Heat Medium Bypass Control to Prevent Freezing in Air Conditioning
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Solution Overview
Problem
Existing air-conditioning apparatuses for office buildings face issues such as refrigerant leakage into indoor spaces, high energy consumption due to long heat medium circulation paths, complex and costly installations, and the risk of heat medium freezing in zeotropic refrigerant systems.
Innovation Solution
An air-conditioning apparatus with a refrigerant circuit and a heat medium circuit that includes a bypass pipe to prevent refrigerant entry into heat exchangers when the heat medium temperature approaches freezing, reducing energy consumption and installation complexity by minimizing pipe connections and using a bypass to manage refrigerant flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a refrigerant is circulated up to an indoor unit, then heating or cooling can be performed directly, but refrigerant may leak into the indoor space
Solution Approach 1:
The system is divided into two separate circulation paths: a refrigerant circuit confined to the outdoor unit and a heat medium circuit that distributes thermal energy to indoor units. This segmentation prevents refrigerant from entering indoor spaces while maintaining heating/cooling functionality through the heat medium (water or antifreeze) that carries thermal energy from the outdoor unit to indoor units via heat exchangers.
2Object-affected harmful factors
If a heat medium is circulated through a long path from an outdoor unit to indoor units, then refrigerant leakage is prevented, but energy consumption increases
Solution Approach 1:
Multiple indoor units share a common heat medium circulation system with a single outdoor unit, merging their thermal requirements into one centralized heat source/sink. This reduces the total length of heat medium pipes compared to having separate systems for each indoor unit, thereby reducing conveyance power requirements while still preventing refrigerant leakage through the heat exchanger interface.
3Adaptability or versatility
If four water pipes are arranged between outdoor unit and indoor units for heat recovery chiller, then cooling and heating can be simultaneously supplied, but installation becomes complex
Solution Approach 1:
The heat medium circulation system serves multiple functions: it provides cooling during hot weather, heating during cold weather, and can operate in heat recovery mode where one indoor unit's waste heat is transferred to another indoor unit needing heating. This multi-functionality is achieved through a simplified two-pipe configuration (supply and return) with electronic expansion valves and four-way valves that redirect heat medium flow, eliminating the need for separate four-pipe installations for cooling and heating.
4Temperature
If the heat medium temperature drops to freezing point in zeotropic refrigerant system, then heat exchange efficiency improves, but heat medium may freeze
Solution Approach 1:
The system incorporates temperature sensors that continuously monitor the heat medium temperature in the heat exchangers. When the temperature approaches the freezing point of the heat medium (water or antifreeze), the control system automatically adjusts the electronic expansion valves to modify refrigerant flow rates, preventing the heat medium temperature from dropping below its freezing point. This feedback control maintains optimal heat exchange efficiency while preventing freezing damage.
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 solution improves safety, reduces energy consumption, and prevents heat medium freezing, making the system more efficient and easier to install while maintaining safety by controlling refrigerant flow and minimizing pipe connections.
Implementation Method 1
the heat exchangers related to heat medium exchange heat between the heat source side refrigerant and the heat medium
Implementation Method 2
the air-conditioning apparatus performs a heat medium anti-freezing operation that blocks entry of the heat source side refrigerant into the heat exchanger related to heat medium that functions as the evaporator, and causes the heat source side refrigerant to flow via the bypass pipe
Data Source
AI summary
When using at least one of heat exchangers related to heat medium that exchange heat between a heat source side refrigerant and a heat medium as an evaporator, in a case where an air-conditioning apparatus has detected, in the heat exchanger related to heat medium that functions as the evaporator, an evaporating temperature of the heat source side refrigerant which causes the temperature of the heat medium passing through this heat exchanger related to heat medium to become equal to or lower than a freezing temperature, the air-conditioning apparatus performs a heat medium anti-freezing operation by blocking entry of the heat source side refrigerant into the heat exchanger related to heat medium that functions as the evaporator, and causing the heat source side refrigerant to flow to a bypass pipe.