The global heating, air conditioning, and refrigeration (HVACR) industry has been witnessing a shift towards use of refrigerants with lower carbon footprint. Refrigerant that transfers the heat between the indoor unit and the outdoor unit of air conditioners is taking a toll on the environment as it depletes ozone layer and also contributes to global warming.
In the beginning, Methyl Chloride, Methyl Formate and Ammonia were used as refrigerants for mechanical refrigeration systems. Toxic nature of Methyl Chloride and Methyl Formate paved the way for the introduction of Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) having high thermodynamic efficiency and non-toxic nature. Later, CFCs and HCFCs were replaced by hydrofluorocarbons (HFCs) due to environmental concerns about depletion of the ozone layer. However, Kyoto Protocol to the Framework Convention on Climate Change put HFCs under scanner due to their impact on the environment.
The Montreal Protocol, the Kigali Amendment, the Convention on Climate Change (COP21) etc. have been adopted in order to lower or eliminate the impact of these Global Warming Potential (GWP) and Ozone Depletion Potential (ODP) refrigerants. The Montreal Protocol voted to phase down HFCs. The Kigali Amendment provides for a gradual phase down the production and consumption of HFCs based on their GWP value. This has generated urgent need for green refrigerants.
For years, the most common refrigerant gas used in air conditioning systems was R-22, which in the past was viewed as a safe refrigerant. However, it depletes the ozone layer and the industry is aware of this and some have taken measures to curtail its effect on the atmosphere.
“After understanding impacts of manmade refrigerants on the environment, we all are now looking for more sustainable products. Montreal Protocol was one big step to save environment and now after Kigali agreement, we are looking for natural or green refrigerant,” asserts Anand Joshi, Immediate Past President Association of Ammonia Refrigeration and Member ASHRAE (USA), IIAR (USA), IGCC, IETE, IDA, RATA.
An ideal refrigerant would satisfy certain conditions such as zero ODP, very low GWP, less CO2 emission by virtue of reduced power consumption. In addition, the toxicity and flammability of the green refrigerant should be within tolerable limits.
According to Vikash Sekhani, Director, Dry All, “These are chemical free refrigerants and do not pollute atmosphere, water or biosphere. Their production is not energy intensive as even the hydrocarbons can be obtained without chemical transformation. Natural refrigerants are widely used in some RAC applications, for example isobutane in domestic refrigerators and ammonia in large cooling processes.”
Natural refrigerants such as Ammonia, Propane, Isobutane, R-32, CO2 and the newly developed Olefin group of refrigerants may be considered as green refrigerants under today’s scenario. In addition, air and water may also be considered as green refrigerants, although their application areas are limited.
According to Professor Bijan Kumar Mandal, Department of Mechanical Engineering, Indian Institute of Engineering Science and Technology, the Hydro-olefins (HFO) group are the best examples of green refrigerants as they have zero ODP and extremely low GWP values (GWP ≤ 6). Some common refrigerants belonging from HFO group are R1234yf, R1233zd, and R1234ze. In present scenario, global refrigerant manufacturers are blending HFO and HFC components to create low-GWP blends like R448A and R449A designed to match the characteristics and performance of mainstream HFCs. “These refrigerants give higher capacity with minimum power requirement,” informs Sekhani of Dry All.
According to Carel which provides control solutions for HVACR, the main characteristics of the most commonly used natural refrigerants are summarised in Table 1.
As per Carel, Carbon dioxide (CO2, R-744) being a non-toxic substance is classified as A1 according to ASHRAE Standard 34. The effect of R-744 on the ozone layer is null, having an ODP value of 0. As regards its global warming impact, their GWP is 1, which is as compared to the direct impact of other refrigerants. However, it can be considered that R-744 does not contribute to climate change since it is a product from industrial processes and would otherwise be emitted into the atmosphere.
