State-based control in an air handling unit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
HVAC systems, particularly air handling units (AHUs), face inefficiencies when operating outside predetermined load ranges, as they often sacrifice energy efficiency to maintain temperature and humidity conditions, relying on pressure sensors and other control loops.
Innovation Solution
A state-based control system for AHUs that transitions between high and low cooling load states, using a finite state module to modulate fan speed and cooling stages based on temperature sensors, and includes a feed-forward module to adjust fan speed and maintain energy efficiency by anticipating changes in cooling demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AHU uses constant volume fan to provide constant airflow, then building zone temperature control is maintained, but energy efficiency deteriorates when operating outside predetermined load ranges
Solution Approach 1:
The system dynamically switches between two operating states: high cooling load state (variable volume fan) and low cooling load state (constant volume fan). This dynamic adaptation allows the AHU to optimize energy efficiency across different load conditions while maintaining reliable temperature control through state-based transitions triggered by supply air temperature and zone temperature measurements
2Adaptability or versatility
If AHU sacrifices energy efficiency to provide heating or cooling outside predetermined range, then adaptability improves, but energy efficiency deteriorates
Solution Approach 1:
The control system segments the operating range into distinct states (high cooling load state and low cooling load state) with different control strategies. This segmentation allows the AHU to apply the most efficient control method for each load condition, improving overall adaptability without sacrificing energy efficiency in either regime
3Reliability
If AHU relies on downstream pressure sensors or input from other control loops, then setpoint conditions are achieved, but device complexity increases
Solution Approach 1:
The system extracts the pressure sensor dependency by using a state-based control approach that relies on supply air temperature and zone temperature measurements instead. This eliminates the need for downstream pressure sensors and complex multi-loop control while maintaining reliable setpoint achievement through direct temperature feedback
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 allows AHUs to maintain energy efficiency across varying load conditions without relying on pressure sensors, effectively managing cooling demand and reducing energy consumption by optimizing fan speed and cooling stage usage.
Implementation Method 1
a supply air fan configured to provide a supply airstream to a building zone
Implementation Method 2
one or more cooling stages configured to chill the supply airstream
Data Source
AI summary
A state-based control system for an air handling unit (AHU) includes a finite state machine configured to transition between a high cooling load state and a low cooling load state. In the high cooling load state, the system maintains the temperature of a supply airstream provided by the AHU at a fixed setpoint and controls the temperature of a building zone by modulating the speed of a supply air fan. In the low cooling load state, the system operates the supply air fan at a fixed speed and controls the zone temperature by modulating an amount of cooling applied to the supply airstream by one or more cooling stages. A feed-forward module manages disturbances caused by adding or shedding cooling stages by applying a feed-forward gain to the supply air fan setpoint.