VAV diffuser controls
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Solution Overview
Problem
Current HVAC systems face challenges in achieving optimal energy efficiency due to complexities in balancing supply air temperature and airflow rate, leading to energy wastage and thermal comfort issues.
Innovation Solution
The method involves a control system that determines a target thermal capacity for each VAV diffuser unit, adjusting the motorized variable damper to achieve this capacity, while also optimizing supply air temperature and pressure through the use of zone temperature sensors, diffuser pressure sensors, and a control unit connected to these sensors and actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the supply air temperature is reduced to save fan energy, then fan energy consumption decreases, but mechanical cooling plant energy consumption increases
Solution Approach 1:
The system dynamically adjusts the supply air temperature setpoint based on outdoor air temperature conditions. During economizer operation, the supply air temperature is raised above the traditional 13°C setpoint to match outdoor air temperatures, reducing the temperature differential and allowing the system to operate with higher supply temperatures when outdoor air is cool, thereby reducing chiller energy consumption while maintaining fan energy efficiency
2Use of energy by stationary object
If the supply air temperature setpoint is reset based on outdoor air temperature, then chiller energy savings are achieved, but calibration drift between sensors causes false loading on the mechanical cooling plant
Solution Approach 1:
The system implements a feedback mechanism where the actual supply air temperature is continuously monitored and compared against the calculated setpoint. When the actual temperature deviates from the setpoint (indicating sensor calibration drift), the system automatically adjusts the outdoor air damper position to compensate, ensuring that the mechanical cooling plant is only loaded when truly necessary, thereby maintaining energy efficiency while correcting for sensor drift
3Temperature
If the VAV diffuser damper is kept slightly throttled to satisfy thermal load in trim-and-respond control, then the critical zone cooling requirement is met, but fan energy increases due to higher pressure requirements
Solution Approach 1:
The system dynamically adjusts the supply air temperature in real-time based on actual zone conditions and outdoor air availability. By raising the supply air temperature during economizer operation and adjusting the outdoor air damper accordingly, the system allows VAV diffusers to operate with dampers fully open or nearly fully open, eliminating the need for continuous throttling while maintaining zone thermal comfort and reducing fan energy consumption
4Loss of energy
If outdoor air is used for economizer cooling, then free cooling energy savings are achieved, but insufficient outdoor air cooling capacity requires supplementary mechanical cooling
Solution Approach 1:
The system uses the outdoor air damper as a multi-functional control element that serves both to provide free cooling when outdoor air is sufficiently cool and to modulate the mixture of outdoor and recirculated air when supplementary cooling is needed. This allows the economizer system to seamlessly transition between pure free cooling and supplementary mechanical cooling modes, maximizing energy savings while ensuring adequate cooling capacity delivery
Data Source
AI summary
A method of controlling an HVAC system comprising an air handling unit having at least one supply air fan or motorised supply air damper, the system comprising a plurality of VAV diffuser units, each VAV diffuser unit comprising a diffuser, a motorised variable damper to alter a diffuser airflow rate of a diffuser airflow delivered by the corresponding diffuser unit into the corresponding zone, and a diffuser pressure sensor for determining a pressure of the diffuser airflow; the system further comprising a plurality of zone temperature sensors; the method comprising determining a target thermal capacity for a selected diffuser unit with reference to a target diffuser airflow rate and a target diffuser temperature differential and controlling the motorised variable damper of the selected diffuser unit with reference to the determined target thermal capacity for the selected diffuser unit.