Liquid desiccant air conditioning system
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Solution Overview
Problem
Conventional vapor compression HVAC systems are inefficient in dehumidifying air in humid climates, leading to energy-intensive reheat systems and increased costs, while existing liquid desiccant systems face challenges with desiccant carry-over and energy consumption due to high fan power and pressure drops, and require careful air flow management to prevent condensation on cold surfaces.
Innovation Solution
A liquid desiccant DOAS system using micro-porous membranes with a falling film desiccant flow and counter-flow heat transfer fluid, allowing for efficient dehumidification and cooling of air streams while preventing condensation, by circulating the desiccant and heat transfer fluid through a network of membrane plates at ceiling height, with regeneration facilities for constant desiccant concentration and energy recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional vapor compression systems are used for dehumidification, then cooling capacity is provided, but the systems overcool the air and require energy-intensive reheat systems
Solution Approach 1:
A liquid desiccant solution is introduced as an intermediary substance between the humid air and the cooling system. The desiccant absorbs moisture from the air through mass transfer, providing dehumidification without the need for overcooling and subsequent reheating, thereby reducing energy consumption while maintaining effective humidity control
Solution Approach 2:
The system changes the operating parameters by using liquid desiccant concentration and flow rate as control variables instead of traditional temperature-based control. By adjusting the desiccant solution concentration and circulation rate, the system achieves precise humidity control without overcooling the air
2Productivity
If liquid desiccant systems use concentrated salt solutions, then dehumidification efficiency is improved, but desiccant carry-over to the air stream occurs
Solution Approach 1:
A micro-porous membrane is introduced as an intermediary barrier between the liquid desiccant and the air stream. The membrane allows water vapor to pass through while blocking liquid desiccant carry-over, enabling the use of concentrated salt solutions for high dehumidification efficiency without the harmful effect of desiccant particles entering the treated air
Solution Approach 2:
The system employs micro-porous membranes with specific pore sizes that permit vapor transmission while preventing liquid carry-over. These porous materials enable efficient mass transfer of water vapor from the air to the desiccant while physically blocking the concentrated salt solution from entering the air stream
3Productivity
If packed bed systems are used for direct contact dehumidification, then dehumidification capability is improved, but fan power and pressure drops increase
Solution Approach 1:
The system replaces the bulky packed bed structure with thin film liquid desiccant layers flowing over smooth surfaces. This reduces the flow resistance and pressure drop significantly, lowering fan power requirements while maintaining effective dehumidification capability through the thin film contact area
4Productivity
If air flow rates are increased in open desiccant systems, then dehumidification rate is improved, but desiccant carryover risk increases
Solution Approach 1:
The micro-porous membrane acts as an intermediary that decouples the relationship between air flow rate and desiccant carryover. It allows high air flow rates to achieve high dehumidification rates while the membrane physically prevents desiccant particles from being carried over, even at turbulent flow conditions
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 system provides a cost-effective, thermally efficient method for dehumidifying and cooling air streams at ceiling locations, reducing energy consumption and eliminating condensation risks, while being compatible with existing building infrastructure and maintaining air quality.
Implementation Method 1
micro-porous membranes to separate the liquid desiccant from the air stream
Implementation Method 2
liquid desiccant systems have been used for many years and are generally quite efficient at removing moisture from the air stream
Implementation Method 3
counter-flow heat transfer fluid... circulating the desiccant and heat transfer fluid through a network of membrane plates
Implementation Method 4
the fluid streams (air, heat transfer fluids, and liquid desiccants) are made to flow turbulently so that high heat and moisture transfer rates between the fluids can occur
Data Source
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AI summary
An air-conditioning system includes a plurality of liquid desiccant in-ceiling units, each installed in a building for treating air in a space in the building. Dedicated outside air systems (DOAS) for providing a stream of treated outside air to the building are also disclosed.