1

Emissions and Environmental Impacts

from Air-Conditioning and Refrigeration Systems

James M. Calm, PE

Engineering Consultant

10887 Woodleaf Lane, Great Falls, VA 22066-3003 USA

phone and fax (automatic): +1-703/450-4313 π e-mail: jmc@spectrum-internet.com

Abstract

The impacts of air conditioning and refrigeration systems on stratospheric ozone are primarily linked to release

of ozone-depleting refrigerants. Their contributions to global warming stem both from release of refrigerants

and from emission of greenhouse gases (GHGs) for associated energy use. Because the energy-related

component has a significantly higher warming impact, phaseout of hydrofluorocarbon (HFC) refrigerants with

less efficient options will increase net GHG emissions. The same conclusion applies for perfluorocarbon

(PFCs), though they are less commonly used as refrigerants. Integrated assessment of ozone depletion, global

warming, and atmospheric lifetime provides essential indications in the absence of ideal refrigerants, namely

those free of these problems as well as safety, stability, compatibility, cost, and similar burdens. This paper

examines the trend in refrigerant losses from chiller use. It documents both substantial progress in release

reductions and the technical innovations to achieve them. It contrasts the impacts of current refrigerants with

alternatives and with the chlorofluorocarbons (CFCs) they replaced. The paper also summarizes thermodynamic

and environmental comparisons of options to show that phaseout decisions based on chemical composition

alone, without regard to attributes of individual substances, can result in greater environmental harm than

benefit.

1 Introduction

The final conclusion of the latest Scientific Assessment (WMO, 1999), the fourth in a series by an international

panel of leading scientists since adoption of the Montreal Protocol, recognizes that:

“The issues of ozone depletion and climate change are interconnected; hence, so are the Montreal

and Kyoto Protocols.”

This conclusion is based on meticulous consideration of the underlying atmospheric science and extensive sets of

supporting data (WMO, 1999). It also follows intuitively from recognition that the phenomena of ozone

depletion and climate change involve the same atmosphere (Albritton, 1997).

The primary global environmental impacts from air-conditioning and refrigeration (ACR) systems arise from

emissions of refrigerants and of gases associated with energy use. Those gases usually are released at the power

plants that provide the electricity, steam, or hot water used to manufacture, transport, install, operate, service,

and ultimately dispose the equipment and ancillary devices. They can occur on-site when the equipment is

driven by engines or turbines or with use of direct-fired absorption cycles. Of the total, releases of refrigerants

and of combustion emissions to provide operating power dominate. Specifically, discharge or leakage of stable

refrigerants containing chlorine, bromine, and – though generally negligible – other halogens affects the

stratospheric ozone equilibrium. Likewise, both the common refrigerants and the combustion products, notably

carbon dioxide (CO2) and to a lesser extent nitrous oxide (N2O), act as GHGs. Refrigerant releases have

multiple effects, variously including ozone depletion following breakdown, direct action as GHGs, and

efficiency reduction leading to increased energy use. The performance reductions occur with departures from

the optimal charge or – for refrigerant blends – charge and composition. Hence, the critical issues in addressing

stratospheric ozone depletion and climate change for ACR systems come down to selection of refrigerants that

minimize impacts, reducing their release, and increasing net efficiencies to lower energy-related GHG emissions.

The severe consequences of ozone depletion are being averted through international adherence to the Montreal

Protocol. The levels of chlorine and bromine reaching the stratosphere, referred to as chlorine-bromine loading

(CBL), have peaked or are now peaking, and the ozone layer has begun or soon will start to recover (WMO,

1999). The outlook for global warming and the severity of its consequences are far more threatening. Even if

releases stopped for all other GHGs, carbon dioxide emissions from energy use still would increase in concert

with foreseen economic improvement in developing countries and with population growth (IPCC, 1996).

Whereas the net carbon dioxide impact overshadows the combined effects of all other GHGs, reduction in

energy demands and efficiency improvement are crucial. As a minimum, no changes that decrease efficiency

can be deemed acceptable.

The functional measures of the Montreal and Kyoto Protocols, beyond those addressing scientific assessments

and international assistance, differ. The Montreal Protocol restricts the production of the individual chemicals of
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concern, leading to their ultimate phaseout for most uses (UN, 1987; UNEP, 1996). The Kyoto Protocol imposes

national limits on emissions of important GHGs, but does so by a collective approach encompassing six specific

gases or groups of gases (UN, 1997). The most critical gas among them is CO2. Although they have a much

lower impact, namely 1.6% of the total for the USA at present (EIA, 1998), HFCs and PFCs as groups constitute

two of the six GHGs in the Kyoto Protocol “basket.” Some studies project that their impact will reach 4-10% of

the global total by 2100 and double that if not controlled (Ko et al., 1993).

