Development of an Energy Rating Tool for Australian Existing Housing

Abstract

Australia aims to achieve net-zero emissions by 2050, and its building sector needs rapid change. The Nationwide House Energy Rating Scheme (NatHERS) is supported by the Australian Government to expand the current building envelope thermal performance energy star rating to a whole-of-home (WoH) energy rating. The NatHERS Administrator supports CSIRO to develop a benchmark WoH energy rating tool for new and existing housing, respectively. The tool for new housing was released in June 2023. This study presents the tool development for Australian existing housing. A case study was conducted using the tool for the eight capital cities of Australian states and territories. It shows that with a detached house built in the 1900s being updated to six or more stars and replacing old equipment and appliances with high-energy-efficient ones, more than 50% of energy can be saved in all the eight cities. To be zero-energy (carbon) housing, 5 kW solar PV needs be installed in Darwin and Hobart, 4 kW in Melbourne and Canberra, 3.5 kW in Adelaide and Sydney, and 3 kW in Brisbane and Perth. It demonstrates that this tool can be used for housing retrofitting to be low/zero-carbon emissions and low operational cost.

1. Introduction

The actual energy consumption of a household is impacted not only by the building shell’s thermal performance and installed equipment and appliances but also by the occupancy profiles and behaviors. Building thermal-energy performance is related to the constructure components (i.e., windows, walls, roof, ceiling, floor, and doors), local climate, size, and orientation. How people run their housing is related to their income, cultural background, societal life, and so on.

It is not easy, if not impossible, to find possible ways to reduce energy from an energy bill, as the actual energy consumption cannot be separated and assigned to individual elements such as occupant behaviors or building components, etc. It is also not easy for surveys and field studies alone to estimate the impact of individual elements on total house energy usage. Controlled experiments are ideal but very expensive. A validated and calibrated whole-house energy consumption model can be used to investigate the components that impact total house energy consumption and measures to reduce them. A range of whole-house energy simulation tools (http://www.buildingenergysoftwaretools.com, accessed on 25 September 2023) have been developed. The most widely used methods for building energy simulation are engineering, statistical, and artificial intelligence methods. Some of the tools based on artificial intelligence methods were reviewed by Krarti [1] and Dounis [2]. Zhao and Maoulès [3] provided a review on engineering and hybrid approaches that combined the above methods for calculating building energy consumption, including some of the tools developed outside Australia (such as the USA, UK, Italy, China, etc.). The recent progress on the engineering methods was reviewed by Gonzalo, Santamaria, and Burgos [4]. EnergyPlus [5], ESP-r [6], RETScreen [7], TRNSYS [8], and HOMER [9] are five popular physically based engineering programs for building energy simulation. Some modules required for Australian whole-house energy value calculation and scale rating are missing, such as household hot water, spa and swimming pool, and cooking and plug-in loads.

Based on the engine of EnergyPlus, a number of programs have been developed (http://www.buildingenergysoftwaretools.com, accessed on 25 September 2023), including Sefaira [10], BuildSimHub [11], Honeybee [12], gEnergy [13], FineGREEN [14], Autodesk Insight [15], Autodesk Green Building Studio [16], ResStock [17], EFEN [18], and Simergy [19]. The recent progress in the tool development based on other engines is summarized by Ali et al. [20]. The modules missing in EnergyPlus mentioned above still need to be developed for these programs for estimating total household energy consumption and scale rating.

In February 2019, the Trajectory for Low Energy Buildings was agreed upon by the Council of Australian Governments (COAG) Energy Council. The Trajectory suggested energy-saving measures by expanding building shell energy performance to whole-house energy consumption along with considering appliance energy efficiency and on-site renewable energy generation. This results in the NatHERS being supported by the Australian Government to expand the current building envelope energy star rating to a WoH energy rating (https://www.nathers.gov.au/, accessed on 25 September 2023). CSIRO was commissioned by the NatHERS Administrator to deliver a benchmark tool in the required timeframe for new and existing housing, respectively.

With the inputs from the technical expert panel (TEP) organized by the NatHERS Administrator, the NatHERS Whole-of-Home National Calculations Method [21] was developed. A benchmark tool for new housing was developed [22] and released in June 2023 (https://www.nathers.gov.au/WholeofHome/software-development, accessed on 25 September 2023) based on the Method [21]. With the major assumptions/settings adopted from the Method [21] and Scorecard [23], CSIRO developed a WoH energy rating tool for existing housing by modifying the AusZEH design tool [24,25] with considering the energy performance of Heating, Ventilation, and Air Conditioning (HVAC) for space heating and cooling and implementing new modules of lighting, water heating, spa and swimming pool, other appliances, and on-site solar PV. This document details the assumptions/settings implemented in the existing housing benchmark tool.

This study aims to develop a benchmark tool for housing retrofitting to be low/zero emissions in Australia. The three main objectives are:

• An integrated tool will be developed for existing housing energy rating purposes considering the building envelope, installed equipment and appliances, and on-site PV battery system;
• The tool can be used for whole-of-home annual energy consumption calculation with hourly data before and after the dwelling is retrofitted;
• Whole-house energy rating will be provided by the tool based on the hourly data of each module.

2. Methodology

In this study, the Chenath engine [26,27] developed by CSIRO is used to estimate annual energy loads for space heating and cooling with hourly data. Considering the energy efficiency of installed equipment and appliances, modules are developed for WoH energy calculation and rating, which are detailed below.

2.1. Energy Consumption for Space Heating and Cooling

Based on hourly space heating and cooling (H/C) energy requirements predicted by the Chenath engine, the hourly energy consumption for space H/C of a zone is calculated:

$$E_{h.z}=\frac{L_{h.z}}{\left(1-LOS\right)\times CO{P}_S}.$$

(1)

where:

E_h.z = Hourly energy consumption of the zone (MJ);

L_h.z = Hourly energy requirement of the zone (MJ) predicted by the Chenath engine;

COP_S = Energy coefficient of performance of the installed heating/cooling air conditioners, refer to [21] for details;

LOS = The system loss, default values for specified appliances are detailed in [21].

With the NatHERS star rating simulation, the house is defined to be fully occupied all the time (i.e., at least one person staying at home for 24 h every day for a whole year), and the thermal comfort environment is satisfied by the household at any time. In this study, two different occupancy profiles defined in the National Construction Code (NCC) 2022 [28] are applied to develop a single combined scenario for the whole-house energy calculation, which is described as [21]:

$$X_{WH}=0.6\times X_{All-Day}+0.4\times X_{Work-Day}$$

(2)

where:

X_WH = The weighted H/C load;

X_All-Day = The H/C load predicted under the occupancy scenario of All-Day (The house is occupied by at least one person for any time);

X_Work-Day = The H/C load predicted under the occupancy scenario of Work-Day (one person staying at home during work time between 9:00 am and 5:00 pm).

2.1.1. Insulation

Insulation to the construction components (wall, ceiling, and floor) is difficult to estimate for existing dwellings, in particular when the components are not assessable. For this study, insulation assumptions are adopted from the Scorecard methodology [23]. For insulation that is not accessible to view and has no other document (e.g., floor plan) available, R-values are estimated based on the age of the dwelling and prevailing regulations when the building was built, which are summarized in

Table 1. R values of wall insulation.

