Down-Fired Water Heater Flue Layout for Low-Condensate Venting
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Solution Overview
Problem
High heat exchange efficiency in water heaters leads to excessive condensate production in exhaust vents, compromising system efficiency and requiring additional drainage systems, while operating below efficient condensation levels reduces heating efficiency.
Innovation Solution
A water heater design featuring a non-positive vent static pressure and vent gas temperature, utilizing a first pass flue tube, down-fired burner assembly, expansion chamber, and multiple second pass flue tubes to promote heat transfer and reduce condensate formation, with a combustion gas outlet positioned above the tank to manage combustion gases under non-positive pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heat exchange efficiency is increased to maximize heat transfer from combustion gases to water, then heat exchange efficiency is improved, but condensate production in the exhaust vent increases excessively
Solution Approach 1:
The flue system is divided into multiple passes (first pass flue tube, second pass flue tubes) with an expansion chamber in between. This segmentation allows the combustion gases to undergo multiple heat exchange cycles, maintaining higher exit temperatures while achieving high overall heat exchange efficiency. The expansion chamber acts as an intermediate stage that redistributes the thermal energy.
Solution Approach 2:
The patent introduces a vertical dimension to the heat exchange process by using multiple passes with flue tubes extending from top to bottom of the water storage tank. The combustion gases flow down through the first pass flue tube and then up through the second pass flue tubes, creating a multi-dimensional heat exchange path that maximizes thermal transfer while maintaining gas temperature.
2Productivity
If heat exchange efficiency is increased, then heat exchange efficiency is improved, but additional condensate drainage systems are required
Solution Approach 1:
The patent converts the potentially harmful condensation into a beneficial pre-heating mechanism. The expansion chamber and multi-pass flue system are designed to maintain combustion gas temperatures above the dew point, preventing condensation in the vent while still achieving high heat exchange efficiency. The heat that would otherwise cause condensation is instead utilized to pre-heat the combustion gases for the next cycle.
3Productivity
If combustion gases are cooled to increase heat transfer to water, then heat exchange efficiency is improved, but condensate formation on heat exchange surfaces increases
Solution Approach 1:
The expansion chamber performs a preliminary action by redistributing and pre-heating the combustion gases before they enter the second pass flue tubes. This preliminary thermal processing ensures that the gases maintain sufficient temperature throughout the heat exchange process to prevent condensation, while still allowing efficient heat transfer to the water in the storage tank.
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
The design maintains high heat exchange efficiency while minimizing condensate production, eliminating the need for condensate drainage systems and reducing heat loss, thus extending appliance life and maintaining efficient operation.
Implementation Method 1
The expansion chamber promotes heat transfer between the combustion gases in the expansion chamber and water in the water storage tank through a bottom surface of the water storage tank
Implementation Method 2
a down-fired burner assembly positioned to direct combustion gases into the first pass flue tube
Implementation Method 3
the combustion gases tend to be condensed in greater quantities... as the temperatures of the combustion gases decrease as the result of successful exchange of heat from the combustion gases to water
Data Source
AI summary
Disclosed is a water heater that has a water storage tank, a first pass flue tube extending from a top of the water storage tank to a bottom of the water storage tank, a down-fired burner assembly positioned to direct combustion gases into the first pass flue tube, a plurality of second pass flue tubes extending from the bottom of the water storage tank to a top of the water storage tank, and an expansion chamber positioned below the bottom of the water storage tank. The expansion chamber receives the combustion gases from the first pass flue tube and delivers the combustion gases to the second pass flue tubes. The water heater operates with a non-positive vent static pressure and with a vent gas temperature that avoids or reduces excessive condensate production in an exhaust vent connected to receive combustion gases from the water heater.