Method and system for controlling a combination boiler
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Solution Overview
Problem
Current combination boiler systems face challenges in quickly reaching desired temperatures for domestic hot water demands, managing low flow draws, and allowing hot water circulation or recirculation, due to minimum flow rate requirements and frequent firing cycles that lead to thermal cycling and reduced boiler lifespan.
Innovation Solution
A combination boiler system with a primary and secondary heat exchanger, and a controller that monitors temperatures to initiate pre-heat operations by circulating heated water without firing the burner when inlet and output temperatures fall below certain thresholds, and ends pre-heat when temperatures exceed cancellation thresholds, allowing for efficient heat transfer and circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flow switch with minimum flow rate setting is used to detect DHW draw, then the boiler can be triggered to fire, but low flow draws below the minimum setting cannot be detected and the boiler will not fire
Solution Approach 1:
The system changes the detection parameter from flow rate (which has a minimum threshold) to temperature differential across the heat exchanger. By monitoring the temperature difference between inlet and outlet water, the system can detect even very low flow conditions without being constrained by the flow switch's minimum flow rate setting.
Solution Approach 2:
The patent replaces the mechanical flow switch detection mechanism with a thermal detection system using temperature sensors. This substitution allows for more precise detection of low flow conditions by measuring temperature changes in the water rather than relying on mechanical flow rate thresholds.
2Speed
If the boiler fires immediately upon DHW draw detection, then hot water is provided quickly, but frequent firing cycles cause thermal cycling of the heat exchanger and reduce boiler lifespan
Solution Approach 1:
The system performs preliminary heating of the heat exchanger and water storage tank before actual DHW demand occurs. By pre-heating the water in the storage tank during periods of low demand or using waste heat from the boiler loop, the system reduces the need for frequent full-firing cycles, thereby extending boiler lifespan while still meeting hot water demands quickly.
Solution Approach 2:
The system implements periodic circulation of heated water through the heat exchanger and storage tank, creating a thermal buffer that reduces the frequency of burner firing. This periodic thermal cycling maintains hot water availability without subjecting the boiler to excessive firing cycles.
3Ease of operation
If hot water circulation is implemented with full circulation flow passing through the combination boiler, then hot water recirculation is achieved, but the flow rate is insufficient to trigger the flow switch
Solution Approach 1:
The patent extracts the circulation detection function from the flow switch and places it in the temperature monitoring system. By measuring temperature differences across the heat exchanger during circulation mode, the system can detect and control hot water circulation without requiring the circulation flow to meet the flow switch's minimum triggering threshold.
Solution Approach 2:
The temperature monitoring system serves multiple functions: it detects both actual DHW draws and hot water circulation conditions, and it controls both burner firing and circulation pump operation. This multi-functionality allows the system to manage low flow draws and circulation without being constrained by the flow switch's minimum flow rate requirement.
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 solution reduces the time to reach desired temperatures, manages low flow conditions, and enables hot water circulation/recirculation, thereby extending boiler lifespan and optimizing energy usage.
Implementation Method 1
a secondary heat exchanger configured to transfer heat energy from the boiler loop to the domestic water loop
Implementation Method 2
a burner configured to provide heat to the primary heat exchanger
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A combination boiler (100) provides heated water to a boiler loop and domestic hot water (DHW) to a domestic water loop. The combination boiler (100) includes a primary heat exchanger (PHE; 106) connected to the boiler loop and a burner (108) to provide heat to the primary heat exchanger (106). A secondary heat exchanger (SHE; 116) transfers heat energy from the boiler loop to the domestic water loop. A controller (120) monitors a PHE inlet temperature and a DHW output temperature, obtains a pre-heat initialization temperature threshold and a pre-heat cancellation temperature threshold, and detects a low temperature condition. A pre-heat operation is initiated responsive to the low temperature condition by circulating heated water from the PHE (106) to the SHE (116). The burner (108) is selectively fired at least in part according to an outlet temperature of the PHE (106).