White Paper: Contain Or Convert?

How To Extend The Life Of Negative-Pressure Chillers Through The Responsible Use of CFCs

By Michael Zales, Containment Products Marketing Manager, Carrier Commercial Applied Equipment & Services.

Michael Zales With the Clean Air Act of 1990's phase out deadline for domestic CFC production behind us, the question of what to do with the estimated 60,000 negative-pressure chillers using chlorine-based refrigerant CFC-11 in the United States weighs more heavily with each passing day. If you operate one of these chillers, you face a decision that will have a profound impact on your operation and budget for years to come.

While the issues are complex, the alternatives are well-defined: contain the refrigerant in your existing chiller using specialized containment devices; replace your chiller; or convert your existing chiller to use an alternate refrigerant.

Determining which option is the most cost-effective requires a careful examination of your individual situation. Such analysis typically begins with a consideration of the age and condition of the chiller in question.

Too Young To Replace?

It is further estimated that half of the negative-pressure chillers in the United States -- approximately 30,000 chillers -- are less than 15 years old. With the life span of the average chiller at 30 years, these chillers have many years of useful life remaining. Understandably, many chiller owners are not ready to accept the expense of replacing equipment that is performing well.

While the decision to replace an aging, inefficient chiller is fairly clean-cut, the dilemma with a younger chiller is typically whether to convert to an alternate refrigerant such as HCFC-123 or to responsibly contain the CFC-11 currently used, as outlined in the Clean Air Act, Title VI, Section 608, and in conjunction with specialized containment products and improved service practices.

The Conversion Option

For most negative-pressure chillers, conversion to HCFC-123 is costly. Typically, all original gaskets and seals, and other major components (such as the motor stator), must be replaced with HCFC-123 compatible materials. Often it is necessary to install a new impeller wheel to minimize capacity and efficiency losses.

The implications go beyond the upfront costs of converting. Since exposure limits are much lower for HCFC-123 than for other common refrigerants, consideration of a refrigerant monitor, self-contained breathing apparatus and ventilation system improvements should accompany any refrigerant change, per ASHRAE 15-1994 standards. Moreover, because HCFC-123 contains chlorine, refrigerant containment devices are required even after conversion.

In total, converting a typical, 500-ton chiller to HCFC-123 is likely to cost as much as $88,000, or approximately 60 percent the cost of complete replacement. And that figure does not include the hidden expense of higher operating costs due to efficiency and capacity losses, or the cost of the same containment devices required of CFC-11 chillers.

The efficiency loss is not something to gloss over. If we convert our 500-ton example, chiller efficiency will drop a minimum of three percent, significantly decreasing system performance while increasing operating costs. Consider, for example, a 15 year-old, 500-ton chiller with a full load efficiency of .75 kW/ton operating 3,000 hours per year. A drop in efficiency to .77 kW/ton would add at least $3,000 annually in energy costs (500 tons x .02 kW/ton x 3,000 hrs. x $.10/kWh). Multiplied over the remaining life of a converted chiller, that is an additional cost of $30,000 to $45,000. When the multi-year cost of chiller efficiency loss is added to the initial conversion costs, the lifetime cost of a CFC chiller conversion is nearly as high as the one-time cost of a replacement chiller.

Cost Analysis Favors Containment

For chillers less than 15 years old, a cost analysis of conversion versus containment proves that containment is by far the more economical solution, in the first year and well beyond. For the same 500-ton chiller, the installed cost of a complete containment package is currently estimated at $29,500, one-third the upfront cost of conversion. Additionally, many chillers require only selected containment devices, making the actual containment cost substantially less.

The reduced need of expensive refrigerant replacement can quickly offset the initial cost. The U.S. Environmental Protection Agency currently allows a 15 percent annual leakage rate for commercial applications and a 35 percent leakage rate for industrial installations. Yet with today's new technologies and improved service practices, annual refrigerant emission rates of two percent or less are achievable.

What does this mean in the long run? ASHRAE 15-1994 allows a maximum of 330 lbs of refrigerant to be stored in a mechanical room. At a two percent leakage rate, a 500-ton chiller could continue to operate for more than 13 years on that initial supply.

The Long Term Solution

A refrigerant containment strategy is an economical and responsible way to add years to the life of a CFC chiller in good working order. Containment is the first and least expensive option compared to conversion or replacement. While a refrigerant containment program improves the operation, maintenance and servicing of negative-pressure centrifugal chillers, it also saves money by capturing the refrigerant lost to the atmosphere during normal use and servicing.

In addition to reducing CFC emissions, a refrigerant containment program also extends the useful life of an existing chiller, providing the you ample time to plan a clear migration path to a chlorine-free future for your facility.

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