Predictive Humidity Control Using CO2 Setpoints in Demand Ventilation
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Solution Overview
Problem
Current humidity control systems in HVAC systems face challenges with reactive control methods that lead to wide swings in airflow, causing discomfort and impacting system performance due to varying occupancy in conditioned spaces, and are often complex and costly to implement.
Innovation Solution
A predictive humidity control system that uses alternative CO2 set points, adjusting airflow based on occupancy and water vapor emission rates to deliver dehumidified air proactively, employing a dedicated outdoor air system with an air valve and a controller that adjusts airflow rates according to humidity metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reactive control systems increase outside air supply in response to humidity increases, then humidity control is achieved, but wide swings in airflow occur causing discomfort and impacting system performance
Solution Approach 1:
The system performs preliminary action by predicting future humidity levels based on occupancy forecasts and proactively adjusting the outside air supply before humidity problems occur. This prevents the need for reactive adjustments that cause wide airflow swings, thereby maintaining both humidity control reliability and airflow stability.
2Reliability
If reactive control systems adjust airflow to manage humidity, then humidity limits are maintained, but comfort and acoustics are adversely impacted
Solution Approach 1:
By forecasting occupancy and predicting humidity trends in advance, the system proactively adjusts ventilation rates to maintain humidity within limits while avoiding the abrupt airflow changes that disrupt occupant comfort and acoustic quality. The predictive approach ensures smooth, gradual adjustments rather than reactive swings.
3Reliability
If complex solutions with multiple control computations are implemented, then humidity and CO2 control are achieved, but system complexity and cost increase
Solution Approach 1:
The system performs preliminary action by integrating occupancy forecasting with humidity prediction to proactively determine optimal ventilation rates. This unified predictive approach consolidates control computations into a single forward-looking algorithm, achieving both humidity and CO2 control while reducing overall system complexity compared to multiple separate reactive control loops.
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.