HVAC Ventilation Control via Capacity Modulation
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Solution Overview
Problem
HVAC systems face challenges in ventilating a target space while maintaining thermal comfort and energy efficiency, as the thermal load required to regulate outdoor ventilation airflow often exceeds the system's capacity.
Innovation Solution
The HVAC system determines its current capacity and compares it to its total capacity, operating in a modulated ventilation mode if the current capacity exceeds the total capacity. This involves duty cycling the blower, using a variable speed blower, or regulating airflow with variable dampers to maintain set-point temperature while ventilating the space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the HVAC system operates in full ventilation mode to reduce gas concentration, then the gas concentration is brought below the threshold, but the thermal load exceeds the system capacity and thermal comfort is lost
Solution Approach 1:
The system dynamically adjusts the ventilation rate based on real-time comparison between current capacity and total capacity. When outdoor conditions change, the system transitions between different ventilation modes (full ventilation, modulated ventilation, or halted ventilation) to optimize both gas concentration reduction and thermal comfort maintenance.
Solution Approach 2:
The system changes the ventilation parameter (outdoor airflow rate) based on capacity availability. By modulating the ventilation rate from full capacity to reduced levels or temporarily halting it, the system adapts to varying thermal loads while still achieving gas concentration control over time.
2Quantity of substance
If the HVAC system prioritizes ventilation to reduce gas concentration, then the gas concentration is brought below the threshold, but excess energy is consumed
Solution Approach 1:
Instead of always providing full ventilation, the system applies partial ventilation action by modulating the outdoor airflow rate to match available capacity. This partial action is sufficient to gradually reduce gas concentration while avoiding the excessive energy consumption of full ventilation mode.
Solution Approach 2:
The system uses periodic duty cycling of the blower, alternating between on and off periods, to provide ventilation in a staggered manner. This periodic action allows the system to reduce gas concentration over time without continuously operating at full capacity, thereby reducing overall energy consumption.
3Temperature
If the HVAC system uses duty cycling to maintain thermal comfort during ventilation, then the temperature is maintained within threshold, but the ventilation effectiveness is reduced
Solution Approach 1:
The system employs periodic duty cycling of the blower, switching between on and off states, to balance thermal comfort and ventilation effectiveness. During on-periods, ventilation occurs to reduce gas concentration; during off-periods, thermal comfort is maintained by reducing or eliminating outdoor airflow. This periodic action allows both objectives to be achieved over the complete cycle.
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 reduces energy utilization during ventilation modes while minimizing the loss of thermal comfort in the target space, allowing for effective gas concentration reduction without compromising temperature regulation.
Implementation Method 1
A first heat exchanger in the duct system is configured to receive a refrigerant from the refrigerant conduit. A blower in the duct system moves a return airflow across the first heat exchanger to transfer heat between the refrigerant and the return airflow
Data Source
AI summary
The disclosure provides a method of operating a (HVAC) system. The method includes measuring a concentration of a gas in the target space, and determining that the concentration exceeds a gas concentration threshold. The method includes determining that operation of the HVAC system in a ventilation mode is indicated to reduce the concentration of the gas. The method includes determining a total capacity of the HVAC system, and determining a current capacity of the HVAC system. The method includes causing the HVAC system to operate in the ventilation mode after validating that the total capacity is greater than the current capacity during operation of the HVAC system in the ventilation mode.