HVAC Supply and Return Sound Reduction for Quiet Classrooms

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Solution Overview

Problem

Existing HVAC units generate excessive noise, making it difficult to meet stringent sound level standards like 35 dbA in classrooms without major redesigns, which are costly and impractical.

Innovation Solution

The implementation of sound reduction systems within HVAC units, including supply air and return air sound reducers with sound-absorbing materials and perforated layers, integrated into the unit or as separate chambers, to minimize noise transmission and perception.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If sound reduction elements are added to HVAC units, then sound levels are reduced to meet 35 dbA standards, but device complexity and manufacturing costs increase

Engineering Contradiction:

Improvesound levelsVSAvoidunit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The sound reduction elements are nested within the existing HVAC unit structure. The supply air sound reduction element is positioned within the supply air plenum, and the return air sound reduction element is positioned within the return air plenum, allowing sound reduction functionality to be integrated without adding external components.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The sound reduction elements utilize porous sound absorbing materials with specific flow resistance characteristics (0.05 to 0.50 inches water gauge per porosity unit) to absorb sound waves while maintaining air flow. The porous structure allows sound energy to be converted to thermal energy through friction within the material pores.

Inventive Principle:

Principle #31Porous materials

2Object-affected harmful factors

If sound reduction elements are added to HVAC units, then sound levels are reduced to meet 35 dbA standards, but manufacturing costs increase

Engineering Contradiction:

Improvesound levelsVSAvoidmanufacturing cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The invention specifies optimal parameter ranges for the sound reduction elements, including flow resistance (0.05 to 0.50 inches water gauge per porosity unit) and thickness (0.5 to 2.0 inches), which balance sound reduction effectiveness with manufacturing cost. These parameter specifications allow manufacturers to select materials and dimensions that meet the 35 dbA standard without excessive cost.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The sound reduction elements are designed as relatively simple, replaceable components that can be manufactured at low cost using common materials such as fiberglass, foam, or cotton batting. The elements are positioned to be easily accessible for replacement if needed, treating them as consumable components rather than permanent structural elements.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Object-affected harmful factors

If sound reduction elements are added to HVAC units, then sound levels are reduced, but the unit requires extensive redesign

Engineering Contradiction:

Improvesound levelsVSAvoidredesign requirement

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The sound reduction system is segmented into separate, modular elements: a supply air sound reduction element and a return air sound reduction element. Each element is independently positioned within its respective plenum, allowing them to be added as separate components rather than requiring integrated redesign of the entire HVAC unit.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sound reduction elements serve multiple functions: they absorb sound waves to reduce noise levels, maintain air flow through their porous structure, and can be installed in various HVAC unit configurations without requiring custom design for each specific unit type, making them universally applicable.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Significantly reduces sound levels to or below 35 dbA, meeting stringent noise standards without the need for extensive redesigns, thereby reducing costs and improving acoustic environments.

Implementation Method 1

sound-absorbing materials and perforated layers, integrated into the unit or as separate chambers, to minimize noise transmission and perception

Methodology Applied

Scientific EffectSound absorption: Acoustic Absorption

Data Source

PatentUS8336672B2Air treatment and sound reduction system

Publication Date: 2012.12.25 BARD MFG

AI summary

A device for reducing sound from an air treatment unit includes, in one embodiment, an air treatment system, including a wall mount HVAC unit with a supply air opening and a return air opening. A supply air sound reducer is provided in communication with the supply air. The supply air sound reducer includes a housing defining a supply interior provided with sound reducing material. The sound reducing material is overlaid with a layer of perforated material. A return air sound reducer is provided in communication with the return air opening. The return air sound reducer includes a housing defining an interior return volume provided with sound reducing material applied to one or more inside surfaces of the interior return volume and a layer of perforated material disposed over the sound reducing material. Mid-structure including sound reducing material is disposed in each of the supply and return air assemblies.