Air-conditioning system with variable subcooling
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Solution Overview
Problem
Traditional air-conditioning systems face challenges in efficiently handling increased outside air requirements due to new ventilation standards, leading to over-ventilation and increased energy consumption, while lacking effective capacity control and modulation capabilities.
Innovation Solution
A dedicated outside air-conditioning system (DOAS) is designed with heat exchanger coils, sensors, and fluid control valves to combine the effects of variable subcooling refrigerant and modulating hot discharge gas, enhancing system capacity and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional central HVAC systems are oversized to handle peak latent load and meet new ASHRAE ventilation standards, then humidity control and ventilation requirements are satisfied, but energy consumption increases significantly
Solution Approach 1:
The system separates dehumidification and cooling functions into distinct components: a DOAS unit handles latent load (dehumidification) by cooling outdoor air to saturation and reheating it, while the main HVAC unit handles sensible load (temperature control). This segmentation allows each system to be optimally sized for its specific function, eliminating the need to oversize the entire system for peak latent conditions.
Solution Approach 2:
The system implements dynamic control through sensors and modulating valves that continuously adjust refrigerant flow and hot gas injection based on real-time conditions. This enables the system to adapt capacity to actual load requirements rather than operating at fixed high capacity, reducing energy consumption during part-load conditions.
2Reliability
If traditional air conditioning systems increase outside air flow rate to meet ventilation standards, then indoor air quality improves, but moisture removal difficulty increases and energy efficiency deteriorates
Solution Approach 1:
The DOAS unit performs preliminary dehumidification of outdoor air before it enters the main HVAC system. By cooling the outdoor air to saturation and removing moisture in advance, the system prevents excess moisture from entering the building, eliminating the need for the main HVAC system to work harder to remove moisture later.
Solution Approach 2:
The system uses sensors to monitor humidity levels and continuously adjusts the DOAS unit's operation to maintain optimal moisture removal. This feedback control ensures the system responds dynamically to changing outdoor conditions and indoor moisture loads, optimizing energy efficiency while maintaining indoor air quality.
3Device complexity
If conventional air conditioning systems lack capacity control and modulation capabilities, then system design is simplified, but system efficiency and performance deteriorate
Solution Approach 1:
The system incorporates modulating valves and sensors that enable continuous adjustment of refrigerant flow and hot gas injection rates. This dynamic capability allows the system to optimize performance across varying load conditions, significantly improving part-load efficiency without requiring complex variable speed compressors or multiple stages.
Solution Approach 2:
The system changes operational parameters (refrigerant flow rate, hot gas injection amount, evaporator temperature) based on real-time conditions to optimize efficiency. By dynamically adjusting these parameters rather than operating at fixed settings, the system achieves high efficiency across a wide range of loading conditions.
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 improved DOAS achieves better latent capacity, energy efficiency, and intelligent control, allowing for flexible system sizing and optimized moisture removal efficiency, thereby meeting new efficiency requirements and load demands.
Implementation Method 1
heat exchanger coils configured with sensors, fluid and gas refrigerant control valves that combine the effects of variable subcooling refrigerant and modulating hot discharge gas
Implementation Method 2
an evaporator, which is cooled by the evaporating refrigerant, cools the air
Implementation Method 3
A conventional air-conditioning system includes a condenser, an evaporator, and a compressor for recirculating refrigerant through the condenser and evaporator
Data Source
AI summary
A dedicated outside air-conditioning system (DOAS) that may automatically generate variable subcooling refrigerant delivered to the evaporator; and modulate hot discharge gas to reduce the relative humidity of the discharge air from the DOAS. The DOAS may include fluid control valves configured to regulate delivery of the refrigerant in order to seamlessly flex between maximum latent capacity (minimum discharge dewpoint) and maximum sensible capacity (minimum leaving air discharge dry bulb temperature) to match load and/or ventilation air requirements.