Insulation Description	R-Value (m2.K/W)
No document is available on when the building was built.	0
The building was built before the insulation regulation was introduced in 1991.	0
The building was built after 1991 and before 2004 with a timber floor.	R1.5
The building was built after 1991 and before 2004 with a slab floor (foil insulation assumed).	R0.85
The building was built between 2004 and 2010.	R1.5
The building was built after 2010.	R2.0

,

Table 2. R values of ceiling insulation.

Insulation Description	R-Value (m2.K/W)
No document is available on when the building was built.	0
Foil insulation	R0.75
The building was built before the insulation regulation was introduced in 1991.	R1.5
The building was built between 1991 and 2003.	R2.2
The building was built after the introduction of 5-star in 2004 and before 2009.	R3.0
The building was built after the introduction of 6-star in 2010.	R3.5

and

Table 3. R values of floor insulation.

Insulation Description	R-Value (m2.K/W)
No document on when the building was built	0
Insulated with foil (standard reflective and concertina foil)	R0.75
Insulated with board (rigid bulk insulation products such as polystyrene)	R1.5
Insulated with batt (glass wool, rockwool, natural wool or polyester)	R1.5

for walls, ceiling, and floors, respectively.

For ceiling insulation that is accessible to view, the R-value can be estimated based on the insulation product and thickness, which are summarized in

Table 4. R-Value of ceiling insulation when the ceiling is accessible.

Insulation Product	R Value (m2.K/W) for Measured Thickness (mm)
	1	1.5	2	2.5	3	3.5	4
Cellulose fibre	40	60	80	100	120	140	160
Glass fibre	57	86	114	143	165	190	210
Polyethylense foam	40	60	80	100	120	140	160
Polyester	63	95	126	158	185	210	235
Polystyrene (expanded)	39	59	78	98	117	137	156
Polystyrene (excluded)	28	42	56	70	84	98	112
Polyurethane rigid foam	28	42	56	70	84	98	112
Rockwool loose fill	40	60	80	100	120	140	160
Rockwool batt	33	50	66	83	99	116	132
Wool loose fill	80	120	160	200	240	280	320
Wool/polyester batt	59	89	118	148	177	207	236

.

2.1.2. Windows

A simplified window database is developed for existing housing by modifying the NatHERS window system, which includes frame material, type and amount of glazing, and size (height and width).

2.1.3. Ventilation

The opening and closing of windows and doors are operated for ventilation. Ventilation on and off times are defined in

Table 5. Ventilation settings.

	On (O’Clock Time)	Off (O’Clock Time)
Occupied all day	0	24
Unoccupied during the day	18	7

.

2.1.4. Shading

The operable shading devices are assumed to be operated all the time. This simulates occupants shutting blinds when they leave the house on hot days, rather than simulating the blinds being open at all times. Settings are therefore defined in the Chenath Scratch documentation.

2.1.5. Air Infiltration

Air infiltration is the air movement into a building through leakages of windows, doors, downlights, exhaust fans, and chimneys. In general, infiltration gaps of these components are made to be small, medium, and large, and calculations of infiltration rates through these gaps are described in [29].

2.2. Hot Water

2.2.1. Hot Water Energy Consumption

Water heating accounts for a major part of the whole-house energy consumption, which is impacted by a range of factors, including hot water demand, cold water supply temperature, water heating type and performance, ambient air temperature (a main factor for storage systems and heat pump water heaters), and solar radiation levels (for solar water heaters). With the daily winter peak demand being assumed at 40 L for each occupant [21], the related energy demand can be calculated using Equation (3) [21],

$$W_{wp}=\frac{40\times N_{occ}}{y}$$

(3)

where:

W_wp = The daily energy demand for water heating at winter peak (MJ/day);

N_Occ = The occupant number of the house;

y = The average liters of hot water per MJ for a 1MJ winter peak load by climate zone, defined in [21] for 4 solar water heater zones 1–4 and 5 heat pump zones HP1-AU to HP5-AU.

The number of occupants is calculated as [21]

$$N_{Occ}=1.525\ln \left(A_D\right)-4.533$$

(4)

where:

N_Occ = Occupant number in the residential building, which is between 1 and 6, and rounded to be the nearest 2nd decimal place;

A_D = The residential building floor area (m²), including all the zones (garage and roof space excluded).

The annual energy requirement for hot water is estimated as [21]:

$$E_{water}=365\times 0.904521\times W_{wp}$$

(5)

where:

E_water = The annual energy demand of hot water (MJ/year);

W_wp = The peak energy load for water heating in the winter (MJ/day).

Three hundred sixty-five is the number of days in a standard year, and 0.904521 is a converting factor from a peak load at winter MJ/day into an average annual daily load considering the hot water loads varying with seasons in AS/NZS4234 [30] and days per month.

In this study, the Scorecard methodology [23] is applied for hot water energy calculation, which can be expressed as:

$$E_W=HWSL\times T_{adj}+\frac{E_{water}}{HWF}\times T_{adj}$$

(6)

where:

E_w = The yearly energy usage of hot water (MJ/year);

HWSL = The energy losses related to the hot water system (MJ/year), detailed in [23];

HWF = The marginal energy conversion efficiency of the hot water system, described in [23];

T_adj = The corrected factor related to climate zones (Table 6);

E_water = The yearly hot water energy loads (MJ/year).

Table 6. Tadj and NatHERS climate zone.

Climate Zone Number	Climate Name	Tadj
1	Darwin	0.988
2	Port Hedland	0.988
3	Longreach	1.000
4	Carnarvon	1.000
5	Townsville	0.988
6	Alice Springs	1.010
7	Rockhampton	0.988
8	Moree	1.010
9	Amberley	1.003
10	Brisbane	1.000
11	Coffs Harbour	1.003
12	Geraldton	1.003
13	Perth	1.010
14	Armidale	1.047
15	Williamtown	1.022
16	Adelaide	1.022
17	Sydney East	1.003
18	Nowra	1.022
19	Charleville	1.010
20	Wagga	1.035
21	Melbourne	1.035
22	East Sale	1.047
23	Launceston	1.054
24	Canberra	1.054
25	Cabramurra	1.073
26	Hobart	1.054
27	Mildura	1.022
28	Richmond	1.022
29	Weipa	0.988
30	Wyndham	0.988
31	Willis Island	0.988
32	Cairns	0.988
33	Broome	0.988
34	Learmonth	0.988
35	Mackay	0.988
36	Gladstone	0.988
37	Halls Creek	0.988
38	Tennant Creek	0.988
39	Mt. Isa	0.991
40	Newman	1.000
41	Giles	1.000
42	Meekatharra	1.000
43	Oodnadatta	1.000
44	Kalgoorlie	1.010
45	Woomera	1.010
46	Cobar	1.022
47	Bickley	1.022
48	Dubbo	1.022
49	Katanning	1.022
50	Oakley	1.010
51	Forrest	1.022
52	Swanbourne	1.003
53	Ceduna	1.022
54	Mandurah	1.010
55	Esperance	1.022
56	Mascot	1.010
57	Manjimup	1.035
58	Albany	1.035
59	Mt. Lofty	1.073
60	Tullamarine	1.047
61	Mt. Gambier	1.047
62	Moorabbin	1.043
63	Warrnambool	1.054
64	Cape Otway	1.043
65	Orange	1.073
66	Ballarat	1.073
67	Low Head	1.043
68	Launceston Air	1.073
69	Thredbo	1.073

Table 6. Tadj and NatHERS climate zone.

