Regional-scale variability of cold water temperature: Implications for household water-related energy demand

Abstract

Residential water use accounts for at least 80% of water-related energy (WRE) demand (primarily through water heating) in the residential urban water system. Cold water temperature (CWT) is a key determinant in predicting residential WRE but variation of CWT within water networks has not been quantified and is not accounted for in water heating energy consumption guidelines. Here, we analysed the spatiotemporal variability in CWT over the course of a year (2013) using 5760 measurements from 1255 urban water system sampling locations across the Yarra Valley Water region in Melbourne, Australia. CWT varied across the study site from 12–28°C during summer and 9–15°C during winter. Spatial clusters of higher CWT regions (hot spots) and lower CWT regions (cold spots) were also observed. The CWT variability impact on annual household WRE demand was estimated to be between −17 to +19% (−640 to +680kWh/hh.yr) change in water heating for sample households, which is dependent on the geographical location of the household within the study site. However, households located in cold spot regions will have almost twice the amount of WRE demand than average, conversely, WRE demand will be lower than average in hot spot regions.Monthly mean CWTs diverged from the Australian Standards for hot water system energy consumption guidelines value by −21 to +47%. The magnitude of CWT variability and associated energy required for water heating are comparable with the total energy used by water utilities to deliver water supply and sewage disposal services. Variation in water heating could be as large as −4.6kWh/hh.d (hot spot in March) and 3.6kWh/hh.d (cold spot in July), more than three times the total energy used to deliver water supply and sewage disposal services for this region. Accounting for CWT variability could increase accuracy of regional-scale WRE demand and hot water system performance.