Plant Energy Balance
Effective Energy Management
• Develop baseline
– Utility analysis
– Plant energy balance
– Lean energy analysis (LEA)
• Take action
– Identify and quantify energy saving opportunities
– Prioritize energy saving opportunities
– Implement energy saving opportunities
• Measure and benchmark to sustain efforts
– Develop metrics for system energy efficiency
– Measure energy efficiency improvement with sliding NAC
– Compare energy efficiency between facilities with NAC
Plant Energy Balance
• Energy Balance: Ein – Eout = DEstored
• Plant Energy Balance: Where does Ein go?
Ein
E,out
• In some cases, detailed sub-metered data may be available.
• However, a useful approximation can be derived from the method that
follows.
• This chapter shows how to calibrate approximate the energy use by
equipment against total energy input using the energy balance concept.
• This information is helpful in
– focusing efforts on large energy users
– calibrating engineering models of equipment
Efficiency
• Pinput – Plost – Puseful,output = 0
• Energy efficiency is defined as the
ratio of useful power output to
total power input.
Plost
Pin
• Efficiency = Puseful,output / Pinput
• Many pieces of energy using equipment are rated by
energy or power output. Thus, energy input is:
• Einput = Euseful,output / Efficiency
Puseful,out
Electricity Energy Balance:
Data Supplied By Facility
Number
10
4
200
1
1
2
Type
40-hp stamping machines
50-hp chilled water pumps
400-W MH Lights
100-ton chiller
20-hp cooling tower fan
100-hp air compressors
Rated
Output Power
(hp, kW or tons)
40
50
0.465
100
20
100
Fraction
Loaded
0.50
0.75
1.00
0.50
0.75
0.90
Operating
Hours
(hours/year)
4,000
6,000
7,000
4,000
3,500
6,000
Electricity Energy Balance
Number
10
4
200
1
1
2
Type
40-hp stamping machines
50-hp chilled water pumps
400-W MH Lights
100-ton chiller
20-hp cooling tower fan
100-hp air compressors
Total Listed Equipment
Other Equipment
Measured Total
Rated
Output Power
(hp, kW or tons)
40
50
0.465
100
20
100
Fraction
Loaded
0.50
0.75
1.00
0.50
0.75
0.90
Operating Efficiency
Hours
(hours/year)
4,000
0.90
6,000
0.90
7,000
1.00
4,000
1.00
3,500
0.90
6,000
0.90
Conversion
0.746
0.746
1.000
0.800
0.746
0.746
Annual
Energy Use
(kWh/year)
663,111
746,000
651,000
160,000
43,517
895,200
2,495,717
104,283
2,600,000
Example:
E = 10 motors x 40 hp/motor x 50% / 90% x 4,000 hr/yr x 0.746 kW/hp
E = 663,111 kWh/yr
Fraction
Total
Energy
25.5%
28.7%
25.0%
6.2%
1.7%
34.4%
4.0%
Electricity Energy Balance:
Sorted from Highest to Lowest
Fuel Energy Balance:
Data Supplied By Facility
Number
2
15
2
1
Type
Boilers
Hanging unit heaters
Make-up air units
Dry-off ovens
Rated
Output
(Btu/hour)
3,000,000
100,000
2,000,000
1,600,000
Fraction
Loaded
0.80
1.00
0.70
0.60
Operating
Hours
(hours/year)
6,000
3,000
3,000
6,000
Fuel Energy Balance
Number
2
15
2
1
Type
Boilers
Hanging unit heaters
Make-up air units
Dry-off ovens
Total Listed Equipment
Other Equipment
Measured Total
Rated
Output
(Btu/hour)
3,000,000
100,000
2,000,000
1,600,000
Fraction
Loaded
0.80
1.00
0.70
0.60
Operating
Hours
(hours/year)
6,000
3,000
3,000
6,000
Efficiency
0.80
0.80
1.00
0.85
Annual
Energy Use
(mmBtu/year)
36,000
5,625
8,400
6,776
Fraction
Total
Energy
60.0%
9.4%
14.0%
11.3%
56,801
3,199
60,000
5.3%
Example:
E = 2 boilers x 3 mmBtu/hr-boiler x 80% x 6,000 hr/yr / 80%
E = 36,000 mmBtu/yr
Fuel Energy Balance:
Sorted from Highest to Lowest