Desiccant air conditioning systems
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Solution Overview
Problem
Existing liquid desiccant systems for air conditioning face challenges in efficiently controlling desiccant concentrations, fluid levels, and reacting to space and outdoor conditions while preventing crystallization and membrane damage, especially in humid climates where conventional vapor compression systems overcool and require energy-intensive reheat.
Innovation Solution
A liquid desiccant air conditioning system employing micro-porous membranes with a heat transfer fluid loop that allows independent control of air temperature and humidity, using a refrigerant compressor or external heat sources for efficient heat transfer, and incorporating sensors to monitor membrane porosity and desiccant levels to prevent failures and crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If concentrated salt solutions (LiCl, LiBr, CaCl2) are used as liquid desiccant, then dehumidification efficiency is improved, but corrosiveness to system components increases
Solution Approach 1:
A micro-porous membrane is introduced as an intermediary barrier between the concentrated salt solution desiccant and the system components. The membrane allows water vapor to pass through for dehumidification while preventing direct contact between the corrosive desiccant and structural components, thus maintaining high dehumidification efficiency while eliminating corrosiveness.
Solution Approach 2:
The system employs micro-porous membranes with controlled pore sizes that permit selective passage of water molecules while blocking larger desiccant molecules. This porous structure enables the concentrated salt solution to function effectively for dehumidification without its corrosive effects being transmitted to system components.
2Object-affected harmful factors
If micro-porous membranes are used to contain desiccant, then desiccant carry-over is prevented, but membrane damage and failure risk increases
Solution Approach 1:
The system replaces mechanical pressurization methods with gravity-induced flow (siphoning) to circulate the liquid desiccant. This eliminates high-pressure stresses that could damage the micro-porous membrane, while still preventing desiccant carry-over through the membrane's selective porosity.
Solution Approach 2:
The system incorporates monitoring and control mechanisms that detect approaching hazardous conditions (such as excessive pressure or temperature) before they can damage the membrane. By cushioning against these conditions in advance, the membrane's service life is extended while maintaining effective desiccant containment.
3Productivity
If desiccant concentration is increased to improve dehumidification, then moisture removal efficiency is improved, but risk of crystallization increases
Solution Approach 1:
The system incorporates sensors and control mechanisms that continuously monitor desiccant concentration, temperature, and pressure conditions. When parameters approach levels that could cause crystallization, the system automatically adjusts operation (such as reducing desiccant flow or increasing regeneration) to maintain safe operating margins while preserving dehumidification performance.
Solution Approach 2:
The system dynamically adjusts operational parameters (temperature, pressure, flow rates) based on real-time conditions to prevent crystallization. By changing these parameters in response to monitoring data, the system maintains high desiccant concentration for efficient dehumidification while staying below the crystallization threshold.
4Temperature
If conventional vapor compression systems are used, then cooling capacity is provided, but overcooling occurs requiring energy-intensive reheat
Solution Approach 1:
The system extracts the dehumidification function from the conventional cooling process. By using liquid desiccant to selectively remove moisture from air, the system avoids the overcooling inherent in vapor compression systems, thereby eliminating the need for energy-intensive reheat while still providing comfortable conditions.
Solution Approach 2:
The system separates cooling and dehumidification into independent functions. Dehumidification is achieved through the liquid desiccant membrane process, while cooling is provided separately by conventional AC units operating at lower capacities. This segmentation prevents the coupling of overcooling with dehumidification that plagues conventional systems.
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 system effectively dehumidifies and conditions air efficiently, reducing energy costs by avoiding overcooling and reheat needs, while protecting the membrane from damage and ensuring proper desiccant concentration, thus providing a cost-effective and reliable air conditioning solution.
Implementation Method 1
employing micro-porous membranes to contain the desiccant
Implementation Method 2
micro-porous membranes with a heat transfer fluid loop
Implementation Method 3
liquid desiccants to dehumidify and cool, or heat and humidify an air stream
Implementation Method 4
The conditioner receives concentrated liquid desiccant and extracts moisture from an air stream
Implementation Method 5
employing micro-porous membranes with a heat transfer fluid loop that allows independent control of air temperature and humidity
Implementation Method 6
both latent and sensible heat are absorbed from the air stream into the liquid desiccant
Implementation Method 7
using a refrigerant compressor or external heat sources for efficient heat transfer
Implementation Method 8
The cold heat transfer fluid is cooled by a refrigerant compressor or an external source of cold heat transfer fluid
Implementation Method 9
incorporating sensors to monitor membrane porosity and desiccant levels to prevent failures and crystallization
Implementation Method 10
The heat exchangers can use gravity induced pressures (siphoning) to keep the micro-porous membranes properly attached to the heat exchanger structure
Implementation Method 11
use gravity induced pressures (siphoning) to keep the micro-porous membranes properly attached
Implementation Method 12
preventing desiccant crystallization or undue dilution
Implementation Method 13
protect the equipment in freezing conditions by lowering the desiccant concentration in such a way as to avoid crystallization
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A desiccant air conditioning system for treating an air stream entering a building space, the desiccant air conditioning system being switchable between operating in a warm weather operation mode and in a cold weather operation mode The conditioning system comprises a conditioner configured to expose the air stream to a liquid desiccant such that the liquid desiccant dehumidifies the air stream in the warm weather operation mode and humidifies the air stream in the cold weather operation mode, the conditioner including a plurality of plate structures arranged in a vertical orientation and spaced apart to permit the air stream to flow between the plate structures, each plate structure including a passage through which a heat transfer fluid can flow, each plate structure also having at least one surface across which the liquid desiccant can flow, each plate structure further comprising a membrane positioned proximate the at least one surface of the plate structure between the liquid desiccant and the air stream. The conditioning system also comprises a fan positioned at an outlet of the conditioner for applying negative pressure to the conditioner to draw the air stream through the conditioner. The conditioning system further comprises a regenerator connected to the conditioner for receiving the liquid desiccant from the conditioner, said regenerator causing the liquid desiccant to desorb water in the warm weather operation mode and to absorb water in the cold weather operation mode from a return air stream. The conditioning system yet further comprises a liquid desiccant loop for circulating the liquid desiccant between the conditioner and the regenerator, a reservoir coupled to the liquid desiccant loop for collecting liquid desiccant flowing from the conditioner, a vertical tube proximate a desiccant entry port at a plate structure in the conditioner coupled to the liquid desiccant loop to detect flow of liquid desiccant to the conditioner based on the height of the liquid desiccant in the vertical tube and an overflow tube coupling an upper end of the vertical tube to the reservoir to inhibit application of excessive pressure by the liquid desiccant on the membranes in the conditioner. The conditioning system further comprises a heat source or cold source system for transferring heat to the heat transfer fluid used in the conditioner in the cold weather operation mode, for receiving heat from the heat transfer fluid used in the conditioner in the warm weather operation mode, for transferring heat to the heat transfer fluid used in the regenerator in the warm weather operation mode, or for receiving heat from the heat transfer fluid used in the regenerator in the cold weather operation mode. The conditioning system yet further comprises a conditioner heat transfer fluid loop for circulating heat transfer fluid through the conditioner and exchanging heat with the heat source or cold source system and a regenerator heat transfer fluid loop for circulating heat transfer fluid through the regenerator and exchanging heat with the heat source or cold source system.