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Douglas Reindl, Ph.D., P.E. Professor, University of Wisconsin-Madison
Director, Industrial Refrigeration Consortium
Exploring Industrial Refrigeration Systems and Energy Efficiency Opportunities
© (2012) Reindl, All Rights Reserved
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Regional Electric Consumption (SIC 20)
Census Region 2006 Electricity
Consumed [million kWh]
Northeast 5,441 Midwest 30,774 South 24,169 West 13,057 Total 73,441
Source: EIA, 2009
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Food Industry Energy Costs Increase Projected
230
240
250
260
270
280
290
300
310
320
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Proj
ecte
d El
ectr
icity
Pur
chas
es
(tril
lion
Btu)
Elec
tric
ity E
xpen
ditu
res
(b
illio
ns, 2
008
$US)
Year
Electricity expenditures ($US)
Purchased Electricity
Source: EIA “Energy Outlook”, 2010
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Single Stage Compression System
Flooded Evaporator
Evaporative Condenser Evaporative
Condenser
High Pressure Receiver
3
King valve (automatic)
3
Evaporative Condenser Evaporative
Condenser
High pressure gas
Suction Trap
Compressor(s)
T T
DX evaporator
Refrigerant Transfer System
To HPR
Dry suction
Hig
h pr
essu
re li
quid
1
4’ Pumped
recirculator 4”’
Wet return
Compressor(s)
4
2
Overfed evaporator(s)
T
Equa
lizer
line
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Two-Stage Compression System
5
Equalizer
Evaporative Condenser(s)
Low temperature evaporator(s)
Intercooler
Booster Compressor(s)
High-Stage Compressor(s)
High Pressure Receiver
1 2
3
5
5’
6
5’’
4’
King valve
4’
4
7
Low temp
recirculator
High stage discharge
High stage suction Booster discharge
Boos
ter s
uctio
n
High pressure liquid
Medium pressure liquid
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Let’s Explore Some Energy Efficiency Improvement
Opportunities
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10 Efficiency Improvement Opportunities
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Lowering Head Pressure
Refrigerant Efficiency Gain [%/°F]1 Application
R22 1.2 Refrigeration [High stage] R410a 1.4
R717 1.3 R22 1.6
Air conditioning R410a 1.8
Rules-of-thumb
1 Percent efficiency gain per °F decrease in saturated condensing temperature
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Raising Suction Pressure
Refrigeration Duty
Efficiency Gain [%/°F]1 Comments
High stage 1.7 Relatively insensitive to refrigerant type Low stage 2.2
Rules-of-thumb
1 Percent efficiency gain per °F increase in saturated suction temperature
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Applying VFDs
• Condenser fans o All or none – expect 2 to 3% savings
• Evaporator fans o 2 to 4% savings range o Simple paybacks range from 1 to 5 years
• Compressor o At most, one VFD comp per suction level o Simple paybacks range from 1 to 4 years
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Case Studies
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Madison Ice Arena
• New system (one year old) • City-owned and operated • Rink operated year round • 103 tons capacity • Six compressors – max power = 240 kW • R22 with ethylene glycol to rink • Evaporatively condensed • Annual electrical operating cost: $45,600
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Madison Ice Arena
• As-installed – head pressure controlled 220-235 psig
• Proposed –condenser pressure allowed to ‘float’ down to 150 psig
• Required change – fan controller set point
• Advantages
o Fewer machines running = lower maintenance
o 21% operating cost savings = $9,600/yr
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VFD
System #1 (1992)
System #2 (1998)
Water Pumps Total [HP] 300 450
Fan Total [HP] 480 900
Compressor [HP] 9,100 14,000
System NH3 Charge [kg] 88,400 83,900
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Condenser VFD Retrofit
System #1 retrofit project • Installed 12-15HP, 12-25HP VFDs for 6 evaporative
condensers • Set 15 Hz minimum condenser fan speed • Did not upgrade to inverter duty motors • Did not have motor failures due to VFDs
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Condenser VFD Retrofit (continued)
Energy & economics
51% reduction in fan kWh
4% reduction in system kWh
1.5 year simple payback
Other benefits
Soft-start with no more fan squealing
Better head pressure control
Quiet
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Dairy Plant (Ice Cream)
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Plant Energy Efficiency Opportunities
• Major addition 3 years prior • New industrial ammonia
refrigeration system installed • State-of-the-art design, controls • No industry energy benchmarks to
compare: o Annual energy use = 29,179,000 kWh o Peak demand = 13 MW o Annual energy cost = ~$8,000,000
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Significant Savings Opportunities Identified
Non capital
($411,121) savings
Immediate payback
+Capital ($732,900) savings
<2 year payback
That’s a LOT of ice cream!
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Keys To Success
• Identify energy efficiency improvement opportunities • Evaluate cost/benefit • Assess operational risk/constraints • Methodically implement/verify • Don’t let low hanging fruit grow back
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Questions?
Douglas Reindl, Ph.D., P.E. Professor, University of Wisconsin-Madison
Director, Industrial Refrigeration Consortium
Thank you!