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Cool chiller choices

As green building solutions hit the top of the construction agenda, Mike Thompson explains how the choice of chiller refrigerant can play a large part in meeting regulations.

INTERVIEWS, MEP

As green building solutions hit the top of the construction agenda, Mike Thompson explains how the choice of chiller refrigerant can play a large part in meeting regulations.

Throughout the history of the heating, ventilation and air conditioning (hvac) industry, many different refrigerants have been used. When technology was first developed, the primary focus was getting equipment to work effectively.

In the 1940's, the focus began to shift to safety and it was at this time that chlorofluorocarbons (CFCs) were developed as safe alternatives to many of the dangerous chemicals that had previously been used.

Environmental regulations

In the 1970's, however, it was discovered that CFCs were contributing to the depletion of the ozone layer. Concern over this issue resulted in the international agreement the Montreal Protocol, which set out to eliminate the use of ozone depleting substances, with CFCs being one of the primary targets.

The industry began to develop alternatives and the newer classification of chemicals known as hydro-chlorofluorocarbons (HCFCs) and hydro-fluorocarbons (HFCs) were born.

While HCFCs also have some impact on the ozone layer, this is negligible by comparison. HFCs have almost zero impact on the ozone layer, and began to be thought of in many cases as the perfect solution for many hvac applications.

In 1992, HCFCs were added to the Montreal Protocol and phase-out dates were established. As the ozone impact of HCFCs is far less than that of CFCs, the phase-out dates were set at 30 or more years later than for CFCs.

The Protocol also classified countries into Developed (Article 2) and Developing (Article 5) based on their annual per capita consumption of CFCs. Developed countries, with an annual consumption of more than 0.3kg per capita, were required to cease production and phase-out consumption of CFCs from 1 January 1996 and 2030 for HCFCs.

Developing countries, with an annual consumption of less than 0.3kg per were granted a ten-year grace period to comply with the phase-out targets in an orderly and economical way (2010 for CFCs and 2040 for HCFCs).

Environmental concerns did not stop with the ozone depletion issue.

A growing unease in the scientific community that many of the chemicals used in the hvac industry were contributing to global warming led to the formation of The Kyoto Protocol. Signed into force in 2005, this was specifically developed to address the issue of global warming and began to mandate for reductions in global warming gases, including HFCs.

Today there is no phase-out of HFCs by the Kyoto Protocol, but they are mentioned as one of the chemicals that should be controlled.

An additional significant impact to global warming from hvac equipment is energy efficiency. As hvac plant consumes significant power, the efficiency that a refrigerant can deliver is now a significant environmental consideration.

As the issue of global warming has gained prominence, the industry has realised that some refrigerants that were due for phase-out under the Montreal Protocol have significant environmental benefits with regards to global warming. Scientists are is now starting to question some of the earlier phase-out choices made as a single determining factor for phasing-out refrigerants (ozone depletion potential) was used.

Current guidelines

Given the latest scientific evidence, what should the industry be looking at when determining what refrigerants to use? Publications from the Refrigeration, Air Conditioning, Technical Options Committee (RTOC) formed by the United Nations Environmental Programme (UNEP) provide guidelines. The RTOC is the technical reference used by the Montreal Protocol, however it has now suggested revised guidelines for the evaluation of refrigerants for use in hvac applications. These include:

• Zero or low ozone depletion potential (ODP);

• Zero or low global warming potential (GWP);

• High energy efficiency;

• Short atmospheric life;

• Minimal leakage rates.

When the most common refrigerants in use today are compared with these five criteria, it becomes obvious that among the HCFCs and HFCs there are no clear winners, although some HCFCs are superior to the HFCs in terms of global warming, energy efficiency and leakage rates.

It has been suggested that the Montreal Protocol should revisit the phase-out of those HCFCs that have minimal impact on the ozone layer but offer significant benefits for global warming.

Lower pressure refrigerants such as HCFC-123 and HFC-245fa also offer environmental benefits as they remain liquid at room temperature and pressure. Liquid refrigerants are inherently easier to keep contained inside chillers and are therefore safer.

A refrigerant that remains liquid at room temperature is very difficult to accumulate in any concentration in a plantroom and the risk of asphyxiation - the biggest safety risk of any refrigerant - is almost zero.

Today, because of the higher global warming potential of some HFCs, several markets are beginning to regulate their use. This is a dramatic turnaround for a chemical that was once considered the perfect environmental alternative.

