Water Journal : Water Journal March 2011
refereed paper smart water systems & metering water MARCH 2011 99 supplied end use breakdown, along with all other mains-supplied end uses in the brief pilot study (Figure 5). Determining Water End Use Event Energy Intensity Understanding the energy intensity of various pumping configurations across a range of end use events is essential in order to optimise the design of, and policy for, future internally plumbed rain tank installations. Retamal et al. (2009) indicates that an energy intensity range for an internally plumbed rain tank is in the order of 0.9 to 2.3 Wh/L. This study goes beyond total rain tank system energy intensity to reveal the energy intensity of individual end use events for a variety of system configurations. Table 1 details energy intensity sample results for the five particular end use events supplied by the pump at one of the pilot study households. The pilot study results confirmed that the experimental equipment had sufficient data resolution to match pump energy directly to each end use event. The energy and flow rate profile for each of these events will be explained further. Half-flush events were recognised as having the highest energy intensity (ie, 1.67 Wh/L) among the end use events (Figure 6). Expectedly, these low flow and shorter events also have higher greenhouse gas (GHG) emission intensity rates. This high-energy intensity for half-flush events relates to the short period of that event and the low flow rate to refill the toilet cistern. Similarly, Figure 7 illustrates a full-flush event, which also has high pump energy intensity when compared to other end uses (ie, 1.52 Wh/L). The results indicate that fixed speed and/or high pressure pumps are not optimally configured for such low flow and short duration events. Figure 8 illustrates the energy intensity for a particular clothes washer event (1.09 Wh/L). While some washer cycles had Table 1: Rain tank pump energy intensity for mandated end use events. Individual end use event Event volume (L) Event energy (Wh) Event energy intensity (Wh/L) Event GHG intensity (kg CO2-e/L)* Long irrigation 450.30 467.20 1.037 0.00108 Short irrigation 13.13 13.60 1.040 0.00109 Clothes washer (cold-water wash) 118.16 128.80 1.090 0.00114 Full-flush toilet 7.50 11.40 1.520 0.00159 Half-flush toilet 4.30 7.20 1.670 0.00175 *Note: 1.046 kg CO2-e per kWh rate applied for GHG emissions (Source: Queensland Department of Environment and Resource Management.) Figure 5: Mains-water-supplied end use summary. Figure 7: Full-flush toilet event energy intensity plot. Figure 6: Half-flush toilet event energy intensity plot.
Water Journal April 2011