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USE OF LOW GWP REFRIGERANTS IN SUPERMARKETS

Supermarket refrigeration systems will be very different in the future, predict industry experts. Low GWP Refrigerants applied in refrigeration systems will soon replace the use of HFCs or even HCFC, wherever they are still in use in legacy systems.

Large supermarkets have central direct-expansion (DX) systems consisting of display cases on the floor that are connected by long runs of refrigerant piping to condensers and condensing units located outdoors or in a remote mechanical room or on the roof. These systems are designed to be easy to access and service, as all the mechanical equipment is located in one area; however, the sizeable amount of piping can mean a greater chance for refrigerant leaks, which is becoming a growing environment concern.

A typical, large supermarkets refrigeration system has a refrigerant charge of 2000 kg with an average annual leak rate of about 25 per cent based on high operation pressures and less than perfect maintenance. That means leaks could cause a supermarket to annually emit up to 500 kg of refrigerant – usually HFCs or even HCFCs — every year. Multiply that by thousands of supermarkets across India, and it is possible to see how this may be cause for concern.

Refrigerant phase down regulations are another reason why change is coming, as HCFCs are already mandated to be phased out, given their high global warming potential (GWP) and HFCs will likely be phased down by 2030 as well. At some point, supermarkets will need to start considering low GWP alternatives such as HFO blends, as well as zero GWP refrigerants such as propane R 290, ammonia R717, or CO2 R744 for their refrigeration systems, that work 24 hours a day and 365 days a year.

Multi-national food brands favour the use of propane refrigerant systems in self-contained refrigeration units such as display shelves. The use of multiple self-contained refrigerated display shelves is far more flexible than central DX systems. So, if a supermarket decides to highlight a brand-new soft drink, they could move a propane refrigeration case to a prominent place near the front without disrupting the floor plan or making costly changes to the rest of the refrigeration equipment in the store.

In addition, self-contained propane units have been designed for safety. They contain only a small charge (no more than 150 grams per refrigerant circuit) and have a very low leak rate of about 2 per cent. Depending on the size, a supermarket using only self-contained refrigeration equipment could theoretically only have 50 kg of propane.

Another factor leading to change is that young people are increasingly moving to densely populated cities to live in remote suburban areas where they may not have ready access to supermarkets. Supermarket owners are likely to start opening smaller stores to cater to suburban markets.

Self-contained refrigeration cases may be a good solution, particularly, if a supermarket is taking over an existing building that offers less flexibility with the layout.

Supermarket owners may have even more choices of self-contained units in the near future, because several industry groups are trying to raise the maximum charge size for flammable refrigerants such as propane in commercial self-contained cases from 150 to 500 grams. That is because while 150 grams of propane is adequate for small-to-medium-sized display cases, the larger display cases need more propane for cost-effective operation. Safe design and more efficient systems will allow larger charge systems to be acceptable.

Larger self-contained propane units will take time to become available because of current limitations on maximum charge and supermarket owners await that. Refrigeration contractors, however, may not be as excited about the widespread adoption of self-contained units. That’s because these units typically require less maintenance than large rack systems, and since they’re virtually plug-and-play. Supermarket owners may choose to buy a new unit rather than pay to have an older one repaired. Although in a world with a shrinking base of service technicians, perhaps that’s a good thing. That way experienced service techs could be used to work on the complex refrigeration systems that will likely still be used in the large megastores for many years to come.

Another natural refrigerant that is fast gaining application in refrigeration systems is carbon dioxide. Carbon dioxide as a refrigerant is not a new concept. CO2 as an operating fluid in refrigeration systems was in use until the second half of the 19th century. It is with the development of synthetic refrigerants like CFC, HCFC and HFC that CO2 was put to rest as a refrigerant.

But with such unique properties, CO2 has made a comeback as a refrigerant with the development of Transcritical CO2 Systems since early 2000s. Such systems put CO2 in a transcritical cycle, meaning CO2 is made to undergo different phases with varying pressures and temperatures.

One of the main advantages of the transcritical system is that CO2 is abundantly available in the environment. Waste produced CO2 can also be used in this system reducing the overall greenhouse gases in the environment.

With all these advantages, the transcritical system is still not perfected. But we might be closer with India’s first transcritical refrigeration system developed at IIT Madras.

Researchers from the Department of Mechanical Engineering in the Indian Institute of Technology, Madras, presented India’s first CO2 transcritical system recently. It is the first of its kind in India, and it is operating successfully in very high ambient temperatures of up to 45C according to Professor Maiya, a member of the research team.

The researchers tweaked the system by adding a liquid ejector and flooding the evaporator in the system. This resulted in an improvement of the CO2 cooling stability and an overall reduction in power.

