HVAC Unit Setpoint Reset for Multi-Unit System Stability
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Solution Overview
Problem
HVAC systems in data centers experience instability and inefficiency due to cross-coupling between multiple units controlling return or discharge air temperatures, leading to unstable operation and increased energy consumption.
Innovation Solution
Implementing a return air or discharge air temperature setpoint reset system that adjusts the temperature setpoint of each unit based on operational criteria, such as compressor speed or valve position, to decouple the output of one unit from its own return air temperature, thereby stabilizing the system and optimizing energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If multiple HVAC units operate with decentralized controls to maintain temperature setpoints, then temperature control capability is improved, but system stability deteriorates due to cross-coupling between units
Solution Approach 1:
The patent implements a centralized control system that collects temperature measurements from all HVAC units and uses this feedback to coordinate unit operations. The central controller adjusts individual unit setpoints based on overall system conditions, preventing the instability that arises from decentralized units independently responding to cross-coupled temperature changes.
Solution Approach 2:
The patent merges multiple decentralized control decisions into a single centralized control architecture. By combining the control functions of individual HVAC units under one central controller, the system achieves coordinated operation that maintains temperature control capabilities while eliminating the instability caused by independent unit responses.
2Ease of operation
If HVAC units operate independently to control return air temperature, then individual unit control simplicity is improved, but energy efficiency deteriorates due to unstable operation and flipping behavior
Solution Approach 1:
The centralized control system continuously monitors temperature measurements from all units and uses this feedback to optimize energy consumption. By coordinating unit operations based on real-time system state, the system prevents energy-wasting flipping behavior while maintaining simple temperature control, achieving both ease of operation and energy efficiency.
Solution Approach 2:
The patent implements dynamic setpoint adjustment where the central controller continuously modifies individual unit setpoints based on current system conditions. This dynamic coordination allows the system to maintain simple operation while optimizing energy efficiency by preventing unstable flipping behavior and coordinating unit startup/shutdown sequences.
3Reliability
If redundant HVAC units are deployed for reliability, then system reliability is improved, but system complexity and coordination difficulty increase
Solution Approach 1:
The patent merges the control of multiple redundant HVAC units into a single centralized control system. This approach maintains the reliability benefits of redundancy while reducing coordination complexity by having one central controller manage all units, eliminating the need for complex inter-unit communication and coordination protocols.
Solution Approach 2:
The centralized control system uses feedback from temperature sensors to automatically coordinate redundant units, simplifying their operation. The feedback mechanism allows the central controller to intelligently manage redundant capacity, turning off units when sufficient cooling is provided and activating them when needed, thereby maintaining reliability without requiring complex manual coordination.
Data Source
AI summary
Systems and methods of stabilizing HVAC systems with multiple HVAC units configured to control return air temperature or discharge air temperature are provided. HVAC units that are controlled by the return air temperature compare the return air temperature to a setpoint that determines whether the HVAC unit's operation increases, decreases, or stays the same. By adjusting the setpoint of an HVAC unit based on certain criteria (e.g., a desired operational effort of an HVAC unit) the system can be stabilized. A temperature setpoint reset (TSPR) system can be included in each HVAC unit that resets the temperature setpoint (TSP) of the HVAC unit so that the HVAC unit operates within a desired operational effort (e.g. compressor speed or valve position). A master feedback loop and optimizer loop may be implemented to further control the behavior of the HVAC system.