A heat rejecting heat exchanger and a method of controlling one or more fans thereof
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Solution Overview
Problem
Vapour compression systems face instability and high electrical energy consumption due to the strong response of refrigerant outlet temperature to fan speed variations, making it difficult to control fans effectively, especially with heat recovery systems that reduce the heat needing to be rejected.
Innovation Solution
A method to control the fan speed based on the temperature difference between the refrigerant leaving the heat rejecting heat exchanger and ambient air, using threshold values to adjust fan speed to maintain efficient operation while reducing energy consumption, involving direct or indirect temperature measurement and controlled ramping or jumping of fan speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fan speed is increased to reject heat more effectively, then heat rejection efficiency is improved, but electrical energy consumption increases
Solution Approach 1:
The fan speed is made dynamically adjustable rather than fixed, allowing the system to optimize between heat rejection efficiency and energy consumption by varying fan speed based on actual thermal conditions and system load requirements
Solution Approach 2:
The system changes the operating parameters of the fan (speed, rotational frequency) based on measured temperature differences and system conditions, transitioning between different speed levels to achieve optimal balance between heat rejection and energy consumption
2Use of energy by moving object
If fan speed is decreased to reduce energy consumption, then electrical energy consumption is reduced, but system stability deteriorates due to strong temperature response
Solution Approach 1:
The system implements feedback control by continuously measuring the temperature difference between refrigerant and ambient air, and using this information to adjust fan speed accordingly, thereby maintaining system stability while optimizing energy consumption
Solution Approach 2:
The control system operates in periodic cycles, measuring temperature, determining optimal fan speed, and adjusting accordingly, which helps stabilize the system response and avoid excessive temperature fluctuations that would occur with continuous high-speed operation
3Use of energy by moving object
If fan speed is controlled dynamically to optimize energy consumption, then electrical energy consumption is reduced, but control difficulty increases due to non-linear temperature response
Solution Approach 1:
The control system uses an intermediary approach by implementing a lookup table or control algorithm that maps temperature difference measurements to appropriate fan speed settings, simplifying the control process while accounting for the non-linear relationship between fan speed and temperature response
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 stabilizes the operation of vapour compression systems by maintaining the temperature difference within a desired range, reducing electrical energy consumption without risking instability, by adjusting fan speed asymmetrically to quickly address high energy consumption and avoid excessive speed.
Implementation Method 1
a heat rejecting heat exchanger arranged to exchange heat with a secondary fluid flow across the heat rejecting heat exchanger in such a manner that heat is rejected from the vapour compression system and transferred to the secondary fluid flow
Implementation Method 2
one or more fans arranged to cause the secondary fluid flow across the heat rejecting heat exchanger
Data Source
Figure 1~2
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AI summary
A method of controlling a fan of a vapour compression system is disclosed. The vapour compression system comprises a compressor, a heat rejecting heat exchanger, e.g. in the form of a gas cooler or a condenser, an expansion device and an evaporator arranged in a refrigerant circuit. The fan is arranged to provide a secondary fluid flow across the heat rejecting heat exchanger, e.g. in the form of an air flow. The method comprises the steps of establishing a temperature, T1, of refrigerant leaving the heat rejecting heat exchanger, establishing a temperature, T2, of ambient air of the heat rejecting heat exchanger, and deriving a temperature difference, DeltaTau=Tau1-Tau2, between the temperature (T1) of refrigerant leaving the heat rejecting heat exchanger and the temperature (T2) of ambient air of the heat rejecting heat exchanger. The temperature difference, DeltaTau, is compared to a first threshold value and to a second threshold value, the second threshold value being smaller than or equal to the first threshold value, and the rotational speed of the fan is controlled on the basis of the comparing step. The method allows the electrical energy consumption of the fan to be reduced without risking instability of the vapour compression system.