The focus of the present meeting, and this paper, is on options to limit emissions of HFCs and PFCs, both of

which are among the primary alternatives to ozone-depleting substances. This paper addresses the measures

taken and available to minimize their release, with emphasis on the refrigerants used in chillers.1 Such measures

include design changes and enhancements to reduce leakage, regulations to reduce intentional and unintentional

discharges, and use of alternatives. In doing so, the paper focuses on the trades in refrigerant selection to

balance actions as ozone-depleting substances (ODS), impacts as GHGs, and impacts on release of other GHGs

to power the systems.

 

1 Chillers are refrigeration machines that cool water, other heat transfer fluids (brines), or process fluids by a vaporcompression (reverse Rankine), absorption, or other thermodynamic cycle. Their most common use is in central systems

in large buildings or complexes, such as offices, campuses, shopping centers, hospitals, hotels, and military installations.

The chilled water or brine is piped through the building or buildings to other devices, such as zoned air handlers, that use

the cooled water or brine to air condition (cool and dehumidify) occupied or controlled spaces. By their nature, both

efficiency and reliability are critical attributes of chillers.

Table 1: Chiller refrigerant losses (%/yr)

time frame and, if applicable, location (study) initial annual disposal

earlier anecdotal data (Fischer et al., 1991) –– 12 - 37 ––

1970s - 1980s Japan (Miyasaka, 1989) –– 2.2 - 18 ––

1970s - 1980s USA (Hummel et al., 1991) –– 7.4-10.2 ––

1980s USA, “historical” (Calm, 1993) –– 8 10

1987-1989 France (Climafort, 1998; Sauer, 1998) –– 12.6 - 30.6 ––

1990 (UNEP 1991) –– 8 - 15 ––

1990s, “parametric” (Fischer et al., 1991) –– 0 - 16 0 - 5

1990-1992 (Climafort, 1998; Sauer, 1998) a –– 15.3 - 18.2 ––

1991 USA, “current” (Calm, 1993) a –– 4 5

1993-1995 France (Climafort, 1998; Sauer, 1998) a –– 7.9 - 10.7 ––

late 1990s, “parametric” (Sand et al., 1997) –– 1⁄2 - 4 5

1996 USA (Calm et al., 1999) a 0.7 b 1.0 b,c 1.5 b

1992-1997 (Trane 1997) a –– 0.46% ––

1999 USA, manufacturer claims –– <0.1 - <0.5 d ––

projected ~2000, “future” (Calm, 1993) ~0 <1⁄2 <1⁄2

refrigerant conversions

1991-1994 USA (Clark, 1999) –– 0-154 e ––

1996 USA (Calm et al., 1999) a 0.7-3.5 b 1.0 - 10 b,c 1.5 b

1992-1997 (Trane 1997) a –– 0.62% ––

a actual releases since 1991 are increasingly lower than indicated due to use of make-up rates as a proxy to

determine loss rates (see discussion in text) b includes adjustments for upstream losses (see discussion in text) c annual sum of operating and intermittent losses d claims do not elaborate the specific losses included or how they were determined e several converted machines had repeated, catastrophic losses: The average for operation from 1994 through

1998 was 3.2 %/yr with exclusion of the four worst machines.
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2 Refrigerant Emission Reductions

A number of studies have compiled data or estimated losses from centrifugal chillers, as summarized in table 1.

Some of the dates shown reflect inferences by the author for studies that did not specifically identify this

information. The dates for conversions, from CFCs to either R-123 or R-134a, indicate the when the conversion

was performed.

The terminology of initial, annual (which includes both operating and annualized intermittent), and disposal

losses is explained in Calm et al. (1999). All of them are expressed as a fraction of the operating refrigerant

quantity, or charge. The disaggregation is useful to assess the timing of emissions and their impacts. Briefly:

• Initial: This group includes all losses associated with making equipment functional, and specifically

those associated with manufacturing, performance and leak testing, transportation, installation, initial

charging, field leak testing, and initial start up. These losses are very small, except in cases where a

significant leak is discovered or a failure occurs during start up.

• Operating: Unlike the initial losses, which occur once in the life of a machine, the operating losses are

recurring. They include both leakage and purge releases.

• Intermittent: Also recurring, these releases include those from maintenance (for example in

disconnecting hoses and opening systems for major service procedures), accidents, failures,

unintentional venting, technician errors, and nonspecific causes.

• Disposal: This amount accounts for the refrigerant lost at equipment retirement, a one-time event per

machine.

The progression of leak data in table 1 shows a clear trend in release reduction, by as much as two orders of

magnitude in several decades. This remarkable achievement was driven, for the most part, by growing

environmental awareness, market economics including manufacturer competition to claim reduced emissions,

and anticipation of refrigerant shortages and future regulations. Historical loss rates were very low in small,

sealed systems (factory charged and tested circuits with hermetic compressors). Examples include window air

conditioners, other appliances, packaged terminal air conditioners and heat pumps, and water-source heat pumps.

