Understanding Energy Consumption For Urban Water Supply In China

To reduce greenhouse gas(GHG) emissions and help mitigate climate change, urban water systems need to be adapted so that electrical energy use is minimised. In this study, energy data from 2011 was used to quantify energy use and GHG emissions in China's urban water supply sector. The objective was to calculate the energy and climate co-benefits of urban water conservation policies and compare energy use between China and other countries. A further objective was to investigate influencing factors with the aim of assisting the development of energy efficient urban water infrastructure. The average energy use per cubic metre and per capita for urban water supply in China in 2011 were 0.29 kWh/m3 and 33.2 kWh/cap·yr, respectively.Calculations using these indicators showed significant energy savings could result from water conservation measures.Per unit and per capita GHG emissions for water supplied to urban areas in China in 2011 were 0.213 kgCO2e/m3 and 24.5 kgCO2e/cap·yr, respectively, where CO2 e is carbon dioxide equivalent.A comparison between provinces of China showed a direct correlation between energy intensity of urban water supply and the population served per unit length of pipe. This may imply energy and emissions intensity can be reduced if more densely populated areas are supplied by a corresponding pipe density, rather than by a low density network operating at higher flow rates. This study also found that while the percentage of electrical energy used for urban water supply tended to increase with the percentage of population served, this increase was slower where water supply was more energy efficient and where a larger percentage of population was already supplied. Electrical energy use for urban water supply as a percentage of total province-wide electricity use correlated directly with the rate of leakage and water loss within the water distribution system. This highlights controlling leakage as a possible means of reducing energy use and the contribution of urban water supply to GHG emissions. An inverse correlation was established between energy per unit water and average per capita daily water use, which implies water demand tends to be higher when per unit energy use is lower.This study also investigated energy use for pumping in high-rise buildings. China's urban residential housing is dominated by apartment buildings, in which large amounts of energy are required to lift water to consumers. Energy and flow data from a number of residential buildings in urban areas of China was used to calculate the average energy consumption for two types of water pumping systems. Results revealed that buildings can save up to 50 per cent in pumping energy by replacing a booster pump and break tank(BPBT) systemwith an entirely pressurised booster(EPB) system. The latter system capitalises on pressure already supplied by the water distribution network, whereas the former first stores water at atmospheric pressure in a break tank, thus losing any energy supplied by the network. Energy per cubic metre per metre lift for the EPB system and BPBT system was 0.010 kWh/m3·m and 0.019 kWh/m3·m, respectively.Results were extrapolated to city-level using building height and population data for a megacity in China. This revealed daily electricity savings of around 33000 kWh could be achieved if 25% of buildings in the case city replaced BPBT systems with EPB systems. Electricity savings were equivalent to 0.009% of the total daily electricity requirements for the case city. Lifting water within buildings required more energy than the combined processes of sourcing, treating and distributing this water within the urban water distribution system.The results obtained have important implications for China. The number of people living in high-rise buildings and the energy required for water supply is likely to rise with government plans to increase urbanisation by 2020. Meanwhile, China must also meet energy and GHG emissions reductions targets as outlined in the country's 12 th Five Year Plan. To reach both these objectives, urban planning and water policy must focus on making the final 50 metres of the water supply process more efficient. This study provides a realistic and practical method of achieving this aim.