Variable-Speed HVAC Fan Control Without Damper Position Sensing

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Solution Overview

Problem

Existing HVAC systems face inefficiencies at part-load conditions, requiring costly terminal damper position measurements, being sensitive to communication and unit failures, and being difficult to tune, especially in large variable-air-volume systems.

Innovation Solution

A fan control strategy using zone temperature sensors and a controller to adjust fan speed based on temperature setpoints and learned commands, without needing terminal damper position measurements, which includes adaptive bounded controls and calibration modes to optimize fan speed and setpoints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If constant static pressure control strategy is used, then system stability is maintained, but part-load efficiency deteriorates

Engineering Contradiction:

Improvestatic pressure stabilityVSAvoidpart-load efficiency

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The patent implements dynamic static pressure reset based on the position of the most-open terminal damper. Instead of maintaining a constant static pressure setpoint, the system continuously adjusts the setpoint according to the damper position signal, allowing the static pressure to vary dynamically with system load conditions. This resolves the contradiction by enabling energy-efficient operation at part-load while maintaining adequate pressure when needed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the static pressure parameter from a fixed constant to a variable parameter that resets based on terminal damper position. The control system modifies the static pressure setpoint parameter dynamically, transitioning from a fixed value to a variable value that adapts to changing system conditions, thereby improving part-load efficiency while maintaining system stability.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If terminal damper position measurement is implemented, then static pressure reset accuracy is improved, but system cost increases

Engineering Contradiction:

Improvedamper position measurement accuracyVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent leverages the existing terminal unit control device and its inherent damper position sensing capability. Instead of adding separate measurement devices, the system uses the control device already present in the terminal unit to provide the damper position signal. This self-service approach obtains precise measurement information without increasing system cost or complexity.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The terminal unit control device performs multiple functions: it controls the terminal damper and simultaneously provides damper position feedback to the fan control system. This multi-functionality eliminates the need for dedicated position measurement devices, reducing system cost while maintaining measurement precision.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If digital communication network is used for damper position feedback, then real-time control is achieved, but system sensitivity to communication failure increases

Engineering Contradiction:

Improvecontrol response speedVSAvoidsensitivity to communication failure

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent prepares for communication failures by implementing alternative control strategies that do not rely on real-time digital communication. The system includes fallback mechanisms such as using last-known-good values or switching to constant pressure control when communication is lost, cushioning against the potential failure mode while maintaining real-time control capability when communication is available.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Loss of energy

If static pressure reset based on most-open damper is implemented, then part-load efficiency is improved, but sensitivity to terminal unit failure increases

Engineering Contradiction:

Improvethrottling lossesVSAvoidsensitivity to terminal unit failure

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the fan control system continuously monitors the position of the most-open terminal damper and adjusts the static pressure setpoint accordingly. This closed-loop feedback enables the system to maintain optimal static pressure that keeps the most-open damper nearly fully open, minimizing throttling losses while adapting to changing system conditions and providing resilience to individual terminal unit failures.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8688243B2Method and apparatus for controlling fans in heating, ventilating, and air-conditioning systems

Publication Date: 2014.04.01 VIGILENT CORP

AI summary

Systems, apparatus, and methods of controlling a variable-speed fan of an environmental maintenance module that controls temperatures of a plurality of zones of a building are provided. A first critical zone of the building is identified by analyzing the first zone temperature errors, which are used to determine a final speed setting of the variable-speed fan. Systems, apparatus, and methods of calibrating an environmental maintenance module that controls a temperature of a zone of a building are also provided. A location parameter is calculated for a plurality of zone temperatures, and a scale parameter is computed that quantifies a variation of the zone temperatures relative to a location parameter. A first temperature setpoint for the zone is determined and used in controlling the temperature of the zone.