Carrier Context:
Working For A Better World...

EVALUATING
ALTERNATIVE
REFRIGERANTS

A GUIDE TO THE CRITERIA
FOR REFRIGERANT
SELECTION

By Jim Parsnow

INTRODUCTION

The mandated phase-out of chlorofluorcarbon (CFC) refrigerants by January 1, 1996 has brought many building owners and managers face-to-face with a difficult question: Which new refrigerant is the best choice for the future? Because the information surrounding refrigerant selection is complex and dynamic, there is a tendency to think in terms of automatic replacements (i.e., "I have CFC-11, so my only choice is to convert to HCFC 123"). This "knee-jerk" kind of thinking is limiting, and unlikely to lead to the optimum solution. A broad look at the criteria for refrigerant selection leads to a better understanding of the optimum solution.

ENVIRONMENTAL CRITERIA

Environmentalists tend to consider two criteria when evaluating refrigerants: ozone depletion and global warming. However, ozone depletion is not a concern so long as refrigerants are not vented to the atmosphere, a practice that is now prohibited by law. Moreover, new equipment must contain non-chlorine containing refrigerants. As for global warming, the more scientists study the issue, the clearer it becomes that refrigerants contribute less than 2% to this problem.

The environmentalists' criteria shed limited light on today's refrigerant selection issue. In fact, if we consider these two criteria alone, the refrigerants R-718 (water) and R-717 (ammonia) appear to be viable options. Of course, other considerations which limit these options - economics, energy, safety and so on - immediately come to mind.

BROADENING THE SELECTION CRITERIA

Expanding the criteria for refrigerant selection helps clarify priorities and ultimately, produce the optimum refrigerant choice. A broader list of criteria for alternative refrigerant selection would include:

Future conversion

ALTERNATIVE REFRIGERANTS:
A SAMPLE ANALYSIS

Before beginning the analysis, it is a good idea to prioritize the above criteria for your specific situation. The sample analysis below compares the three primary alternative refrigerants for the future - HFC 134a, HCFC 22 and HCFC 123 - based on the above criteria:

ACCELERATED PHASE-OUT DUE TO
OZONE DEPLETION

When vented to the atmosphere, the high chlorine content of CFCs is a catalyst that destroys ozone, allowing harmful ultraviolet rays to reach the earth's surface. Refrigerants like HCFCs (i.e., 22 and 123) also contain chlorine, but in much smaller amounts. HCFCs are not currently subject to the same accelerated phase-out underway for CFCs. However, HCFC production has been capped for 1996 and a stepped phase-out has begun. The industry is clearly moving toward a chlorine-free future. In light of this, HFC 134a has the edge as the most viable long-term solution.

Both CFCs and HCFCs cannot be vented by law under the U.S. Clean Air Act. There is some argument as to the long-term vs. short-term life of these refrigerants in the atmosphere, however this must be balanced against the quantity used and the move by environmentalists to ban all chlorine-containing refrigerants. Already, several nations are moving to ban not only CFCs but also HCFCs. It is noteworthy that the Montreal Protocol Copenhagen Agreement has a stepped down phase-out of HCFCs that resembles its original stepped phase-out schedule of CFCs in 1987. The CFC schedule under the Copenhagen Agreement has moved CFC phase-out up to the end of 1995. It is clear that the HFCs and HFC 134a have the edge as a viable long-term solution.

GLOBAL WARMING

How does replacing CFCs with HCFCs and HFCs affect the energy we consume and thus contribute to global warming? The U.S. Department of Energy's new Total Equivalent Global Warming Impact (TEWI) measure defines the contribution of systems. TEWI is a measure of the total amount of gas released to the atmosphere as a result of burning fossil fuels.

TEWI is the sum of direct releases (refrigerant emissions) and indirect releases (from fuels that emit global warming gases). Once CFCs are replaced, direct releases are immaterial (2%), and good containment vessels will reduce emissions even further. Indirect releases are the key (98%), and they are defined by system efficiency, not refrigerant type. In fact, the Department of Energy has stated that where HCFCs and HFCs replace CFCs, the difference in TEWI due to refrigerant is minor.

The U.S. National Action Plan for climate change will have an impact on global warming reduction. It contains 50 options to reduce U.S. greenhouse gas emissions to 1990 levels by the year 2000. As this plan is enacted, greater emphasis will be placed on substituting HFCs for CFCs and HCFCs. Containment will be critical in meeting the plan's goals for non-venting CFCs, HCFCs and even HFCs.

EFFICIENCY

There is no question that converting a chiller's lifeblood, its refrigerant, impacts system efficiency. The good news is that manufacturers have done an excellent job of designing new equipment and modifying existing designs to make up for efficiency losses. In most cases, the efficiencies of the new alternative refrigerant-based systems match or exceed those of existing CFC-based systems.

Comparing refrigerants as thermodynamic fluids in simple cycles is very misleading. These ratings are strictly theoretical and reflect the fluid's performance under ideal conditions.

In the real world of a chiller, actual refrigerant efficiency is affected by a host of factors related to normal chiller operation, including mechanical, thermal and aerodynamic factors. In the end, superior chiller design is far more important than a superior theoretical rating. And in fact, the positive pressure refrigerants offer an advantage for improved efficiency by utilizing the larger pressure differential between condensing and cooling pressures for advanced sub-cooling technology. Negative pressure refrigerants such as HCFC 123 do not offer this advantage.

