Outdoor AC Unit Heater Power Limits for Flammable Refrigerants
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Solution Overview
Problem
Air-conditioning units using low-GWP refrigerants face the challenge of suppressing ignition at electric heaters when refrigerant leakage occurs, as these refrigerants are often flammable and pose a risk of ignition, especially when high electric power consumption is involved.
Innovation Solution
The air-conditioning unit incorporates a compressor and heat exchanger with an electric heater, where the electric power consumption of the heater is controlled to be within specific limits, and uses refrigerants like trans-1,2-difluoroethylene (HFO-1132(E)), trifluoroethylene (HFO-1123), and 2,3,3,3-tetrafluoro-1-propene (R1234yf) to maintain a low GWP and prevent ignition, even with refrigerant leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If low-GWP refrigerants (such as HFO-1132(E), HFO-1123, R1234yf) are used to reduce global warming potential, then the environmental performance is improved, but the refrigerants become flammable and pose ignition risk at electric heaters
Solution Approach 1:
The patent changes the electrical parameter (power consumption) of the heater from a conventional high value to a specifically controlled low value (≤300W, preferably ≤100W, more preferably ≤75W). This parameter change reduces the thermal energy available for ignition while maintaining the heater's functional effectiveness for its intended purposes (preventing refrigerant condensation, preventing drain pan freezing, etc.).
Solution Approach 2:
The patent converts the potential harm of refrigerant leakage and flammability into a benefit by carefully selecting heater power levels that are sufficient to perform heating functions but insufficient to cause ignition of leaked refrigerant. The heater becomes a controlled heat source that prevents other problems (condensation, freezing) without creating the ignition hazard.
2Reliability
If electric heater power consumption is reduced to ≤300W to suppress ignition risk, then safety is improved, but the heating function may become insufficient
Solution Approach 1:
The patent identifies and optimizes multiple parameters simultaneously: heater power consumption (≤300W, preferably ≤100W, more preferably ≤75W), heat exchanger internal volume (≥0.4L and <3.5L, preferably ≥1.4L and ≤3.5L), and refrigerant charge amount (50g-150g). These combined parameter changes ensure that the reduced heater power is sufficient for its intended functions while maintaining safety.
Solution Approach 2:
The heater is designed to provide partial heating action rather than full heating capacity. The heater's power is intentionally limited to what is necessary for specific preventive functions (preventing condensation, preventing freezing) rather than providing complete space heating, which is achieved through the combined system of heat exchanger and refrigerant cycle.
3Productivity
If heat exchanger internal volume is increased to ≥0.4L to ensure sufficient refrigeration capacity with single fan, then cooling performance is improved, but the device size and complexity increase
Solution Approach 1:
The patent optimizes the heat exchanger internal volume to a specific range (≥0.4L and <3.5L, preferably ≥1.4L and ≤3.5L) that provides sufficient refrigeration capacity while maintaining a compact form factor suitable for single-fan operation. This parameter optimization balances performance and size constraints.
Solution Approach 2:
The heat exchanger is designed to serve multiple functions: primary heat exchange for cooling/heating, and secondary function as a refrigerant storage reservoir. This multi-functionality allows the system to achieve sufficient refrigeration capacity with a compact heat exchanger volume by utilizing the refrigerant charge stored in the heat exchanger itself during high-demand periods.
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 effectively suppresses ignition at the electric heater while maintaining a low GWP and ensuring the refrigerant's performance is equivalent to that of R410A, with a sufficient refrigeration capacity and coefficient of performance, and is classified under lower flammability standards.
Implementation Method 1
a compressor configured to compress refrigerant containing 1,2-difluoroethylene
Implementation Method 2
a heat exchanger configured to exchange heat between outside air and refrigerant containing 1,2-difluoroethylene
Data Source
AI summary
An air-conditioning unit that is able to suppress ignition at an electric heater even when leakage of refrigerant occurs while a low-GWP refrigerant is used is provided. In an outdoor unit (20) including a casing (60), a compressor (21) provided inside the casing (60) and configured to compress refrigerant containing 1,2-difluoroethylene, and a drain pan heater (54) provided inside the casing (60), an electric power consumption of the drain pan heater (54) is lower than or equal to 300 W.