Airside Economizer Changeover Using Dry-Bulb and Dew-Point Control
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Solution Overview
Problem
Existing airside economizer systems face inefficiencies due to inaccurate enthalpy measurements, particularly in dry-coil conditions, leading to incorrect enabling or disabling of the economizer, resulting in energy waste and suboptimal energy savings.
Innovation Solution
A method that measures moisture-related properties of return air and outside air to determine if conditioning results in wet-coil or dry-coil conditions, calculating energy measures for both scenarios, and comparing these to selectively enable the economizer based on which air source requires less energy for conditioning, ensuring accurate economizer operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential enthalpy measurement is used to control economizer, then economizer can be enabled when outside air enthalpy is lower than return air enthalpy, but measurement inaccuracies in dry-coil conditions lead to incorrect enabling/disabling decisions
Solution Approach 1:
The patent changes the control parameter from enthalpy (which combines temperature and humidity) to separate measurements of dry-bulb temperature and dew-point temperature. This allows independent assessment of sensible and latent cooling requirements, eliminating the measurement accuracy issues that arise when using enthalpy alone in dry-coil conditions.
Solution Approach 2:
The patent segments the single enthalpy measurement into two separate temperature measurements (dry-bulb and dew-point). This segmentation allows the system to independently evaluate sensible cooling load (using dry-bulb temperature) and latent cooling load (using dew-point temperature), providing more reliable control decisions.
2Loss of energy
If economizer is enabled based on enthalpy comparison alone, then energy savings can be achieved, but energy waste occurs when incorrect enabling decisions are made due to measurement inaccuracies
Solution Approach 1:
The patent changes from using a single enthalpy parameter to using two separate temperature parameters (dry-bulb and dew-point). This allows the system to accurately determine both sensible and latent cooling requirements, preventing energy waste from incorrect economizer control decisions while maintaining operational simplicity through automated control logic.
Solution Approach 2:
The patent implements feedback control by continuously monitoring both dry-bulb and dew-point temperatures and adjusting economizer operation based on the combined assessment of sensible and latent cooling loads. This feedback mechanism ensures the economizer is enabled only when it will actually reduce energy consumption.
3Device complexity
If only dry-bulb temperature measurement is used for economizer control, then system complexity is reduced, but measurement of latent cooling load is insufficient leading to suboptimal energy savings
Solution Approach 1:
The patent adds dew-point temperature measurement to the existing dry-bulb temperature measurement. This addition allows the system to assess latent cooling load capability while maintaining the simplicity of temperature-based measurements. The combined information from both temperature measurements enables accurate determination of total cooling load (sensible plus latent).
Solution Approach 2:
The patent makes the temperature measurement system multi-functional by using both dry-bulb and dew-point temperature measurements to simultaneously assess both sensible and latent cooling requirements. This universal approach allows a single measurement system to evaluate the complete cooling load picture.
Data Source
AI summary
Methods and apparatus for controlling an economizer in a ventilation system based upon moisture related properties of a first input air source and a second input air source to minimize energy for conditioning air in a structure.