50 tips for saving energy_refrigeration_web_r2

50Low- and No-Cost Tips for Saving Energy

IndustrIal refrIgeratIon energy effIcIency

© Copyright 20132 50 LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

If you pay the power bill at an industrial cold storage or food distribution center,

you know that refrigeration systems never stop consumIng energy. As the largest

electrical energy consumers in cold storage or distribution facilities,

refrIgeratIon systems should be a major savings target for spend-weary

corporations. Yet, in today's economic climate where budgets for capital projects

are small or non-existent, finding ways

to reduce your energy spend can be a

challenge.

the solutIon? Driving energy savings

through low- or no-cost operations

and maintenance activities. This eBook

offers fIfty of the best opportunities for

achieving savings at little or no capital cost.

loW- and no-cost solutIons that Increase energy effIcIency

CONTENTS

1 Evaporator Opportunities

2 Compressor Opportunities

3 Evaporative Condenser Opportunities

4 Control System Opportunities

5 System Opportunities

6 Systems Influencing Refrigeration Load

SAFETY ALERTThe improper execution of the activities outlined in this eBook could result in poor

system performance, property damage, product quality issues, and serious bodily harm.

Put safety first. Get qualified third-party contractors or certified refrigeration operators

to implement the O&M actions in this guide, if your staff does not have the expertise.


1 Cleaning Coils – Evaporator coils should be regularly inspected and cleaned, particularly in docks

or production areas where dirt, cardboard dust, rubber tire particulate, and other contaminants are

common. Dirty coils may prevent a space from achieving temperature, force the system to run at

lower suction pressure, or hinder evaporator fan cycling or variable frequency drive (VFD) control

effectiveness. Dirty coils may not defrost well.

2 Tune Overfeed Rates – Systems with liquid recirculation (also called overfeed) design utilize

hand expansion valves to meter liquid refrigerant at a 3:1 or 4:1 overfeed rate. If the valve is

throttled too low, the coil will starve. If the valve is too open, the evaporator will brine. Adjust the

valve to provide the maximum air temperature drop across the coil.

3 Adjust Defrost Relief Regulators – Hot gas defrost is often managed with a gas relief

regulator at the coil exit to maintain a target pressure within the coil during the hot gas phase of the

cycle. If this regulator is set too low, the defrost will be too long (due to low refrigerant temperature)

and the regulator will freely allow gas to pass and load the engine room. If the regulator is set too

high, this may force the system’s minimum condensing pressure to be set higher, or cause steaming

during defrost. A reasonable target is 70-75 pounds per square inch gauge (psig) for ammonia

systems.

4 Adjust Master Hot Gas Regulator – Some systems

utilize a master hot gas pressure regulator to maintain

consistent pressure in the main hot gas header serving the

coils. Pressure that is too high in the main header, results in

excessive coil temperature and increased false loading in the

engine room. The minimum system condensing pressure must

be set at least 5-10 psig above the master regulator set point.

A reasonable target pressure for the master regulator is 85-90

psig for ammonia systems.

evaporator opportunItIes

t i p A service provider should ensure

coils are clean and clear of heavy

frost before tuning.


evaporator opportunItIes

5 Remove Oil – In most systems, any oil that migrates from the compressor eventually ends up

in low-pressure receivers or evaporator coils. Oil in evaporator coils hinders cooling, and makes it

extremely difficult to achieve a complete defrost at the bottom of the coil. Ice builds up and may

eventually bridge to the defrost pan. It is important to remove this oil.

6 Repair Valves and Regulators – It is important that hot gas solenoids fully close and do not

leak hot gas into the liquid or suction line. Also, regulators should fully close, as well as smoothly

and consistently maintain target pressures.

7 Remove Aging Ductwork – Older system designs included wooden or metal ductwork to

distribute air flow throughout a space. Unfortunately, this ductwork cannot be cleaned and may

also prevent cleaning the evaporator coil fans (usually centrifugal) and coil surface. Modifying or

removing this legacy ductwork can dramatically improve zone temperature management and system

efficiency.

8 Tuning Pressure Regulators – Some evaporator coils or process heat exchangers (e.g., water

or glycol chillers) are equipped with fixed or dual-pressure regulators. Ensure that the regulators are

set for the greatest temperature difference allowed by system limitations (such as freeze protection,

high humidity, etc.). Consult the original design engineer or contractor to determine the limits of the

application.

t i p Differing frost patterns on valves

during a given mode of operation

indicates inefficiency.


