Rooftop HVAC Fan and Damper Control for CO2-Based Ventilation
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Solution Overview
Problem
Existing single-zone rooftop air conditioning units lack energy-saving features and sophistication, leading to high energy consumption, discomfort, and poor indoor air quality, with no effective retrofits available for the millions of existing units.
Innovation Solution
A control system that varies the speed of the fan drive motor in response to different operation modes and CO2 levels, using a power supply, control circuit, and CO2 detection circuit, which can be retrofitted into conventional systems without modifying the thermostat or refrigerant system, employing face split or interlaced DX coils to manage airflow and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional single-zone rooftop units operate at full fan speed continuously, then adequate airflow and cooling/heating are provided, but energy consumption is high and indoor air quality deteriorates
Solution Approach 1:
The patent applies dynamics by varying the fan speed according to operating conditions. The control system adjusts fan speed based on whether the system is in heating, cooling, or ventilation mode, and based on outdoor air requirements. This dynamic adjustment allows the fan to operate at lower speeds when full airflow is not needed, reducing energy consumption while maintaining adequate ventilation and air quality through controlled outdoor air intake.
Solution Approach 2:
The patent changes the operational parameters of the fan by introducing variable speed control. The system monitors operating modes and outdoor air requirements, then adjusts fan speed as a variable parameter rather than maintaining constant full speed. This parameter change enables energy savings during periods when reduced airflow is acceptable, while still meeting ventilation requirements through coordinated outdoor air damper control.
2Use of energy by moving object
If fan speed is reduced to save energy, then energy consumption decreases, but airflow distribution and comfort may be compromised
Solution Approach 1:
The patent applies local quality by differentiating airflow requirements for different zones and functions within the HVAC system. The control system provides separate control paths for supply air fan speed and outdoor air damper position, allowing localized optimization. During certain operating modes, the system can reduce supply fan speed while maintaining outdoor air intake to ensure local ventilation requirements are met, preserving comfort and air quality while saving energy.
Solution Approach 2:
The patent segments the airflow control into separate controllable elements: the supply air fan speed and the outdoor air damper position. This segmentation allows independent optimization of each function. The supply fan can be slowed for energy savings while the outdoor air damper is adjusted to maintain required ventilation rates, ensuring that airflow distribution and comfort requirements are met through coordinated control of separate system components.
3Ease of operation
If outdoor air intake is increased to maintain indoor air quality, then CO2 levels are controlled, but energy consumption for conditioning outdoor air increases
Solution Approach 1:
The patent applies feedback by using CO2 sensors to monitor indoor air quality and dynamically adjusting outdoor air intake accordingly. The control system receives feedback from CO2 level measurements and adjusts the outdoor air damper position to maintain acceptable indoor air quality. This feedback-based control ensures outdoor air intake is optimized rather than operating at fixed positions, reducing energy consumption for conditioning outdoor air while maintaining adequate ventilation when CO2 levels indicate good air quality.
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
The system reduces energy consumption by up to 85%, improves comfort by minimizing drafts and noise, and maintains acceptable indoor CO2 levels, while being cost-effective and easy to install and maintain, with proportional airflow distribution and reduced relative humidity.
Implementation Method 1
a circuit for detecting CO2 concentration and a circuit that provides for driving motor speed in response to the CO2 levels detected
Data Source
AI summary
An energy saving air quality control system modulates supply fan speed by use of controlled, variable-frequency drive controls for automatic dampers or suction pressure to maintain adequate air flow across the evaporator coil at partial cooling loads. Demand ventilation in the system balances air quality and energy consumption by controlling the outdoor air damper in response to indoor CO2 levels. The control system variously either (1) produces a variable 0-10 VDC output signal to modulate the outside ventilation air damper as required to keep the CO2 concentration below a set point; (2) produces a 0 or 24 VAC signal to either open or close a two-position outside air damper for as long a time period as is required in order to keep the CO2 concentration below a set point; or (3) allows manually setting the outside air damper to provide proper ventilation air at maximum occupancy and maximum air flow and modulates the supply fan speed as required to keep the CO2 concentration as measured by a CO2 monitor below set point.