UFC 3-520-01
June 10, 2002
B-12
Table B-1. Example Adjustable Speed Drive Energy Savings Worksheet
Input Data for Existing Application
Motor ID #
HVAC Fan - 1
Comments
Motor Horsepower/Watts
60/44,760
Larger motors provide greater payback.
Motor Efficiency (From Nameplate)
91.7%
Evaluate efficiency at less than full load.
Motor Load Factor
50.0%
Existing energy usage is lower if the
motor is operating at less than full load.
This value is obtained from metering or
monitoring.
Number Hours Operation per Year
8,760
Hours of operation per year is particularly
important to energy analysis.
Existing Motor Energy Use (kWh/yr)
213,794
= [(60
×
0.746)/0.917]
×
8760
×
0.5
Calculation for Adjustable Speed Operation
ASD Efficiency
95.0%
Operating Schedule With ASD
Frequency
Percent
Speed
Percent Time
Energy
(kWh)
32,812 = [213,794
×
(0.9)
3
×
0.2]/.95
54
90.0%
20.0%
32,812
40,328 = [213,794
×
(0.8)
3
×
0.35]/.95
48
80.0%
35.0%
40,328
27,017 = [213,794
×
(0.7)
3
×
0.35]/.95
42
70.0%
35.0%
27,017
4,861 = [213,794
×
(0.6)
3
×
0.1]/.95
36
60.0%
10.0%
4,861
Estimated Energy Use With ASD
Total:
105,018
Economic Analysis and Payback Calculation
Annual Energy Savings (kWh):
108,776
= (213,794 - 105,018)
Cost per Kilowatt Hour:
$0.06
Based on local commercial power rates.
Annual Cost Savings:
$6,527
= (108,776
×
$0.06)
Estimated Installation Cost Per Motor
Horsepower:
$225
Estimate based on ASD operating
requirements and features.
Estimated Installation Cost:
$13,500
= (60 hp
×
$225)
Payback Period (Years)
2.07
= (13,500/6,527)
B-7.4
Payback periods greater than 5 years should not be approved solely on the
basis of economic savings; operating system improvements should also be an identified
need for these cases.
B-8
SURGE VOLTAGE LET-THROUGH BY EXCESSIVE LEAD LENGTH.
B-8.1
Lead length refers to the length of conductor between the circuit connection
and a surge protector, and is the critical installation attribute for parallel-type surge
protectors. For typical installations, the lead conductor has negligible resistance, but a
significant inductance when subjected to a high frequency surge transient. This
inductance can develop a substantial voltage drop under surge conditions, thereby
proportionately increasing the let-through voltage. Figure B-6 shows the circuit model