The selection criteria of refrigerants

Salim Deramchi, Senior Building Services Engineer at BSRIA

Salim Deramchi, Senior Building Services Engineer at BSRIA

This is part two of a three part series from Salim. You can read part 1 here

There is no general rule governing the selection of refrigerants, however there are of course the five classic criteria and those are:

  • thermophysical properties
  • technological
  • economic aspects
  • safety
  • environmental factors

However, in addition to these criteria, others have to be considered such as local regulations and standards as well as maintainability and ‘cultural’ criteria associated with skills to support the units, application, and user training requirements.

The best approach when presenting evolution and trends is certainly the per-application approach. The desirable characteristics of “ideal” refrigerants are considered to be:

  1. Normal boiling point below 0°C
  2. Non-flammable
  3. Non-toxic
  4. Easily detectable in case of leakage
  5. Stable under operating conditions
  6. Easy to recycle after use
  7. Relatively large area for heat evaporation
  8. Relatively inexpensive to produce
  9. Low environmental impacts in case of accidental venting
  10. Low gas flow rate per unit of cooling at compressor

The choice of alternative refrigerants should involve a review of recycling or disposal of refrigerants. You must decide which criteria for the ideal refrigerant is of most importance to your organisation. It must be considered that the operation phase is the key factor when determining the environmental impact of the various refrigerants as there is less impact to the environment in the production and disposal stages. As an example, supermarket retailers are steadily moving away from long-established HFC refrigeration systems.

Decision making for new refrigeration plant using refrigerant alternatives such as ammonia, CO2 or hydrocarbons, which have comparatively little or no impact on global warming and zero impact on ozone layer, should consider not only the impact on the environment but the additional required skills to maintain (Ko Matsunaga).

You can  find out more information in BSRIA’s library

Refrigeration Part 1 – Choosing the right refrigerant

Salim Deramchi, Senior Building Services Engineer at BSRIA

Salim Deramchi, Senior Building Services Engineer at BSRIA

Refrigerants are a key component for air conditioning and refrigeration. Since the 19th century there have been many refrigerants developed and used but none of them has as yet become the industry standard.

As an industry we should not consider reducing F-Gas emissions as just complying with legislation to meet government set targets, but reducing them will also have a positive effect on operating costs.  We can make cost savings through efficient operation and we can also help enhance market reputation by being more environmentally friendly.

To have a good understanding of this we need to look at:

  • Available refrigerant types
  • Our selection criteria
  • How we evaluate the available refrigerants

Traditionally commercial businesses have been using R12, a CFC, and R502a CFC/HCFC. In addressing the ozone depletion problem, most manufacturers have adopted either R404A a HFC blend or R134a. However, both are potent greenhouse gases (Nicholas Cox).

So the industry needs to look at future solutions which might be natural refrigerants, although some design change might be required on the equipment used. The following refrigerant replacements all require system and operational changes to current practice:

20140213_132647_resizedIsobutane (R600A) is a hydrocarbon , and hence is flammable. The thermodynamic properties that are very similar to those of R134a. Isobutane presents other advantages, such as its compatibility with mineral oil and better energy efficiency and cheaper than that of R134a. The use of isobutane requires minimal design changes, such as the relocation of potential ignition sources outside of the refrigerated compartment. Operational changes will also be required.

Propoane (R290). With a boiling point of -42C, propane is an excellent alternative to R22 as it requires similar working pressures. An added advantage is that except for added safety measures because of its flammability, virtually no design change is required in systems when switching from R22 to propane. The combination of its good thermodynamic and thermophysical properties yields systems that are at least as energy efficient as those working with R22. The use of propane is increasing in countries where regulations allow it.

Ammonia (R171). Ammonia has been continuously used throughout modern refrigeration history. Despite its numerous drawbacks, it is toxic and flammable in concentrations between 15.5% and 28% in air. It is not compatible with copper, thus requiring other materials of construction. Its thermodynamic and thermophysical properties also yield very efficient refrigeration systems. Because of its acute toxicity, stringent regulations apply for ammonia systems, which require close monitoring and highly skilled engineers and technicians.

20140213_132339_resizedCarbon dioxide (CO2) is not a new refrigerant. Rather, it was ‘rediscovered’ in the early 90’s. The use of carbon dioxide as a refrigerant has gone back well over a century. Its application was abandoned in the mid-50s, with the widespread use of the CFC refrigerants, which were more efficient, more stable and safer. Due to its low environmental impact, low toxicity and non-flammability, CO2 is now regaining popularity from refrigeration system designers when an alternative to fluorocarbons is being sought. (Ahmed Bensafi and Bernard Thonon)

So there are alternatives on the market and technology development is tackling this issue it is now up to the designers and operators to specify something new to move the industry forward. With F-Gas regulation 2 coming we need to get ahead of the game.

We have tried to cover some of the available refrigerants seen in the market and we will be evaluating and discussing the selection criteria in our future blogs.

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