• The average cost of electricity is $0.05/kWh ($15/MMBtu)
• There are 2000 hours per year per shift (based on the assumption that one shift is 8 hours per day, 5 days per week, 50 weeks per year)
• Switching from electric heat to natural gas or #2 fuel oil can reduce heating costs by 78%
• Average cost savings for demand reduction:  By shifting an operation to off-peak hours, the following savings are achieved:  $75/Hp/year
• The average benefit of shifting other electrical equipment to off-peak hours is: $120/kW/year

    Pay back estimates for the following recommendations will use the equation below.  They will vary depending on the, application, type of installation, and purchase quantity of material and labor associated with each recommendation.  It will be up to the person doing the analyses to use the URL references below each equation to help estimate an implementation cost.

    The data correlating to the variables below each equation will be prompted for in order to execute a calculation.  Frequently the fuel cost (FC) associated with the specific recommendation will be prompted for in order to calculate the annual cost savings (ACS). Unless otherwise specific to a particular recommendation the ACS will calculated as follows:
 

1. Optimize plant power factors
2. Install demand controller/load shedder
3. Install power factor controllers on motors
4. Reduce transformer capacity
5. Check accuracy of power meter
6. Reduce rates
7. Take advantage of utility controlled power management for price reduction
8. Reduce late fees
9. Install efficient rectifiers

      The power factor is the ratio between the resistive component of AC power and the total (resistive and inductive) power supplied.  The installation of capacitors to improve power factor will reduce utility demand charges. There will also be some additional savings from the reduced in-plant power line losses (improving the power factor results in a proportionally decreased current, and thus a reduction in the line power losses, which are proportional to the square of the current). There will be no energy savings from the reduction in utility demand charge. Since it costs more to provide electricity with a low power factor it is common for electrical utilities to make an additional charge if the power factor is less than some value (typically 0.90).  Equipment that contributes to a low power factor includes welding machines, induction motors, power transformers, electric arc furnaces, and fluorescent light ballasts. The following equation shows the utility savings that can occur.

2.  Install demand controller/load shedder

     Install demand controller or load shedder to limit peak demand. There will be no energy savings since demand is shifted, not reduced.  The following equation shows the savings that can be achieved.

3.  Install power factor controllers on motors

    Power factor controllers when properly installed on AC motors will reduce reactive currents produced by the quality of the AC power (ie how much the current leads or lags the voltage supplied).  The power loss from the reactive currents does no useful work and contributes to energy losses.  The size of power factor controllers for T-frame motors may be higher than those of U-frame motors of the same horsepower, speed and design.   Typically the power factor for T-frame motors is less than that of U-frame motors.  The following equation illustrates the potential savings that can be derived when the installation of a power factor controller is considered.
 
 








Power Engineering Books
NEMA
Thomas Register

PFLKW = Present Full Load KW = HP x CON x 1/PME
HP = motor horsepower
CON = conversion factor, 0.746 KW/hp
PME = present full load motor efficiency (choose Motor efficiency table for a value)

PIKW = Present Idling KW = PFLKW x LF
LF = load factor at idling

NFLKW = New Full Load KW = HP x CON x 1/NME
NME = new full load motor efficiency

NIKW = New Idling KW = PFLFW x NLF
NLF = new load factor at idling
FOH = operating hours at full load
IOH = operating hours of idling

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4.  Reduce transformer capacity

     De-energize excess transformer capacity to avoid utility charges; redistribute existing loads to permit removal of under loaded transformers.  Note:  consider power loss as well as initial loads and growth in sizing transformers.
    Transformers have substantial continuing no-load losses, related to the primary side voltage, so they incur power losses on the basis of their full load rating (ref.- South Carolina Energy Conservation Manual, Governor's Division of Energy Agriculture and Natural Resources).  The following equation illustrates the potential energy savings that can be achieved.

Power Engineering Books
Thomas Register
NEMA

RC = rated capacity, KW
NL = fractional loss with no load^*
OT = off time for transformers, hrs/yr

* According to "Kent's Mechanical Engineers Handbook, 12th Edition", the no load loss of transformers is between 0.3% of the rated capacity for small power transformers (500 kVA and more) and 1% for small distribution transformers (500 kVA and less).

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5.  Check accuracy of power meter

     The accuracy of a power meter can be an underlying reason why a particular trend of unknown energy loss has occurred in a manufacturing plant  The following equations are used to determine the annual cost savings with the installment of an accurate metering device.
 

 
Power Engineering Books
Thomas Register
NEMA

ED = excess demand due to meter error (KW)^*
RU = rate per unit of electrical power, ($/KW)
^*User demand can be calculated from a watt-hour meter using the following formula:



Kh = gearing ratio between disk rotation and movement of hands on the meter
M = product of the ratio of current or potential transformers, if in use
R = number of disk revolutions measured in time T
T = time in seconds

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6.  Reduce rates

    Reduce rates and/or restructure rate schedules or make other changes in electric service in order to obtain lowest possible rates.  The following equation illustrates the potential savings that can occur when rate schedule changes are made to obtain the least possible rates.

7.  Take advantage of utility controlled power management for price reduction,

    Pay utility bills on schedule to avoid late fees. Annual cost savings will equal the amount which would have been paid as late fees.  The following equation provides an insight to the potential savings that can be achieved.
 

Power Engineering Books
Thomas Register
 

NB = original billed amount, $ (from utility bill)
PLC = percent charged as late fees (from utility bill)

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9.  Install efficient rectifiers

    Install efficient rectifiers in place of existing rectification or DC generating equipment  The following equation shows the savings that can be achieved.