Disposal losses typically were 100% for them, but recovery is becoming the norm and now is required in most

developed countries. Progress also was made in unitary equipment and other ACR product groups, but some still

have high loss rates. Higher losses still occur with automotive air conditioners, transport refrigeration, and

systems employing field-installed piping, such as supermarket (commercial refrigeration) systems.

Most of the data from before 1990 is necessarily from chillers employing CFCs. They were used in more than

95% of centrifugal chillers, led by R-11 in approximately two-thirds. There is no reason to expect differences in

leakage rates by chemical composition (for example, between CFCs, hydrochlorofluorocarbons or HCFCs, and

HFCs) for equipment fabricated with similar materials and technologies. Different loss rates are likely for R-717

(ammonia) based on the materials and fabrication differences. One distinction that is likely to influence

emission rates is dissimilar operating pressures.

Climafort (1998), Dazin (1998), Hummel (1991), and Sauer (1998) document higher losses, by as much as 50%,

in older chillers using low-pressure refrigerants. These differences are consistent with expectations based on old

purge designs, which vented appreciable refrigerant quantities along with the air removed, but they are not

indicative of current and projected practice. Low-pressure chillers and refrigeration systems fitted with

condensing purges coupled with vapor recovery systems, for purge venting, should offer a small advantage.

Leaks, when they occur, in the subatmospheric portion of such systems generally will suck air in, rather than

release refrigerants. A purge device removes this air. A small amount of refrigerant vapor accompanies the air,

but the purge condenses most of this refrigerant and returns it to the chiller. The vapor recovery canister

(commonly a tank filled with activated charcoal) absorbs most of the remainder for recovery in periodic

processing. The majority of R-11 and R-113 (both CFCs) retrofits and new R-123 (an HCFC) chillers employ

purge and vapor recovery systems; the same advantage is expected with low-pressure HFCs or

hydrofluoroethers.

Whereas the driving force in a leak is pressure differential, a shift to high-pressure refrigerants – whether HFCs,

hydrocarbons (HCs), ammonia, or others – is likely to increase releases when leaks occur. There is little

difference in loss rates in new, tight equipment based on design compensation, but the available data and

anecdotal accounts for high-pressure refrigerants point to higher releases when failures do occur. A tiny leak

will increase purge run time with almost no refrigerant loss in a low-pressure machine, but the same small

opening will discharge increasing refrigerant amounts with increasing operating or standby pressure. The full

refrigerant charge may be lost in a high-pressure system before a leak or rupture is detected or attended to.

The common practice of using refrigerant additions (make-up) and removals as a proxy for actual releases,

which are difficult to measure, introduces three errors that exaggerate emissions. First, some of the make-up

refrigerant in low-pressure chillers offsets amounts removed in purge venting, even though very small in tight
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chillers. Most of the vented refrigerant is or could be – as discussed below – recovered, but recovery usually is

left out of the accounting. The actual releases, therefore, may be as much as 25% lower for low-pressure chillers

where the recovery tanks are correctly reprocessed. Second, some of the initial and early make-up amounts do

not reflect actual losses. The portion of the refrigerant that is not recovered from factory testing remains inside

the chiller, dissolved in the lubricant or absorbed in other materials. This amount reduces startup charge

requirements. Likewise, some early additions reflect original undercharging rather than actual releases. Third,

replacements for contaminated refrigerants, such as from motor burn-outs or high acid levels, do not imply

releases when the old refrigerant is recovered for reclaim or disposal.

A fourth error partially offsets the first three, in the majority of studies, namely omission of upstream losses.

This term refers to fugitive emissions in manufacturing, packaging, repackaging in distribution, transportation,

storage, and handling of the refrigerant before use, including amortization of associated catastrophic losses in

transportation, distribution, and storage accidents. In short, it accounts for all releases of the refrigerant prior to

its introduction into equipment for use. Although it is a small fraction of the total for the container sizes used for

large chillers, this adjustment can be appreciable for some ACR applications. As an example, upstream losses

may exceed 25% in small containers for consumer use to “top off” the charge in automobile air conditioners.

Future emissions are likely to be reduced to or less than the low levels projected by Calm (1993) by the

improvements discussed below. Those levels were determined through a survey of the product development and

engineering departments of equipment manufacturers. The results are supported by proprietary data obtained in

the interim for more than 4000 chillers.

3 Changes to Reduce Refrigerant Releases

The preceding discussion summarizes remarkable reductions in refrigerant losses in the last two decades,

typically by factors exceeding ten over the life of a chiller. Such dramatic decreases required hundreds of

modification in the design, manufacture, and service of chillers. Some of the key changes were:

SEALS AND JOINTS

• design changes to minimize the number of joints in refrigerant circuits: Modifications and use of

special assemblies enabled ten-fold or greater reductions.

