HVAC Low Ambient Cooling Control Using Temperature Offset Correction
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Solution Overview
Problem
HVAC systems experience inaccurate outdoor ambient temperature measurements due to heat transfer from the condenser, leading to abnormal system behavior such as improper fan operation and excessive cycling, which reduces the lifetime of the fan and compressor.
Innovation Solution
An HVAC system with a controller that adjusts fan speed based on refrigerant saturated liquid temperature thresholds and generates an outdoor ambient temperature offset to correct for condenser heat-induced measurement errors, preventing abnormal system behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor measures outdoor ambient temperature near the condenser, then the temperature measurement is readily available, but the condenser heat causes inaccurate measurements leading to abnormal system behavior
Solution Approach 1:
The patent extracts the harmful thermal influence by introducing a virtual temperature sensor that calculates ambient temperature through offset adjustment, separating the measurement function from the physical proximity to the condenser heat source
Solution Approach 2:
The patent uses an offset value as an intermediary element to compensate for thermal interference. This offset acts as a mediator between the actual sensor reading and the true ambient temperature, correcting the measurement without requiring physical separation from the condenser
2Temperature
If the fan speed is increased to cool the condenser in low ambient conditions, then the refrigerant temperature is reduced, but the system experiences excessive cycling that reduces fan and compressor lifetime
Solution Approach 1:
The patent implements feedback control by continuously monitoring the refrigerant saturated liquid temperature and adjusting fan speed accordingly. The system uses threshold-based feedback to increase fan speed when temperature is too high and decrease it when appropriate, preventing excessive cycling while maintaining reliable operation
Solution Approach 2:
The patent applies dynamic fan speed control instead of fixed speed operation. The fan speed is continuously adjusted based on real-time refrigerant temperature conditions, allowing the system to adapt to changing thermal conditions and avoid the wear associated with frequent on/off cycling
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 solution extends the lifetime of the compressor and fan by reducing excessive cycling and maintaining efficient operation during low ambient conditions.
Implementation Method 1
During low ambient conditions, the condenser typically operates at a temperature that is higher than the outdoor ambient temperature of the air... heat from the condenser may cause the outdoor ambient temperature measurements from the sensor to rise
Implementation Method 2
a fan configured to transfer an airflow across a condenser... increase a speed of the fan to decrease the saturated liquid temperature of the refrigerant
Data Source
AI summary
A method of operating an HVAC system is provided. The method includes receiving an outdoor ambient temperature (OAT) and determining that the HVAC system should operate in a low ambient cooling mode of operation if the OAT is below a first threshold temperature. In the low ambient cooling mode of operation, the method includes storing the OAT as a baseline OAT. The method includes measuring a plurality OATs during a first pre-determined duration and determining a maximum OAT. The method includes generating an OAT offset based on a difference between the maximum OAT and the baseline OAT. The method includes generating an adjusted OAT based on a difference between a second OAT and the OAT offset. If the adjusted OAT is greater than a second threshold temperature, the method includes exiting the low ambient cooling mode of operation.