Test chamber and method for controlling
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Solution Overview
Problem
Current climate test chambers using carbon dioxide as a refrigerant are limited by high costs, complex structures, and large size, making them unsuitable for small systems due to high volumetric cooling capacity and transcritical operation pressures, which also lead to frequent compressor switching and reduced compressor lifespan.
Innovation Solution
Incorporating an internal heat exchanger and medium-pressure bypass in the cooling circuit, allowing for adjustable refrigerant flow and operating states between subcritical and transcritical, reducing refrigerant flow through the expansion valve and utilizing a second expansion valve to redirect refrigerant for temperature control, enabling efficient temperature regulation and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If carbon dioxide is used as refrigerant in a cooling circuit, then environmental friendliness and cost are improved, but the system requires high pressure range up to 120 bar during transcritical operation, making components expensive and the design complex
Solution Approach 1:
The cooling circuit is segmented into multiple independent components (low-pressure compressor, high-pressure compressor, internal heat exchanger, expansion valve, gas cooler) that can be optimized and controlled separately. This segmentation allows the system to manage the high pressure range requirements of CO2 refrigeration through staged compression and heat exchange, reducing the complexity burden on any single component while maintaining overall system efficiency
Solution Approach 2:
The system dynamically switches between subcritical and transcritical operating modes based on cooling demand. The control device adjusts the operation of compressors and expansion valve to maintain optimal pressure and temperature conditions, allowing the system to adapt to varying load requirements without requiring permanently oversized components designed for maximum pressure operation
2Productivity
If carbon dioxide with very high volumetric cooling capacity is used, then cooling performance is improved, but the system becomes unsuitable for small test chambers due to large installation space requirements
Solution Approach 1:
The internal heat exchanger is nested within the test chamber volume, utilizing the chamber's internal space for heat exchange functions. The cooling circuit components are integrated into a compact arrangement where the internal heat exchanger serves dual purposes: cooling the refrigerant and utilizing chamber space efficiently, thereby reducing the external installation footprint while maintaining high cooling capacity
Solution Approach 2:
The system changes operating parameters (pressure, temperature, refrigerant flow rate) dynamically to match the cooling demand of small test chambers. By adjusting the expansion valve opening and compressor operation, the system delivers appropriate cooling capacity for small volumes without requiring permanently oversized components, thus reducing installation space requirements
3Adaptability or versatility
If compressors are frequently switched on and off to adjust cooling capacity, then cooling control flexibility is improved, but compressor service life is reduced
Solution Approach 1:
The control device dynamically adjusts compressor operation and expansion valve opening to match cooling demand continuously, avoiding frequent on/off switching. The system modulates refrigerant flow and compression rate to provide variable cooling capacity while keeping compressors running, thereby extending their service life while maintaining cooling control flexibility
Solution Approach 2:
The compressors operate continuously with adjusted parameters rather than being frequently switched on and off. The internal heat exchanger and expansion valve work continuously to regulate refrigerant flow and temperature, providing continuous cooling control without interrupting compressor operation, thus maintaining both adaptability and 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 configuration allows for efficient temperature control in a compact and cost-effective manner, extending compressor lifespan by reducing frequent switching and enabling operation in smaller test chambers with adjustable cooling capacity and reduced thermal load.
Implementation Method 1
the internal heat exchanger is cooled on the intermediate-pressure side, and thus the refrigerant on the high-pressure side of the internal heat exchanger is cooled
Implementation Method 2
refrigerant is metered from the high-pressure side to the medium-pressure side via the internal heat exchanger by means of a second expansion valve
Implementation Method 3
a low-pressure compressor and a high-pressure compressor following the low-pressure compressor in the direction of refrigerant flow
Implementation Method 4
a heat exchanger in the test chamber... to cool the air flowing through the duct or the test chamber
Data Source
Figure 1~2
AI summary
The invention relates to a method for conditioning air in a temperature-insulated test chamber that can be sealed off from the environment, and to a test chamber, in particular a climate chamber, for holding test specimens, wherein a temperature control device of the test chamber, comprising a cooling circuit (11) with carbon dioxide (CO2) as a refrigerant, a heat exchanger (12) in the test chamber, a low-pressure compressor (13) and a high-pressure compressor (14) following the low-pressure compressor in the direction of refrigerant flow, a gas cooler (15) and an expansion valve (17), is used to establish a temperature within a range of -20 °C to +180 °C within the test chamber, wherein the temperature in the test chamber is controlled and/or regulated by means of a control device of the test chamber, and wherein the cooling circuit has an internal heat exchanger (16).which is connected to a high-pressure side (21) of the cooling circuit downstream of the gas cooler and upstream of the expansion valve in the flow direction, wherein the internal heat exchanger is coupled to a medium-pressure bypass (22) of the cooling circuit, wherein the medium-pressure bypass is connected downstream of the internal heat exchanger or the gas cooler and upstream of the expansion valve on the high-pressure side, as well as upstream of the high-pressure compressor and downstream of the low-pressure compressor to a medium-pressure side (20) of the cooling circuit, wherein refrigerant is metered from the high-pressure side to the medium-pressure side via the internal heat exchanger by means of a second expansion valve (23).