The ratification of the 1987 Montreal protocol has led to the phasing out of the hydrochlorofluorocarbon (HCFC) and chlorofluorocarbon (CFC) refrigerants including R22, R123, R12, and R11. The main demerit of these chemicals with regards to widespread and commercial is their high ozone depletion potential value (ODP). Research has shown that the aforementioned refrigerants have a high potential of depleting the earth’s ozone layer, and, therefore, they pose grave danger to the global population and to our environments.
In the 1990s, the HVAC&R turned their attention to hydrofluorocarbon (HFC) refrigerants such as R404A, R410A, R134a, and R407C as a substitute owing to their zero ozone depletion value. However, while HFCs are gentle to the ozone layer, research has found them to have a high global warming potential (GWP).
As such, there presence in our atmosphere means that they exacerbate global warming as they help trap heat within our atmosphere absorbing infrared energy. Furthermore, the HFC molecules tend to last quite long in the atmosphere, therefore their absorption properties last quite long.
With global warming being a global burden for all of humanity to bear, the HVAC&R industry has not been left behind. Efforts have been made to also phase out the HFCs. As such, we are once again transitioning to new generation of refrigerants, all of which inherently have a low GWP. Some of the proposed refrigerants include hydrocarbons such as isobutene (R600a), Propylene (R1270), and propane (R290), ammonia (R717), and carbon dioxide (R744).
To understand what the new generation of refrigerants will offer businesses and homeowner, it is important to understand their nature and the R-22 pros and cons. As such, herein we will explore some of the features characteristics of the new gen refrigerants.
#1. Hydrocarbon Refrigerants – HC refrigerants are a stellar HFC alternative. As chemical compounds, they are readily available and, therefore, an economical replacement refrigerant. The abundant availability makes using propane and isobutene cost-efficient options.
However, it is the potential performance benefits that should excite property owners across the world. For starters, HC refrigerants much lower GWP rating than the HFC refrigerants. For instance, they it has been estimated that when propane is used as a HFC-13a replacement, there is an 80% greenhouse gases emissions reduction.
On the performance front, HC refrigerants tend to have positive thermodynamic attributes, coefficient of performance, and lower condensing point. These properties combine to make HC refrigerants highly energy efficient. in many regards, users can expect these new type of refrigerants to yield better performance when compared to the HCFC and HCF refrigerants.
However, one of their worrying characteristics is their flammability. Hydrocarbons are very flammable. It is for this reason they are mainly used as fuel. Therefore, their use will require significant system redesigns to factor in flammability, a consideration that has not been in the cards with regards to refrigerants for a long time.
#2. Ammonia – ammonia is increasing becoming a popular refrigerant for people looking to replace the CFCs, HF, and HCFCs as the chemical is an efficient and cost-effective alternative but also more environmentally safe. On the commercial front, anhydrous ammonia- ammonia with a concentration of about 99.98% is used. On the other hand, the residential ammonia tends to have a concentration of about 10% and it is mixed with water.
On the environmental front, Ammonia has a GWP rating of 0. This means that is has nearly zero potential to cause or exacerbate global warming. Furthermore, it has an ozone depletion potential rating of 0. In a nutshell, ammonia as a refrigerant is generally safer than HFC refrigerants and CFS refrigerants.
On to the performance front, ammonia refrigerant has been found to be between 3% and 20% more efficient. As such, it requires far lesser energy to run, therefore, lowering the operating cost. It also requires smaller diameter piping, which reduces the cost of manufacture by 10% to 20%, depending on the models. Furthermore, due to its abundance on the global market (and due to the diminishing supply of CFCs refrigerants and HCFCs refrigerants), ammonia refrigerants are less expensive than both the CFCs and the HCFCs types of refrigerants.
A critical safety concern with using ammonia is the hazards it causes. It has a pungent smell and it is highly flammable as well.
#3. Carbon dioxide – carbon dioxide has a low viscosity, stellar heat transfer coefficient, and the as a refrigerant it is generally insensitive to pressure loses. However, in practice, the performance of the carbon dioxide system is dependent on the prevailing climate whereby there is increased inefficiencies with increased condensing temperature.
Carbon dioxide is a high-pressure refrigerant where systems are designed to typically work under pressures of 90 bars. However, it has a low compression ratio compared to both ammonia and HFCs, giving carbon dioxide better volumetric efficiency for better performance. However, the critical point and the triple point of carbon dioxide are quite close to the working range. As such, special procedures and equipment are necessary during system servicing.
Since the carbon dioxide exist in nature, it has a 0 GWP rating and 0 ozone depletion potential. It is therefore a very environmentally friendly refrigerant for businesses and homes. Furthermore, the substance is readily available, making it quite cheap for businesses and homeowners.
In conclusion, keeping in mind some of the characteristics of the new generation of refrigerants with lower GWP value, they have a potential of outperforming even the best of refrigerants that they are mean to replace moving into the future. With HVAC system redesigns and further developments of the refrigerants, the new generation of refrigerants along with the systems they are used will yield adequate performance advantage over the old generation of HVAC systems.
That being said, there is need for new safety codes, standards, and regulation to be established to take into consideration of the flammable refrigerants. While the safety and standards codes are being rolled out, authorities need to expedite the process, where possible, to make the transition to the new refrigerants as smooth as possible and as quick as possible.