Enhancing Performance of an Air Conditioner by Preheating and Precooling of Liquid Desiccant and Non-processed Air

In hot and humid climates, air conditioning is an energy-intensive process due to the latent heat load. A unitary air conditioner system is proposed, here, to reduce the latent heat of the humid air using a liquid desiccant followed by an evaporative cooling system. The heat liberated by the desiccant is removed by a solution to the solution heat exchanger. To restore the concentration of the liquid desiccant, the desiccant solution is regenerated by any low-temperature heat source such as solar energy. In order to make the system compact, the membrane heat exchanger is used for the dehumidifier and regenerator. This paper presents the numerical investigation of heat and mass transfer characteristics of a selected membrane dehumidifier under different climatic parameters. Membrane-based parallel-plate and hollow-fiber exchangers are used for this application. A parallel-plate heat-and-mass exchanger (contactor) is composed of a series of plate-type membrane sheets to form channels. On the other hand, hollow-fiber membranes are packed in a shell to form a shell-and-tube heat-and-mass exchanger. The two streams of both contactors are in a counter parallel flow, separated by micro-porous semi-permeable hydrophobic membranes. In this research, the equations governing the transport of heat and mass between the two streams along with the membrane effect in both contactors are solved numerically. The results are compared at different number-of-transfer units (NTU) on the airside and thermal capacity ratios. It is found that the hollow fiber is more efficient than the parallel plate.

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A Feasibility Study of Using Solar Liquid-Desiccant Air Conditioner in Queensland, Australia

Journal of Solar Energy Engineering ◽

10.1115/1.2844426 ◽

2008 ◽

Vol 130 (2) ◽

Cited By ~ 9

Author(s):

Shahab Alizadeh

Keyword(s):

Feasibility Study ◽

Storage System ◽

Cross Flow ◽

Hot Water ◽

Operating Costs ◽

Air Conditioner ◽

Direct Expansion ◽

Liquid Desiccant ◽

System A ◽

Good Agreement

A feasibility study of using solar liquid-desiccant air conditioner (LDAC) developed in Queensland has been undertaken. The system uses high effectiveness cross-flow polymer plate heat exchanger (PPHE), as the absorber unit. Outside air is dehumidified by strong liquid desiccant and indirectly cooled within the PPHE. The warm dry air is, subsequently, cooled and humidified through a direct evaporative cooler and supplied to the conditioned space. The weak desiccant solution from the absorber unit is concentrated in a scavenger air regenerator using hot water from flat plate solar collectors. The prototype of the absorber unit of the liquid-desiccant system has been tested under the summer conditions of Brisbane, using lithium chloride as the absorbent solution. The results of the experiments indicate that they are in good agreement with a previously developed model for the absorber unit. The tests further reveal that the unit has a satisfactory performance in controlling the air temperature and relative humidity when installed on a commercial site of 120m2 area in Brisbane. A commercialization strategy has been proposed in this study for a solar operated LDAC in Queensland and compared with the conventional direct expansion (DX) system. Based on the computer modeling results obtained from the system simulation for a building in Cairns, North Queensland, the operating costs of the LDAC are significantly lower than its conventional DX counterpart. This study further reveals that using the solar operated LDAC with a storage system will result in considerable savings in operating costs when compared with the equivalent gas-fired system. A simple payback of five years was determined for the solar components in this study.

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Performance characterisation of liquid desiccant columns for a hybrid air-conditioner

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2007.10.015 ◽

2008 ◽

Vol 28 (11-12) ◽

pp. 1342-1355 ◽

Cited By ~ 28

Author(s):

B. Shaji Mohan ◽

M. Prakash Maiya ◽

Shaligram Tiwari

Keyword(s):

Air Conditioner ◽

Liquid Desiccant

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Experimental Investigation of Electrical Conductivity of Liquid Desiccant Solution

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.516-517.1910 ◽

2012 ◽

Vol 516-517 ◽

pp. 1910-1916 ◽

Cited By ~ 1

Author(s):

Qing Cheng ◽

Xiao Song Zhang

Keyword(s):

Experimental Data ◽

Electrical Conductivity ◽

Energy Consumption ◽

Energy Analysis ◽

Cooling System ◽

Air Conditioner ◽

Regeneration System ◽

Liquid Desiccant ◽

Energy Saving Potential ◽

Good Energy

Liquid desiccant cooling system is a novel air conditioner with good energy saving potential, which should be a promising choice to meet the needs of cooling and moisture loads. Among all regeneration methods, ED regeneration method should be a promising choice for liquid desiccant cooling system. In this paper, systematic experiments were carried out to investigate the electrical conductivity of desiccant solution. Experimental data of electrical conductivity of desiccant solution is acquired in the experiment, which will be greatly helpful to the energy analysis of ED regeneration system. The experimental results show that the energy consumption in the concentrated chambers is more than others for ED regeneration system cells. Moreover, increasing the temperature of desiccant solution may be a measurement to reduce the energy consumption of ED regeneration system.