Climate Zone Number	Climate Name	Tadj
1	Darwin	0.988
2	Port Hedland	0.988
3	Longreach	1.000
4	Carnarvon	1.000
5	Townsville	0.988
6	Alice Springs	1.010
7	Rockhampton	0.988
8	Moree	1.010
9	Amberley	1.003
10	Brisbane	1.000
11	Coffs Harbour	1.003
12	Geraldton	1.003
13	Perth	1.010
14	Armidale	1.047
15	Williamtown	1.022
16	Adelaide	1.022
17	Sydney East	1.003
18	Nowra	1.022
19	Charleville	1.010
20	Wagga	1.035
21	Melbourne	1.035
22	East Sale	1.047
23	Launceston	1.054
24	Canberra	1.054
25	Cabramurra	1.073
26	Hobart	1.054
27	Mildura	1.022
28	Richmond	1.022
29	Weipa	0.988
30	Wyndham	0.988
31	Willis Island	0.988
32	Cairns	0.988
33	Broome	0.988
34	Learmonth	0.988
35	Mackay	0.988
36	Gladstone	0.988
37	Halls Creek	0.988
38	Tennant Creek	0.988
39	Mt. Isa	0.991
40	Newman	1.000
41	Giles	1.000
42	Meekatharra	1.000
43	Oodnadatta	1.000
44	Kalgoorlie	1.010
45	Woomera	1.010
46	Cobar	1.022
47	Bickley	1.022
48	Dubbo	1.022
49	Katanning	1.022
50	Oakley	1.010
51	Forrest	1.022
52	Swanbourne	1.003
53	Ceduna	1.022
54	Mandurah	1.010
55	Esperance	1.022
56	Mascot	1.010
57	Manjimup	1.035
58	Albany	1.035
59	Mt. Lofty	1.073
60	Tullamarine	1.047
61	Mt. Gambier	1.047
62	Moorabbin	1.043
63	Warrnambool	1.054
64	Cape Otway	1.043
65	Orange	1.073
66	Ballarat	1.073
67	Low Head	1.043
68	Launceston Air	1.073
69	Thredbo	1.073

With solar radiations ‘G_s’(Table 7), the factor of solar hot water system is calculated [23]:

$$F_s=\frac{\left(0.4736-0.0562\times \frac{60-\frac{18.2}{T_{adj}}}{E_{water}}\times 365\right)\times 4\times G_s-0.1564\times \left(60-18.2/T_{adj}\right)}{E_{water}}\times 365$$

(7)

Note that F_s must not be less than 0 and greater than 0.95 [23].

Table 7. Solar radiation level for state.

State	Value of Solar Radiation ‘Gs’ (MJ/m2)
NSW	17.9
VIC	15.9
QLD	20.1
SA	17.3
WA	19
TAS	15
ACT	18
NT	22.3

Table 7. Solar radiation level for state.

State	Value of Solar Radiation ‘Gs’ (MJ/m2)
NSW	17.9
VIC	15.9
QLD	20.1
SA	17.3
WA	19
TAS	15
ACT	18
NT	22.3

The hot water energy efficiency needs be adjusted considering solar hot water fraction and T_adj, which is estimated as [23]:

$$HW{F}_{adj}=HWF\times T_{adj}/\left(1-F_s\right)$$

(8)

HWF_adj = The adjusted energy efficiency for water heating.

For solar hot water systems, the energy consumption can be calculated by substituting HWF with HWF_adj in Equation (6).

Considering the impact of air temperature difference in each location, COP can be calculated using Equation (9) [23]:

$$CO{P}_{adj}=-0.001397\times T_{av}{}^2+0.080852\times T_{av}-0.634242$$

(9)

where:

COP_adj = The adjusted COP of heat pump water heating equipment;

T_av = The annual average ambient temperature.

For each NatHERS climate zone, the COP_adj can be looked up from

Table 8. COP_adj for heat pump hot water systems.

NatHERS Climate Zone	Average Temperature (°C)	COPadj
1	27.7	0.533
2	26.1	0.525
3	24.0	0.502
4	21.7	0.463
5	24.3	0.505
6	21.2	0.451
7	22.5	0.478
8	19.0	0.398
9	20.1	0.427
10	20.1	0.426
11	18.6	0.385
12	19.6	0.414
13	18.3	0.377
14	13.5	0.203
15	17.5	0.353
16	17.2	0.344
17	18.6	0.385
18	16.3	0.314
19	20.9	0.446
20	15.4	0.279
21	15.1	0.268
22	13.7	0.210
23	12.8	0.172
24	13.1	0.183
25	8.5	-0.045
26	12.7	0.167
27	17.1	0.339
28	16.9	0.335
29	26.8	0.529
30	29.9	0.534
31	26.3	0.526
32	24.8	0.512
33	26.7	0.529
34	24.4	0.507
35	22.8	0.484
36	22.6	0.479
37	26.7	0.529
38	26.1	0.525
39	24.8	0.512
40	24.4	0.507
41	23.0	0.486
42	22.2	0.472
43	21.9	0.467
44	18.4	0.381
45	19.2	0.404
46	18.5	0.382
47	16.6	0.323
48	16.6	0.323
49	15.9	0.300
50	18.4	0.379
51	18.0	0.367
52	18.3	0.377
53	16.9	0.332
54	18.1	0.370
55	16.5	0.319
56	17.6	0.358
57	15.0	0.265
58	15.0	0.266
59	11.3	0.103
60	14.2	0.232
61	13.4	0.196
62	14.0	0.223
63	13.0	0.181
64	27.7	0.533
65	11.3	0.099
66	12.7	0.166
67	13.5	0.204
68	11.5	0.112
69	9.6	0.015

below.

2.2.2. Hourly Energy Consumption of Water Heating

AS/NZS4234 [30] describes that energy consumption for water heating has seasonal and regional changes, as shown in Figure 1 in Australia, where four zones are used for solar hot water, and five zones for heat pump hot water systems (Figure 2).

The climate data used to represent each climate zone are:

Zone 1 = Rockhampton

Zone 2 = Alice Springs

Zone 3 = Sydney

Zone 4 = Melbourne

Zone HP5-AU = Canberra

Figure 1. Climate zones specified in AS/NZS4234 for solar thermal systems.

Figure 1. Climate zones specified in AS/NZS4234 for solar thermal systems.

Figure 2. AS/NZS4234 Amendment 3 for heat pump systems.

Figure 2. AS/NZS4234 Amendment 3 for heat pump systems.

The associated hot water zones are given in

Table 9. Climate regions classification for hot water module [21].

Hot Water Climate Region	Existing Climate Zones in AccuRate
One	1, 3, 5, 7, 19, 29, 32, 35, 36
Two	2, 4, 6, 30, 31, 33, 34, 37, 38, 39, 40, 41
Three	8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 24, 25, 27, 28, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 56, 57, 59, 65, 69
Four	21, 22, 23, 26, 55, 58, 60, 61, 62, 63, 64, 66, 67, 68

for each of the 69 NatHERS climate zones used in the Chenath engine.

Table 10. Hot water use factor F_m by month per climate zone.

