Instrumentation .1 Water meter.1 Water meter

For a basic monitoring setup, two water meters, one for the mains water inflow (into the tank) and another for total water out of the tank pumping system, are minimum requirements to enable comparisons between rainwater and mains water consumption. The simple setup would also help analyse the impact of rainwater on diurnal water consumption, including volumetric reliability of rainwater supply and percentage contribution to total water usage. For intensive monitoring, additional meters to measure individual end uses (such as different household appliances and garden water taps) can also be installed.

Residential main meters are typically sized at 15, 20 or 25 mm. Rainwater tank connections are either copper pipes or HDPE and these are generally 20 or 25 mm. The best meters to use are positive

displacement meters (Figure 4.4), which function by water flowing into compartments of a known volume, which continuously fill and empty, turning the counter wheel as they move. As the counter rotates it causes a reed switch to open or close, which generates a low voltage pulse. The pulse ratio varies with the make and size of the meter ranging from 1 pulse per 0.5 litre to 1 pulse per 5 litres depending on the model of meter. For most rainwater tank and domestic use studies, 20 mm pipe diameter, 0.5 L/pulse meters are preferred for their greater accuracy in measuring the low flow rates of most domestic end uses.

Meter type Positive displacement (A) Rotary piston measurement (B) Description Water flows into compartments of a known

volume, which continuously fills and empties

Rotary piston measurement

Size range 15 mm- 40 mm 15 mm-25 mm

Pulse 0.5 to 5 L/pulse 0.014 L/pulse

Minimum flow

detection 0.048 L/min - 0.6 L/min 0.25 L/min - 0.6 L/min

(a) (b)

(a) (b)

Figure 4.4 Flow meters used to measure residential water flow (for demonstration purposes only).

Higher resolution meters (Figure 4.4), such as rotary piston measurement type meters, can be used to achieve greater resolution of data. This is required where a single flow meter is used to measure and estimate (by signal deconvolution) consumption of different downstream end uses. Pulse ratios in these high resolution meters can be as low as 0.014 L/pulse and are usually used in studies in conjunction with the flow trace software such as Trace Wizard (Mayer et al. 1996) to determine water end use characteristics (see Talebpour et al. (2011).

4.4.2.2 Electricity meter

In addition to water flow monitoring, rainwater pumping energy can be monitored at a small cost. Desktop studies have typically shown between 0.9 and 2.3 kWh/kL of energy intensity for rainwater use, a much lower range compared to in-situ studies in Australia which showed anywhere between 0.4 kWh/kL to 11 kWh/kL (Tjandraatmadja et al. 2012). Electricity meters used for domestic metering by some of the notable electricity generating companies in Australia such as Energy Australia, measure root mean square (RMS) power to accurately gauge true power consumption. They emit a pulse for each Watt-hour used and are able to capture quiescent loads. They are rated at +/−1% accuracy, which is standard industry practice for single phase meters.

Figure 4.5 shows an electric meter, which is a direct connect, single phase, static Watt-hour meter used to measure electrical energy. It delivers a pulse for each Watt-hour that passes through, which is recorded by a data logger (refer Figure 4.6). Measuring instruments of various makes/types are available in the market. Users are advised to thoroughly investigate these instruments based on their needs. For a tank monitoring setup, standard residential electricity meters (Figure 4.5) with pulse output capability have been modified by adding an inlet and outlet power cord, and a cable for the pulse outputs. The meters are usually modified to ensure the units are waterproof, and are made electrically safe for residential use by sealing the rear terminal connectors, and checking and tagging before deployment in a residency. It is important that the rainwater pumps being monitored are ‘plug-ins’ into power outlets and not hard-wired into the domestic power circuit, thereby avoiding the need for an electrician to visit each site. This power connection set-up needs to be confirmed during the household recruitment process.

Figure 4.5 Electricity meter attached to data logger setup (for demonstration purposes only).

Figure 4.6 Remote terminal data logger (for demonstration purposes only).

