Evaporator Inlet Sensor Calibration Without Compressor Flooding
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Solution Overview
Problem
Existing methods for calibrating temperature sensors in vapor compression systems, such as refrigeration and air conditioning systems, often require flooding the evaporator, which can lead to liquid refrigerant entering the compressor and causing damage, and do not allow for accurate calibration during system operation.
Innovation Solution
A method involving alternatingly increasing and decreasing the opening degree of the expansion device in the vapor compression system to monitor temperatures at the evaporator inlet and outlet, calculating a calibration value based on these measurements to adjust the temperature sensor readings, ensuring accurate and reliable measurements without flooding the evaporator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the evaporator is flooded to calibrate temperature sensors, then calibration accuracy is improved, but liquid refrigerant may enter the suction line and reach the compressor causing damage
Solution Approach 1:
The expansion valve opening is alternated between maximum and minimum positions in periodic cycles during calibration. This periodic action creates repeated flooding and non-flooding states, allowing temperature calibration to be performed by analyzing temperature differences across multiple cycles without maintaining continuous flooding that would cause liquid refrigerant to reach the compressor.
Solution Approach 2:
Temperature measurements from sensors at the evaporator inlet and outlet are continuously monitored during the periodic cycles. The calibration process uses feedback from these temperature measurements to determine the relationship between sensor readings and actual temperatures, enabling accurate calibration without requiring the system to remain in a flooded state.
2Measurement precision
If traditional calibration methods are used, then temperature sensor accuracy is improved, but the calibration process requires system shutdown and evaporator flooding
Solution Approach 1:
The calibration is performed during normal system operation by periodically alternating the expansion valve opening. This allows the system to remain productive while the calibration process occurs in the background, eliminating the need for system shutdown that would be required by traditional calibration methods.
Solution Approach 2:
The calibration process maintains continuous refrigerant flow and system operation throughout the procedure. The periodic alternation of the expansion valve occurs within the continuous operating cycle, ensuring that cooling or heating functionality is not interrupted while temperature sensors are being calibrated.
Data Source
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AI summary
A method for calibrating a temperature sensor (6) arranged in a vapour compression system (1) is disclosed. The opening degree (9) of an expansion device (3) is alternatingly increased and decreased. Simultaneously a temperature (10) of refrigerant entering the evaporator (4) and a temperature (11) of refrigerant leaving the evaporator (4) are monitored. For each cycle of the opening degree (9) of the expansion device (3), a maximum temperature, T1, max, of refrigerant entering the evaporator, and a minimum temperature, T2,min, of refrigerant leaving the evaporator are registered. A calibration value, ΔΤ1, is calculated as ΔΤ1= C-(T2, min- T1, max) for each cycle, and a maximum calibration value, among the calculated values is selected. Finally, temperature measurements performed by the first temperature sensor (6) are adjusted by an amount defined by ΔT1, max.