Predictive Humidity Control Using CO2-Based Airflow Adjustment in DOAS
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Solution Overview
Problem
Current humidity control systems in HVAC systems face challenges with wide swings in airflow due to varying occupancy, leading to discomfort and inefficient dehumidification, especially in spaces with variable refrigerant flow (VRF) or chilled water (CW) systems, which struggle to maintain stable humidity levels.
Innovation Solution
A predictive humidity control system that adjusts airflow based on CO2 setpoints, using a processor-controlled air valve to deliver dehumidified air at specific flow rates calculated from occupancy and water vapor emission rates, ensuring stable humidity and CO2 levels through a dedicated outdoor air system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reactive control system increases outside air supply in response to humidity increases, then humidity control is achieved, but wide swings in airflow occur causing discomfort and acoustic issues
Solution Approach 1:
The system performs preliminary dehumidification by delivering dehumidified outdoor air through the DOAS before occupancy occurs or before humidity levels rise. By proactively dehumidifying the space in advance, the system eliminates the need for reactive airflow increases, thereby maintaining stable airflow conditions while achieving reliable humidity control.
2Reliability
If a reactive control system responds to humidity increases, then dehumidification is achieved, but the system cannot stabilize before population changes again
Solution Approach 1:
The system performs dehumidification in advance before occupancy changes occur. By delivering dehumidified outdoor air through the DOAS proactively, the space is pre-conditioned to handle upcoming occupancy loads, eliminating the time lag and instability associated with reactive responses to humidity increases.
3Reliability
If a reactive control system increases airflow to manage humidity, then humidity limits are met, but acoustics and occupant comfort are adversely impacted
Solution Approach 1:
The system proactively delivers dehumidified outdoor air through the DOAS before humidity levels rise to problematic thresholds. This preliminary dehumidification action ensures humidity limits are met without requiring large reactive airflow increases, thereby maintaining stable airflow that preserves acoustic quality and occupant comfort.
4Reliability
If a second control computation is added to determine DOAS airflow volume based on humidity, then humidity control is achieved, but system complexity increases
Solution Approach 1:
The system merges humidity control and CO2-based demand control ventilation into a single integrated control framework. By using the same DOAS airflow computations to achieve both ventilation requirements and humidity control objectives, the system eliminates the need for separate control computations, thereby reducing complexity while maintaining reliable humidity control.
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 maintains steady humidity and CO2 levels, improving occupant comfort and system performance by proactively adjusting airflow according to occupancy changes, reducing the need for costly and complex humidity control solutions.
Implementation Method 1
a Dedicated Outdoor Air System (DOAS) that dehumidifies outdoor air which is then supplied to the conditioned space
Implementation Method 2
direct expansion (DX) DOAS equipment that uses the vapor-compression refrigeration cycle
Data Source
AI summary
Systems, apparatus and methods for operating an environmental control system that delivers dehumidified outdoor air into a conditioned space through an air valve. The method includes establishing CO2 setpoints corresponding to a ventilation outdoor air flow rate and a dehumidification outdoor air flow rate, determining a humidity metric of the conditioned space, and delivering outside air to the conditioned space at the ventilation outdoor air flow rate or dehumidification outdoor air flow rate based upon the humidity metric. The outside air may be tempered with return air from the conditioned space. The dehumidification CO2 set point is determined by predicting the dehumidification CO2 set point based on the airflow quantity per occupant and the relationship of the occupant predicted water vapor emission rate and CO2 emission rate.