Variable-Speed Compressor and Fan Control for HVAC 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
The implementation of a variable-speed compressor and circulation fan system, where a controller measures and adjusts the speeds of both components to ensure the indoor blower speed remains below the Normal cooling Cubic Feet per Minute (CFM), thereby maintaining a low S/T ratio and optimizing latent capacity without the need for re-heat dehumidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the circulation fan speed is increased to meet high sensible cooling demand, then the sensible cooling capacity is improved, but the latent capacity decreases and the S/T ratio exceeds 0.8
Solution Approach 1:
The patent applies dynamics by implementing variable-speed control for both the circulation fan and compressor. The system continuously adjusts their speeds based on real-time sensing of cooling demand and humidity conditions, allowing the S/T ratio to be maintained below 0.8 across varying load conditions. This dynamic adjustment resolves the contradiction by enabling the system to adapt fan and compressor speeds to simultaneously meet sensible cooling demands while preserving latent capacity.
Solution Approach 2:
The patent changes operating parameters (fan speed and compressor speed) based on detected conditions. When high sensible cooling demand is detected, the system increases compressor speed more than fan speed, thereby changing the ratio of refrigerant circulation to air flow. This parameter change maintains the S/T ratio below 0.8, ensuring latent capacity is preserved even when sensible cooling capacity is increased.
2Reliability
If the circulation fan speed is reduced to maintain low S/T ratio and latent capacity, then the latent capacity is improved, but the sensible cooling capacity decreases
Solution Approach 1:
The variable-speed control system dynamically adjusts the compressor speed to compensate for reduced fan speed. When the fan speed is reduced to maintain latent capacity, the compressor speed is increased proportionally to maintain adequate refrigerant circulation and cooling capacity. This dynamic coordination allows the system to preserve latent capacity while still meeting sensible cooling demands through optimized refrigerant flow.
Solution Approach 2:
The system changes the operating parameters by adjusting the compressor speed in response to fan speed changes. When fan speed is reduced to maintain S/T ratio below 0.8, the compressor speed is increased to compensate for reduced air flow, thereby maintaining sensible cooling capacity despite the lower fan speed. This parameter coordination resolves the contradiction between latent capacity and sensible cooling capacity.
3Device complexity
If a fixed-speed system is used, then the device complexity is reduced, but the ability to optimize latent capacity under varying conditions is worsened
Solution Approach 1:
The patent applies self-service by implementing a control system that automatically senses cooling demand and humidity conditions, then autonomously adjusts fan and compressor speeds to maintain optimal S/T ratio. The system serves itself by making real-time adjustments without manual intervention, optimizing latent capacity across varying conditions while keeping the control logic integrated within the existing HVAC controller, thereby limiting the increase in device complexity.
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.