Combination Boiler Temperature-Based Flow Estimation for DHW Control
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Solution Overview
Problem
Current combination boilers face issues with undershooting and overshooting domestic hot water (DHW) temperatures due to inadequate initialization and control of the burner fan, especially at low flow rates, and the addition of a DHW flow sensor increases cost and complexity without detecting low flow rates effectively.
Innovation Solution
A method and system that determine the boiler loop flow rate and DHW flow rate based on measured temperatures, allowing the controller to initialize or modify the input fan according to the required heat output, ensuring precise temperature control without the need for a DHW flow sensor, by calculating the required heat output as the DHW flow rate multiplied by the temperature differential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DHW output flow sensor is provided to detect DHW output flow rate, then the flow rate can be used to adjust boiler loop temperature, but cost and device complexity increase
Solution Approach 1:
The patent creates a virtual copy of the flow sensor function by calculating an estimated DHW output flow rate using the formula: estimated flow rate = (boiler loop flow rate × boiler loop temperature differential) / DHW temperature differential. This calculation replicates the information a physical flow sensor would provide without adding hardware complexity or cost.
Solution Approach 2:
The patent replaces the mechanical/physical DHW flow sensor with a computational approach using temperature measurements and flow rate calculations. The controller uses readily available temperature data from the boiler loop and DHW loop to compute the estimated flow rate, substituting a physical sensing mechanism with a mathematical model.
2Ease of operation
If the burner input fan is initialized only on a proportional term, then the control is simple, but significant temperature undershoot or overshoot occurs
Solution Approach 1:
The patent performs preliminary actions by calculating the required heat output before burner initialization using the formula: required heat output = estimated DHW flow rate × DHW temperature differential. This pre-calculation allows the system to set the appropriate fan speed and heat input level in advance, preventing temperature undershoot or overshoot during burner startup.
Solution Approach 2:
The patent implements dynamic control by continuously adjusting the burner input fan speed based on real-time calculations of required heat output. The system dynamically responds to changing conditions in the DHW loop and boiler loop, adjusting fan speed proportionally and integrally to maintain precise temperature control rather than using a fixed initialization value.
3Device complexity
If the boiler operates with standard proportional control, then the control system is simple, but heated water provision is delayed and temperature control is inaccurate
Solution Approach 1:
The patent performs preliminary calculations of the required heat output and estimated DHW flow rate before the burner actually fires. This allows the system to pre-determine the appropriate fan speed and heat input level, enabling immediate and accurate heating response when demand occurs, rather than reacting with delayed proportional control.
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors the DHW output temperature, boiler loop temperature, and flow rates, then adjusts the burner input fan speed accordingly. This closed-loop feedback ensures rapid response to temperature deviations and maintains accurate temperature control throughout operation.
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 quick provision of heated water with minimal temperature overshoot or undershoot, improving the accuracy and efficiency of DHW 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.