Are you a supplier of water and you want to effectively manage it? Have you already thought, how important is the accuracy of measurement and selection of a suitable water meter for your purpose? Most international, national or regional standards including European, relating to water meters intended for measuring billing supplies or water consumption are based on the recommendations of OIML R49. This recommendation is based on OIML and European Standard EN 14154 and many other national standards. Twofold errors of measurement are permitted for water meters after operational use in the case of the control and according to the above recommendations we are talking about, ± 4% in the range of flow rates Q2 ÷ Q4 and ± 10% in the range of flow rates Q1 ÷ Q2. What does it mean?
Consider water meters VMi with following dimensions and nominal flow:
• VM1 … DN 50, Q3 = 25 m3/h
• VM2 … DN 100, Q3 = 100 m3/h
• VM3 … DN 200, Q3 = 400 m3/h
For our case, we can suppose that the relevant flow through the flow meters VMi is in size of 50% of the nominal flow rate Q3 for a period of one year. The volume of water by individual water meters for one year is Vi and we are assuming a 4% measurement error. Then the absolute magnitude of the error of the measured flow volume is 0.04 multiplied by Vi. If we take account of the average price of water 3 EUR/m3, then we have got the price of measured volume of water per year ΔCi.
V1 = 109.500 m3, ΔC1 = 0,04 x 109.500 x 75 = 13.140 EUR
V2 = 438.000 m3, ΔC2 = 0,04 x 438.000 x 75 = 52.560 EUR
V3 = 1.752.000 m3, ΔC3 = 0,04 x 1.752.000 x 75 = 210.240 EUR
That means that the financial compensation for the supply or consumption of water may be 210 thousand € per year with permissible error of measurement 4% and water meter dimension DN 200.
Long-term accuracy of mechanical water meters fully meets the above standards, and is actually on the edge of ± 4%, respectively ± 10%. With regard to the dimension and volume flown in your system it is possible to derive the annual financial loss due to inaccurate measurements.
Is it possible to change this situation? Yes, the possibility of reducing the risk of excessive financial losses due to measurement error is the use of modern electronic, especially ultrasonic water meters, see e.g. http://www.elis.cz/en/ultrasonic-water-meters-flomic-fl5024-and-fl5044.html. These modern water meters provide 2 times better accuracy and long term stability measurement without influence on water quality and wear of flow measuring parts of flow meters, it means a permanent accuracy of measuring.