4.4.2.3 Data logger

Data loggers are essential to record the measured electrical pulses over a given time period or frequency. A basic monitoring setup consists of a four-channel data logger, which is set up with a subscriber identification module (SIM) card and batteries with easy connectivity to a power outlet. The reed switches generating pulse outputs from the water and electricity meters are wired to the switch closure input channel of the data logger. Additional loggers may be required if the flow meters are located too far apart (due to signal interference and /or decay) to be wired to one logger. Raw data can be retrieved directly from the loggers or converted to engineering units of litres (for flow meters) and Watt-hours (for energy meters) before or after download from the logger. The units of data will be cumulative litres, or Watt-hours, in each monitoring interval.

On-site data loggers can be accessed either on-site or remotely downloaded. Remote logging is necessary for the studies where access to the study site is challenging due to issues of privacy, remote site location, household access difficulties or guard dogs and so on.

Remote logging equipment is favoured for intensive (e.g., every 30 second interval) data collection studies to ensure logger memory capacity is not exceeded and the ability to remotely detect any failure in the data logging system. Two types of remote metering data loggers have commonly been used for these studies in Australia. One type of data logger transmits the collected water meter pulse data by radio frequency to a hub, which can then be accessed via the phone line for data downloads. These smaller units need to have a clear line of radio communication to the hub, meaning that they need to be in fairly close proximity (less than 1 km) and have a clear line of sight to the hub. Loggers can be either individual or multichannel units based on the number of input channels (i.e., sensors) they need to monitor. Data loggers have finite internal memories (quantities of bytes), hence data flow rates and data duration of the samples being measured must be taken into consideration when choosing the combination of internal storage capacity and download frequency.

Other types of data logging systems use an inbuilt mobile phone transmitter which requires a unique SIM card supplied by a mobile phone network carrier/provider (Figure 4.6). These units can be located anywhere in the surrounding area that has a strong mobile phone signal, and are able to download data to remote servers on a regular basis, either daily or more frequently depending on the battery life and study requirements.

They use a low voltage circuitry, so a unit transmitting twice a day is capable of remaining in the field for five years or more without a change in batteries. There are several brands of data loggers available which are capable of monitoring 1, 2, 4, 8 or 16 meters. Some can be mains powered while others can be battery charged by a solar panel for longer deployment periods. Users should investigate available loggers in the market based on their needs. The data logger shown in Figure 4.6 connects to sensors in the field and collects pulse outputs from water meters and electricity meters and transmits the data via a GPRS/CDMA/3G mobile telecommunications network to a central server at pre-set intervals. The data is then viewed on the internet and can be manipulated and analysed. Water and energy data are collected in 1 minute intervals.

4.4.2.4 Rainfall measuring devices

Rainfall data is an essential part of the monitoring system. It can be obtained from a local weather station but more usually is measured on site using a tipping bucket rain gauge or pluviometer (Figure 4.7). This type of rain gauge consists of a collection funnel of standard diameter (e.g., 200 mm) which directs collected rainwater to a small ‘tipping bucket’ that tips to alternating sides with every pre-set amount of precipitation, which in turn generates a pulse output signal from a reed switch similar to that of the water meters. These pulses are countered and recorded by the data logger, which can be inbuilt as part of the rain gauge (Figure 4.7).

Figure 4.7 The internal tipping bucket and data logger of a typical pluviometer (for demonstration purposes only).

Monitoring studies can also comprise rain gauge stations in order to obtain localised rainfall for individual buildings; however, it is recommended that the gauges are located away from areas that are likely to collect dust and debris (such as rooftops), which may cause disturbances to the data being logged.

A typical rain gauge station used in monitoring studies is programmed to record data for every 2 mm of rainfall, which is equivalent to ten pulses by the tipping bucket. A cylinder of standard diameter (200 mm) goes around this chassis to funnel rainfall into the tipping buckets. Sub-hourly data from rain gauges can be used to supplement daily metrological data that is usually available at a detailed spatial scale for most cities in Australia. Temperature measurements may also be useful to study evaporative effects of roof materials on the volume of rainfall collected.