In recent years, there is a rapid increase in the cooling demand. Hence, not only the consumption of energy, but also the quantity of the refrigerants released into the air is increasing globally leading to planetary heating. Carbon dioxide (CO2, R744) is a natural refrigerant which is emerging as a potential replacement for HFCs and HCs nowadays because of its attractive properties.

However, to avoid liquid entry into the compressor, conventional systems are designed and optimised to keep the exit part of the evaporator dry ensuring no liquid exits the evaporator. This requires superheating of the fluid which also contributes to internal irreversibility leading to lower COP. Hence, the liquid ejectors appeared as the potential option to improve the system COP by facilitating complete use of the evaporator by avoiding superheating and securing a safe return of liquid refrigerant.

It is observed that the increment in evaporator pressure and decrement in compressor power consumption are 4.5 per cent and 5.5 per cent respectively. From the reduced superheat, the design reduces the heat transfer area in the evaporator due to nonlinear refrigerant distribution and thus, contributes to energy saving.

This design shall result in commercial applications such as in refrigeration systems for supermarkets typically used in supermarkets, hospitality catering and medical storage with significantly lower energy consumption.

Synthetic refrigerants – HCFCs and HFCs are very harmful to the environment. Natural refrigerants including Propane, CO2 and Ammonia shall soon be the green replacements that the world is looking for.

So, perhaps the refrigerated supermarket facilities of the future will turn out to be a win-win for everyone based on changes in the refrigerants they use.

A third natural refrigerant is ammonia. The use of ammonia is on the rise as a choice of refrigerant not only because it is safer for the environment, but it is more energy efficient than other traditional refrigerants. It absorbs large amounts of heat during evaporation, it can pass through smaller pipes, but maintain the same amount of refrigeration capability as other refrigerants.

It is thermal capacity enables it to use less energy than other refrigerants, particularly when used in industrial applications, like supermarket refrigeration systems. This is a good thing since supermarkets are high energy users. In fact, more than half of their energy usage is attributed to refrigeration.

Supermarket owners that look to apply ammonia should be confident that a properly implemented system can be extremely safe and efficient. Beyond this, there are no deterring code restrictions preventing its use. Utilising ammonia commercially doesn’t require the reinvention of the wheel. Ammonia systems have been used in India and around the world for many years in various types of industries and applications – and more recently – in supermarkets.

With the success of ammonia-based refrigeration systems so far, it makes sense for supermarkets to take a further look at the new technology.

To date there are at least five US supermarkets that have installed a refrigeration system that use ammonia, along with CO2. This makes an NH3 or CO2 system one of the most unusual of natural refrigeration technologies (propane or CO2 is in use too), with the efficiency and environmental advantages it offers.

However, supermarket owners have a reason for slow adoption of ammonia namely fear. The fear stems from ammonia’s toxic properties as well as the noxious odour it exudes; an ammonia leak is not something they would accept,

From a safety standpoint, there is no need to be overly concerned about having 100 kg of ammonia at multiple locations in a supermarket when correct equipment location and easy venting can be a part of the installation design.

One US Store, is the first all-natural refrigerant store that uses ammonia on the roof on the high side with CO2 circulated in the store in a cascade configuration. It also employs a redundant R407A system to run energy-efficiency comparisons with the ammonia or CO2 system. The energy consumption of the ammonia or CO2 system and versus the redundant R407A system, found the former to be12 per cent -16 per cent more efficient than the latter.

This study is certainly good guidance for early adoption of natural refrigerants in an extended central refrigeration system in a supermarket.

While anxiety about ammonia appears to be an obstacle that can be overcome, the high cost of hybrid ammonia or CO2 systems remains a major deterrent to the implementation of these systems by food retailers, who operate in a very low-margin business.

Some of the ammonia or CO2 systems in US supermarkets have demonstrated energy-saving capabilities just via the refrigeration cycle efficiency. At one particular store, an ammonia refrigeration Unit consumed 22 per cent less energy on an average compared to similar application HFC refrigeration unit, during a four-month period.

Natural refrigerants – Propane, CO2, ammonia and hybrid ammonia CO2 refrigeration will soon be common in supermarkets in Europe and the US, because of the rapid push to phase down HFCs there. It may take longer in India but good research and regulation will hasten the process. Installation and operation safety protocols must be in place before their adoption.

Synthetic refrigerants – HCFCs and HFCs are harmful to the environment. Natural refrigerants including Propane, CO2 and ammonia shall soon be the green replacements that the world is looking for.

So, perhaps the refrigerated supermarket facilities of the future will turn out to be a win-win for everyone based on changes in the refrigerants they use.