Hydrocarbons are odourless organic compounds made of nothing more than carbon and hydrogen atoms. They are flammable, and therefore, their safety classification is A3. Its ODP of 0 and extremely low GWP value mean they are harmless to the ozone layer and do not contribute to global warming. Propane (R-290), Isobutane (R-600a) and Propylene (R-1270) are the most common hydrocarbons currently used in HVACR. Hydrocarbons operate at standard working pressures and have excellent thermodynamic properties, leading to high energy efficiency. Latent heat of vaporisation of hydrocarbons is almost two times higher than that of the most common HFC refrigerants. The major challenge of the use of Hydrocarbons as refrigerants comes from their high flammability. Hydrocarbons are technically viable for small and medium-sized refrigeration and air-conditioning applications as well as chillers domestic fridges, beverage coolers, vending machines, industrial refrigeration, transport refrigeration, small air conditioning systems and water heaters.
Ammonia (NH3, R-717) is an alkaline and colourless chemical compound at atmospheric pressure. Being a mildly flammable, it is classified as B2L. R-717 is also corrosive, but its strong odour makes it easy to detect. Regarding environmental impact, it does not have any impact on the ozone layer and global warming when released into the atmosphere, thus its ODP and GWP values are 0.
R-717 is widely available in the market at a very low price. However, the toxicity and flammability of R-717 has limited its used in public places. Many advances have been made recently to health, such as the development of hermetically sealed equipment or leak detection systems.
Green Refrigerants in India
Natural refrigerants have gained momentum globally due to their zero GWP, ODP and the evolution of technology for their safe use. Green refrigerants have also found applications in Indian HVACR industry owing to environmental concerns. As a result, Indian system manufacturers are treading the path of natural refrigerants in order to comply with Montreal Protocol and Kigali Amendment. They have started investing in R&D of green refrigerants. Vikash Sekhani of Dry All says, “Now, in India many system manufacturers are moving towards environment friendly refrigerants such as Propane, Butane, R32, R410A, NH3. Many Indian manufacturers have started manufacturing components to support this effort of OEM to move to green refrigerants.”
Ammonia is one of oldest refrigerants being used in air conditioning and refrigeration industry since 1875 and in India it has been used since 1914. While talking about the acceptance of natural refrigerants in India, Anand Joshi says, “The use of Ammonia as refrigerant has various industrial refrigeration applications such as ice, meat, poultry, dairy, ice cream, breweries, beverages, seafood or aqua culture processing, cold storage, vegetable freezing, chemical, dye stuff, pharmaceuticals, bulk drug and many more. Indian technicians are conversant with Ammonia. It is the cheapest refrigerant.”
The use of R32 refrigerant as natural refrigerant in air conditioning systems is gaining prominence due to its zero-depletion potential and the initiative of the global industry as a part of the phasedown program introduced by the Montreal Protocol and Kigali Agreement. Daikin is the first company in the world to have successfully used R-32 in air conditioners.
Some Indian refrigeration and air conditioning manufacturers have already implemented R32 as a green alternative to R410a. R452A being a non-flammable HFO blend is implemented in transport refrigeration. CO2 is used in supermarket applications in as it is widely implemented in sub-critical and trans-critical cycles. However, sub-critical cascade systems with a R134a primary refrigerant and a R744 secondary refrigerant can be upgraded easily to a non-flammable HFO blend such as R513A, asserts Mandal.
Honeywell is a global leader in the development and production of high-performance Fluorocarbon refrigerants and thermal working fluids. Honeywell develops HFO 1234yf as a replacement for R134A in mobile air conditioning applications. Honeywell Genetron Performax LT (a ternary blend of HFC-32/HFC-125/HFC-134a), serves as a non-ozone depleting replacement for HCFC-22 in various commercial refrigeration applications, particularly in low-temperature applications. Genetron 422D and 407C are non-ozone-depleting HFC based refrigerants for replacement of HCFC-22 in air conditioning systems. In fact, there will be no alternative in near future other than using green refrigerant not only in India, but also across the entire globe, he elaborates.
The cooling industry has always proactively addressed environmental concerns and will continue to do so in the future.