Refrigeration, air conditioning and heat pumps

Refrigeration, air conditioning and heat pumps

1. General remarks

The economic impact of refrigeration technology is much more significant than generally believed; 300 million tonnes of goods are continuously refrigerated. While the yearly consumption of electricity may be huge, and where the investment in machinery and equipment may approach US$100,000 million, the value of the products treated by refrigeration either alone will be four times this amount. This is one of the reasons that economic impacts of the phase-out of refrigerant chemicals (such as CFCs in the past, and HCFCs in Article 5 countries in the foreseeable future) have been and still are difficult to estimate.

Refrigeration and air conditioning applications vary enormously in size and temperature level. A domestic refrigerator has an electrical input between 50-250 W and contains less than 30-150 g of refrigerant (dependent on the type of refrigerant), whereas industrial refrigeration and cold storage is characterised by temperatures between -10 C and -40 C, with electrical inputs up to several MW and refrigerant contents of many hundred kilograms. Air conditioning and heat pumps may show evaporation temperatures between 0 C and +10 C, significantly different from refrigeration applications, and vary enormously in size and input.

In principle one can therefore discriminate between four main areas which each have subsectors: (i) the food chain in all its aspects, from cold storage via transport to domestic refrigeration, (ii) process air conditioning and refrigeration, (iii) comfort air conditioning, from air cooled equipment to water chillers, including heat pumps, and (iv) mobile air conditioning, with very specific, different aspects. This is one of the reasons that all the equipment is considered in this report in a large number of separate chapters or sections.

Options and aspects for the refrigeration vapour compression cycle deserve most attention, since it is unlikely that during the next 10-20 years other principles will take over a substantial part of the market. In all application sectors described in the separate chapters in this report, most of the attention is focused on the vapour compression cycle. As stated, this cycle has so far provided the simplest (?), economic, efficient and reliable way for refrigeration (this includes cycles using ammonia, fluorochemicals and hydrocarbons as refrigerants).

The process of selecting a refrigerant for the vapour compression cycle is rather complex, since a large number of parameters need to be investigated concerning their suitability for certain designs, including:

- thermodynamic and transport properties;

- temperature ranges

- pressure ratios

- compressor requirements;

- material and oil compatibility;

- health, safety and flammability aspects;

- environmental parameters such as ODP, GWP and atmospheric lifetime.

These selection criteria were elaborated upon in various chapters of various UNEP RTOC Assessment Reports, and these selection criteria have not changed during the last years. Since then, it is the emphasis on the emissions of greenhouse gases that has increased; this can be directly translated to thermodynamic efficiency and quality of the equipment (leakage of refrigerant).

The future of mankind, and his food supply in particular, depends on the availability of sufficient energy and on the availability of efficient refrigeration methods. Of course, this aspect must be more than balanced by a concern for the conservation of the biosphere, including in particular the global warming effect. Energy efficiency, therefore, is one of the most important aspects.

2. Long term options and energy efficiency

It should be noted, however, that the changing refrigerant options are only part of the driving force for innovations in refrigeration and A/C equipment. Innovation is an ongoing independent process, which has to take into account all the environmental issues involved.

In the long term, the role of non-vapour compression methods such as absorption, adsorption, Stirling and air cycles etc. may become more important; however, vapour compression cycles are thought to remain the most important candidates.

For the long term, there remain, in fact, only five important different refrigerant options for the vapour compression cycle in all refrigeration and A/C sectors, listed alphabetically:

• 
  ammonia (R-717);
  
• 
  carbon dioxide (R-744);
  
• 
  hydrocarbons and blends (HCs, e.g. HC-290, HC-600a, HC-1270 etc.);
  
• 
  hydrofluorocarbons (unsaturated HFCs (HFOs) with a four digit number, HFC-blends with 400 and 500 number)
  
• 
  water (R-718).
  

Similarly, energy efficiency research is partly spurred by the role of energy production in carbon dioxide emissions. Options for energy efficient operation of equipment form an important issue in each of the chapters of this 2014 RTOC Assessment report.

2. Set up of the 2014 RTOC Refrigeration, A/C and Heat Pumps Assessment Report

Chapters 3, 4, 5 and 6 deal with the food chain and investigate the technical feasibility of options. They all consider non-ODP options and deal with aspects such as the use of non-fluorochemicals, the reduction of charges, energy efficiency improvements etc. Particularly the energy efficiency aspect plays an important role in chapter 3 on domestic refrigeration. Chapter 4 discusses the options for the 3 types of commercial refrigeration equipment. Chapter 5 deals with industrial refrigeration and cold storage, chapter 6 with transport refrigeration. Chapters 7 and 8 deal with air conditioning and heat pumps. Chapter 9 deals with the various aspects of chillers, which includes important considerations on energy efficiency. Chapter 10 describes the options for mobile air conditioning; in a first instance, it deals extensively with HFC-134a, but it also evaluates the potential the options carbon dioxide, hydrocarbons, the unsaturated HFCs (i.e., HFC (HFO)-1234yf) and other options will have. Chapter 11 deals with sustainability issues in refrigeration.

All chapters have drafted an executive summary; these summaries were put together and are presented in the first part of the report. The executive summaries are preceded by a shortened (“abstract”) executive summary (e.g. for policy makers) which has been abstracted from the separate executive summaries. This is again preceded by key messages derived from the abstract executive summaries.

Chapter 2

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Daniel Colbourne

Asbjørn Vonsild