April 1997 Volume 3 Issue 8
Setting Up a Refrigeration System Monitoring Plan
Does the quality of your products depend on proper freezing or cooling? Does operating your plant’s refrigeration systems involve a significant electricity expense? If your response to either question is YES, and you don’t already have a refrigeration monitoring procedure in place, you might want to create one. This article outlines a way of going about it. Use it for ideas, and as a general guide in creating your own plan — perhaps in consultation with whoever services your firm’s refrigeration systems.
A comprehensive review of your facility’s current freezing/cooling activities and systems is a sensible starting place. To facilitate this review you might want to refer to the checklist of refrigeration savings opportunities that appeared in the last issue of $mart Energy User (Vol. 3 No. 7). It highlights many common refrigeration problems. This might also be an appropriate time to have your systems checked over by a refrigeration specialist — and to review the checklist with that person.
It would be a good time, too, to correct any deficiencies in system instrumentation. To know how your system is performing you need to be able to measure temperature — both air temperature, and the temperature of the refrigerant tubing at various points in the system. Each refrigerated space needs its own accurate thermometer, but one portable electronic contact thermometer should be sufficient to periodically check refrigerant tubing temperatures. It is also essential to keep tabs on refrigerant pressure, both compressor input (suction) pressure and compressor output (head) pressure. If your major refrigeration systems do not already have permanently installed pressure gauges, obtain a set for each system.
Permanently installed refrigerant pressure gauges (suction and head) make it easy to monitor system performance and diagnose problems.
It helps if one person is responsible for monitoring and maintaining refrigeration system performance. Among that person’s responsibilities will be periodically taking measurements and recording them in a Refrigeration Log. Setting up the log and gathering the initial data should preferably be done just after the system has been thoroughly checked over and properly adjusted. The goal, at this point, is to provide benchmark figures representing normal system operation. The initial data should include:
1. Air temperature of the refrigerated space.
2. Air temperature going into and coming out of the condenser.
3. Temperatures of the refrigerant tubing at condenser input, condenser output, evaporator input, and evaporator output.
1. Head and suction pressures under a variety of typically-encountered operating conditions. (While cooling warm product, after the product has been cooled, etc.)
2. Appearance of the sight glass under various operating conditions.
3. The duration of compressor ON and OFF times under various conditions of refrigeration load.
4. From motor nameplates, the voltage and FLA (full load amps) rating for each compressor motor, evaporator fan motor, and condenser fan motor. Also, the actual motor voltage and current for all three electrical phases under various operating conditions — as measured with a voltmeter and clip-on ammeter.
Finally, compile a comprehensive list of monitoring and maintenance tasks and assign each task to a DAILY, WEEKLY, MONTHLY or YEARLY list. The following are examples of such lists, but are not intended to fit every situation.
1. Glance at the suction and head pressure gauges several times a day to make sure that pressures are staying within their usual ranges. If abnormal readings are noticed, take some of the additional measurements suggested on the PROBLEMS list.
2. Pay attention to compressor run time duration and go to the PROBLEMS list if short cycling or exceptionally long run times are noted.
If production throughput is fairly constant, and if the refrigeration system itself appears stable, attending once a month to the items on this list is probably adequate. Where things change frequently, doing it weekly or bi-weekly might make more sense.
1. Record the suction- and head-pressure gauge readings under various conditions of refrigeration load. (While cooling warm product, after the product has cooled, etc.)
2. When taking the above readings, look at the sight glass and record its appearance.
3. As you gather the above data, also note and record compressor ON and OFF durations.
4. Measure and record the air temperature of the refrigerated space.
5. Check evaporators for frost, dirt, and free air flow.
6. Check the condenser for dust accumulation and free air flow.
7. As the months go on, follow recommended lubrication schedules for motors, compressors, and bearings.
P.E.I. Department of Environmental Resources regulations (EC619) require that owners of “field built” refrigeration systems greater than 3 hp verify annually that the system is holding its charge. When making this annual check, why not also purge contaminants from the system and check thermostat and gauge calibration? Also, once a year:
1. Repeat the initial measurements outlined in the GETTING STARTED section and compare them with the previous year’s data. If there are differences, are the reasons for them clear?
2. Check compressor and fan belts for alignment, tightness, and wear.
3. Check the condition of insulation in cold room walls (is it dry?) and on cold refrigerant pipes (is it attached and undamaged?).
4. Check the condition of walk-in freezer/cooler door gaskets and door alignment.
If abnormal conditions are noted at any time, gather additional data that might help diagnose the problem.
1. What is the air temperature of the refrigerated space?
2. What are the air temperatures going into and coming out of the condenser?
3. What are the temperatures of the refrigerant tubing at condenser input, condenser output, evaporator input, and evaporator output?
4. Are the evaporator and condenser fans running?
5. Are motor voltages and currents normal?
6. What are the durations of compressor ON and OFF periods?
7. Should the system be checked for low refrigerant charge?
For more information on energy-efficient refrigeration call Ron Estabrooks or Mike Proud at 1-800-236-5193 (toll free). Request the free booklet Energy Efficient Refrigeration Systems.