• replacement of flared and other mechanical connections with brazed connections: While brazed joints

increase the cost of fabrication, they are not prone to loosening with vibration and service errors.

• augmentation of threaded joints with o-rings: Addition of o-ring seals on the threaded joints that

cannot be eliminated, for service or other access needs, lowers seepage.

• use of new gasket materials: A new class of flat gasket materials provides tighter seals, in some cases

at lower sealing pressures. Similarly, systematic screening tests identified materials that are more

durable and that absorb less refrigerant.

• augmentation of flat face gaskets with silicone beads: This change increases the local pressure in

places where it is difficult to achieve high sealing pressure due to bolting patterns.

• replacement or augmentation of gaskets and o-rings with adhesive sealants: The new sealing materials

reduce losses.

PURGE SYSTEMS

• use of condensing purges: Older purges used a variety of thermal, buoyancy, and pressure methods to

separate air from refrigerants in low-pressure chillers and in subatmospheric operation of medium- and

even high-pressure systems, at low or very low temperatures, for refrigeration. Modern purges cool

the removed air below the boiling point of the refrigerant, separate the two, and return the condensed

liquid refrigerant to the chiller or refrigeration machine. Condensing purges typically use a small,

hermetic refrigeration circuit, but greatly reduce the refrigerant quantity released in venting the purged

air. Other designs use lubricants or other fluids cooled by the chiller itself instead of separate

refrigeration circuits; they are simpler, but cannot run when the chiller is off.

• use of vapor recovery systems in purge venting: Even though the amount of refrigerant released by

condensing purges is very small, it can be reduced to virtually none by passing the air through a

material that absorbs any residual refrigerant vapor before its discharge. Typical systems employ

activated charcoal pellets in tanks, which are then reprocessed to recover the refrigerant. A new

approach will be introduced in the next year, to promote wider use, with in situ processing and

recovery as part of the annual maintenance.
5

SERVICE

• incorporation of on-board refrigerant storage or means for charge recovery during service: Some

designs include receivers or provisions to isolate the refrigerant in the evaporator or condenser, so

some internal service procedures can be performed without having to remove the charge from the

chiller. Others facilitate recovery into and recharge from permanently connected or portable storage

systems. Both strategies are effective in containing the refrigerant during service.

• introduction of, and in some countries requirements for, refrigerant recovery equipment: Utilization of

such equipment enables reuse of the refrigerant, often after passing it through filter-driers to clean it,

and reduces the likelihood of intentional venting.

• use of cylinders instead of drums to transport and store low pressure refrigerants: Although they have

a higher first cost, use of cylinders of the type commonly used for high-pressure refrigerants enables

service technicians to draw vacuums on emptied containers to extract any residual refrigerant. The

older drums would buckle when evacuated, so some refrigerant was lost each time one was disposed.

Moreover, the bungs used to open and close those drums were more leak-prone than protected cylinder

valves. The cylinders can be returned for reuse, which also reduces other waste.

• shift from scheduled lubricant changes to when needed: By reducing the frequency of oil changes,

both the dissolved refrigerant and lubricant quantities are conserved. Periodic oil analyses and

chemical monitoring assure lubricant integrity with reduced chemical use, waste, and disposal burdens.

• increased diagnostic measures in preventative maintenance: Checking for conditions that suggest the

likelihood of imminent failures, such as periodic eddy-current testing of heat exchanger tubes, enables

corrective actions before failures and associated refrigerant releases occur.

• license requirements for technicians: Some countries, states, and local jurisdictions require that

technicians servicing specified equipment obtain licenses to do so. Candidates usually must

demonstrate training through prescribed courses, testing, apprenticeship, or some combination of them.

Such requirements provide a limited assurance of competence and frequently also verify awareness of

environmental protection measures.

• education and training of technicians: A number of associations, manufacturers, and labor unions have

instituted training programs, often culminating in proficiency testing, to improve the qualifications of

technicians who install and service ACR equipment. Such programs improve the prospect that

technicians learn the procedures necessary to minimize failures and to perform their tasks with

lowered refrigerant losses.

• increasing role of manufacturers in service operations: Whereas most chiller systems were installed

and serviced by independent companies in the past, and sometimes by the staffs of building owners

and/or managers, equipment manufacturers have increased their roles in and technical support for

service operations. Similarly, both manufacturers and a greater number of independent laboratories

now offer chemical analyses of refrigerants and lubricants, to improve maintenance and to identify

imminent failures. These shifts improved both the likelihood and the competence of preventative

maintenance.

OTHER CHANGES

• use of enhanced heat transfer surfaces: Although the primary incentive for this change is to improve

efficiency, it also reduces internal volumes, thereby lowering the refrigerant charge size and the

amount lost in catastrophic failures and upstream releases. Related advances in heat exchanger design,

such as in tube-bundle configuration and spray nozzle placement, and – in some chillers – shifts to

compact plate heat exchangers provide similar benefits.

