Analysis of the available technological alternatives that directly influence to achieve a lower environmental impact on HVAC/R.
by Eng. Carlos C. Obella*
Three key global trends in the refrigeration and air industry: There are three key global trends to which the commercial refrigeration and air conditioning industry must respond immediately: Sustainability, Energy Efficiency and Connectivity (Fig. 1).
The three trends are intimately linked to each other. A sustainable refrigeration or air conditioning system, with a lower overall environmental impact, must be energy efficient. In turn, it must have electronic control devices that allow it to operate sustainably and efficiently.
The same three trends pose the challenge of balancing the reduction in terms of total environmental impact, with the technological development needed to do so, and the economic impact that this poses.
Fig.1
A "Complete Historical Circle" for Refrigerants
Sustainability as a key trend has generated a striking phenomenon. The history of refrigeration dates back to the application of natural refrigerants at the beginning of the last century (CO2, NH3, HC). Aspects related to toxicity, flammability and high operating pressures led the industry to develop non-toxic and non-flammable synthetic alternatives. This is how the so-called CFC refrigerants (R12, R502, among others) emerged. The depletion of the ozone layer, highlighted internationally by the Montreal Protocol (1987), led to the search for alternative refrigerants without chlorine in their composition: the so-called HFCs (R410A, R404A, R134a, and others).
None of these alternatives turned out to be "ecological" since, although they do not affect the ozone layer, their impact on the so-called "greenhouse effect", also known as global warming or climate change, is more than significant.
Therefore, at the beginning of this century, alternatives with a lower environmental impact began to be evaluated; and natural refrigerants returned to the scene, to close the so-called "Historical Circle of Refrigerants" (Fig. 2)
Fig.2
Influence of International Regulations and World Organizations: the European Union with the so-called "F-Gas" regulation, which seeks the gradual reduction of emissions of gases that impact on climate change by 80% by 2030; along with other incentives in this regard such as those carried out by "EPA" (Environmental Protection Agency) in the United States; in addition to the Montreal Protocol Amendment, signed in October 2016, and effective january 2019; even what is happening in "CARB" (California Air Resources Board) in the USA, and in "ECCC" (Environmental Climate Change Canada). All these initiatives will have an impact on the trends that govern technological evolution in our markets in Latin America.
Just to give an idea, beyond 2021 in Europe it will be necessary to transition to refrigerants with GWP (Global Warming Potential) less than 1,000, which implies preparing so that from there only natural refrigerants or some slightly inflatable synthetic mixtures are applied.
The Montreal Protocol Amendment in particular has been leveraged by the success of more than 30 years of its original implementation, having contributed to significantly reducing emissions of gases that affect the ozone layer. Latin America is part of the group of signatory countries A5 within Group 1, for which a freeze is expected in 2024, a first reduction of 10% in 2029, and a reduction of more than 80% in the manufacture, marketing and application of HFC refrigerants in 2045 (Fig. 3).
Fig. 3
When is a refrigerant a long-term option?
When considering possible long-term alternatives that include refrigerants with a lower environmental impact, whether natural or synthetic refrigerants, there are four basic premises that need to be analyzed with a "holistic" approach. These are safety, environment, performance, and economy (Fig.4).
Fig. 4
This means that each of these four premises could not be considered in isolation from the rest. Therefore, the considerations that arise will always imply some level of commitment to assume. Let's see below what this is about:
- "Safety" is related to the possible toxicity and flammability of the adopted refrigerant, in addition to its working pressures. R744 (CO2), for example, poses a relatively safe option for the first two factors (it is non-toxic, although it can generate suffocation in high concentrations within enclosed spaces); but its operating pressures can reach relatively very high values, to the point that certain particular security measures are required to be adopted in the design and operation of the systems that apply it, which will have an impact on the "Economy" or on the cost of the system. This is beyond the fact that the cost of R744 can be considered much lower than that of other possible synthetic alternatives that are currently being proposed.
- The impact on the "Environment", is related to regulations that try to reduce emissions that affect the ozone layer or that impact on the so-called "Greenhouse Effect", "Global Warming", or "Climate Change". R410A, for example, poses an option with ODP=0 versus R22 for residential and commercial air conditioning and heat pump applications. But its GWP value (~1800) is somewhat higher than that of R22 (~1700), so its direct impact is greater than that of the latter. Although its operating pressure is higher, and its thermodynamic and heat transfer properties are better than those of R22.
This means that with R410A you can design systems with more efficient heat exchangers, which use a lower gas load, with a lower risk of leaks and a lower environmental impact both direct and indirect than with R22. But what impact does this have on the cost of redesigning systems moving from applying R22 to R410A? The air conditioning industry has already gone through this and now faces a new challenge: looking for a replacement with less direct environmental impact than R410A, such as R32 or some mixtures that are slightly flammable (for example, R454B among other possible ones).
There are extreme cases such as R404A whose GWP is on the order of ~3900, even if its ODP is 0. Leaving R22 to move to R404A in commercial refrigeration facilities with large gas loads and high risks of leakage means moving in the opposite direction, in terms of environmental impact, under current and future regulations. The Refrigeration industry is looking for intermediary alternatives, with GWP in the order 1500, while continuing the evolution of norms, standards, and codes that will govern the application of slightly flammable or flammable refrigerants, such as Propane, for example.