9 Solve Current Limiting / Forced Unloading – Screw compressor microprocessor panels

usually include settings to prevent overloading of the motor. If the panel sees motor current driving

above nameplate or the service factor, the compressor will stop loading or even unload. This causes

the compressor to lose efficiency by running in an unloaded condition. This may force the control

system or operators to fire off another compressor to

supply capacity. Use a clamp-on current meter to ensure

that the current reading of the compressor microprocessor

is correct. Also ensure that the current limiting parameters

in the panel correctly match factory recommendations for

stop-load or force-unload settings. It is not uncommon for

current transformer (CT) multipliers to be in error or for

the incorrect current limiting parameters to be entered

into the controller.

10 Ensure Economizer Operation – Ensure that economizer ports function properly. The

economizer pipe should be cold to the touch when the system is operating. Most economizers

have a pressure regulator; ensure that the regulator is set to its factory recommended level. Most

microprocessor panels will disable economizer function below a prescribed slide valve position (e.g.,

75%) since economizer port gas is open to main suction pressure as the compressor unloads. Ensure

that this setting is correct. It is not uncommon for a failure on the microprocessor board, or a failed

economizer solenoid to prevent function altogether.

11 Auto VI Feature – Some screw compressors have automatic volume ratio controls. This matches

the compressor internal compression ratio to the external system pressures to prevent over or under

compression and loss of efficiency. Ensure the auto VI system is calibrated and operating correctly.

If an external control system is managing compressor VI, ensure the system is calibrated and

functioning properly.

t i p Most modern screw compressors have a

microprocessor panel and control sensors,

both of which must be calibrated correctly

or else compressor performance can suffer.

compressor opportunItIes


compressor opportunItIes

12 Manual VI Feature – Other screw compressors may be equipped with a manually-adjustable

volume ratio feature. Read the factory operating manual to determine the proper VI setting.

13 Repair Shaft Seals – Repair any leaking compressor shaft seals, ESPECIALLY systems operating

in a vacuum. Air entering the system will impact condensing pressure, place a burden on the purging

system, and introduce water into the refrigerant charge.

14 Avoid Excessively Low Cut-Out – If compressor cut-out suction pressure is set too low, a

compressor may not turn off under extremely low-load conditions. The compressor will simply pull

down to extremely low suction pressure and draw fully-unloaded power. If the compressor is set up

this way on purpose (e.g., it has problems starting, see below), resolve this issue.

15 Solve Starting Issues – If a compressor cannot reliably start and stop, it may be tempting to

operate it in an unloaded state to avoid the problem. Instead, resolve the issue that prevents reliable

starting, whether the issue is with the motor starter or controls. If the concern is excessive motor

restarts, consult with the compressor or motor manufacturer to determine the minimum allowable

anti-recycle time to allow the compressor to restart promptly and avoid system disruption.

t i p Critical set points for

compressors include economizers,

pressure sensors, VFD settings,

current transducers, and

compression ration settings.


16 Unplug Spray Nozzles – Regularly inspect evaporative condenser spray nozzles to ensure

nozzles are not plugged.

17 Water Treatment – It is critical that water be treated for

solids and biological content. It only takes a small amount of

buildup on condenser tubes to dramatically reduce capacity

(e.g., 1/16” of calcium carbonate can reduce condenser

capacity by nearly 50%). Hold your water treatment

contractor accountable for system performance. This will

require regular inspection of condenser tubes.

18 Water Pressure – Although tempting, increased water pressure does not improve evaporative

condenser performance. Most condensers are designed with modest water pressure at the header,

perhaps 3-6 psi. Install a glycerin-filled 0-15 psig gauge in the condenser water distribution header

and throttle the condenser pump to deliver the correct pressure. If substantial throttling is required,

have the pump impeller trimmed to provide the proper amount of pressure for the application.

19 Clean Strainers – Regularly inspect and clean the condenser sump pump inlet strainer. A plugged

strainer will reduce condenser capacity and waste pump energy.

20 Adjust Sump Water Level – Ensure that condenser sump float level is correct and that water

level is not too low. Low water level can result in poor pump performance and water flow.

21 Plugged Fill or Drift Eliminators – Regularly clean fill material on induced draft condensers

and drift eliminators on most condensers. Otherwise, reduced air flow will impact condenser

performance.

