case studies in Australia

Flow metering technologies have been used to conduct water efficiency audits since 1996 by consultants across Australia, including Sydney Water (Aravinthan et al. 2012). Extensive end-use studies on urban residential water consumption using flow monitoring methods were conducted in South East Queensland (SEQ), Australia (Beal et al. 2011; Beal et al. 2013; Umapathi et al. 2013; Willis et al. 2011a). A brief summary of some of these recent studies conducted in Australia for household rainwater supply monitoring are outlined in the following sections.

4.2.2.1 Sydney Water, Sydney

Sydney Water recognized a considerable knowledge gap in existing research on the impact of using rainwater tanks on the mains water consumption in Sydney households that were designed under the State Government’s Building Sustainability Index (BASIX) Scheme (Ferguson, 2011). The main driver for the study was to determine the performance of household rainwater tanks in saving mains water. Sydney Water conducted an 18-month study of 52 households around Sydney using rainwater. Rainwater usage and mains water top-up for non-potable demands and the corresponding energy consumption of rainwater pumps were monitored remotely, all at one-minute intervals.

4.2.2.2 UWSRA, South East Queensland

The SEQ study involved monitoring, over a cumulative 12-month period, 20 households with rainwater tanks (Umapathi et al. 2012; Umapathi et al. 2013) installed to meet fit-for-purpose household demands.

Similar to Sydney Water’s investigation, the SEQ households were monitored for mains water use (including rainwater tank top-up), rainwater use and rainwater pumping energy consumption. The main drivers for this study were to determine the effectiveness of the rainwater tanks; to validate the savings expected from the rainwater tank systems based on local building codes; and to assess the corresponding energy consumption. Earlier desktop studies, conducted in 2011 by Beal et al. (2012) and Chong et al. (2011), reported that the rainwater tanks installed in new households under the Queensland Development Code (QDC) MP 4.2 failed to meet their predicted water savings target of 70 kilolitres per household per year (kL/hh/year), prompting a detailed investigation into water and rainwater demand in selected rainwater tank households distributed across the region. Further detail on these studies can be found in Chapter 3.

4.3 rAInwAter system components, AccessorIes And conFIgurAtIons

The majority of rainwater tank systems consist of an above ground tank connected to a rainwater catchment area (the roof) together with a combination of system components comprised of filtering, pumping and backup equipment to supply water to specific end-uses (Australian Government, 2013). Some household rainwater tanks may be built underground to save space. However, this is usually a more expensive option as underground tanks cost more and can hinder maintenance and ongoing monitoring efforts in case of system faults. It can also be difficult to measure tank volume if the tank specifications are unknown prior to monitoring (Australian Government, 2013).

In Australia, different configurations for household rainwater tank systems have been identified which include gravity fed systems with pumps, pumping systems, dry systems, wet systems and gutter storage systems (Australian Government, 2013), of which, uncharged conveyance systems (dry systems) and charged conveyance systems (wet systems) are more commonly found. These systems are described in detail in Chapter 5. An above-ground household rainwater tank system setup in South East Queensland is shown in Figure 4.1.

A typical household rainwater collection system (Figure 4.1) consists of roof catchment areas that have attached gutters, which are in turn connected to downpipes that transport water through gravity flow into the rainwater tank reservoir. The size and slope of roof catchment areas can be measured to determine the efficiency and catchment losses of collection areas. This data is used in conjunction with monitored flow data to determine the relationships between weather patterns and rainfall and the reliability of rainwater tank supply. Methods to estimate catchment areas in the absence of building plans were described by Chong et al. (2014) and Chong et al. (2012) as well as in Chapter 5. Aerial photographs were used during

on-site household inspections to match the roof catchment slopes with those downpipes that were plumbed to the rainwater tank. This method can also determine the approximate roof area connected to rainwater tank when there is more than one downpipe connected along a run of gutter. Collection system components such as first flush devices and mesh guards may be present to improve water quality during rainfall event (Figure 4.1). These components are discussed in further detail in Chapter 5.