Month	Hot Water Demand (%)
	Zone 1	Zone 2	Zone 3	Zone 4	HP5-AU
January	7.23	8.36	7.52	7.49	7.50
February	7.46	8.11	7.76	7.73	7.74
March	8.51	8.75	8.66	8.66	9.32
April	8.22	8.06	8.25	8.28	8.70
May	8.49	7.65	8.39	8.29	9.09
June	7.99	7.31	8.02	8.12	8.53
July	8.26	7.26	8.11	8.23	8.18
August	8.47	7.72	8.28	8.55	8.18
September	8.88	8.53	8.55	8.62	8.21
October	9.23	9.51	9.21	9.03	8.22
November	8.99	9.49	8.88	8.66	8.16
December	8.26	9.26	8.37	8.35	8.18

summarizes every month’s hot water use for each zone [21].

With the percentage of hot water demand per month (Table 10), daily energy usage can be calculated as:

$$E_d=\frac{F_m\times E_{year}}{N_{d,m}}$$

(10)

where E_d is the daily energy usage (MJ/day), F_m is the factor given in Table 10 for the corresponding month and zone, E_year is the annual energy consumption as determined by Equation (6), and N_d,m is the number of days in the month.

Regarding time of hot water loads, some broad assumptions/settings are proposed in [21], as shown

Table 11. Water heater schedules.

Water Heater Type	Heating Schedule
Solid fuel (f)	Additional research required
Off-peak electric (e)	Overnight
Continuous electric (e)	Time of use
Solar thermal standard efficiency (e)	Additional research required
Solar thermal instant gas (g)	Time of use
Heat pump (e)	Daytime
Gas storage (g)	Time of use
Gas instant (g)	Time of use

.

The heating schedules listed in Table 11 are defined in

Table 12. Daily hot water demand profile, the hourly factor, F_h.

Hour	Time of Use	Daytime	Overnight
1	0	0	0.25
2	0	0	0.25
3	0	0	0.25
4	0	0	0.25
5	0	0	0
6	0	0	0
7	0	0	0
8	0.15	0	0
9	0.15	0.125	0
10	0	0.125	0
11	0	0.125	0
12	0.1	0.125	0
13	0	0.125	0
14	0.1	0.125	0
15	0	0.125	0
16	0.125	0.125	0
17	0.125	0	0
18	0.125	0	0
19	0.125	0	0
20	0	0	0
21	0	0	0
22	0	0	0
23	0	0	0
24	0	0	0

(refer to Table A4 of AS/NZS4234).

The hourly energy use for water heating can be calculated as

$$E_h=F_h\times E_d$$

(11)

where E_h is the hourly energy use for water heating (MJ), F_h is the hourly factor of hot water demand (Table 12), and E_d is the daily hot water demand (MJ) defined using Equation (10).

2.3. Lighting Module

The annual lighting energy consumption for the house without the installation of halogens is calculated as [21]:

$$E_{tot}=\frac{365\times P_L\times H_{avg}\times A_D\times 3.6}{1000}$$

(12)

where:

E_tot = The yearly lighting energy usage (MJ);

P_L = The power density of lighting (W/m²), in this study 5 W/m² is applied;

H_avg = The number of average lighting hours per day (hours), in this study 1.6 h are applied [21];

A_D = The residential building floor area (m²), including the entire zone (garage and roof space excluded).

Three hundred sixty-five is the number of days in a standard year, 3.6 converts kWh to MJ, and 1000 converts Wh to kWh.

When the house is installed with halogens, the number of the halogens can be counted by visiting the dwelling. The areas lit by halogens and other lamps are:

$$A_H=\frac{N_H}{N{H}_{sqm}}$$

(13)

$$A_{LO}=A_{tot}-A_H$$

(14)

where:

A_H and A_LO are the areas (m²) lit by halogens and other lamps, respectively. N_H is the number of halogens, and NH_sqm is the density of halogens (number of lamps per square meter). In this study, the power of halogens is defined to be 60 W and NHsqm 0.4 based on the study of the Scorecard methodology [23].

When there are halogens, the yearly energy usage is estimated as:

$$E_H\frac{365\times H_{avg}\times N_H\times 60\times 3.6}{1000}$$

(15)

where:

E_H = Yearly energy usage of halogen lighting (MJ);

H_avg = Number of average lighting hours per day (hours), in this study 1.6 h are applied [21];

N_H = The number of halogens.

Three hundred sixty-five is the number of days in a standard year, 3.6 converts kWh to MJ, and 1000 converts Wh to kWh.

The annual energy consumption of other lamps can be calculated using Equation (12) by replacing A_D with A_LO.

The hourly energy use for lighting is estimated as [21]:

$$E_{m,hr}=E_{tot}\times F_{L,hr}$$

(16)

where:

E_m,hr = Hourly lighting energy usage (MJ/hour);

E_tot = Yearly lighting energy usage for lighting (MJ);

F_L,hr = Hourly factor of lighting (refer to Table 62 of [21]).

2.4. Pool and Spa Equipment

2.4.1. Energy Consumption for Pool Pump and Cleaning

In this study, yearly energy usage for pool pump and salt cleaning is estimated based on the calculation of Scorecard [23], which is shown in

Table 13. Annual energy consumption for pool pump and cleaning.

State/Territory	Pump Energy (kWh)	Chlorinator Energy (kWh)
Victoria	1300	263
South Australia	1322	281
New South Wales	1424	302
Australian Capital Territory	1529	302
Tasmania	1238	263
Queensland	1529	325
West Australia	1337	302
North Territory	1529	325

.

2.4.2. Hourly Energy Usage for Swimming Pool Pumping

In general, for outdoor swimming pools the pool pumps will run longer in swimming seasons than in non-swimming seasons (see

Table 14. Poop pump operating schedule [21].

Season	Cycles Per Day	On Time
Swimming	1.5	8 am
Non-swimming	1	8 am

). The swimming and non-swimming seasons are defined in [21], as shown in

Table 15. Swimming season.

Month	Season
January	Swimming
February	Swimming
March	Swimming
April	Swimming
May	Non-Swimming
June	Non-Swimming
July	Non-Swimming
August	Non-Swimming
September	Non-Swimming
October	Swimming
November	Swimming
December	Swimming

.

Pool pumps will start at the setting time and stop at the cycles being achieved. The pump off time is calculated as

$$Off time=On time+T_{cyc}\times Cycles per day$$

(17)

T_cyc = The number of hours of the swimming pool pump running a cycle; the pump is assumed to run 3 h for a cycle.

The pump needs to run 4.5 h a day in swimming seasons and 3 h a day in other seasons (

Table 16. Scheme of pool pumping.

Month	Pool Pumping	Number of Hours
January	8:00 am–12:30 pm	4.5
February	8:00 am–12:30 pm	4.5
March	8:00 am–12:30 pm	4.5
April	8:00 am–12:30 pm	4.5
May	8:00–11:00 am	3.0
June	8:00–11:00 am	3.0
July	8:00–11:00 am	3.0
August	8:00–11:00 am	3.0
September	8:00–11:00 am	3.0
October	8:00 am–12:30 pm	4.5
November	8:00 am–12:30 pm	4.5
December	8:00 am–12:30 pm	4.5
Number of hours for a year		1413

).

As shown in Table 16, pumps need to work 1413 h a year. So, the hourly pool pump energy usage can be calculated using Equation (18):

$$Powe{r}_{pump}=E_{pump}/1413$$

(18)

E_pump = Annual energy consumption (kWh) of the pool pump.

Power_pump = Hourly energy consumption (kWh) for pool pumping.

