Energy Consumption in Urban Water Cycle 1876 6102 © 2016 The Authors Published by Elsevier Ltd This is an open access article under the CC BY NC ND license (http //creativecommons org/licenses/by nc n[.]
Available online at www.sciencedirect.com ScienceDirect Energy Procedia 104 (2016) 123 – 128 CUE2016-Applied Energy Symposium and Forum 2016: Low carbon cities & urban energy systems Energy consumption in urban water cycle Muhammad Wakeel1, Bin Chen1* State Key Joint Laboratory of Environmental Simulation and Pollution Control, School Of Environment, Beijing Normal University, Beijing100875, P.R China Abstract Water-energy relationship is an important element for urban planning and management, and has therefore grabbed worldwide attention in assessing urban ecosystem’s sustainability Energy is a driving agent for urban water cycle and is consumed at each stage of the water cycle i.e extraction, storage, distribution and end-use consumption, which depends upon multiple factors such as water abundance, energy availability and geographic conditions to name few The current research was designed to investigate energy consumption at each stage in the water cycle of Lahore city, Pakistan The result shows that 0.62 kWh/m3 of electrical energy is consumed during extraction of groundwater which is 10% higher compare to 0.058 kWh/m3 for surface water Lahore has 7700 kilometre long urban water distribution network consumed energy in the range of 5.7 kWh/m3 per kilometre similarly, the end-use energy consumption in the city is intensive i.e 5.71 kWh/m3 which is higher than most of the cities in the developed and energy rich countries Therefore, we recommend that renewable energy options such as solar water heaters should be installed to reduce energy consumption at domestic level Similarly, we observed that the city does not have any large scale waste water recycle and reuse policy and management; therefore, waste water should be recycled to avoid energy consumption during extraction stage Keywords: Water, Energy, Urban water cycle, Life cycle assessment Introduction Energy and water carry great importance in human life and are two fundamental resources that play a vital role in various aspects of socioeconomic systems [1] In most of the manmade systems water and energy are interrelated to each other, this relationship is called water-energy nexus [2] Gleick introduced nexus approach for the first time in 1994 [3] but recently, it has gained much attention due to inextricably intertwined sustainability of water and energy Water is used in the life cycle of energy and energy is used * Corresponding author Tel.: +86-10-58807368; fax: +86-10-58807368 E-mail address: chenb@bnu.edu.cn 1876-6102 © 2016 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, CUE2016: Low carbon cities and urban energy systems doi:10.1016/j.egypro.2016.12.022 124 Muhammad Wakeel and Bin Chen / Energy Procedia 104 (2016) 123 – 128 into different stages of urban water cycle; therefore water-energy nexus exists in every urban ecosystems [4-8] Energy is consumed across every stage of urban water cycle (UWC), which starts from the acquisition of ground and surface water followed by raw water treatment, local distribution, end uses, wastewater collection and treatment [9] Approximately, 7% of the total global energy was consumed during UWC in 2001 [10] Energy consumption in UWC vary significantly from city to city, depending on local factors such as topography, location, quality of water sources, pipe dimensions and configurations Operational strategies and technology selection for water industry also have significant impacts on energy use [11].This poses a questions that how much energy is consumed in the urban water cycle and how to maintain a future water supply with the minimum energy input As a result, energy use in water cycle especially in the urban water cycle has gained attention of researchers in last few years Several studies have dealt with various aspects of water supply and energy uses For example, Elias-Maxil et al [12] calculated the energy consumption in UWC in Netherland in order to reduce the total expenditures of fossils fuels Wilkinson [13] investigated the energy usage for urban water supply Kenway et al [14] studied the energy usage in the provision and consumption of urban water in Australian and New Zealand cities at the system level, object level (household level) and total urban energy use Zhou et al [15] estimated the energy consumption of the total water system in Changzhou, China and results showed that water system consumed 10 % of total city energy consumption Racoviceanu et al [16] did life cycle assessment in order to calculate energy uses for urban water supply in Toronto with remarkable finding 94 % electrical energy is used for water supply with 90% of total CO2 emission However, energy consumption in UWC has been rarely investigated in Pakistan, and therefore limited literature exist related to the current topic According to authors knowledge this is the first study to quantify the energy consumption in the UWC at city level in Pakistan A life cycle based conceptual framework (model) for UWC with energy consumption in Lahore city is given in Figure as under Figure 1A conceptual model of water processes with energy uses in Lahore (Pakistan) Muhammad Wakeel and Bin Chen / Energy Procedia 104 (2016) 123 – 128 Material and Methods 2.1 Life-cycle Assessment The methodological framework mainly consist of life cycle assessment (LCA) that is systematic and quantitative approach dealing with “Cradle to grave” analysis, first introduced by society for Environmental Toxicology and Chemistry (SETAC) (SETAC 1991) and refined by US EPA in 1993 is mostly use to calculate energy for water [17-19], that was designed for this study based on the UWC wherever data was available The framework in order to calculate energy consumption was divided in four stages: acquisition, treatment, local distribution and end use To obtain the outputs (energy), the framework required some additional information depending on the water sources, such as elevation changes from source to facility and pump efficiency The multiplier used within the LCA tool was calculated