Boiler Integrated Control Using Non-Linear Outdoor Reset Curve
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Solution Overview
Problem
Conventional hydronic water heating systems with linear outdoor reset curves are inefficient due to non-linear heat output from common heat emitters, requiring higher water temperatures on warm days to maintain comfort, and are complex to program and integrate with existing boiler controls.
Innovation Solution
An integrated boiler control system that generates a non-linear output reset curve using three simple parameters: coldest outdoor design temperature, required water temperature for the coldest day, and desired indoor temperature, allowing for easy fine-tuning and compatibility with various heat emitters without requiring emitter-specific programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a linear outdoor reset curve is used to scale supply temperature set points, then the system meets regulatory requirements and is simple to implement, but the system sets water temperatures higher than necessary on warm days to compensate for reduced convective heat transfer, resulting in inability to run at optimal efficiency
Solution Approach 1:
The patent changes the mathematical relationship from linear to non-linear, specifically using a quadratic equation to model the outdoor reset curve. This allows the supply temperature to be more accurately matched to the actual heat output of radiators at different temperatures, enabling optimal boiler efficiency without compromising temperature setting accuracy
Solution Approach 2:
The system incorporates feedback by using actual outdoor temperature measurements to dynamically calculate the required supply temperature based on the non-linear relationship. This closed-loop approach ensures the boiler operates at optimal efficiency by adjusting temperatures according to real conditions rather than following a fixed linear schedule
2Loss of energy
If a non-linear outdoor reset curve is implemented to match heat emitter output, then energy efficiency is optimized, but the programming complexity increases significantly
Solution Approach 1:
The patent transforms the complex non-linear control problem into a manageable form by using a quadratic equation with physically meaningful parameters (outdoor design temperature, supply temperature at design condition, and supply temperature at balance point). This parameterization approach maintains energy efficiency while significantly reducing programming complexity compared to generic non-linear models
Solution Approach 2:
The system performs self-calibration by automatically determining the non-linear reset curve parameters based on standard radiator performance characteristics and local climate data. This eliminates the need for manual programming of complex non-linear relationships while maintaining optimized energy efficiency
3Reliability
If higher water temperatures are supplied on warm days to maintain comfort, then heat emitter output is sufficient, but boiler combustion efficiency decreases and energy consumption increases
Solution Approach 1:
The patent changes the temperature scaling relationship to account for the non-linear heat output characteristics of radiators. By using a quadratic outdoor reset curve, the system supplies lower temperatures on warm days when radiator convective output is reduced, maintaining comfort while decreasing boiler energy consumption
Data Source
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AI summary
A boiler assembly includes a user interface which receives user-defined water temperature set point corresponding to a minimum outdoor temperature, and an integrated controller generates a nonlinear outdoor reset curve between the user-defined set point and a second set point corresponding to maximum outdoor temperature for which heating is required, and regulates the boiler to heat water to a temperature corresponding to a set point along the nonlinear output reset curve and based on a detected outdoor temperature. The nonlinear outdoor reset curve may be generated based on aggregated heat output functions for various types of heat emitters. A linear outdoor reset curve may be generated between a maximum water temperature set point and the user-defined set point, having a slope equal to an instantaneous slope of the nonlinear outdoor reset curve at the user-defined set point.