• design changes to extend service intervals: Some refrigerant, such as that trapped under gaskets or

absorbed by motor insulation materials, is lost each time equipment is opened even with recommended

pump-down procedures. By reducing service frequencies through design modifications and use of

more durable materials, some refrigerant releases are avoided.

• design changes to reduce failures and extend equipment life: As an example, manufacturers changed

the baffle designs and materials inside shell-and-tube heat exchangers, which are the type most widely

used in water-cooled chiller condensers and most chiller evaporators, to reduce tube vibration and

wear. Doing so minimizes one cause of potential leaks. Similarly, manufacturers also strengthened

tube headers in heat exchangers and improved the fabrication methods to attach tubes; both of these

changes improve initial tightness and reduce the likelihood of future leaks.
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• manufacturing advances: Modern extrusion and other fabrication methods improve the integrity of

refrigerant circuits. The seamless copper or other tubes used today, as an example, are less prone to

failure than welded tubes of the past.

• factory tests: The majority of manufacturers now check all assemblies (not just random samples) for

leaks with helium mass spectrometers or other methods that are capable of detecting even very small

leaks. These methods are more sensitive, reliable, and economical that older methods that used more

primitive refrigerant detectors, air bubbles, or soap solutions. Manufacturers check all completed

chillers in the best cases.

• use of leak detectors: Although promoted to improve technician safety in refrigeration machinery

rooms, use of detectors set at very low concentration levels provides an early warning of incipient

leaks, before significant refrigerant losses occur. Both leak detectors and microcomputer controls,

discussed below, can be connected to remote annunciators or phone dialers to notify technicians of

leaks. New fire and mechanical regulations in some locations require remote annunciation, at

constantly attended locations staffed with trained personnel, to assure that detector alarms are heeded.

• microcomputer control of operation: Computerized control systems have become the norm for chillers

and other sophisticated ACR equipment in the last 15 years. Tracking of critical operating parameters

enables detection of failures before their severity increases refrigerant losses and other damage. These

microcomputers also monitor run time, purge operation, and refrigerant leak detectors to facilitate

preventative maintenance and alert technicians of service needs and impending failures. Their primary

benefit is to optimize operation, particularly in installations with multiple chillers, to attain the highest

operating efficiencies and, thereby, reduce energy use and related GHGs. As the technologies

advance, some of these systems are incorporating anticipatory logic and schedules to project future

loads and optimally control operation, for example with integrated thermal storage. Moreover, the

computerized controls enable remote supervision and intervention by service technicians and trained

supervisory staffs, technicians, and engineers.

• bearing advances to reduce or eliminate compressor lubricants: Reducing or eliminating lubricant

needs also reduces or eliminates release of the refrigerant dissolved in the oil when changed. New

approaches including magnetic, advanced hydrostatic, ceramic, permanently lubricated, and other

bearing technologies are being tested that may completely eliminate the need for compressor oils and

oil changes. Some of these developments have been announced and others probably will be within the

next two years.

• regulations to prohibit intentional venting: While deliberate release of refrigerants during service or

upon equipment retirement historically was common in smaller systems, it was not a common practice

in large chillers, for which the refrigerant amounts and costs already justified recovery measures. The

regulations have some impact for chillers, for example to limit releases when the quantities taken from

containers in charging do not fully empty them or when components are serviced (e.g., system

cleaning after a hermetic motor burnout).

• regulations to require repairs when refrigerant make-up amounts exceed prescribed thresholds: Such

regulations assure that chronic leaks are repaired or that the equipment involved is taken out of use or

replaced. Again, chiller operating economics generally assured the same results, but the restrictions

address the worst cases and increase the penalties for deferring prudent service and replacements.

This list of technology, service, and regulatory advances to reduce emissions suggests a revolution, rather than

evolution, in measures to reduce refrigerant releases. Moreover, this list highlights only the key changes; there

were many others.
7

The measures to reduce refrigerant releases are not limited to CFCs, HCFCs, HFCs, and PFCs. Many of them

also are applicable to ammonia, carbon dioxide, hydrocarbons, water, and other nonfluorocarbon refrigerants.

Their release could increase flammability or toxicity hazards, risk pressure injuries, degrade system reliability, or

exacerbate other environmental problems. For example, hydrocarbon emissions may contribute to local smog

formation; such releases will be concentrated in urban areas in which smog problems are most acute. Released

ammonia that is washed into surface water by rain is highly toxic to aquatic life. And most importantly, loss of

refrigerant from vapor-compression machines, or air leaks into subatmospheric equipment, reduces operating

efficiency and thereby increases energy use and GHG emissions.

