Modulating Furnace Burner Rate Control for Variable Heat Demand
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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 firing rates based on varying heat demands.
Innovation Solution
A method of operating a modulating furnace with a controller that adjusts burner firing rates using predetermined functions, such as linear, piecewise linear, or exponential functions, based on historical and current operating parameters, and signals from thermostats to optimize heating cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the burner operates at a fixed firing rate, then the system is simple to control, but energy efficiency and occupant comfort deteriorate due to inability to adapt to varying heat demands
Solution Approach 1:
The burner firing rate is dynamically adjusted based on the length of the thermostat call for heat. The system transitions from a fixed firing rate to a variable firing rate that changes over time, allowing the furnace to adapt to varying heat demands while maintaining reasonable control complexity through a time-based control strategy.
Solution Approach 2:
The system uses feedback from the thermostat call for heat duration to control the burner firing rate. The controller monitors how long the thermostat has been calling for heat and adjusts the burner firing rate accordingly, creating a closed-loop control system that improves adaptability without excessive complexity.
2Speed
If the burner firing rate is increased quickly to meet heat demand, then heating response speed improves, but energy efficiency deteriorates due to excessive fuel consumption
Solution Approach 1:
The burner firing rate dynamically increases over time based on the length of the thermostat call for heat rather than immediately jumping to maximum capacity. This gradual increase allows the system to respond to heating demands while consuming fuel more efficiently, avoiding unnecessary energy waste.
Solution Approach 2:
The system implements a time-based periodic adjustment of the burner firing rate. The firing rate changes at different stages of the heating cycle, starting lower and increasing progressively, which optimizes the balance between heating response speed and fuel consumption over the heating period.
3Loss of energy
If the burner operates at minimum firing rate for extended periods, then fuel consumption decreases, but heating effectiveness deteriorates when high heat demand occurs
Solution Approach 1:
The burner firing rate is dynamically adjusted based on the duration of the thermostat call for heat. The system starts at or near minimum firing rate to conserve fuel, then progressively increases the firing rate as the call for heat continues, ensuring that heating effectiveness is maintained when high heat demand persists.
Solution Approach 2:
The system preliminarily operates the burner at a lower firing rate when the thermostat call for heat is short in duration, conserving fuel during minor heating demands. However, the control strategy is prepared to quickly increase the firing rate if the heating demand continues, ensuring reliability is maintained when needed.
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 dynamic adjustment of burner firing rates, improving energy efficiency and comfort by ensuring the furnace operates at optimal heat levels based on current and historical data, enhancing the responsiveness to changing heat demands.
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
Implementation Method 2
The combustion gases typically proceed through the heat exchanger, are collected by a collector box
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
Implementation Method 4
a combustion blower is provided to pull in combustion air into the burner, pull the combustion gases through the heat exchanger into the collector box, and to push the combustion gases out the vent
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.