22 Address Non-Condensables – Ensure the purger is working properly and that air is being

eliminated from the condenser. Do this by measuring pressure and temperature at the condenser to

verify the values correspond.

evaporatIve condenser opportunItIes

t i p Good water treatment is critical to

avoiding scaling on the tubes that

causes a reduction in performance.


23 Tension Belts – Check condenser fan belt tension to ensure there is no slip. Slip will reduce air

flow and waste fan energy through the slip itself.

24 Address Recirculation or Bad Environment – Poor condenser configuration may result

in warm, moist exhaust air from one condenser being drawn into a neighboring condenser. Poor

rooftop layout may result in a boiler blow-down stack or process exhaust air stream placed near the

inlet to a condenser. In all cases, address the issue to relocate, raise, or otherwise reduce moist or

warm air entering the condenser.

25 Correct Poor Drift Eliminator Strap Configuration – To properly inspect condenser

performance, hold-down straps must be loosened to allow drift eliminators to be removed. In some

cases, these straps are configured so that they’re difficult or impossible to remove. Reorient, or

otherwise modify the strapping system to correct this issue.

26 Wet vs. Dry Operation – Evaporative condensers are inefficient when operated dry, particularly

when ambient temperatures are above 30-40°F. Ensure that condensers are properly winterized

(sump heaters, heat trace, etc.) so they safely operate wet down to 25-30°F ambient.

27 Sump Heaters – Ensure any electric sump heaters (often 10 kW, 20 kW or more) are functioning

properly. Failed or incorrectly adjusted thermostats can result in inappropriate energy use by the

heaters, and heating of the water that elevates discharge pressure.

t i p Proper maintenance helps avoid

the top threats to condenser

performance: non-condensable

gases, scale on the tube bundle,

and poor spray-water dispersion.

evaporatIve condenser opportunItIes


28 Zone or Process Temperatures – Warehouse cooler or freezer temperatures should be set at

an appropriate value as determined by product or customer requirements. Product, glycol, or other

process temperatures should not be set lower than required. This may seem obvious, but systems

are often set to maintain lower temperatures than necessary.

29 Suction Pressure – Raise system suction pressure to the

highest allowable value (which is usually dictated by the

worst-case temperature zone or process load). Note that this

will affect evaporator fan cycling or VFD control, so some

optimization may be in order.

30 Condensing Pressure – Operate the system at the lowest

allowable minimum condensing pressure set point. If a

system can be operated as low as 90-100 psig (for ammonia)

without problems, this is a reasonable target. Note that

defrost, freezer floor heat, liquid injection performance, and compressor oil carryover are potential

barriers to reduced minimum condensing pressure. Discuss possible limitations with the equipment

manufacturer, refrigeration contractor, and system operators.

31 Condenser Wet Bulb Approach – If the control system offers a condenser wet bulb approach

control feature, activate it and target an approach in the 12-15 degree range. The optimum value

may require experimentation. This feature ensures an appropriate balance of condenser capacity

relative to refrigeration load and compressor operation.

32 Evaporator Fan Cycling – If the control system offers an evaporator fan cycling feature,

activate it. In some cases, a swirl feature will operate the fans a minimum duty cycle to mix room air.

Set up the swirl feature for the minimum required. If the control system has separate cut out and cut

in set points for liquid solenoids and fans, energy savings is maximized when the cut in and cut out

set point is the same for the solenoid and fan control.

control system opportunItIes

t i p Fine-tuning control systems and using

them to take advantage of demand-

response programs or varying utility

rate schedules – can be a considerable

source of energy and cost savings.

33 Condenser Staging – Operate the most efficient condenser in the lead list first. Generally, the

most efficient condensers are axial fan units with integral sumps. Centrifugals are less efficient,

as are those with remote sump pumps or limitations to operation during frigid weather. Evaporative

condensers are most efficient when wet with air flow at mid-range fan speeds. Avoid turning all

system pumps on first, and then starting to add fans. Turn on a condenser pump, then the fans,

then the next condenser pump, then fans, etc. The goal is wet with air movement for the greatest

efficiency.

34 Defrost Schedule – If the control system only offers a fixed

defrost schedule, experiment with the number of defrosts per

day to minimize defrost count. Do not let frost build up so

much that it becomes difficult to achieve a full, clean defrost.

There is no rule of thumb for defrost interval – many coils can

operate 8-16 hours or more between defrosts. In dry climates,

it is not uncommon for evaporators to be defrosted only once

or twice a week.

