Text Box: AccuRate and the Chenath Engine for Residential House Energy Rating

Dong Chen

September, 2016

Enquiries should be addressed to:

Dong Chen, CSIRO Land and Water

 

Important Disclaimer

While all due care and attention has been taken to establish the accuracy of the material presented, CSIRO and the author disclaim liability for any loss which may arise from any person acting in reliance upon the contents of this document.

 




EXECUTIVE SUMMARY

AccuRate is a software tool used for the calculation of annual space heating/cooling requirements of residential buildings. It is currently used for compliance with the building code to regulate energy efficiency of new houses. AccuRate provides a useful tool for optimising energy efficient house designs for Australian local climates.

AccuRate includes a graphical user interfaces (GUI) written in Delphi and a simulation engine written in fortran for thermal heat flows in the house. The simulation engine, known as the Chenath engine, and its previous generations has been developed over five decades by CSIRO. The methodologies, algorithms and rules implemented in AccuRate and the Chenath engine may have been published in various journal or conference papers, in reports or technical notes over the years. However, a single repository is required to list the algorithms and methodologies used. Commissioned by the Department of Climate Change and Energy Efficiency, this document forms a single repository for AccuRate and the Chenath engine. This document will be updated regularly whenever adequate new information is available to CSIRO.


1.        BACKGROUND

The Australian Government continuously supports residential energy efficiency and low carbon emission strategies and schemes, demonstrated by its substantial investment in various energy efficiency initiatives, in particular, the Nationwide House Energy Rating Scheme (NatHERS). During the last two decades, NatHERS accredited software tools such as NatHERS, AccuRate, FirstRate and BERS house energy rating tools have been successfully adopted and played important roles in energy efficient house designs in Australia. These tools contribute to gain in-depth understanding of house energy use in Australian climates and influence green building practices.

Served as the benchmark tool for the NatHERS scheme, AccuRate includes a graphical user interfaces (GUI) written in Delphi and a simulation engine written in fortran for thermal heat flows in the house. The simulation engine, known as the Chenath engine, and its previous generations has been developed over five decades by CSIRO. The methodologies, algorithms and rules implemented in AccuRate and the Chenath engine may have been published in journal or conference papers, in reports or technical notes over the years. However, a single repository is required to list the algorithms and methodologies used.

Commissioned by DCCEE, CSIRO initiated a repository for the collection and documentation of the methodologies, algorithms and rules implemented in AccuRate and the Chenath engine. This document forms a single repository for AccuRate and the Chenath engine. The document will be updated regulatory whenever adequate new information is available to CSIRO.

2.        HISTORY OF ACCURATE AND THE CHENATH ENGINE

AccuRate’s Chenath engine and its predecessors CARE, STEP and ZSTEP have been evolved and enhanced over the last five decades. CSIRO’s research and development in building energy modelling went back to 1950’s. Dr R.W.R. Muncey and his co-works were among the pioneers of computational building thermal modelling [1-4]. In 1950’s, Muncey at CSIRO Division of Building Research developed a single zone harmonic analysis/synthesis program CARE. In early 1960’s, Muncey developed the STEP program for modelling one zone building using the matrix method which established the core methodology of today’s AccuRate Chenath engine [5,6]. The STEP program was subsequently refined by J.W. Spencer. In 1977, STEP was extended by P.J. Walsh to handle multi-zoned buildings and was named as ZSTEP [5,6].

 

From 1984 to 1986, A.E. Delsante and his colleagues developed the house thermal modelling software CHEETAH (Cooling and HEating Energy Tool for ArcHitects) using ZSTEP as the modelling engine and a TurboPascal (DOS) User Interface [7]. In 1990, the 1st generation nationwide house energy rating tool NatHERS was released with the Chenath engine (improved ZSTEP) and an ObjectVision User Interface. In 2003, NatHERS was further upgraded to the 2nd generation NatHERS tool - AccuRate with an enhanced Chenath engine particularly the inclusion of air flow modelling to account for natural ventilation and a Delphi User interface [8].

