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Answering the Question: Which Process Gauge Should I Choose?

Answering the Question: Which Process Gauge Should I Choose?

Does operating your plant’s refrigeration and HVAC systems involve significant electricity expenses? If so, WIKA’s R-1 pressure transmitter, when used in conjunction with a PLC-based control system, can significantly reduce the energy these systems consume.

Permanently installed pressure transmitters simplify monitoring the performance of your system and identifying potential problems. Figures 1 and 2 show an HVAC system and a refrigeration unit where R-1 pressure transmitters would be used.

　figure 1 (HVAC)     figure 2 (refrigeration)

 

A Typical Refrigeration Cycle

What happens during a typical refrigeration cycle, and when do the WIKA pressure transmitters come into play? A typical refrigeration cycle involves four steps:

  • Step 1: Beginning at the compressor, the refrigerant is compressed and leaves the compressor as a high temperature, high pressure gas.
  • Step 2: The hot refrigerant enters the condenser, where it is cooled by fan-forced air; then the refrigerant leaves the condenser as a warm liquid and continues on to the thermal expansion valve.
  • Step 3: The expansion valve meters the proper amount of refrigerant into the evaporator.
  • Step 4: The sudden pressure drop after the expansion valve converts the high pressure warm liquid refrigerant into a low pressure, cold gas. The cold gas absorbs ambient heat from fan-forced air passing through the evaporator. This ambient heat converts the refrigerant into a cool dry gas. From here the refrigerant reenters the compressor to be pressurized again, and the cycle repeats.

How the Pressure Transmitters Work

Pressure transmitters are used on the high pressure side and low pressure side of the compressor to control and optimize the cycle. A WIKA pressure transmitter located at or near the compressor outlet detects low refrigerant charge by monitoring the compressor’s discharge of pressure and temperature.

Output signals from the pressure transmitter are sent to a PLC. When a high discharge temperature with a low discharge pressure is detected, the PLC provides a low charge signal. The PLC can also receive additional input about operating characteristics of the refrigeration system, providing a more accurate low charge signal. The PLC is connected to a warning indicator and/or compressor so that the low charge signal activates the indicator and/or deactivates the compressor.

Potential Problems

Refrigeration systems often suffer from hidden equipment faults and inefficient controls. Undetected problems in a refrigeration system can result in high energy costs and shorter equipment life. By installing the proper monitoring equipment and adopting an efficient control strategy, costly problems such as these can be prevented:

  • If one of the filters becomes clogged, the restricted flow will create a pressure drop in the system, reducing efficiency and leading to unnecessary costs. Suction line filters keep the refrigerant clean and protect the compressor from taking in debris.
  • Hidden refrigerant leaks can eventually lead to a low refrigerant charge. A low charge can lessen efficiency and add to annual operating costs. Repairing leaks can remarkably boost performance.
  • In many refrigeration systems, head pressure stays at a fixed level to assure reliability over a wide range of temperatures. This also assists in maintaining sufficient refrigerant flow, freeze protection for the condenser, and an adequate pressure difference across expansion valves.　

Advantages of the WIKA Pressure Transmitters

The R-1 and the AC-1 pressure transmitters offer quite a few advantages:

  • The R-1 and the AC-1 pressure transmitters meet or exceed all test requirements, including resistance to high pressure steam jets, condensation, dust tightness, and icing. They were both tested using strict protocols, including the "Trane test" that was designed specifically for the refrigeration and HVAC industry.
  • Both pressure transmitters are produced on a modern, highly flexible production line which meets the highest quality standards. With these products, WIKA offers absolute reliability at a low cost, without compromising quality, safety, or affordability.
  • The R-1's offers high long-term leak resistance: A hermetically sealed weld binds the thin film sensor to the process connection.
  • On the process side of the R-1, the monolithic design of the sensor makes any additional seals unnecessary. Elimination of the soft sealing material also removes the need for additional material compatibility testing.
  • The R-1 pressure transmitter has proven condensation resistance, the most important requirement for refrigeration and HVAC applications.
  • The economical AC-1 pressure transmitter features a ceramic thick film sensor and provides a non-linearity of less than 1.0% B.F.S.L. and has no measurable hysteresis error.