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Auditing Commercial Refrigeration What to Look for?
Steve Rottmayer P.E.
© 2013 kW Engineering, Inc.
Q: Why is this sector important? A: Grocery has the highest energy intensity
Grocery stores and food service have
higher end use intensities (kWh/sf)
than any other common
commercial building type.
- 10 20 30 40 50 60
Grocery
Food Service
Health Care
Other
Office
Public Order and Safety
Retail
Lodging
Public Assembly
Education
Service
Warehouse
Religious Worship
Energy Use Intensity (kWh/sf)
Commercial Building Stock Energy Use
© 2013 kW Engineering, Inc.
Source: 2003 Commercial Building Energy Consumption Survey (CBECS),
U.S. DOE, www.eia.doe.gov/emeu/cbecs/.
Refrigeration End Use in Grocery Stores
• Refrigeration is largest end use by far in grocery stores
• Typical use is over 50% of store’s total
© 2013 kW Engineering, Inc.
Source: 2006 Commercial Building Survey Report, Pacific Gas &Electric.
Vapor Compression Cycle
© 2013 kW Engineering, Inc.
Fuller Moore, Environmental Control Systems, McGraw Hill Inc., 1993, pg 220.
www.dataaire.com
Efficient Refrigeration Guiding Principles 1. Minimize loads from
infiltration, defrost, lighting and motors
2. Maintain lowest possible head pressure
3. Maintain highest possible suction temps and maximize compressor efficiency
© 2013 kW Engineering, Inc.
www.copeland-corp.com
low pressure
in
high pressure
out
Avoid lowest common denominator operation.
Use the capabilities of your system & controls!
Principle 1 – Minimize Loads • Strip Curtains • Glass Doors and Night Covers • Door Gaskets and Auto Closers • Case Loading • Insulate Suction Lines
© 2013 kW Engineering, Inc.
• Evaporator Fan Controllers • High Efficiency Evaporator Fan Motors • Anti-sweat Heater Controls • Defrost Controls • Case-lighting Controls • High Efficiency Case Lighting
Refrigerated Case Airflow
© 2013 kW Engineering, Inc.
Improper Case Loading
© 2013 kW Engineering, Inc.
SOURCE: PROPER PRODUCT LOADING IN DISPLAY CASES IMPACTS FOOD SAFETY AND ENERGY EFFICIENCY, Southern California Edison Refrigeration Technology and Test Center, Energy Efficiency Division
Night Covers • Helps reduce infiltration &
radiation heat losses when store is closed
• Made with durable materials
• Helps maintain product temperatures
• Savings require that employees use them!
© 2013 kW Engineering, Inc.
SOURCE: Market Group Ventures Inc. 1-800-519-1222 www.econofrost.com
Night Covers: Savings & Benefits
© 2013 kW Engineering, Inc.
SOURCE: Effects Of The Low Emissivity Shields On Performance And Power Use Of A Refrigerated Display Case, Southern California Edison Refrigeration Technology and Test Center, Energy Efficiency Division, Aug 8, 1997
Overall Compressor Savings were about 9% of daily use or 36% of load when covers were used.
Check defrost time clocks! • Don’t defrost more often than necessary • Don’t defrost during the peak energy use
periods – 12 to 6pm
© 2013 kW Engineering, Inc.
Example of Over-Defrosting • Customer was defrosting – 4 times/day for 70
minutes each • Freezer temperature hit 50°F • Reset to 4 times/day for 15 minutes each • Energy Savings = 79% or $820/year
© 2013 kW Engineering, Inc.
Anti-sweat Heater Controls • Electric resistance
heaters in the doors of freezer cases that use heat to prevent fogging of case door windows
• Often run continuously
• 10 to 20 kW is typical
© 2013 kW Engineering, Inc.
Anti-sweat Control – Costs & Savings • Simple paybacks are in the range of
6 months to 3 years • Savings depend on climate, with dry areas
having greater opportunity for savings than humid areas.
• Typical anti-sweat cycling savings can range from 20% to 80% of the anti-sweat heater load plus associated refrigeration system savings
• May have significant peak kW savings if the summer peak is not humid. Throughout most of the western U.S. the electrical system peak is not usually coincident with humid weather.
© 2013 kW Engineering, Inc.
Case-lighting Controls • Cases are typically
illuminated continuously • In most stores these lights
are on one or two electrical panels
• Adding controls to turn off the case lights at night is very cost effective. It not only reduces the amount of energy the lights consume, but also reduces the amount of heat that is added to the cases by the lights.
© 2013 kW Engineering, Inc.
Case-lighting Controls – Costs & Savings • Typical savings are 25% of the
case lighting load • Plus refrigeration load • May amount to 5% to 7% of
the overall refrigeration load at the store
• Typically 70,000 kWh • No associated peak demand
savings with case lighting controls.
