I thought all of you might find this useful. It was posted on another site.
The definitions below have been questioned in past postings.
a) Load factor - the ratio of the load that a piece of equipment actually draws when it is in operation to the load it could draw (which we call full load). For example, an oversized motor - 20 hp - drives a constant 15 hp load whenever it is on. The motor load factor is then 15/20 = 75%.
b) Use (or utilization) factor - the ratio of the time that a piece of equipment is in use to the total time that it could be in use. For example, the motor above may only be used for eight hours a day, 50 weeks a year. The hours of operation would then be 2000 hours, and the motor use factor for a base of 8760 hours per year would be 2000/8760 = 22.83%. With a base of 2000 hours per year, the motor use factor would be 100%. The bottom line is that the use factor is applied to get the correct number of hours that the motor is in use.
c) Diversity factor - the probability that a particular piece of equipment will come on at the time of the facility's peak load. The diversity factor is the most complicated of these factors. For example, we might have ten air conditioning units that are 20 tons each at a facility. In Florida we typically assume that the average full load equivalent operating hours for the units are 2000 hours per year. However, since the units are each thermostatically controlled, we do not know exactly when each unit turns on. If the ten units are substantially bigger than the facility's actual peak A/C load, then fewer than all ten units will likely come on at once. Thus, even though each unit runs a total of 2000 hours a year, they do not all come on at the same time to affect the facility's peak load. The diversity factor gives us a correction factor to use, which results in a lower total kW load for the ten A/C units. If the energy balance we do for this facility comes out within reason, but the demand balance shows far too many kW for the peak load, then we can use the diversity factor to bring the kW into line with the facility's true peak load. The diversity factor does not affect the kWh; it only affects the kW.
a) Load factor - the ratio of the load that a piece of equipment actually draws when it is in operation to the load it could draw (which we call full load). For example, an oversized motor - 20 hp - drives a constant 15 hp load whenever it is on. The motor load factor is then 15/20 = 75%.
b) Use (or utilization) factor - the ratio of the time that a piece of equipment is in use to the total time that it could be in use. For example, the motor above may only be used for eight hours a day, 50 weeks a year. The hours of operation would then be 2000 hours, and the motor use factor for a base of 8760 hours per year would be 2000/8760 = 22.83%. With a base of 2000 hours per year, the motor use factor would be 100%. The bottom line is that the use factor is applied to get the correct number of hours that the motor is in use.
c) Diversity factor - the probability that a particular piece of equipment will come on at the time of the facility's peak load. The diversity factor is the most complicated of these factors. For example, we might have ten air conditioning units that are 20 tons each at a facility. In Florida we typically assume that the average full load equivalent operating hours for the units are 2000 hours per year. However, since the units are each thermostatically controlled, we do not know exactly when each unit turns on. If the ten units are substantially bigger than the facility's actual peak A/C load, then fewer than all ten units will likely come on at once. Thus, even though each unit runs a total of 2000 hours a year, they do not all come on at the same time to affect the facility's peak load. The diversity factor gives us a correction factor to use, which results in a lower total kW load for the ten A/C units. If the energy balance we do for this facility comes out within reason, but the demand balance shows far too many kW for the peak load, then we can use the diversity factor to bring the kW into line with the facility's true peak load. The diversity factor does not affect the kWh; it only affects the kW.