4 Efficiency and Warming Impacts

Figure 1 shows the consequences of reduced emissions, both refrigerant and energy-related, from centrifugal

chillers on GHG emissions. The data shown are for 1750 kW (500 ton) R-11 and R-123 chillers. Approximately

60% of the centrifugal chillers installed in the years shown used these refrigerant. Similar conclusions can be

drawn for replacement of R-12 with R-134a for the same time frame, although the absolute emissions both start

and end at higher levels. The underlying analyses, commonly described as total equivalent warming impact

(TEWI) analyses, and data are detailed in Calm (1993) and Calm and Didion (1997). The only change herein is

recalculation with the refrigerant global warming potentials (GWPs) from the latest scientific assessment

(WMO, 1999). The updated GWPs for the four cited refrigerants, namely R-11, R-12, R-123, and R-134a, for

100-year integration were increased from 3800, 8100, 90, and 1300 relative to CO2 to 4600, 10600, 120, and

1600, respectively.

R-11 dominated in centrifugal chillers almost since its introduction. Refrigerant losses were high; they often

exceeded 15% of the total charge each year, as shown in figure 1 for 1985. Small efficiency gains appeared by

1990, but more significant gains were introduced in system tightening and improved purge technologies. Figure

1 shows the resultant drop in impacts from emissions. R-123 use also had begun, though the first machines –

essentially R-11 designs with materials changes for compatibility – yielded 14-16% lower efficiency. The direct

warming impact of R-123 emissions is barely visible, owing to the difference in GWPs, a decrease of more than

97%.

1985 1990 1992 1995 2000

comparative warming impact (%)

100

0

20

40

60

80

R-11 R-11 R123 R-11 R123 R-123 R-123 average average average average average average best available average best available

energy related

refrigerant emissions

Figure 1: Progression and projection for comparative warming impacts (relative

TEWIs) for centrifugal chillers for 1985-2000 with replacement of R-123 for R-11
8

Release reductions continued both by equipment tightening and improved service practices, as discussed above.

By 1992, the last year in which R-11 chillers were manufactured for domestic use in the United States, net

refrigerant emissions for machines of comparable capacities were half of those in 1985 and before.

These reductions offer several benefits beyond reduced global warming. They also lower the impact on ozone

depletion. The ozone depletion potential (ODP) and GWP of a chemical only are relevant for the portion that is

released. Refrigerant that does not escape, and is recovered for reuse or safe disposal, does not harm the

environment. Reduced losses also eliminate the need for makeup, thereby saving other resources and lowering

costs, improving safety, and avoiding performance losses from insufficient refrigerant charge.

Figure 1 also shows the dramatic improvements made by 1995 in R-123 chiller optimization, leading to higher

practical efficiency than available with the retired R-11 designs. This achievement, and subsequent further

gains, are all the more impressive since R-11 holds a small theoretical efficiency advantage over R-123 (Calm

and Didion, 1997).

Further improvements in performance followed and will continue, but the pace will slow as gains approach

theoretical limits. Coupled with emission reductions and the lower GWPs of R-22, R-123, and R-134a, the best

chillers in 1995 reduced net global warming impacts by approximately 45% compared to typical machines a

decade earlier. This fraction will exceed 48% by the year 2000 as shown in figure 1.

Figure 2 illustrates the comparative magnitudes of warming impacts from emission of refrigerants and use of

energy by water-cooled chillers. The efficiencies used in this example were the highest commercially available

in late 1996, as determined by an industry survey (ARI, 1996). The survey was restricted to equipment with

certified performance ratings, and the submissions were verified. Once again, the analyses are explained by

Calm and Didion (1997), but were updated herein with the new GWP data cited above (R-22 increased from

1500 to 1900 on a consistent basis).

As shown in figure 2, the direct effect of refrigerant emissions amounts to only 3-5% of the annual total for

chillers using R-22, which has the highest GWP of the three refrigerants shown. These fractions drop to

approximately 3% with R-134a and to less than 0.2% with R-123, which also offers the lowest energy-related

impact based on its efficiency.

From a comparative warming or TEWI perspective, phaseout of the HCFCs and HFCs provides only a small

gain in the refrigerant-related warming component for chillers with low refrigerant releases. There is far greater

opportunity in efficiency improvement. The same conclusion holds true for most other air-conditioning and

refrigeration products as well. Two exceptions are mobile air conditioners and supermarket refrigeration

systems. They have high loss rates, but their energy-related impacts still dominate over those from refrigerant

releases.

Table 2 summarizes efficiency limits in theoretical cycles for current and candidate refrigerants (Calm and

Didion, 1997). Theoretical efficiency limits alone do not govern practical efficiencies. Other properties, such as

viscosity and thus heat transfer coefficients, may have significant impacts on overall performance. Likewise,

cycle design impacts performance. Increased subcooling may reduce the efficiency distinctions for some emissions (kg CO2/kW yr) · emissions (lb CO2/ton yr) ·

0

100

200

0

500

1000

1500

R22 R123 R134a R22 R123 R134a

1230 kW (350 ton) 3500 kW (1000 ton)

refrigerant

emissions

energy

related

Figure 2: Greenhouse gas emissions (expressed as equivalent carbon dioxide) per unit of

cooling per year – TEWI – for the best available chillers in two representative capacities
9

refrigerants in simple cycles, as seen by examination of the data presented. Notwithstanding these cautions, the

performance data summarized in the table imply comparative limits to achievable performance.

