

approximately 20 to 25W/m 2 .

If the zone geometry is varied, for example by changes to shape, exclusion of roof, etc., it is

expected there will be a similar variation across the heating energy use as occurred when the

geometry was fixed and the internal flux level varied (as shown in Fig. 8, 9, 10 and 11).

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Fig. 8 - NORTH ZONE HEATING

Fig. 9 - EAST ZONE HEATING

14.0

30.0

12.0

25.0

Energy Use, MJ/m².a

10.0

8.0

6.0

4.0

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

Energy Use, MJ/m².a

20.0

15.0

10.0

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

2.0

y = -0.1243x + 9.607

5.0

y = -0.2686x + 22.629

R 2 = 0.5661

0.0

0 10 20 30 40 50 60 70

R 2 = 0.5193

0.0

0 10 20 30 40 50 60 70

Internal Load, W/m²

Internal Load, W /m²

Fig. 10 - SOUTH ZONE HEATING

Fig. 11 - WEST ZONE HEATING

80.0

60.0

70.0

50.0

Energy Use, MJ/m².a

60.0

50.0

40.0

30.0

20.0

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

Energy Use, MJ/m².a

40.0

30.0

20.0

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

Linear (Hobart)

10.0

0.0

y = -0.8336x + 65.292

R 2 = 0.76

10.0

0.0

y = -0.5612x + 42.573

R 2 = 0.6829

0 10 20 30 40 50 60 70

0 10 20 30 40 50 60 70

Internal Load, W/m²

Internal Load, W/m²

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When the north zone was modelled

with varying solar apertures for fixed

internal loads of 19.5W/m 2 and

47.5W/m 2 , the energy use increased

with increasing aperture level but not

in a uniform manner. The results of

the modelling are shown in Figure

12.

It should be noted that the north zone

heating energy use varies from

approx. 1 to 9 MJ/m 2 .annum. This

needs to be compared with the

corresponding change in the cooling

energy for Hobart from

approximately 100 to

250MJ/m 2 .annum. Relatively, the

heating energy use is insignificant

when compared to the cooling

energy use.

Energy Use, MJ/m².a

Fig. 12 - NORTH ZONE HEATING

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Solar aperture

Hobart(19.5)

Hobart(47.5)

Canberra(19.5)

Canberra(47.5)

Melbourne(19.5)

Melbourne(47.5)

Adelaide(19.5)

Adelaide(47.5)

As a final part of the analysis, the effect of varying the internal flux level on heating energy

use for the Form E building was evaluated. The energy use varied in a somewhat random

manner, increasing with reduced flux levels over a small range, and with maximum energy

use (at 1.5MJ/m 2 .annum) occurring at an internal flux level of 9.5W/m 2 . The low heating

energy use is due to the heat transfer between the zones, and results in a lowering of heating

requirements for the coldest zones.

Hours of HVAC Operation

The Form E building was modelled for varying hours of operation, but with a constant

internal load of 32.5W/m 2 (equivalent to 1 person/10m 2 , lighting at 15W/m 2 and equipment

absorbed power at 10W/m 2 .)

The effect on cooling energy use is shown in Fig. 13 below. The heating energy use was

negligible because the internal load was set at 32.5W/m 2 and there was no allowance for

infiltration or outside air for ventilation.

The cooling energy use varies almost linearly with changes to hours of operation. The highest

degree of non-linearity occurs for Darwin, but even when a linear line of best fit is fitted to

the results, the correlation coefficient is 0.985 - a very good fit.

The observation to be made from the above graph is that if the hours of operation are changed

in a uniform manner around a base, say HVAC operation of 3,000h/annum, the energy use

will vary approximately linearly up or down by approximately 30% depending on the

direction of change in hours of use.

The uniformity relies on HVAC operation around midday, with similar changes either side of

midday. For example, for HVAC operation of 3,000h/annum the plant was assumed to start

at 6:00am and stop at 6:00pm. When the hours of operation were increased to 3,500h/annum

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the HVAC time was changed to operate from 4:00am to 8:00pm. The combination of internal

loads, people occupancy, lighting and equipment power was similarly varied.

Fig. 13 - FORM E COOLING

700.0

600.0

Energy Use, MJ/m².a

500.0

400.0

300.0

200.0

100.0

Hobart

Canberra

Melbourne

Sydney

Brisbane

Darwin

Perth

Adelaide

0.0

1500 2000 2500 3000 3500 4000 4500

Hours of operation

The preceding evaluation was based on increasing or reducing the hours of operation using

the office building Activity Profiles for occupancy, lights, equipment power and HVAC

operation. Other analyses need to be undertaken using Activity Profiles developed for retail,

home units, motels, hotels, etc. It is expected that these analyses will also show a linear

variation in energy use.

An additional set of studies need to be undertaken to examine the effect on energy use of

hours of operation that are in different time blocks, that is 00:00 to 6:00, 6:00 to 12:00, 12:00

to 18:00, 18:00 to 24:00. It is expected that for the same Activity Profiles, there will be linear

variations with hours of use across different internal flux levels, but variations between the

hours of use time sets. The study needs to be carried out in order to gain an appreciation on

the effect of different hours of operation on different facilities.

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Conclusion

The modelling in this study has been carried out to determine if fabric energy efficiency

measures could be evaluated on an internal flux level (comprising occupancy, lighting power

density and equipment absorbed power density) and hours of operation, rather than on

Building Class. The analysis was undertaken on the fabric only, without including outside air

ventilation air or infiltration. The effects of outside air for ventilation and infiltration are

independent of fabric construction and building geometry.

The effect of changing the internal flux levels for a single zone with different orientations,

caused:

° the cooling energy use to uniformly (linearly) increase with increasing internal flux

levels in all cities from Darwin to Hobart;

° the heating energy use to vary in an unpredictable manner when heating energy use

was low, and to approach some degree of linearity when the heating energy use is

above about 20 to 30MJ/m 2 .annum.

From the point of future modelling, the fabric could be evaluated by considering two different

internal flux levels (selected to provide a range) when cooling is expected to predominate

(warm and hot climates), and interpolating for other flux levels. In the case of cool and cold

climates, and in spaces where heating predominates, additional internal flux levels would

need to be considered in order to establish confidence in the outcome.

The impact of uniformly varying the hours of operation for a whole building also shows that

the cooling energy use varies in a linear manner. Consequently, the effect of changing the

hours of operation on a particular feature being evaluated could be estimated by extrapolating

from two sets of (uniform) operating times.

In general, the lack of infiltration air and outside air for ventilation caused the heating energy

to be almost negligible, except in cases where the zone orientation resulted in insufficient

solar radiation to reduce the heating needs of the zone. In cool and cold climates, where

heating energy use is significant, it may be necessary to examine the impact of hours of

operation in greater detail. This will be evaluated by considering the operation of the building

and its services in six hour time blocks.

The outcome of the changes of internal flux levels and hours of operation individually cause

the cooling energy use to vary linearly. The heating energy use varies in a non linear manner

but, generally, is much smaller than cooling energy use. Hence, the building fabric energy

saving provisions can be evaluated independent of Building Class for the BCA Deemed-to-

Satisfy provisions.

18 April 2002 Page 13 of 13

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