HVAC Discharge Air Offset Lookup for Return Air Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
HVAC systems often lack dedicated return air temperature sensors, making it difficult to detect faults and optimize performance, as direct measurement of return air temperature is not possible due to design constraints, cost, and signal processing limitations.
Innovation Solution
A controller in the HVAC system measures discharge air temperature when the system is not in heating or cooling mode, using this as a proxy for return air temperature, and stores temperature offsets in a lookup table for later use to determine return air temperature without a dedicated sensor, allowing for proactive fault detection and performance optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated return air temperature sensor is installed, then measurement precision of return air temperature is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses discharge air temperature as an intermediary measurement to infer return air temperature. Instead of directly measuring return air temperature with a dedicated sensor, the system measures discharge air temperature (which is easier to access) and uses it as a proxy, resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The patent creates a temperature offset lookup table that copies the relationship between discharge air temperature and return air temperature under various conditions. This allows the system to estimate return air temperature from discharge air temperature measurements, avoiding the need for direct return air temperature sensing
2Device complexity
If discharge air temperature is used as a proxy for return air temperature, then device complexity is reduced, but measurement precision deteriorates due to temperature changes in the duct
Solution Approach 1:
The patent performs preliminary measurements of discharge air temperature under various known return air temperature conditions to build a lookup table. This preliminary action captures the relationship between discharge and return air temperatures before actual operation, allowing accurate estimation during normal operation without real-time complex measurements
Solution Approach 2:
The patent changes the operational parameters (airflow rates, temperature conditions) during the calibration phase to build a comprehensive lookup table. By measuring discharge air temperature across multiple parameter combinations, the system accounts for temperature changes in the duct under different operating conditions, maintaining measurement precision while using a simple sensor configuration
3Adaptability or versatility
If the blower operates at different airflow rates, then adaptability of the system is improved, but the temperature offset varies requiring multiple measurements
Solution Approach 1:
The patent performs preliminary calibration measurements at multiple airflow rates to build a complete lookup table before normal operation. This preliminary action captures all necessary temperature offset data for different airflow conditions, allowing the system to adapt to various airflow rates during operation without requiring additional calibration time
Solution Approach 2:
The patent systematically varies airflow rate parameters during calibration to build a comprehensive lookup table. By pre-measuring temperature offsets across the full range of expected airflow rates, the system achieves high adaptability to different operating conditions while minimizing calibration time to a single initial setup phase
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
Enables proactive detection of system faults and improves efficiency by allowing for adjustments in operating parameters without the need for a dedicated return air temperature sensor, reducing downtime and maintenance costs.
Implementation Method 1
a temperature sensor positioned and configured to measure a discharge air temperature of the flow of air provided to the conditioned space
Implementation Method 2
a blower configured to provide a flow of air through at least one air duct and into a conditioned space
Data Source
AI summary
An HVAC system includes a blower configured to provide a flow of air into a conditioned space. A temperature sensor measures a discharge air temperature of the flow of air provided to the conditioned space. The blower provides the flow of air at a predefined flow rate. The controller determines that the measured discharge air temperature satisfies predefined stability criteria associated with a change in the discharge air temperature during a first period of time being less than a threshold value. If the stability criteria are satisfied, a temperature offset is determined between the discharge air temperature and an indoor temperature. The temperature offset is stored in a memory and is associated with the flow rate of air provided by the blower and the outdoor temperature.