PRESSURE SWITCHES The largest range of high quality air conditioning systems
Solving the high-pressure chal- lenge
Every component in today’s systems is specified to certain operating conditions and pressure ranges. While CO2
is not combustible,
it operates at almost twice the typical pressure level in a modern air conditioning system. This necessitates the design of specialised components such as pressure switches to ensure reliable operation in applications where CO2
is used, which in turn affects product manufacturing.
Some beverage manufacturers, for example, are now requiring their beverage cooler vendors to switch from use of R134a HFC refrigerants to CO2
. These cooling units now need a pressure switch incorporated for safety.
In addition to causing safety challenges, CO2
also operates
less efficiently in comparison to hydrocarbons, requiring a greater amount of electricity to achieve the same heating or cooling power. Pressure switches required in
CO2
refrigeration systems protect against high pressure bursts or over-pressure situations that could cause the coils to rupture. When the pressure builds up to a certain point, the switch opens the electrical contact and turns off the compressor in the system. When the pressure drops to normal levels, it automatically switches the compressor back on.
In today’s market, however, even more safety is needed. Since switches are an electro-mechanical device, they can spark when the contacts make or break, and this, of course, can be dangerous. So what is the solution?
Sealing in safety for flammable refrigerants
To prevent a spark from accidentally causing ignition of hydrocarbon refrigerants, component designers such as Sensata have built extra safety into their pressure switches with a sealed design that ‘seals the spark’ inside by isolating the specific pressure media (Propane 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 to the system whether the switch is open or closed. This 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.
Whichever switches you choose, make sure they have been rigorously tested by an authorised external agency to withstand the conditions to which they are being exposed, and that they are compatible with the refrigerants with which they will be operating.
Pressure sensors and system feedback
In environments where system pressure information is required, a pressure sensor, as opposed to a switch, is required. A pressure switch is strictly for safety; in contrast, a pressure sensor provides safety information as data that can be used to increase energy efficiency in the system.
If the goal is to maintain pressure within a constant range, the pressure sensor can be used to regulate the system. For example, if the pressure goes outside the normal operating range in a supermarket, a pressure sensor could provide feedback that could activate the pressure switch or turn off the condenser system to bring the pressure within the specified range. In addition, the pressure sensor could notify a technician or maintenance organisation of the issue, for a more permanent fix. This could be a simple local alert or it could send an alert via the cloud to the appropriate person or company.
Many system OEMs could also use the data generated by a pressure sensor to understand how their HVAC and cooling systems function over time.
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www.acr-news.com January 2018 23
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