35 Defrost Initiation – If the control system offers a liquid run-time feature or frost sensors, use this

feature to initiate defrost only when necessary.

36 Defrost Pump Down – Ensure that all liquid is fully boiled out of the evaporator coil before hot

gas is introduced. Watch a coil closely during a test pump down and measure fin temperature with

a laser thermometer, or watch air temperature drop to determine when a coil is completely dry. This

may require 30-60 minutes for a frosted coil or one with VFD control operating at reduced speed.

37 Defrost Hot Gas Duration – Most evaporator coils should be able to clear all frost with 10-20

minutes of hot gas. If you find a coil needing 45-60, or more minutes of hot gas to clear all frost,

there is probably something wrong that should be addressed (e.g., hot gas regulator pressure,

inadequate pump down, etc.).

38 Transducer & Sensor Calibration – Use an ice bath to calibrate key zone or process

temperature sensors. Calibration pressure gauges ensure that the pressure transducers, used by

a central control system, are properly calibrated. You may need to adjust offsets in the control

system or even replace a failed pressure transducer. For compressors operating off their local

microprocessor panels, calibrating control pressure transducers is critical (particularly suction).



t i p Make sure the winterizing heat trace

and sump heaters are functioning so the

system performs well in frigid weather.


39 Poor Ambient Probe Location – If a control system ambient temperature probe is located in

direct sun, the probe will not read properly. This is particularly important when utilizing a condenser

wet bulb strategy.

40 Frigid Weather Condenser Strategies – Many central control systems can turn off condenser

water pumps (or drain condenser sumps) during frigid weather for freeze protection. It is important

that these set points be set at reasonable values to minimize dry operation of the condensers.

41 Tune Internal VFD Parameters – For evaporator and

condenser fans, the most efficient VFD configuration is

typically a low carrier frequency and a “square” or “variable”

torque curve. There may also be energy-saving features or

settings that can improve efficiency. The best method is to

measure VFD input power with an appropriate power meter

and experiment with these parameters to obtain the

minimum power.

42 Optimum Evaporator VFD Strategies – In general,

evaporator fan VFDs can be operated with a minimum speed in the range of 40-50%. There is little

additional savings from going slower. Limiting evaporator maximum speed to 90 or 95% can add

savings with very little impact on net evaporator capacity. Liquid feed or pressure regulators should

stay at full capacity until the fan VFDs are at minimum speed. Simultaneous speed control will save

more energy than sequential ramping of speed when there are multiple coils in the zone.

43 Optimum Compressor VFD Strategies – Compressor minimum speed is dictated by

compressor or motor limitations, typically in the range of 20-50%. Consult the manufacturer for

proper settings. In nearly all cases, the compressor micro-processor manages the VFD and slide

valve. Speed should be reduced first. Once at minimum speed, then the slide valve can be closed.

Avoid simultaneous adjustment of speed and slide.

44 Optimum Condenser VFD Strategies – Implement pump and fan staging, minimum and

maximum fan speeds to target the general strategy of “wet with air at mid-range speeds.”

Mid-range can be defined as 30 to 80% speed. Once all condensers are online, fan speed can be

allowed to rise to 100%.


t i p All VFDs have internal parameters such

as carrier frequency, torque curves,

minimum and maximum speeds. It is vital

that VFDs do exactly what the control

system tells them to.


45 Purger Performance – Ensure that the purger is operating properly. The purger counter should

show a reasonable level of purging, but note that no system is perfect. There are control fuses,

check valves or solenoids that can fail and prevent proper operation.

46 Water in the System – Regularly test the system refrigerant for excessive water content.

Excessive water will change the properties of the refrigerant and substantially reduce system

performance and efficiency.

47 Pump Drum Tuning – A gas pressure system (also called a Phillips or Pumper Drum System) has

a number of critical pressure control regulators. Flash gas from a controlled-pressure receiver (CPR) or

low pressure vessels should be properly routed to an appropriate suction (or economizer ports). Any

hot gas supply regulators should be carefully adjusted to prevent false loading of the system. Liquid

transfer units (LTUs) that utilize hot gas for dumping and liquid transfer should be carefully set up to

avoid false loading of the system. Set CPR pressure to the lowest allowable value to maximize sub-

cooling and prevent the CPR from acting as a barrier to minimum allowable condensing pressure.

