Discharge air reset for a constant volume air changeover bypass
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Solution Overview
Problem
Constant volume changeover bypass HVACR systems are inefficient due to frequent cycling between heating and cooling modes, leading to excessive energy consumption as they deliver either cold or warm air, failing to adapt to varying temperature deviations in conditioned spaces effectively.
Innovation Solution
A method and system that calculates an average deviation from the setpoint temperature across multiple VAV boxes to dynamically adjust the discharge air setpoint temperature, reducing the need for constant mode switching by allowing the HVACR unit to output airflow at intermediate temperatures, thereby optimizing energy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the HVACR unit frequently cycles between heating and cooling modes to meet varying temperature demands, then the system can satisfy different space temperature requirements, but energy consumption increases due to excessive mode switching
Solution Approach 1:
The discharge air temperature setpoint is made dynamic by continuously adjusting it based on the average deviation from setpoint temperatures across multiple VAV boxes. This dynamic adjustment allows the system to adapt to varying thermal conditions without requiring frequent mode cycling, thereby reducing energy consumption associated with mode transitions while maintaining temperature adaptability.
Solution Approach 2:
The system changes the discharge air temperature parameter based on calculated average deviations from setpoint temperatures. By modifying this key parameter continuously rather than switching between fixed heating and cooling modes, the system achieves better energy efficiency while maintaining the ability to meet diverse temperature requirements across different zones.
2Device complexity
If the HVACR unit delivers only cold or warm air in fixed modes, then the system operation is simplified, but the system fails to adapt effectively to varying temperature deviations in conditioned spaces
Solution Approach 1:
The discharge air temperature setpoint is made dynamic by continuously adjusting it based on the average deviation from setpoint temperatures across multiple VAV boxes. This dynamic adjustment allows the system to adapt to varying thermal conditions without requiring frequent mode cycling, thereby reducing energy consumption associated with mode transitions while maintaining temperature adaptability.
Solution Approach 2:
The system uses feedback from temperature sensors in multiple conditioned spaces to calculate the average deviation from setpoint temperatures. This feedback mechanism informs continuous adjustments to the discharge air temperature setpoint, enabling the system to adapt effectively to varying thermal conditions while maintaining relatively simple binary mode operation.
Data Source
AI summary
A method of controlling a discharge air reset in an heating, ventilation, air conditioning, and refrigeration (HVACR system includes determining, by a controller, a space temperature in a conditioned space, a setpoint temperature of the conditioned space, and an operating mode of a variable-air-volume (VAV) box for the conditioned space. The controller determines whether the operating mode of the VAV box matches an operating mode of an HVACR unit. A deviation from the setpoint temperature of the conditioned space for the VAV box for the conditioned is calculated in response to determining the VAV box is in a same mode as the HVACR unit. An average deviation from the setpoint temperature of the conditioned space is calculated. A discharge air setpoint temperature is determined based on the average deviation from the setpoint temperature of the conditioned space. The controller sets the discharge air setpoint temperature of the HVACR unit using the determined discharge air setpoint temperature.