Refrigeration and Global Warming
An Independent Review of the Role of HFC Refrigerants
by March Consulting Group
prepared for the European Fluorocarbon Technical Committee,
a Sector Group of CEFIC
September 1997
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Contents
SUMMARY...... 1
1. INTRODUCTION...... 1
PART A BACKGROUND TO REFRIGERATION AND REFRIGERANTS
2. REFRIGERATION APPLICATIONS...... 1
3. SELECTING REFRIGERANTS...... 1
PART B BACKGOUND TO GLOBAL WARMING ISSUES
4. THE IMPACT OF REFRIGERATION ON GLOBAL WARMING...... 1
5. INTERNATIONAL EFFORTS TO REDUCE GLOBAL WARMING IMPACT...... 1
PART C ANALYSIS OF GW IMPACT OF REFRIGERATION
6. OPPORTUNITIES TO REDUCE THE GW IMPACT OF REFRIGERATION...... 1
7. DIRECT EMISSION REDUCTION OPPORTUNITIES...... 1
8. ENERGY EFFICIENCY OPPORTUNITIES...... 1
9. SAFETY ISSUES...... 1
10. END USE SECTOR REVIEW...... 1
11. HISTORICAL AND FUTURE GLOBAL WARMING IMPACT...... 1
APPENDIX 1 GLOSSARY OF TERMS …………………………………………………...25
APPENDIX 2 REFERENCES ………………………………………………………………26
March Consulting Group1EFCTC/CEFIC
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SUMMARY
1.This report presents a review of alternative options for refrigerants and examines ways in which the future global warming impact of refrigeration can be minimised.
2.The report was prepared by March Consulting Group at the request of the European Fluorocarbon Technical Committee during August/September 1997.
3.There is excellent potential for the refrigeration and air-conditioning user sectors to make a very positive contribution to solving the major environmental problem of global warming. The following figures show the global warming impact of EU refrigeration and air-conditioning systems expressed in Mtonnes CO2 equivalent.
Direct Impact / Indirect Impact / Overall Impact1990 actual / 200 / 150 / 350
2010 forecast / 30 / 110 / 140
% reduction / 85% / 25% / 60%
4.This forecast reduction in the global warming impact of refrigeration can be achieved with widespread usage of HFC refrigerants.
5.The majority of other emitters of global warming gases are unable to make such a positive contribution. For example, the transport sector had EU global warming emissions of 220 GWP Mtonnes in 1990. However, it is estimated there will be an increase of 10% by 2010. This increase is because the growing number of vehicles and journeys outweighs improved energy efficiency.
6.There are three main refrigerant options currently available i.e. ammonia, hydrocarbons and HFCs. It is shown that each of these refrigerant options has a role to play in the future of refrigeration.
7.The various ways in which global warming emission reduction will be achieved are discussed. These include leakage and refrigerant charge reduction, improved energy efficiency and use of ammonia and hydrocarbons where appropriate.
8.HFC refrigerants are shown to be of vital importance for many refrigeration applications when safety considerations are taken into account.
9.When systems are properly designed to ensure low levels of refrigerant leakage and to maximise energy efficiency there is little or no difference between the global warming impact of ammonia, hydrocarbon or HFC systems. All can achieve considerable reductions in GW emissions when compared to the 1990 baseline.
10.Comparisons made in this report are based on the ‘real’ situation in 1990, when significant CFC and HCFC emissions were being made. Many publications ignore emissions of ozone depleting substances and hence give a false picture when comparing future emissions to the 1990 baseline.
1.INTRODUCTION
Users of refrigeration are facing new choices with regard to selection of refrigerants because CFC and HCFC refrigerants are being phased out to protect the ozone layer. There is considerable confusion and controversy regarding the best choices, particularly when the environmental issue of global warming is taken into account. This report is intended to provide a balanced review of competing options in order to help users, designers and policy makers fully understand their relative benefits.
A key theme within this report is to examine the role of HFC refrigerants as alternatives. There is mounting pressure against these fluids from some environmental groups because it is claimed that refrigeration systems using HFCs have an excessive global warming impact. Is this pressure fair and how do HFCs compare to other options (and the CFC systems they are replacing)? Key factors that influence the global warming impact of refrigeration are discussed in order to identify the appropriate refrigerant for use in different applications.
The choice between competing refrigerants has always been complex. Nevertheless, there used to be fairly clear divisions between different types of refrigerant. CFCs and HCFCs were the refrigerant of choice for the vast majority of small and medium sized refrigeration systems (and many large ones). This was because of their excellent safety characteristics (non-toxic and non-flammable) and good materials compatibility (allowing use of copper components). Ammonia, a traditional refrigerant used for over 100 years, maintained a significant niche market in large industrial systems, particularly in the food and drink manufacturing industry and cold storage. Hydrocarbons were also used, but their market was restricted, mainly to large systems in certain petrochemical companies who were handling these highly flammable fluids within their manufacturing process.
