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Preserving Food (and the Planet)

Keeping food cool has long been a method of its preservation, from the primitive burying of foods in the relative cool ground, to building subterranean ice houses in the Victorian era. This was very much a passive approach to preservation.

05.01.2017

It is with the advance of science and the understanding of the physics of phase changes of a compound that has lead, to a very recent leap in technology, in human terms, to allow cooling technology to exist within the home and work place.

It was observed that whilst an ice cube melts, i.e. changing phase from a solid to a liquid, in a warm environment, the water surrounding the ice remains a constant temperature until all the ice has melted. This may seem obvious, but it is the application of this science that is transformational. The inventive leap, is to say, 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, whilst its molecules change phase, and in doing so, cooling 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”.

This can be demonstrated, by simply pouring a volatile liquid, such as acetone, or nail varnish remover onto the back of your hand, and feeling the skin temperature drop.

Refrigeration technology is the industrialisation of this physical effect. It is the containment and controlling of this process, which allows us to cool spaces. Refrigeration requires a liquid at room temperature, which will easily evaporate. Under pressure many gases at room temperature will liquefy, therefore this effect can be magnified with the correct choice of 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 a very costly process, both in terms of energy, but also in machinery.

With the development of organic chemistry many new chemicals were developed, which optimised the temperature and pressure at which these phase changes could be harnessed. These chemicals were typically Chloro-Fluoro Carbons, or CFC’s. They were cheap to produce, operated at much lower pressures, and ideal for domestic applications.

It was not until the 1980’s that it was discovered that these chemicals, when released into the atmosphere, had a significant detrimental effect to the ozone layer surrounding the world. Ozone is not only a Green House Gas, i.e. keeps heat in, but also is an ultraviolet filter, keeping harmful radiation out. Because of this the preservation of this layer is very important to the Earths bio existence.

It was found that Fluoro-carbons 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 which, whilst they were Non Ozone Depleting, did have significant Global Warming Potential (GWP). The effect of their atmospheric build up was to insulate the Earth, and could cause mean 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 Tetro-Fluoro-Carbon (HFC) of 1,300.

This means Methane is 25 times worse than Carbon Dioxide and HFC’s are seriously bad.

The Global community has recognised the seriousness of Global Warming and has now set up initiatives to reduce this risk, which includes the reduction in the use of refrigerants with a high GWP. There are various regulations in force on this, the latest being the EU F-Gas Regulation (517/2014), which came into force on 1st Jan 2015.

This regulation limits the total amount of F-Gases (Fluorinated Gases) which can be sold, and also phases them down each year until 2030. It also bans the use of F-Gases, in new equipment where better alternatives are already available, and finally also requires the checking and servicing of equipment to prevent leaks.

A recent global agreement has been reached on the use of hydrofluorocarbons, which takes effect from 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, zero ozone depletion and low GWP. There are very few refrigerants which meet all these requirements, currently, hydrocarbons, ammonia, hydro-fluoro-olefins and carbon dioxide are the most prevalent solutions, each with their own short comings, but all share the properties of being refrigerants with low GWP, typically less than 10.

The long term impact of this regulation, will be the significant 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 the major issue remains, which is this material, to work as a refrigerant, has to operate at very high pressures typically of 130 ba, or equivalent to the pressure at 1250 m below the surface of the sea.

Such high pressures means pipe connection systems and leak prevention are critical.

SANHA, a European manufacturer of pipe connection systems, have introduced SANHA Ref HP, a range of high pressure CuFe2P ferrous copper fittings and tube, for brazing, which are robust and secure. This material is an alloy of copper thus harder than traditional copper and formulated to have high tensile strength, and be easily brazed utilising 5 % silver hard solder wire.

The SANHA Ref HP system is ideal for specification and usage in refrigeration schemes where the high operating pressure of up to 130bar and temperatures of up to 150° are required.

The fittings are all produced in their own factory ensuring that set manufacturing standards to ISO EN: 9001:2008 are guaranteed.

With a Declaration of Compliance in accordance with EN 10204:2004 peace of mind is assured and you have the back up of a major European manufacturer founded over 50 years ago.

A Victorian Ice house for food preservation