according to Pakistan’s water and energy use The energy consumption is calculated by following equation ܧൌ ୀ ߛܳܪ ݐ כǥ ǥ ǥ Ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ Ǥ ሺͳሻ ͳͲͲͲᢡ ENEi =σୀሺο ݅ܪ οܲ݅ ܲ݅ݑݏሻߩ כ ݃ כ ݎ݁ݐܽݓ EH = EW = ಹఘο் ᢡ WW ଵ ଷ כ ଵ ଵ כ ଵ ᢡ כ ଵ ᢡೝ ǥ ǥ Ǥ ǥ Ǥ ǥ ǥ ǥ ǥ Ǥ Ǥ ሺʹ) ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ Ǥ ǥ Ǥ Ǥ ǥ ǥ ǥ Ǥ Ǥ Ǥ Ǥ ሺ͵ሻ * φǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ ǥ Ǥ Ǥ Ǥ ǥ ǥ ǥ Ǥ Ǥ ǥ ǥ ሺͶሻ Here, E = energy use in acquisition of ground and surface water, γ = Specific weight of water, H = total dynamic head of water, Q = total amount of water ɳ = Operational efficiency of pump, t = duration of pump service, ECDWP = annual energy consumption in water treatment plant (kWh /year), i= type of treatment plant ( surface ,groundwater or desalination, ܷܵ݅= ,Utilization share of each treatment plant = share of water (%), = ݅ܧܰܧEnergy consumed in pumping (ܹ݄݇/݉3) , ݅ = Pipeline section which connect two points , ο= ݅ܪ Height difference (݉ )ܿݓ, ∆ܲ݅ = Pressure losses due to friction (݉ )ܿݓ, ܲ = ݅ݑݏSupplied pressure for the final consumer (݉ )ܿݓ, ߩ = ݎ݁ݐܽݓDensity of water (1000݇݃/݉3) , ݃ = Gravity (9.81 ݉/ݏ2) ,ߟ݉݁ܿ = Average mechanical efficiency, ߟ݁݊݁ = ݎElectrical average efficiency of motor , mwc = meter water column ,ൌ ǡhf = height of roof ߙ ൌ ǡF = number of floor in buildingǡEH = Energy consumed for water heating at end use , VH = volume of water heated in the building, c = specific heat capacity of water (4185 J/kg-K) and ∆t = temperature difference between ambient and heated water Ecol = energy used for water cooling, [20-23] 2.2 Study Area The study area consisted of Lahore which is the second biggest city in the country and 42nd mega city of the world The total area of this mega city is 1772km2 and total population of the district of Lahore is over 125 126 Muhammad Wakeel and Bin Chen / Energy Procedia 104 (2016) 123 – 128 10 million in 2014 with a population density of about 7,000 persons per square kilometre 2.3 Data Sources Water consumption data was obtained by some published reports [22] and was thoroughly reviewed The ground and surface water lost (leakage) during the different stages of UWC was not considered Ground water is the main source of water in Lahore for domestic, industrial and agricultural uses that is extracted from a depth of 120-200 metres (m) for drinking purposes and 60 to 70 meters for agriculture and other uses Total 7.17 Mm3/day ground water is extracted out of which 3.79 Mm3/day goes for domestic, 0.77 Mm3/day for commercial, 0.92 Mm3/day for industry and 1.70 Mm3/day for agriculture (irrigation +live stocks) uses The total surface water diverted to Lahore is 6.02 million cubic metre per day (Mm3/day) and is mainly used for agricultural purposes The average annual rainfall of Lahore is 715 mm but there is no proper system available to collect rainwater and uses Results and Discussion Energy consumption in the UWC depends upon the source of water and additional local factors In 2014 Lahore‘s water portfolio mostly depends upon ground water Ground water extraction consumed 0.62 kWh/m3 as compared to 0.058 kWh/m3 in surface water It means ground water extraction consumed almost 10 % more energy than surface water due to difference of dynamic head The drinking water source mainly consist of ground water extracted from depth of 150 m to 200 m which is supplied for public use without any treatment, therefore energy consumption during treatment has not been considered The energy consumed during water end use is notoriously difficult to estimate due to the lack of available data; obstacles in data collection; and the shear enormity of end users, water uses, and various water using technologies Energy consumption of water end uses is mainly considered in water heating for industrial, household use and circulating cooling water system during industrial process, other energy consumption for end water uses was considered little and not calculated in this study The result further shows that energy consumption in the end uses is very larger as compared to other stages due to water heating Water heating at end uses alone consumes energy in the range of 5.71 kWh/m3 Conclusion Urban water cycle requires significant amount of energy depending upon quantity, quality, source of water and some local indicators, In Pakistan ground water is a major source of water supply for domestic, commercial and industrial use The preliminary results of this study concludes that in the extraction of ground water almost 10% more energy is consumed as compared to surface water In this study energy demand for urban water system was interpreted by LCA but it is still a challenge to progress from using LCA as an evaluation tool to using it as an operational tool for energy in water issues owing to the Muhammad Wakeel and Bin Chen / Energy Procedia 104 (2016) 123 – 128 requirements of scope and boundary and a lack of unified technical data that is, A more comprehensive study by using ecological network analysis (ENA) along with complete life cycle assessment (LCA) of water-energy nexus will be figured out in future Acknowledgement This work was supported by the Fund for Innovative Research Group of the National Natural Science Foundation of China (No 51421065), National Natural Science Foundation of China (No 71573021), and China-EU Joint Project from Ministry of Science and Technology of China (No SQ2013ZOA000022) References [1] Zhang C, Anadon LD Life cycle water use of energy production and its environmental impacts in China Environmental Science & Technology 2013; 47(24):14459-14467 [2] Schnook JL Water–energy nexus Environmental Science & Technology 2011; 45(12):5065- 5065 [3] Gleick 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use and circulating cooling water system... future water supply with the minimum energy input As a result, energy use in water cycle especially in the urban water cycle has gained attention of researchers in last few years Several studies... Muhammad Wakeel and Bin Chen / Energy Procedia 104 (2016) 123 – 128 into different stages of urban water cycle; therefore water -energy nexus exists in every urban ecosystems [4-8] Energy is consumed