What are the options for the future? Well over 95% of refrigeration applications use vapour compression refrigeration. Whilst other options such as absorption refrigeration and air cycle systems have a small market potential it is unlikely that there will be a significant move away from vapour compression cycles during the next 20 years. Hence, this document restricts itself to the options for vapour compression systems.
Currently, there are four main options that an end user can consider: HFCs, hydrocarbons (HCs), ammonia and elimination of the need for refrigeration. There are advantages and disadvantages for each. Some of the key issues include safety, cost (first cost and operating cost) and global warming impact. This report reviews refrigerant options and provides a logical and balanced framework to help users select the best one for them. Our general belief is that all four options are applicable in certain circumstances. The key issue is to identify what these circumstances are.
The report has been written to be of broad interest, both to those with relatively little refrigeration knowledge and to those with an in depth understanding of design issues. Hence, some background material is included early in the report followed by more detailed analysis. The document is split into three main parts. Part A, provides background to refrigeration and refrigerants. Part B gives background to global warming. Finally Part C analyses the global warming impact of refrigeration.
2. refrigeration APPLICATIONS
To properly understand the difficulties facing refrigeration systems designers it is important to be aware of the enormous range of applications. Refrigeration represents one of the most important energy-using utilities in all sectors of human activity: domestic, commercial and industrial. People often find it surprising that refrigeration and air-conditioning systems represent approximately 15% of EU electricity demand (Source - EEBPP 1). This makes it one of the largest definable electricity using groups (larger than, for example, lighting).
Refrigeration applications range enormously in size and temperature level. A domestic refrigerator has a cooling load of a few hundred watts whereas large industrial systems can have loads in excess of 10 MW. Small systems contain less than 100g of refrigerant whereas large ones can contain many tonnes. Temperatures range from specialist cryogenic applications (below -150oC), through a wide variety of industrial and food chain requirements between -40oC and 10oC, to air-conditioning and heat pump applications at temperatures of 20oC and above. Some refrigeration systems can be operated in restricted locations where only trained personnel are present. Other systems, such as those for supermarkets and building air-conditioning, operate where there are numerous untrained members of the public. All these variations lead to widely differing refrigeration system designs. Because of the wide variety of circumstances in which refrigeration is used, there is no single refrigerant that suits all applications; there is a need for various refrigerants with different properties.
The main requirements for refrigeration systems fall into four distinct groups:
- The food and drink chain, including agricultural, manufacturing, storage, transport, retailing and domestic requirements.
- Other industrial processes, including applications in sectors such as chemicals, pharmaceuticals and electronics.
- Comfort conditioning, including domestic, commercial and industrial buildings
- Mobile air-conditioning in cars and other vehicles.
In this short report we cannot give an adequate description of the full variety of applications and designs. However, it is worth noting that most very small systems (such as domestic refrigerators and small commercial units like icemakers, small retail displays etc) are based on hermetic designs. These are factory built units using only welded or brazed joints. They contain very small refrigerant charges and suffer very little from leakage. Larger systems usually require some or all of construction to be carried out on site and there are numerous pipe joints and seals required. Refrigerant charge is much higher and the chance of refrigerant leakage is significant.
It is also useful to distinguish between ‘Distributed Systems’ that circulate the refrigerant itself to cool a building or a process and ‘Secondary Refrigerant Systems’ that incorporate a secondary fluid to transmit cooling to the user (often water or an ‘anti-freeze’ solution). Secondary refrigerant systems have the advantages that they can reduce the quantity of primary refrigerant required and allow it to be contained within a limited physical area such as a plant room. This considerably limits the potential for leakage and eases safety problems if flammable or toxic refrigerants are used. However, there will usually be an energy penalty, because of the need to pump the secondary refrigerant and to account for the extra temperature difference between the primary and secondary circuits.
One can attempt to quantify the size of the refrigeration market in a number of different ways including number of systems, quantity of refrigerant used and energy consumption. The following estimates are based on References EC DGIII, UK DoE 1, UK DoE 2 and March Consulting Group estimates.
In terms of number of systems the domestic sector is totally dominant, with some 200 million systems in use in the EU. This compares with about 30 million small systems for retailing and air-conditioning and about 2 million larger systems for supermarkets, large buildings and industrial applications. However, if we analyse the quantity of refrigerant contained within all these systems or the annual energy consumption a quite different picture will be obtained. In terms of refrigerant quantities the supermarket, industrial and air-conditioning sectors become the most important, with domestic systems being the 4th largest segment. Figure 1 gives an approximate breakdown of the EU refrigerant bank in terms of end use sectors.
The various fluorocarbons including CFCs, HCFCs (and more recently HFCs) represent in the region of 80 to 85% of the total EU refrigerant bank. Ammonia represents a further 10 to 15%. Hydrocarbons have historically represented a very small proportion of the total bank, probably in the region of 1 to 2%. Recent growth in the market for hydrocarbons in the domestic and small refrigeration field will have caused this to grow but the total is currently less than 3% of the EU bank.