 

From 2008, D. Chen led the further development of AccuRate and the Chenath engine. AccuRate has been upgraded to AccuRate Sustainability which includes energy and CO2 emission calculations for lighting, hot-water system and the water usage modules.

 

3.        FUNDAMENTALS

The Chenath engine is one of the first building simulation tools which couple a frequency response multi-zone thermal model and a multi-zone air flow model for energy requirement calculation for residential buildings. Taking into account the local climate and building fabrics, the Chenath engine automatically switches the building operation between mechanical air conditioning and natural ventilation operation whenever natural ventilation satisfies occupant thermal comfort. The Chenath engine can calculate hourly heating and cooling energy requirement over a period of one year or multiple years.

3.1           Matrix Method

The matrix method of the Chenath engine was based on the pioneer work by Muncey published in 1953.

 

Muncey, R.W.R., The calculation of temperatures inside buildings having variable external conditions, Australian Journal of Applied Science, 4(2), 1953, 189-196.

3.2           Multi-Zone Thermal Modelling

The Chenath engine uses response factor method for the thermal modelling in multi-zone buildings. Detailed descriptions of the multi-zone response factor calculation and the treatment of internal walls, radiative heat transfer, the calculation of heating and cooling requirements can be found in Walsh and Delsante [9].

 

Walsh PJ and Delsante AE. Calculation of the thermal behaviour of multi-zone buildings, Energy and Buildings 1983; 5: 231-242.

3.3           Multi-Zone Airflow Modelling

The Chenath engine v2.13 in AccuRate v1.1.4.1 and AccuRate Sustainability v2.0.2.13 uses the MIX 2.0 (Multi-zone Infiltration and eXfiltration) air flow model developed by Li et al. [10]. This model was found to diverge when model some building designs with permanent openings. An improved air flow model has been developed and implemented in the Chenath engine [11]. This new engine is now implemented in the existing AccuRate Sustainability V2.3.3.13.

 

Li Y, Delsante A, Symons J. Prediction of natural ventilation in buildings with large openings. Building and Environment 2000; 35: 191-206.

 

Ren Z.G. and Chen Z.D., Enhanced air flow modelling for AccuRate – A nationwide house energy rating tool in Australia, Building and Environment 2010; 45: 1276–1286.

 

4.        INPUT, BEHAVIOURAL SETTINGS AND ASSUMPTIONS

4.1           Thermal Properties of Building Materials

A list of the materials and their properties can be found in the document “Material Properties Used in NatHERS Software Tools”.

 

4.2           Climatic Data

AccuRate and the Chenath engine uses Reference Meteorological Year (RMY) weather files which adopt the Australian Climatic Data Bank (ACDB) weather file format originally defined by CSIRO and the Australian Bureau of Meteorology. RMY weather data are specially selected so that it represents the range of weather phenomena for the location and gives annual averages that are consistent with the long-term averages for the location in question. RMY weather files currently used for AccuRate were derived from the Australian Bureau of Meteorology weather data for the period from 1976 to 2004 [12]. RMY weather files for 69 locations in Australia are available in the existing AccuRate software as listed in Table 1.

 

NATIONWIDE HOUSE ENERGY RATING SCHEME (NatHERS) – SOFTWARE ACCREDITATION PROTOCOL; 2012

 


Table 1. ACDB climate zones

ACDB Climate Zones

Location

Longitude

Latitude

Postcode

State

1

Darwin

130.9

-12.4

800

NT

2

Pt Hedland

118.6

-20.4

6721

WA

3

Longreach

144.3

-23.4

4730

QLD

4

Carnarvon

113.7

-24.9

6701

WA

5

Townsville

146.8

-19.3

4810

QLD

6

Alice Springs

133.9

-23.8

870

NT

7

Rockhampton

150.5

-23.4

4700

QLD

8

Moree

149.9

-29.5

2400

NSW

9

Amberley

152.7

-27.6

4306

QLD

10

Brisbane

153.1

-27.4

4000

QLD

11

Coffs Harbour

153.1

-30.3

2450

NSW

12

Geraldton

114.7

-28.8

6530

WA

13

Perth

115.9

-31.9

6000

WA

14

Armidale (old Tamworth)    

