This presentation summarized an engineering assessment of the refrigeration system at Stonyfield Farm Yogurt to optimize efficiency. The assessment analyzed the existing compressor sequencing strategy and developed two proposed optimized strategies estimated to save 27,471 kWh annually and 18,322 kWh annually, respectively. Additional opportunities for further study were also identified, such as floating head pressure controls, condenser and evaporator fan upgrades, and refrigerant cycling for evaporators.
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Optimization of industrial refrigeration plants
1. Main Headquarters: 120 Water Street, Suite 350, North Andover, MA 01845 With offices in: NY, ME, TX, CA, OR www.ers-inc.com
OPTIMIZATION OF INDUSTRIAL REFRIGERATION PLANTS:
INCLUDING A CASE STUDY AT STONYFIELD FARM YOGURT
Prepared and presented by
Mark D’Antonio: Energy & Resource Solutions, Inc. (ERS)
Satyen Moray: Energy & Resource Solutions, Inc. (ERS)
Lisa Drake: Stonyfield Farm Yogurt
Randy Dixon: Public Service of Ne Hampshire
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
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 ers
energy&resource
solutions
4. OVERVIEW - US INDUSTRIAL
REFRIGERATION MARKET
Food & Beverage Sectors have high PC&R %
Food & Chemicals comprise a high % of consumption in the
industry (55%)
Process Cooling &
Refrigeration
(PC&R) (A)
Total
(B)
Food 311 17,679 67,390 26.2% 28.6%
Beverage and Tobacco Products 312 2,349 8,242 28.5% 3.8%
Chemicals 325 16,109 215,008 7.5% 26.1%
All Manufacturing Industries 311-339 61,763 (D) 1,025,149 6.0% 100.0%
% of Total
US PC&R (A/D)
Energy Consumption (Millions of kWh)
Industries
PC&R %
of Total (A/B)
NAICS Code
Source: EIA
PC & R = Process Cooling & Refrigeration
5. INDUSTRIAL REFRIGERATION SYSTEMS -
OVERVIEW
Refrigerant – typically Ammonia
Compression
Single Stage
Multi-Stage
Economizer
Evaporators
Direct Expansion
Flooded (Shell)
Liquid Overfeed
Hybrid
Controls
6. INDUSTRIAL REFRIGERATION SYSTEMS -
OVERVIEW
45-50 F
Cooling Loads
High
Pressure
Receiver
(Liquid)
135-165 psia
Liquid
Ammonia
(NH3) Gas
Liquid +Gas
Thermal
Expansion Valve
Backpressure
Valve
Intermediate
Pressure
Receiver
(Liquid+Gas)
Throttle Valve
25-30 F
Cooling Loads
Pump
Throttle
Valve
Low Pressure
Receiver
(Liquid+Gas)
-10 to -15 F
Cooling Loads
Pump
Gas
Liquid +Gas
Gas
Gas
Compressor #1
Compressor #2
Condenser
Hybrid Liquid Overfeed & DX
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
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
9. 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
10. 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)
11. 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
12. 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
13. 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
14. 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
15. 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
16. EVAPORATORS - PERFORMANCE
Optimized Operations can save 10-15%
in System Energy Consumption
Source: Energy Center of Wisconsin
17. 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
18. 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
CASE STUDY – STONYFIELD FARM YOGURT
19. 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)
CASE STUDY – STONYFIELD FARM YOGURT
SYSTEM DETAILS
20. CASE STUDY – STONYFIELD FARM YOGURT
SYSTEM DETAILS
Compressor #1
250 HP, 198 tons
Compressor #2
125 HP, 105 tons
Compressor #4
50 HP, 38 tons
Condenser
Low Pressure Receiver
(Gas & Liquid)
Ice Storage
HTST, Vats,
Silos, Cream
Tanks
15 HP
High
Pressure
Receiver
5 HP
Space Cooling
(20) Chill Cells
(9) Warehouse
Coolers
(1) Plate Freezer
Glycol Loop
HX
Ammonia (NH3) Gas
Ammonia (NH3) Liquid
(NH3)
Liquid
(NH3)
Gas & Liquid
Ammonia
(NH3) Gas
Suct
Press
Manually Controlled
Compressor #3
350 HP, 268 tons
Ammonia (NH3) Gas
Valve
21. 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
22. Case Study – Stonyfield Farm Yogurt
System Performance
Refrigeration Compressor Performance Curves
1.00
1.20
1.40
1.60
1.80
2.00
2.20
2.40
2.60
2.80
3.00
3.20
3.40
3.60
3.80
4.00
4.20
4.40
4.60
4.80
10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Capacity
BHP/TTt
350 HP 250 HP 125 HP 50 HP
24. CASE STUDY – STONYFIELD FARM YOGURT
ENERGY SAVING STRATEGIES FOR SEQUENCING
EXISTING
Cooling Load,
Tons
250 HP
#1
125 HP
#2
350 HP
#3
Step 1 0 - 30 OFF OFF OFF
Step 2 27 - 105 OFF ON-25% OFF
Step 3 150 - 198 ON-77% Backup OFF
Step 4 209 - 268 Backup OFF ON-78%
Step 5 227 - 303 ON-75% ON-75% Backup
Step 6 269 - 373 Backup ON-65% ON-75%
Step 7 275 - 466 ON-85% Backup ON-40%
Step 8 400 - 571 ON-70% ON-70% ON-70%
Existing Sequencing
25. CASE STUDY – STONYFIELD FARM YOGURT
RECOMMENDATIONS
Sequencing MeasuresEnergy Demand Annual Simple
Savings Reduction Installed Cost Payback
Energy Efficiency Measure (kWh) (kW) Cost Savings (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 $1,332 0.0
Proposed Sequencing
Option 1
OPTION 2
Cooling Load,
Tons
250 HP
#1
125 HP
#2
350 HP
#3
Step 1 0 - 30 OFF OFF OFF
Step 2 27 - 105 OFF ON-45% OFF
Step 3 110 - 268 OFF OFF ON-40%
Step 4 270 - 373 OFF ON-100% ON-60%
Step 5 374 - 466 ON-100% OFF ON-65%
Step 6 470 - 570 ON-100% ON-100% ON-60%
OPTION 1
Cooling Load,
Tons
250 HP
#1
125 HP
#2
350 HP
#3
50 HP
#4
Step 1 0 - 38 OFF OFF OFF ON-20%
Step 2 50 - 105 OFF ON-47% OFF OFF
Step 3 106 - 268 OFF OFF ON-40% OFF
Step 4 269 - 306 OFF OFF ON-87% ON-100%
Step 5 310 - 373 OFF ON-100% ON-75% OFF
Step 6 374 - 466 ON-100% OFF ON-66% OFF
Step 7 470 - 504 ON-100% OFF ON-85% ON-100%
Step 8 520 - 570 ON-100% ON-100% ON-80% OFF
Proposed Sequencing
Option 2
26. 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