Modulating Furnace Burner Rate Control for Partial-Load Heating
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
There is a need for improved methods to determine burner firing rates in modulating furnaces to enhance energy efficiency and occupant comfort, as existing systems lack effective strategies for adjusting fuel and air intake based on varying heat demands.
Innovation Solution
A method for operating a modulating furnace with a controller that adjusts burner firing rates using predetermined functions, such as linear, piecewise linear, or exponential increases, based on historical and current operating parameters, and signals from thermostats to optimize heat delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the burner operates at a fixed high firing rate to meet peak heating demand, then the heating capability is sufficient, but energy efficiency deteriorates during partial load conditions
Solution Approach 1:
The burner firing rate is dynamically adjusted based on actual heating demand rather than operating at a fixed rate. The controller modifies the burner firing rate in response to thermostat calls and historical operating parameters, enabling the system to match output with demand and avoid energy waste during partial load conditions while maintaining sufficient heating capability when needed
Solution Approach 2:
The system changes the operating parameter of burner firing rate from a fixed value to a variable parameter. By adjusting the burner firing rate based on historical off-time data and current heating demands, the system optimizes energy efficiency across different load conditions while preserving the ability to provide adequate heating when required
2Speed
If the burner firing rate is increased rapidly to meet heating demand, then the response speed is improved, but thermal shock and system stress increase
Solution Approach 1:
The system performs preliminary action by using historical operating parameters, particularly the off-time from previous cycles, to pre-determine an appropriate initial burner firing rate. This prevents sudden rapid increases in firing rate that could cause thermal shock, while still enabling the burner to reach necessary temperature levels efficiently by starting from an optimized baseline rather than from minimum or zero fire rate
3Ease of operation
If the initial burner firing rate is set to a fixed minimum value, then the control simplicity is maintained, but the adaptability to varying heating demands is reduced
Solution Approach 1:
The system implements feedback by using historical operating data, specifically the off-time from previous heating cycles, to automatically adjust the initial burner firing rate for subsequent cycles. This maintains control simplicity from the user perspective while internally adapting the firing rate based on actual system performance and heating demands, resolving the contradiction between simple control and system adaptability
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 approach allows for precise control of burner firing rates, improving energy efficiency and comfort by dynamically adjusting fuel and air intake according to changing heat demands, ensuring optimal heating cycles.
Implementation Method 1
a furnace employs a burner that burns a fuel such as natural gas, propane, oil or the like, and provides heated combustion gases to the interior of a heat exchanger
Implementation Method 2
The combustion gases typically proceed through the heat exchanger... over or through the heat exchanger, thereby heating the air
Implementation Method 3
a circulating blower typically forces return air from the building, and in some cases ventilation air from outside of the building, over or through the heat exchanger, thereby heating the air
Data Source
AI summary
A modulating furnace having a variable rate burner and a controller is operated at a first burner firing rate for a first period of time, and a higher burner firing rate once the first period of time has expired. In some instances, the burner may be operated only while the controller is receiving a call for heat from a thermostat or the like.