Parallel HVAC Outdoor Unit Control for Low Coolant Flow
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Solution Overview
Problem
In large-scale commercial air conditioning systems, low indoor unit loads can trigger alarms or system shutdowns due to insufficient coolant flow rates in outdoor units, affecting reliability and user experience.
Innovation Solution
An air conditioning system and control method that adjust the number of actively operating outdoor units based on the number of operating indoor units and total units, ensuring a minimum coolant flow rate is maintained to prevent freezing and alarm triggering, using a controller to set an upper limit for outdoor units and adjust their operating frequency or number based on temperature sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the coolant flow rate is reduced to match low indoor unit load, then energy efficiency is improved, but the outdoor unit heat exchanger may freeze due to insufficient flow rate
Solution Approach 1:
The system segments the outdoor units into multiple independent operational units. By controlling the number of outdoor units operating based on indoor load conditions, the system ensures that each operating outdoor unit receives sufficient coolant flow rate to prevent freezing, while still matching the overall system output to the actual cooling demand.
Solution Approach 2:
The system dynamically adjusts the number of actively operating outdoor units based on real-time conditions. The controller monitors the total load of indoor units and automatically determines the appropriate number of outdoor units to operate, ensuring optimal flow rate distribution and preventing freezing conditions while maintaining energy efficiency.
2Reliability
If the number of operating outdoor units is increased to maintain flow rate, then freezing is prevented, but system energy consumption increases
Solution Approach 1:
The system dynamically determines the optimal number of outdoor units to operate based on the total load of indoor units. This dynamic control ensures that outdoor units are not unnecessarily operated at high flow rates when indoor demand is low, thereby preventing freezing while avoiding excessive energy consumption.
Solution Approach 2:
The system changes the operational parameters (number of active outdoor units) based on load conditions. By adjusting this parameter, the system maintains sufficient flow rate through operating outdoor units to prevent freezing, while optimizing overall energy consumption by not keeping excess outdoor units running at high capacity.
3Reliability
If a fixed threshold flow rate is set for outdoor units, then freezing is prevented under high load, but false alarms occur under low load conditions
Solution Approach 1:
The system replaces fixed threshold control with dynamic control that adapts to actual operating conditions. The controller calculates the appropriate number of outdoor units to operate based on the total load of indoor units, ensuring that the flow rate threshold is appropriately adjusted for each operating scenario, thereby preventing false alarms while maintaining freezing protection.
Solution Approach 2:
The system implements feedback control by continuously monitoring the total load of indoor units and using this information to determine the optimal number of outdoor units to operate. This feedback mechanism ensures that the flow rate requirements are appropriately matched to actual cooling demand, preventing both freezing and false alarms.
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
Prevents outdoor unit freezing and alarm triggering by maintaining a sufficient coolant flow rate, enhancing system reliability and user experience by dynamically adjusting outdoor unit operation in response to indoor unit loads and temperature feedback.
Implementation Method 1
a coolant circulation circuit which circulates coolant through each of the indoor units connected in parallel and each of the outdoor units connected in parallel respectively, and which exchanges heat with each of the indoor units and each of the outdoor units
Implementation Method 2
the refrigerant therein exchanges heat with the coolant circulation circuit through a heat exchanger (for example, a welded plate heat exchanger) in the refrigerant circuit
Data Source
AI summary
An air conditioning system and a control method thereof. The air conditioning system includes: a plurality of indoor units connected in parallel; a plurality of outdoor units connected in parallel; and a coolant circulation circuit which circulates coolant through each of the indoor units connected in parallel and each of the outdoor units connected in parallel respectively, and which exchanges heat with each of the indoor units and each of the outdoor units; wherein the air conditioning system further includes a controller which, based on a number of actively operating indoor units, a total number of the indoor units and a total number of the outdoor units, defines an upper limit of a number of actively operating outdoor units, so that the flow rate of the coolant flowing through the actively operating outdoor units is not lower than a preset flow rate.