Cooling Coil Reverse Airflow Defrost for Low-Dew-Point Dehumidification
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Solution Overview
Problem
Mechanical cooling and dehumidification systems face inefficiencies due to frost buildup in cooling coils, which restrict airflow and require interruptive defrosting methods, increasing energy consumption.
Innovation Solution
Implementing a reverse airflow defrost system that reverses airflow through the cooling coil when frost forms, allowing frost to melt using warmer entering air, thereby maintaining operation and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling coil operates at low temperatures to maintain low dew point, then cooling effectiveness is improved, but frost buildup occurs restricting airflow
Solution Approach 1:
The patent reverses the airflow direction through the cooling coil to defrost. Instead of continuing forward airflow that causes frosting, the system reverses airflow so that warmer air from the supply plenum flows over the frosted coil surface, melting the frost. This inversion of airflow direction resolves the contradiction by allowing the coil to operate at low temperatures for effective cooling while periodically removing frost buildup that would otherwise restrict airflow.
2Object-generated harmful factors
If hot gas is introduced to defrost the cooling coil, then frost is removed, but operation is interrupted and energy consumption increases
Solution Approach 1:
The patent converts the harmful cold air from the return plenum into a beneficial defrosting medium. Instead of discarding this cold air or using separate hot gas from the refrigeration plant, the system redirects it through the cooling coil during defrost mode. The cold air absorbs heat from the frost, melting it efficiently. This approach eliminates the need for energy-intensive hot gas defrosting and operational interruptions, as the system uses readily available air from the return plenum to accomplish defrosting.
Solution Approach 2:
The patent enables continuous operation by seamlessly transitioning between cooling and defrosting modes without interrupting the overall system operation. The controller automatically switches airflow direction and coil activation based on frost detection, allowing the HVAC system to maintain continuous cooling functionality while periodically removing frost buildup. This eliminates the operational interruptions and energy losses associated with traditional hot gas defrosting methods.
3Adaptability or versatility
If cooling coil is designed for low temperature operation, then dehumidification capability is improved, but frost formation becomes more likely
Solution Approach 1:
The patent implements periodic defrosting cycles by monitoring coil temperature and airflow direction. When the coil temperature approaches the frost formation threshold or frost is detected by the sensor, the controller automatically reverses airflow direction and activates the defrost sequence. This periodic action allows the cooling coil to operate at low temperatures for effective dehumidification while systematically preventing frost accumulation from becoming problematic. The system alternates between cooling/dehumidifying mode and defrost mode, maintaining optimal performance.
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
This approach allows for continuous operation while efficiently defrosting the cooling coil, reducing energy consumption and preventing airflow restrictions, and enabling lower dew point temperature control.
Implementation Method 1
Cooling coils typically comprise tubes, through which flows a coolant such as water, brine or a refrigerant. The inner surface of the tubes can have enhancements to improve heat transfer between the coolant and the tube. Air, flows over the outside of the tubes where fins can be added to enhance heat transfer between the tube and air.
Implementation Method 2
Frost formation begins during operation when coolant temperature is below freezing and air temperature reaches saturation. Frost accumulates over time and eventually restricts airflow, requiring some means for defrosting.
Implementation Method 3
When the frost threshold is reached, airflow through the cooling coil is reversed, and frost is now exposed to warmer entering air, giving up its heat to the airstream and defrosting the cooling coil.
Implementation Method 4
frost is now exposed to warmer entering air, giving up its heat to the airstream and defrosting the cooling coil
Data Source
AI summary
A low temperature cooling and dehumidification system uses a reverse airflow arrangement to defrost a frosted cooling coil while not interrupting operation. Automatic air dampers are used to reverse the airflow at the proper time to initiate defrost of that section of frosted cooling coil. This system is useful for low temperature cooling and dehumidification in situations where the inlet air is above freezing, however exiting air below freezing can be supplied if desired. It is advantageous for operation if the coolant flow and temperature internal to the cooling coil are regulated to create the conditions for frost formation to begin closer to the air leaving side of the active cooling coil.