Cold Link Africa June 2024 | Page 13

INCORPORATING COLD CHAIN

FEATURE

HFCs about to enter the start of the phase-down process Compiled by Eamonn Ryan

Transcritical carbon dioxide ( CO 2

) R744 refrigeration systems have gained wide acceptance in the supermarket refrigeration industry and there is some movement in the light commercial and other sectors of the industry .

© Cold Link Africa

According to GEA Heating & Refrigeration Technologies : “ Ammonia is the most efficient and cost-effective natural refrigerant available today . It can generate 1.75kW out of 1m 3 / h mass flow . Because of its high capacity , less ammonia is needed for the equivalent output of alternative refrigerants . Ammonia ( R717 ) was already in use back in the 19th century . With an ODP and GWP of zero , it is a particularly climate-friendly refrigerant and also a particularly efficient one . It has excellent thermodynamic properties , reflected in very low operating costs for refrigeration technology . It has consistently been used in food processing plants , the beverage and dairy industries , as well as in breweries and cold stores .

“ The Coefficient of Performance ( COP ) of an ammonia-based heat pump running at typical conditions for a district heating network or for process heating below 100 ° C is for example up to 40 % higher , compared to synthetic refrigerants , which means up to 40 % lower emissions , up to 40 % less energy usage and up to 40 % lower cost . So , the use of ammonia reduces costs as well as emissions into the environment . Naturally these reduced production costs mean that margins increase for companies that switch to ammonia , as production becomes significantly more efficient .

“ The inexhaustible supply of ammonia , and the fact that it has zero GWP also mean that refrigeration systems with ammonia are future-proof .”

GRANT LAIDLAW ANSWERS YOUR QUESTIONS

In South Africa , HFCs for example are about to enter the start of the phase down process . This will have a massive impact on our

industry and in particular the air conditioning sector . Both R32 and R410a are HFCs and are to be phased down in accordance with the Kigali amendment of the Montreal Protocol . Although R32 has a GWP 32 % lower than R410a the fact remains that R32 ’ s GWP of 675 is above the cut off GWP of 500 .

Grant Laidlaw , owner of Airconditoning and Refrigeration Academy ( ACRA ) says : “ Given that CFCs are long gone , HCFC ’ s are being phased out , and HFCs are about to begin being phased down , where do we go ? Naturals are the future , and the selection revolves around ammonia , hydrocarbons , some hydrofluoroolefin ( HFO ) refrigerants and carbon dioxide . I am aware of some research around using water ( H

2

O ) as a refrigerant – but we have yet to see commercially viable results .”

Technology advancements in CO

2 systems are making these systems more

economically viable , in terms of both equipment and installation costs but also energy and operating costs .

“ Looking at some background information we find that CO

2 is a naturally occurring compound in Earth ’ s atmosphere and it is the fourth most common atmospheric compound , behind nitrogen , oxygen and argon . As we all know carbon dioxide is an integral part of the life cycle of plant and animals , as the primary product of respiration in animals and humans . In turn , the carbon dioxide is absorbed by trees and converted back to oxygen .

“ Through the process of photosynthesis , leaves draw in carbon dioxide and water and use sunlight to convert this into chemical compounds such as sugars that feed the tree . As a byproduct of that chemical reaction , oxygen is produced and released by the tree . It has been calculated that one

Presenter Werner Terblanche of A-Gas South Africa describing the Kigali Amendment to the Montreal Protocol phase-out and phase-down regulations . large tree can provide oxygen for up to four people ,” says Laidlaw .

“ Trees also store carbon dioxide in their fibres , helping to clean the air and reduce the negative effects that this CO 2 could have had on our environment . According to the Arbor Day Foundation , in one year a mature tree will absorb more than 48 pounds of carbon dioxide from the atmosphere and release oxygen in exchange .”

Carbon sinks : A carbon sink is anything that absorbs more carbon from the atmosphere than it releases – for example , plants , the ocean and soil . In contrast , a carbon source is anything that releases more carbon into the atmosphere than it absorbs – for example , the burning of fossil fuels or volcanic eruptions .

“ In recent decades , carbon dioxide has been identified as the most significant greenhouse gas in Earth ’ s atmosphere . It is used as the comparative unit of measure when discussing the global warming impacts of various activities , leading to the term ‘ carbon footprint ’. CO 2 as a refrigerant has emerged as one of the possible refrigerants of the future . It is environmentally friendly , has good heat transfer properties and a high latent heat of vapourisation . CO 2 is also nonflammable and non-toxic with the refrigerant number R744 .

“ CO 2 is commercially available at several different purity levels . The common names and percent purity recommended for refrigeration systems using CO 2 with a purity equal to or greater than Bone Dry Purity .”

Examples of various grades of CO 2 are shown below : Industrial Grade – 99.5 % Bone-Dry Grade – 99.8 % Anaerobic Grade – 99.9 % Instrument Grade – 99.99 % Research Grade – 99.999 % Ultra-Pure Grade – 99.9999 % He lists key factors to note as follows :

• CO 2 used in commercial refrigeration systems must be of a purity level high enough to prevent the introduction of non-condensable gases into the system .

• A build-up of these gases can block the heat transfer surface and cause inefficient operation or malfunction of the system .

“ Mixing of higher purity grades of CO 2 is acceptable . Lower grades of CO 2 will be less expensive but are not recommended . In addition to non-condensable gases , these lower grades contain higher levels of contaminants and water . Higher levels of moisture may react with the CO 2 and form carboxylic acid that can degrade system component integrity .

© Cold Link Africa Supplied by Grant Laidlaw

Zayd Fredericks , industrial refrigeration representative at Metraclark .

Carbon dioxide as a refrigerant has an extremely low carbon footprint , compared to common synthetic refrigerants . The absence of ODP and extremely low GWP make CO 2 attractive as a refrigerant from an environmental perspective .”

Laidlaw adds : “ Unfortunately the primary disadvantages of CO 2 as a refrigerant are the relatively high operating pressures and fairly complex refrigeration systems . Oil management needs particular attention .

“ Let us have a look at a transcritical system . A transcritical system is defined as a system that operates above the critical point . Above this point , the refrigerant is not considered liquid or gas , but an undefined fluid . This can be seen on a Mollier diagram . Fluorinated refrigerant systems operate below the critical point . In the case of

CO 2 systems this temperature is often exceeded when ambient air is used for condensing .

Critical point on a Mollier diagram .

SAFETY WHEN USING CO 2

The physical properties of CO 2 present a unique set of considerations to ensure safety . CO 2 is classified as an A1 refrigerant by ASHRAE 34 meaning it is non-toxic and non-flammable . However , like many refrigerants currently in use , a large enough leak in a confined space can displace available oxygen for breathing .

At typical refrigeration temperatures , CO 2 operates at considerably higher pressures than synthetic refrigerants – up to around 10

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