The power factor listed on a motor is very useful to the technician when making motor horsepower and current calculations. Every motor has a metal nameplate or data plate listing the manufacturer, motor type, and electrical requirements for the motor. Subscribe Within the service factor, the brake horsepower driving an air compressor can be higher than the motor's nominal horsepower. However, these calculations are useful wherever electric motors are used. A common service factor on motors is a SF of 1.15. Small motors usually do not consume enough power to pay back the cost of the higher efficiency. A higher efficiency motor wastes less power to heat loss and may run less to get the same amount of work accomplished than a lower efficiency motor. If the motor name/data plate information such as the rated voltage, rated FLA, rated efficiency, and listed power factor are placed in the formula, the resulting answer will be the rated horsepower. A technician measures the actual running amperage and voltage and finds the motor is getting 230 volts and is drawing 16 amps. This is why it is so important to keep condensers clean, evaporator air filters replaced, and airflow on both condensers and evaporators up to normal. Centrifugal Compressor Power Calculation using Process Simulator I want to hear from you. The percent of cfm change is proportional to the percent of rpm change. Locked Rotor Amps (LRA) Service Factor Remember, the power the utility bill reflects is all the power the motor uses, not just what the motor converted to useful rotational work but even the power lost to heat. If the efficiency is not given, it can still be determined using basic math. Copyright ©2020. The voltage listed on the data plate is the design voltage the motor was made for. k = 1.41 = adiabatic expansion coefficient. The gas power is directly proportional to head and mass flow and inversely proportional to efficiency. He is the author of a new book by PAL Publications titled HVAC Technician's Certification Exam Guide. Understanding the elements and process of basic motor horsepower calculations also increases awareness of energy consumption, motor operation, and potential problem areas. The LRA rating of a motor is the most amperage the motor can draw under any condition. Voltage A change in any one of the operating conditions will have an important effect on several others. The brake horsepower can be determined from the following equation: (7.53) BHP = 0.0857 Z AVG 1 k Z 1 k − 1 k Q g T 1 η m η a kn p k − 1 P 2 P 1 k − 1 kn p − 1. where: BHP = brake horsepower per stage. But what amount of work is it actually doing? If and when it becomes available, would you require employees to get a COVID-19 vaccine? HP = TQ x RPM ÷ 5,252 HP = (435.8 x 4,000) ÷ 5,252 = 331.91 However, the energy savings from the higher efficiency may offset the higher initial cost. For example; a 10 hp motor with a SF of 1.15 could actually provide service for a short time up to 11.5 hp. He can be reached at norman.christopherson@york.com. The number of horsepower required to provide each ton of cooling varies with the suction pressure and head pressure. A single-phase blower motor has the following data plate information: 5 hp, 230 volts, FLA 20.72, Percent Efficiency 0.86, PF 0.91, SF 1.15. Generally higher efficiency motors are those that use more metal in their construction and the metal is laminated and insulated between laminations to reduce eddy currents, which create heat. Generally, it pays to purchase higher efficiency motors unless the motor is a small one. The formula given above is used to determine the actual operating horsepower of any single-phase motor. This is why the 746 watts per horsepower is divided into the watts on the top of the formula. Sponsored Content is a special paid section where industry companies provide high quality, objective, non-commercial content around topics of interest to the ACHR News audience. Power Factor By using the equation, we get polytropic head is 79,075.11 ft lbf/lbm. Use this formula just like the single-phase version. Tuition Fee (50%) will be return after completion. Since the rpm and cfm are directly proportional, the two are interchangeable in formulas. Both wattage and horsepower are two ways of stating the same thing. If a blower motor, for example, is going to get a drive pulley change, this formula will give the motor's actual operating horsepower prior to the change so the technician can tell if the motor has enough horsepower capacity available or if the motor must be changed. The higher power factor is always more desirable. To increase cfm, the blower rpm must be increased. Special price on parts [Original & Replacement], " A ship in port is safe; but that's not what ships are built for ", Pre-Owned Screw Compressors' Parts -- Heat Exchangers. A motor with a high service factor is used in applications where the load may vary and may occasionally result in an unexpected overload in horsepower. Common power factor (PF) ratings range from 0.70 to 0.98. This rule will not work for applications other than comfort cooling air conditioning applications. The power efficiency of a compressor is the ratio of the air delivered by the compressor and its input electrical requirements. P2 = 125 + 14.7 (139.7) P1 = 85 + 14.7 (99.7) C2 = 448.39 Total CFM requiredWe need an additional 128.39 CFM to … Visit our updated, Emerson Motor Technologies: FRACTIONAL HORSEPOWER MOTORS, GE ECM by Regal-Beloit: Fractional-Horsepower Motor, Emerson Motor Co., Division of Emerson Electric Co.: REPLACEMENT MOTORS, Troubleshooting & Servicing Electric Furnances. By visiting this website, certain cookies have already been set, which you may delete and block. HP = [144 N P1 V k / (33000 (k - 1))] [ (P2 / P1)(k - 1)/N k - 1] (1) where. It would not be correct to say the motor has a locked rotor. Gas horse power GHP = 3.6( ) Brake horse power, BHP = GHP/ηM (kW) (1) where ηM is mechanical efficiency, see Appendix A. We can help you to manage or discuss with your Karmic Debtors! Single-phase hp = E x I x Percent Efficiency x PF/746. P2 = Desired pressure. The formula given above is used to determine the actual operating horsepower of any single-phase motor. When the voltage and current are not in phase, Ohm's law will not work unless the power factor is used to correct for this phase difference. All Sponsored Content is supplied by the advertising company. These simple calculations can be used to solve motor installation and troubleshooting problems in a variety of applications. This is a directly proportional change. The rated percent efficiency for the motor is listed on most motors but not all. Unlike pure resistive circuits like electric heaters and incandescent lights, motors operate with strong magnetic fields present. Design, CMS, Hosting & Web Development :: ePublishing, American Standard Heating & Air Conditioning. If a motor such as a compressor motor does not state the motor horsepower, then this formula will also work to determine the rated or actual operating horsepower. Three-phase motors use the same calculation as was used for single-phase motors with one addition to the formula.

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