Use of Pressure Transducers to Control Superheat in Clean Room Systems

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Methods to Control Superheat

A clean room is a controlled environment with a low level of contaminants such as dust particles, microbes, and chemical vapors. Products that are very sensitive to contamination, such as semiconductors or pharmaceuticals, for example, must be manufactured in clean rooms.

A clean room has a controlled level of contamination typically measured by the number of particles per cubic meter of a given particle size. Clean rooms are maintained under positive pressure and have high-efficiency air conditioning systems to produce a laminar air flow throughout the room to maximize filtration of particles.

Clean room HVAC systems use a refrigeration cycle just like other air conditioning systems. The equipment required for a refrigeration cycle includes an evaporator, a compressor, a condenser, an expansion valve, and system monitoring devices such as temperature and pressure transducers. The refrigeration cycle can be modeled as a seven-step process:

  1. Cool, low-pressure gaseous refrigerant enters the compressor
  2. Hot, high-pressure gaseous refrigerant leaves the compressor and enters the condenser
  3. Hot, high-pressure gaseous refrigerant in the condenser releases heat externally
  4. Warm, high-pressure liquid refrigerant exits the condenser coil and enters the expansion valve
  5. The expansion valve controls the amount of liquid refrigerant entering the system
  6. Cold, low-pressure liquid refrigerant absorbs heat from inside to cool the internal environment
  7. Refrigerant exits the evaporator as a cool, low-pressure gas, and the cycle is repeated

Minimization of the superheat in refrigeration cycles has emerged as a relatively easy method to significantly increase the efficiency of air conditioning units. Superheat can be defined in the context of the HVAC industry as the temperature difference between the boiling temperature of the refrigerant and the actual temperature of the refrigerant as it exits the evaporator coil.

The overall goal is to minimize the superheat phenomenon for maximum efficiency. This requires accurate pressure and temperature measurement with electronic temperature sensors and pressure transducers at the evaporator coil outlet and the compressor inlet.

Pressure and temperature measurement allows for designed control of the flow rate of refrigerant so as to maximize the efficiency of the air conditioning unit. When greater cooling is required, an electronic expansion valve increases the refrigerant flow rate. When less cooling is needed, the expansion valve decreases the refrigerant flow rate. This control process is made possible through accurate, dependable temperature and pressure measurement.

Pressure Transducer Applications to Control Superheat in Clean Rooms

Pressure transducers are used for controlling superheat in air-conditioning and refrigeration systems. They are used in several clean room HVAC measurement applications including:

  • Compressor Inlet Pressure
  • Compressor Inlet Temperature (with WIKA Electronic Temperature products)
  • Evaporator Coil Outlet Pressure
  • Evaporator Coil Outlet Temperature (with WIKA Electronic Temperature products)
  • Expansion Valve Flow Rate Monitoring

Pressure transducers used clean room applications need to be compatible with common HVAC refrigerants and be able to measure over a wide range of pressure. Information about the pressure at the evaporator outlet and the compressor inlet is provided by pressure transducers, and this information is used to control the flow of refrigerant at the expansion valve to minimize superheat and maximize air conditioner efficiency. The WIKA Refrigeration and Air Conditioning Pressure Transmitters R-1 and AC-1 are specifically designed for performance, reliability, and compatibility with all common refrigerants in clean room HVAC and refrigeration systems applications.


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