Reverse Airflow Defrost for Low-Temperature Dehumidification Coils
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Solution Overview
Problem
Mechanical cooling and dehumidification systems face inefficiencies due to frost buildup in cooling coils when operating below freezing, leading to air restriction and increased energy consumption during defrosting processes.
Innovation Solution
Implementing a reverse airflow arrangement within the cooling coil to defrost frost buildup without interrupting system operation, using automatic dampers to reverse airflow when a frost threshold is reached, allowing warmer air to melt frost while maintaining continuous airflow and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling coil operates below freezing to maintain low dew point temperatures, then dehumidification performance is improved, but frost buildup occurs causing air restriction
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 warm inlet air contacts the frosted coil surface, melting the frost. This inversion of airflow direction resolves the contradiction by allowing the system to maintain below-freezing operation for dehumidification while periodically removing frost to prevent air restriction.
Solution Approach 2:
The system implements periodic defrost cycles by monitoring frost accumulation (via pressure drop sensors or temperature sensors) and reversing airflow when thresholds are reached. This periodic action allows the cooling coil to operate continuously at below-freezing temperatures for effective dehumidification while intermittently removing frost buildup that would otherwise restrict airflow.
2Object-generated harmful factors
If hot gas is introduced into cooling coil tubes to defrost, then frost is removed, but operation is interrupted and energy consumption increases
Solution Approach 1:
The system uses the incoming ambient air itself as the heat source for defrosting, rather than introducing external hot gas. The warm inlet air naturally contacts the frosted coil surface during reverse airflow, melting the frost using its own heat content. This self-service approach eliminates the need for additional heating equipment and reduces energy consumption compared to hot gas defrost methods.
Solution Approach 2:
The patent converts the harmful effect of warm inlet air (which would normally cause frosting) into a beneficial defrosting mechanism. During reverse airflow, the same warm inlet air that causes frost formation in forward mode becomes the heat source that melts accumulated frost, transforming a harmful factor into a useful defrosting resource and reducing overall energy requirements.
3Duration of action of stationary object
If airflow is reversed to defrost cooling coil, then continuous operation is maintained, but system complexity increases due to damper control
Solution Approach 1:
The system employs feedback control through sensors (pressure drop sensors across the coil or temperature sensors) that monitor frost accumulation in real-time. When frost reaches a predetermined threshold, the feedback signal triggers automatic damper actuation to reverse airflow. This feedback mechanism enables continuous operation with automated defrost cycles, managing the added complexity through intelligent control that responds to actual coil conditions.
Solution Approach 2:
The patent replaces complex multi-coil mechanical switching systems with a simpler single-coil reverse airflow system using dampers. Instead of requiring multiple cooling coils and complex valve arrangements to switch between cooling and defrost modes, the system uses a single coil with reversible airflow controlled by dampers, reducing mechanical complexity while maintaining continuous operation capability.
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 method effectively prevents air restriction and reduces energy consumption by allowing continuous operation while efficiently defrosting cooling coils, maintaining low dew point temperatures and controlling frost formation in low-temperature cooling and dehumidification systems.
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. The coolant inside the tubes removes heat from the air and thus cools the 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 air stream 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. The dehumidified generated condensate can be collected and used as grey water and/or potable water.