Methods and system for demand-based control of a combination boiler
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Solution Overview
Problem
Current combination boilers face issues with initially and continuously undershooting and overshooting domestic hot water (DHW) temperatures due to inadequate burner fan control, which can be exacerbated by the absence of a DHW flow sensor and the use of proportional fan speed initialization, leading to delayed or incomplete heating.
Innovation Solution
A method and system for controlling DHW output temperature in a combination boiler that involves determining the boiler loop flow rate, measuring temperatures, estimating the DHW flow rate, and adjusting the input fan rate based on the required heat output to minimize temperature deviations from the set point, without relying on a DHW flow sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a DHW output flow sensor is installed to detect flow rate and adjust boiler loop temperature, then temperature control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the flow sensing function from a dedicated flow sensor and implements it using the existing temperature sensors and boiler loop parameters. The DHW flow rate is calculated indirectly using the formula: DHW flow rate = (boiler loop flow rate × boiler loop temperature differential) / DHW temperature differential, eliminating the need for a separate flow sensor while maintaining control accuracy
Solution Approach 2:
The patent uses the boiler loop temperature differential as an intermediary parameter to infer DHW flow rate. By measuring the temperature change in the boiler loop and using it to calculate the DHW flow rate, the system achieves flow detection without direct flow sensing, reducing device complexity while maintaining measurement capability
2Device complexity
If proportional fan speed initialization is used, then device complexity is reduced, but temperature control accuracy deteriorates due to significant undershoot and overshoot
Solution Approach 1:
The patent performs preliminary calculations of the required heat output and corresponding fan speed before the burner actually fires. By determining the appropriate fan initialization rate in advance based on the DHW flow rate and temperature requirements, the system avoids temperature undershoot without requiring complex real-time control algorithms
Solution Approach 2:
The patent implements dynamic fan speed adjustment by continuously monitoring the DHW output temperature and comparing it to the set point. The controller dynamically modifies the fan operating rate during operation to compensate for temperature deviations, transitioning from static proportional control to dynamic adaptive control
3Device complexity
If burner fan speed is not dynamically adjusted based on DHW flow rate, then device complexity is reduced, but heating speed and productivity decrease due to delayed DHW output
Solution Approach 1:
The system performs preliminary determination of the DHW flow rate and required heat output before the burner operates. This advance calculation allows the fan to be initialized at the optimal speed from the start, immediately providing the necessary heating capacity without gradual ramp-up delays
Solution Approach 2:
The patent implements a feedback control mechanism where the controller continuously monitors the DHW output temperature and uses this information to dynamically adjust the fan operating rate. This closed-loop feedback ensures the heating system responds appropriately to actual demand conditions, maintaining high heating speed while adapting to varying flow rates
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 enables faster provision of heated water with minimal overshoot or undershoot of the desired temperature, improving the efficiency and accuracy of DHW output temperature control in combination boilers.
Implementation Method 1
a secondary heat exchanger configured to transfer heat energy from the boiler loop to a domestic water loop
Implementation Method 2
a burner configured to provide heat to the primary heat exchanger
Data Source
AI summary
A combination boiler provides heated water to a boiler loop and heated domestic hot water (DHW) to a DHW loop. A primary heat exchanger is connected to the boiler loop. A burner provides heat to the primary heat exchanger and an input fan supplies a fuel and air mixture to the burner. A secondary heat exchanger transfers heat energy from the boiler loop to a domestic water loop. A controller determines a boiler loop flow rate. The controller measures an input temperature of the boiler loop, an output temperature of the boiler loop, and a DHW output temperature of the domestic water loop. The controller determines a DHW input temperature and estimates a DHW flow rate. The input fan speed is initiated or operated according to a required heat output of the burner corresponding to the DHW flow rate.