Recovery Wheel Speed Control for Low Carry-Over Ventilation
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Solution Overview
Problem
Variable air-volume HVAC systems face challenges in maintaining effective purge operation and reducing energy consumption when used with energy recovery wheels, leading to high contaminant carry-over levels due to changes in system pressures and airflows, which is unacceptable in applications like research laboratories and hospitals.
Innovation Solution
The system controls the recovery wheel's speed and purge flow by adjusting parameters such as pressure, differential pressure, flow rate, and fan speed, using sensors and digital controllers to maintain purge effectiveness and limit contaminant carry-over, while minimizing purge airflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed purge angle is used in a variable air-volume system, then the system structure is simple, but contaminant carry-over increases due to changing pressure and flow conditions
Solution Approach 1:
The patent applies the dynamics principle by making the purge angle adjustable rather than fixed. The purge angle is dynamically modified based on system operating conditions (flow rate, pressure differential) to maintain effective purge operation across varying airflow conditions in variable air-volume systems, thereby preventing contaminant carry-over while managing system complexity.
2Object-affected harmful factors
If purge airflow is increased to maintain purge effectiveness, then contaminant carry-over is reduced, but energy consumption increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the purge angle based on operating conditions such as flow rate and pressure differential. This optimization allows the system to maintain effective purge operation (limiting contaminant carry-over) while minimizing purge airflow and associated energy consumption, rather than using a constantly high purge airflow rate.
3Use of energy by moving object
If the recovery wheel speed is increased to improve heat transfer, then energy recovery efficiency increases, but purge effectiveness decreases due to higher contaminant transfer risk
Solution Approach 1:
The patent applies dynamics by dynamically adjusting the purge angle in response to changes in recovery wheel speed and operating conditions. When the recovery wheel operates at higher speeds for improved energy recovery, the purge angle is modified to maintain effective purge operation, preventing contaminant carry-over while allowing the recovery wheel to operate at optimal speeds for energy efficiency.
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 ensures effective purge operation with reduced energy consumption, achieving contaminant carry-over levels below 0.1% and optimizing energy recovery efficiency across varying airflow conditions, thus enabling the use of energy recovery wheels in stringent applications.
Implementation Method 1
recovery wheel 10 rotates about axle 11 in the direction shown, transferring heat, moisture, or both, between return/exhaust airstream 16 and outside/supply airstream 14
Implementation Method 2
recovery wheel 10 rotates about axle 11 in the direction shown, transferring heat, moisture, or both, between return/exhaust airstream 16 and outside/supply airstream 14
Implementation Method 3
the pressure of the outside air may he higher than the pressure of the exhaust air at the recovery wheel, and a portion of the outside air may be diverted to purge the return or exhaust air from a portion of the rotating recovery wheel
Implementation Method 4
the baffle plate or purge section of the recovery wheel typically uses the pressure differential between the outside/supply airstream and the return/exhaust airstream, to force high velocity, unconditioned, clean outside air through the wheel media as it rotates
Data Source
AI summary
Control systems for recovery wheels, ventilation systems with recovery devices, buildings having ventilation, and methods of controlling recovery wheels and controlling or modifying ventilation systems. A parameter of ventilation systems or recovery devices, such as the speed of a recovery wheel, may be controlled as a function of pressure, differential pressure, flow rate, or fan speed, for example, to provide appropriate purge flow to maintain purge effectiveness and limit the carry-over of contaminants from a return/exhaust airstream to an outside/supply airstream, for instance, in a variable air-volume system. A purge angle may be set at a minimum position commensurate with a maximum flow rate and recovery-wheel speed may be reduced at lower flows to maintain purge effectiveness. In some embodiments, temperature and humidity are measured, and wheel speed is also controlled as a function of these measurements. Systems may utilize sensors, input devices, digital controllers, variable-speed drives, and alarms.