Cascade Refrigeration System Using Low-GWP HFO Blends to Prevent Frost
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Solution Overview
Problem
The refrigeration industry faces challenges in replacing high global warming potential (GWP) refrigerants with safe, efficient, and cost-effective low GWP alternatives, particularly in commercial refrigeration systems, where existing low GWP refrigerants like carbon dioxide and hydrocarbons suffer from safety and financial drawbacks such as poor energy efficiency, high system complexity, and flammability.
Innovation Solution
A cascade refrigeration system using a low stage refrigerant comprising at least 60% by weight of HFO-1234yf and a high stage refrigerant comprising at least 77% by weight of HFO-1234ze (E) or other blends, which are non-flammable and have a GWP of less than 150, to maintain evaporator temperatures above the freezing point of water, preventing frost accumulation and ensuring efficient heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If low GWP refrigerants like carbon dioxide and hydrocarbons are used, then environmental impact is reduced, but system flammability increases and safety deteriorates
Solution Approach 1:
The patent uses composite refrigerant blends combining HFO-1234yf and HFO-1234ze(E) in specific proportions. This composite approach creates a refrigerant mixture that achieves low GWP (below 150) while maintaining non-flammability (ASHRAE Class A1), resolving the contradiction between environmental protection and safety.
2Object-generated harmful factors
If existing low GWP refrigerants are used, then environmental impact is reduced, but system energy efficiency deteriorates
Solution Approach 1:
The patent optimizes the compositional parameters of the refrigerant blend, specifically adjusting the weight percentages of HFO-1234yf (30-70%) and HFO-1234ze(E) (30-70%). This parameter optimization achieves both low GWP and improved energy efficiency by tuning the thermodynamic properties of the refrigerant mixture to match system requirements.
3Productivity
If evaporator temperatures are lowered to improve cooling efficiency, then cooling performance is improved, but frost accumulation increases
Solution Approach 1:
The refrigerant blend's thermodynamic parameters are optimized to maintain evaporator temperatures above freezing point (0°C) while achieving effective cooling. The specific composition of HFO-1234yf and HFO-1234ze(E) provides appropriate saturation temperature characteristics that prevent frost formation on evaporator surfaces, eliminating the need for defrost cycles.
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 proposed system achieves efficient cooling while avoiding frost formation, maintaining safety, and reducing environmental impact by using non-flammable and chemically stable refrigerant blends, enhancing system reliability and reducing maintenance costs.
Implementation Method 1
an inter-circuit heat exchanger in which said low stage refrigerant condenses
Implementation Method 2
a high stage refrigeration circuit comprising a high stage refrigerant which evaporates in said inter-circuit heat exchanger by absorbing heat from said refrigerant in said low stage refrigeration circuit
Data Source
AI summary
The present invention provides cascade refrigeration systems in which the low stage consists essentially of R454A and the high stage comprises a refrigerant that is either Class A1 or Class A2L and comprises at least about 75% by weight of HFO-1234ze(E).