Does the HVAC pressure thermometer need to be recalibrated after long-term use

During HVAC system operation, HVAC pressure thermometers serve as crucial instruments for monitoring the refrigeration system's status, providing real-time readings of pressure and temperature. Over extended periods of operation, the accuracy of these readings directly impacts system commissioning, maintenance, and energy efficiency. Whether the equipment needs recalibration is a crucial maintenance issue.

Pressure Thermometer Calibration Principles
HVAC HVAC pressure thermometers typically employ mechanical (such as spring tubes and bimetallic strips) or electronic (such as thermocouples, thermistors, and pressure sensor chips). Regardless of the principle, measurement accuracy is limited by the physical stability of the sensing element, environmental conditions, mechanical wear, and electronic aging. The pressure component relies on the linear response of the pressure transmission system, while the temperature component relies on the material's thermal expansion coefficient or resistance variation. These physical properties can undergo subtle changes over time, leading to measurement errors.

Common Sources of Error After Long-Term Use: Spring Fatigue
Prolonged exposure to pressure shocks can cause spring tubes to fatigue and lose their deformation, resulting in inaccurate needle readings.

Bimetal Deformation
Under frequent temperature fluctuations, the thermal expansion differences between bimetallic materials can accumulate and cause deformation, gradually deviating from the true temperature reading.

Capillary Tube Aging

Prolonged exposure of the filling medium in the capillary tube to alternating high and low temperatures may cause leakage, volatilization, or performance degradation.

Dust and Corrosion

Installation environments with high humidity or dust may cause contamination inside the pressure thermometer head, affecting mechanical rotation or electronic component stability.

Electronic Component Drift

The sensor, circuit board, or amplifier components in electronic HVAC pressure thermometers may experience zero point drift or decreased sensitivity after years of use.

Calibration Frequency Recommendations

Most HVAC manufacturers and industry standards (such as ASHRAE and ISO 9001) recommend periodic calibration of HVAC pressure thermometers. The recommended intervals are as follows:

General commercial systems: Calibrate every 12 to 24 months

High-precision applications (such as laboratories or pharmaceutical cold chains): Calibrate every 6 to 12 months

Extreme environments or high-frequency use: Every 6 months or less

For newly installed systems or before initial commissioning, initial factory accuracy verification is recommended. Instruments that have not been calibrated for an extended period should be replaced or sent for inspection by a qualified service provider.

Calibration Methods and Equipment

Standard Pressure Source Comparison
Use a standard pressure pump and a standard pressure gauge to perform pressure point calibration, typically selecting low, medium, and high test points.

Constant Temperature Water Bath Comparison
Place a pressure thermometer and a standard thermometer simultaneously in a constant temperature bath and compare the readings at different temperature points.

Multifunctional Calibrator
This multifunctional temperature and pressure calibration instrument automatically outputs multiple ranges and records deviation data, suitable for electronic instruments.

Zero and Full-Scale Adjustment
Some mechanical instruments have rear-mounted fine-adjustment screws for manual zero and full-scale adjustment.

Calibration Criteria
National metrological verification regulations and manufacturer's technical manuals typically provide permissible error ranges. For example:
Pressure deviation should not exceed ±1.0% of full scale.
Temperature deviation should not exceed ±1°C or ±1% of the nominal accuracy grade. Items exceeding this permissible range should be marked as "unacceptable" and require adjustment or replacement.

Calibration Records and Compliance Management
HVAC systems are a core component of building energy efficiency and environmental control. Many industries require the recording of calibration certificates for critical measuring equipment. Especially in the pharmaceutical, food, and laboratory sectors, regulations (such as GMP and HACCP) mandate regular calibration of temperature and pressure monitoring equipment and the maintenance of traceability records.
Maintaining a comprehensive calibration documentation system, including calibration time, calibration units, error data, and processing results, effectively enhances system reliability.

Potential Risks of Non-Calibration:
Decreased System Energy Efficiency:
Measurement deviations can lead to misjudgment of control logic for expansion valves, compressors, condensers, and other components, increasing system energy consumption.
Safety Hazards:
Inaccurate high-pressure readings can mask the risk of excessive system pressure, potentially leading to expansion valve damage and compressor overpressure.
Troubleshooting Difficulties:
Relying on inaccurate data during troubleshooting can lead to misjudgment of system status, extending maintenance intervals.
Quality or Compliance Issues:
In industries such as food and pharmaceuticals that require precise temperature control, data distortion directly impacts product quality and compliance.