Heat Source Machine Control for Chilled Water Overshoot
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Solution Overview
Problem
Centrifugal chillers face issues with temperature overshoot in chilled water output, leading to potential freezing and reduced heat exchange efficiency, especially when the set outlet temperature is around 0° C., and high load conditions cause refrigerant condensation pressure increases, necessitating forced stops and efficiency drops.
Innovation Solution
A heat source machine with a computing unit to calculate evaluation values based on inlet temperature, flow rate, and load rate, and a set temperature changing unit to adjust the outlet temperature to prevent overshoot, using a heat pump cycle with multiple heat exchangers to manage temperature fluctuations and refrigerant condensation pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the set outlet temperature of chilled water is set to around 0° C. to improve cooling efficiency, then heat exchange efficiency is improved, but temperature overshoot causes the chilled water to freeze
Solution Approach 1:
The control method performs preliminary detection of fluctuation evaluation values (based on inlet temperature, flow rate, and load rate changes) before temperature overshoot occurs. When the evaluation value exceeds a threshold, the set temperature is proactively adjusted before the actual temperature deviation happens, preventing freezing while maintaining efficient cooling.
Solution Approach 2:
The system continuously monitors fluctuations in inlet temperature, flow rate, and load rate, calculates evaluation values, and uses this feedback to dynamically adjust the set outlet temperature. This closed-loop control prevents temperature overshoot while maintaining optimal cooling efficiency.
2Device complexity
If conventional control methods are used, then the system structure is simple, but temperature overshoot occurs when inlet temperature or flow rate fluctuates significantly
Solution Approach 1:
The control method introduces a feedback mechanism that calculates fluctuation evaluation values based on real-time measurements of inlet temperature, flow rate, and load rate. This feedback loop dynamically adjusts the set temperature to prevent overshoot, significantly improving reliability while adding only moderate computational complexity.
3Power
If the heat source machine operates under high load and high outside temperature conditions, then cooling capacity is increased, but refrigerant condensation pressure increases causing forced stops
Solution Approach 1:
The control method proactively detects increases in refrigerant condensation pressure under high load conditions and adjusts the set outlet temperature before pressure reaches critical levels. This preliminary action prevents forced stops and ensures continuous operation while maintaining high cooling capacity.
Solution Approach 2:
The system monitors refrigerant condensation pressure as a feedback parameter and dynamically adjusts operating parameters to maintain pressure within safe limits, enabling continuous high-load operation without forced stops.
4Reliability
If antifreeze solution is used instead of chilled water to prevent freezing, then temperature control stability is improved, but heat exchange efficiency decreases
Solution Approach 1:
Instead of using antifreeze solution to prevent freezing, the invention converts the potential harm of temperature fluctuations into a benefit by using predictive control. The system detects fluctuation patterns and adjusts the set temperature proactively, allowing chilled water to be used at 0° C. without freezing risks, thereby maintaining high heat exchange efficiency while ensuring temperature control stability.
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 effectively suppresses temperature overshoot, allowing chilled water to be used as a heat medium without freezing and preventing forced stops due to high load and temperature conditions, enhancing thermal efficiency and maintaining stable operation.
Implementation Method 1
performing, in the second heat exchanger, heat exchange between a heat medium supplied from an external load and a refrigerant to thereby cool or heat the heat medium
Implementation Method 2
performing, in the first heat exchanger, heat exchange between a heat source and a refrigerant to thereby cool the heat source
Data Source
AI summary
The present invention has an object to suppress an overshoot in the outlet temperature of a heat medium. A heat source machine controlling apparatus includes a computing unit and a set temperature changing unit. The computing unit calculates a load change rate using a predetermined arithmetic expression. The set temperature changing unit determines whether or not the load change rate calculated by the computing unit exceeds a predetermined threshold value. In the case where the load change rate exceeds the predetermined threshold value, the set temperature changing unit changes a set chilled water outlet temperature so as to suppress a change in a chilled water outlet temperature. For example, in the case where the chilled water outlet temperature is on a falling trend, if the set chilled water outlet temperature is set to a relatively high value, the heat source machine load decreases, and the chilled water outlet temperature is controlled to coincide with the set chilled water outlet temperature after the change. Consequently, an overshoot can be suppressed.