D8) Saving water and energy on water systems. W.G. van der Schee (1) Abstract. Keywords. 1 Introduction. (1)

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1 D8) Saving water and energy on water systems W.G. van der Schee (1) (1) Abstract The last decennia houses were more and more insulated to reduce the energy consumption for heating. This is the result of campaigns in Europe and the different countries reduce the energy consumption in buildings. The part of the total energy consumption for a house to heat the water for hot water is nowadays 32 % and it will rise the next years. Also it becomes increasingly important to focus on the energy consumption to heat the water. The first step is to reduce the cold and hot water consumption. This paper gives a summary of a literature study and focuses on practical measures to reduce the water consumption and energy consumption to distribute and heat water. To construct energy saving houses and buildings in the future more attention must be paid to reducing the use of cold water and reducing the energy consumption for hot water. This goal can be reached for example with the next measures: Reduce the consumption of water by using faucets and devices with an efficient flow rate. Stimulate the use of waterless urinals. Efficient distribution systems for cold and hot water. Design an efficient circulation system. Thermal insulation, thickness 30 mm, maximal thermal conductivity 0,035 W/m.K. Knowledge of the water demands for different purposes in buildings. Heat recovery of hot water used in showers Keywords Water saving, energy consumption, efficiency. 1 Introduction The European Commission said on July European citizens and industry must curb water consumption and use water in a more efficient way or face severe droughts and water scarcity in the next decades. EU member states must raise water prices, promote water savings and water efficiency and adapt economic activities to the amount of water available locally, the commission said. Sustainable water use is absolutely vital if we are to ensure that enough water is available to all European citizens and economic activities, said EU 269

2 Environment Commissioner Stavros Dimas. Conclusion: There is international an on-going demand for water efficient appliances for sustainable buildings. 2 Water consumption in the Netherlands In billon m 3 of water was used in the Netherlands. The amount for domestic purposes was 714 billon m 3 of water. Table 1 shows the average water consumption per person per day. Table 1 Average water consumption per person per day Volume per person per day (litre) Hot water per person per day (60 C) Bath Shower Wash basin Toilet 35.8 Washing clothes by hand Washing clothes by 18.0 machine Washing dishes by hand Washing dishes by machine 3.0 Preparing food 1.8 Drinking water, coffee, thee 1.6 Miscellaneous consumption 6.4 Total Conclusion of the data as mentioned in table 1: The water consumption for the shower, toilet and washing clothes is responsible for 80% of the total water consumption. The total domestic water consumption is slightly decreasing the last years from 130 to 123 litres per person per day. This is caused by a lesser use of the bath. The water consumption for showers is slightly increasing caused by the frequency and the time. There is an expectation that the water consumption for showers will increase more and more next years. The water consumption of washing machines decreases; in 2001 washing machines needed 80 litres for each wash, and nowadays washing machines need 64 litres for each wash. To heat the hot water the average amount of gas in the Netherlands in 2005 was 390 m 3. In practice there is a spread of m 3 gas equivalents, depending on the type of water heater. While the gas consumption to heat the houses clearly decreases the last decades, the gas consumption to heat hot water slightly increases. The part of the total energy consumption for a house to produce hot water is nowadays 32% and this part will increase the next years. Therefore the demand for energy saving in the field of the hot water system becomes increasingly important. 3 Reducing the water and energy consumption How to reduce the water consumption? The first step is to reduce the flow rate at the taps. Is it possible to reduce the flow rate, temperature or duration time? Also attention to leakages 270

3 from taps is required. Table 2 shows the relation between the drips of water when a tap leaks and the waste of water in a year. 3.1 Flow rate Table 2 Waste of water on dripping taps Drips per minute water per year (m 3 ) In large buildings with more storeys the water flow on each storey differs, depending on the pressure of the water supply. The pressure compensating flow regulator maintains a constant flow rate regardless of variations in line pressure. Precise flow control improves system performance and in the case of plumbing systems provides comfort of use at low pressure as well as water and energy saving at high pressure. The pressure compensating flow regulator can be used in buildings with different storeys to compensate the different pressures on the storeys. Figure 1 shows the principle for multi storey buildings. Figure 1 Different flow rates in showers without or with flow rate regulators Figure 2 illustrates the principle of saving water with the flow rate regulator. 271

