Optimization of industrial refrigeration plants

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

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

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

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)

IndustriesPC&R %

of Total (A/B)NAICS Code

Source: EIA PC & R = Process Cooling & Refrigeration

Industrial Refrigeration Systems - Overview

Refrigerant – typically Ammonia Compression

Single Stage Multi-Stage Economizer

Evaporators Direct Expansion Flooded (Shell) Liquid Overfeed Hybrid

Controls

Industrial Refrigeration Systems - Overview

45-50 FCooling Loads

HighPressureReceiver(Liquid)

135-165 psia

Liquid

Am m onia(NH 3) Gas

Liquid +G as

Therm alExpansion Valve

BackpressureValve

Interm ediatePressureReceiver

(Liquid+Gas)

Throttle Valve

25-30 FCooling Loads

Pum pThrottleValve

Low PressureReceiver

(Liquid+G as)-10 to -15 F

Cooling Loads

Pum p

G as

Liquid +G as

G as

G as

Com pressor #1

Com pressor #2

Condenser

Hybrid Liquid Overfeed & DX

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

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

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

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)

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

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

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

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

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

Evaporators - Performance

Optimized Operations can save 10-15% in System Energy Consumption

Source: Energy Center of Wisconsin

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

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

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 YogurtSystem Details

Case Study – Stonyfield Farm YogurtSystem Details

Compressor #1250 HP, 198 tons



Condenser

Low Pressure Receiver(G as & L iquid)

Ice Storage

HTST, Vats,S ilos, C ream

Tanks

15 HP

H ighPressureReceiver

5 HP

Space Cooling

(20) Chill Cells

(9) W arehouseCoolers

(1) P late F reezer

G lycol Loop

HX

Am m onia (NH 3) Gas

Am m onia (NH 3) Liquid

(NH 3)Liquid

(NH 3)Gas & Liquid

Am m onia(NH 3) Gas

Suct

Press

Manually Controlled


Am m onia (NH 3) GasValve

Case Study – Stonyfield Farm YogurtAnalysis

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

Case Study – Stonyfield Farm YogurtSystem 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

BH

P/T

Tt

350 HP 250 HP 125 HP 50 HP

Case Study – Stonyfield Farm YogurtSystem Performance

FES - 350 HP

Slide Valve Position % Tons 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% 268.2 305.7 1.1 228.1

Case Study – Stonyfield Farm YogurtEnergy Saving Strategies for Sequencing

EXISTINGCooling Load,

Tons250 HP

#1125 HP

#2350 HP

#3

Step 1 0 - 30 OFF OFF OFFStep 2 27 - 105 OFF ON-25% OFFStep 3 150 - 198 ON-77% Backup OFFStep 4 209 - 268 Backup OFF ON-78%Step 5 227 - 303 ON-75% ON-75% BackupStep 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

Case Study – Stonyfield Farm YogurtRecommendations

Sequencing MeasuresEnergy Demand Annual SimpleSavings 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 2Cooling Load,

Tons250 HP

#1125 HP

#2350 HP

#3

Step 1 0 - 30 OFF OFF OFFStep 2 27 - 105 OFF ON-45% OFFStep 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 1Cooling Load,

Tons250 HP

#1125 HP

#2350 HP

#350 HP

#4

Step 1 0 - 38 OFF OFF OFF ON-20%Step 2 50 - 105 OFF ON-47% OFF OFFStep 3 106 - 268 OFF OFF ON-40% OFFStep 4 269 - 306 OFF OFF ON-87% ON-100%Step 5 310 - 373 OFF ON-100% ON-75% OFFStep 6 374 - 466 ON-100% OFF ON-66% OFFStep 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

Case Study – Stonyfield Farm YogurtRecommendations

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