SUPUESTOS DE NORMALIDAD Y HOMOCEDASTICIDAD DE LAS

The first investigation aim is to address Research Question 1 by providing a comparison between the observed and predicted subfloor ventilation rate, as defined in Section 3.2. The research

method for Investigation 1 is summarized visually in a process map in Figure 3.1. Each column of the process map is now described in more detail.

3.3.1 Investigation 1 Inputs

The first column in Figure 3.1 represents the input data.

The first group of inputs comprises the building geometry and site terrain terms, including the building’s floor area, the subfloor height above ground level, and assessment of the local terrain. These are constant values that can be measured or assessed at any time during the investigation.

Building geometry and site terrain

Wind speed Calculation of observed subfloor ventilation rate Input Ventilation measurements Analysis Calculation of AccuRate’s predicted subfloor ventilation rate Output Comparison of observed and predicted subfloor ventilation rate Computational fluid dynamics modeling of test cell and test site

Assessment of test site suitability Building geometry

and site terrain

Wind speed Calculation of observed subfloor ventilation rate Input Ventilation measurements Analysis Calculation of AccuRate’s predicted subfloor ventilation rate Output Comparison of observed and predicted subfloor ventilation rate Computational fluid dynamics modeling of test cell and test site

Assessment of test site suitability

Figure 3.1: Research process map for Investigation 1, Subfloor Ventilation

The next input is wind speed. This is a time-dependent series of data. As shown in Equation 2.6 in Section 2.4.2, the only weather parameter expected to drive subfloor ventilation is the

meteorological wind speed. Meteorological wind speed at a variety of sites is available from the Bureau of Meteorology (BOM). However, as the closest BOM site is approximately 18 kilometres away, it is instead preferred to measure wind speed on-site. The on-site weather station records wind speed at the building height (Dewsbury 2011), not 10m above ground level, so this height difference must be accounted for in the analysis.

The last group of inputs includes anything used for the experimental measurement of subfloor ventilation. For a tracer gas decay test this includes the tracer gas concentration as a function of time.

3.3.2 Investigation 1 Analyses

The second column in Figure 3.1 represents various manipulations of the inputs.

The first analytical task is a computational fluid dynamics (CFD) assessment of the test cell. The purpose of this task is to gauge to what extent the ventilation in the subfloor can be influenced by the test cell surrounds. This involves modelling the test cell in isolation to assess the surrounding wind pattern, and then noting how this wind pattern changes when nearby buildings are included in the model.

The next group of analyses calculates AccuRate’s predicted theoretical rate of subfloor ventilation. The entire AccuRate program does not necessarily need to be run because the subfloor ventilation model for a detached building with an obstructed wall cavity junction is completely identified in Equation 2.6. Equation 2.6 inputs meteorological wind speed but the test cell records building height wind speed. Therefore a conversion method between these two values must be used. This conversion formula is a function of both the wind speed measurement height and an assessment of terrain. This formula and all calculations used to tailor the theoretical subfloor ventilation rate to suit test conditions are provided in Section 4.5.

The final group of analyses addresses the experimentally obtained ventilation data. There are several available methods for measuring ventilation in buildings and many of those methods are feasible if the ventilation is expected to be constant in time. However if the ventilation is expected to depend on wind, and therefore time, a tracer gas test is an ideal choice. There are several types of tracer gas tests, including pulse injection, decay, constant injection rate and constant

concentration. Pulse injection and constant injection tests are very similar. If the ventilation rate varies with time, then the decay method and constant concentration method give more accurate results. Of the decay and constant concentration tests, the decay test requires less set-up time and lower cost, and it yield more data points in the same amount of time. (McWilliams 2002; Roulet and Vandaele 1991). Thus, the decay test is the preferred method of tracer gas test and is used in this research.

At the time this research commenced, a tracer gas decay ventilation test had already been performed on the test cell room, roof and subfloor by Deakin University’s Mobile Architectural Built Environment Laboratory, MABEL (Dewsbury 2011; Sequeira et al. 2010a). Testing occurred over a period of only two days but it encompassed a broad range of wind speeds and provided a sufficient number of data points. Wind speed, wind direction and tracer gas concentration were recorded as a function of time as described in Section 4.3. MABEL provided the raw data but all processing was performed by the author as described in and 4.4. Thus, as all needed inputs were available the data was found suitable for use in this research.

3.3.3 Investigation 1 Outputs

The third column of Figure 3.1 represents the outputs of the investigation. The first output is the CFD assessment of test site suitability. This is a qualitative assessment indicating what other key areas should be explored with the observed data. For example, the CFD analysis may suggest that winds direction may have great impact on the test cell, or that the relationship between the building height wind speed and meteorological wind speed may become non-linear.

The next output is a comparison between the observed and theoretical subfloor ventilation rate. As the ventilation rate is expected to be a linear function of windspeed, both the observed and

theoretical subfloor ventilation rates are summarized by their adder and scalar on windspeed. Other relationships in the data, as prompted by the CFD analysis or trends observed in the literature, are then explored.

All results of this investigation are provided in Chapter 4.