Motor load, use and diversity factors: Sometimes motor load factors that are too low are chosen because the auditor has not properly determined the hours of use of the motors - i.e. the auditor uses an incorrect use factor. For example, just because a facility has a production shift that is 2000 hours per year it does not mean that all of the production-related motors in that facility are operated for 2000 hours per year. Some motors - or machines - might only be used one day a week rather than every day. Other motors might be used every day, but for only half the day, i.e. 4 hours per day. Other motors might be in use throughout the day so that their use really is 2000 hours per year. The auditor must collect data on the use factor - or hours of use - for every motor in the facility during site visit. For each machine, line, process or operation, ask "How many hours a day does this machine (line, process or operation) operate?" This data then needs to be entered into the energy balance. Motor load factors in many facilities are more in the range of 40% - 50%, than in the range of 80% that had been a standard assumption for many years of doing audits. Rarely do you find a motor running at 100% load factor. However, not all motors at a facility are running at the same load factors. Ventilating fans that come from a supplier as a packaged unit with a fan and a motor are most often assumed to be operating at near full load. You should probably use a load factor of 80% here, since the manufacturer of the ventilating fans should have reasonably matched these loads. Other motors may also be in this category - some engineering judgment and common sense are required to determine which other motors these are. Motors with variable loads are going to have the lowest load factors in general. A dust collector fan motor will normally have quite a variable load, and would often be expected to have a low load factor. Other examples are saws, presses, milling machines, sanders and grinders, waste grinders, water pumps, hydraulic pumps, etc. If a group of motors do not all operate together all of the time, then using a diversity factor is appropriate. This is the case with a number of separate air conditioning units (considering the motors for the compressors) that are individually thermostatically controlled. It could also be the case for a group of production motors if some of the motors are not in use all of the time. You should use a diversity factor in your motor calculations, since it is not often the case that a facility has all of the motors on at the same time. Reconciling the energy balance: When you perform an energy balance, do not use the motor load factor as the first and only adjustment made to reconcile the estimated energy use (energy balance) with the energy bills. Making this adjustment too quickly results in failure to pick up other things that have been overlooked. For example, if the energy use does not balance with the energy bills, the first step is to check to see that all of the equipment and uses have been accounted for. Do the items on the energy balance spreadsheet match your recollection of the equipment you saw in the facility?Does anything appear to be missing?Are the utility bills for total energy use and peak kW recorded correctly? The next step is to check the hours of use for lights and other equipment to see if it matches your knowledge of the facility's operation. Remember that each motor - as well as each other piece of equipment - does not necessarily operate the same number of hours each day or year. Finally, if some of the equipment does not come on at the same time as the facility peaks in kW use, then utilize the diversity factor to account for this.Adjusting the motor load factors should probably be the last thing you do to reconcile the energy and demand balances. Now, if all other information and all other factors are correct to the best of your knowledge, then adjust the load factors. While motor load factors are not often in the range of 80-100%, you should be equally suspect of very low motor load factors. If you get motor load factors in the range of 20-30%, it is more likely that you have the hours of use wrong.
The definitions below have been questioned in past postings.
a) Load factor - the ratio of the load that a piece of equipment actually draws when it is in operation to the load it could draw (which we call full load). For example, an oversized motor - 20 hp - drives a constant 15 hp load whenever it is on. The motor load factor is then 15/20 = 75%.
b) Use (or utilization) factor - the ratio of the time that a piece of equipment is in use to the total time that it could be in use. For example, the motor above may only be used for eight hours a day, 50 weeks a year. The hours of operation would then be 2000 hours, and the motor use factor for a base of 8760 hours per year would be 2000/8760 = 22.83%. With a base of 2000 hours per year, the motor use factor would be 100%. The bottom line is that the use factor is applied to get the correct number of hours that the motor is in use.
c) Diversity factor - the probability that a particular piece of equipment will come on at the time of the facility's peak load. The diversity factor is the most complicated of these factors. For example, we might have ten air conditioning units that are 20 tons each at a facility. In Florida we typically assume that the average full load equivalent operating hours for the units are 2000 hours per year. However, since the units are each thermostatically controlled, we do not know exactly when each unit turns on. If the ten units are substantially bigger than the facility's actual peak A/C load, then fewer than all ten units will likely come on at once. Thus, even though each unit runs a total of 2000 hours a year, they do not all come on at the same time to affect the facility's peak load. The diversity factor gives us a correction factor to use, which results in a lower total kW load for the ten A/C units. If the energy balance we do for this facility comes out within reason, but the demand balance shows far too many kW for the peak load, then we can use the diversity factor to bring the kW into line with the facility's true peak load. The diversity factor does not affect the kWh; it only affects the kW.
a) Load factor - the ratio of the load that a piece of equipment actually draws when it is in operation to the load it could draw (which we call full load). For example, an oversized motor - 20 hp - drives a constant 15 hp load whenever it is on. The motor load factor is then 15/20 = 75%.
