PRESSURE SWITCHES
William Bentley of Sensata Technologies takes a look at the part pressure switches play in the move away from high GWP refrigerants.
Cool runnings G
overnments are increasingly mandating equipment manufacturers to migrate to using chemicals that do not adversely impact the environment. In the refrigeration and cooling arena, this means replacing the old classes of chemical refrigerants with less damaging, ‘green’ refrigerants that do not deplete the ozone layer and have a low impact on global warming. These alternative refrigerants are naturally occurring, non-synthetic substances that can be used as cooling agents in refrigerators and air conditioners and include hydrocarbons (propane, butane, and cyclopentane), CO2
, ammonia, water and air.
For OEMs, building refrigeration and air conditioning systems, new regulations bring new challenges, not only for selecting the appropriate refrigerant, but also for selecting components that can handle the specific refrigerant’s technical challenges and performance characteristics. So, what are the options available, and how do you choose?
Refrigerant options
There are two important criteria in measuring whether or not a refrigerant is environmentally acceptable: one is its ozone depletion potential (ODP); the second is its global warming potential
(GWP). ODP is a measure of the relative amount of damage a substance can cause to the ozone layer. GWP is a relative measure of how much heat a greenhouse gas traps in the atmosphere. Current HFC refrigerants R404a and R134a have extremely high GWP values – 3,922 and 1,430 respectively – that are harmful to the environment. By comparison, Propane R290 Hydrocarbon, which is a newer, natural refrigerant version of R404A, has an extremely low GWP of only 3.
At this time, most of the industry has transitioned away from R404A and has moved to R134A, but there are even greater benefits of transitioning to R290 in the future.
Hydrocarbons
Many of the new generation of natural refrigerants are hydrocarbon based, and include Propane (R290); Isobutane (R600a), typically for use in small capacities like appliances; and R32, a blend of R290 Propane and another refrigerant. Propane R290’s thermodynamic properties are superior to both the old HFC refrigerants R134a and R404a. Additionally, its heat capacity is approximately 90% greater than R134a and 140% greater than R404a.
These characteristics allow R290 to absorb
more heat at an accelerated rate, resulting in higher device efficiency, with faster temperature recovery and lower energy consumption. The downside to this new generation of hydrocarbon refrigerants is that they are highly flammable, and require different and safer technologies for refrigeration and cooling systems and components.
operates at almost twice the pressure of hydrocarbons in a typical air conditioning system, making it much more difficult to manage. On the other hand, CO2
Carbon dioxide CO2
has a GWP of only 1, whereas
hydrocarbons have three times more GWP. Ammonia
Ammonia measures zero for both ODP and GWP and breaks down rapidly. The challenge is that its alkalinity is extremely corrosive, so components used in applications require careful consideration of material compatibility.
Regardless of the refrigerant you choose, every option comes with its own set of challenges for OEMs and component manufacturers to overcome, not least in the types of pressure switches and sensors that can be used, and how they are designed and tested in turn.
22 January 2018
www.acr-news.com
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