151.7

-30.5

2350

NSW

15

Williamtown

151.8

-32.8

2300

NSW

16

Adelaide

138.6

-34.9

5000

SA

17

Sydney RO (Observatory Hill)

151.2

-33.9

2000

NSW

18

Nowra

150.5

-35

2541

NSW

19

Charleville

146.3

-26.4

4470

QLD

20

Wagga

147.5

-35.2

2650

NSW

21

Melbourne RO

145

-37.8

3000

VIC

22

East Sale

147.1

-38.1

3852

VIC

23

Launceston (Ti Tree Bend)

147.1

-41.4

7250

TAS

24

Canberra

149.2

-35.3

2600

ACT

25

Cabramurra (old Alpine)

148.4

-35.9

2629

NSW

26

Hobart

147.5

-42.8

7000

TAS

27

Mildura

142.1

-34.2

3500

VIC

28

Richmond

150.8

-33.6

2753

NSW

29

Weipa

141.9

-12.7

4874

QLD

30

Wyndham 

128.1

-15.5

6740

WA

31

Willis Island

150

-16.3

4871

QLD

32

Cairns

145.8

-16.9

4870

QLD

33

Broome

122.2

-18

6725

WA

34

Learmonth

114.1

-22.2

6707

WA

35

Mackay

149.2

-21.1

4740

QLD

36

Gladstone

151.3

-23.9

4680

QLD

37

Halls Creek

127.7

-18.2

6770

WA

38

Tennant Creek

134.1

-19.6

860

NT

39

Mt Isa

149.2

-21.1

4825

QLD

40

Newman 

119.7

-23.4

6753

WA

41

Giles

128.3

-25

6438

WA

42

Meekatharra

118.5

-26.6

6642

WA

43

Oodnadatta

135.5

-27.6

5734

SA

44

Kalgoorlie

121.5

-30.8

6430

WA

45

Woomera

136.8

-31.2

5720

SA

46

Cobar

145.8

-31.5

2835

NSW

47

Bickley   

116.1

-32

6076

WA

48

Dubbo        

148.6

-32.2

2830

NSW

49

Katanning

117.6

-33.7

6317

WA

50

Oakey

151.7

-27.4

4401

QLD

51

Forrest

128.1

-30.8

6434

WA

52

Swanbourne

115.8

-32

6010

WA

53

Ceduna

133.7

-32.1

5690

SA

54

Mandurah

115.7

-32.5

6210

WA

55

Esperance

121.9

-33.8

6450

WA

56

Mascot (Sydney Airport)

151.2

-33.9

2020

NSW

57

Manjimup

116.1

-34.2

6258

WA

58

Albany

117.8

-35

6330

WA

59

Mt Lofty 

138.7

-35

5240

SA

60

Tullamarine (Melbourne Airport)

144.9

-37.7

3020

VIC

61

Mt Gambier

140.8

-37.8

5290

SA

62

Moorabbin  

145.1

-38

3189

VIC

63

Warrnambool 

142.4

-38.3

3280

VIC

64

Cape Otway  

143.5

-38.9

3220

VIC

65

Orange

149.1

-33.4

2800

NSW

66

Ballarat   

143.8

-37.5

3350

VIC

67

Low Head  

146.8

-41.1

7253

TAS

68

Launceston Airport

147.2

-41.5

7120

TAS

69

Thredbo (Village)

148.3

-36.5

2625

NSW

 

 

