What are the characteristics of hfo refrigerants

Tongue-twisting terms used to identify the chemical make-up of the refrigerants we use are a long standing tradition in the HVACR industry. Throughout our history we’ve dealt with Dichlorodifluoromethane (R-12), Chlorodifluoromethane (R-22)… which, as if one chemical term to describe it wasn’t enough to describe this one, Difluoromonochloromethane and
Monochlorodifluoromethane are also used… and of course there’s Tetrafluoroethane (R-134A) and Difluoromethane and Pentafluoroethane (R410a). And now, we can add Tetrafluoropropene, R-1234yf.

From a technician’s perspective, rather than use the specific chemical identifiers for refrigerants, we, of course, lean on the categories…CFC – Chlorofluorocarbon…(R-12) HCFC – Hydro-chlorofluorocarbon….(R-22), and HFC – Hydrofluorocarbon (R-134a and R-410a) to label what we’re working with when it comes to servicing refrigeration systems. And to this alphabet soup of identifiers we can add now HFO – Hydrofluoroolefin, refrigerants that are listed as having a zero Ozone Depletion Potential and a very low Global Warming Potential.

Figure One breaks things down into a timeline from the 1930s when the refrigeration industry was in its infancy, to where we are today.

Figure One

One way to consider the impact of an HFO refrigerant on the environment is to compare it to carbon dioxide. Compared to R-134a, which has a GWP that is 1,430 greater than carbon dioxide, and R-410a, which is listed as having a GWP that is 2,090 times greater, R-1234yf is identified as having a GWP that is just 4 times that of carbon dioxide.

Other factors that have been reported relative to pure HFOs are that they have no temperature glide and they have an excellent coefficient of performance. They are also described as having other characteristics similar to R-134a, including its toxicity rating, and the previously mentioned system performance. When it comes to the issue of flammability of HFOs,

Figure Two (courtesy of ESCO Group) shows a table that is used to categorize refrigerants in regard to their flammability and toxicity.

Figure Two

HFO refrigerants are in the category A2L, which means they are considered to be low toxicity and a rated as being slightly flammable. HFO 1234yf is also categorized as a medium pressure refrigerant.

When it comes to rating HFO 1234yf in regard its capacity to transfer heat, the partial temperature/pressure chart shown in Figure Three (courtesy of ESCO Group) provides some insight on this.

Figure Three

The concept to consider here is the idea that the lower the boiling point of a refrigerant, the more work it can do. And comparing the three refrigerants in the highlighted areas shown illustrates the capacity of HFO 1234yf.

Note that the boiling point for R-12 is shown as being between -20°f and -25°F. In the case of R-134a, the chart shows that the boiling point is between -10°F and -15°F. And, when considering HFO 1234yf, the area of temperature is, like R-12, between -20°F and -25°F.

In addition to the importance of staying up to date regarding new developments in refrigerants in regard technicians taking a green approach to servicing HVACR equipment, there’s also the aspect of testing for EPA Section 608 certification to consider. Recent changes to rulings and information about new refrigerants are now part of the updated exam. And, while technicians who already hold an EPA cert are grandfathered and don’t have to re-test, those preparing for their initial certification will be testing under the new regulations. For more information, you can contact ESCO Group at 800-726-9696.

Learn From Yesterday….Live For Today….Look Forward To Tomorrow

Jim

N. A. : The development of so-called synthetic refrigerants became possible because so-called natural refrigerants were dangerous, ineffective, and expensive to use. The rebirth of these so-called natural fluids is due to their low GWP. Today, the new generation of HFOs have more than just performance and safety features similar to HFCs, they also have good environmental properties characterised by low GWP. Several conditions must be met in order to choose the right refrigerant.

There is no single solution for all applications, which is why there is a large range of refrigerants to meet every need. There may be room for natural fluids, such as when using hydrocarbons in home refrigeration, where the refrigerant's load is low and permitted by safety standards.

CO2 for example, has good qualities for low-temperature applications, and we see it used in low-temperature commercial refrigeration, especially in Nordic countries. To overcome the technical limitations of CO2 at high ambient temperatures, CO2/HFC hybrid systems been developed. This solution will also exist in the future with CO2/HFO systems to reduce the carbon footprint. For the vast majority of applications, HFO fluids will be the choice of tomorrow. At present, we already have HFO mixtures to replace most existing fluids.

