Air Handling Unit VFD Retrofit for Coil-Safe Variable Airflow
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Solution Overview
Problem
Existing constant volume air handling systems waste energy by heating or cooling a constant and often larger-than-necessary volume of air, leading to high operational costs and inefficiencies, and retrofitting with variable frequency drives has introduced issues like coil freezing and overheating, necessitating a cost-effective solution for converting these systems to variable air flow without extensive mechanical or control system modifications.
Innovation Solution
Installation of temperature sensors, a damper end switch, air quality sensors, and motion detectors to control a variable frequency drive within the existing air handling unit, allowing for dynamic adjustment of fan speed and air volume based on demand, enabling economizer mode operation and precise control of heating, cooling, and ventilation, without replacing mechanical components or control systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a variable frequency drive is installed to reduce air volume through the air handling unit, then energy consumption for heating or cooling is reduced, but coil freezing or overheating problems occur
Solution Approach 1:
The system continuously monitors air temperature before and after the heat exchange coils using temperature sensors. This feedback mechanism allows the control system to detect temperature differences and adjust fan speed accordingly, preventing coil freezing or overheating while maintaining energy efficiency. The feedback loop ensures reliable coil operation during variable air volume conditions.
Solution Approach 2:
The fan speed is dynamically adjusted based on real-time temperature conditions rather than operating at a fixed speed. The system transitions from static constant volume operation to dynamic variable air volume operation, allowing the fan to respond to changing thermal conditions and prevent coil issues while optimizing energy consumption.
2Use of energy by stationary object
If the air volume is reduced through the air handling unit, then heating or cooling energy requirements are reduced, but heating elements or heat exchangers overheat
Solution Approach 1:
Temperature sensors positioned before and after the heat exchange coils provide continuous feedback on the temperature differential. When the air volume is reduced and the temperature difference indicates potential overheating, the control system increases fan speed to maintain proper heat exchanger temperature, preventing damage while preserving energy efficiency.
Solution Approach 2:
The system changes the operating parameters of the fan based on thermal conditions. By adjusting fan speed in response to temperature measurements, the system maintains optimal heat exchanger temperature even when air volume is reduced for energy efficiency, preventing overheating while preserving the energy benefits of variable air volume operation.
3Adaptability or versatility
If extensive mechanical modifications and control system replacements are made to convert to variable air flow, then variable frequency drive functionality is achieved, but capital investment costs increase
Solution Approach 1:
The control system is designed to work with the existing air handling unit without requiring replacement of mechanical components. The same control system handles both constant volume and variable air volume operations, as well as heating and cooling functions, eliminating the need for separate control systems and reducing overall system complexity and capital costs.
Solution Approach 2:
The system uses the existing control infrastructure to manage the variable frequency drive and air handling unit operations. Rather than requiring extensive new mechanical and control system installations, the retrofit leverages the existing control capabilities to achieve variable air flow functionality, significantly reducing capital investment requirements.
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 solution reduces energy consumption by heating or cooling only the required air volume, saving energy costs and preventing coil issues, while maintaining indoor air quality and comfort, thus offering a cost-effective retrofit to variable air flow without capital-intensive modifications.
Implementation Method 1
retrofitting a variable frequency drive to an existing air handling unit
Implementation Method 2
Temperature sensors are installed before and after the heating and cooling coils for determining the air temperature difference
Implementation Method 3
A damper end switch is installed, if necessary, on the outside air dampers to indicate the system is operating in economizer mode
Data Source
AI summary
A system and methods providing real-time monitoring, management and control of a variable frequency drive retrofit to a constant volume air handling unit without making significant mechanical or control system changes. Customers and vendors are provided with a more informative and economically attractive air handling unit. The system also provides a finer granularity of control over conditioned air properties such as temperature, humidity and air quality.