EDITOR’S NOTE: This is part one of a two-part series. Part two will run in the March 7 Refrigeration Zone.
The world of refrigeration is constantly evolving, and refrigerants represent a particularly challenging area. The cycle of chemical obsolescence and new product development can seem never-ending and has caused great trepidation and confusion for many OEMs, system owners, and service technicians. However, these challenges also present our industry with opportunities for growth and differentiation through education and understanding.
HISTORY REPEATING ITSELF
The cyclical pattern of change in refrigerants is linked directly to our growing understanding of the unintended consequences of refrigerant interactions with our atmosphere, coupled with advancements in technology and shifts in societal values toward sustainability. One only needs to look at the evolution of refrigerants to see these trends at play (Figure 1).
The first refrigerants were natural products by default, such as carbon dioxide and ammonia, as they existed in nature at the time. Unfortunately, many early refrigerant solutions were far from ideal and posed threats to human health and safety that were difficult to mitigate at the time. Others, limited by the technology of the day, were not practical for widespread application. These products largely fell by the wayside for most applications once the synthetic chlorofluorocarbons (CFCs), such as R-12 and hydrochlorofluorocarbons (HCFCs), such as R-22 — originally referred to as the “safety refrigerants” — were developed and gained global acceptance and usage.
Increased awareness of the phenomena of ozone depletion and global warming led to the coupling of environmental factors with safety concerns. During the 1980s, the Montreal Protocol established a global framework for phasing out ozone-depleting substances, such as CFCs and HCFCs. Hydrofluorocarbons (HFCs), which are non-ozone-depleting, were initially viewed as potential long-term replacements to their chlorinated cousins. But a new focus on the issue of global warming has dragged HFCs onto the carpet and called their longevity into question.
Recent regional regulatory actions, such as the European F-Gas regulations and the U.S. Environmental Protection Agency’s (EPA’s) Significant New Alternatives Policy (SNAP) program, have thrown open the door to force alternative solutions. These include HFCs with a lower global-warming potential (GWP), the relatively new-on-the-scene hydrofluoroolefins (HFOs), low-GWP synthetic refrigerants, the rediscovered natural refrigerants, and blends or combinations of these products. Implementation of new system designs and technologies also has expanded the role of products, such as carbon dioxide, ammonia, and hydrocarbons (HCs) from niche applications to wider spread regional acceptance. International and domestic pressures on the mainstream fluorinated chemicals only appear to be increasing.
So, given the volatility and codependence of the refrigerant-regulatory landscape, what’s someone working with refrigerants today in the U.S. to do? After all, although it’s always good to plan ahead, though most can’t afford to skip the here and now.
R-22, long a workhorse of our industry, is still one of the most widely used refrigerants in the world. The European Union has largely left this refrigerant behind, and developing countries are just starting the process of eliminating it while the U.S. is in the midst of a full-blown R-22 phaseout. Since Jan. 1, 2010, R-22 has been banned from use in new air conditioning and refrigeration systems. The EPA also has issued a final allocation rule for R-22 from 2015-2019 (Figure 2), decreasing the supply of the refrigerant each year until 2020, at which point it can no longer be produced for the servicing of systems in the U.S. A key point to remember, however, is that there is no use ban on R-22, and both virgin and reclaimed refrigerant can be used to service systems after 2020. That means R-22 inventory management is more critical now than ever. For owners of large or multiple R-22 systems, having a plan in place to minimize refrigerant leakage and bank new or recovered refrigerant is a must.
Our experience with the CFC phaseout demonstrated that, as refrigerant supplies tighten, many service personnel and equipment owners will consider refrigerant retrofits. While there are many R-22 retrofit refrigerants available, there are no drop-in replacements, and the use of any of these products will change system operating characteristics. The decision to retrofit should not be taken lightly, as there are many issues to consider, including the fact that there may not be a viable retrofit option for some systems.