4.3           Infiltration

In AccuRate, the infiltration rate, in air changes per hour for each zone, is specified as A + B*v, where v is the hourly wind speed (m/s) from the AccuRate weather files multiplied by a terrain factor. For details of the infiltration calculation, please refer to the following document [13]:

Download:

Chen D., Infiltration Calculations in AccuRate, 2013

4.4           Internal Heat Gains

The heat loads in Tables 2 to 4 are for a 160 m2 dwelling with two adults and two children, with a floor area split of 80 m2 for all the living areas and 80 m2 for all the bedroom areas. The load is for the one hour period up to the time stated, i.e. a time of 1:00 am indicates the period between midnight and 1:00 am.

Table 2 - Internal sensible and latent heat loads - for living spaces, including kitchens [12]

Time

Sensible heat load (Watts)

Latent heat load (Watts)

Appliances and cooking

Lighting

People

Total

1:00 am

100

0

0

100

0

2:00 am

100

0

0

100

0

3:00 am

100

0

0

100

0

4:00 am

100

0

0

100

0

5:00 am

100

0

0

100

0

6:00 am

100

0

0

100

0

7:00 am

100

0

0

100

0

8:00 am

400

180

280

860

400

9:00 am

100

180

280

560

200

10:00 am

100

0

140

240

100

11:00 am

100

0

140

240

100

Noon

100

0

140

240

100

1:00 pm

100

0

140

240

100

2:00 pm

100

0

140

240

100

3:00 pm

100

0

140

240

100

4:00 pm

100

0

140

240

100

5:00 pm

100

0

140

240

100

6:00 pm

100

300

210

610

150

7:00 pm

1100

300

210

1610

750

8:00 pm

250

300

210

760

150

9:00 pm

250

300

210

760

150

10:00 pm

250

300

210

760

150

11:00 pm

100

0

0

100

0

Midnight

100

0

0

100

0

 

Table 3 - Internal sensible and latent heat loads - for living spaces that do not include a kitchen [12]

Time

Sensible heat load (Watts)

Latent heat load (Watts)

Lighting

People

Total

 

1:00 am

0

0

0

0

2:00 am

0

0

0

0

3:00 am

0

0

0

0

4:00 am

0

0

0

0

5:00 am

0

0

0

0

6:00 am

0

0

0

0

7:00 am

0

0

0

0

8:00 am

180

280

460

140

9:00 am

180

280

460

140

10:00 am

0

140

140

70

11:00 am

0

140

140

70

Noon

0

140

140

70

1:00 pm

0

140

140

70

2:00 pm

0

140

140

70

3:00 pm

0

140

140

70

4:00 pm

0

140

140

70

5:00 pm

0

140

140

70

6:00 pm

300

210

510

105

7:00 pm

300

210

510

105

8:00 pm

300

210

510

105

9:00 pm

300

210

510

105

10:00 pm

300

210

510

105

11:00 pm

0

0

0

0

Midnight

0

0

0

0

 


 

Table 4 - Internal sensible and latent heat loads - for bedrooms [12]

Time

Sensible heat load (Watts)

Latent Heat load

(Watts)

Lighting

People

Total

 

1:00 am

0

200

200

100

2:00 am

0

200

200

100

3:00 am

0

200

200

100

4:00 am

0

200

200

100

5:00 am

0

200

200

100

6:00 am

0

200

200

100

7:00 am

0

200

200

100

8:00 am

0

0

0

0

9:00 am

0

0

0

0

10:00 am

0

0

0

0

11:00 am

0

0

0

0

Noon

0

0

0

0

1:00 pm

0

0

0

0

2:00 pm

0

0

0

0

3:00 pm

0

0

0

0

4:00 pm

0

0

0

0

5:00 pm

0

0

0

0

6:00 pm

0

0

0

0

7:00 pm

0

0

0

0

8:00 pm

100

0

100

0

9:00 pm

100

0

100

0

10:00 pm

100

0

100

0

11:00 pm

100

200

300

100

Midnight

0

200

200

100

 

 

 

 

 

4.5           Thermostat Settings

Cooling Thermostat Settings

The NatHERS Scheme requires that for an energy assessment, all conditioned spaces must be maintained within a certain range of thermal comfort. The upper temperature limit for thermal comfort in each Climate Region is indicated in Table 5. These settings represent an assumed thermostat trigger point for the operation of space cooling appliances. Baharun el al. [14] gave a brief description on how these cooling thermostat settings are derived.