4 Figure 2 Saving water with a pressure independent flow rate regulator 3.1 Water temperature in the shower In collective water systems, as swimming pools and sport accommodations, the consumption of energy for hot water can be reduced by decreasing the temperature of the hot water. With a combination of the lower water temperature and a shorter duration time for showering it is possible to save on the use of hot water. Table 3 shows the relation between the temperature and the saved volume water without regarding the duration time. 3.2 Shower Flow 14 [l/min] 12 SAVING Pressure [kpa] Normal Constant pressure Table 2 Saved volume water in relation to the water temperature Temperature ( C) Saved volume (%) (standard) The characteristics for a shower for domestic purposes are: Relative high water consumption in households. It is the biggest water consumer in the house. 35% of the total water consumption per person per day. The water consumption takes a long time. Average time for having a shower is 8 minutes. Hot water temperature 38 C. There is an increasing tendency to use luxury showers with a high flow rate and also larger hot water heaters. There is a possible combination between the use of luxury showers and the aim of saving water and energy. Producers design showerheads for a luxurious experience with low water flow rates. The EN 1112 (Shower outlets for (PN10) sanitary tap ware) is a standard to specify: - the dimensional, leak tightness, mechanical, hydraulic and acoustic characteristics with which shower outlets shall comply; - the procedures for testing these characteristics. It applies to shower heads and hand showers of any material used for ablutionary purposes and intended for equipping and supplementing sanitary tap ware for baths and showers. The curves in figure 3 show the flow rate from the different classes shower heads. 272

5 dummie D C B S A Z Pressure [kpa] Figure 3 Flow rate for different classes shower heads (EN 1112) Considering the next guide lines it is possible to reduce the consumption of water and energy on showers: Flow Choose [l/min] water saving shower heads or hand showers with class Z in according with EN Use a pressure independent flow rate regulator on the shower head. Reduce the waiting time for hot water at the taps. Use self closing taps and showers in collective water systems. Adjust a low hot water temperature at shower heads in collective water systems. Use heat a recovery system to reuse the heat in the drainage water of the shower. 3.3 Reuse hot water of showers The shower heat exchanger reuses the heat from the drainage water from showers. Drainage water from the shower flow through a copper pipe and exchange the heat to the cold water supply that enters on the other side of the copper pipe. The cold water supply is warmed a few degrees. A thermostatic faucet controls the adjusted water temperature. The efficiency of the shower heat exchanger is 40% - 60%, In an average household the shower heat exchanger saves 150 m 3 gas in a year. Figure 4 shows the shower heat exchanger and figure 5 shows principles how to build it in. 273

6 Figure 4 The shower heat exchanger Figure 5 Principles to build in the shower heat exchanger 3.4 Water monitoring system Water monitoring system offers besides monitoring, the possibility of optimum operation of the water system. For households there are appliances to reduce the consumption of water and energy. Figure 6 shows an example of a product for households: the Shower monitor. In the Shower monitor sensors measure the water flow and temperature to calculate the hot water usage. When the shower is turned on the Shower Monitor will wake up and display the current time, temperature and a full bar graph. As warm water flows from the shower the Shower Monitor calculates the amount of hot water used and reduces the bar graph accordingly. The higher the shower water temperature and/or flow the quicker the bar graph will decrease, conversely the lower the temperature and/or flow the slower the bar graph will decrease. After a preset amount of hot water has been used a beeper will sound. The only way to turn the beeper off is to turn the shower off. If the shower is turned back on within the adjustable delay period the beeper will come back on. After the shower has been turned off for more than the delay period the Shower Monitor will re-set automatically ready for the next person. 274

7 Figure 6 The Shower monitor (source Watersave Australia) 3.5 Toilets and household water After the shower the toilet is the point with the highest water consumption. The average is 36 litres a day, 29% of the total water consumption per person per day. Water saving on toilets is possible with the next measures: Reducing the volume of flush water. The minimum is about 6 litres. Flush interrupter. Separation of faeces and urine. Flushing the faeces need a water volume of about 6 litres, Flushing urine need theoretical 0.2 litres. Practical 2 3 litres to flush the toilet paper. These measures will not be explained in this paper. A new product is the Ecoplay system. A cleaning tank collects the drainage water from bath and shower. A skimmer removes light particles such as foam, hairs and soap. Heavier particles sink to the bottom and are flushed through the sewerage system. The clean water from the middle of the tank is transferred to the storage tank with a volume of 100 litres. A built in control unit takes account of the householders activity (how often bath and shower water is drained off, how often the toilet is flushed), and monitors how long the water is stored. Water that is stored too long is drained off to prevent disagreeable odours. The water is removed via the sewerage system. Figure 7 shows this system. Figure 7 Household water system for toilets 275

