Counter-Flow Heat Exchanger Control for Refrigerant Glide Matching
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Solution Overview
Problem
Conventional air-conditioning apparatuses using non-azeotropic refrigerant mixtures face inefficiencies due to temperature glide changes, leading to suboptimal heat exchange and energy savings issues, particularly when the temperature glide of the refrigerant and heat medium do not match, resulting in poor energy efficiency and heat exchange performance.
Innovation Solution
An air-conditioning apparatus with a refrigerant circuit and heat medium circuit connected through heat exchangers, featuring a controller that adjusts the temperature difference between heat medium detection points to maintain optimal counter-flow operation, allowing for efficient energy management and preventing heat medium freezing, even with non-azeotropic refrigerant mixtures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If counter-flow heat exchange is used with non-azeotropic refrigerant mixture, then heat exchange efficiency is improved, but temperature glide mismatch causes energy efficiency to deteriorate
Solution Approach 1:
The patent dynamically adjusts the water flow rate through the heat exchanger based on the refrigerant's temperature glide characteristics. By making the flow rate variable rather than constant, the system adapts to changing temperature differences between refrigerant and heat medium, maintaining optimal heat exchange efficiency throughout the temperature glide process
Solution Approach 2:
The patent changes the operating parameters of the heat exchanger, specifically adjusting the water flow rate in response to the refrigerant's temperature glide. This parameter adjustment ensures that the heat exchange process remains efficient despite the non-constant temperature difference caused by the non-azeotropic refrigerant mixture
2Temperature
If water flow rate is controlled to maintain constant supply temperature, then temperature stability is improved, but heat exchange efficiency deteriorates due to temperature glide mismatch
Solution Approach 1:
The patent transitions from static temperature control to dynamic flow rate control. Instead of maintaining constant water flow rate to achieve stable supply temperature, the system dynamically adjusts the flow rate to match the refrigerant's temperature glide, thereby maintaining both temperature stability and heat exchange efficiency
Solution Approach 2:
The patent implements a feedback control mechanism where the actual water supply temperature is measured and used to adjust the water flow rate. This closed-loop control ensures that the supply temperature remains stable while simultaneously optimizing the heat exchange efficiency by adapting to the refrigerant's temperature characteristics
3Productivity
If non-azeotropic refrigerant mixture is used, then refrigerant performance is improved, but circulation composition changes cause temperature glide variations leading to control complexity
Solution Approach 1:
The patent employs a self-adjusting control strategy where the system automatically adapts to changes in refrigerant circulation composition. By using the actual water supply temperature as feedback, the control system self-regulates the water flow rate without requiring complex sensors or algorithms to directly measure refrigerant composition changes
Solution Approach 2:
The patent focuses on controlling the water side parameters (flow rate) rather than directly monitoring or controlling refrigerant side parameters. This approach simplifies the control system by changing the controlled parameter from refrigerant composition to water flow rate, which is easier to measure and adjust while still achieving optimal heat exchange
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 apparatus improves energy efficiency and achieves energy savings by maintaining optimal temperature differences between refrigerant and heat medium flows, ensuring efficient heat exchange and preventing freezing, while accommodating non-azeotropic refrigerant mixtures.
Implementation Method 1
a refrigerant flowing through a refrigerant flow passage of a heat exchanger related to heat medium and a heat medium flowing through a heat medium flow passage of the heat exchanger related to heat medium are in counter flow relative to one another
Implementation Method 2
a heat medium flow control device, the heat medium flow control device being disposed in an inlet-side passage or outlet-side passage of the use side heat exchanger and controlling a flow rate of the heat medium circulating in the use side heat exchanger
Implementation Method 3
a first heat medium temperature detection device that is disposed in the inlet-side passage of the use side heat exchanger and that detects a temperature of the heat medium; a second heat medium temperature detection device that is disposed in the outlet-side passage of the use side heat exchanger and that detects a temperature of the heat medium
Implementation Method 4
to prevent freezing of the heat medium while keeping the temperature of the heat medium at the inlet of the heat exchanger related to heat medium constant
Data Source
AI summary
An air-conditioning apparatus includes a heat medium flow control device that adjusts the flow rate of a heat medium circulating in a use side heat exchanger, temperature sensors that are disposed in an inlet-side passage and an outlet-side passage of the use side heat exchanger and that detect temperatures of the heat medium, and a controller that controls the heat medium flow control device so that a temperature difference between a detection value of the temperature sensors is equal to a first target value. A refrigerant flowing through a refrigerant flow passage of the heat exchanger related to heat medium and a heat medium flowing through a heat medium flow passage of the heat exchanger related to heat medium are in counter flow relative to one another, and the controller changes the first target value in accordance with an operation state of a refrigerant circuit.