November 4, 2014
Throughout much of the year, cold storage warehouses and some production facilities operate with partial refrigeration capacity. Reasons for this may include cooler temperatures than the hottest summer days, doors remaining closed due to lower product movement, or varying product cooling/freezing requirements. Variable frequency drives (VFDs) on screw compressors, condenser fans, and evaporator fans can provide considerable energy savings by slowing motor speed when only a portion of the full refrigeration capacity is needed. In addition to using less energy, VFDs can provide smoother starting and operating control.
A screw compressor typically lowers its capacity with a slide valve. The slide valve reduces compressor capacity without reducing energy consumption as much. For instance when a slide valve unloads to 50% refrigeration capacity, the compressor may still be requiring 65% energy. By slowing the motor with a VFD to 50% refrigeration capacity, the energy needed would be closer to 50% which can result in significant savings as compressors use the most energy in a refrigeration system.
Evaporative condensers are typically controlled by cycling fans on and off. Due to the characteristics of fans, VFDs reduce energy consumption greatly when slowing the fans. For instance an evaporative condenser with two 10 horsepower fans would cycle off one fan when needing half of the airflow, therefore using 10 horsepower. Under the same conditions with VFDs, both fans would run at half speed but realistically use about 1.5 horsepower each or only 3 horsepower total.
A similar energy reduction occurs when slowing evaporator fans or air unit fans when the cooling needed is less than the design refrigeration capacity. Additionally, because fans add heat energy into refrigerated rooms, less energy used is less heat energy added to the room resulting in less refrigeration needed throughout the system. If fans aren’t already being cycled off when cooling isn’t needed, even more significant energy savings would be seen. Many times, the VFD investment to energy cost payback is quickest with evaporator fans.
Jay Voissem, P.E., CIRO
Industrial Refrigeration Technical College
October 3, 2014
IRTC is happy to be hosting the Old Dominion RETA Chapter Meeting on March 12, 2015. Our lead instructor, Jay Voissem will be the featured speaker and will be focusing on CO2 Refrigeration. Everyone will also be given a tour of the new CO2 lab at IRTC.
September 3, 2014
Industrial Refrigeration Technical College is pleased to announce the offering of the brand-new Industrial Refrigeration Energy Specialist course beginning December 8-12, 2014. The course will provide a strong learning foundation on how to make your refrigeration system and facility more energy efficient. At the end of the course, participants will be able to take the RETA CRES examination on site.
Jason Quick, Campus Director, said, "It is exciting to be the first hands-on training school to offer such a class to the refrigeration industry".
"When you have the opportunity to help the refrigeration industry by offering such a class as this makes you feel like you are creating a positive return for the companies that trust in us to train their employees", said Mike Baker, Director of Marketing.
"Our priority is to make sure we offer the most comprehensive training classes and that's why we decided to add the Industrial Refrigeration Energy Specialist course", added Jay Voissem, Director of Training.
August 4, 2014
Modern Technology for Preventative Maintenance
What has relatively recent technology given facility managers and operators new tools and improvements concerning their industrial refrigeration systems? I can think of many ways but in this report we will focus on non-destructive and preventative maintenance technologies that have been developed or have had their costs lowered over the recent decades. These technologies can allow you to take action sooner and with more accurate information as well as likely lower system costs over time.
This is a non-destructive method of determining bearing faults, misalignment, worn components, oil overfeeding (for screws), etc... It allows us to extend the life of equipment by identifying problems before they spread or damage other components. By investing a small amount with routine vibration analysis (roughly twice a year) we are typically able to save many times over in rebuild or replacement costs. For instance, instead of only relying on run hours for replacement or rebuild, the equipment may be able to operate without a rebuild for many times the standard interval. Keep in mind that vibration analysis typically takes at least two or more data collections to properly determine faults. Occasionally the first collection, commonly called the baseline, will identify major faults such as misalignment but usually it’s the increasing severity that accurately provides guidance. One point to make from discussing vibration analysis with a few facility managers: it is not just for screw compressors and motors but vibration analysis is also useful with reciprocating compressors and other types of compressors, even pumps when they are large enough to justify it.
Similar to the life of components and vibration analysis, instead of replacing the oil at a scheduled interval, oil analysis commonly allows us to wait much longer to take action. An example that most or all of us would be familiar: replacing the oil and filter in your car every 3,000 miles (or something higher like 5,000 or 7,500 miles with full synthetic oil). Instead of a standard car oil change costing about $30, changing the oil in a screw compressor can cost thousands of dollars. Rather than just letting the compressor run until the poor oil quality damages the compressor, performing oil analysis tells us when it should be changed. Clearly, oil analysis appears to be a wise investment considering the frequency of oil changes can be reduced. Finally, in addition to possibly increasing the oil change interval, the analysis will also include wear metals which can show problems with compressor components as well as indicate the number of particles at various sizes which typically relates to the effectiveness of the oil filter.
Although we can visually inspect pipe for external corrosion and paint wear, we can’t see corrosion under insulation or, uncommon for industrial systems, internal corrosion / erosion. The lower cost method is ultrasound testing. This involves removing insulation, cleaning the pipe of rust, then determining the pipe thickness. If the insulation was in reasonable condition before removal, it can be re-installed with a fresh vapor retarder applied. By checking many locations including the pipes most prone to pitting (think defrost relief or defrost condensate, warmer suction pipes, chilled high pressure liquid pipes, and locations that cycle in temperature) or where the vapor retarder is poor, an overall assessment is usually made in addition to the exact reading found at tested locations. Although a few times more expensive, x-ray technologies allow a scan of all insulated pipes without insulation removal and a more thorough assessment of the pipe condition. Either of these non-destructive methods will allow you to determine if pipe needs to be replaced and if your insulation vapor retarder is holding up well. Rather than being used for pipe degradation, infrared scanning finds loose or poor electrical connections and terminations. It creates a picture of temperatures which can show hot areas and arcing. By catching these issues early, a correction can be made before your electrical panel looks like that burnt meal you forgot was still in the kitchen stove.
Jay Voissem, P.E., CIRO
Industrial Refrigeration Technical College