SAFETY/RISK OF USE

All three of the new refrigerants can be applied at different levels of precaution, and users assume different levels and types of risks with each refrigerant. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) provides an excellent Safety Code for Mechanical Refrigeration in its new standard 15-1992. However, this standard does not review the risks and liabilities associated with refrigerant exposure in light of the exposure limits recommended in documents such as the Program for Alternate Fluorocarbon Toxicity Testing (PAFTT) . The refrigerants of the past (i.e., CFC-11) had very high safe exposure levels. The higher the exposure level, the lower the potential for risk and liability.

The PAFTT analysis led to ASHRAE's safety classification for refrigerants.

CONTAINMENT

Which new refrigerants require no add-on containment systems? This is a particularly important consideration in light of the first cost and the ongoing maintenance/service costs associated with containment devices.

Both HFC 134a and HCFC 22 operate in positive pressure systems, which typically have built-in containment. No add-on containment devices (or the additional maintenance associated with them) are necessary. In addition, the pressure vessels in positive pressure chillers are constructed to meet the high performance standard of the American Society of Mechanical Engineers (ASME) - seven times normal operating pressures. The production process is scrutinized at each succeeding step before the vessel may leave the factory bearing an ASME-certified stamp. These vessels are so reliable that refrigerant can even be stored and transported to the job site in the chiller.

ASME construction also ensures a quality containment product, not only from the quality of the steel used but also fabrication requirements, quality checks, proof testing and national registration approval by an independent inspector. The final result is a guaranteed pressure vessel for maximum containment. This is demonstrated by the new leak specifications for the latest chiller designs, which are as low as .05 ounces per year. The performance history of installed positive pressure chillers demonstrates that even 20- to 30- year-old chillers typically run with their original refrigerant charge.

HCFC 123 operates in negative pressure systems, as did most of the centrifugal chillers of the past when containment was not a concern. To safely operate a negative pressure system today, add-on containment devices are a must. These include high-efficiency purges, which an reduce emissions by as much as 99% and range in price from $4,400 to $6,000, and refrigerant sensors, which are required under ASHRAE 15-1992 and range from $3,000 to $15,000. Other containment devices that bring negative pressure chillers up to positive pressure standards include: refrigerant management systems, pressurizing systems, back-up pressure relief valves, along with other containment factors. All add to the up-front cost and the servicing costs of the system.

SIZE

Is your machine room already bursting at the seams? Chiller size is important, particularly since one that is too large may require the removal of a wall for its installation. Larger systems also have large parts, which, of course, cost more to replace.

Since they require no add-on containment devices, positive pressure systems tend to be significantly smaller than their negative pressure counterparts (i.e., storage is built in). The smaller size is also due to the smaller molecular size of the positive pressure refrigerants

(HFC 134a and HCFC 22), which allows more mass of refrigerant circulation in a smaller space per capacity of cooling.

Smaller chillers are typically easier and less costly to install, and their smaller parts are significantly less expensive initially.

POTENTIAL FOR CORROSION

Another advantage of HFC 134a and HCFC 22, the positive pressure refrigerants, is that these systems historically have required fewer tube and tube joint replacements (even when mechanically expanded into these joints) due to corrosion. By nature, negative pressure systems tend to take in air, which contains moisture that mixes with the refrigerant (specifically, its chlorine and hydrogen) to form acids that eventually cause corrosion problems. (For further reading on this subject, see the March 1976 ASHRAE Journal.)

AVAILABILITY

No matter how terrific your refrigerant of choice may be, if there's not enough of it to go around in 5, 10 or 20 years, your system will be in jeopardy. HFC 134a has the edge here because this stable refrigerant is being adopted by many other industries, including automotive, pharmaceutical and industrial processing. By the end of 1995, HFC 134a will have the highest production demand in the global market, at 116,000 tons per year. Conversely, as industries move away from CFCs and later, HCFCs, their production will fall off sharply. HCFCs may rise in price due to excise taxes (the U.S. government is currently reviewing this tax proposal). HCFC 22 will have a good supply as a result of the broad usage. On the other hand, HCFC 123 is just now being applied, by just two manufacturers and only in centrifugal chillers. No chlorine-free commercial replacement is planned for HCFC 123. HCFC 22 will be replaced in new designs with HFC combinations.

THE REFRIGERANT OF THE FUTURE

Based on the above analysis, HFC 134a emerges as the refrigerant of the future, with

HCFC 22 a strong, viable transition solution. Not surprisingly, a review of the product lines currently offered by the major chiller manufacturers reveals that most manufacturers are planning for a CFC/HCFC-free future as well. Some are moving quicker than others, which reflects the cost and time involved in converting manufacturing facilities and redesigning base products.

CONCLUSION

Environmental concerns about ozone depletion and global warming are only two of the many criteria to consider when comparing alternative refrigerants. A systematic evaluation of all the criteria based on your priorities will lead to the best choice for your facility, both today and in the future. As with any environmental issue, corporations that choose to move ahead of legislation and ahead of the industry demonstrate environmental responsibility. If your company does not have a strategic refrigerant plan, start one now. By the end of 1995, virgin CFC production will stop. Good solutions exist today if you choose wisely.

( top of page | back )