The data collected was aimed at a quantitative analysis, and is itself quantitative in nature.
From the literature review conducted, it was determined that the many measurements to be carried out are generally required to be taken at regular intervals, potentially at a very high frequency, and would be somewhat precise. All examples from the literature use some sort of data logging equipment to facilitate an automatic collection of the various data sets.
This allows for experiments to be set and left running continuously without the presence of the researcher, which expands the experimental windows of opportunity, such as overnight or weekends. This was particularly useful for carrying out research using the co-heating test as the building should not be accessed during the test, and the equipment can simply be left running. It also allowed for experiments to be run while other research or analysis was conducted.
Selection of Equipment
Equipment was selected as a balance between products demonstrated in the literature to be useful in this field, and those which were easily available through RMIT University and CSIRO. Using the same, or similar, equipment from the same manufacturers as used by the experts in the field increases confidence in the integrity of the data. It was also useful to use equipment well known to researchers at RMIT University and CSIRO as it provided easy access to expert advice in the face of any issues. Detailed descriptions of the equipment can
65 be found in Chapter 4. In addition to on site equipment, weather data was gathered from the Bureau of Meteorology weather stations located at Moorabbin Airport, 5.5 km south-east from the test cell location, and Tullamarine Airport, 35 km to the north-west.
Calibration of Equipment
The equipment used was generally brand new, and pre-calibrated by the manufacturer.
HOBO sensors were newly purchased from Onset by RMIT University at the time of installation. Though the sensors were already calibrated by Onset, a comparison of a subset was conducted in a small insulated box. No particular patterns were observed outside reported variation of the sensors. Hukseflux heat flux sensors were also newly purchased and specifically calibrated by the manufacturer. The calibration figures reported by the manufacturer were programmed to the CR3000 datalogger when the sensors were installed.
The K-type thermocouples were not independently calibrated beyond programming of the datalogger. This is an oversight in the experimental set up and uncertainty associated with the temperature readings from these sensors is unknown.
The CR3000 datalogger includes a self-calibration procedure based on monitoring internal voltage. The data reported by the logger was checked for validity each time the unit was reinitialised after data was downloaded. This was usually within a two week period, and follows guidelines included in the CR3000 manual for setting up the datalogger and programming. The unit was not checked for imperfections between the analogue terminals.
The watt-meter readings were confirmed by calculating the expected readings when the electric blow heater, known to be 2 kW, was in use. The pulses, recorded on 30 second intervals, count 16 or 17 watt-hours, which equated to 1920 W or 2040 W. The watt-meter only sends the pulse when the full 1 Wh is used, and over time this averaged to the expected 2000W.
External weather data from the Bureau of Meteorology is collected in accordance with World Meteorological Organization standards. Data available for use from the Bureau also follows a quality assurance procedure incorporated in the same standards. Details of the weather station operated by CSIRO are unavailable, and thus the CSIRO data is used only as a qualitative guide to confirm consistency between the local conditions and the conditions at the weather station 5.5 km south-east of the test site.
66 Limitations and Risks
The lack of calibration of the K-type thermocouple represents the most serious limitation on the dataset’s quality. This is compounded by the lack of external calibration of the CR3000 datalogger.
The CR3000 has the capacity to measure pulse frequencies up to 250 kHz. The Elster AC100 Wattmeter used in this study sends a square wave, each pulse lasting 100 ms, for every 1 Wh of energy used. Based on the equipment monitored in this research, the frequency of the pulses recorded is less than 1 Hz and well within operating standards for the CR3000 datalogger.
The basic resolution of the analog inputs used for collecting the heat flux meter and thermocouple data is 33.4 µV. The sensitivity of the heat flux meter output is 60 µV, and the expected range of operation is between -10 and 70 mV. The size of the signal from the heat flux meter is three orders of magnitude higher than the sensitivity range of the datalogger, and these readings should not therefore be influenced by any uncertainty inherent in the CR3000 circuitry.
Uncertainty in the K-type thermocouple cannot be estimated accurately. This data is only used for the calculations of the material R-value, meaning the accuracy of the R-value estimates cannot be quantified. To mitigate this, calculated R-values are compared with theoretical R-values based on manufacturer specifications where available, or standard conductivities if specific data is unavailable. This mitigates the risk of large inaccuracies in the estimates by ensuring the readings are in a range that is sensible given the building materials. The R-values calculated in the heat flux analysis are used for an initial theoretical estimate of the test cell HTC, and to inform the base models for the EnergyPlus simulations.
No conclusions are drawn based on the theoretical HTC as to the effectiveness of the decay method. The risk of inaccurate R-value estimates in the building models is a concern;
however, part of the analysis of the EnergyPlus simulations includes altering the model’s R-values and comparing performance of an array of models to observed performance of the test cell, so eliminating the risk of drawing inaccurate conclusions based on this data set.
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