Dynamic Compressor Startup Pressure Ratio Using Temperature Sensing
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Solution Overview
Problem
Dynamic compressors face challenges in accurately determining the pressure ratio during startup due to the discharge check valve preventing high-pressure refrigerant from reaching the pressure sensor, making it difficult to avoid operating in surge or choke conditions.
Innovation Solution
A system and method that utilize temperature sensors in the evaporator and condenser to estimate the start-up pressure ratio of the dynamic compressor, allowing the controller to set a speed setpoint within a safe operating envelope by calculating the pressure ratio from heat transfer fluid temperatures, thereby controlling the compressor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pressure sensors are used to measure pressure ratio during compressor startup, then measurement precision is improved, but the discharge check valve prevents high pressure refrigerant from reaching the pressure sensor, making accurate measurement impossible
Solution Approach 1:
The patent uses temperature sensors as intermediary measurement points. Instead of directly measuring pressure at the compressor discharge (which is blocked by the check valve), the system measures temperatures in the evaporator and condenser, then uses these temperature readings to infer the pressure ratio through thermodynamic relationships. This intermediary approach bypasses the measurement obstacle created by the check valve.
Solution Approach 2:
The patent replaces direct mechanical pressure measurement with a thermal-based measurement system. By substituting pressure sensors with temperature sensors and using thermodynamic calculations, the system achieves pressure ratio determination without requiring direct access to high-pressure refrigerant, thus avoiding the limitation imposed by the discharge check valve.
2Loss of time
If the compressor operates without accurate pressure ratio information during startup, then the startup routine can begin immediately, but the compressor may operate in surge or choke regions, reducing reliability
Solution Approach 1:
The patent performs preliminary determination of the pressure ratio using temperature-based measurements before the compressor enters unsafe operating regions. By calculating the pressure ratio from evaporator and condenser temperatures at the start of the startup routine, the system establishes safe operating parameters in advance, allowing the compressor to be immediately started without delay while ensuring it operates within safe margins.
Solution Approach 2:
The system continuously monitors temperatures in the evaporator and condenser during startup and uses this feedback to determine the actual pressure ratio. This real-time feedback allows the control system to adjust the speed setpoint dynamically, ensuring the compressor remains within the safe operating envelope throughout the startup transient, thereby preventing surge or choke conditions.
3Productivity
If the compressor speed is increased to reduce startup time, then productivity is improved, but the risk of operating in surge or choke regions increases, worsening reliability
Solution Approach 1:
The patent implements dynamic speed control during startup by continuously adjusting the speed setpoint based on the real-time pressure ratio determined from temperature measurements. Rather than using a fixed high speed that might cause surge or choke, the system dynamically adapts the compressor speed to match the actual operating conditions, allowing aggressive startup when safe and conservative operation when conditions require it, thus achieving both fast startup and high reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the dynamic compressor to limit its operation time outside a safe operating envelope during startup, improving reliability by accurately determining the pressure ratio without direct pressure measurements.
Implementation Method 1
The evaporator includes a first working fluid path and a first heat transfer fluid path thermally coupled thereto. The condenser includes a second working fluid path and a second heat transfer fluid path thermally coupled thereto.
Implementation Method 2
The evaporator includes a first working fluid path and a first heat transfer fluid path thermally coupled thereto. The condenser includes a second working fluid path and a second heat transfer fluid path thermally coupled thereto.
Data Source
AI summary
A controller for a system having an evaporator, a condenser, and a dynamic compressor includes a processor and a memory, which stores instructions that program the processor to determine a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator, determine a first pressure at a first working fluid path based on the first heat transfer fluid temperature, determine a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser, determine a second pressure at a second working fluid path based on the second heat transfer fluid temperature, calculate a pressure ratio of the compressor from the first and second pressures, determine a speed setpoint of the compressor based on the pressure ratio, and operate the compressor at the speed setpoint to compress a working fluid until a condition is met.