2.4.3. Cleaning Energy

The filter is assumed to run for 3 h every day. Cleaning on time is the same as pump on time (defined in Table 14). So, the cleaning off time can be expressed as:

$$Off Time=On Time+3$$

(19)

The hourly cleaning energy can be defined in Equation (20):

$$Powe{r}_{Clean}=Energ{y}_{Clean}/\left(3\times 365\right)$$

(20)

where:

Power_Clean = Hourly energy (in kWh) for pool cleaning;

Energy_Clean = Energy consumption for swimming pool cleaning (Table 13), in kWh.

2.5. Energy Consumption of Cooking and Other Plug-In Appliances

Energy consumption for cooking and other equipment will be addressed in this section. Except for cooking, the other plug-in appliances include white goods, computers and peripherals, audiovisual, small appliances, and other electronic and standby power.

Based on the study of Sustainability Victoria [31] and the Australian Building Codes Board (ABCB) [28], the yearly energy consumption of cooking and plug-in appliances per person was derived [21], which is described below.

Annual energy consumption for cooktops is estimated as [21]:

$$E_{Cooktop}=C_{CT}+N_{Occ}\times F_{CT}$$

(21)

where:

E_Cooktop = Annual energy consumption of cooktop (MJ/annual);

N_Occ = Occupant number of the dwelling (refer to Equation (4));

C_CT = Cooktop constant (Table 17);

F_CT = Cooktop factor (Table 17).

Annual energy consumption for ovens is estimated as [1]:

$$E_{Oven}=C_O+N_{Occ}\times F_O$$

(22)

where:

E_Oven = Annual energy consumption of oven (MJ/year);

N_Occ = Number of occupants in the dwelling (Equation (4));

C_O = Oven constant for relevant cooktop type (Table 17);

F_O = Oven factor for relevant cooktop type (Table 17).

The annual energy consumption for plug-in appliances is assessed as [21]:

$$E_{Plug}=7022.4+N_{Occ}\times 441.65$$

(23)

where:

E_Plug = Yearly energy consumption of plug-in appliances (MJ/year);

N_Occ = Occupant number in the dwelling (refer to Equation (4)).

Table 17. Cooking load factors [21].

	Gas Cooktop	Electric Cooktop	Induction Cooktop	Electric Oven	Gas Oven
Constant, Cx	800.13	518.47	356.47	426.53	849.87
Factor, Fx	266.67	172.77	118.77	142.23	283.37

Table 17. Cooking load factors [21].

	Gas Cooktop	Electric Cooktop	Induction Cooktop	Electric Oven	Gas Oven
Constant, Cx	800.13	518.47	356.47	426.53	849.87
Factor, Fx	266.67	172.77	118.77	142.23	283.37

Cooking and plug-in loads vary with the day and the seasons. The methodology of [21] developed for breaking annual cooking and plug-in loads into hourly data is adopted for this study. Hourly loads are estimated using Equation (24):

$$E_{x.hr=}{E}_x\times F_{x.hr}$$

(24)

where:

E_x.hr = Hourly energy consumption (MJ);

E_x = Yearly energy consumption for cooking/plug-in appliances (MJ/year);

F_x.hr = Hourly energy consumption factor defined in [21].

2.6. Module for On-Site Solar PV Generation

2.6.1. Electricity Generation from On-Site Solar PV

The electricity power produced from a PV array is estimated using Equation (25):

$$E_{sol}=f\times Y\times \frac{I_T}{1000\times I_S}$$

(25)

where:

E_sol = The hourly electricity power produced by a PV array (kW);

Y = The rated capacity of the PV array (kW) under standard test conditions [21];

I_S = The standard solar radiation (1 kW/m²) for rating the solar PV panel;

I_T = The global solar irradiation on the PV array surface (W/m²), described in [21];

f = The PV derating factor, which is used to account for system losses (see the section below), impacts of shading, etc.

Note: 1000 converts W to 1 kW.

2.6.2. PV System Losses

This study considers four different system losses that are associated with ambient temperature, soiling, DC wiring, and conversion, detailed in [21].

Considering the total system losses, the hourly electricity generation by the PV array can be calculated using Equation (25).

2.7. Energy Value and Whole-of-Home Rating

2.7.1. Societal Cost

To calculate the energy value of a dwelling, the “societal cost” of the associated energy source is applied in this study, which is estimated by summarizing the energy tariff and the cost related to the carbon emissions of the fuel. Three different tariffs (peak, off-peak, and shoulder) are used for electricity, and the timing of these three tariffs is defined in [21]. A flat tariff is applied for other non-electric sources. The societal energy costs are summarized in

Table 18. Energy value (societal cost) of fuel for NatHERS assessments [21].

Parameters	Societal Energy Costs for Calculations
	NSW	VIC	QLD	SA	WA	TAS	NT	ACT
Electricity—peak (c/kWh)	39.80	38.41	33.46	51.29	41.24	29.96	37.32	33.88
Electricity—shoulder (c/kWh)	25.97	25.17	21.91	33.20	26.83	19.34	24.30	21.86
Electricity—off-peak (c/kWh)	20.44	19.88	17.29	25.97	21.06	15.09	19.09	17.05
Electricity—controlled load (c/kWh)	14.07	20.61	16.74	20.43	12.73	13.50	26.90	14.83
PV Export (c/kWh)	10.08	13.34	11.11	11.64	7.89	9.71	26.85	9.21
Natural gas (c/MJ)	3.46	2.43	4.95	4.30	4.08	3.74	3.74	3.64
LPG (c/MJ)	5.58	5.58	5.58	5.58	5.58	5.58	5.58	5.58
Wood (c/MJ)	1.86	1.86	1.86	1.86	1.86	1.86	1.86	1.86

for the states and territories of Australia (New South Wales-NEW, Victoria-VIC, Queensland-QLD, South Australia-SA, West Australia-WA, Tasmania-TAS, Northern Territory-NT, and Australian Capital Territory-ACT).

2.7.2. The Energy Value of the Dwelling

In this study, the WoH hourly energy usage is calculated by seven modules, including hot water, lighting, space heating, space cooling, swimming pool and spa, plug-in appliances, and cooking. The WoH hourly electricity usage can be described as:

$$E_{Tot.hr}=E_{He.hr}+E_{Co.hr}+E_{Wh.hr}+E_{Li.hr}+E_{Sw.hr}+E_{Ck.hr}+E_{Pl.hr}$$

(26)

where:

E_Tot.hr = The WoH hourly electricity consumption (kWh);

E_He.hr = The hourly electricity consumption for space heating of all the zones in kWh (refer to Equation (1) for the space heating calculation of individual zones);

E_Co.hr = The hourly electricity usage for space cooling of all the zones in kWh (refer to Equation (1) for the space cooling calculation of individual zones);

E_Wh.hr = The hourly electricity consumption for water heating (kWh), refer to Equation (11);

E_Li.hr = The hourly electricity consumption for lighting (kWh), refer to Equation (16);

E_Sw.hr = The hourly electricity consumption for swimming pools (kWh), refer to Equation (18) for pool pumping and Equation (20) for pool cleaning;

E_Ck.hr = The hourly electricity consumption for cooking (kWh), refer to Equation (24);

E_Pl.hr = The hourly electricity consumption for plug-in appliances (kWh), refer to Equation (24).