Figure 4.1 An aboveground household rainwater tank system setup in South East Queensland, Australia.

The storage system is obviously a critically part of a rainwater tank system. The volume of rainwater inflow into the storage tank (Figure 4.2) is dependent on weather conditions including rainfall, wind speed and direction and characteristics of the roof catchment area, such as the slope angle. Outflow of rainwater from the tank is dependent on supply factors such as the pumping capacity, supply pipe characteristics and most importantly, connected end-uses such as toilets or washing machines.

Pumps used in rainwater tanks systems come in different sizes (kilowatt ratings) and specifications including pressure cut off settings; hence, the water supply rate and energy used by the pumps vary.

The performance of pumps also depends on characteristics external to the pumping system such as the distribution plumbing system. Monitoring of pumping systems can help in optimising pump sizing in rainwater tank systems which are generally known to be highly energy intensive. From an experimental monitoring perspective, it is preferable for the pump to be plugged into a general power outlet (GPO), rather than hard wired into the household electricity system.

In most cases, rainwater tank pumping systems also include tank level sensors (generally float based) and top-up devices including trickle top-up systems or switching device systems that provide mains water

backup. Backup systems are an important component of rainwater tank systems; they deliver uninterrupted water supply to end uses when the water level in the rainwater tank is too low for pumping. The type of backup system employed will impact the water demand profiles from the rainwater tank and mains water back up supply. Detailed discussions on pumping systems, backup systems and the energy consumption aspects are discussed in Chapters 5 and 6. Pumping systems may also have other ancillaries such as pressure vessels, header tanks and so on (Retamal et al. 2009; SEWL, 2009) which are also discussed in Chapter 6.

Figure 4.2 Typical end use connections for household rainwater use.

Household end use connections that receive water supply from the rainwater tank form the demand-end of the system. From a monitoring perspective, information on the water and energy demands for the various end uses can yield many useful insights for designing supply systems suited to unique end use configurations. Characteristics unique to any rainwater supply system, such as energy intensity of the pumps, reliability of the rainwater tank and sizing of collection, storage and pumping accessories, can all be estimated based on end use demand. Toilets, washing machines and garden taps are the most common end uses of rainwater (Figure 4.2). Hot water systems have also been connected in some cases. As there is often minimal or no water treatment requirement for these non-potable end uses, water quality concerns are addressed by limiting rainwater use on a fit-for-purpose basis.

4.4 experImentAl ApproAches 4.4.1 monitoring methods

In developing an experimental methodology, it is necessary to identify the different water sources (e.g., rainwater and mains water) in the system and the corresponding end uses associated with the water sources. Figure 4.3 depicts a general schematic outline of a simple water and energy monitoring setup in a household setting. As rainwater is collected in the storage tank, the change in volume of water in the tank can be measured using water level sensors. Water flow meters monitor supply from the rainwater tank to indoor and outdoor end uses, total mains water supply to the household, and mains water backup to the rainwater tank. An energy meter is installed to measure the energy consumption by the rainwater pump.

Figure 4.3 Process flow diagram of the water and energy monitoring setup in a typical household rainwater tank.

A data logger continuously records water flow through the meters and this data can be downloaded remotely using wireless connections. Water flow and energy consumption data are generated when water uses such as washing machine, showers or toilet flushing create electrical pulses in the water meter (via a reed switch) that can be logged against time stamps of a pre-determined frequency, for example, every 60 seconds The data collected using meters can vary in resolution (i.e., pulses per litre of flow) based on the specifications of the meters and data loggers. Metering of residential water supply can be tailored to meet the information requirements of researchers and other stakeholders. Case studies based on standard monitoring methodologies are further discussed in later sections.

An alternate method to installing multiple meters is to employ a high resolution meter and high frequency logger that can be used to record water supply from a primary water source (such as mains water supply and/or the rainwater tank supply) wherein the data in the form of high resolution flow traces can be disaggregated for various end uses using available commercial software. More details on this method of analysis can be found in Mayer et al. (1999) and Talebpour et al. (2011).

4.4.2 Instrumentation