3.selecting refrigerants
As already discussed the process of refrigerant selection is quite complex. This is because there are a significant number of parameters that need to be assessed and few available fluids ‘score well’ on all of them. The key parameters include the following:
Thermodynamic performance - for the required evaporating and condensing temperature levels the fluid should be able to provide energy efficient performance (i.e. a high coefficient of performance or COP).
Appropriate operating pressures - the evaporating pressure should not be too low and the condensing pressure should not be too high (under the relevant operating temperatures). Ideally the evaporating pressure should be higher than atmospheric pressure and condenser pressure should be below around 20 bar(g).
Compressor size - the thermophysical properties for the fluid should result in as small a compressor as possible
Toxicity - the fluid should be of zero or low toxicity
Flammability - the fluid should be non-flammable and non-explosive.
Materials compatibility - the fluid should be compatible with various materials used in the construction of a refrigeration plant (e.g. pipes, vessels, gaskets, seals etc).
Oil compatibility - the fluid should perform well with available lubricating oils.
Stability - the fluid should remain stable throughout many years of operation and must not chemically react with system components, lubricating oil and contaminants.
Cost - the fluid should have reasonable cost.
Ozone Depletion Potential - the fluid should have a zero ODP.
Global Warming Potential - the fluid should have a zero or low GWP.
Prior to the Montreal Protocol, CFCs and HCFCs were the obvious choice for many applications. Whilst they were not the cheapest refrigerants to buy (e.g. ammonia was less than 25% of the price of CFCs) they led to plants with minimum ‘total ownership cost’. They had good materials compatibility and it was easy to deal with safety issues. CFCs can no longer be selected because of their high ODP. In the future we should only consider zero ODP fluids and we also need to ensure minimum global warming impact. In simplistic terms this may seem to suggest fluids with zero or low GWP are best. However, as we shall see later in this report, the use of a fluid with a higher intrinsic GWP does not necessarily lead to the highest overall global warming impact.
Bearing in mind the list of issues described on the previous page it is useful to examine the advantages and disadvantages of the four main refrigerant options listed in the introduction.
Ammonia
Ammonia is a refrigerant that has been used since the very earliest days of vapour compression refrigeration. It has good thermodynamic properties for systems operating with evaporating temperatures above about -50oC and with condensing temperatures below about +40oC. Ammonia is not an appropriate refrigerant for very low temperature applications (below –50oC). Ammonia has good compatibility with mineral lubricating oils and excellent stability over long system lifetimes. It is one of the cheapest available refrigerants in terms of cost per kilogram. The environmental properties are excellent, as the fluid has zero ODP and zero GWP.
The main drawbacks of ammonia are toxicity, flammability and materials compatibility. The fluid is highly toxic and causes severe risk to humans when significant leakage occurs. The dangers are particularly significant if untrained personnel are involved, as the noxious fumes can create panic. Ammonia is flammable in certain concentrations, although it is actually relatively hard for a fire or explosion to occur. On the more practical side ammonia is incompatible with copper which restricts the materials that can be used for plant construction. All copper and brass components must be avoided and ammonia systems are constructed mainly with steel components. For small plants this can add significantly to the cost.
HFCs
HFCs also have good thermodynamic properties and the added advantage over ammonia that they are a family of fluids with different operating pressures. Hence, HFCs can be used across a wider range of application temperatures and can be more carefully selected to optimise system efficiency. Most HFCs have very low toxicity and zero flammability and they have excellent materials compatibility. Hence they do not suffer some of the drawbacks of ammonia.
On the negative side HFCs have a significant GWP; if they are to be responsibly used it is essential that emissions should be minimal. They are relatively expensive fluids although this usually is only an issue in large refrigeration systems. They are not compatible with conventional mineral lubricating oils and it has been necessary for new synthetic oils to be developed for HFC refrigeration systems. This development has been successfully completed.
Hydrocarbons
As with ammonia and HFCs, hydrocarbons have good thermodynamic properties and as they form a family of fluids, there can be good selection over a relatively wide range of application temperatures. Hydrocarbon refrigerants have low toxicity and good materials compatibility. They also have good environmental properties with zero ODP and very low GWP.
The key drawback to HCs is their very high flammability. Any significant leakage could lead to a fire or an explosion. For this reason, hydrocarbons have historically been restricted to use in petrochemical facilities that are handling these flammable fluids as part of the main manufacturing process. More widespread application requires very careful attention to flammability safety issues.
Elimination of refrigeration
This fourth option is always worth considering when developing plans for a new refrigeration plant. If refrigeration can be eliminated there are obvious and significant environmental benefits. No refrigerant fluid is used so the GWP is irrelevant. More importantly, no energy is used hence there may be a significant reduction in the overall global warming impact. There are numerous examples of elimination of refrigeration, ranging from use of ambient free cooling, to reductions in load from better process integration to completely new approaches to processing (e.g. use of irradiated food instead of refrigerated food).