As shown, neither ammonia nor the hydrocarbons match the efficiencies of the best fluorochemical options.

Such comparisons strongly suggest that the fluorochemical refrigerants be retained to reduce global warming,

until comparable or superior efficiencies can be demonstrated without them and without compromising occupant

safety. To avoid any misinterpretation, there are applications where ammonia and hydrocarbons offer

advantages, but nobody should infer that they are similarly attractive in all refrigerant uses. Ammonia already is

widely used in food and beverage processing and storage. One hydrocarbon option that holds promise, but

which is not frequently mentioned, is ethane (R-170) for use in ultra-low temperature systems with small charge

sizes. Ethane’s efficiency appears to be low in table 2 because chiller operating conditions are near its critical

point temperature. That is not the case for extremely-low temperatures, where high GWP fluids (primarily

CFCs, PFCs, and blends of them) are common. R-601 (n-pentane) and its isomers offer both high efficiency and

low-pressure operation at chiller conditions, but they are highly flammable and pose a considerable safety risk in

the quantities needed by large chillers.

Calm and Didion (1997) present a detailed analysis that shows that there are no ideal refrigerants. Such fluids

would offer zero ozone depletion, zero global warming, high efficiency, very low toxicity, and no flammability –

even without practical constraints such as cost, materials compatibility, and chemical and thermal stability. The

referenced paper also provides a rationale based on thermodynamics and chemical composition to suggest that

the elusive ideal refrigerant probably does not exist.

5 Necessary Refrigerant Compromises

Most first generation refrigerants (1830s-1930s, selected based on availability and thermal suitability) were

retired for safety reasons. Some, such as ammonia and hydrocarbons, survived or were later revived for limited

applications in which their risks were manageable, such as industrial or small-charge systems (see Calm and

Didion, 1997, for elaboration). Most second generation refrigerants (1930s-1990s, selected for safety, durability,

and performance) have been or are being retired to protect the stratospheric ozone layer. The criteria for third

generation refrigerants (“alternative refrigerants”) include both safety and environmental issues. Whereas the

first generation lasted approximately 100 years and the second approximately 60, care is needed in dismissing

options with minor defects if manageable. The third generation will be more vulnerable as the global population

increases, industrial and economic development expands, and environmental understanding increases. These

considerations demand greater attention to atmospheric lifetime to ensure that we not repeat the error made with

CFCs and halons, namely releasing large quantities of long-lived compounds before we discover their impacts.

Likewise, far more attention is needed to containment and recycling instead of phaseout.
10

Table 2: Comparative refrigerant efficiencies at standard chiller rating conditions

ideal cycle a,b typical conditions b,c

conditions (°C) (%) (°F) (°C) (%) (°F)

average evaporating temperature 6.7 44.0 5.0 41.0

superheat 0.0 0.0 1.0 1.8

average condensing temperature 29.4 85.0 35.0 95.0

subcooling d 0.0 0.0 5.0 9.0

isentropic compressor efficiency 100 80

motor efficency 100 95

control and other power use 0 0

COP specific power COP specific power

refrigerant (kW/kW) (kW/ton) (kW/kW) (kW/ton)

R-11 11.52 0.31 6.58 0.53

R-12 10.99 0.32 6.29 0.56

R-22 10.88 0.32 6.18 0.57

R-32 10.60 0.33 5.97 0.59

R-113 11.37 0.31 6.52 0.54

R-114 11.04 0.32 6.34 0.56

R-123 11.38 0.31 6.52 0.54

R-124 11.00 0.32 6.31 0.56

R-125 9.88 0.36 5.68 0.62

R-134a 10.89 0.32 6.24 0.56

R-141b 11.51 0.31 6.58 0.54

R-152a 11.13 0.32 6.34 0.56

R-170 (ethane) 6.58 0.54 e e

R-236fa 10.90 0.32 6.26 0.56

R-245ca 11.29 0.31 6.47 0.54

R-245fa 11.19 0.31 6.42 0.55

R-290 (propane) 10.73 0.33 6.14 0.57

R-410A 10.40 0.34 5.91 0.60

R-500 10.92 0.32 6.24 0.56

R-600 (n-butane) 11.19 0.31 6.42 0.55

R-600a (isobutane) 11.05 0.32 6.34 0.56

R-601 (n-pentane) 11.33 0.31 6.50 0.54

R-717 (ammonia) 11.17 0.31 6.24 0.56

R-1270 (propylene) 10.68 0.33 6.10 0.58

a Conditions are those for standard chiller ratings for water-cooled chillers (ARI, 1998). b Calculations were made with CYCLE_D 2.0 (Domanski et al., 1999) and R-601 data (McLinden, 1999) c Conditions approximate those typically encountered on the refrigerant side of water-cooled chillers. The

“typical” efficiencies shown can be exceeded by optimizing subcooling and superheat, employing multiple

stages, or using similar cycle modifications. Likewise, poor designs do not meet them. d Typical subcooling varies by refrigerant; the level shown is a representative selection for comparisons. e Condensing temperature exceeds the critical point; practical use requires major cycle modifications.

