Cold Climate Heat Pump Ejector Design for Wide Pressure Ratios
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Solution Overview
Problem
Cold climate heat pump systems face limitations in capacity and efficiency due to reduced compressor suction density and isentropic efficiency at high pressure ratios, often requiring supplemental heating and multiple scroll compressors to achieve desired thermal comfort.
Innovation Solution
A heat pump system featuring a variable speed compressor with a maximum pressure ratio of at least 5.0, a supersonic ejector to extend pressure and volumetric flow ranges, optimized heat exchangers, and high-efficiency fans to provide a two-phase refrigerant with a quality of less than or equal to 0.05, enhancing capacity and COP at extremely low ambient temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single scroll compressor is used, then device complexity is reduced, but capacity and volumetric flow are insufficient in cold climates
Solution Approach 1:
The patent employs a variable speed compressor that can dynamically adjust its operating speed and pressure ratio to match varying heating demands and ambient conditions. This dynamic operation allows a single compressor to deliver the full capacity range that would otherwise require multiple fixed-speed compressors, resolving the contradiction between device simplicity and heating capacity.
Solution Approach 2:
The system changes operational parameters including pressure ratio, suction density, and refrigerant flow rate to optimize compressor performance across different operating conditions. By adjusting these parameters, the single compressor maintains high efficiency and adequate capacity throughout the heating season, eliminating the need for multiple compressors.
2Productivity
If compressor pressure ratio is increased to meet heating demands, then heating capacity is improved, but compressor isentropic efficiency decreases
Solution Approach 1:
The variable speed compressor dynamically adjusts its pressure ratio based on ambient temperature and heating demand. During mild cold weather, it operates at lower pressure ratios with high efficiency. During extreme cold snaps, it increases pressure ratio to meet heating demands while minimizing efficiency losses through optimal speed matching.
Solution Approach 2:
The system optimizes the relationship between compressor speed and pressure ratio to maintain high isentropic efficiency. By coordinating speed changes with pressure ratio adjustments, the system achieves the necessary heating capacity while minimizing energy losses in the compressor.
3Productivity
If compressor suction density is increased to improve capacity, then volumetric flow is improved, but discharge temperature decreases causing cold blow
Solution Approach 1:
The system adjusts multiple parameters including refrigerant charge, heat exchanger configuration, and compressor operating conditions to achieve the optimal balance between suction density and discharge temperature. This ensures high volumetric flow for adequate capacity while maintaining discharge temperatures sufficient to prevent cold blow.
Solution Approach 2:
The heat exchangers are designed to perform multiple functions: condensing refrigerant, subcooling liquid refrigerant, and preheating refrigerant before the compressor. This multi-functionality allows the system to increase suction density while simultaneously managing discharge temperature to prevent cold blow.
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 system achieves increased capacity and efficiency in cold climates, reducing dependence on auxiliary heating and maintaining performance across a wide range of pressure ratios, thereby improving thermal comfort without the need for supplemental heating.
Implementation Method 1
an ejector disposed on the refrigerant circuit upstream of the compressor to extend a pressure ratio range and a volumetric flow range of the compressor
Implementation Method 2
a heat absorption heat exchanger
Implementation Method 3
a heat rejection heat exchanger
Implementation Method 4
at least one variable speed fan configured to move air through the heat rejection heat exchanger
Implementation Method 5
a separator disposed downstream of the ejector and upstream of the heat absorption heat exchanger
Implementation Method 6
at least one variable speed compressor operating with a maximum pressure ratio of at least 5.0
Data Source
AI summary
A heat pump system includes a refrigerant circuit, at least one variable speed compressor operating with a maximum pressure ratio of at least 5.0 and a variable speed range of at least three times (3×), a heat absorption heat exchanger, a heat rejection heat exchanger, an ejector disposed on the refrigerant circuit upstream of the compressor to extend a pressure ratio range and a volumetric flow range of the compressor in the cold climates, a separator disposed downstream of the ejector and upstream of the heat absorption heat exchanger, and at least one variable speed fan configured to move air through the heat rejection heat exchanger to provide a predefined an air discharge temperature greater than 90° F. A two-phase refrigerant is provided to an inlet of the heat absorption heat exchanger with a quality of less than or equal to 0.05.