VAV Valve Characterization Using Limited Data Points for HVAC Systems
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Solution Overview
Problem
Current methods for calibrating VAV valves in HVAC systems are inefficient, as they often require measuring airflow at multiple data points for each valve, which is time-consuming and impractical, especially in factory environments or when re-characterizing valves in the field.
Innovation Solution
A method that involves creating a generic characterization of airflow versus valve position for a group of similar VAV valves, followed by a custom characterization for a specific valve by shifting the generic characterization based on limited data points, and converting volumetric flow rates to log10 values to achieve a linear relationship, facilitating accurate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods measuring airflow at multiple data points for each valve are used, then measurement precision is improved, but time consumption increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-characterizing a group of VAV valves to establish a generic characterization curve before individual valve calibration. This pre-established reference allows individual valves to be calibrated using only limited data points (one or two measurements) rather than requiring multiple measurements, significantly reducing calibration time while maintaining accuracy through comparison to the generic characterization.
Solution Approach 2:
The patent uses copying by creating a generic characterization that represents the typical behavior of a group of similar VAV valves. This generic characterization serves as a template or copy that can be quickly adapted to individual valves through minimal measurements, avoiding the need to perform full characterization procedures on each individual valve while still capturing individual variations.
2Productivity
If generic characterization for a group of valves is used, then productivity is improved, but manufacturing precision may worsen due to variations between individual valves
Solution Approach 1:
The patent applies local quality by allowing each individual VAV valve to have its own custom characterization derived from the generic characterization. While the generic characterization provides a common baseline for all valves in the group, the system then applies local adjustments based on measurements taken from each individual valve, ensuring that each valve's specific characteristics are captured while maintaining the efficiency of the generic approach.
Solution Approach 2:
The patent uses parameter changes by adjusting the generic characterization parameters to create custom characterizations for individual valves. The system measures one or two data points from each individual valve and uses these measurements to modify the generic characterization parameters, thereby adapting the general model to fit individual valve variations and improving accuracy without sacrificing productivity.
3Ease of operation
If logarithmic transformation of flow rates is applied, then the relationship between airflow and valve position becomes linear, but calculation complexity increases
Solution Approach 1:
The patent applies parameter changes by transforming the airflow rate data from linear scale to logarithmic scale (log10 transformation). This parameter transformation converts the inherently non-linear relationship between airflow and valve position into a linear relationship, making it easier to work with mathematically and simplifying the creation of custom characterizations from generic ones, despite adding a transformation step to the data processing.
Data Source
Figure 1A
Figure 1B
Figure 2~3
AI summary
An HVAC system and method for characterizing a chosen VAV valve involves measuring the valve's volumetric flow rate versus valve position at just one or at some other limited number of data points and comparing that to the average characteristics a rather large group of similar valves. A custom characterization of airflow versus valve position for the chosen VAV valve is then created based on a difference between the characteristics of the chosen valve and that of the group of valves. In some examples, the VAV valve is of a venturi style such that a generic characterization of the group of valves is substantially linear when their flow rates are expressed logarithmically.