- The "Performance" depends on the physical and thermodynamic properties of the refrigerant. But, fundamentally, it depends on how these same properties positively or negatively affect both the capacity and the energy efficiency of the system in which that same refrigerant is being applied, to certain and certain operating conditions.
- The "Economy" depends on the cost of implementing the technological changes to be applied and the total cost of the system; not just the cost of the refrigerant considered.
A refrigerant with ODP =0 and low GWP compared to R22, whose application is safe, may not be economical, if its volumetric capacity is lower than that of R22, so the application of compressors with larger displacements is required to reach the same capacity, in certain and certain applications and conditions. That may be the case with R134a or some other GWP blends <1500, which work with low operating pressures in certain and certain applications (not in all cases).
These are just a few examples of what is intended to be enunciated as a holistic approach to an analysis that must be done in each particular case, avoiding general considerations.
Possible refrigerants with lower environmental impact for refrigeration and air conditioning:
Figure 5 shows the most common current options and some of the possible future candidates, with their respective comparative GWP values.
Fig. 5
R22 is the only non-zero ODP refrigerant in the figure, and has been included only for reference and as a comparison with the rest, as its future application is totally ruled out.
The graph is divided into horizontal stripes that define the most common applications in the industry. For example, the central strip brings together various current and future options for common commercial refrigeration applications and residential and commercial air conditioning.
In general, all refrigerants that are in the same horizontal strip have similar characteristics of capacity and working pressure.
The colors of the small boxes match the code specified in ASHRAE 34, in relation to flammability and toxicity.
The A2L category, purple, brings together those refrigerants called Slightly Flammable. In general, a refrigerant is considered Slightly Flammable or A2L (according to ASHRAE 34), when large concentrations are required for a combustion to start which, in turn, will require a very high energy in the spark to start; the flame will propagate with a very low speed once the combustion has begun, and with a very low heat generated during the process; all this compared to refrigerants included in category A3 or "Flammable" (See Fig. 6 below).
Returning to Figure 5 above, the abscissa axis shows approximate gwp levels, measured in mass values, for equivalent carbon dioxide (CO2) emissions. Refrigerants R404A and R507 fall outside the practical scale of the figure, so their relative location is only illustrative, compared to the rest. The same is true if the operating pressures of CO2 are considered compared to those of the rest of the substances in the graph.
The diagonal lines of strokes bring together mixtures with similar components, although in different proportions of R32 and / or HFO among other components. In general, the higher the proportion of R32 in the mixture, the greater the volumetric capacity and working pressure.
The graph also allows you to draw some preliminary conclusions in a general way. As you try to decrease the GWP on the same diagonal that brings together refrigerants with ASHRAE categories A1 or A2L, the capacities and working pressures are also reduced. Even maintaining efficiency levels becomes a challenge.
On the other hand, if you try to reduce the GWP in the same horizontal strip, at similar operating pressures, the options become slightly flammable (A2L) from GWP values below 600.
R410A, for example, has been widely adopted as a long-term solution by industrialized countries in Europe and North America for residential and commercial air conditioning applications, although its GWP value is somewhat higher compared to the displaced R22. its greater volumetric capacity, better transmission coefficient, higher density, and greater isoentropic efficiency allow to compensate for a higher value of direct impact, with a lower refrigerant gas load and a more efficient operation of the system, with a lower total environmental impact. 50% of the composition of R410A is R32. This last component now appears as an alternative to R410A, with a lower environmental impact.
In the same horizontal strip in which R32 is found as a pure substance, there are some mixtures that contain it, with GWP values of the order of 400 to 750, all of them slightly flammable. Both R32 and its mixtures with HFO in this same horizontal strip, can present performance characteristics very similar to those of R410A, becoming potential future options in the medium term, especially in certain countries that have not yet made a complete transition to exit R22, and that they do not want to go through multiple redesigns.
The central horizontal stripe shows some intermediate zeotropic alternatives to R22, R507, and R404A with GWP less than 1500, in category A1. Further left, mixtures with working capacities and pressures similar to the previous ones appear, with GWP values in the order of 150 and 300, all of them slightly flammable (A2L). Further to the left is R290 (Propane), as a flammable hydrocarbon (A3).
In the lower horizontal strip, there is the R134a with a GWP <1500. The application of R134a extends a little further in time through existing global regulations for commercial secondary cycle and direct or hybrid cascade refrigeration applications, in combination with R744. On the left are some A1 azeotropic mixtures that can replace it in the medium term, with GWP values of the order of 600.
The graph also includes pure HFOs (Hydro Fluoro Olefin) that are slightly flammable, and have low operating pressures.
Fig. 6
Note: The second part of this interesting article will be published in the next print edition (ACR 22-6 Nov / Dec.) and soon in this digital edition.
* Eng. Carlos C. Obella. VP of Engineering Services and Product Management
Emerson Commercial & Residential Solutions Latin America. [email protected]
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