1. Optimization of Industrial
Refrigeration Plants:
Including a Case Study at
Stonyfield Farm Yogurt
prepared and presented by
Mark D’Antonio:
Satyen Moray:
Lisa Drake:
Randy Dixon:
Energy & Resource Solutions, Inc. (ERS)
Energy & Resource Solutions, Inc. (ERS)
Stonyfield Farm Yogurt
Public Service of New Hampshire
ACEEE 2005 Summer Study
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2. Presentation Overview
Introductions
The US Industrial Refrigeration Market
Overview of Industrial Ammonia Refrigeration
Systems
Primary Refrigeration Components
Compressors
Condensers
Evaporators
Energy Savings Strategies
Case Study
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3. Introductions
Public Service of New Hampshire (PSNH)
Funded Technical Assistance – Engineering Assessment
Incentives
Stonyfield Farm Yogurt
Supported the Engineering Assessment
ERS
Conducted the Engineering Assessment
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4. Overview - US Industrial Refrigeration Market
Ene rgy C onsumption (M illions of kW h)
PC& R %
% of Tota l
P roc e ss C ooling &
N A IC S C ode
Industrie s
Tota l
of Tota l (A /B ) U S P C & R (A /D )
R e frige ra tion
(B )
(P C & R ) (A )
Food
311
17,679
67,390
26.2%
28.6%
B e ve ra ge a nd Toba c c o P roduc ts
312
2,349
8,242
28.5%
3.8%
C he mic a ls
325
16,109
215,008
7.5%
26.1%
A ll M a nufa c turing Industrie s
311-339
61,763 (D )
1,025,149
6.0%
100.0%
Source: EIA
PC & R = Process Cooling & Refrigeration
Food & Beverage Sectors have high PC&R %
Food & Chemicals comprise a high % of consumption in
the industry (55%)
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5. Industrial Refrigeration Systems - Overview
Refrigerant – typically Ammonia
Compression
Single Stage
Multi-Stage
Economizer
Evaporators
Direct Expansion
Flooded (Shell)
Liquid Overfeed
Hybrid
Controls
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6. Industrial Refrigeration Systems - Overview
Hybrid Liquid Overfeed & DX
Liquid
Condenser
High
Pressure
Receiver
(Liquid)
135-165 psia
Ammonia
(NH3) Gas
Thermal
Expansion Valve
45-50 F
Cooling Loads
Throttle Valve
Backpressure
Valve
Gas
Liquid +Gas
Compressor #2
Intermediate
Pressure
Receiver
(Liquid+Gas)
25-30 F
Cooling Loads
Pump
Throttle
Valve
Compressor #1
Gas
Gas
Low Pressure
Receiver
(Liquid+Gas)
Liquid +Gas
-10 to -15 F
Cooling Loads
Pump
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7. Refrigerant - Ammonia
Refrigerant - Ammonia (R-717) is typical for
industrial systems
Less expensive
3-10% > efficiency than HCFC-22 and HCFC134a
More tolerant of moisture than other refrigerants
Lubricants are easily separated out
High latent heat capacity results in smaller equipment
Strong odor - leaks are easily detected
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8. Compressors
Consume a large % of system energy
Should be optimized for load profile
Predominant Types
Reciprocating
Single Stage
Internally compounded
Typically < 100 HP
Good efficiency at part load
Screw
Fixed Volume Index - slide valve or bypass ports
Variable Volume Index - slide valve or VFD
Part load efficiency dependent on controls
Output capacity control from 10%-100%
Typically > 100 HP
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9. Compressors – Part Load Performance
Source: (Evaporative Condenser Control in Industrial Refrigeration Systems, 2001, K. A. Manske, D.T. Reindl, and S.A. Klein,
Mechanical Engineering Department, University of Wisconsin – Madison)
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10. Compressors – Performance Factors
Suction Pressure
Lower suction pressure = increased energy consumption
Condensing Pressure
Dependent on condenser capacity & ambient conditions
Lower condensing pressure = lower temp = lower compressor energy
(likely higher fan energy)
Efficiency
Design Selection
Sequencing to Match Load Profile
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11. Compressors – Load Sharing Strategies
Multiple Screw Compressors of Same Size
Loads between 50%- 65%: split equally between compressors
Loads greater > 65%: Base Load one, trim with other
Multiple Reciprocating Compressors of Same Size
Loads between 50%- 65%: split equally between compressors