b) Use (or utilization) factor - the ratio of the time that a piece of equipment is in use to the total time that it could be in use. For example, the motor above may only be used for eight hours a day, 50 weeks a year. The hours of operation would then be 2000 hours, and the motor use factor for a base of 8760 hours per year would be 2000/8760 = 22.83%. With a base of 2000 hours per year, the motor use factor would be 100%. The bottom line is that the use factor is applied to get the correct number of hours that the motor is in use.
c) Diversity factor - the probability that a particular piece of equipment will come on at the time of the facility's peak load. The diversity factor is the most complicated of these factors. For example, we might have ten air conditioning units that are 20 tons each at a facility. In Florida we typically assume that the average full load equivalent operating hours for the units are 2000 hours per year. However, since the units are each thermostatically controlled, we do not know exactly when each unit turns on. If the ten units are substantially bigger than the facility's actual peak A/C load, then fewer than all ten units will likely come on at once. Thus, even though each unit runs a total of 2000 hours a year, they do not all come on at the same time to affect the facility's peak load. The diversity factor gives us a correction factor to use, which results in a lower total kW load for the ten A/C units. If the energy balance we do for this facility comes out within reason, but the demand balance shows far too many kW for the peak load, then we can use the diversity factor to bring the kW into line with the facility's true peak load. The diversity factor does not affect the kWh; it only affects the kW.
Motor load, use and diversity factors: Sometimes motor load factors that are too low are chosen because the auditor has not properly determined the hours of use of the motors - i.e. the auditor uses an incorrect use factor. For example, just because a facility has a production shift that is 2000 hours per year it does not mean that all of the production-related motors in that facility are operated for 2000 hours per year. Some motors - or machines - might only be used one day a week rather than every day. Other motors might be used every day, but for only half the day, i.e. 4 hours per day. Other motors might be in use throughout the day so that their use really is 2000 hours per year. The auditor must collect data on the use factor - or hours of use - for every motor in the facility during site visit. For each machine, line, process or operation, ask "How many hours a day does this machine (line, process or operation) operate?" This data then needs to be entered into the energy balance. Motor load factors in many facilities are more in the range of 40% - 50%, than in the range of 80% that had been a standard assumption for many years of doing audits. Rarely do you find a motor running at 100% load factor. However, not all motors at a facility are running at the same load factors. Ventilating fans that come from a supplier as a packaged unit with a fan and a motor are most often assumed to be operating at near full load. You should probably use a load factor of 80% here, since the manufacturer of the ventilating fans should have reasonably matched these loads. Other motors may also be in this category - some engineering judgment and common sense are required to determine which other motors these are. Motors with variable loads are going to have the lowest load factors in general. A dust collector fan motor will normally have quite a variable load, and would often be expected to have a low load factor. Other examples are saws, presses, milling machines, sanders and grinders, waste grinders, water pumps, hydraulic pumps, etc. If a group of motors do not all operate together all of the time, then using a diversity factor is appropriate. This is the case with a number of separate air conditioning units (considering the motors for the compressors) that are individually thermostatically controlled. It could also be the case for a group of production motors if some of the motors are not in use all of the time. You should use a diversity factor in your motor calculations, since it is not often the case that a facility has all of the motors on at the same time. Reconciling the energy balance: When you perform an energy balance, do not use the motor load factor as the first and only adjustment made to reconcile the estimated energy use (energy balance) with the energy bills. Making this adjustment too quickly results in failure to pick up other things that have been overlooked. For example, if the energy use does not balance with the energy bills, the first step is to check to see that all of the equipment and uses have been accounted for. Do the items on the energy balance spreadsheet match your recollection of the equipment you saw in the facility?Does anything appear to be missing?Are the utility bills for total energy use and peak kW recorded correctly? The next step is to check the hours of use for lights and other equipment to see if it matches your knowledge of the facility's operation. Remember that each motor - as well as each other piece of equipment - does not necessarily operate the same number of hours each day or year. Finally, if some of the equipment does not come on at the same time as the facility peaks in kW use, then utilize the diversity factor to account for this.Adjusting the motor load factors should probably be the last thing you do to reconcile the energy and demand balances. Now, if all other information and all other factors are correct to the best of your knowledge, then adjust the load factors. While motor load factors are not often in the range of 80-100%, you should be equally suspect of very low motor load factors. If you get motor load factors in the range of 20-30%, it is more likely that you have the hours of use wrong.
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