Pumps – Condition responsive control of pump drive motor – Single motor control element responsive to means sensing...
Patent
1992-02-26
1993-12-14
Bertsch, Richard A.
Pumps
Condition responsive control of pump drive motor
Single motor control element responsive to means sensing...
417 20, 417 45, 417 53, 417 63, F04D 2700
Patent
active
052696600
DESCRIPTION:
BRIEF SUMMARY
The invention relates to adjusting the flow rate of air in a network of ducts, and it is applicable, in particular, to adjusting the air supply flow rate in a mine or in industrial or underground works.
The flow of air through the network is generally maintained by one or more fans. The air flow rate must be sufficient to ensure the comfort and the safety of workers: in particular it must be sufficient to maintain acceptable chemical and physical qualities for the air in the network, in particular by diluting harmful gases, by removing dust, and by limiting temperature rises. In practice, the reference air flow rate to be maintained varies a great deal with the activity in the works and must therefore be adjustable by controlling the fans.
There are several ways in which an air flow rate maintained by a fan may be adjusted. Fans may be provided with variable-pitch blades, but that solution requires an expensive mechanical system and leads to pauses whenever the flow rate is changed. It is not appropriate when the reference flow rate needs to be modified continuously or frequently. The invention performs adjustment by controlling the speed of rotation of the fan, which is more flexible and can easily be achieved by using a fan having an asynchronous motor powered by a variable frequency converter capable of operating over a wide range.
The invention seeks in particular to provide a method and apparatus for adjusting the flow rate of air by controlling the frequency at which the motor of a ventilation fan or of each ventilation fan in a network of ducts is powered in a manner that is at least semi-automatic, and for optimizing operating conditions when a plurality of fans are used.
To this end, the invention provides, in particular, a method of adjusting air flow rate in a network of ducts (such as a mine, or industrial or underground works) by controlling the speed of at least one rotary fan for causing air to flow, the fan being provided with an electric motor whose speed is a function of the frequency delivered by an adjustable frequency converter controllable by a central calculation unit, the method being characterized in that:
a) at least one characteristic curve of total pressure as a function of flow rate at least one predetermined speed is stored in the central calculation unit;
b) at least the flow velocity and the total pressure supplied by the fan are measured under steady operating conditions and the flow rate at a current instant and the resistance of the gallery are deduced therefrom by calculation by means of the central unit;
c) the reference flow rate to be supplied by the fan is input into the central unit, and the theoretical total pressure to be supplied by the fan is deduced therefrom by calculation by the central unit;
d) the speed to be given to the fan is determined by interpolation between the characteristic curves as stored and as deduced by calculation, and the converter is set to the corresponding frequency by means of the central calculation unit; and
e) the velocity and the total pressure measurements are repeated to determine the resulting real flow rate, and the frequency of the converter is optionally corrected to obtain the required reference flow rate.
The above-defined sequence is performed under the control of the central calculation unit which, in particular, picks up the necessary information (total pressure and speed) in digital form and which controls the converter.
The central calculation unit may be constituted by a personal computer and it may be assisted by a local microcontroller for each fan. The necessary reference flow rate may be entered manually or it may be controlled by other parameters, for example the concentration of pollutants or the temperature in the network of ducts or at certain points in said network.
The invention also provides an installation for adjusting the air flow rate in a network of ducts, the installation comprising:
at least one air flow fan provided with an electric motor whose speed is a function of the frequency of the electricity s
REFERENCES:
patent: 4158527 (1979-06-01), Burkett
patent: 4225289 (1980-09-01), Burkett
patent: 4468171 (1984-08-01), Katsumata et al.
patent: 4526513 (1985-07-01), Bogel
patent: 5137428 (1992-08-01), Poll et al.
Bertsch Richard A.
Compagnie Generale des Matieres Nucleaires
Scheuermann David W.
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