FEATURE HVAC SYSTEMS
HOW TO SOLVE THE CHALLENGES OF USING NATURAL REFRIGERANTS IN COOLING SYSTEM DESIGN
William Bentley from Sensata Technologies explores how the use of natural refrigerants are on the rise, creating a new set of challenges for cooling system design
E
volving government mandates dictate that equipment manufacturers migrate
to using chemicals that do not adversely impact the environment. In the refrigeration/cooling arena, this means that manufacturers are replacing the old classes of chemical refrigerants that emit potent greenhouse gases, such as hydrofluorocarbons (HFCs) hydrochlorofluorocarbons (HCFCs), and chlorofluorocarbons (CFCs), with less damaging, green refrigerants that do not deplete the ozone layer and have low impact on global warming. These alternative types of 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, these government regulations bring new challenges, not only for selecting the best type of refrigerant for the given application, but also for selecting components that can handle the specific refrigerant’s technical challenges and performance characteristics. The last five years have shown
significant progress in this evolution as countries phase out the use of environmentally harmful synthetic refrigerants. The U.S. has already banned R22 (the halocarbon compound CHClF2 monochlorodifluoromethane), an ozone depleting refrigerant, from being used for air conditioning and moved to the next generation of R410A. While R410A is still not a natural refrigerant, it is an important first step towards a cleaner, greener direction. Some natural refrigerants are more
efficient for air conditioning while others are more efficient for refrigeration. It is somewhat surprising then that Propane R290, which is a higher efficiency refrigerant, is being used in both markets. Usage seems to vary by geography in its application. In Asia, R290 is being used
12 WINTER 2017 | ENERGY MANAGEMENT
significantly for air conditioning applications while in the U.S. and Europe, it is being used primarily in refrigeration applications.
OZONE DEPLETION POTENTIAL (ODP) Ozone depletion potential (ODP) is a measure of the relative amount of damage a substance can cause to the ozone layer. UV radiation from sunlight causes the release of chlorine in CFCs and HCFCs into the atmosphere, which then damages the ozone. Natural refrigerants, on the other hand, have an ODP of zero, meaning that they will not have any depleting effect on the ozone layer if they escape the system. Global warming potential (GWP) is a
relative measure of how much heat a greenhouse gas traps in the atmosphere. The lower the GWP, the better a substance is for the environment. GWP compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide. A specific GWP is calculated over a time interval, typically 20, 100, or 500 years. One of the biggest
Figure 1:
sensata-natural- refrigerants-cooling- system-design
challenges of natural hydrocarbon refrigerants is flammability. To prevent a spark from accidently causing ignition of hydrocarbon refrigerants, Sensata has built extra safety into their pressure switches with a sealed design that ‘seals the spark’ inside by isolating the specific pressure media (R290) from the electrical switch assembly. Each switch is manufactured with a hermetic seal around the gas path as well as a sealant around the electrical connections. The electrical switch connections signal back to the system whether the switch is open or closed. This safety design completely eliminates the potential for explosion by stopping the gas from entering the electrical switch compartment where the arcs can be generated during contact make or break operations. In researching the effects of natural
refrigerants on their systems, OEMs need to know if the pressure switch has been tested with the specific refrigerant that they are planning to use. For R290 use, they need to know what the maximum current level of the switch is that prevents the arc from igniting the refrigerant, and whether it meets the required pressure actuation point and switch point. For C02
systems, operating “To stay at the forefront of the green
cooling trend, industry leaders are developing
specialised components that are compatible with the latest common refrigerants..."
with twice the pressure of conventional systems, the big concern is burst pressure. What kind of high pressure can it withstand? How long will it reliably operate under sustained high pressure environments? Given the changes in refrigerants being
used around the world, it is clear that natural refrigerants are important to the future landscape of the industry. As OEMs research their choices, component manufacturers must meet the design challenges posed by these non-synthetic refrigerants in order to optimise safety and efficiency.
Sensata Technologies
www.sensata.com e:
info-sse@list.sensata.com
/ ENERGYMANAGEMENT
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