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EVAPORATOR OPERATION AND DEFROST

Presented by: Rob Travis, P.E.

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PLATINUM GOLD

Our online sponsors

Thank you, sponsors

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TOP 4 LOW COST EVAPORATOR ACTION ITEMS

• 1. Evaporator Fan Cycling
• 2. Defrost Setpoints
• 3. Verify Room Temperature Set‐points
• 4. Address Fan Motor and VFD Issues

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Courtesy: Evapco Courtesy: Guntner

HOW EVAPORATOR COILS WORK

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• Functions to remove heat from the space
• Heat energy moves from hot to cold, or from cold to colder
• Room temperature control:
• Liquid solenoid opens and

closes to supply refrigerant when needed

• Fans draw air through

the coil and pushes it out into the room

Refrigerant Temperature

• 10°F

Entering “Return” Air Temperature +3°F Exiting “Supply” Air Temperature ‐2°F Average Room Air Temperature 0°F Heat Rises Cold Falls

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• 1. EVAPORATOR FAN CYCLING & VFD CONTROL

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• Enable fan cycling on the control

system for each evaporator zone

• Fans turn off when liquid

solenoid closes

• Fans turn on when liquid

solenoid opens

• Fans operate only when

refrigeration is needed in the room

• Saves evaporator fan energy

AND fan motor heat load

Fan Motor Heat

• What about air temperature stratification?
• Effect is nominal in most situations. Enable stir cycle if needed.
• Remember, heat rises up to the evaporator
• Air temperature ≠ product temperature
• What about condensation/moisture on the dock?
• May be an issue in warm, humid climates.
• Disable fan cycling for summer months (June – August)
• What about heated rooms?
• Operate fans continuously in when in heating mode
• Fans help air circulate instead of keeping the heat at the ceiling

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ISSUES / CONCERNS

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EVAPORATOR FAN CYCLING SAVINGS POTENTIAL

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• Evaporators constitute 15‐20% of total

facility energy

• Fan cycling may reduce evaporator energy

by 30% on average

• Example of a typical refrigerated distribution

center savings when fan cycling was enabled

• 380,000 kWh annual energy savings
• 5.6% reduction in division electrical

consumption

• $25,300 annual electrical cost savings
• 2. DEFROST SETPOINTS

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How much hot gas is really needed?

• Too much hot gas pumps heat into the room and incurs a false

load on the compressors – double energy penalty.

• Liquid runtime setpoints
• Pump‐out setpoints
• Hot gas setpoints
• Seasonal setpoints

Good Frost Pattern: 25‐30% Blockage

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Defrost Cycle

• If any cooler or freezer evaporators are being

defrosted more than twice per day:

• Investigate the defrost cycle or involve

contractor

Pump Out Time

• If the pump out time is <20 minutes:
• Change the setpoint to 20 minutes

Hot Gas Time

• If the hot gas time is >20 minutes:
• Watch a defrost cycle or involve contractor

Defrost Initiation

• Liquid runtime vs. scheduled
• Will required testing

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DEFROST SETPOINTS

51°F Surface in a 0°F Freezer

Ensure the room temperature setpoints are appropriate and not lower than necessary

• Typical room temperatures:
• Low temperature setpoints = more refrigeration and more

evaporator fan energy

• For freezers, try a ‐2°F or ‐3°F setpoint

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• 3. VERIFY TEMPERATURE SETPOINTS

Temperature Zones Design Temperature General Cooler 34‐38°F Meat Cooler 28°F Produce Cooler 47‐55°F Refrigerated Dock 38‐45°F Main Freezer < 0°F Ice Cream Freezer ‐10°F to ‐20°F

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• Check evaporators for fan motors

that have failed and replace

• Ensure VFDs are being controlled

correctly in the control system

• Inspect the actual VFD to make sure

it has not been bypassed

• Verify the minimum and maximum

speeds setpoints

• Minimum Speed: 40%
• Maximum Speed: 90%

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• 4. ADDRESS FAN MOTOR AND VFD ISSUES
• Significant energy savings can be realized by ensuring the

evaporators are operating efficiently.

• Most recommendations are either simple setpoint changes or

maintenance issues.

• Defrost setpoint adjustments may be improved incrementally
• ver time and require vigilance to ensure defrosts are

complete.

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CONCLUSION