Modulating Furnace Blower Control for Comfort-Efficiency Balance
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Solution Overview
Problem
Modulating furnaces with variable speed circulating air blowers face a challenge in balancing energy efficiency and occupant comfort, as high blower speeds at higher firing rates can cause wind chill effects, compromising comfort while maintaining efficiency.
Innovation Solution
Regulating the circulating air blower speed in relation to burner firing rates to allow non-constant discharge air temperature, with increased temperature at higher firing rates, and using sensors and models to determine or estimate discharge air temperature or flow, allowing user preference settings for energy efficiency or comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the circulating air blower speed is increased at higher firing rates to maintain constant discharge air temperature, then energy efficiency is improved, but occupant comfort deteriorates due to wind chill effect
Solution Approach 1:
The patent allows the discharge air temperature to vary as a parameter rather than maintaining it constant. At higher burner firing rates, the discharge air temperature is permitted to increase, which enables the circulating air blower to operate at lower speeds while still meeting heating demands, thereby reducing the wind chill effect and improving occupant comfort without sacrificing energy efficiency
2Object-affected harmful factors
If the circulating air blower speed is decreased to reduce wind chill effect, then occupant comfort is improved, but energy efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts the discharge air temperature parameter in response to changing burner firing rates. When the burner operates at higher firing rates, the discharge air temperature is allowed to rise, which compensates for reduced blower speed and maintains energy efficiency while enabling lower blower speeds that reduce wind chill effect and improve comfort
3Device complexity
If constant discharge air temperature is maintained across all firing rates, then system simplicity is preserved, but adaptability to different operating conditions deteriorates
Solution Approach 1:
The control system transitions from a static constant temperature approach to a dynamic approach where discharge air temperature varies with burner firing rate. The system adapts the discharge air temperature based on operating conditions, allowing optimal blower speed selection for each firing rate while maintaining manageable control complexity through established relationships between temperature and firing rate
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 reduces wind chill effects at higher firing rates while maintaining energy efficiency by adjusting blower speed and burner operation based on user preferences, enhancing both comfort and efficiency.
Implementation Method 1
a circulating air 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 2
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
Data Source
AI summary
A furnace controller for a modulating furnace that helps provide a balance between energy efficiency and occupant comfort across various burner firing rates and/or across various circulating blower speeds. In some cases, the furnace controller can be configured to permit a user to customize operation of the furnace in accordance with their particular needs and/or desires with respect to efficiency and comfort. A selection may be made between an energy efficiency setting and a user comfort setting. Then, a plenum parameter such as a discharge air temperature (DAT) or discharge air flow (DAF) may be regulated in accordance with the selected setting.