Variable-Speed HVAC Compressor Control for Latent Capacity
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Solution Overview
Problem
HVAC systems face challenges in optimizing latent capacity, particularly when there is a high relative humidity and low sensible cooling load, as existing systems struggle to maintain a low Sensible-to-Total (S/T) ratio below 0.8, which is crucial for effective moisture removal.
Innovation Solution
A variable-speed compressor and circulation fan system controlled by a controller that measures and adjusts their speeds to maintain the S/T ratio below 0.8 by reducing the indoor blower speed or increasing the compressor speed when the circulation fan's speed exceeds the normal cooling Cubic Feet per Minute (CFM), ensuring optimal latent capacity without re-heat dehumidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the circulation fan speed is increased to meet high sensible cooling demand, then the sensible cooling capacity is improved, but the latent capacity deteriorates due to S/T ratio exceeding 0.8
Solution Approach 1:
The patent implements dynamic speed adjustment of both the circulation fan and compressor based on real-time sensing of evaporator coil temperature and ambient conditions. The controller continuously monitors the S/T ratio and dynamically adjusts fan speed to maintain it below 0.8, while simultaneously adjusting compressor speed to match the reduced fan capacity, thereby maintaining both sensible and latent cooling effectiveness under varying load conditions.
Solution Approach 2:
The system changes operational parameters by adjusting the circulation fan speed and compressor speed as control variables. When latent capacity is compromised (S/T ratio approaching 0.8), the fan speed is reduced and compressor speed is adjusted proportionally. This parameter change strategy maintains the S/T ratio within the optimal range while adapting to different cooling demands, effectively resolving the contradiction between sensible and latent capacity.
2Reliability
If the circulation fan speed is reduced to maintain low S/T ratio for dehumidification, then the latent capacity is improved, but the sensible cooling capacity deteriorates
Solution Approach 1:
The system dynamically adjusts the compressor speed in response to circulation fan speed changes. When the fan speed is reduced to maintain S/T ratio below 0.8 for effective dehumidification, the controller simultaneously reduces compressor speed to match the lower air flow capacity. This coordinated dynamic adjustment prevents oversizing the cooling capacity relative to air flow, maintaining both latent and sensible cooling effectiveness.
Solution Approach 2:
The patent uses parameter changes by adjusting both fan speed and compressor speed as interconnected variables. The compressor speed is modified in proportion to fan speed changes to maintain appropriate cooling capacity. This dual parameter adjustment resolves the contradiction by ensuring that when fan speed is reduced for latent capacity, the compressor capacity is also reduced to prevent excessive cooling that would otherwise occur with fixed-speed compressors.
3Device complexity
If a fixed-speed compressor is used with variable-speed circulation fan, then the device complexity is reduced, but the adaptability deteriorates due to inability to optimize latent capacity
Solution Approach 1:
The patent implements variable-speed control for the compressor, transforming it from a fixed-speed to a dynamically adjustable component. The compressor speed is continuously adjusted based on circulation fan speed and sensed evaporator coil temperature to maintain optimal S/T ratio. This dynamic capability enables the system to adapt to varying cooling demands and optimize latent capacity removal, resolving the adaptability limitation of fixed-speed compressors.
Solution Approach 2:
The system incorporates feedback control by sensing evaporator coil temperature and using this information to adjust compressor speed. The controller receives feedback from temperature sensors and ambient condition sensors, then modifies compressor operation accordingly. This feedback mechanism enables automatic optimization of latent capacity without requiring complex manual intervention, achieving adaptability while keeping the control system practical and manageable.
Data Source
AI summary
An HVAC system includes an evaporator coil and a metering device fluidly coupled to the evaporator coil. The HVAC system also includes a variable-speed circulation fan and a condenser coil fluidly coupled to the metering device. The HVAC system also includes a variable-speed compressor fluidly coupled to the condenser coil and the evaporator coil and a controller operatively coupled to the variable-speed compressor and the variable-speed circulation fan. The controller is configured to measure a speed of the variable-speed compressor, calculate a normal cooling Cubic Feet per Minute (CFM), measure a speed of the variable-speed circulation fan, and determine if the speed of the variable-speed circulation fan exceeds the normal cooling CFM. If the speed of the variable-speed circulation fan exceeds the normal cooling CFM, the HVAC controller adjusts a speed of at least one of the variable-speed compressor and the variable-speed circulation fan.