Heat Pump Compressor Frequency Control for Stable Water Heating
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Solution Overview
Problem
Conventional heat pump water heaters face challenges in stabilizing the refrigerant circuit state, leading to potential overshoot or undershoot of the heating medium temperature due to independent correction values for compressor speed, which are not adequately adjusted for varying outside air temperatures.
Innovation Solution
A heat pump system that controls the compressor's operating frequency based on a fundamental frequency calculated from the temperature difference and outside air temperature, with additional correction values added when the temperature difference is significant and the outlet temperature variation is minimal, to stabilize the refrigerant circuit and prevent temperature overshoot or undershoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed correction value is added to the compressor rotational speed during operation, then the control is simple, but the temperature control accuracy deteriorates when outside air temperature varies
Solution Approach 1:
The correction value for compressor rotational speed is changed from a fixed value to a dynamically adjustable value that varies with outside air temperature. The control device calculates different correction values based on detected outside air temperature, allowing the system to adapt to varying thermal conditions and maintain accurate temperature control regardless of ambient temperature variations.
Solution Approach 2:
The system changes the parameter of correction value based on outside air temperature conditions. When outside air temperature is high, a smaller correction value is applied; when outside air temperature is low, a larger correction value is applied. This parameter adaptation resolves the contradiction by maintaining temperature control accuracy across different environmental conditions while keeping the control logic relatively simple.
2Stability of the object's composition
If the compressor rotational speed is increased to prevent temperature undershoot, then the temperature stability improves, but the risk of temperature overshoot increases
Solution Approach 1:
The control device continuously monitors outlet temperature and uses this feedback to dynamically adjust the compressor rotational speed. By detecting the current temperature and comparing it with the target temperature, the system calculates appropriate correction values that prevent both undershoot and overshoot, maintaining temperature stability while avoiding extreme adjustments that could cause oscillations.
Solution Approach 2:
The system applies correction values in advance based on predicted temperature trends and outside air temperature conditions. When a temperature deviation is detected, the control device calculates and applies a correction value before the temperature can significantly deviate, preventing both undershoot and overshoot by anticipating the thermal response of the system.
3Speed
If a large correction value is added to the compressor frequency, then the response speed to temperature changes improves, but the refrigerant circuit stability deteriorates
Solution Approach 1:
The correction value parameter is dynamically adjusted based on outside air temperature conditions. When outside air temperature is high, a smaller correction value is applied to maintain refrigerant circuit stability; when outside air temperature is low, a larger correction value is applied to ensure adequate temperature response. This adaptive parameter change resolves the contradiction by optimizing the balance between response speed and stability for each operating condition.
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 approach effectively stabilizes the refrigerant circuit and prevents temperature overshoot or undershoot of the heating medium, improving efficiency regardless of outside air temperature conditions.
Implementation Method 1
a compressor (3) configured to compress a refrigerant
Implementation Method 2
a heating heat exchanger (4) configured to exchange heat between the refrigerant compressed by the compressor (3) and a liquid heating medium
Implementation Method 3
a decompressor (5) configured to decompress the refrigerant
Implementation Method 4
an evaporator (6) configured to exchange heat between the refrigerant decompressed by the decompressor (5) and outside air
Data Source
Figure 1
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Figure 3
AI summary
Outlet temperature ΔThw, which is temperature of a heating medium flowing out from a heating heat exchanger for exchanging heat between a refrigerant compressed by a compressor and a liquid heating medium is acquired (step S1). A fundamental frequency is calculated in accordance with a temperature difference obtained by subtracting current outlet temperature Thw from target outlet temperature and in accordance with current outside air temperature Ta (step S3). A positive first correction value is added to a correction frequency when the temperature difference is larger than a positive first reference value and a temporal variation in the outlet temperature Thw is smaller than a reference (step S6). An operating frequency of the compressor is controlled in accordance with a sum of the fundamental frequency and the correction frequency (step S10).