District Heating Grid Flow Control Using Bypass Valve Extraction
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Solution Overview
Problem
District thermal energy distribution systems face challenges during low load situations, where flowrates of heat transfer fluid become low or stop, leading to significant cooling or freezing, which can result in failure to deliver heat at specified temperatures and cause equipment wear and potential leaks in fixed by-pass installations.
Innovation Solution
A method and system that use a control valve in a thermal energy extraction unit to create a bypass from the feed conduit to the return conduit when the thermal energy extraction unit is not delivering thermal energy, ensuring flow through the unit only when needed, and using a control unit to manage this bypass based on temperature or time thresholds, thus preventing stationary fluid and reducing the need for in-ground by-passes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the temperature of heat transfer fluid is increased at the central heating plant, then the delivered temperature to remote buildings is improved, but the flowrate in the district grid decreases further causing the delivered temperature to drop
Solution Approach 1:
The district grid is divided into segments with individual control valves at each building or zone. This allows localized flow regulation without affecting the entire grid's flowrate, enabling temperature control without the flowrate penalty associated with centralized temperature increases.
Solution Approach 2:
The system implements dynamic control of flowrate and temperature through automated valves that respond to real-time conditions. This allows the system to adjust flow distribution dynamically, maintaining optimal flowrates while delivering required temperatures to different locations based on actual demand and thermal losses.
2Productivity
If a by-pass valve is added to the fixed by-pass installation, then the problems at high load are reduced, but the risk of leaks and welding seam failure increases
Solution Approach 1:
The control valve is extracted from the traditional in-ground fixed by-pass installation and relocated to the thermal energy extraction unit at each building. This removes the vulnerable welding connections from the by-pass function, eliminating the leak risk associated with underground welded joints while maintaining the by-pass capability when needed.
Solution Approach 2:
The thermal energy extraction unit serves as an intermediary that provides both the heat exchange function and the by-pass function. By integrating the control valve within this unit, the system achieves flow control and by-pass capability without requiring separate vulnerable by-pass installations in the ground.
3Ease of operation
If control valves are used to regulate flowrate at buildings, then individual temperature control is improved, but the valves frequently switch between open and closed positions causing noise and wear
Solution Approach 1:
The control system implements periodic or continuous modulation of valve positions rather than frequent on/off switching. This maintains stable flow conditions and reduces mechanical wear on valve components while still achieving the required temperature control through gradual adjustments based on thermal demand and fluid temperature.
Solution Approach 2:
The system uses feedback from temperature sensors and flow measurements to continuously adjust valve positions. This closed-loop control prevents excessive switching by maintaining valves in stable positions that satisfy thermal demands, reducing wear and noise while preserving individual temperature control capability.
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 prevents significant cooling or freezing of heat transfer fluid, ensures delivery of heat at minimum temperatures, reduces equipment wear, and avoids the weaknesses of in-ground by-passes, such as leaks and strain on welding seams.
Implementation Method 1
a control valve configured to control a flow of heat transfer fluid of the district thermal energy distribution grid from the feed conduit via the thermal energy extraction unit to the return conduit
Implementation Method 2
a thermal energy extraction unit connected to a district thermal energy distribution grid
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A method for ensuring a flow of heat transfer fluid in a district thermal energy distribution grid (120) comprising a feed conduit (130) and a return conduit (140) is presented. The method comprising: checking if a thermal energy extraction unit (310) connected to the district thermal energy distribution grid is called for delivering thermal energy; upon the thermal energy extraction unit (310) not being called for delivering thermal energy, opening a control valve (340) configured to control a flow of heat transfer fluid from the feed conduit (130) via the thermal energy extraction unit (310) to the return conduit (140), thereby achieving a by-pass from the feed conduit (130) to the return conduit (140). Also control unit for controlling a thermal energy extraction unit (310) is presented.