Condensing Gas Water Heater Flow Control for Cold Water Sandwich
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Solution Overview
Problem
Existing gas instantaneous water heaters experience a rapid temperature drop when hot water is turned on again shortly after being turned off, known as the 'cold water sandwich' issue, which affects user comfort and requires costly auxiliary heating measures.
Innovation Solution
A thermostatic condensing gas water heater with a main heat exchanger, a condensing heat exchanger, and a controller that adjusts flow control valves to maintain stable water temperature by utilizing the latent heat of vaporization in burnt flue gas, incorporating a housing-and-tube heat exchanger and electrical heating device for efficient temperature regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If auxiliary heating measures such as water pumps or electronic water heaters are added to solve the cold water sandwich problem, then user comfort is improved, but investment cost increases significantly
Solution Approach 1:
The patent divides the water heating system into two separate heat exchangers: a main heat exchanger for primary heating and a condensing heat exchanger for secondary heating and storage. This segmentation allows the system to use the condensing heat exchanger as a thermal buffer to prevent cold water sandwich without requiring complex auxiliary heating devices like electronic water heaters or pumps.
Solution Approach 2:
The condensing heat exchanger serves dual purposes: it condenses flue gas to recover latent heat while simultaneously storing hot water that can be quickly delivered when cold water is detected. The system uses its own condensing process to provide the auxiliary heating function, eliminating the need for external auxiliary heating devices and reducing overall system complexity.
2Use of energy by moving object
If a condensing heat exchanger is added to utilize latent heat of vaporization, then heat exchanger efficiency is improved, but device complexity increases
Solution Approach 1:
The condensing heat exchanger is designed to perform multiple functions simultaneously: it condenses water vapor from flue gas to recover latent heat, heats the incoming water, and stores hot water in its internal water channel. This multi-functionality allows the system to improve heat exchanger efficiency without adding separate auxiliary heating devices, thereby avoiding increased device complexity.
Solution Approach 2:
The water channel is nested within the condensing heat exchanger structure, with the flue gas flowing through the outer shell and water flowing through the inner channel. This nested design allows the condensing heat exchanger to efficiently transfer latent heat from flue gas to water while compactly integrating the storage function, improving energy utilization without significantly increasing system complexity.
3Measurement precision
If flow control valves are used to adjust water flow distribution between heat exchangers, then temperature control precision is improved, but device complexity increases
Solution Approach 1:
The controller continuously monitors the water temperature from the main heat exchanger and dynamically adjusts the flow control valves to regulate the proportion of water flowing through the condensing heat exchanger. This feedback control mechanism enables precise temperature control by automatically adjusting water flow distribution based on real-time temperature measurements, achieving high temperature control precision while using a relatively simple control system.
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
The solution effectively stabilizes the water temperature within a set range without increasing user costs, ensuring user comfort and safety by efficiently utilizing latent heat and preventing temperature drops when hot water is reactivated.
Implementation Method 1
the latent heat of vaporization in the burnt flue gas is absorbed through the second heat exchanger (condensing heat exchanger) to heat the water
Implementation Method 2
a first heat exchanger (main heat exchanger), a second heat exchanger (condensing heat exchanger)... along the flow direction of the burnt flue gas
Implementation Method 3
the second heat exchanger is provided with an electrical heating device heating the water in the second heat exchanger
Data Source
AI summary
A thermostatic condensing gas water heater, comprising a burner; a first heat exchanger (7), a second heat exchanger (4), a water inlet pipe (10), and a water outlet pipe (9) provided in succession along the flow direction of the burnt flue gas; a controller; and a water flow channel connecting the first heat exchanger (7) and the second heat exchanger (4) in parallel between the water inlet pipe (10) and the water outlet pipe (9), wherein flow control valves (3, 5) capable of adjusting the water flow distribution of the first heat exchanger (7) and the second heat exchanger (4) are provided on the water flow channel and controlled by the controller.