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UDC 628.311
Choosing the method of gravity flow measurement in public sewers
Summary
The aspects of choosing the method of measuring the flow rate and volume of wastewater gravity flow, particularly in case when the measurement results are used in accounting procedures (commercial accounting) are considered. It is shown that before studying the methods of measurement possible replacing gravity flow with pressure flow shall be considered because pressure flow rate can be measured more accurately. This measurement option is optimal from the technical point of view; however, in case the pressure section in the gravity pipeline is not available additional expenses are required for the water main reconstruction. In case this option is unacceptable the following methods of gravity flow measurement shall be considered (in the order of application priority): «levelflow rate» with the use of standard orifices (weirs and flumes) according to MI 240697 regulatory document; «levelflow rate» without any orifices with preliminary calibration of the measuring section according to MI 222013; «velocitysurface area» with the use of ultrasound flow meters; studying the velocity profile of the crosssection of the water main; calculationinstrumental (balance). By the specific example of an ultrasound flow meter it is shown that the flow rate error subscribed by the technical documentation can be several times lower than the actual one.
Key words
flow rate , measurement error , wastewater , ultrasonic flowmeter , gravity flow , flow measuring flume , calibration of measuring section

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UDC 697.317.2
Petrov D. Yu.
Investigating the dynamic mode of a heating system operation
Summary
Main specifications of the hydraulic mode of the advanced heating systems are given. The standard hydraulic calculation does not provide for the complete amount of information on the heating system operation. Accordingly a mathematic instrument (softwaremodel) was developed to calculate a hydraulic circuit of an advanced heating system in a transit mode of operation. Hydraulic calculations of the two heating systems of similar structure, however, equipped with different balancing fittings were carried out. Typical tendencies of the system active elements operation were analyzed. Recommendations on specific use of the control valves were formulated.
Key words
flow rate , pressure drop , hydraulic condition , heating system , resistance characteristic , thermostatic control valve , balancing valve

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UDC 621.65:62531.3
Economic efficiency of using pumping units with variablespeed drives at low water supply
Summary
In the process of operating pumps with variablespeed drive at low water flow rates the reduction of the pumping unit efficiency factor is observed. It is suggested to determine the amount of energy lost during the operation of such pumping units with actual efficiency factor differing from the rated one. In some instances operating with low water flow rate results in power consumption increase. In this context experimental studies on determining the pumping unit efficiency factor at different impeller speeds were carried out. The results of the studies provided for identifying the optimal operation zone where the pumping unit efficiency factor was reduced by less than 2% of the maximum value, and the less economic zone where the efficiency factor was reduced to 35% of the maximum value. To evaluate the economic efficiency and determine the optimal operation area of pumping units with variablespeed drives at low water flow rate the efficiency curves for different pump impeller speeds are required. It is appropriate to include this data in pump catalogues.
Key words
adjustable electric drive , water supply , flow rate , head , frequency of pump impeller rotation , pump , water disposal , lifting efficiency , electric motor power