4.4.2.5 Other monitoring equipment

Water level monitoring in tanks is very useful to compare rainfall (in millimetres) with tank catch (in litres). Continuous monitoring of water levels within rainwater tanks often use a hydrostatic pressure monitor that have submersible, differential pressure transducers. These are available with inbuilt data loggers and generally require manual downloads.

Differential pressure sensors measure the pressure difference between the reference location of the sensor submersed in the tank and the outside atmospheric pressure. One side of the differential pressure unit is exposed to the air through a vent tube exiting the top of the tank. The other side is in contact with the water in the tank. Differential pressure monitoring is a convenient method to monitor rainwater tank levels and requires little to no processing before data display and analysis.

Absolute pressure sensors, on the other hand, are generally housed in a submersible casing and measure the pressure (and in some cases the temperature) at the sensor suspension reference point in the tank.

However, due to the absence of venting tubes, they do not measure the changes in atmospheric pressure.

Hence, an atmospheric reference sensor of the same configuration needs to be suspended in the air above the water surface to allow correction for day-to-day variation in atmospheric pressure. Figure 4.8 shows a typical absolute pressure sensor setup configured to download data to a computer. The pressure sensor is

connected to a base station through a magnetic coupler which enables the downloading of data through an infra-red sensor. The software used is a propriety product of the logger manufacturer.

Figure 4.8 An absolute pressure sensor setup to download data to a laptop computer. The sensor has been retrieved from the rainwater tank (for demonstration purposes only).

A capacitance water level sensor and data logger (Figure 4.9) uses the varying potential between two concentric plates within the logger to determine the depth of water in the tank. The levels are recorded every 15 minutes and stored in the data logger until the data can be downloaded to a computer. Capacitance water level sensors are applicable to both absolute and differential type pressure sensors. Users should investigate the suitability of the commercially available sensors based on their needs. The water level sensors were not used in the case studies described in this chapter, however Moglia et al. (2014) used these sensors for rainwater tank water level monitoring in Melbourne.

Figure 4.9 A capacitance water level sensor (for demonstration purposes only).

4.4.2.6 Protective casing

Outdoor monitoring equipment must be well protected from possible environmental damage. Equipment can be encased in a protective enclosures or casing to shield from weather damage caused due to rainfall, humidity, dust, extreme temperatures and from direct sunlight. Ideally, all equipment that is susceptible to weather damage should have an Ingress Protection (IP) rating (IEC, 2004). Equipment specifications should be consulted when deciding the level of protection required ensuring safe operating conditions are provided.

Disruptions in data logging have been observed in the past as a result of accidental damage to the wiring, hence data monitoring equipment should preferably be placed away from common reach. Metering and logging equipment malfunction due to accidental or environmental damage could also be a contributing factor towards discrepancies in logged data. Enclosing equipment casing in waterproof bags can also provide added protection.

4.4.2.7 Recent developments in monitoring instrumentation

An advanced real-time water and energy monitoring system has been set up to study the water usage in an urban development (Lochiel Park) in South Australia (Whaley et al. 2010). The houses and apartments (total of 106) in the development are designed to receive their water supply from three sources (mains, rainwater and recycled stormwater). All connected water sources in the development are being monitored at medium (1-minute) to high (5-second time intervals) resolution, with a pulse ratio of 1 litre per pulse. The digital outputs from each sensor are connected to an in-home touch screen display (EcoVision) (Ecovision Systems, 2014).

This is a part of a detailed monitoring system consisting of various analogue (rain tank level, temperature, relative humidity) and digital (water use, electricity use, gas and photovoltaic) sensors (Whaley et al. 2010).

The EcoVision display unit (Figure 4.10) allows homeowners to monitor their water consumption in real time, together with electricity and gas usage. This feedback information is highly beneficial in aiding consumer self-management of their energy and water use, including detection of leaks within their water supply plumbing.

Figure 4.10 Screenshot of the in-home ‘EcoVision’ display screen (for demonstration purposes only).

A system such as the Ecovision system is very sophisticated and requires installation by qualified plumbers and electricians.