Preserving Food, And The Planet

From fridges and freezers to air conditioning systems and heat pumps, scientific breakthroughs in cooling technology have changed the way we live. But progress has come at a cost. It wasn’t until the 1980s that scientists discovered that CFCs, once thought the ideal refrigerants, were depleting the ozone layer. A few years later, their popular successor, fluorocarbons, were also found to have ‘global warming potential’ (GWP). The search is still on to find more environmentally friendly alternatives.

There are very few refrigerants that have a low enough GWP to comply with global regulatory changes due to come in from January 2019. The clear long-term frontrunner is carbon dioxide. But there is one major issue with the use of this gas: to work as a refrigerant, it has to operate at very high pressures. Such high pressures mean fail-safe pipe connection systems and leak prevention are critical. This is where SANHA’s range of Ref HP high pressure fittings and tubes comes into its own. Designed to withstand operating pressures of up to 130 bar and temperatures up to 150°C, you can rest assured that you are using the best-quality pipe connection systems available. 

The science of refrigeration 

From the primitive burying of foods in cool ground, to 17th Century subterranean ice houses, keeping food cool has long been a method of its preservation. Perhaps surprisingly, it is only relatively recently that this passive approach to preservation has been overtaken by scientific breakthroughs, allowing cooling technology to exist within the home and workplace in the form of fridges and freezers, air conditioning systems and, more recently, heat pumps. 

Advances in the understanding of the physics of phase changes have been transformational. It was observed that while an ice cube melts in a warm environment, i.e. changing phase from a solid to a liquid, the water surrounding the ice remains a constant temperature until all the ice has melted. This may seem a simple observation, but its application has changed the way we live. 

Crucially, if a liquid changes phase from a liquid to a gas, the same phenomenon occurs. So the liquid is absorbing energy from its surrounding environment, while its molecules change phase. In doing so it cools down its environment until such point as all the material has evaporated, or the temperature of the liquid and the gas are the same temperature.  This is called the ‘energy of vaporisation’. It can be easily demonstrated by pouring a volatile liquid, such nail varnish remover (acetone) onto the back of your hand, and feeling your skin cool.

Refrigeration technology is the industrialisation of this physical effect; it is the containment and controlling of this process that allows us to cool spaces. Refrigeration requires a liquid at room temperature, which will easily evaporate, and during this change absorb a significant amount of energy. In practice, many gases will liquefy at room temperature under enough pressure. 

Choosing the best refrigerant

Very early refrigerators used carbon dioxide as a refrigerant, as this was easily available. But due to the high pressures required to liquefy it, it was very costly, both in terms of energy and also in the design of the robust machinery needed for the process.

With the evolution of organic chemistry, many new chemicals were developed to optimise the temperature and pressure at which phase changes could be harnessed. These chemicals were typically chlorofluorocarbons, or CFCs. They were cheap to produce, operated at much lower pressures, and were thought ideal for domestic applications.

It was not until the 1980s that it was discovered that these chemicals, when released into the Earth’s atmosphere, had a significant detrimental effect on the ozone layer. Ozone is not only a greenhouse gas that keeps heat in, but also an ultraviolet filter that keeps harmful radiation out. Because of this, the preservation of the ozone layer is vital to the Earth’s bio-existence. 

The search for an environmentally friendly refrigerant

It was then found that fluorocarbons were ‘non-ozone depleting’, and these became the principal refrigerant of choice. However, as the debate on global warming gained traction, it was found that some refrigerants, while non-ozone depleting, did have significant ‘Global Warming Potential’ (GWP). The effect of their build up in the atmosphere was to insulate the Earth, potentially causing surface temperatures to rise. Many of these gases have significant life spans exceeding 10 years, so there was and is a cumulative build up in concentration.

The effect of these gases is measured in comparison to the global warming impact of carbon dioxide. So, for example, carbon dioxide has a GWP of 1, methane of 25 and tetrofluorocarbon (HFC) of 1300.

The global community has recognised the seriousness of global warming and has now set up initiatives to reduce this risk, including regulations aimed at reducing the use of refrigerants with a high GWP. The latest of these is the EU F-Gas Regulation (517/2014), which came into force in January 2015. This regulation limits the total amount of F-gases (fluorinated gases) which can be sold, and phases them down each year until 2030. It bans the use of F-gases in new equipment where better alternatives are already available, and also requires the servicing of equipment to prevent leaks. 

A recent global agreement has been reached on the use of hydrofluorocarbons, which takes effect from January 2019, and is believed to be the single most important step in reducing global warming. So the search is on for a refrigerant which is non-toxic, non-flammable, isn’t ozone depleting and has a low GWP. There are very few refrigerants which meet all these requirements: currently hydrocarbons, ammonia, hydrofluoroolefins and carbon dioxide are the most prevalent solutions, each with their own shortcomings, but all share the properties of being refrigerants with a low GWP, typically less than 10.

Facilitating the use of carbon dioxide

The long-term impact of this regulation will be the substantial growth in the use of carbon dioxide as a refrigerant. It is non-flammable, generally non-toxic, low cost and readily available. Technology has caught up with the original downsides in the use of this gas, but one major issue remains: to work as a refrigerant, carbon dioxide has to operate at very high pressures, typically of 130 bar, or equivalent to the pressure at 1250 metres below the surface of the sea. Such high pressures mean fail-safe pipe connection systems and leak prevention are critical.

SANHA, a European manufacturer of pipe connection systems, have introduced SANHA RefHP, a range of high pressure CuFe2P ferrous copper fittings. Stronger than copper in its purest form, this material is a copper alloy and is formulated to have high tensile strength, and to be easily brazed utilising 5% silver hard solder wire.

The SANHA Ref HP system is ideal for use in refrigeration schemes where operating pressures of up to 130 bar and temperatures of up to 150° are required. The fittings are all produced in SANHA’s own factory in Belgium, ensuring that set manufacturing standards to ISO EN: 9001 are guaranteed. With a Declaration of Compliance in accordance with EN 10204:2004, and the backup of a major European manufacturer founded over 50 years ago, you can rest assured that you are using the best-quality pipe connection systems available.