HVAC Coil Inlet Liquid Sensing for Freeze Prevention Control
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Solution Overview
Problem
Conventional building HVAC systems rely on air temperature sensors to monitor coil conditions, which are inadequate for accurately measuring fluid temperatures, leading to potential freezing issues in heat exchanger coils, resulting in operational problems and increased energy costs.
Innovation Solution
A freeze protection system with a temperature sensor at the coil inlet and a controller that measures the liquid temperature, compares it to a threshold, and engages preventive actions such as adjusting flow rates or airflow velocities to prevent freezing, using a heat transfer model to calculate optimal flow rates and switching to air temperature measurements if the liquid temperature sensor is unreliable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If air temperature sensors are used to monitor coil conditions, then the system structure remains simple, but the temperature measurement accuracy deteriorates because air temperature does not directly reflect fluid temperature
Solution Approach 1:
The patent introduces an intermediary mathematical model that correlates air temperature measurements with fluid temperature. Instead of directly measuring fluid temperature (which would require complex intrusion into the coil), the system uses air temperature as an indirect indicator and applies a mathematical relationship to estimate the actual fluid temperature, thus achieving accurate measurement without direct contact sensors
Solution Approach 2:
The patent replaces physical temperature sensors that would need to be installed inside the coil with a mathematical modeling approach. The system substitutes direct mechanical/physical measurement with computational estimation based on air temperature readings and heat transfer equations, reducing hardware complexity while maintaining measurement accuracy
2Reliability
If fluid temperature is monitored more accurately with direct sensors, then freeze detection reliability improves, but the system complexity and installation difficulty increase
Solution Approach 1:
The patent implements a feedback mechanism where air temperature measurements are continuously fed into a mathematical model that predicts fluid temperature. The system constantly compares the predicted fluid temperature against freeze thresholds and adjusts operations accordingly, creating a reliable closed-loop control system that uses readily available air temperature data to ensure freeze protection
Solution Approach 2:
The system uses the existing air temperature sensor and mathematical models to self-determine fluid temperature conditions without requiring additional dedicated fluid temperature sensors. The mathematical model automatically processes the air temperature data and provides freeze risk assessment, making the system self-sufficient using existing components
3Reliability
If conventional air temperature monitoring is used, then installation remains simple, but operational reliability deteriorates due to inaccurate freeze detection
Solution Approach 1:
The patent performs preliminary actions by establishing mathematical models and correlation relationships between air and fluid temperatures during system design and commissioning. These pre-established models are then used during operation to accurately predict fluid temperature from air temperature readings, ensuring reliable freeze detection without requiring complex real-time calculations or additional sensors during 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 provides more accurate temperature measurements, reduces the risk of coil freezing, minimizes operational issues, and optimizes energy usage by closely tracking the actual freezing temperature of the fluid, thereby enhancing the efficiency and reliability of HVAC systems.
Implementation Method 1
obtain a measured temperature of the liquid at the inlet of the coil from a temperature sensor positioned at an inlet of a coil
Implementation Method 2
compare the measured temperature of the liquid at the inlet of the coil with a freeze prevention temperature threshold
Implementation Method 3
a valve operable to control a flow rate of the liquid through the coil
Implementation Method 4
a fan or damper operable to control a velocity of an airflow across the coil
Implementation Method 5
use a heat transfer model for the coil to calculate a threshold flow rate of the liquid through the coil sufficient to prevent the liquid from freezing
Data Source
AI summary
A freeze protection system for a heating, ventilation, or air conditioning (HVAC) system is shown. The freeze protection system includes a temperature sensor positioned at an inlet of a coil within which a liquid is at risk of freezing, and a controller comprising a processor and memory. The memory stores instructions that are executed by the processor. The processor is instructed to obtain a measured temperature of the liquid at the inlet of the coil from the temperature sensor, compare the measured temperature of the liquid at the inlet of the coil with a freeze prevention temperature threshold, engage a freeze prevention action in response to a determination that the measured temperature of the liquid at the inlet of the coil is less than or equal to the freeze prevention temperature threshold.