Airflow-confirming HVAC systems and methods with variable speed blower

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Solution Overview

Problem

HVAC systems with variable-speed blowers face challenges in reliably determining airflow, as static pressure drops significantly with reduced blower speeds, leading to potential misinterpretation of airflow cessation by the blower-proving switch, which can result in inefficiencies and non-compliance with airflow regulations.

Innovation Solution

Incorporating a blower-proving switch and a processing unit that records making and breaking point pressures, controlling the variable-speed blower to maintain an operating pressure above the breaking point with a buffer margin, ensuring proper operation and airflow confirmation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If variable-speed blower reduces operating speed to improve energy efficiency, then energy consumption decreases, but static pressure drops significantly causing false airflow cessation indications

Engineering Contradiction:

Improveenergy consumptionVSAvoidairflow detection reliability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The system performs preliminary action by establishing buffer margins above the breaking point pressure before operation begins. The processing unit records the breaking point pressure and sets a buffer margin, then controls the variable-speed blower to maintain operating pressure above this threshold. This preliminary setup prevents false airflow cessation indications from occurring during variable-speed operation, allowing energy-efficient low-speed operation without compromising airflow detection reliability.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If variable-speed blower operates at low speed to reduce energy consumption, then energy efficiency improves, but the blower-proving switch may misinterpret airflow as ceased leading to non-compliance with airflow regulations

Engineering Contradiction:

Improveenergy efficiencyVSAvoidairflow regulation compliance

Core Design Contradiction:

Use of energy by moving objectVSAdaptability or versatility

Solution Approach 1:

The system implements feedback control by continuously monitoring static pressure and comparing it against the recorded breaking point pressure plus buffer margin. The processing unit receives feedback from the blower-proving switch and adjusts the variable-speed blower operation accordingly. This feedback mechanism ensures the system maintains compliance with airflow regulations across all operating speeds while optimizing energy efficiency, as the blower speed is dynamically adjusted to keep pressure above the threshold that would trigger false airflow cessation indications.

Inventive Principle:

Principle #23Feedback

3Device complexity

If the system uses a fixed pressure threshold for airflow detection, then the control logic is simple, but it cannot accommodate variable-speed operation where static pressure varies significantly

Engineering Contradiction:

Improvecontrol logic complexityVSAvoidvariable-speed operation compatibility

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The system applies dynamics by transitioning from a fixed pressure threshold to a dynamic threshold based on recorded breaking point pressure and buffer margin. The processing unit records the breaking point pressure during commissioning and dynamically adjusts the effective threshold based on actual system characteristics. This dynamic approach allows the control logic to adapt to variable-speed operation where static pressure varies significantly, maintaining airflow detection accuracy across all operating conditions without requiring overly complex control algorithms.

Inventive Principle:

Principle #15Dynamics

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 solution enables efficient operation of variable-speed blowers by preventing false airflow cessation indications and maintaining compliance with airflow regulations, ensuring reliable airflow delivery and system efficiency.

Implementation Method 1

a blower for moving air to a building

Methodology Applied

Scientific EffectPressure differential: Pressure Gradient

Implementation Method 2

a cooling unit downstream of the variable-speed blower for cooling the airflow delivered from the variable-speed blower

Methodology Applied

Scientific EffectHeat transfer: Heat Exchanger

Data Source

PatentUS9692347B2Airflow-confirming HVAC systems and methods with variable speed blower

Publication Date: 2017.06.27 LENNOX IND INC

AI summary

Systems and methods involve controlling a variable-speed blower in a heating, ventilating, and air conditioning (HVAC) system to ensure the setting of a blower-proving switch to confirm airflow in a building. In one instance, a method involves ramping up the variable-speed blower so that the associated static pressure reaches a making point pressure of the blower-proving switch and then reducing the power to a desired power level. The method may also include maintaining the power level above a breaking point pressure. Other systems and methods are presented.