There is no common denominator to equate the demerits of ozone depletion and global warming. It is clear,

however, that a 13-19% increase in global warming to switch from R-123 to R-134a, at the best performance

levels, is more significant than a 0.002% or lower peak impact on ozone depletion (Wuebbles and Calm, 1997;

Calm, Wuebbles, and Jain, 1999). This comparison is more dramatic for newer data, namely increases of 14-

20% in carbon equivalent GHG emissions versus less than a 0.001% increase in peak CBL. The new

comparison employs efficiency improvements since 1996 and reduced refrigerant release rates, both of which are

evident in figure 1. It combines them with updated ODP values and new GWP data (WMO, 1999). Moreover,

four factors increase the importance of the comparison. First, correction is underway for ozone depletion

(Wuebbles and Calm, 1997; WMO, 1999). Second, ozone depletion will not be discernibly increased with a

reprieve for R-123 (Calm, Wuebbles, and Jain, 1999), which has an ODP of only 0.012 and atmospheric lifetime

of 1.4 yr (WMO, 1999). Third, recovery of the ozone layer will not be retarded with a reprieve for R-123

(Wuebbles and Calm, 1997; Calm, Wuebbles, and Jain, 1999). And fourth, the options to adequately address

global warming are far more limited, and a reprieve for R-123 is one of them (Calm and Didion, 1997; Calm,

Wuebbles, and Jain, 1999).
11

It is highly probable that HCFC-123 and possibly other short-lived CFC replacements would have survived

restrictions for stratospheric ozone protection had the global warming response occurred first. With keener

awareness of the more-limited options remaining (Wuebbles and Calm, 1997), the framers of the Montreal

Protocol might then have been more cautious in rejecting chemicals with indiscernible ozone impacts and

offsetting environmental benefits.

Likewise, phaseout of HFCs from chiller use for very small benefits in direct (refrigerant-related) warming

impacts at the expense of greater CO2 and N2O emissions will increase rather than decrease net warming.

The key distinction that makes most ACR applications, and especially chillers, unique from other HCFC, HFC,

and PFC uses is that the refrigerant is used in closed systems with very low life-cycle release rates. Most of the

refrigerant can be, and is being, recovered upon ultimate equipment retirement. A second difference, at least for

HCFC-123 and HFCs, is that abandoning these proven options would increase the GHG emissions from

associated energy use.

6 Conclusions

Historic releases of refrigerants from centrifugal chillers have been dramatically reduced from annualized

(amortizing initial and disposal losses) rates of 8-37 %/yr to less than – or significantly less than – 1 %/yr. The

refrigerant needs for make-up in old chillers far exceeded those for initial charging, amounting to more than ten

full charges over the operating life in the worst cases. By contrast, more than three-quarters of the original

charge can be recovered for re-use or safe disposal when current equipment reaches retirement; that fraction

exceeds 90% in the best systems. On average, the lifetime refrigerant needs for chillers have been reduced more

than tenfold.

Most of the technologies applied to achieve these loss reductions also can be applied in smaller ACR equipment.

The driving forces for the changes in large chillers was economics, including competitive marketing advantage,

and growing environmental awareness.

The importance of a refrigerant’s ODP or GWP diminishes with very low losses. For refrigerants with low ODP

and low GWP, the most damaging environmental effect from refrigerant losses is suboptimal operation resulting

in increased energy use and, thereby, increased emission of CO2 and other GHGs to power the system.

Suboptimal efficiency thus exacerbates climate change even with zero-GWP refrigerants.

Any refrigerant substitution that lowers overall efficiency is likely to have more adverse impact than benefit

based on net global warming impacts (e.g., life-cycle GHG emissions or TEWI).

Phaseout of R-123 – the most-widely used refrigerant in centrifugal chillers today – as an HCFC will increase

HFC use, and therefore HFC releases, but more importantly will significantly increase global warming with

lowered operating efficiencies for no discernible benefit in stratospheric ozone protection. An integrated

assessment of ozone protection, climate change, local environmental and safety issues, and the likelihood of

future environmental concerns suggests the need for distinction between short-lived, low-ODP chemical and

those with high ODPs, particularly in low-emission applications such as R-123 in chillers.

Whereas no ideal refrigerants exist, care is needed to not dismiss options with minor flaws without examination

of their net environmental advantages.
12

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