One may ask why the PHR of the building is calculated in the average form, or why we don’t calculating it as PHR building, max = E dem, max /ATD max. D dem is the energy required to provide the domestic hot water of the building. In addition, C dem /COP abc is the heat consumed by an absorption chiller with coefficient of performance of COP abc to provide the cooling demand of the building. Where E n o m is the nominal electrical capacity of the prime mover, E d e m ¯ is the yearly average of electrical demand of the building, and ATD is the aggregated thermal demand of building. (3-12) A T D = H d e m + C d e m / C O P a b c + D d e m In addition, a reduction also occurs in peak polished rod loads when electric motors with high-slip properties are used. In many cases, torque reductions can be so substantial that the use of a smaller-capacity reducer is also possible. Consequently, they operate with a considerable variation in motor speed over the pumping cycle, thereby enabling the utilization of inertial torques of the rotating parts (crank arm, counterweights) to decrease the net torque peaks. Motors with higher slip, in turn, respond to higher loads with a decrease of their speed and have a lower current demand. ![]() Low slip means a stiff motor that tries to maintain its speed and draws high currents when the load on the motor shaft is increased. The choices are the low-slip NEMA B and NEMA C, the high-slip NEMA D, and the ultrahigh-slip (UHS) special motors. In addition to the required nameplate power, the type of electric motor to be used as prime mover must also be decided. Gabor Takacs PhD, in Sucker-Rod Pumping Handbook, 2015 4.7.5.2 Selection of motor type
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