Crankcase heater systems and methods for variable speed compressors
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Solution Overview
Problem
Compressors face issues with 'cold starting' due to low temperature lubricant viscosity, leading to potential damage and decreased performance, as existing crankcase heaters operate inefficiently and wastefully by maintaining constant power even when not required.
Innovation Solution
A variable frequency drive system that controls the electric motor's stator to heat the compressor only when necessary, using temperature sensors to determine the required power and maintain a desired lubricant temperature, eliminating the need for additional heating elements and optimizing energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant power crankcase heater is used to heat the compressor, then the lubricant temperature is maintained above the threshold to prevent 'cold starting', but energy is wasted by heating continuously even when not required
Solution Approach 1:
The heater power is made dynamic rather than constant. The controller adjusts the heater power level based on real-time temperature measurements from sensors, increasing power when temperature drops below thresholds and reducing or eliminating power when thresholds are maintained, thus preventing energy waste while ensuring reliability
Solution Approach 2:
A feedback control system is implemented where temperature sensors continuously monitor the lubricant and crankcase temperatures, and the controller uses this feedback information to adjust the heater power output accordingly, creating a closed-loop system that optimizes energy usage while maintaining reliable operation
Solution Approach 3:
The heater power parameter is changed dynamically based on temperature conditions. The system transitions from a fixed power mode to a variable power mode where the heater output is adjusted according to the measured temperature parameters, allowing the system to adapt to varying thermal conditions and minimize energy consumption
2Temperature
If additional heating elements are added to the crankcase, then the heating capability is improved, but the device complexity increases
Solution Approach 1:
The motor stator is given a dual function: it serves as both the motor component for driving the compressor and as a heating element when the compressor is off. By utilizing the existing stator's electrical resistance for heating purposes, the system achieves improved heating capability without adding separate heating elements, thus maintaining simplicity
Solution Approach 2:
The motor stator serves itself by providing heating functionality as an inherent property of its electrical resistance. Rather than requiring separate dedicated heating elements, the stator's existing structure and material properties are utilized for heating, eliminating the need for additional components and reducing system complexity
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
The system efficiently maintains lubricant temperature above a threshold to prevent 'cold starting' while minimizing energy waste, enhancing compressor performance and extending bearing lifetimes by heating only as needed.
Implementation Method 1
supplies electric current to a stator of the electric motor in the off state to heat the compressor
Data Source
AI summary
A system includes a compressor having a shell housing a compression mechanism driven by an electric motor in an on state and not driven by the electric motor in an off state. The system also includes a variable frequency drive that drives the electric motor in the on state by varying a frequency of a voltage delivered to the electric motor and that supplies electric current to a stator of the electric motor in the off state to heat the compressor.