The hourly electricity generation of on-site PV is estimated by the rooftop PV module (refer to Equation (25)). For this study, without energy storage when the whole-of-home hourly electricity consumption is greater than the hourly electricity generated by the rooftop PV system (limited by its availability at that hour), electricity imported from the grid is required and calculated as:

$$E_{Im.hr}=E_{Tot.hr}-E_{So.hr}$$

(27)

where:

E_Im.hr = The hourly electricity imported from the grid (i.e., net whole-of-home hourly electricity consumption, kWh);

E_Tot.hr = The whole-of-home electricity hourly electricity consumption (kWh), refer to Equation (26);

E_So.hr = The hourly electricity generation by the PV system (kWh), refer to Equation (25).

Electricity will be exported to the grid when the PV generation is greater than the whole-of-home electricity consumption. The hourly electricity exported to the grid can also be calculated using Equation (27) (but the value is negative). The PV export energy value is calculated by multiplying the societal cost of PV by the total exported electricity which is summarized as the hourly electricity exported to the grid.

Only annual energy consumption is required for other fuel sources. The energy value of the other fuel sources is calculated by multiplying the annual energy consumption by the relevant societal costs.

The net energy value of the assessed dwelling (E.V_Assessment) is calculated by adding the energy value of the imported electricity with the other fuel sources minus the energy value of the PV export.

2.7.3. The Energy Value of the Benchmark Dwelling

The calculation of the energy rating of the assessed dwelling is described in [21], in which the benchmark building energy value is used as a reference. The benchmark building defined in [21] is a 7-star building with the same floorplan, climate zone, and orientation of the assessed dwelling for estimating loads of the benchmark dwelling.

For calculating the annual space heating/cooling load of the benchmark dwelling, an adjustment factor is used, which is defined in [21]:

$$Adjustment Factor=\frac{E_{Rat}}{E_{7-star}}$$

(28)

where:

E_Rat = Yearly air conditioning energy requirements of the assessed dwelling (MJ/m²);

E_7-star = Yearly air conditioning energy requirements of the benchmark dwelling with an equivalent 7-star in the climate zone for the assessed house (MJ/m²).

Adjustment factors for all 69 NatHERS climate zones in Australia were developed in [21] for rating from 0.5 to 10 stars with increments of 0.1 star.

As mentioned above, the benchmark building is powered by electricity for space heating and cooling, lighting, and plug-in appliances and cooking (if an electric cooktop or/and oven is installed). For energy value calculation of the benchmark dwelling, the yearly electricity usage for each of these modules is calculated and then segmented into the peak, off-peak, and shoulder components with the relevant percentages of the assessed dwelling. As it is assumed that the benchmark dwelling is not installed with an on-site solar PV system, its energy value of the electricity usage is calculated by multiplying the data (of peak, off-peak, and shoulder) with the associated societal costs (Table 18). The energy value of gas consumption for water heating and cooking (if a gas cooktop or/and oven is installed, annual gas) is calculated by multiplying the annual data by the relevant societal costs. The total energy value of the benchmark dwelling is obtained by summarizing the electric and non-electric energy values.

2.7.4. Energy Rating of the Assessed Dwelling

The benchmark house energy value is used as a reference for the energy rating of the assessed dwelling [21]. The rating scale is defined as between 0 and 150 in [21], in which 0 is representative for the worst performance of existing housing, 150 for the best performance, 100 for net-zero societal cost, 50 (Benchmark 1) for the benchmark dwelling, and 60 (Benchmark 2) for 70% of the benchmark regulated loads, the plug-in and cooking loads.

These values are expressed as

$$E.V_{50}=Benchmark Regulated+Plug and Cooking$$

(29)

$$E.V_{60}=0.7\times Benchmark Regulated+Plug and Cooking$$

(30)

$$E.V_{100}=0$$

(31)

$$E.V_0=W.F\times Benchmark Regulated+Plug and Cooking$$

(32)

The “Worst Factor” (WF) is defined in [21] based on a building with a 1-star thermal shell installed with electric space heating and water heating, and ducted 1.5-star reverse-cycle cooling for all the NatHERS climate zones, which indicates the worst reasonable expectation of the assessed dwelling.

Depending on where the energy value (E.V_Assessment) of the assessed dwelling is relative to E.V₅₀ and E.V_60, the rating scale is generated by these four “break points”:

When E.V_Assessment is E.V₅₀ < E.V_Assessment ≤ E.V₀, the rating scale is calculated as:

$$Rating Scale=50-\left(E.V_{Assessment}-E.V_{50}\right)\times \frac{50}{E.V_0-E.V_{50}}$$

(33)

When E.V_Assessment is E.V₆₀ ≤ E.V_Assessment ≤ E.V₅₀, the rating scale is calculated as:

$$Rating Scale=60-\left(E.V_{Assessment}-E.V_{60}\right)\times \frac{10}{E.V_{50}-E.V_{60}}$$

(34)

When E.V_Assessment is E.V₁₀₀ ≤ E.V_Assessment < E.V₆₀, the rating scale is calculated as:

$$Rating Scale=100-E.V_{Assessment}\times \frac{40}{E.V_{60}}$$

(35)

For whole-house energy value ratings, an integral number is used by rounding down to the nearest whole number (i.e., 40.9 is 40, 60.1 is 60).

3. Case Study

With the modules described in the section above, the WoH energy rating software for existing dwellings is developed by implementing them into the AusZEH design tool [1,6]. The main section of the software is shown in Figure 3. The top section includes the settings for calculation of energy requirements for air conditioning and star rating (the left six subsections from Project to Ventilation). The settings for energy consumption calculation for related modules are described in the remaining subsections. Subsection Summary provides the annual energy consumption of the assessed dwelling. Its details are shown in the middle section, including electricity imported from/exported to the grid, electricity generated by the solar panel, total annual consumption of electricity, gas, and other sources, and related energy value and rating scale. The annual energy consumption of “All-day” and “Work-day” for air conditioning is also listed.

The bottom section describes the outputs of the reference dwelling.

3.1. Energy Consumption, Energy Value, and Rating

For this case study, a detached single-storey double-cavity brick house built in the 1990s (Figure 4) is used to investigate the energy consumption and rating of dwellings under different climates of Australian capital cities. It faces north. The gross floor area of the dwelling is 293 m², and the net air-conditioned floor area is 207 m². The roof space is insulated with R 1.5 glass fiber batt, and all the windows are aluminum single-glazed with large gaps.

To make sure the modules are being implemented properly, for each module the simulated hourly data over a period of one year were tested against the corresponding data from the Excel files. We found that the results are identical to the fourth decimal places used.

The tool can be used for building shell energy star rating and WoH energy prediction under Typical Meteorological Year (TMY) weather files. Based on the predicted annual loads for space heating and cooling, a star rating between 0 and 10 is assigned to the assessed dwelling for the specified NatHERS climate zone. At present, there are 69 NatHERS climate zones defined with related TMY weather files across Australia.

The Building Code of Australia introduced the first minimum energy-efficiency requirements for residential buildings in 2003 [32], updated to 5 stars in 2006 and then to 6 stars in 2011. A 7-star rating is required by the NCC 2022 (https://ncc.abcb.gov.au/editions/ncc-2022/preview/volume-one/j-energy-efficiency, accessed on 25 September 2023). As expected, the energy performance of the residential buildings will vary from region to region if they were built in the 1990s or earlier. This is demonstrated in this case study (Figure 5). As shown in Figure 5, the highest star of 4.7 is achieved for the assessed house located in Perth and the lowest of 2.7 stars in Darwin.

