Monitoring devices for occupancy statuses

The occupied and unoccupied statuses of monitored homes were indirectly reflected by the measurements of energy use and hygrothermal conditions to a certain extent. By applying state loggers, such as Hobo® U9-001 and Hobo® U11-001 and the configured event recording sets as demonstrated in Table 4-4, the occupancy statuses were also directly detected in this study. The event button on the front panel of the Hobo® logger can be pressed to manually record extra events, such as the use of space heating out of programmed heating hours.

The one-state Hobo® U9-001 logger and included magnate reed-switch were directly mounted onto window or door frames for status-recording. The three-state Hobo® U11- 001 logger was used with other sensors to configure event-detection equipment sets. For example, the stand-alone motion / light intensity detection box in Table 4-4 consisted of two Rapid® PIR sensors and one adjustable light switch to make full use of the three-state channels. The two PIR sensors facing opposite directions can be used

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simultaneously or as maintenance back-up for each other. The PIR Fresnel lens can detect a change of infrared energy radiated from a moving human body or other heat sources similar to the temperature of human bodies. To avoid faulty detections from moving pets in certain houses, opaque taps were used to deactivate parts of the vertical detectable angles of Fresnel lens. The internal memory capacity of Hobo® logger and the mAh capacity of AA batteries were bottleneck factors when the detection box was used in living areas that were frequently occupied or in seasons when frequent light-intensity variations occurred around the pre-set values of light-switch. The configured detection box, which evolved from a former prototype using wired system, was considered as the prototype of the latest-series compact loggers as demonstrated in the acknowledgement letter in Appendix Two. The newly developed Hobo® logger, although convenient and economical to use and free from the bottleneck factors, arrived on the market too late to be applied in this research.

Another type of configured equipment set is the mattress pressure detector shown in Table 4-4. By inserting the pressure mat underneath the door mattress adjacent to the main entrance, digital pulses were recorded by Hobo® U11-001 to reflect the occupational patterns of the house. This research did not seek to distinguish the entry and exit events and calculate the frequencies of presence and motions. Therefore, the use of the other entry and exit points that could not be covered by the pressure mat was not a major influential factor in meeting the monitoring requirement. One major drawback of using the portable pressure mat is that the mat can be moved by the residents for various reasons, such as house cleaning or the prevention of home pets from chewing the input cable. Missing data under such circumstances can lead to a faulty conclusion of unoccupied status being assigned to the house, if no appropriate validation is conducted.

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Table 4-4 Occupancy status monitoring devices used in this research (photo sources: Hobo(2010))

Name Picture Specifications

Hobo® U9- 001 state data logger

Internal memory: 64Kb (43,000 entries), non-volatile;

One internal reed-switch to establish a magnet field with the included magnet or out-sourced strip;

One state: triggered by either an external contact closure via the included input cable, or by the included magnet strip;

One event: triggered by pressing the button on the logger surface for one second

Hobo® U11- 001 state data logger

Internal memory: 64Kb (43,000 entries), non-volatile;

Three states: triggered by either an external contact closure via the included input cables;

One event: triggered by pressing the button on the logger surface for one second

Mattress pressure detector

The passive contact closure, which can be triggered by the pressure sensor in the pressure mat, is wired to the Hobo® U11-001 state data logger via one included input cable.

The motion / light intensity detection box

Two Rapid® PIR sensors are set on two opposite sides of the box. The Fresnel lens: horizontal detectable angle ±50ºC, vertical detectable angle ±30 ºC, 1.0 to 2.0 mA constant DC current draw;

One light switch is set on the front cover of the box;

The positive contact closure of each PIR sensor is powered by three rechargeable 1.5 V AA batteries and wired to the Hobo® U11-001 state data logger via one included input cable;

The passive contact closure of the light switch, tunable using adjustable resistor, on the top cover is wired to the Hobo® U11-001 state data logger via one included input cable.

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The power profiles measured by Current Cost® devices and the occupancy statuses recorded by the window / door status loggers, the motion / light intensity detection box and the mattress pressure detector were used interactively to detect the actual occupancy statuses, especially when any type of measurements was incomplete.

4.7

Chapter summary

Starting from the selection criteria for monitoring devices and configured schemes for a long-term and longitudinal monitoring project on the scale of this research, this chapter presented the technical details of each type of selected equipment, with the focus being placed on the monitoring devices for analogue parameters. The monitoring devices for the measurement of energy use and power demand were succinctly introduced, including the flawed measurements that were caused by equipment- inherent limitations. Therefore, appropriate pre-processing procedures need to be effectively conducted prior to using the raw data for further analyses. The monitoring interval of electricity use at mains power was reduced from two hours to five minutes by utilising peripheral Internet equipment. The five-minute interval meets the requirements for measurements at mains power set out in the monitoring protocol of the Energy Saving Trust (2009; 2011). The actual values of acquired house use were larger than the utility meter readings, since the measuring mechanism of the CT-based off-the- shelf meters is different from the pulse output data acquisition in the EST protocol. Validating acquired data by using collected utility bills and manually recorded utility meter readings is thus important. Although the electricity and power measurements have been extended to the end-use level, the acquired plug loads require pre- processing prior to the visualisation-based and algorithm-based examinations. The pre- processing of raw data is conducted in Chapter Six, after the actual deployment of the selected devices in the case study homes is introduced in the next chapter.

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