Loads greater > 65%: Base Load one, trim with other
Multiple Compressors of Varying Types & Sizes
Optimize to Load Profile
Base Load Screws, trim with Recips or VFD controlled units
Part Load Operation of Screw Compressors should be avoided (except
w/VFD control)
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12. Condensers
Rejection of heat from the system
Consume approx. 15%-20% of system energy
Air Cooled
Function of Ambient Conditions
Less Capacity, Lower efficiency
Water Cooled
Operate at Lower Condensing Pressures
Greater Capacity, Higher efficiency
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13. Condensers - Control
Evaporative Condensers
Capacity Control
Head Pressure Control (altered by airflow rate)
Shutting off spray water (winter)
Fan Flowrate Control
On/Off
Two Speed
VFD
Source: Energy Center of Wisconsin
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14. Condensers – Efficiency Strategies
Use High Efficiency Motors on Fans & Pumps
Use VFDs on Fans & Pumps where appropriate
VFD control can result in considerable reduction over ON/OFF strategy
Greater Surface Area = Improved Efficiency
Oversized Condenser
Optimization of Condenser Systems
Staging of Multiple Condensers
VFDs & Floating Head Pressure Control
Keep Surfaces Clean for Optimal Heat Transfer
Water Treatment – free of mineral and bacterial
buildup
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15. Evaporators
Properly Sized for Design Loads
Types
Pumped Liquid Overfeed – higher efficiency, lower temperatures and
more uniform liquid
Flooded Shell & Tube – indirect or secondary cooling through
water/brine
Direct Expansion – not typically used with Ammonia Systems (low
efficiencies and higher refrigerant temperatures)
Hybrid – a combination of evaporator types
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16. Evaporators - Control
At Design Conditions only a small % of the time
Fan Control Strategies
Fan Cycling –maintain space setpoint temperature
Refrigerant Cycling – refrigerant delivery is controlled, fan operates continually
Fan Speed Control – speed is varied to maintain space setpoint temperature
using VFD or Two-Speed Fan
Shell & Tube Capacity
Control the Return Liquid Temperature
Defrost
Hot Gas Bypass – preferred, when needed vs. timed
Hot Water
Electric
Warm Air
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17. Evaporators - Performance
Source: Energy Center of Wisconsin
Optimized Operations can save 10-15% in
System Energy Consumption
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18. Overall Energy Savings Strategies
Reduce Heat Loads – low cost
Turn Off Lights, Increase Insulation,Reduce Infiltration, Maintain Clean Heat Exchanger
Surfaces
Reduce Temperature Lift in the Refrigeration Plant
Optimize Compressor Plant Efficiency (lowest BHP/Ton)
Equipment Selection
Controls
Aux Pumping Efficiency
Optimize Defrost Control Strategy
Optimize Evaporator/Condenser Relation
Lowest Condensing Temperature and Highest Evaporator Temperature
Optimize Fan Usage (condenser, evaporator)
Staging or VFD
Automated Real-time Central Controls
Heat Recovery
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19. Case Study – Stonyfield Farm Yogurt
Founded 1983
All Natural and Organic Dairy Products
Yogurts
Smoothies
Ice Cream
100,000 Square Foot Facility
24/7 Operation
$90 Million in Annual Sales
Produces 45,000 cases of yogurt/day
Primary Focus was to verify Sequencing Strategy
1+ MW, 6 Million kWh
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20. Case Study – Stonyfield Farm Yogurt
System Details
Ammonia – Pumped Liquid Overfeed
Peak Summer Load = 570 Tons
Multiple Screw Compressors w/Slide Valve Capacity Controls
350 HP, 250 HP, 125 HP, 50 HP
Central Sequencer Controls
The 50HP was not on the system
Set to maintain 25 psig suction pressure
Process & Space Cooling Loads
High Temp Short Time Pasteurizers
Pasteurization & Culture Vats
Silos & Cream Tanks
Chill Cells
Warehouse
Space Conditioning
Refrigeration = 35% of Facility Electrical Usage(~2 million kwh)
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21. Case Study – Stonyfield Farm Yogurt
System Details
Condenser
