As most facilities and maintenance engineers know, proper maintenance of chiller and condensing units is critical to efficient, trouble-free operation. However, when you combine the fact that most chillers and condensing units are situated in low-traffic locations and are out of sight (i.e., behind buildings, behind walls, on rooftops, etc.) with the fact that the coil-cleaning portion of the maintenance process is an unpleasant and time-consuming task, chiller and condensing-unit maintenance is not a job looked forward to by most maintenance engineers. In situations in which the maintenance department is busy or understaffed, coil cleaning is likely to be deferred beyond the time when maintenance is required.
Even the slightest coil fouling leads to what can be described as the first level of failure, which is distinguished by the following characteristics:
Higher operating compressor head pressure (caused by elevated refrigerant pressure resulting from restricted airflow and poor heat exchange).
Reduced cooling capacity (caused by poor airflow through the coils).
Increased kilowatt draw, coupled with a reduction in cooling tonnage capacity.
The unit runs longer and works harder to achieve temperature set points.
The compressor cycles off and on under high head pressure.
Chillers suffering from high-head-pressure conditions pass the impact along in the form of tenant discomfort, customer complaints, a reduction in employee productivity, and higher energy costs. While tenant and employee discomfort manifests itself during occupancy periods, the energy penalty occurs during all hours of operation (during both part- and full-load operation). Unless the chiller kilowatt draw is monitored with an energy-management system or a separate metering device, you most likely will discover the problem when it is hot and you are unable to maintain chilled-water and/or environmental temperatures, when you see your energy consumption skyrocketing, or when your compressor fails.
In process-cooling applications in which a chiller supports production, fouled coils have other ramifications, such as the overheating of production equipment, which can cause product-quality problems and even failure of equipment, bringing production to a grinding halt.
Consider this real-life situation: A 20-ton chiller used to cool a computer control room of a major automotive-parts manufacturer becomes fouled and is in need of cleaning. Because the maintenance department is short-handed, it does not have time to perform the maintenance when needed. Hence, maintenance is put off for an unspecified period of time. Eventually, the debris load completely fouls the chiller coils, resulting in a second level of failure, which has a catastrophic impact on the business:
The compressor fails.
The computer room experiences computer failure because of overheating. The company is forced to replace the failed computer equipment while running production at reduced capacity until the chiller is back online.
Procurement of a new compressor takes two days and results in two days of downtime and lost productivity on three computer-controlled production lines, resulting in a $500,000-per-day production loss.
Management sends home production workers with full pay and benefits until the chiller is back up and running.
The company misses shipments, resulting in customer dissatisfaction.
Compressor-replacement cost: $7,500.
Compressor-installation cost: $4,000.
Production-equipment start-up cost: $10,000 (includes the cost of raw-material waste resulting from make-ready and production-line startup).
Coil-cleaning cost: $1,500.
As can be seen, if coil cleaning and maintenance had been performed before the first level of failure, it would have cost only $1,500. However, because it was deferred and operation continued until the second level of failure, the cost was more than $1 million.
You might be wondering why there was not a backup unit in place for this mission-critical application. The fact is, the “backup” consisted of spot coolers that were moved around the computer room to vital locations and used only to augment the cooling when needed. They were not designed for the full load of the computer room. So, the question still stands: Where was the backup chiller? The answer is, the manufacturers did not have one. This particular operation had converted its mechanically controlled production equipment to new computer control systems. As a result, the computer room supported by the chiller took on additional cooling loads and greater strategic significance to the business. Even though the computer room had both computer and electrical backup systems, the cooling system had not been upgraded and was the Achilles' heel of the production facility. Preventative maintenance should have been of vital importance in this facility.
Facilities and maintenance directors cite many reasons for deferring maintenance on chiller and condensing equipment, including:
Budgetary constraints (“We will put off the maintenance until next month, so we do not go over budget”). When you consider all of the risks to a business associated with a system failure, deferring maintenance because of budgetary constraints usually is not a sound decision. When budgetary constraints are placed on the maintenance of process- and comfort-critical equipment, the results can be catastrophic to a business.
Manpower and time constraints (“We'll get around to cleaning the chiller as soon as we can, as we have too many other things to do right now”). This reason for deferring maintenance is more common today than ever before. Why? Because companies have been forced to reduce staff and streamline operations to conform to the economic realities of the business, or they cannot find qualified personnel. This places additional demand on maintenance engineers because they have to do more with less. If chillers and condensing units support mission-critical operations and facilities, then maintenance of these systems should be near the top of the to-do list, even when the maintenance department is busy or short-handed. To help improve maintenance efficiency and save time, maintenance should be outsourced to a reliable service company, or technologies that can optimize operational efficiency and reduce the maintenance effort should be considered.
Maintenance complexity and knowledge constraints (“We don't have the skills to maintain this equipment correctly”). This reason is especially common in companies using advanced mechanical systems. Maintenance workers must be trained to maintain them properly, or the maintenance work should be outsourced to a service company with knowledge of the maintenance process.
Unfriendly maintenance process (“We hate cleaning chiller and condensing units because it's a dirty job”). Although cleaning coils is, in fact, a dirty job, that is not a sound reason to defer maintenance. When cleaning coils, proper safety equipment, including eye and respiratory protection, rubber gloves, and protective outerwear, should be worn to protect against coil-cleaning chemicals and possible mold or bacteria problems.
The list of reasons for deferring maintenance can go on and on, but one thing is clear: Deferring maintenance on HVAC equipment can be risky and increase the odds that a system failure will occur. When it does, it usually costs more than the maintenance that could have prevented the failure in the first place.
In the end, the decision to perform or defer maintenance on HVAC systems falls squarely on the shoulders of maintenance and facilities directors as they balance their maintenance and budgetary decisions, recognizing all of the risks involved.
For HPAC Engineering feature articles dating back to January 1992, visit www.hpac.com.
Randy Simmons is vice president of Air Solution Co., a manufacturer of air-intake filtration systems for chiller and condensing coils, cooling towers, rooftop units, and other high-volume/high-velocity air-intake systems. He can be contacted at airsolutioncompany@hotmail.com.