• Inexpensive to implement - $2000 to $8,000 per store
• Simple paybacks 0.2 to 2 yrs
© 2013 kW Engineering, Inc.
Case lighting alternatives
• Number of manufacturers now coming out with LED products
• Save lighting and cooling energy • Dimmable • Long lifetimes
© 2013 kW Engineering, Inc.
www.gelcore.com
Case Study – LEDs w/ Occ Sensors
© 2013 kW Engineering, Inc.
Source: LED Freezer Case Lighting Systems, Dave Bisbee, CEM, SMUD, July 25, 2008.
Monitored Results - LEDs and Occupancy Sensors
© 2013 kW Engineering, Inc.
Source: LED Freezer Case Lighting Systems, Dave Bisbee, CEM, SMUD, July 25, 2008.
Energy Efficiency – Principle 2 Principle 2 • Clean Condensing Coils • Verify Set-points and Sensor Calibration • Evaporative Pre-cooling • Minimize Head Pressure • Floating Head Pressure Controls • Heat Reclaim
© 2013 kW Engineering, Inc.
Typical Air-cooled Control Strategies 1. Interlock with compressor
(simplest – self contained) 2. Fixed pressure
(e.g. dead band around setpoint) 3. Linear reset, e.g.
4. Floating head pressure
© 2013 kW Engineering, Inc.
OAT Number of Fans
67 1
72 2
77 3
82 4
Typical Condenser Fan Controls: Evaporative • Indirectly sets
system head pressure
• Two-speed fans are typical
• Set manually with pressure switches or temperature controls (sump temp or dew point)
© 2013 kW Engineering, Inc.
Low-cost EEM’s: Minimize Head Pressure • Keep condensers clean and clear
from obstructions • Verify setpoints of controllers &
check for successive fan operation • Verify sensor calibration • Make sure VFD’s are not bypassed
and are unloading when they should
© 2013 kW Engineering, Inc.
Floating Head Pressure Controls • Head pressure is allowed
to “float” to a lower level • Control the fans to
maintain a fixed approach at the condenser: – Low temp systems:
target ΔT of 8°F to 12°F – Medium temp:
target ΔT of 10°F to 15°F.
• Trade off condenser fan energy for compressor energy savings
© 2013 kW Engineering, Inc.
Floating Head Pressure - Costs & Savings • Savings range from 3% to
10% of refrigeration system use
• Savings vary depending on – previous condenser fan
control strategy – heat reclaim – sub-cooling – condenser capacity
• If condensers are undersized for refrigeration loads, savings may be minimal
• Paybacks 1 to 4 years
© 2013 kW Engineering, Inc.
Source: P Cuneo, Source for HVAC and Refrigeration.
Energy Efficiency – Principle 3 Principle 3 • Check Refrigerant Lines • Maximize Suction Pressure • Floating Suction Pressure Controls • Mechanical sub-cooling • Multiplex systems conversion • High Efficiency Compressors • Variable Frequency Drives on Compressors
© 2013 kW Engineering, Inc.
Typical Suction Controls • Suction pressure sets
temp that system can serve
• Fixed pressure setpoint – compressor cycles on when suction pressure rises
• Manual setting • Used for staging in
parallel systems • Can be set lower than
necessary by techs and forgotten
© 2013 kW Engineering, Inc.
Check refrigerant level and recharge
© 2013 kW Engineering, Inc.
If the sight glass is clear there is a full charge.
If the system needs service, hire a professional.
If the sight glass has bubbles or foam during normal operation (not startup), call a technician
If the indicator turns pink, you have moisture in the refrigerant
Check refrigerant lines for icing
© 2013 kW Engineering, Inc.
call service company if ice is present.
Suction Pressure Commissioning • Pressure switches at the
compressors are often old and difficult to set precisely
• Often the pressure setpoints are unnecessarily low to avoid complaints
• Set suction setpoints as high as possible to meet the needs of the circuit
© 2013 kW Engineering, Inc.
Post Avg Suction 16 psig
Post Avg SST -22°
Pre Avg Suction 8 psig
Pre Avg SST -35°
Suction Pressure Cost & Savings • Savings in the range of 1%
to 5% of the total refrigeration system energy
• Savings are approximately 2% gain in efficiency for each 1°F rise in suction temperature
• Demand impacts are relatively small but they exist - about 1% to 2% of total refrigeration system demand © 2013 kW Engineering, Inc.
General Replacement Guide: CFC to an HCFC CFC or HCFC to an HFC
2011
© 2013 kW Engineering, Inc.
References and Resources • Compressor performance at
www.emersonclimate.com • Benchmark at:
poet.lbl.gov/cal-arch • Summary of measures and tools
www.focusonenergy.com/Business/Commercial-Business/Grocery
• www.refrigeration-engineer.com Good discussions on diagnostics © 2013 kW Engineering, Inc.
Thanks! Any Questions?
© 2013 kW Engineering, Inc.