science

Natural refrigerant

Natural refrigerant is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Natural refrigerant rather than just read about it. In short: Natural refrigerants are considered substances that serve as refrigerants in refrigeration systems (including refrigerators, HVAC, and air conditioning). They are alternatives to synthetic refrigerants such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) based refrigerants.

Key takeaways

Natural refrigerant belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Natural refrigerant to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Natural refrigerant from memory before moving on to harder problems.

Reference excerpt

Natural refrigerants are considered substances that serve as refrigerants in refrigeration systems (including refrigerators, HVAC, and air conditioning). They are alternatives to synthetic refrigerants such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) based refrigerants. Unlike other refrigerants, natural refrigerants can be found in nature and are commercially available thanks to physical industrial processes like fractional distillation, chemical reactions such as Haber process and spin-off gases. The most prominent of these include various natural hydrocarbons, carbon dioxide, ammonia, and water. With the current technologies available, almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants.

Background

Synthetic refrigerants have been used in refrigeration systems since the creation of CFCs and HCFCs in 1929. When these refrigerants leak out of systems and into the atmosphere they can have adverse results on the ozone layer and global warming. CFC refrigerants contain carbon, fluorine, and chlorine and become a significant source of inorganic chlorine in the stratosphere after their photolytic decomposition by UV radiation. Released chlorine also becomes active in destroying the ozone layer. HCFCs have shorter atmospheric lifetimes than CFCs due to their addition of hydrogen, but still have adverse effects on the environment from their chlorine elements. HFCs do not contain chlorine and have short atmospheric lives, but still absorb infrared radiation to contribute to the greenhouse effect from their fluorine elements. In 1987 the Montreal Protocol first acknowledged these dangers and banned the use of CFCs by 2010. A 1990 amendment included agreements to phase out the use of HCFCs by 2020 with production and import being eliminated by 2030. HFC refrigerants, which have a negligible impact on the ozone layer, were seen as viable replacements, but these too have a high impact on global warming. The Kigali amendment of 2016 calls for these HFCs to be cut back by 80% over the next 30 years. Natural refrigerants are one of the potential options for replacement of HFCs, and are growing in usage and popularity as a result. The natural refrigerant industry is expected to have a compounded annual growth rate of 8.5% over the next 4 years, and is expected to become a US$2.88 billion industry by 2027.

Sustainability metrics Refrigerants are typically evaluated on both their global warming potential (GWP) and ozone depletion potential (ODP). The GWP scale is standardized to carbon dioxide, where the refrigerant's value is the multiple of the heat that would be absorbed by the same mass of carbon dioxide over a period of time. This is generally measured over a 100-year period. ODP measures the relative impact of a refrigerant to the ozone layer, standardized to R-11, which has a value of 1. GWP and ODP vary greatly among the different refrigerants. CFCs are generally the highest impact, with a high GWP and ODP. HCFCs have similar GWP values and medium ODP values. HFCs again have similar GWP values but a zero ODP value. Natural refrigerants have low to zero GWP values and zero ODP values. Natural refrigerants are therefore gaining increased interest to replace HFCs and offer a more sustainable option for refrigeration.

Refrigerants

Hydrocarbons as refrigerants Pure hydrogen compounds see moderate use in refrigeration. Hydrocarbons are a viable option as refrigerants because, besides providing cooling properties, they are also plentiful and energy efficient. They are rated to be up to 50% more energy efficient than synthetic refrigerants. Hydrocarbons are also environmentally friendly, as they exist in nature and rank low on the global warming potential (GWP) scale. Historically, hydrocarbons have mainly seen use as a refrigerant for industrial chilling and refrigeration, but with the current shift towards natural refrigerants they are starting to see an increase in use in other areas of refrigeration. They are the favored refrigerant of many European countries. Hydrocarbons used as refrigerants include:

Methane (CH4) [R-50] Ethane (CH3CH3) [R-170] Propane (CH3CH2CH3) [R-290] Ethylene (CH2CH2) [R-1150] n-butane (CH3CH2CH2CH3) [R-600] Isobutane (CH(CH3)3) [R-600a] Propylene (CH3CHCH2) [R-1270] Pentane (CH3CH2CH2CH2CH3) [R-601] Isopentane (CH(CH3)2CH2CH3) [R-601a] Cyclopentane ((CH2)5)

Flammability The main detriment of using hydrocarbons as refrigerants is that they are extremely flammable at higher pressures. In the past, this risk was mitigated by turning hydrocarbons into CFCs, HCFCs, and HFCs, but with the increasing avoidance of such substances, the problem of flammability must be addressed. Refrigeration systems work by pressurizing the refrigerant to a point where it begins to display refrigerant properties, but with the risk of pressurizing hydrocarbons there is a higher level of caution needed for the internal pressure. In order for hydrocarbons to combust, there must first be a release of hydrocarbons which mix with the correct proportion of air, and then an ignition source must be present. The range of flammability for hydrocarbons lie between 1 and 10%, and an ignition source must have an energy greater than 0.25 J or a temperature greater than 440 °C. Current safety measures regarding the usage of hydrocarbons are outlined by the Environmental Protection Agency (EPA). EPA guidelines of hydrocarbon usage as a refrigerant include specifically designating pressure ranges for hydrocarbon refrigerant systems, ensuring the removal of potentially fire-starting components from hydrocarbon refrigerant systems such as electrical components prone to sparking, and placing standards on the construction of the systems to ensure a higher level of safety. Installing ventilation such that the concentration in air would be less than the flammability limit and reducing the maximum charge size of the refrigerant are other viable safety measures. Technological advances to reduce the total refrigerant charge amount have been recently obtained using aluminum mini-channel heat exchangers.

Applications and uses Hydrocarbon refrigerant markets have been growing as a result of increased concern for environmental effects of typical synthetic refrigerants. According to ASHRAE, available equipment that utilizes hydrocarbon refrigerant includes the following:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Natural refrigerant

Start with the simplest possible case. Write down what Natural refrigerant claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Natural refrigerant before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Natural refrigerant ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Natural refrigerant

In research: Natural refrigerant appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Natural refrigerant in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Natural refrigerant is common in secondary-school and first-year university syllabi. It links to neighbouring topics Environmental controversies, Heating, ventilation, and air conditioning, Refrigerants, so understanding it makes those chapters shorter.
In everyday life: Look for Natural refrigerant outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Natural refrigerant in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Natural refrigerant means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Natural refrigerant out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Natural refrigerant in simple terms?

Why does Natural refrigerant matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Natural refrigerant?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Natural refrigerant.