HOW A NEW CROP OF REFRIGERANTS CAN DELIVER BETTER PERFORMANCE AND LOWER EMISSIONS
Refrigerants for air conditioning systems are going through a fundamental transition.
Air conditioning systems and the refrigerants they require account for 3% of greenhouse gases and about 10% of global electricity use. Legislation
to tackle refrigerants' direct and indirect environmental impact, such as the American Innovation and Manufacturing (AIM) Act of 2020, have led to a new generation
of refrigerants with lower global warming potential (GWP).
The good news is that some of these also match or exceed the efficiency of the products they replace. Therefore, choosing one of this new crop of refrigerants doesn’t just
have to be about the environment; it can also be advantageous for building performance. Moreover, with energy costs and inflation at historic highs, greater efficiency isn’t just an environmental consideration — it’s also good for
the wallet.
Here’s what building professionals need to know to make informed decisions about HVAC equipment and refrigerants.
BALANCING MULTIPLE FACTORS
As building professionals evaluate their options for HVAC systems and the associated refrigerants, they have many factors to balance. The first are the overarching project goals,
including anything from footprint and efficiency to installation limitations and service requirements. They must also balance multiple factors that impact HVAC performance across a building’s life cycle. This goes beyond the GWP of the refrigerant,
which measures how greenhouse gases such as hydrofluorocarbons (HFCs) trap heat in the atmosphere, and also includes a refrigerant’s
flammability, toxicity, and efficiency
According to the ASHRAE 34 - 2024 standard, flammability ratings range from Class 1 to Class 3 (Figure 1). Refrigerants
used in the U.S. for HVAC applications have predominantly been Class 1, posing no flame propagation risk (sometimes incorrectly called ‘non-flammable’). When low-GWP refrigerants were introduced, Class 2L was added to the rating system.
This was to account for refrigerants with lower flammability but not requiring the more stringent safety and mitigation requirements of the ‘higher flammability' Classes 2 and 3.
Similarly, a refrigerant's toxicity is classified
as A (lower toxicity) or B (higher toxicity), based on allowable exposure.
Many of the low-GWP refrigerants are A2Ls. They require additional safety measures, such as refrigerant detection sensors incorporated into the building design or mitigation actions in case of a leak.
Other variables are a refrigerant’s
efficiency — how much cooling it provides for the energy consumed; its charge quantity — the amount needed to charge an HVAC unit fully; and its capacity — the relative amount of cooling it can deliver.
Figure 1: ASHRAE Standard 34 - 2024 refrigerant safety classification rating system, including HVAC refrigerants and their corresponding safety classifications and operating pressure.
TAKING A HOLISTIC APPROACH
A Life Cycle Climate Performance (LCCP) framework can help structure these factors. LCCP considers the life-long environmental impact, including both GWP and efficiency, enabling comprehensive assessments and future-proof HVAC equipment decisions.
LCCP combines the direct effects of refrigerant leakage into the atmosphere with the indirect effects from embodied carbon and HVAC energy use impacted by refrigerant efficiency to calculate the overall environmental impact over the equipment's
lifespan (Figure 2).
Depending on the specific project conditions, a refrigerant with a very low GWP could turn out to be less efficient, use more electricity, or require larger charge quantities. Therefore, it could contribute more to
global warming than a slightly higher-GWP alternative with a lower refrigerant charge and higher efficiency, resulting in reduced efficiency of the HVAC equipment and building.
Let’s look at how these considerations play out for three
key refrigerant replacements.
Figure 2: Comparison of lifetime emissions of high efficiency residential heat pumps utilizing R-410A, R-32, and R-454B
R-410A REPLACEMENTS
R-410A is a refrigerant widely used in residential and commercial air-conditioning units and heat pumps. Both low-GWP replacements R-454B and R-32 are A2Ls and used by a wide variety of manufacturers (Figure 3).
R-454B’s performance properties
are close to those of R-410A, with a slight efficiency advantage. It enables an easier transition to low-GWP refrigerants with less redesign effort for equipment manufacturers.
R-32 is a single-component refrigerant with increased capacity
and efficiency compared to R-410A and R-454B. In many scenarios, a smaller refrigerant charge per ton of cooling can be used. Even though R-32’s GWP is higher than that of R-454B, the lower refrigerant charge means that both are comparable from
a direct emissions point of view.
Figure 3: Comparison of lifetime emissions of high efficiency residential heat pumps utilizing R-410A, R-32, and R-454B
SIMULATING EFFICIENY SAVINGS BETWEEN UNITS USING R-32 AND R-454B
The graph below shows energy and operating cost savings for an elementary school modelled across various climate zones (Figures 4 and 5). The model is based on two air-cooled chillers of comparable design and simulates efficiency savings between units
using R-32 vs. R-454B.
While efficiency differences can vary by model, type, manufacturer and other factors than the refrigerant, this model quantifies the financial impact of small changes in unit efficiency over time.
The simulated
efficiencies were 11.18 EER and 17.11 IPLV for the R-32 unit and 10.09 EER and 16.18 IPLV for the R-454B unit. The building model comparison showed between 1.6% to 4.4% annual energy savings and up to $117,000 over the lifetime of the equipment, depending
on the climate zone. In all four climate zones, switching to the higher efficiency R-32 model would lower a building’s electricity consumption and improve its overall energy performance, making R-32 a highly cost-effective choice.
Figure 4: Comparison of both energy and cost savings in different climates utilizing both R-32 and R-454B.
Figure 5: Operating cost savings in different climates over the course of 15 years using R-32.
R-134A REPLACEMENTS
R-134a was the previous standard for screw and centrifugal compressor chillers.
Initially, R-513A was introduced as a stopgap to comply with regulations. However, its efficiency is lower than that of R-134a, and since then, R-515B and R-1234ze(E)
have emerged as longer-term replacements (Figure 6).
R-515B is an A1, allowing for the same safety design requirements as R-134a. Its efficiency is higher than R-513A when machines are optimized for it, but it has less capacity.
R-1234ze(E) is an A2L, which requires additional mitigation measures such as increased ventilation, which could make retrofits more challenging. Like R-515B, the efficiency is higher than R-513A, with machine optimization, but it has less capacity.
However, with a GWP value of 1 and comparable efficiency, it is a viable long-term replacement.
Figure 6: Comparison of properties for common medium-pressure refrigerants.
R-123 REPLACEMENTS
R-123 was a low-pressure refrigerant primarily used in centrifugal chillers. Its replacement, R-1233zd(E), is unusual because it is an A1 with a low GWP and good efficiency. It also offers slightly better capacity
than its predecessor and has, therefore, quickly established
itself in the market (Figure 7).
Another replacement option, R-514A, is a proprietary blend similar to R-123 in performance but with lower pressures. However, as a B1 refrigerant, its toxicity is higher, and it has a lower capacity than R-1233zd(E). For these reasons, R-1233zd(E) has
become the more commonly adopted alternative for R-123.
Figure 7: Comparison of properties for common low-pressure refrigerants.
MAKING BETTER CHOICES
As we have seen, lowering GWP involves many trade-offs that must be considered not only at the outset but also throughout the refrigerant’s life cycle. The efficiency profile of the refrigerant can make a large difference not just in carbon emissions
but also in the HVAC system’s performance. Taking a holistic approach to selecting the most appropriate refrigerant means that we don’t just match but improve performance outcomes.