HVAC Terminal Unit Flow Control to Reduce Transient Power Waste
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Solution Overview
Problem
HVAC systems face challenges with hydronic balancing due to varying hydraulic resistances over time, leading to inadequate or excessive flow through terminal units, resulting in power waste and wear on valve components.
Innovation Solution
A control algorithm that regulates heat exchange by reading supply temperature signals, estimating demand, and adjusting flow control signals to match available power, using cooling or heating curves and temperature set points to optimize fluid flow through HVAC circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If valve positions are determined based on default flow rate and opening curve, then valve positions can be determined after design stage, but the determined valve positions depend on default flow rate which becomes inadequate as hydraulic resistances change over time
Solution Approach 1:
The system continuously measures actual flow rate through the terminal unit and uses this feedback to dynamically adjust the valve position. The controller compares the measured flow rate with the desired flow rate and modifies the valve opening accordingly, ensuring accurate flow control despite changing hydraulic resistances over time.
Solution Approach 2:
The valve position is no longer fixed based on design-stage calculations but becomes a dynamic parameter that continuously adapts to changing system conditions. The controller adjusts the valve opening in real-time based on measured flow rate and temperature differential, allowing the system to respond to varying hydraulic resistances and maintain optimal performance.
2Adaptability or versatility
If limit positions are determined using temperature measurements and temperature rise quantities, then flow settings can be adjusted after design stage, but excessive flow through terminal units still occurs during transients causing power waste and valve wear
Solution Approach 1:
The system uses real-time feedback from flow rate sensors and temperature measurements to continuously monitor actual heat exchange. During transient conditions, the controller detects when actual flow exceeds the amount needed for desired heat exchange and immediately restricts the valve, preventing excessive flow and associated power waste.
Solution Approach 2:
The controller proactively restricts valve opening during transient conditions before excessive flow can occur. By anticipating potential over-flow situations and pre-adjusting the valve position based on measured parameters, the system prevents energy waste and valve wear before they happen.
3Productivity
If valve opening is increased to meet heating or cooling demand, then demand can be satisfied, but excessive flow occurs during transients causing additional wear on moving parts of valve
Solution Approach 1:
The system continuously monitors the relationship between valve position, flow rate, and temperature differential. When the desired heat exchange is achieved with a smaller valve opening, the feedback mechanism detects this and maintains the reduced opening, preventing excessive valve movement and wear while still satisfying heating or cooling demands.
Solution Approach 2:
The system dynamically changes the operating parameters by optimizing valve opening based on actual system conditions rather than using fixed or overly conservative settings. By adjusting the valve position to the minimum necessary opening that still meets demand, the system reduces mechanical stress and wear on valve components.
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 algorithm mitigates excessive flow and power waste by ensuring that heat exchange matches available power, reducing wear on components and improving system efficiency.
Implementation Method 1
Terminal units can be heating devices and/or cooling devices. A terminal unit of a domestic heating system can be a heat exchanger such as a radiator.
Implementation Method 2
Factors such as pipe cross-sections, valve characteristics, positions of terminal units within the distribution network etc. affect the flow through the circuits of a HVAC installation. These factors yield hydraulic resistances that vary throughout the system.
Data Source
AI summary
Various embodiments include a method of controlling heat exchange via a terminal unit of a terminal-side circuit of a system for HVAC with a source-side circuit coupled to the terminal-side circuit comprising: reading a terminal-side supply temperature signal; producing a supply temperature from the terminal-side supply temperature signal; estimating a percentage demand signal as a function of the supply temperature; estimating an actual demand for power by rescaling a value of maximum available power by the percentage demand signal; comparing the actual demand for power to the value of maximum available power; and if the actual demand for power exceeds the value of maximum available power: producing a first flow control signal based on the value of maximum available power; and controlling a flow of a fluid through the source-side circuit based on the first flow control signal.