عنوان مقاله [English]
Water meters, as one of the most important components of the urban water distribution network, like other mechanical equipment, are gradually degraded and lose their desired efficiency. The poor performance of the water meter for estimating the amount of subscribers’ water consumption has a negative effect on planning for the provision of water production resources and also causes financial losses to water and wastewater companies. Therefore, in the present study, the accuracy of measurement of domestic water meters including 2 new meters (Baylan and Talayeh) and 7 used meters (about 35 years old) has been experimentally investigated in the range of water consumption rates of evaporative coolers (up to the start-up flow-rate). For this purpose, each of the above meters is separately installed on the test bench and placed in the water flow path in series with an ultrasonic test meter (owned by South Khorasan Province Water and Wastewater Company) and a digital turbine meter (owned by the project manager). Then, the flow rate shown by each of these three meters (apparent flow rate) was simultaneously read and compared with the actual flow rate (measured by a calibrated container and a stopwatch). Therefore, in the range of flow rates of evaporative coolers, the error of meter operation in measuring the correct amount of water consumption (or unaccounted-for water) and the values of Root-Mean-Square Error can be determined. The results showed that the best operating range of domestic meters is between 15 and 22 liters per hour and RMSE values for this range of rates for the two new meters of Baylan and Talayeh are 7.79 and 3.61 liters per hour, respectively. Also, the start-up flow-rate values for Baylan and Talayeh meters were measured at 13.8 and 7.7 liters per hour, respectively, which are closely similar to the results of other researchers. In addition, by changing the network’s water pressure by means of a pressure regulating valve, the effect of this parameter on the accuracy of the meters is evaluated. Moreover, the effect of changing the parameters such as altitude, dry-bulb temperature, and relative humidity on water consumption of an evaporative cooler with a capacity of 7500 m3/h was theoretically investigated for 4 cities of South Khorasan province. Through psychrometric calculations, it was observed that the highest consumption of water cooler occurred in conditions of high dry temperature, low relative humidity, and higher air pressure (Tabas city) at the rate of 56.39 L/h.