Elements of the scientific community have suggested that the use of hydrocarbons and other natural refrigerants offer promise for replacing fluorocarbons. To date, fluorocarbons have proven to be the superior technical and environmental choice for hvac applications due to their energy efficiency and safety benefits.

Natural refrigerants have been used in some applications, the most notable of these being ammonia. This has proven to be a high energy performer in many refrigeration applications, but is inferior to fluorocarbons for hvac applications.

Hydrocarbons are in use in some small-charge applications, but for applications utilising large volume of refrigerants the hydrocarbons cannot compete on either energy efficiency or safety.

The future of refrigerants

In today's hvac industry, many are concerned about the future availability of refrigerants that are currently scheduled for phase-out. Will the those that are currently in use be available in the future?

The history of refrigerant phase-outs tells us that concerns for the future availability of refrigerants are grossly overstated. In developed countries, the phase-out of CFCs occurred in 1996, so we now have the benefit of eleven years of history; when we look at the availability of the most common refrigerants, the answers should give great comfort in respect of slated phase-out dates for HCFCs.

• CFC-11 is a low-pressure refrigerant that is used for large tonnage centrifugal chillers and was replaced by HCFC-123. Due to its low operating pressure, the refrigerant has a very low leakage potential and therefore, low demand for replacement refrigerant. Eleven years after its phase-out, it is readily available and even cheaper than it was when it was phased out in 1996.

• CFC-12 is a medium-pressure refrigerant that is used for large tonnage centrifugal chillers and automotive air conditioners. The price of CFC-12 initially spiked to a high after its 1996 phase-out, this was primarily due to its automotive application, which is known for high leakage rates. Today, eleven years after its phase-out, the price of this refrigerant is dropping as most automobiles that used CFC-12 are no longer in operation.

Middle East concerns

In order to comply with the Montreal Protocol, in the GCC countries the phase-out of CFCs will be implemented from 1 January 2010. After this date it will be prohibited to import equipment containing CFC or virgin CFC refrigerant for service purpose. However, existing equipment reliant on CFCs can be used after 2010 and serviced using recovered or recycled refrigerant.

Today, based on Air Conditioning and Refrigeration Institute (ARI) shipment statistics, many of the centrifugal chillers sold use HCFC-123 as the refrigerant of choice. The current phase-out for HCFCs in developed countries is from 2030; in developing countries it is from 2040, with a cut-off date of 2030 for new equipment.

The prospects for the future availability of HCFC-123 after the 2030 and 2040 phase-outs look very strong. Drawing on the history of CFC-11, the outlook for HCFC-123 looks even better due to a number of reasons, including:

  • ÃLike CFC-11, HCFC-123 is a low-pressure refrigerant and has a very low leakage tendency;
  • compared to CFC-11 chillers, HCFC-123 chillers leak far less. The technology improvements in leak detection and joint design over the past decade have led to a leakage rate much lower than those CFC-11 units maintained in the past;
  • Low-pressure chillers require a refrigerant purge. In the unlikely event of a leak occuring, low-pressure chillers leak air in, rather than refrigerant out. A purge detects air in a chiller and quickly removes it from the system, this acts as a leak-detection device and can detect even very minor leaks before any refrigerant is lost;
  •  The recovery practices of today will be even better in the future, this means even less refrigerant loss due to accidents;
  •  The Montreal Protocol allows for the unrestricted continued use of recycled, recovered and stockpiled supplies of refrigerant after the published phase-out dates, plus the importation of these recycled and recovered supplies;
  •  the phase-out of HCFCs generally include an initial ban on the production of equipment that uses the refrigerants, with an additional service-tail of ten years to cater for existing plant; the phase-out of CFCs had no service-tail period.

Mike Thompson is director of environmental affairs with Trane Commercial Systems.

Refrigerant phase-out in brief

  •  Phase-out doesn't mean no longer available or banned.
 
  • In simple terms, phase-out means that a regulated refrigerant may not be supplied in newly manufactured equipment or as a virgin gas.
 
  • Existing equipment may continue to operate indefinitely with a regulated refrigerant.
 
  •  Recycled refrigerants may be used to service equipment indefinitely.
 
  •  Regulated refrigerants can continue to be manufactured if they are used as an ingredient in other products eg HCFC-22 is used to make fluoro-polymers for non-stick cooking utensils.

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