The cooling thermostat for each climate zone is set equal to the neutral temperature in January for the corresponding climate zone defined in Eq. (1), up to a limit of 28.5°C, above which both the neutral temperature and the cooling thermostat are taken to be 28.5°C. The low limit of the thermostat is set at 22.5°C. If the neutral temperature in January is below 22.5°C, both the neutral temperature and the cooling thermostat are taken to be 22.5°C.

 

Tn = 17.8 + 0.31Tm                                                                     (1)

 

where Tn is the neutral temperature in January and Tm is the mean January ambient air temperature.

 

Heating Thermostat Settings

In the NatHERS scheme, the heating thermostat settings are as follows:

  • For living spaces (including kitchens and other spaces typically used during the waking hours): a heating thermostat setting of 20o Celsius.
  • For sleeping spaces (including bedrooms, bathrooms and dressing rooms, or other spaces closely associated with bedrooms): a heating thermostat setting of 18o C from 0700 to 0900 and from 1600 to 2400; and a heating thermostat setting of 15o C from 2400 to 0700.

 

 

 

 

 

 

 

Table 5 - Cooling Thermostat Settings

Climate Region

All conditioned spaces (°C)

 

Climate Region

All conditioned spaces (°C)

1

26.5

 

36

26.0

2

27.0

 

37

27.0

3

27.0

 

38

27.0

4

26.0

 

39

27.0

5

26.5

 

40

28.0

6

26.5

 

41

27.5

7

26.0

 

42

28.0

8

26.0

 

43

27.0

9

26.0

 

44

26.0

10

25.5

 

45

26.0

11

25.0

 

46

26.5

12

25.0

 

47

24.5

13

25.0

 

48

25.0

14

24.0

 

49

24.5

15

25.0

 

50

25.0

16

25.0

 

51

25.5

17

25.5

 

52

25.0

18

24.5

 

53

24.5

19

27.0

 

54

25.0

20

25.0

 

55

24.0

21

24.0

 

56

24.5

22

23.0

 

57

23.5

23

22.5

 

58

23.5

24

24.0

 

59

23.0

25

23.0

 

60

24.0

26

23.0

 

61

23.5

27

25.0

 

62

24.0

28

24.5

 

63

23.0

29

26.0

 

64

23.0

30

27.5

 

65

23.0

31

26.5

 

66

23.5

32

26.5

 

67

23.0

33

27.0

 

68

23.5

34

26.5

 

69

22.5

35

26.0

 

 

 

 

 

 

4.6           Operational Behaviours

In the NatHERS scheme, the schedules of indoor and outdoor adjustable settings are as follows:

Indoor adjustable shading

·         Closed at 1800, open at 0700.

·         Closed if all the following three conditions satisfied:

o   Outdoor temperature exceeds Cooling thermostat setting + 2.5°C;

o   Incident solar irradiance on glazing exceeds 200 W/m2, and

o   Outdoor blind non-exist or cannot be drawn.

Outdoor adjustable shading

·         Closed if outdoor temperature exceeds T, where:

o   T = Cooling thermostat setting - 0.5°C, except

§  If Cooling thermostat setting - 0.5°C > 26.0°C, T = 26.0°C

§  If Cooling thermostat setting - 0.5°C < 24.0°C, T = Cooling thermostat setting

·         Closed when incident solar irradiance on glazing exceeds 75 W/m2.