More specifically, what are the main characteristics of hydrofluoroolefins (HFOs)? Why do you recommend this alternative?

N. A. : HFO (Hydrofluoro-Olefines) are a class of unsaturated molecules that contain at least one carbon-carbon double bond. These molecules are highly reactive in the atmosphere, and consequently have a relatively short lifespan. This short lifespan partially contributes to the low GWP of these new fluids.

HFOs have excellent environmental properties, which could have a favourable long-term impact on climate change and abide by current and future legisltion, owing to their low GWP and energy efficiency.

Most HFOs have service conditions similar to those of HFCs. This means that best practises developed over the years by engineers are not lost, and existing equipment can still be used with little or no modifications.

Solstice™ products from Honeywell

Are these new molecules toxic?

N.A. : Honeywell takes safety very seriously. These new molecules are subjected to extensive toxicity tests. The purpose of the toxicity tests is to evaluate a compound's potential hazards and determine acceptable exposure levels that will not have unfavourable, lasting, or irreversible effects on human beings and the environment.

There are industry standards that cover safety, such as ISO 5149 and the EN 378 standard. Refrigerants are divided into two toxicity classes. Class A for low toxicity refrigerants and Class B for for higher toxicity. The two main molecules HFO 1234yf and HFO 1234ze are both Class A, and mixtures containing these molecules will also be Class A.

Many questions have been raised about the flammability of these new products. What can you tell us about this?

N.A. : Since ammonia ignites between 100 and 300mJ, and the minimum ignition energy of hydrocarbons is less than 1mJ, these products are classified as flammable.

For the first two HFO molecules available, the flammability characteristics have been measured. It has been found that HFO-1234ze(E) is entirely non-flammable at ambient temperatures below 30C.

The minimum ignition energy of HFO-1234yf is between 5000 and 10000mJ, which is much higher than for R-32, which ignites between 30 and 100mJ. As a result, the safety classification of refrigerants in accordance with the ASHRAE 34 standard and the ISO 817 standard has been modified to take into account the low flammability of the new fluids. A new class 2L was therefore created, for fluids with low flammability and a rate of burn below 10cm/s.

This is true of HFO 1234yf, which with a very unstable flame burning at 1.5 cm/s was approved by the automobile industry to replace R-134a..

Will installers need to change existing systems to use these new molecules?

N.A.

: Unlike CO2, HFOs have been developed to match the current characteristics of HFC refrigerants. We have identified alternatives for each HFC fluid. They can be used is existing equipment with little or no modification..

Will investment be high to convert HFC installations over to HFO fluids?

N.A. : As I said, these new fluids were designed to be used in existing installations with little or no modification. This implies a minimal investment cost.

In concrete terms, what molecules are currently available, and for which refrigeration and air conditioning applications?

N.A. : Currently, three new pure fluids and several mixtures made from these molecules are available.
SolsticeTM yf, with its characteristics similar to those of R-134a, can be used in current R-134a applications, taking into account its A2L classification. At the moment it is mainly used in automobile air-conditioning. Solstice™ ze is another HFO to replace R-134a, with lower instant capacity but better efficiency. Many chillers have adopted this new HFO SolsticeTM ze. Even the Turbocor compressor has been approved to work with this fluid.

When will HFOs be available on the market for other applications?

N. A.

: Solstice™ yf and Solstice™ ze are available. Solstice™ yf is available in limited quantities for the automobile industry, unlike SolsticeTM ze which is available without restrictions. The various HFO-based mixtures are in development, but are already available for partners who wish to conduct tests. We are now in the process of evaluating these mixtures with multiple OEMs, both for refrigeration and air-conditioning applications. These mixtures will be available in 2013.

Finally, what feedback has been received from using these new molecules?

N.A

. : The feedback from Solstice™ ze used in chillers has been very positive. This is because measurements have shown a better COP compared to R-134a. Multiple compressor technologies have been approved with this fluid. The Turbocar centrifuge from Danfoss is also available for these applications. The trend is clear: future chillers will be loaded with 1234ze.

Mélange HFO Solstice™ pour utilisation à moyenne ou haute pression