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CFCs and centrifugal chillers.


More and more property owners and managers are facing the dilemma of replacing or retrofitting building materials or equipment that have been determined to be environmentally unsound. Asbestos is the most common example of a widely used material that has now proved a hazard, but many other substances are similarly becoming suspect.

Chlorofluorocarbon (CFC) refrigerants, commonly used in centrifugal chillers, are one such substance. These products remain the most widely used refrigerants available today, in spite of recent caps on production. However, international agreements are likely to ban CFC production entirely by the year 2000, as alternative refrigerants reach commercial production levels.

Naturally, these restrictions are driving the price of CFCs up. The U.S. Environmental Protection Agency (EPA) forecasts the price of CFC-11 will rise from its current level of $3.50 to $4.00 per pound to around $12.00 per pound by 1999. In round numbers, a 1,000pound charge of CFC-11 that costs $3,500 to $4,000 today is expected to cost as much as $12,000 within 10 years.

Another factor is that the EPA has reclassified CFCs as "non-hazardous waste;' allowing reclamation and recycling of CFCs to proceed. In fact, it is widely believed that CFC containment and recycling procedures will be mandated by federal law.

A number of manufacturers have introduced on-site refrigerant reclaim/ recycle equipment; some are providing training to HVAC contractors. In addition, a variety of off-site refrigerant recycling centers are in operation. Taken together, these developments are assuring the availability of replacement CFC refrigerants for some time to come. Just how long, and at what cost, are questions without clear-cut answers.

A promising alternative

Alternatively, the hydrochlorofluorocarbon (HCFC) refrigerants, which have only 2 to 5 percent of the ozone-depleting potential of CFCs, deserve full consideration.

Some open-drive centrifugal chillers (currently using CFC-11) already have been tested and proven fully compatible with HCFC-123. In fact, there are chillers that have been operating successfully with HCFC-123 for almost two years. Hermetic-drive chillers have shown some compatibility problems, which HVAC manufacturers are working to resolve.

What of HCFC-123's availability, price, and performance? Large-scale quantities are expected to be available by the end of 1990. And as production gears up, the price of HCFC-123 is expected to fall in relation to CFC-11. A year ago, HCFC-123 was over four times more expensive than CFC-11. Today it is only twice as costly. By 1993, HCFC-is 123 predicted to be approximately 30 percent less expensive than CFC-11.

The thermodynamic properties of HCFC-123 are now fully defined, and major manufacturers have tested and documented its performance in centrifugal chillers designed for CFC-11. Tests performed by York have found that when HCFC-123 is simply substituted for CFC-11 in an existing chiller, the machine can lose between 5 and 20 percent of its capacity, depending on the original design conditions and the chiller's own characteristics. Chiller energy use, measured in kW/ton, can increase between 4 and 15 percent. The performance of a new chiller, however, can be optimized at the factory for operation with HCFC-123, regaining all of the chiller's capacity and efficiency. This is done primarily by proper gear and motor selection when the chiller system is designed. Manuacturers offering HCFC-123 centrifugal chillers should be able to provide accurate performance ratings alongside those for a comparable CFC-11 machine.

Recommendations for new chillers

Based on the best information currently available, property owners and managers may choose one of several alternatives when installing new large-tonnage chillers.

* Option 1: Install CFC-11 centrifugal chillers that are proven compatible with HCFC-123 and have their performance optimized for future conversion to HCFC-123. Conversion will be largely a matter of withdrawing the CFC-11 and recharging the chiller with HCFC-123, then making minor sensor and control changes.

This option yields the lowest first cost in most cases because CFC-11 currently is less expensive. And it probably will provide the lowest initial operating cost due to CFC-11's greater thermodynamic efficiency. Later, conversion will have minimal impact because chiller performance was based on HCFC-123.

* Option 2: Specify and install a HCFC-123 centrifugal chiller. The chiller's initial cost will be approximately 7 to 8 percent higher due to the differential in the present price of HCFC-123. The advantage is catapulting over the CFC issue and moving directly to an alternative refrigerant that is dramatically safer for the environment. Correct gear and motor selection will minimize capacity and energy penalties.

Option 3: Install a rotary-screw chiller, which operates on HCFC-22, another one of the more environmentally friendly refrigerants. (HCFC-22 has only 5 percent of the ozone-depletion potential of CFC41.) HCFC-22 is readily available, having long been used as a refrigerant in screw and reciprocating chillers, as well as residential systems.

Recommendations for existing chillers

Managers with an existing CFC centrifugal chiller plant with many years of useful life ahead of it face a different set of circumstances. Generally as long as a chiller system is performing as designed and is well maintained, continued use of CFCs probably is the best course to follow.

The refrigerant cost and availability trends must be watched closely. And special attention must be given to chiller maintenance and refrigerant conservation techniques.

It is important to note here, however, that conversion from CFC-11 to the more environmentally acceptable HCFC-123 is technically feasible in many cases.

Continued use of CFCs

Good maintenance is the basic requirement for any centrifugal chiller system that will continue to operate on a CFC refrigerant. Preventing refrigerant leaks is the first important step. Leaks are usually caused by drive vibration (from normal operation as well as misalignment), gasket deterioration, excessive system purging, and heat-exchanger tube corrosion. Once a leak develops, it will only get worse until it is repaired, and its root cause is corrected.

Not only are leaks wasteful and harmful to the environment, they will directly increase chiller energy consumption by making the compressor work harder to achieve desired cooling. Procedures for detecting and correcting leaks are well documented by chiller manufacturers and should be familiar to any professional HVAC service technician.