48 Repair Faulty or Leaking Float Drainers – Liquid float drainers may be installed on main hot

gas defrost headers, individual evaporator defrost relief, under-floor glycol heat exchangers, or other

applications. If the float drainer is leaking hot gas, it will false load the system. Ensure that all liquid

drainers are functioning properly.

system opportunItIes

t i p Water in a refrigeration system

dilutes and impacts the boiling

point of the system’s ammonia.

A water removal system or

hybrid air/water purger should be

installed to maximize efficiency.


49 Door Performance – Dock, cooler, or freezer door

performance directly impacts refrigeration load and defrost

requirements. Door seals, door defrost heaters, sensors,

closing delays, and other characteristics are extremely

important to minimizing refrigeration load. If re-circulatory

air doors are used, proper control of air heaters (electric or

hot gas), adjustment of air flow directional vanes, and clean

return air screens or grates are key to efficiency.

50 Lighting Performance – Warehouse lighting controls,

including motion sensors, bi-level control on high-intensity

discharge lighting, manual or time clock controls all directly

impact refrigeration load. Every watt of light fixture power

ends up as refrigeration load in the space.

systems InfluencIngrefrIgeratIon load

t i p Install motion controls and

set sensor time delays to the

minimum allowable delay for

facility use patterns, safety, and

manufacturer specifications.

t i p Ensure that freezer under-floor

heating systems are set to

the minimum required ground

temperature to prevent heaving.

This should be carefully considered

and implemented.


poInts to consIder

thInk about the folloWIng as you pursue loW- and no-cost effIcIency gaIns:

Be willing to experiment while maintaining system stability and reliability. Every refrigeration system

is unique and displays its own quirks and character. For this reason, each system must be poked,

prodded, and otherwise forced to show its limitations and capabilities.

It is important to remember that functional does not imply efficient.

In most cases, a well-tuned and properly maintained system is more efficient.

A small group of people dictates the energy use for the refrigeration system. These people are critical

to reducing energy use.

You must understand more than how a refrigeration system operates. It is important to understand

what drives the energy use for each component or system in a way that allows you to make wise

decisions regarding configuration, set points, and strategies. Consider a taking class that focuses on

efficiency to improve your understanding and skill set.

It is possible that there are misconceptions that have been passed on by other system operators,

contractors, or vendors that are limiting efficiency of the system. Ask questions, do research, and

talk to experts. Trust but verify.

Design conditions are just that – information used to select components and configure the system.

Often, design conditions are not intended for day-to-day operation, particularly when pursuing

efficiency gains. Avoid clinging to these values unless there is a strong, reasonable, or justified case.

Some system inefficiencies or barriers can only be seen during certain seasons. For example, high

condensing pressure may only manifest during the summer whereas limits to system minimum

allowable condensing pressure may only be addressed during winter. If you utilize a third-party

contractor to operate or maintain your system, the contractor must be involved in pursuit of energy

efficiency. Implement processes, goals, or requirements to ensure alignment and accountability.

123 NE 3rd Ave, Suite 400Portland, OR 97232503.287.8488 main 503.287.8788 fax

INDUSTRIAL STRENGTH ENERGY EFFICIENCY

TALK TO CASCADE ENERGY TODAY! 866.321.4573

20 yEArs

Deep, hands-on technical

expertise over a 20-year span.

2,000 ProjECTs

Analyzed and implemented more

than 2,000 energy efficiency

projects.

350 sITEs

Monitor energy performance at

over 350 industrial sites.

250 FACIlITIEs

On-site tune-up and retro-

commissioning at over 250

industrial facilities.

Cascade Energy provides corporations and utilities with the industrial strength

expertise needed to realize their energy efficiency potential. With a full

complement of services and engineering know-how based on 20 years of

hands-on experience, Cascade has a proven track record of reducing industrial

energy consumption and costs.

cascadeenergy.com energysensei.com [email protected]

Industry ExpErtIsE

• Refrigerated storage

• Food processing and distribution

• Pulp and paper

• Oil and gas

• Steel and heavy industry

• High technology

• Water and wastewater

• Chemicals

• Manufacturing

• Agriculture

systEm ExpErtIsE

• Refrigeration

• Compressed air

• Fans, pumps, blowers

• Manufacturing processes

• Controls and VFDs

• Chillers

• Cooling towers

• HVAC systems

• Thermal systems

• Lighting

EBOOK-003-2 REV 1-OCT-2013

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