Two scenarios of energy supply (electricity only and natural gas available) are analyzed for this case study. With a natural gas supply being available, it is assumed that the house is installed with a 1-star ducted gas room heater, a 1-star instantaneous gas hot water heater, and a gas cooktop and oven. With electricity supply only, it is assumed that the house is installed with a 1-star ducted single-speed heat pump for room heating, an instant electric water heater, and an electric cooktop and oven. In both cases, it is assumed that the house is installed with a1-star ducted single-speed heat pump for room cooling. The house has 5 halogens installed in the family/kitchen room and LED lighting installed for other rooms. The house has no swimming pool and rooftop PV installed. The annual WoH and individual module energy consumptions are shown in

Table 19. Yearly energy usage of the dwelling in the eight cities for natural gas supply being available.

Location	Heating (kWh)	Heating Gas (MJ)	Cooling (kWh)	Lighting (kWh)	Hot Water Gas (MJ)	Plug-in (kWh)	Cooktop Gas (MJ)	Oven Gas (MJ)	Total Gas (MJ)	Total Electricity (kWh)
Adelaide	213.7	51,972.5	1382.3	793.2	23,323.7	2407.1	1792.3	1904.6	78,993.1	4796.3
Brisbane	28.6	6949.4	2164.4	793.2	23,323.7	2407.1	1792.3	1904.6	33,970	5393.3
Canberra	605.6	147,289.9	674.7	793.2	22,969.3	2407.1	1792.3	1904.6	173,956.1	4480.6
Darwin	0	0	17,533.8	793.2	22,969.3	2407.1	1792.3	1904.6	26,666.2	20,734.1
Hobart	646.5	157,254.9	25.3	793.2	23,618.5	2407.1	1792.3	1904.6	184,570.3	3872.1
Melbourne	273	66,396.6	835.9	793.2	24,353.7	2407.1	1792.3	1904.6	94,447.2	4309.2
Perth	140.6	34,192	2019.1	793.2	23,618.5	2407.1	1792.3	1904.6	61,507.4	5360
Sydney	110.5	26,877.2	1093.3	793.2	24,353.7	2407.1	1792.3	1904.6	54,927.8	4404.1

and

Table 20. Yearly energy usage of the dwelling in the eight cities for electricity supply only.

Location	Heating (kWh)	Cooling (kWh)	Lighting (kWh)	Hot Water (kWh)	Plug-In (kWh)	Cooktop (kWh)	Oven (kWh)	Total Electricity (kWh)	Ratio of Electricity Use for Space H/C to Total Electricity
Adelaide	3125.1	1382.3	793.2	2789	2407.1	322.6	265.5	11,084.8	40.7
Brisbane	446.9	2164.4	793.2	3857.4	2407.1	322.6	265.5	10,257.1	25.5
Canberra	9462.8	674.7	793.2	2907.8	2407.1	322.6	265.5	16,833.7	60.2
Darwin	0	17,533.8	793.2	2907.8	2407.1	322.6	265.5	24,230	72.4
Hobart	10,112.4	25.3	793.2	2907.8	2407.1	322.6	265.5	16,833.9	60.2
Melbourne	4269.7	835.9	793.2	2837.4	2407.1	322.6	265.5	11,731.4	43.5
Perth	2055.9	2019.1	793.2	2789	2407.1	322.6	265.5	10,652.4	38.3
Sydney	1616.1	1093.3	793.2	2718.1	2407.1	322.6	265.5	9215.9	29.4

for the two scenarios of energy supply, respectively.

As expected, no energy is required for room heating in the tropical region (Darwin) and a small amount of energy is required for room cooling in Hobart. In heating-dominated regions, such as Hobart and Canberra, a large amount of energy is required for room heating. As shown in Table 20, with the scenario of electricity supply only, the electricity usage for air conditioning accounts for 72.4% (the highest) of the WoH energy consumption in Darwin and 25.5% (the lowest) in Brisbane. The ratio is 29.4% in Sydney. The ratios are over 60% in Canberra and Hobart. The annual electricity usage is greater than 24,300 kWh in Darwin and over 10,000 kWh in other cities (except Sydney). With the scenario of gas supply available, around or less than 5000 kWh is consumed in all the cities except Darwin. For both energy supply scenarios, as shown in

Table 21. Energy value and rating scale of the dwelling in the eight cities for gas supply being available.

Location	Grid Imported (kWh)	Grid Imported (A$)	Gas Value (A$)	Net Energy Value (A$)	Energy Rating Scale
Adelaide	4796.3	1869.3	2393.8	4263.1	14
Brisbane	5393.2	1376.2	527	1903.2	48
Canberra	4480.6	1140.6	5495.8	6636.6	0
Darwin	20,734.2	5929.7	138.3	6067.9	6
Hobart	3872.1	857.9	6019.6	6877.5	0
Melbourne	4309.2	1256.6	1703.3	2959.9	6
Perth	5359.9	1699	1545.9	3244.8	22
Sydney	4404.1	1317.5	1057.9	2375.3	34

and

Table 22. Energy value and rating scale of the dwelling in the eight cities for electricity supply only.

Location	Grid Imported (kWh)	Net Energy Value (A$)	Energy Rating Scale
Adelaide	11,085	4373.5	13
Brisbane	10,257	2640.8	34
Canberra	16,833.9	4394.9	0
Darwin	24,229.5	6953.9	0
Hobart	16,834.5	3884	0
Melbourne	11,731.4	3481.9	0
Perth	10,653	3385.7	20
Sydney	9215.9	2804.7	26

, it is the cheapest to operate the dwelling in Brisbane and then relatively cheaper in Sydney, Melbourne, and Perth. The most expensive city is Darwin under energy supply with electricity only and Hobart under energy supply with gas being available. The worst energy performance (i.e., the rating scale being 0) happened in Melbourne, Darwin, Hobart, and Canberra under energy supply of electricity only and Canberra and Hobart under energy supply of gas being available. For both energy supply scenarios, the building has the best energy performance in Brisbane. But it is still under the benchmark building (the rating being lower than 50).

3.2. Retrofitting for Net-Zero Societal Cost Housing

Australia aims to be zero emissions in 2050, and fossil fuel will not be used in the building section. With electricity supply being available only, this tool is used to investigate potential options for zero-energy (and carbon) housing with low/net-zero societal cost operation. The strategy in this study is to improve the building envelope, update the equipment and appliances with high energy efficiency, and then install PV systems large enough to achieve zero energy. For existing housing, in general the orientation of the assessed building is unable to change and difficult (or expensive) for insulating external walls and floors (in particular for the assessed house with a slab-on-ground floor). In this case study, the house energy performance is improved by sealing the leakage gaps of the windows and doors and exhaust fans, insulating the ceiling with R5, and replacing the windows with timber double-glazed with Argon fill (very high energy performance window in the market) and installing 40% shade cloth to the windows outdoors, replacing the water heating equipment by solar water heating boosted by electricity, updating the air conditioning with a 5-star ducted heat pump system, and replacing the 5 halogens with LED lighting.

With the retrofitting mentioned above, the energy performance of the updated building is improved significantly (Figure 6). Note that a rating of 8.3 stars (the greatest) is achieved in Perth and 5.6 stars (the lowest) in Hobart. It also achieves more than 7 stars in Adelaide and Sydney, and more than 6 stars in the other cities.

Table 23. The annual energy consumption of the dwelling updated to achieve zero energy (carbon) in the eight cities.

