The latest F-gas legislation means you need to choose wisely when selecting refrigerants for individual applications, says Salim Deramchi
The new F-Gas legislation introduces more stringent requirements, such as limiting the amount of F-gases that can be sold in the EU, and banning the use of F-gases in some new equipment if better alternatives are available on the market.
The challenge for businesses is not only choosing the right refrigerant to reduce emissions, but also making the right choice to have a positive effect on operational efficiency, which reduces the operating cost.
Types of available refrigerant
Commercial organisations have traditionally been using a R12, CFC, R502, or CFC/HCFC blend. To enable the government targets to be achieved, most manufacturers have adopted either R404A, a HFC blend, or R134a.
But these are potent greenhouse gases. An alternative and one of the future solutions might be natural refrigerants.
- Isobutane (R600A) is a hydrocarbon, and hence is flammable. The thermodynamic properties are very similar to those of R134a. Isobutane presents other advantages, such as its compatibility with mineral oil and better energy efficiency and it’s cheaper than R134a. The use of isobutane requires minimal design changes, such as the relocation of potential ignition sources outside of the refrigerated compartment.
- Propane (R290) has a boiling point of -42 deg C, making it 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.
- Ammonia (R171) has its numerous drawbacks. It is toxic and flammable in concentrations between 15.5 per cent and 28 per cent in air. It is not compatible with copper, thus requiring other materials for construction. But Amonia’s thermodynamic and thermophysical properties also yield very efficient refrigeration systems.
- Carbon dioxide (CO2) is not a new refrigerant but was “rediscovered” in the early 1990s. Due to its low environmental impact, low toxicity and non-flammability, CO2 is now regaining popularity from refrigeration system designers while an alternative to fluorocarbons is being sought.
Selection criteria for refrigerants
There are five criteria you should take into account:
- Thermophysical properties;
- Technological issues;
- Economic aspects;
- Environmental factors.
Other considerations such as local regulations and standards, maintainability and capability; such as having staff with skills to support the units, application, and user training requirements should be taken into account.
The desirable characteristics of “ideal” refrigerants are considered to be as follows:
- Normal boiling point below 0 deg C;
- Easily detectable in case of leakage;
- Stable under operating conditions;
- Easy to recycle after use;
- Relatively large area for heat evaporation;
- Relatively inexpensive to produce;
- Low environmental impacts in case of accidental venting;
- Low gas flow rate per unit of cooling at compressor.
Suitability of refrigerants
Supermarket retailers are gradually moving away from long-established HFC refrigeration systems towards using a group of non-HFC natural refrigerants. Such installations often use ammonia, CO2 or hydrocarbons, which have comparatively little or no impact on global warming and zero impact on the ozonlayer.
One “quick fix” option for reducing the environmental impact of emissions from a retailer’s existing estate is to replace HFC-404A with a drop-in alternative such as HFC-407F (GWP 1,705) or HFC-407A (GWP 1,990).
While these blends still have a significant environmental impact, their GWPs are about half that of HFC-404A.
Due to its low environmental impact, CO2 (R744) is also gaining popularity from refrigeration system designers. The advantages are:
- Low toxicity;
- Zero ozone depletion potential;
- Very low global warming potential (GWP=1);
- Excellent thermodynamic properties and low energy requirements.
R744 refrigerant properties are surprisingly conducive to the cooling process. Despite the need for high pressure, the R744 agent is capable of running smoothly, efficiently, and with reduced waste as the heat waste can be rerouted and reused in other parts of the production process. In the case when CO2 is used for low temperature refrigeration, it is used either as a heat-conductor refrigerant, or in cascade with another refrigerant (R404A, NH3, R134a, etc.).
So, if one was to consider R744 as a refrigerant then the following must be taken into account:
High pressure CO2 circuits operate at much higher pressures than a conventional R404A system. This requires the use of components and assembly techniques that are unusual in the field of refrigeration.
Maintenance The operation mode requires a different design compared to conventional HFC systems design that is unfamiliar to most technicians in refrigeration for supermarkets.
Cost The high pressures require more binding materials and with R744 not yet widely used there is limited choice and a tendency to cost more.
It is now up to the designers and operators to specify something new to move the industry forward.
Salim Deramchi is senior building services consultant at BSRIA Sustainable Construction Group