First, all of the mainstream R-22 retrofits are blends (400- or 500-Series ASHRAE number) of two or more refrigerant components. Blended refrigerants behave differently than R-22, a single-component refrigerant. These behaviors must be accounted for to ensure a successful retrofit
When charging, blends need to be removed from the cylinder in the liquid phase only (Figure 3). Otherwise, vapor charging with blends may result in unwanted shifts in refrigerant composition (fractionation) that can adversely affect system performance.
In addition, most R-22 retrofits are high-glide blends or refrigerants that produce a range of temperatures during the phase-change process. Under certain scenarios (e.g. dormant systems), noticeable shifts in composition can result from refrigerant leaks with these products. Technicians also will need to understand the different blend pressures, and how to use bubble point and dew point to measure superheat and subcooling or determine average coil conditions. Finally, high-glide blends are typically not recommended for systems with flooded evaporators as pooling of the refrigerant components can produce large losses in system performance.
R-22 retrofits are HFC-based, which means they are not ozone-depleting. However, there are a few other notable side effects resulting from this change in refrigerant chemistry that must be considered. HFCs do not swell elastomers as much as R-22. The net result of this is that retrofitting to a new refrigerant may produce leaks where there were no leaks before. Therefore, service techs should replace O-rings and elastomers and leak-check the system as part of the retrofit process.
Another side effect of using an R-22 retrofit is that these HFC-based products have limited miscibility with the mineral oil (MO) and alkylbenzene (AB) lubricants usually found in original R-22 equipment. While the R-22 retrofits can be used with MO and AB on a limited basis, there are many systems that may struggle with oil return or oil logging. This could negatively impact compressor longevity and system performance. As such, polyolester (POE) or polyvinylether (PVE) oils are strongly recommended when using HFC-based R-22 retrofits.
Some of the R-22 retrofits are made up entirely of HFC components, while many contain a small amount of additives — typically HCs. These additives improve the solubility of the refrigerant blend with mineral oil. However, this is not a cure for the issue of refrigerant-oil immiscibility. Simply put, certain equipment architectures (e.g. many systems with receivers) may prevent oil return with immiscible refrigerant-oil combinations, regardless of whether or not these additives are used.
That being said, there also are systems where the use of these additives can significantly reduce oil logging, particularly in higher-evaporator-temperature applications, such as air conditioning. Oil logging may be reduced enough to improve performance over that of pure HFC blends with MO or AB. Reducing the oil logging can also help preserve evaporator superheat, thereby protecting the compressor from liquid. When all is said and done, even a partial oil change to POE or PVE will often have a greater impact on improving system oil return and reducing or eliminating oil logging than the use of HC additives.
Equipment operating characteristics will also change when using any retrofit refrigerant. Operating pressures and temperatures are different. Cooling capacities are often reduced, particularly at higher condenser temperatures. Mass flow rates may increase noticeably with many of the new refrigerants. Expansion devices will need to be adjusted — or, in some cases, replaced — to obtain acceptable performance. Technicians should familiarize themselves with these expected changes before starting the retrofit. Capturing baseline performance data with R-22, when possible, also can assist with system optimization. Likewise, an analysis of system components is recommended to ensure suitability.
Once the refrigerant discussion moves beyond R-22, the future becomes less certain. HFC alternatives that were acceptable for some new equipment applications a few years ago may no longer be credible replacement options today. This is primarily related to ongoing efforts to regulate refrigerants based on their GWP.
The HVACR industry has launched the Air-Conditioning, Heating, and Refrigeration Institute’s (AHRI’s) Low-GWP Alternative Refrigerants Evaluation Program (AREP) to investigate replacement refrigerant candidates for major application areas. Refrigerant manufacturers have submitted numerous new candidates to this program for testing and evaluation. Many of these candidates are HFCs mixed with the HFOs R-1234yf and R-1234ze. Some of these products are promising and are already being used in a variety of applications. R-32, a mildly flammable HFC, is being used in air conditioning systems in Japan and Asia and is being evaluated as a potential replacement for use in the U.S. in certain R-410A applications.
Equipment manufacturers, particularly in commercial refrigeration, have reacted to these pressures by developing and launching new system/component designs and architectures using natural refrigerants, such as CO2 and/or NH3.
Publication date: 2/1/2016