 

5.        OUTPUTS

 

6.        AREA ADJUSTMENT AND STAR RATINGS

During the development of the second generation NatHERS tools, the Ministerial Council on Energy agreed that the new NatHERS software tools should remove the naturally occurring bias that results in larger houses being advantaged over smaller houses. It was agreed that an Area Correction Factor similar to that developed by the Sustainable Energy Authority of Victoria (SEAV) for FirstRate, be developed for the second generation NatHERS software tools. A study was carried out by Mr Tony Isaacs for the then Australian Greenhouse Office in suggesting the Area Correction Factor for the use in AccuRate. A briefing on the area adjustment can be found in a note by Dong Chen in 2011 [15].

 

Download:

Chen D., Area Correction Factors in AccuRate, note to DCCEE, 2011.

 

 

7.        ACKNOWLEDGEMENT

The success of AccuRate and the Chenath engine is impossible without the contributions from various institutions, associations, consultants, related departments of state and federal governments, software developers and software distribution companies collaborated with CSIRO over the years.

 

 


REFERENCES

  1. Muncey, R.W.R., The calculation of temperatures inside buildings having variable external conditions, Australian Journal of Applied Science, 4(2), 1953, 189-196.
  2. Muncey, R.W.R. and Watterson G.A., Heating of surfaces by buried pipes: Calculation of the steady and periodic states, Australian Journal of Applied Science, 8(4), 1957, 271-278.
  3. Muncey, R.W.R. and Spenser, J.W., Calculation of non-steady heat flow: considerations of radiation within the room, Journal of the Institute of Heating and Ventilating Engineers, 34(1), 1966, 35-38.
  4. Muncey, R.W.R., The conduction of fluctuating heat flow, Applied Science and Research, 18, 1967, 9-14.
  5. Walsh, P.J., Spencer, J.W. and Gurr, T.A., Descriptive guide for program ZSTEP, Thermal Performance of Buildings, CSIRO, Division of Building Research, 1980.
  6. Delsante, A.E. and Spencer, J.W., Computer user manual for program ZSTEP3 – A program for simulating the thermal performance of buildings, 1983, CSIRO, Division of Building Research Report.
  7. Delsante, A.E., A Thermal Design Tool for Small Buildings – CHEETAH (Cooling and Heating Energy Tool for ArcHitects), 1986, Internal Paper 86/45, CSIRO, Division of Building Research Internal Report.
  8. Delsante, A., Is the new generation of building energy rating software up to the task? - A review of AccuRate. Paper presented at ABCB Conference ‘Building Australia’s Future 2005’, Surfers Paradise, 11-15 September 2005.
  9. Walsh PJ and Delsante AE. Calculation of the thermal behaviour of multi-zone buildings, Energy and Buildings 1983; 5: 231-242.
  10. Li Y, Delsante A, Symons J. Prediction of natural ventilation in buildings with large openings. Building and Environment 2000; 35: 191-206.
  11. Z.G. Ren and Z.D. Chen, Enhanced air flow modelling for AccuRate – A nationwide house energy rating tool in Australia, Building and Environment 45 (2010) 1276–1286.
  12. ABCB. Protocol for House Energy Rating Software. Australian Building Codes Board; 2006.

13.  Chen D., Infiltration Calculations in AccuRate V1.1.4.1, note to DCCEE, 2010.

14.  Azhaili Baharun, Koon Beng Ooi and Dong Chen, THERMAL COMFORT AND OCCUPANT BEHAVIORS IN ACCURATE, A SOFTWARE ASSESSING THE THERMAL PERFORMANCE OF RESIDENTIAL BUILDINGS IN AUSTRALIA, Paper T07_O_02, Proceedings of The 5th International Workshop on Energy and Environment of Residential Buildings and The 3rd International Conference on Built Environment and Public Health,  May 27-29, 2009, Guilin, China.

15.  Chen D., Area Correction Factors in AccuRate v1.1.4.1, note to DCCEE, 2011.

 

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