The Simulation Program

The simulation software program for empirical validation is the HERS AccuRate. This software requires comprehensive input of project and construction data. It is important that the input data be accurate, therefore rigorous checking and verification are required. For the purpose of empirical validation two important changes and adjustment were made in the AccuRate built-in input files, called the ‘scratch files’, namely:

bridging of building materials within the insulated building fabric, window glazing framing ratio and adjustments, to reflect a free-running condition of the houses;

 On-site weather data were used in lieu of AccuRate’s inbuilt weather data, to account for the actual external climate conditions.

It is important to note that the normal user of AccuRate is not permitted to modify AccuRate’s scratch file, as this would invalidate the assessment for compliance with the BCA.

4.3.1. As Built Construction Input Data

a) Insulation

In many cases, changes to building design were executed during the construction stage and these were reflected into AccuRate input files. The most common change during the construction stage was the levels of insulation installed into the building fabric. For example, such change was necessary due to the installation of downlights, where Australian Electrical Installation Wiring Rules regulate that bulk insulation in the ceiling space must not be installed within 200mm distance of the recessed downlights and transformer (Australian/New Zealand Standard 3000 2007). With 14 recessed downlights installed in the ceiling, the insulation gap of 200mm around each recessed downlight reduced the overall value of insulation of the ceiling.

b) Infiltration

Another aspect of the as-built condition is the infiltration rate of the house. The infiltration rate represents the volume of air replaced within one hour and this differs from building to building, depending on the site condition and the sealing quality of the building’s external fabric. The task of determining the infiltration rate of the houses was commissioned by the Mobile Architecture and Built Environment Laboratory (MABEL) of the School of Architecture and Building, Deakin University, Geelong. The tests were executed from 26 to 29 September 2007. Additional test details provided by MABEL are described in Chapter 7.

c) Structural Framing Ratio

The framing ratio affects the amount of thermal bridging of timber framing members, such as wall and ceiling members. AccuRate does not incorporate framing ratio calculations and uses an insulation R-value for the entire building fabric area, ignoring the area of timber framing (Belusko 2008). As the R-value of the timber members are considerably lower (R 0.53 for a 90mm timber hardwood studs compared to R 2.5 for bulk insulation), the average R-value of the

building fabric is reduced, depending on the ratio of timber framing to insulation in the building fabric. Kosny et al. (2007) demonstrated that for an insulated timber framed wall structure, the lower R-value of the timber studs reduced the total insulation value of the wall by up to 30%. Dewsbury et al. (2009) modeled three houses using original and revised insulation values, based on the timber framing ratio. When the houses were modeled with AccuRate, the results showed 18% more heating load for the revised case. The New Zealand Standard 4214 (2006) recognizes the importance of framing factors and provides a calculation method to establish the true thermal resistance of a building fabric. The ASHRAE 2009 Handbook of Fundamentals covers the topic of framing ratios and illustrates both calculation methods, namely: the parallel-path method and the isothermal-planes method. For this project, the calculation of the actual framing ratio for the walls and ceiling and the effect of the insulation values of the test houses are presented in Chapter 7: AccuRate Thermal Performance Simulation of the test houses.

d) Glazing Framing Ratio

Windows and sliding doors have different glass framing ratios depending on the window design. The exact ratios of glazing and framing are important data because they affect the thermal bridging of window frames. They can be adjusted in the AccuRate’s scratch file. The calculation of the window framing ratio for window and sliding glass doors is included in Chapter 7.

e) Summary of Changes to AccuRate’s Input Data

AccuRate simulation results were compared with the measured data from the free-running operation of the houses. Modifications to each AccuRate input file were necessary to represent the house’s actual thermal performance, as follows:

 Modification of ceiling insulation value, taking into consideration the large insulation gaps around the 14 recessed light fittings;

 Modification of air change rates of the houses using measured data on site;

 Modification of framing ratio and adjustment of the average insulation values and insulation thickness for walls and ceiling areas;

 Modification of window framing ratios;

 Modification of input files to simulate free-running operation. This included changing the input data to account for the following conditions:

- The houses were not heated and cooled;

- The houses were not ventilated, as all windows and doors were shut during the monitoring period;

- There were no internal heat gains as the houses were unoccupied during the free- running operation.

4.3.2. Site Weather Input Data

For the empirical validation process it was imperative to acquire on-site weather data to achieve more realistic simulations of building thermal performance. The inbuilt AccuRate climate file represents average climate conditions for many years, for a particular climate zone, collected from the nearest Bureau of Meteorology weather station. The climate file consists of twenty- seven input parameters, of which fourteen are necessary for the thermal simulation program. AccuRate’s essential input data and the corresponding units are as follows:

 Month (number);

 Day (number);

 Hour (number);

 Dry bulb air temperature (tenth of degree Celsius);

 Moisture content (tenth gram per kilogram);

 Atmospheric air pressure (tenth of kilopascal);

 Wind speed (tenth of metres per second);

 Wind direction (0-16);

 Cloud cover (0-8);

 Global solar radiation (W/m²);

 Diffuse solar radiation (W/m²);

 Normal direct solar radiation (W/m²);

 Solar altitude (0 to 90 degrees);

 Solar azimuth (0 to 359 degrees).

Determining AccuRate’s climate inputs revealed the essential measurements necessary for the on-site weather station of the test houses. On-site weather data were collected from the test houses, and the on-site weather file was substituted for AccuRate’s default climate file. The specific adjustments to the AccuRate input files, (incorporating the changes to better represent as-built construction conditions and using on-site weather data), are presented in Chapter 7: AccuRate Simulations.

4.3.3. AccuRate’s Output Reports

 Temperature file;

 Energy file;

 Output mean temperature file;

 Star Rating Report;

 Building Report.

The temperature file shows the simulated hourly temperatures for each zone. AccuRate separates the zones into conditioned (heated and cooled) and non-conditioned zones. Apart from the garage, store rooms, toilets and bathrooms, the non-conditioned zones include the roof space and the subfloor area of the house. Table 4.2 shows a sample of an AccuRate temperature file data with the simulated temperature values shown to one decimal place.

Table 4.2: Sample of AccuRate’s out-put data on simulated temperatures

AccuRate’s temperature output data were used as the simulated temperatures for comparison with the measured data from the houses. The output temperature is accurate to a tenth of a degree Celsius and hence, temperatures were measured to the same degree of accuracy for this project. The Energy file provides the energy required to maintain the conditioned zone within a pre- selected temperature range.

The Output files predict the monthly mean temperature and mean temperature ranges for all zones of the house, for each month.

The Star Rating Report represents the number of stars given to a particular house design, including heating and cooling requirements (MJ/m².annum). This report is generally used for the

The building report presents a detailed report of the construction input parameters. This report is a very useful tool for the AccuRate user, for double checking the project’s input data at the completion of a simulation. The building data report summarises the building fabric’s details, including specified areas and thicknesses of building materials.