Modulating Furnace Control with Single-Stage Thermostat Load Adaptation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing modulating gas furnaces lack a thermostat algorithm to provide multiple heating modes, leading to limited control and operational efficiency, especially when using single-stage thermostats which result in large temperature swings.
Innovation Solution
A control system and method that includes a processor with an algorithm to manage multiple heating modes by determining heating loads and adjusting gas valve and blower motor speeds, allowing for intermediate and maximum input rates based on calculated heating load requirements, optimizing furnace operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage thermostat is used to control the furnace, then the device complexity is reduced, but the temperature control precision deteriorates resulting in large temperature swings
Solution Approach 1:
The patent applies dynamics by implementing a multi-rate heating algorithm that dynamically adjusts the furnace heating rate based on temperature differential. The system transitions from static single-stage control to dynamic multi-stage control, where the heating rate changes in real-time based on how far the current temperature is from the setpoint, thereby reducing temperature swings while maintaining simple thermostat hardware
Solution Approach 2:
The patent changes the operational parameters of the furnace by implementing variable heating rates (first stage, second stage, and intermediate rates) instead of a fixed heating rate. This parameter change allows the system to provide aggressive heating when needed and gentle heating when near the setpoint, improving temperature control precision without requiring additional thermostat contacts
2Measurement precision
If a two-stage thermostat is used to provide dual rate heating, then the temperature control precision is improved, but the device complexity increases
Solution Approach 1:
The patent makes the single-stage thermostat universal by implementing software-based multi-rate control that can provide first stage, second stage, and intermediate heating rates. This allows a simple single-stage thermostat to perform the functions of a complex two-stage or multi-stage thermostat through algorithmic control of the gas valve and blower motor
Solution Approach 2:
The patent replaces the mechanical multi-contact thermostat structure with an electronic control system. Instead of using additional mercury bulb contacts and bi-metal sensors to achieve multi-rate heating, the system uses a processor to calculate and implement appropriate heating rates, substituting mechanical complexity with electronic intelligence
3Loss of energy
If modulating gas valves and variable-speed motors are used, then the operational efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent implements feedback control by continuously monitoring the furnace operation and adjusting the gas valve and blower motor speeds based on actual performance. The system uses temperature sensors and operational data to provide feedback to the control algorithm, which then adjusts heating rates to optimize fuel utilization and reduce energy loss
Solution Approach 2:
The patent applies dynamics by implementing variable-speed control of the blower motor and modulating control of the gas valve. These dynamic adjustments allow the system to match heating output precisely to demand, improving fuel utilization efficiency by avoiding both under-heating and overheating conditions
Data Source
AI summary
A method and system for operating a modulating furnace from a single-stage thermostat. The furnace control system may include a processor, a gas valve, a variable-speed motor, and a thermostat. The furnace control may execute a thermostat algorithm comprising the steps of: determining if a heating load needs to be satisfied; running burners at an intermediate input rate, a modulated input rate, and a maximum input rate for each respective first, second, and third time intervals until the heating load is satisfied; calculating a heating load requirement as function of the time intervals; and determining an initial input rate for a next cycle based on the calculated heating load requirement.