8 3.6 Dish Washer The increase demand for luxury and comfort leads to more dish washers in households. Simultaneously the manufactures develop dish washers with a lower energy and water consumption. Table 3 shows the energy and water consumption to do the dishes per year. Table 3 Water and electricity consumption to do dishes per year Electricity (kwh) Gas (m 3 ) Gas equivalent (m 3 ) Water (litres) With hands and ,920 solar panels With hands and ,920 gas saving boiler With hands and ,920 gas standard boiler Dish washer A ,700 label Dish washer C ,000 label With hands and electric water heater , Washing machine After the shower and the toilet the washing machine is the next largest water consumer in the house. With each wash the washing machine uses litres water. For washing machines there is an energy labelling system. Nowadays the most products has the energy label A or B. This means the products are energy friendly. The costs for energy depend mainly on the used water temperature. What is the influence on the energy consumption of the adjusted water temperature. Table 4 shows the energy consumption in relation with the water temperature. The users have to be aware of this influence. Table 4 Energy consumption relation with the water temperature Temperature Annual Energy Energy consumption consumption each usage ( ) (kwh) (kwh) A-label machine, 5 kg clothes, 4 times a week 276

9 3.8 Distribution hot water To avoid the waste of energy there is a maximum waiting time of 20 seconds before hot water reach the taps after the tap is opened. The maximum length of the pipe line to the tap depends on the flow rate and the pipe diameter. A high flow and small pipe diameter allow a long pipeline to the tap. But the higher the volume in the pipeline to the tap, the higher the energy losses. The calculation of the energy losses in distribution pipes for hot water are given in Table 5. Table 4 Energy and water losses per year for different pipe diameters Diameter (mm) Water (litre) Velocity flow 0,083 l/s Waiting time flow l/s Gas (m 3 ) (m/s) (s) 8 2, , , , Copper pipe, not insulated, length 7 metres, efficiency = 0.65, 15 times per day The pipe diameter has a big influence on both the waiting time and the energy losses. 3.9 Circulation system The first step to saving water and energy in the hot water distribution system is to reduce the diameters of the pipe, with the restrictions to keep the necessary minimum volume and maximum water velocity in mind. The maximum water velocity in pipe for cold and hot water is 1.5 m/s. For the hot water circulation system the recommended maximum water velocity is 0.7 m/s. Reduction of the pipe lengths in a hot water circulation system has a big influence on the energy lost by transmission. In practice it is difficult to maintain a sufficiently high operating temperature in large hot water systems. When the hot water return temperature becomes less than 60 C usually the engineer will adjust a higher hot water temperature on the water heater with the intention to increase the return temperature. Recommended is to restrict large and complex hot water circulation systems. Using a smart lay out of the hot water distribution system in combination with the hot water circulation system offers often short pipe lengths. Figure 8 shows two solutions for a combination of the hot water distribution system and the hot water circulation system. 277

10 4 Conclusion Figure 8 Two principles to design a hot water distribution system. The solution on the right leads to saving energy Reducing the consumption of water and energy is necessary. There are several technical appliances to reach this aim in the field of domestic and non domestic buildings taking in consideration the comfort for the consumers. Technicians have to be aware of the choices they make when designing a water system. It is difficult to change the behaviour of the consumers, a good technical solution works definitely. A few recommendations for technicians to minimise the water usage and energy demand: Use water efficient taps class Z in according with EN Avoid high flow rates at the taps in flats by using pressure independent flow rate regulator Use water efficient aerators on taps in large water distribution systems as hotels, swimming pools and camping sites. Design an efficient distribution system and avoid large, complex circulation systems 5 References 1. Saving water and energy on water systems, 2007, TVVL Leusden, the Netherlands 2. NEN 1006, General requirements for water supply installations, 2002, NEN, Delft, the Netherlands 6 Presentation of author Walter van der Schee is a representative of the Netherlands Technical Association for Building Installations (TVVL). He is a member of the board of the department Sanitary Technologies (ST). The objective of the association is to promote research and technology in the field of building services. This is done by networking; giving courses; lectures; organising symposia; subcontracting research and co-financing university-chairs. For further information see Walter van der Schee is working at Wolter & Dros were he is responsible for the engineering of installations in buildings. For further information see 278