The Physical Models

Three two bedroom houses built in Kingston (approximately 9 km south of Hobart) were the physical models for empirical validation. The availability of the houses provided the opportunity to collect environmental data, which were compared with the thermal performance predicted by AccuRate. One of the important arrangements made with the house developer was to keep the houses unoccupied for at least three months, so that data from the houses in free-running operation could be collected. The free-running operation is described as follows:

 No ventilation occurred via doors or windows, as all windows and doors were shut off during the monitoring period;

 No internal electrical loads such as stove, refrigerator or lights, were added to any space within the building, with the exception of the data logger in the garage;

 No internal heat loads from people or animals were added to any space of the houses while they were unoccupied.

The houses were in a controlled state and allowed to float thermally in response to changes in the external environment. Based on the AccuRate input and output requirements, the sensors and the data acquisition system were assembled to measure the external site climate parameters and the interior environment of the houses. Prior to this research project, the research team already had extensive experience with the installation of monitoring equipment for data acquisition at the Launceston test cells. Vale recommended that the same suite of monitoring equipment and installation methods be used for the test houses, in order to save time and more importantly, provide future practical validation comparisons between the test cells and the test houses (R Vale 2008, pers. comm., 28 September). Construction of the test houses started in early January 2007 and was completed at the end of June 2007. The design and construction of the houses are described in detail in Chapter 5.

4.2.1. Definition of AccuRate’s Output Temperature

One of the first tasks was to determine the type of temperature to be measured in the houses. Delsante (2006) stated that the globe temperature is a good approximation of the operative temperature, which is the average of air and mean radiant temperature, weighted by convective and radiative heat transfer coefficients. (American Society of Heating Refrigerating and Air- Conditioning Engineers Inc. 2001). Delsante further advises, that the AccuRate predicted temperature are not in fact pure air temperatures, but so-called environmental temperatures, because AccuRate uses combined radiative-convective heat transfer coefficients at indoor surfaces. The globe temperature is likely to be closer to AccuRate’s predicted temperature than pure air temperature.

A globe thermometer consists of a 150mm diameter hollow sphere made of copper, coated with a matt black paint, and contains a thermometer at the centre of the sphere (Hassal & Richards 1977). The globe temperature depends on the environment in which it is placed. If the walls and other surfaces which surround the globe are warmer than the air, the temperature recorded by the thermometer inside the globe will be above the air temperature because of the radiation. Conversely, when the surrounding walls and other surfaces are cooler than the air, the globe

thermometer will be below air temperature. The environmental temperature can be calculated from the measured air temperature (dry bulb) and globe temperatures, and Williamson (1984) stated their relationship as:

Tei = 6/5 tg – 1/5 ta Equation 4.1 where Tei = environmental temperature (ºC)

Tg = globe temperature (ºC) Ta = air dry bulb temperature (ºC)

The air temperatures and the globe temperatures in a mudbrick house in Melbourne were very similar, with differences mostly being 0.1ºC or less, and the maximum difference of 0.4ºC (Delsante 2006). It is also interesting to note that Delsante further reported that air and globe temperatures were almost identical outside the periods of extra heating, but they differed by up to 2ºC during the heated periods, with the globe temperature being the lower. The value of the globe temperature will usually be between the air and the mean radiant temperature (MRT). Melbourne’s heavyweight mudbrick house was monitored in a free-running condition, and measured air temperatures were very close to globe temperatures. However, since there was no available comprehensive information on the true values of globe temperature-to-air temperature ratios in lightweight brick veneer buildings, it was deemed necessary to also measure the globe temperature in the houses (Refer also to Chapter 8.2.1 for further discussion).

4.2.2. Developing an Environmental Measurement Profile

Dewsbury (2011) reviewed and examined the methods of measuring the temperature of the PASSYS and PASSLINK test buildings in England and the test cells in Newcastle, Australia, and found these methods suitable for the test cells in Launceston. Based on historical analysis of test cell buildings in the United Kingdom, Europe and the United States, Dewsbury found it necessary to maximize the temperature data points for empirical validation projects. Figures 4.2 and 4.3 show the PASSLINK test cell building and the interior placement of sensors.

Figure 4.2: PASSLINK test building (Source: Building and Environment 43 2008)

Figure 4.3: Interior of PASLINK test building (Source: Building and Environment 43 2008)

Temperature at different height levels was also considered with reference to ASHRAE Standard 55 (1992). The standard specifies the measurement of temperature at different heights as shown on Table 4.1 below.

Table 4.1: Environmental measured heights as specified by ASHRAE Standard 55

Height Above Floor Seated Occupants Standing Occupants

100mm Ankle Ankle

600mm Waist

1100mm Neck Waist

1700mm Neck

The specific heights in Table 4.1 are based on how the average human would react to the surrounding environment. This project is not concerned with levels of comfort, but with determining average room temperatures and creating an understanding of temperature stratification within an enclosed space. Hence, temperature was measured at 600mm, 1200mm and 1800mm above floor level of the rooms.

Lomas (1991a) developed a criterion for classifying data sets for the empirical validation process and is of the view that measured building performance data and the weather data must be recorded at least hourly or at more frequent intervals if possible. Lomas further recommends that for validation purposes, single family dwellings should not be substantially modified, should be of typical construction for the local region and if possible, unoccupied. Delsante (2005b) recommended that measurements at 10 minute intervals are appropriate to calculate accurate hourly temperatures. He also suggested that the minimum requirement for the period of measurement should be at least two weeks, with at least one period during the cool months and the other during the warm months.

Prior to this study, three test cells were built in Australia by the University of Newcastle in 2004, for the purpose of measuring the effect of thermal mass in residential buildings (Sugo et al. 2006). Insights of the University of Newcastle’s research team and an actual site visit in March 2007 to observe the installation of measuring equipment were very useful for this study. While the aim of the University of Newcastle’s research was not to validate a simulation program, the practical knowledge of installing sensors and acquiring data was of great importance. The University of Newcastle’s research team provided invaluable technical advice based on their monitoring experience, emphasized some of the problems and failures, and at the same time highlighted and recommended the successful and proven part of their research. Figures 4.4 to 4.7 show the test cells in Newcastle and some of the sensor installation details.

Figure 4.4: Three test cells at University of Newcastle (Source: Sugo 2006)

Figure 4.5: Location of thermocouples and heat flux sensors within the test cells (Source: Sugo,

et al. 2006)

Figure 4.6: Internal view showing the heat flux sensor at the window, air temperature sensors

at the pole, DT 600 data logger and the thermocouple isothermal box (Source: Sugo

2006)

Figure 4.7: Shielded thermocouple installation at the sliding door (Source: Sugo 2006)

The instrumentation of the three Launceston test cells (Dewsbury et al. 2007) was also carefully studied. The major concerns for the test houses were what and where to measure and this was already pre-determined by AccuRate’s input requirements. As mentioned previously, an insight based on the PASSLINK project was to provide a wide range of environmental measurements to establish reliable average environmental data. Figure 4.8 shows the horizontal measuring profile of the test cells in Launceston.

Figure 4.8: Horizontal environmental measurement profile of Launceston test cell with a concrete slab-on- ground floor (Source: Dewsbury 2007)

Measurement profiles in the test houses were based largely on the Launceston test cells. However, air speed in the subfloor and the roof space and humidity in the wall cavity were not measured in the houses.