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Adaption of an Evaporative Desert Cooler into a Liquid Desiccant Air Conditioner: Experimental and Numerical Analysis

Atmosphere ◽

10.3390/atmos11010040 ◽

2019 ◽

Vol 11 (1) ◽

pp. 40 ◽

Cited By ~ 1

Author(s):

Mustafa Jaradat ◽

Mohammad Al-Addous ◽

Aiman Albatayneh

Keyword(s):

Indoor Air ◽

Operating Cost ◽

Dew Point ◽

Air Conditioner ◽

Liquid Desiccant ◽

Human Thermal Comfort ◽

Effectiveness Model ◽

Air Cooler ◽

Maximal Deviation ◽

Air Conditioning Systems

Desert coolers have attracted much attention as an alternative to mechanical air conditioning systems, as they are proving to be of lower initial cost and significantly lower operating cost. However, the uncontrolled increase in the moisture content of the supply air is still a great issue for indoor air quality and human thermal comfort concerns. This paper represents an experimental and numerical investigation of a modified desert air cooler into a liquid desiccant air conditioner (LDAC). An experimental setup was established to explore the supply air properties for an adapted commercial desert cooler. Several experiments were performed for air–water and air–desiccant as flow media, at several solutions to air mass ratios. Furthermore, the experimental results were compared with the result of a numerical simplified effectiveness model. The outcomes indicate a sharp reduction in the air humidity ratio by applying the desiccant solutions up to 5.57 g/kg and up to 4.15 g/kg, corresponding to dew point temperatures of 9.5 °C and 12.4 °C for LiCl and CaCl2, respectively. Additionally, the experimental and the numerical results concurred having shown the same pattern, with a maximal deviation of about 18% within the experimental uncertainties.

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A Zero Carryover Liquid-Desiccant Air Conditioner for Solar Applications

Solar Energy ◽

10.1115/isec2006-99079 ◽

2006 ◽

Cited By ~ 41

Author(s):

Andrew Lowenstein ◽

Steve Slayzak ◽

Eric Kozubal

Keyword(s):

Indoor Air ◽

Mass Exchange ◽

Energy Efficient ◽

Low Flow ◽

Air Conditioner ◽

Liquid Desiccant ◽

Heat And Mass Exchange ◽

Pressure Drops ◽

Simultaneous Heat ◽

Contact Liquid

A novel liquid-desiccant air conditioner that dries and cools building supply air has been successfully designed, built and tested. The new air conditioner will transform the use of direct-contact liquid-desiccant systems in HVAC applications, improving comfort and indoor air quality, as well as providing energy-efficient humidity control. Liquid-desiccant conditioners and regenerators are traditionally implemented as adiabatic beds of contact media that are highly flooded with desiccant. The possibility of droplet carryover into the supply air has limited the sale of these systems in most HVAC applications. The characteristic of the new conditioner and regenerator that distinguishes them from conventional ones is their very low flows of liquid desiccant. Whereas a conventional conditioner operates typically at between 10 and 15 gpm (630 and 946 ml/s) of desiccant per 1000 cfm (0.47 m3/s) of process air, the new conditioner operates at 0.5 gpm (32 ml/s) per 1000 cfm (0.47 m3/s). At these low flooding rates, the supply air will not entrain droplets of liquid desiccant. This brings performance and maintenance for the new liquid-desiccant technology in line with HVAC market expectations. Low flooding rates are practical only if the liquid desiccant is continually cooled in the conditioner or continually heated in the regenerator as the mass exchange of water occurs. This simultaneous heat and mass exchange is accomplished by using the walls of a parallel-plate plastic heat exchanger as the air/desiccant contact surface. Compared to existing solid and liquid desiccant systems, the low-flow technology is more compact, has significantly lower pressure drops and does not “dump” heat back onto the building’s central air conditioner. Tests confirm the high sensible and latent effectiveness of the conditioner, the high COP of the regenerator, and the operation of both components without carryover.

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