Natural refrigerants are alternatives to hydrofluorocarbon (HFC), hydrochlorofluorocarbon (HCFC) and chlorofluorocarbon (CFC) based refrigerants, and have a very low environmental impact: their minimal levels of ODP (Ozone Depletion Potential) and GWP (Global Warming Potential) respect the ozone layer, while their contribution to global warming is below the limits laid down by the Kyoto protocol. Natural refrigerants, being natural gases, fall within the broader scope of Briton Refrigerants extensive expertise, as a company specialized in handling gases at high pressure that may also be toxic or inflammable.
Briton Natural refrigerants can be divided into three families:
> Ammonia (R717)
> Carbon dioxide
Natural refrigerants used in HVAC/R applications today are carbon dioxide (CO2, R-744), hydrocarbons such as propane (R-290), isobutane (R-600a) and propylene (R-1270), and ammonia (NH3, R-717). Other natural refrigerants are water (H2O, R-718) and air (R-729), used only for special applications, or sulphur dioxide (SO2) and methyl chloride (CH3Cl), which are no longer used.
The ammonia used for refrigeration systems based on the use of a compressor, condenser, expansion valve and an evaporator is dry (anhydrous) in that there is no water in solution with it. It has the chemical formula NH3 but as a refrigerant, it is coded with the number R717.
In contrast to its excellent refrigerant properties, ammonia is however toxic for man and inflammable, and is not compatible with copper circuits. To get around these problems, systems with a secondary fluid are used together with glycol water or carbon dioxide. The complexity of these systems means that ammonia is generally used in large industrial plants, supermarkets or sports facilities.
Carbon dioxide (CO2, R-744) is a colourless fluid, heavier than air at normal conditions and odourless at low concentrations. Being a non-flammable and non-toxic substance, it is classified as A1 according to ASHRAE Standard 34. As a refrigerant, CO2 is a great boon to the environment. It’s also the only competitor to traditional HFCs that is similarly non-toxic and non-flammable. Although carbon dioxide is a major contributor to global warming, as a refrigerant, its impact is negligible.
Hydrocarbons are called natural refrigerants because they occur in the earth’s material cycle, e.g. as a byproduct of natural gas production, or in oil refineries. They were first used as refrigerants in the early 1920s, but replaced by fully and partially halogenated fluorinated hydrocarbons in the early 1950s (CFC/ HFC). Being non-toxic and non-flammable, these substances were often referred to as “safety refrigerants”. Meanwhile, it has become generally known that CFC and HCFC have a fatal effect on the environment and the global climate, resulting in them being banned.
Hydrocarbons are technically viable for small and medium-sized refrigeration and air-conditioning applications, as well as chillers. Applications include domestic fridges, beverage coolers, vending machines, industrial refrigeration, transport refrigeration, small air conditioning systems, chillers, heat pumps and water heaters.