Ammonia (NH3) Liquid
HTST, Vats,
Silos, Cream
Tanks
15 HP
Ammonia
(NH3) Gas
High
Pressure
Receiver
Compressor #3
350 HP, 268 tons
Ice Storage
Ammonia (NH3) Gas
Valve
Compressor #1
250 HP, 198 tons
Suct
Press
Ammonia (NH3) Gas
Low Pressure Receiver
(Gas & Liquid)
Compressor #2
125 HP, 105 tons
5 HP
Compressor #4
50 HP, 38 tons
HX
Space Cooling
Manually Controlled
(NH3)
Liquid
Glycol Loop
(20) Chill Cells
(NH3)
Gas & Liquid
(9) Warehouse
Coolers
(1) Plate Freezer
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22. Case Study – Stonyfield Farm Yogurt
Analysis
Goal for this Assessment:
Optimize Sequencing of Compressors
Identify Other Opportunities for Future Study
Developed Load Profile
Power Monitoring – FES Control System
Extracted Data and Developed Load Profile
Established Performance Data
Created Analytical Models of Sequencing Strategies
Combined Load Data & Performance Data
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23. Case Study – Stonyfield Farm Yogurt
System Performance
Refrigeration Compres or Performance Curves
s
4.80
4.60
4.40
4.20
4.00
3.80
3.60
BHP/TT
3.40
3.20
3.00
2.80
2.60
2.40
2.20
2.00
1.80
1.60
1.40
1.20
1.00
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
%Capacity
350 H
P
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250 H
P
125 H
P
50 H
P
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24. Case Study – Stonyfield Farm Yogurt
System Performance
FES - 350 HP
Slide Valve Position %
BHP
BHP/Ton
kW
10%
26.8
77.7
2.9
58.0
20%
53.6
92.9
1.7
69.3
30%
80.5
114.2
1.4
85.2
40%
107.3
141.4
1.3
105.5
50%
134.1
159.8
1.2
119.2
60%
160.9
187.0
1.2
139.5
70%
187.7
220.4
1.2
164.4
80%
214.6
250.8
1.2
187.1
90%
241.4
278.3
1.2
207.6
100%
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Tons
268.2
305.7
1.1
228.1
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25. Case Study – Stonyfield Farm Yogurt
Energy Saving Strategies for Sequencing
Existing Sequencing
EXISTING
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
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Cooling Load,
Tons
0 - 30
27 - 105
150 - 198
209 - 268
227 - 303
269 - 373
275 - 466
400 - 571
250 HP
#1
OFF
OFF
ON-77%
Backup
ON-75%
Backup
ON-85%
ON-70%
125 HP
#2
OFF
ON-25%
Backup
OFF
ON-75%
ON-65%
Backup
ON-70%
350 HP
#3
OFF
OFF
OFF
ON-78%
Backup
ON-75%
ON-40%
ON-70%
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26. Case Study – Stonyfield Farm Yogurt
Recommendations
Sequencing Measures
Energy
Savings
(kWh)
Energy Efficiency Measure
Demand
Reduction
(kW)
Installed
Cost
Annual
Cost
Savings
Simple
Payback
(Years)
EEM-1 Optimization of Refrigeration Sequencer Set Points (Option-1) (Include 50-HP compressor in the sequencer)
Savings Summary
27,471
0.0
$10,000
$1,997
5.0
EEM-2 Optimization of Refrigeration Sequencer Set Points (Option-2) (Optimize existing sequencer set points)
Savings Summary
18,322
0.0
$0
0.0
Proposed Sequencing
Option 2
Proposed Sequencing
Option 1
OPTION 2
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
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Cooling Load,
Tons
0 - 30
27 - 105
110 - 268
270 - 373
374 - 466
470 - 570
250 HP
#1
OFF
OFF
OFF
OFF
ON-100%
ON-100%
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125 HP
#2
OFF
ON-45%
OFF
ON-100%
OFF
ON-100%
350 HP
#3
OFF
OFF
ON-40%
ON-60%
ON-65%
ON-60%
OPTION 1
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
Cooling Load,
Tons
0 - 38
50 - 105
106 - 268
269 - 306
310 - 373
374 - 466
470 - 504
520 - 570
250 HP
#1
OFF
OFF
OFF
OFF
OFF
ON-100%
ON-100%
ON-100%
125 HP
#2
OFF
ON-47%
OFF
OFF
ON-100%
OFF
OFF
ON-100%
350 HP
#3
OFF
OFF
ON-40%
ON-87%
ON-75%
ON-66%
ON-85%
ON-80%
50 HP
#4
ON-20%
OFF
OFF
ON-100%
OFF
OFF
ON-100%
OFF
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27. Case Study – Stonyfield Farm Yogurt
Recommendations
Additional Opportunities Identified for Further
Study
Floating head pressure controls (set at a constant 135-psig)
Oversized condensers
No VFDs on condensers, evaporators or compressors
Evaporator capacity control (refrigerant cycling)
Condenser fans - single speed, ON/OFF
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28. Questions?
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