Gas Furnace Induced Draft Blower Post-Purge Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional gas furnaces face issues with reverse flow of exhaust gases due to external winds, which can cause the filter to melt, leading to reduced efficiency and potential damage, especially in ultra-low NOx furnaces with plastic filters.
Innovation Solution
Implementing a post-purge process with a prolonged blower cool-down cycle and induced draft blower operation to reduce flue temperature below the filter's melting point, extending the purge time to 70 seconds to prevent filter melting during reverse flow conditions without significantly diminishing fuel utilization efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the gas furnace uses a direct vent arrangement with outdoor exposure, then combustion air supply is improved, but exhaust gases can reverse flow back into the furnace during windy conditions
Solution Approach 1:
The system performs a preliminary purge cycle before the filter can be damaged by reverse flow. The purge cycle activates the inducer motor and blower to clear exhaust gases from the heat exchanger and vent system before windy conditions can force hot gases back toward the filter, preventing filter melting in advance
2Use of energy by moving object
If the furnace operates with standard purge timing, then fuel utilization efficiency is maintained, but exhaust gases remain hot enough to melt the filter during reverse flow
Solution Approach 1:
The blower continues running beyond the standard purge cycle duration, maintaining continuous airflow through the heat exchanger to cool exhaust gases for an extended period. This prolonged cooling action ensures exhaust temperatures drop below the filter melting point even during reverse flow conditions, while the extended operation remains efficient
3Object-affected harmful factors
If the blower cool-down cycle is extended to cool exhaust gases, then filter melting is prevented, but fuel utilization efficiency decreases
Solution Approach 1:
The system changes operational parameters by extending the blower run time specifically during purge cycles when reverse flow risk exists. This parameter adjustment (increased cool-down time) is applied selectively rather than continuously, preventing filter melting during critical periods while minimizing overall efficiency impact through targeted rather than constant operation
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 solution effectively prevents filter melting and maintains furnace efficiency by ensuring the filter is not exposed to high temperatures during reverse airflow, enhancing the overall performance and longevity of the gas furnace.
Implementation Method 1
a blower configured to direct air toward the heat exchanger tube
Implementation Method 2
a heat exchanger coupled to the combustion air pipe and the exhaust air pipe. The heat exchanger includes a heat exchanger tube
Data Source
AI summary
Systems and methods for counter-flow heat reduction cycles are disclosed. Embodiments may include a gas furnace having a combustion air pipe, an exhaust air pipe, and a heat exchanger coupled to the combustion air pipe and the exhaust air pipe, the heat exchanger having a heat exchanger tube and an induced draft blower configured to direct air toward the heat exchanger tube, where the air flows over the heat exchanger tube and into the exhaust air pipe. The gas furnace may include a controller configured to determine a call for heat, activate the induced draft blower during a normal heating operation, determine that the call for heat is no longer present, determine that at least 70 seconds have elapsed since determining that the call for heat is no longer present, and deactivate the induced draft blower.