Location	Heating (kWh)	Cooling (kWh)	Lighting (kWh)	Hot Water (kWh)	Plug-in (kWh)	Cooktop (kWh)	Oven (kWh)	Total Electricity (kWh)	Electricity Saving (%)
Adelaide	433.5	263.4	654.5	650	2407.1	322.6	265.5	4996.6	54.9
Brisbane	20.1	456.7	654.5	172.5	2407.1	322.6	265.5	4299.0	58.1
Canberra	1590.6	94.4	654.5	570	2407.1	322.6	265.5	5912.7	64.9
Darwin	0	3833.8	654.5	134.7	2407.1	322.6	265.5	7618.2	68.6
Hobart	1680.1	2	654.5	1057.9	2407.1	322.6	265.5	6389.7	62.0
Melbourne	609	165.5	654.5	890.6	2407.1	322.6	265.5	5314.8	54.7
Perth	221.5	373.2	654.5	362.2	2407.1	322.6	265.5	4606.6	56.8
Sydney	170.2	220	654.5	528.8	2407.1	322.6	265.5	4568.7	50.4

provides the yearly electricity consumption of the retrofitted dwelling. From Table 20 and Table 23, it can be seen that energy consumption for space H/C is reduced significantly, and more than half of the WoH electricity usage is saved in all the regions after the dwelling was upgraded. Darwin has the greatest saving (68.6%), and Sydney has the smallest saving (50.4%).

To achieve zero-energy (carbon) residential buildings, the electricity produced by an on-site renewable energy system needs be greater than the WoH electricity usage. The tool developed in this study is applied for sizing an on-site PV system for a zero-energy (carbon) dwelling.

Table 24. PV systems for zero-energy (carbon) housing in the eight cities after the house was updated for net-zero/low societal cost.

Location	PV Size (kW)	PV Generation (kWh)	Total Electricity Demand (kWh)	PV Exported (kWh)	PV Exported (A$)	Grid Imported (kWh)	Grid Imported (A$)	Net Energy (kWh)	Net Energy Value (A$)	Energy Rating Scale
Adelaide	3.5	5577.1	4996.6	3570.6	415.6	2990.3	1175.8	580.3	760.2	85
Brisbane	3.0	5144.1	4299.0	3459.9	384.4	2614.7	681.9	845.2	297.5	91
Canberra	4.0	6507.7	5912.7	4318.3	397.7	3723	975.4	595.3	577.7	85
Darwin	5.0	8430.4	7618.2	5736.7	1540.3	4924.5	1359.1	812.2	−181.2	103
Hobart	5.0	6667.2	6389.7	4267.6	414.4	3990.3	927.5	277.3	513.1	85
Melbourne	4.0	5661.3	5314.8	3536.5	471.8	3190	947.5	346.5	475.7	86
Perth	3.0	5010.9	4606.6	3208.7	253.2	2804.6	891.2	404.1	638	85
Sydney	3.5	5320	4568.7	3468.3	349.6	2716.8	838.9	751.5	489.3	87

summarizes the sizing results for the retrofitted dwelling in the eight cities. The largest (5 kW) solar PV is required for the retrofitted dwelling located in Darwin and Hobart, the smallest (3 kW) in Brisbane and Perth. Sydney and Adelaide need 3.5 kW, and Melbourne and Canberra need 4 kW. With the dwelling retrofitted and the installation of a 5 kW solar PV system, Darwin achieves free to operate the retrofitted house (negative net energy value, i.e., the household will be paid for by the retail electricity company) in Darwin. Several hundred Australian dollars are still required in the other cities.

4. Discussions

As shown in the case study above, to achieve a zero-emission building section (fossil fuel will not be used), there are three measures to reduce energy consumption and optional costs of existing housing when occupant behaviors are not considered:

• Reducing energy demand for space heating and cooling by retrofitting the dwelling building shell to high energy performance;
• Replacing old and low-energy-efficient equipment and appliances with new and high-energy-efficient ones; and
• Installing an on-site renewable energy and battery system.

In general, in Australia, sealing the gaps and leakages of windows and doors et al. and insulating roof space are cost-effective measures to retrofit the building shell to high energy performance. Replacing single-glazed windows with double-glazed ones (or other high-performance windows) is relatively expensive. Replacing halogen lights with LEDs, installing water-saving shower heads plus a solar booster hot water system, and replacing old and low-energy-efficient space heating and cooling appliances with inverter heat pumps are cost-effective approaches to save energy with high-energy-efficient appliances. Replacing the clothes washer, dishwasher, and refrigerator is relatively less cost-effective. On-site solar PV installation is more cost-effective than battery installation.

This study focuses on the benchmark tool development and detailed cost-effective analysis is not provided due to the length limitation of the paper. Please refer to our previous studies [33] for a detailed cost-effective analysis and prioritized energy-saving options for Australian residential buildings under current and future changing climate.

Note that the case study was conducted under TMY weather files. Climate change has significant impacts on energy requirements for space heating and cooling and also some impacts on hot water (cold water inlet temperature and hot water demand) and solar PV generation (solar radiations and the solar PV system losses related to temperature). Further research is required for this tool to be used for future changing climate.

5. Conclusions

With the major assumptions/settings adopted from the Method [21] and Scorecard [23], we have developed a benchmark software for Australian housing retrofitting. The tool was developed by implementing related modules into the AusZEH design tool. The modules include energy usage for room air conditioning and other household appliances. Modules of an on-site solar panel and energy value and scale rating are also developed and implemented. The comparisons of hourly and annual data for energy consumption of each module and whole house between the tool and Excel files show that the modules were implemented correctly.

To demonstrate functions of the tool for building retrofitting, a case study was carried out for the eight capital cities of Australian states and territories. For the 1990s detached residential building, the results show that Darwin has the lowest star rating of 2.7 and Perth has the highest star rating of 4.7. As expected, Darwin and Hobart need the greatest amount of energy for space cooling and space heating, respectively. To operate the house, Darwin is the most expensive city (near A$7000) with electricity supply only, and Hobart is the most expensive city (near A$6900) with natural gas supply being available. For both energy supply scenarios, Brisbane is the cheapest city. The energy rating scale of the assessed house is 0 (i.e., the worst energy performance, as mentioned previously) in Canberra, Darwin, Hobart, and Melbourne with electricity supply only and in Canberra and Hobart when gas supply is available.

With the assessed building envelope being upgraded to 6 or more stars and replacing old equipment and appliances with high-energy ones, the energy was saved more than 50% in all the eight cities. A 5 kW on-site solar PV needs be installed for the assessed house to be zero-energy (carbon) housing in Darwin and Hobart. Brisbane and Perth need only 3 kW. For the other cities, the PV sizes are between 3 kW and 5 kW. With installation of the on-site PV system, only Darwin achieves free to run the retrofitted dwelling given the tariffs used in this study.

The main contribution of this study is the WoH energy rating tool development with hourly data of each module, including calculations of total annual energy consumption and carbon emissions, energy value, and rating scale. It is a powerful tool for evaluating pathways for housing retrofitted to be triple-zero (zero energy, zero emissions, and zero operational cost) housing in Australia.

Note that the tool was developed based on the National Calculation Method [21] and Scorecard [23], which were based on survey and monitoring studies made for Australian households. The tool can be used for energy rating purposes to represent “typical” or average energy consumption of Australian households. Some assumptions/settings of the tool may not reflect the actual operations of a specific dwelling. Our previous study of the AusZEH design tool [24] was made for this purpose.