Compressor discharge control on a transport refrigeration system
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Refrigeration systems face challenges in controlling compressor discharge superheat, particularly at high ambient temperatures, leading to excessive compressor discharge temperatures that can cause lubricant breakdown and compressor failure, and existing methods like using a quench valve increase system complexity and reduce efficiency.
Innovation Solution
A process and system that monitor ambient and evaporator return air temperatures, calculate evaporator superheat, and adjust the expansion valve to control compressor discharge temperature without injecting liquid refrigerant, using a controller to maintain desired superheat levels and simplify system design by eliminating the quench valve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a quench valve is used to control compressor discharge temperature, then compressor discharge temperature is reduced, but system complexity increases
Solution Approach 1:
The patent removes the quench valve component entirely from the system. Instead of using a valve to bypass liquid refrigerant to the compressor suction, the system relies on the expansion valve and evaporator to control refrigerant flow and temperature, thereby eliminating the source of complexity while still achieving temperature control.
Solution Approach 2:
The expansion valve is made to perform multiple functions: it not only controls the refrigerant flow rate to the evaporator but also indirectly controls the compressor discharge temperature by regulating the evaporator's refrigerant charge and heat exchange efficiency. This multi-functionality eliminates the need for a separate quench valve.
2Temperature
If a quench valve is used to control compressor discharge temperature, then compressor discharge temperature is reduced, but system efficiency decreases
Solution Approach 1:
By removing the quench valve, the patent eliminates the energy loss associated with bypassing liquid refrigerant around the evaporator. All refrigerant flows through the evaporator, maximizing heat exchange efficiency and preventing the energy waste that occurs when liquid refrigerant is dumped directly into the compressor suction.
3Temperature
If a quench valve is used to control compressor discharge temperature, then compressor discharge temperature is reduced, but control precision deteriorates
Solution Approach 1:
The system uses a temperature sensor to monitor compressor discharge temperature or evaporator outlet temperature and feeds this information back to the controller. The controller adjusts the expansion valve position based on this feedback to maintain precise control of refrigerant flow and evaporator superheat, thereby indirectly but precisely controlling compressor discharge temperature without the instability of quench valve control.
4Productivity
If suction modulation is used to reduce capacity, then capacity is reduced, but compressor discharge temperature increases
Solution Approach 1:
The system changes the control parameter from direct capacity modulation to evaporator superheat control. By monitoring and controlling the superheat at the evaporator outlet, the system ensures that the refrigerant entering the compressor is at the correct temperature, thereby preventing excessive discharge temperature even when operating at reduced capacity through suction modulation.
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 effectively controls compressor discharge superheat, reduces system complexity, enhances efficiency, and prevents compressor failure by stabilizing the refrigerant flow and temperature, while maintaining a stable and efficient operation without the need for additional control parameters or plumbing.
Implementation Method 1
an expansion valve coupled to the inlet of the evaporator
Implementation Method 2
an evaporator for drawing heat out of the box by drawing or pushing return air across refrigerant-containing coils within the evaporator
Implementation Method 3
a compressor to pressurize refrigerant vapor
Implementation Method 4
a condenser to cool the pressurized vapor from the compressor, thereby changing the state of the refrigerant from a gas to a liquid
Data Source
Figure 1
Figure 2
Figure 3
AI summary
In a refrigeration system having a compressor, a condenser, an evaporator, and a controller for controlling an expansion valve, a process for controlling compressor discharge during a cooling cycle includes monitoring a compressor discharge temperature, operating the expansion valve in a base mode wherein the expansion valve is controlled in response to a difference between actual superheat and desired superheat of the evaporator; and controlling the expansion valve in response to a difference between a set point and a compressor discharge parameter when the ambient air temperature, the return air temperature and the compressor discharge temperature meet respective limits.