Nested Chimney Stacks for Preheated Combustion Air
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Solution Overview
Problem
Conventional chimney systems do not capture or retain heat from combustion exhaust, leading to inefficiencies in heating appliance operations.
Innovation Solution
A chimney system with integrated waste heat recovery, featuring an inner and outer stack configuration that allows for heat transfer from exhaust gases to combustion air, enhanced by turbulators and insulation, to preheat combustion air and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional chimney systems are used to vent exhaust gases, then exhaust gases are safely conveyed away from heating appliances, but heat in the exhaust gases is not captured or retained
Solution Approach 1:
The patent implements a nested chimney system where an inner stack is positioned within an outer stack, creating a concentric arrangement. The inner stack carries exhaust gases while the outer stack serves as a heat exchanger surface, allowing the exhaust flow to be nested within a functional outer structure that recovers heat without requiring separate external heat exchange components.
Solution Approach 2:
The patent merges the exhaust venting function with the heat recovery function into a single integrated chimney system. The outer stack simultaneously serves as both a structural enclosure and a heat exchanger, combining multiple functions (venting and heat recovery) into one unified device rather than requiring separate systems.
2Use of energy by moving object
If heat recovery components are added to the chimney system, then waste heat is captured from exhaust gases, but the system complexity increases
Solution Approach 1:
The outer stack is designed to perform multiple functions simultaneously: it encloses the inner stack for structural integrity, serves as a heat exchanger surface for waste heat recovery, and provides insulation for thermal efficiency. This multi-functionality allows the system to achieve heat recovery without adding separate dedicated components for each function.
Solution Approach 2:
The annular combustion air passage acts as an intermediary channel that allows combustion air to flow between the inner and outer stacks. This intermediate space enables heat transfer from the hot exhaust gases in the inner stack to the combustion air in the outer passage, facilitating efficient heat recovery without direct contact between exhaust and combustion air.
3Temperature
If insulation is added to reduce skin temperature of the conduit, then surface temperature is reduced, but heat recovery capability is limited
Solution Approach 1:
The patent applies insulation selectively to the outer stack to control surface temperature for safety and condensation prevention, while leaving the inner stack uninsulated to maintain high temperature for heat recovery. This localized insulation approach allows different regions of the chimney system to have different thermal properties according to their specific functional requirements.
Solution Approach 2:
The chimney system is segmented into two distinct stacks (inner and outer) with different insulation characteristics. The inner stack is designed for high temperature heat recovery while the outer stack has insulation applied for surface temperature control. This segmentation allows each component to be optimized for its specific function rather than treating the entire system uniformly.
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
Increases combustion efficiency and reduces exhaust plume appearance by transferring heat from exhaust gases to combustion air, enhancing the heating appliance's performance.
Implementation Method 1
heat is transferred from the exhaust gasses being directed from the heating appliance to the combustion air directed through the combustion air passage
Implementation Method 2
enhanced by turbulators and insulation
Data Source
AI summary
A representative system includes: an inner stack defining a flow path to direct exhaust gasses from the exhaust air outlet of a heating appliance to an exhaust; an outer stack disposed about an exterior of the inner stack and being spaced therefrom to form a combustion air passage in a heat transfer relationship with the exterior of the inner stack; a combustion air opening disposed at the intake end of the outer stack configured to receive combustion air and provide the combustion air to the combustion air passage; an air dam positioned to terminate the combustion air passage; a combustion air conduit configured to direct the combustion air from the combustion air passage to the combustion air inlet of the heating appliance; wherein, in operation, heat is transferred from the exhaust gasses to the combustion air directed through the combustion air passage.