CO2 Refrigeration Defrost Control with Intercooler Bypass
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Solution Overview
Problem
Conventional refrigeration apparatuses using carbon dioxide as a refrigerant face inefficiencies due to high pressure and temperature differences, leading to heat radiation losses and reduced defrosting capacity, especially when operating in supercritical ranges.
Innovation Solution
The refrigeration apparatus incorporates an intercooler bypass tube and a second-stage injection tube with a controllable valve to manage refrigerant flow, preventing heat radiation and maintaining high refrigerant temperature during defrosting, while using an economizer heat exchanger to enhance refrigerant flow rates and reduce frost formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If refrigerant is cooled in the outdoor heat exchanger to reduce temperature difference, then heat radiation loss is reduced, but the refrigerant temperature becomes too low for effective defrosting operation
Solution Approach 1:
The patent divides the heat exchanger into two independent circuits: a first circuit for cooling the refrigerant to reduce heat radiation loss, and a second circuit for heating the refrigerant to maintain defrosting capacity. This segmentation allows each circuit to perform its specific function without interfering with the other, resolving the contradiction between energy efficiency and defrosting reliability
Solution Approach 2:
The outdoor heat exchanger is designed to serve multiple functions simultaneously: it acts as both a cooler (to reduce heat radiation loss) and a heater (to maintain defrosting capacity). By incorporating both cooling and heating circuits within the same heat exchanger structure, the system achieves multi-functionality that resolves the contradiction between reducing energy loss and maintaining operational reliability
2Productivity
If high pressure is used in supercritical range to improve cooling efficiency, then cooling performance is enhanced, but temperature difference increases causing heat radiation loss
Solution Approach 1:
The patent changes the operating parameters of the refrigerant by introducing a dedicated cooling circuit that adjusts the refrigerant temperature independently from the pressure. By controlling the refrigerant temperature through this separate circuit while maintaining high pressure for cooling efficiency, the system reduces the temperature difference and thereby reduces heat radiation loss, resolving the contradiction between productivity and energy loss
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 configuration minimizes heat radiation losses, maintains high refrigerant temperature, and enhances defrosting capacity by optimizing refrigerant flow rates, thereby improving overall operating efficiency and defrosting performance.
Implementation Method 1
The intercooler is a heat exchanger integrated with the heat source-side heat exchanger and having air as a heat source, is provided to an intermediate refrigerant tube for drawing refrigerant discharged from the first-stage compression element into the second-stage compression element, and functions as a cooler of the refrigerant discharged from the first-stage compression element and drawn into the second-stage compression element
Implementation Method 2
The heat source-side heat exchanger is a heat exchanger having air as a heat source
Implementation Method 3
an expansion mechanism for depressurizing the refrigerant
Implementation Method 4
The compression mechanism has a plurality of compression elements, and is configured so that refrigerant discharged from a first-stage compression element, which is one of a plurality of compression elements, is sequentially compressed by a second-stage compression element
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The air-conditioning apparatus (1) uses carbon dioxide as a refrigerant and has a two-stage-compression-type compression mechanism (2), a heat source-side heat exchanger (4), an expansion mechanism (5), a usage-side heat exchanger (6), a switching mechanism (3), an intercooler (7), a bypass tube (9), and an injection tube (19). The air-conditioning apparatus (1) is configured so that when the switching mechanism (3) is switched to the cooling operation state to allow refrigerant to flow to the heat source-side heat exchanger (4) whereby a reverse cycle defrosting operation for defrosting the heat source-side heat exchanger (4) is performed, the refrigerant is caused to flow to the heat source-side heat exchanger (4), the intercooler (7) and the injection tube (19), and after the defrosting of the intercooler (7) is detected as being complete, the bypass tube (9) is used so as to ensure that the refrigerant does not flow to the intercooler (7) and so as to control that the opening degree of an injection valve (19a) of the injection valve (19) is increased.