Ejector-Based Hot Gas Defrost for Dual-Temperature Cooling Systems
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Solution Overview
Problem
Existing cooling systems require large piping and a stepper valve to regulate pressure for hot gas defrost cycles, increasing system footprint and cost, and are inefficient due to frost and ice accumulation on low side heat exchangers.
Innovation Solution
A cooling system that performs hot gas defrost without a stepper valve by directing refrigerant from a medium temperature compressor discharge to low side heat exchangers, using a flash tank, medium and low temperature heat exchangers, and an ejector to mix and direct the refrigerant for defrosting, reducing the need for large piping and refrigerant volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hot gas defrost is implemented using existing systems with stepper valve and large piping, then defrosting capability is achieved, but system footprint and cost increase
Solution Approach 1:
The patent removes the stepper valve from the system, extracting this component entirely. Instead of using a stepper valve to control hot gas flow, the system uses the existing four-way valve and refrigerant pressure differential to achieve defrosting, thereby reducing system footprint while maintaining defrosting capability
Solution Approach 2:
The four-way valve is made multi-functional by using it for both normal refrigeration cycle operation and hot gas defrost control. The same valve that directs refrigerant flow during cooling also controls the hot gas flow during defrost, eliminating the need for separate defrost control components and reducing system footprint
2Reliability
If hot gas defrost is implemented using existing systems with stepper valve and large piping, then defrosting capability is achieved, but system cost increases
Solution Approach 1:
The patent removes the stepper valve, which is a costly component, from the system. By eliminating this expensive part and using existing components for defrost control, the system cost is reduced while maintaining effective defrosting capability
Solution Approach 2:
The system uses standard, readily available four-way valves and existing refrigerant piping instead of specialized expensive components like stepper valves. This approach uses simpler, more cost-effective components to achieve the same defrosting function
3Productivity
If frost and ice accumulate on low side heat exchangers, then cooling function is maintained initially, but heat exchange efficiency decreases
Solution Approach 1:
The system implements periodic defrost cycles where the four-way valve reverses refrigerant flow to send hot gas through the low-side heat exchangers. This periodic hot gas flow melts accumulated frost and ice, restoring heat exchange efficiency while maintaining continuous cooling operation
Solution Approach 2:
The system converts the harmful effect of hot refrigerant gas (which could cause high pressure issues) into a beneficial defrosting tool. By strategically directing this hot gas through the low-side heat exchangers during defrost cycles, the system uses what could be a problem as the solution to melt frost and ice, improving heat exchange efficiency
4Reliability
If stepper valve is used to increase pressure of hot gas for defrost, then defrosting effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent removes the stepper valve, the most complex pressure control component, from the system. Defrosting effectiveness is maintained by using the natural pressure differential between high-side and low-side refrigerant pressures, combined with four-way valve control, eliminating the need for complex stepped pressure regulation
Solution Approach 2:
The system uses its own existing refrigerant pressure differential to achieve defrosting without external pressure control devices. The high-side refrigerant pressure naturally provides sufficient pressure for hot gas flow during defrost, making the system self-sufficient and eliminating complex external control mechanisms
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 solution reduces the system's footprint, energy usage, and refrigerant amount, while maintaining effective defrosting capabilities, thereby lowering costs and improving efficiency.
Implementation Method 1
The ejector directs a mixture of the refrigerant from the first compressor and the refrigerant from the second compressor to the low temperature low side heat exchanger during a defrost cycle
Implementation Method 2
The mixture defrosts the low temperature low side heat exchanger
Implementation Method 3
The mixture defrosts the low temperature low side heat exchanger
Implementation Method 4
The flash tank receives the mixture
Data Source
AI summary
An apparatus includes a flash tank, a medium temperature low side heat exchanger, a low temperature low side heat exchanger, a first compressor, a second compressor, and an ejector. The flash tank stores a refrigerant. The medium temperature low side heat exchanger uses the refrigerant from the flash tank to cool a space proximate the medium temperature low side heat exchanger to a first temperature. The low temperature low side heat exchanger uses the refrigerant from the flash tank to cool a space proximate the low temperature low side heat exchanger to a second temperature that is lower than the first temperature. The first compressor compresses the refrigerant from the low temperature low side heat exchanger. The second compressor compresses the refrigerant from the medium temperature low side heat exchanger. The ejector directs a mixture of the refrigerant from the first compressor and the refrigerant from the second compressor to the low temperature low side heat exchanger during a defrost cycle. The mixture defrosts the low temperature low side heat exchanger. The flash tank receives the mixture.