Particular attention should be given to the chiller's purge unit, which removes air and moisture from the refrigerant loop. Old-style, manually operated purge units make it difficult to tell when air/moisture removal has ended and refrigerant is being exhausted to the atmosphere. Modern, compressor less purge units are Up tO four times more efficient than older models and can be retrofitted to installed centrifugal chillers in many cases. These recently designed purge units have favorable ratios of refrigerant to exhaust air, meaning little refrigerant is wasted as the noncondensables are purged. Modern purge systems also have the ability to alert the operator when excess purging occurs.

CFC recovery and recycling

Even with the best maintenance and operating procedures, CFCs must be removed occasionally from the chiller to service the machine, to clean the refrigerant, or to dispose of contaminated refrigerant. Clearly, the old practices of discarding unwanted refrigerant no longer apply-thus the growing attention to recovery and recycling methods.

HVAC service technicians have two options for handling used CFCs-recover and recycle them on-site or recover them on site and ship them to an off-site refrigerant recycling or disposal center.

On-site recycling requires specialized equipment, now commercially available from a number of manufacturers, and properly trained personnel. Unfortunately, on-site methods generally cannot remove all contaminants.

Off-site recycling offers the advantage of laboratory analysis of the recovered refrigerant. Some centers guarantee their recycled product to meet Air Conditioning and Refrigeration Institute standards. A possible drawback of going off-site is the extra effort and expense to contain and ship the refrigerant properly.

Whichever method is chosen, recycling refrigerants is attractive for several reasons. First, recycled CFCs are exempt from the recently enacted federal tax, making them less expensive than new refrigerant. Also, recycling guarantees a future supply of dwindling CFC stockpiles. Further, recycling helps protect the environment and stays within any state and federal regulations that require containment of CFCs.

Converting existing chillers to HCFC-123

Although continued operation of an existing CFC chiller remains the best option, some properties may choose to convert to HCFC-123. Such conversions may occur if an owner wants to embrace the ozone issue as part of its environmental policy. Conversions may also become more prevalent if CFC prices rise in the face of more stringent controls.

If one of these conditions apply, conversion should be seriously considered. The basic questions to address are these: Is the existing CFC-11 chiller compatible with HCFC-123? If not, can if be made so? How will the existing chiller perform with HCFC-123? Can that performance be optimized?

As noted earlier, HCFC-123 creates compatibility problems in some centrifugal chillers. In chillers with hermetic motors, HCFC-123 tends to attack motor windings. Some manufacturers of hermetic-motor chillers report they have overcome this problem in new chillers and can retrofit some installed chillers with an HCFC-123 compatible motor. This retrofit procedure requires chiller shutdown and removal of the entire refrigerant charge. This is not an issue with open-motor chillers because the refrigerant never comes in contact with any part of the motor.

The second aspect of the compatibility problem is the tendency of HCFC-123 to deteriorate the gaskets, seals, 0-rings, fitting materials, and valve seats in some chillers. The integrity of the refrigerant circuit is thus jeopardized at several points. Refrigerant and equipment manufacturers have been working hard on this problem, too. As HCFC-123 compatible materials are identified, they are being incorporated into new chiller designs.

Some fortunate owners will find the fitting materials used in their chillers are already fully compatible wit HCFC-123. This has been de for certain makes and models of chillers through both laboratory tests and field experience.

Thermodynamically, HCFC-123 has operating temperatures and pressures similar to those of CFC-11 but requires a higher CFM/ton. So capacity and efficiency in an existing chiller designed for CFC-11, theoretically, are likely to suffer.

Actual performance, however, depends on the specific application and the design of the original chiller system. For example, a six-year-old York centrifugal chiller converted to HCFC-123 in 1988 at the DuPont Corporate Data Center actually performed better at some loads than it did with CFC-11.

The fact is, rule of thumb performance measurements do not mean much when it comes to comparing CFC-11 and HCFC-123. Chiller performance will vary, depending largely on the design and operational characteristics of the centrifugal compressor. The important thing for property owners and managers to remember is this: any HVAC contractor or manufacturer proposing to convert a CFC-11 centrifugal chiller to HCFC-123 should provide documented performance ratings for both refrigerants.

The ultimate retrofit

One proven technique for converting CFC-11 chillers to HCFC-123 is driveline retrofit. This method requires the removal of the chiller's old motor, compreSsor, and controls and the installation of a new driveline, connected to the original heat-exchanger shells.

This retrofit has given new life to hundreds of aging CFC-11 centrifugal chillers. It has been especially effective where there is limited or difficult access to HVAC equipment rooms. Here's why:

In most cases, the driveline can include an open motor (that never contacts refrigerant) and a centrifugal compressor whose compatibility with HCFC-123-seals, gaskets, and all-is field proven. With few exceptions, the retrofit can be performed on any CFC-11 centrifugal machine.

Looking ahead

It appears that both CFC-11 and HCFC-123 will be employed in centrifugal chiller plants for many years. For now, either refrigerant can be specified for new chillers, with a relatively high degree of confidence that both technical and legal issues can be accommodated. An alternative deserving consideration is the installation of a new, ozone-friendly HCFC-22 rotary screw chiller.

In existing CFC-11 plants, sound maintenance and recycling programs should enable a property to continue operating within the law and at reasonable cost levels. If not, a realistic option is to convert existing equipment to HCFC-123. Proven techniques, such as the driveline retrofit, exist to accomplish this.

Like concerns about energy that emerged in the 1970s, the refrigerant issue is here to stay. As with the energy crisis, professional property managers are obliged to understand the implications of the ref refrigerant issue as it relates to buildings under their purview. And they need to seek solutions from an HVAC industry which, as in the past, is responding to a critical challenge.
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Title Annotation:chlorofluorocarbons
Author:Kozak, Robert G.
Publication:Journal of Property Management
Date:Sep 1, 1990
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