Heat Pump Flow Rate Calculation Using Evaporator Pressure Drop
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Solution Overview
Problem
Existing heat pump systems face challenges in accurately measuring the heating-medium flow rate using inexpensive differential pressure sensors due to pressure fluctuations caused by the turbo-refrigerator, leading to inaccurate measurements.
Innovation Solution
The system measures the differential pressure between the inlet and outlet of the first heat exchanger, calculates the flow rate using a loss factor specific to the heat exchanger, and corrects for measurement delays to improve accuracy, allowing for reliable operation even with inexpensive sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electromagnetic flowmeter is used to measure the heating-medium flow rate, then measurement accuracy is improved, but device cost increases significantly
Solution Approach 1:
The patent replaces the expensive electromagnetic flowmeter with a cheap differential pressure sensor that can be easily manufactured and replaced. The sensor measures differential pressure across the heat exchanger, and flow rate is calculated from this pressure difference, providing a cost-effective alternative to expensive direct flow measurement devices.
Solution Approach 2:
The patent substitutes a mechanical/electromagnetic flow measurement system with a pressure-based measurement system. Instead of using an electromagnetic flowmeter to directly measure flow, the system uses differential pressure sensors to measure pressure drop across the heat exchanger and calculates flow rate from the pressure difference, replacing complex electromagnetic measurement with simpler pressure measurement and calculation.
2Ease of manufacture
If an inexpensive differential pressure sensor is used to measure flow rate, then device cost is reduced, but measurement accuracy deteriorates due to pressure fluctuations
Solution Approach 1:
The patent employs feedback control where the measured differential pressure is continuously monitored and used to calculate and adjust the heating medium flow rate. The control unit processes the pressure sensor signals and provides feedback control to maintain accurate flow measurement despite pressure fluctuations, allowing the system to compensate for disturbances and maintain measurement accuracy.
Solution Approach 2:
The patent changes the measurement parameter from direct flow measurement to pressure difference measurement. By measuring the differential pressure across the heat exchanger and using the relationship between pressure drop and flow rate, the system achieves accurate flow measurement using inexpensive pressure sensors instead of expensive flowmeters, transforming the measurement approach to overcome the limitations of pressure fluctuations.
3Speed
If pressure-type flow rate control is implemented, then flow rate control speed is improved, but system complexity increases
Solution Approach 1:
The patent extracts the flow measurement function from complex electromagnetic flowmeters and implements it through a simpler pressure measurement system. By taking out only the essential measurement function and implementing it through differential pressure sensing with calculation, the system achieves fast response while reducing overall system complexity, removing unnecessary complexity from the measurement device.
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 enables accurate determination of the heating-medium flow rate with sufficient precision, detects potential faults in the differential pressure sensor, and ensures continuous data transmission to facility-side equipment.
Implementation Method 1
a differential pressure between an inlet-side pressure and an outlet-side pressure of the heating medium in the first heat exchanger is measured using a differential pressure sensor
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A heating-medium flow rate is obtained with sufficient accuracy even if an inexpensive flow rate sensor is used. Provided is a turbo-refrigerator (11) including an evaporator (66) that cools or heats a heating medium flowing from an external load, a condenser (62) that exchanges heat with outside air or cooling water, a coolant circulation path through which a coolant is circulated between the evaporator (66) and the condenser (62), and a turbo-compressor (60) provided in the coolant circulation path, the turbo-refrigerator (11) comprising a differential pressure sensor that measures the differential pressure between the inlet-side pressure and the outlet-side pressure of cold water in the evaporator (66), and a control panel (74) storing a loss factor of the evaporator (66) and calculating the flow rate of the cold water in the evaporator (66) on the basis of the loss factor the differential pressure output from the differential pressure sensor, wherein the control panel (74) performs control using the calculated flow rate of the cold water and transmits the flow rate of the cold water to facility-side equipment.