April 1997 Volume 3 Issue 7
No-Cost/Low-Cost Refrigeration Savings Opportunities
This article presents a checklist of practical, inexpensive ways to reduce refrigeration costs. While not all suggestions will apply in your situation, it is likely that some will. Why not take a couple of minutes to read through the suggestions? As you go, put a check next to any possibility that seems worth looking into. If you have questions about the savings potential of a particular opportunity, or need more details about implementing a corrective measure, call Mike Proud or Ron Estabrooks at 1-800-236-5193 (toll free).
¨ Adjust freeze tunnel temperatures to reduce the amount of defrosting required. Equalize frost buildup along the tunnel by adjusting temperatures in the tunnel’s various sections. This usually involves raising the evaporator temperature in the first part of the tunnel.
¨ Establish and maintain optimum defrosting. Defrosting has an energy price. Failure to defrost has a greater energy price — and a performance price, too. Keep the defrosting system working properly, and consider alternative defrosting methods. Is there another approach that would save energy and energy dollars?
¨ Keep evaporators clean. While frost buildup is the usual concern, evaporators can also get clogged with dust and dirt. At appropriate intervals use brushes, a vacuum cleaner, or compressed gas to clean them.
¨ Eliminate hot gas bypassing. The hot gas bypass technique is used in some systems to avoid evaporator frosting and low suction pressure when the refrigeration load is low. Consider, instead, cycling the compressor on and off.
¨ Ensure that the air entering the condenser is not too warm for adequate condenser cooling.
Fan/condenser assemblies such as the roof-mounted unit shown above are sometimes placed in attics where there is no cool air, or in tight quarters which cause hot exhaust air to recirculate through the condenser. If faced with this problem, relocate the unit or take other corrective steps.
¨ If condenser air temperature is so low that it causes head pressure to fall to an unacceptably low value, consider using a pressure switch to cycle the condenser fan on and off.
¨ Keep condensers clean. Routinely use brushes, a vacuum cleaner, or compressed gas to remove dust and dirt from air-cooled refrigeration condensers. Similarly, keep water-cooled condensers clean. If necessary, use an appropriate acid wash to remove mineral deposits.
Electrical / Controls
¨ Consider wiring the evaporator fans so they are ON only when the compressor is ON. In some situations, evaporator fans must run continuously to keep the temperature of the refrigerated space sufficiently uniform. In other situations, it is enough to run them only when the compressor is running. Since these fans not only consume electricity but also give off heat which must be removed by the refrigeration system, reducing condenser-fan run time saves energy dollars.
¨ Install occupancy sensors to control the lights in refrigerated rooms. The lights used to illuminate walk-in freezers and cold rooms have a double impact on the electric bill — once for the electricity to operate them, and again for the electricity to remove the heat they generate.
¨ Look at the impact of production schedules on refrigeration electrical demand, and see if it is practical to reduce demand by rescheduling freezing and cooling activities. If rescheduling is impractical, consider the possibility of shedding other loads while blast freezers and other high-demand refrigeration systems are operating.
¨ Consider ways of limiting electrical demand after power failures. When the power has been off for a while and then comes back on, all refrigeration compressors are likely to start simultaneously. If this would result in a higher than normal demand peak, consider measures to avoid it.
¨ Eliminate compressor short-cycling. When large motors are started too frequently, they overheat and their life is shortened. If this is happening in your refrigeration system, consider installing an anti-short-cycle timer or a dead-band thermostat.
¨ Equalize compressor run times. Where staged compressors are used to handle varying refrigeration loads, equalize compressor wear by ensuring that the control system causes each compressor to run for approximately equal time. Modify the control system if necessary.
¨ Calibrate controls at regular intervals.
¨ Consider the feasibility of increasing the temperatures used in production processes which involve freezing or cooling — including the temperature of any refrigeration-cooled water supplied to the process. Also, consider the feasibility of increasing suction pressure and/or decreasing head pressure. Sometimes circumstances have changed, yet changes were never made to the plant’s refrigeration systems. Do present levels of temperature and pressure represent the most cost-effective way of meeting current production and product storage requirements?
¨ Correct motor power factor. If your facility’s electrical demand is metered in kVA, consider reducing demand by installing capacitors to compensate for the power factor of refrigeration system motors. (While requiring greater capital expense than most items on this checklist, the payback time for power factor correction is usually two years or less.)
Insulation & Air Leakage
¨ Reduce losses associated with open freezer and cold room doors. Approaches include:
· automatic door closure devices,
· an alarm that sounds if the door has been left open for more than a predetermined period, and
· a plastic-strip barrier across the opening.
¨ Upgrade cold room insulation. Some walk-in freezers and cold rooms are inadequately insulated. Would better insulation significantly reduce your electric bill?
¨ Check/replace walk-in freezer and cold room door gaskets.
¨ Replace missing or damaged insulation on cold refrigerant piping.
¨ Maintain proper refrigerant charge. Insufficient charge reduces both system capacity and system efficiency. Excessive charge commonly results in abnormally high head pressure, and sometimes causes liquid refrigerant to enter the compressor and damage it.
¨ Find and fix all refrigerant leaks. Now required by law and regulation as well as economic common sense, eliminating leaks is the best way to keep refrigerant charge always at the proper level.