Method and controller for signaling icing in a heating, ventilation or air-conditioning equipment
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Solution Overview
Problem
Existing HVAC systems face challenges in reliably detecting icing within heat exchangers and preventing clogging, often relying on single measured quantities which can be unreliable, especially in complex installations, and may not account for changes in temperature or fluid flow rates.
Innovation Solution
A method that utilizes differential pressure and temperature sensors to detect icing by monitoring changes in measured quantities across heat exchangers, employing a differential signal and time derivative analysis, and activating a preheater or reversing fluid flow to prevent icing, while considering operating characteristics like fan speeds and damper positions, and using an icing curve for multi-dimensional inference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single measured quantities are used to detect icing, then the detection system is simple, but the reliability of icing detection deteriorates
Solution Approach 1:
The detection system is segmented into multiple independent measurement channels (pressure drop measurement, temperature measurement, air density measurement) that operate in parallel. Each channel provides a different perspective on the icing condition, and their results are combined to make a final determination, thereby improving reliability without requiring any single channel to be overly complex
Solution Approach 2:
The system uses a multi-functional approach where the same sensor infrastructure serves multiple purposes: pressure sensors detect both normal pressure drops and icing-related pressure changes, temperature sensors monitor both operational temperature and icing conditions, and these measurements are used together with fan curve analysis to make comprehensive icing detection decisions
2Measurement precision
If multiple measured quantities are used to detect icing, then the accuracy of icing detection improves, but the complexity of the detection system increases
Solution Approach 1:
The system transitions from single-dimension temperature-based detection to multi-dimensional detection by adding pressure drop measurements and air density measurements as new dimensions. This allows the system to detect icing conditions more precisely by analyzing patterns across multiple dimensions rather than relying on temperature alone
Solution Approach 2:
Fan curves serve as an intermediary element that connects the raw sensor measurements to the icing detection decision. The fan curves provide a reference framework that helps interpret the multi-dimensional measurements and distinguish between normal operational variations and actual icing conditions, thereby improving precision without requiring direct complex processing of all sensor data
3Reliability
If temperature-based detection is used, then the detection method is simple, but it fails to account for changes in fluid flow rates which reduces reliability
Solution Approach 1:
The system monitors changes in multiple parameters (pressure drop, temperature, air density) rather than relying on a single temperature threshold. By tracking how these parameters change relative to each other and comparing them against fan curve relationships, the system can distinguish between temperature changes caused by flow rate variations and temperature changes caused by icing, thereby maintaining reliability under varying flow conditions
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 provides more accurate and nuanced detection of icing, reducing energy consumption and heat exchanger failures by effectively inhibiting ice buildup and clogging, and allowing for proactive maintenance in HVAC systems.
Implementation Method 1
A sensor may be connected to record a pressure drop across an air-handling unit and/or across a heat recovery unit. An excessive value of pressure drop across an air-handling unit or across a heat recovery unit may suggest build-up of ice inside the respective unit.
Implementation Method 2
Also, a temperature probe can be arranged upstream of the air handling unit and/or upstream of the heat recovery unit. A signal obtained from the temperature probe may thus indicate an imminent risk.
Implementation Method 3
employing a differential signal and time derivative analysis, and activating a preheater or reversing fluid flow to prevent icing
Data Source
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AI summary
Control of heating, ventilation, air-conditioning equipment. A method for signaling icing within a structure (1), the structure (1) comprising a circuit (2 - 4), the circuit (2 - 4) comprising an appliance (6, 7, 10, 11) selected from a fluid conveyor (6, 7) and/or a filter (10, 11); the structure (1) comprising a sensor (8, 9, 12, 13) in fluid communication with the appliance (6, 7, 10, 11); the method comprising the steps of: the sensor (8, 9, 12, 13) recording a first signal; the sensor (8, 9, 12, 13) recording a second signal; processing the first signal to produce a first measure and processing the second signal to produce a second measure; producing a differential measure from the second measure and from the first measure; comparing the differential measure to a predetermined threshold; and producing a signal indicative of icing if the differential measure exceeds the predetermined threshold.