Heat Pump Expansion Valve Control Using Dual Pressure Sensing
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Solution Overview
Problem
Compression heat pumps are inefficient due to deviations from assumed temperatures, especially in geothermal and air heat pumps, where seasonal fluctuations and varying evaporation and condensation temperatures lead to suboptimal control, resulting in reduced efficiency.
Innovation Solution
Incorporating a second pressure sensor in the low-pressure section of the refrigerant circuit to measure evaporation pressure and temperature, allowing the control device to adjust the expansion valve for optimal hot gas overheating, which is calculated based on both high and low-pressure section pressures, thereby improving efficiency across different temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If only a first pressure sensor in the high-pressure section is used to control the expansion valve, then the control device can determine condensation temperature, but it cannot accurately determine evaporation temperature, leading to suboptimal control under varying operating conditions
Solution Approach 1:
The refrigerant circuit is segmented into high-pressure and low-pressure sections, each monitored by dedicated pressure sensors. This segmentation allows independent measurement of condensation and evaporation conditions, enabling precise determination of both temperatures without requiring additional temperature sensors throughout the circuit.
Solution Approach 2:
Pressure is used as an intermediary parameter to indirectly measure temperature. By measuring pressure at strategic locations (high-pressure section for condensation temperature, low-pressure section for evaporation temperature) and using pressure-temperature relationships of the refrigerant, the system derives temperature information without direct temperature sensing, reducing sensor complexity while maintaining precision.
2Device complexity
If the heat pump is optimized for specific operating points with assumed temperatures, then control is simplified, but efficiency decreases when actual temperatures deviate from assumptions due to seasonal fluctuations
Solution Approach 1:
The control system transitions from static optimization at fixed operating points to dynamic adaptation based on real-time measurements. Pressure sensors continuously monitor actual condensation and evaporation conditions, allowing the expansion valve control to adapt dynamically to seasonal fluctuations and varying load conditions, maintaining high efficiency across different operating scenarios.
Solution Approach 2:
The system implements feedback control by continuously measuring actual pressure conditions in both high-pressure and low-pressure sections, comparing them against optimal values, and adjusting the expansion valve accordingly. This closed-loop feedback ensures the heat pump operates at peak efficiency regardless of deviations from assumed operating conditions.
3Measurement precision
If pressure sensors are added to both high-pressure and low-pressure sections, then both condensation and evaporation temperatures can be determined for optimal control, but device complexity increases
Solution Approach 1:
Direct temperature measurement (mechanical/thermal sensing) is replaced with pressure measurement combined with thermodynamic calculation. By substituting temperature sensors with pressure sensors and using refrigerant pressure-temperature relationships, the system achieves equivalent or superior temperature determination precision while reducing the complexity of the sensing system.
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 allows for precise determination of optimal hot gas overheating, maximizing efficiency by adjusting the expansion valve, leading to improved performance across varying outside and flow temperatures, as demonstrated by increased efficiency in simulated conditions.
Implementation Method 1
a first pressure sensor (19) is provided for detecting a pressure P2 in a high-pressure or hot gas section of the refrigerant circuit, wherein the pressure P2 represents a direct measure of the condensation pressure and condensation temperature
Implementation Method 2
a second pressure sensor (17) is provided for detecting a pressure P1 in a low-pressure or suction gas section of the refrigerant circuit, wherein the pressure P1 represents a direct measure of the evaporation pressure and evaporation temperature
Implementation Method 3
a refrigerant is compressed by a mechanical compressor (preferably driven by an electric motor) and circulated through a cycle
Implementation Method 4
During cooling in the condenser, the heat of condensation is extracted from the refrigerant by the condenser's heat exchanger function and transferred to a consumer
Implementation Method 5
after expansion by the expansion valve, the refrigerant moves at reduced pressure and temperature
Implementation Method 6
where the expanded refrigerant evaporates
Implementation Method 7
through which heat is extracted from the ground and transferred to the evaporator, where the expanded refrigerant evaporates
Data Source
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AI summary
The present invention relates to a heat pump and a method for operating a heat pump. According to the invention, a target value for optimized hot gas superheat is set depending on a heat source temperature and a required flow temperature. The instantaneous hot gas superheat is determined from the difference between a temperature determined from the pressure (P2) in the high-pressure or hot gas section of the refrigerant circuit and a temperature determined from the pressure (P1) in the low-pressure or suction gas section of the refrigerant circuit, and the expansion valve (4) is controlled so that the hot gas superheat approaches the target value.