Solar Desiccant Air Conditioning System And Its .
Solar Desiccant Air Conditioning System and ItsPerformance in the Middle-EastMona Shaery and Sarim Al-Zubaidy Abstract—The extensive use of air conditioning for indoorcooling in buildings represents a major part of the electricityconsumption in many parts of the world including the Middle East,North Africa and parts of Asia. With the very high ambienttemperatures occurring particularly in summer, air conditioningsystems consume approximately 50% of the peak power loadrequirements. Exploiting renewable energy in the field of airconditioning is an appropriate alternative to achieve comfortablesurroundings without creating harmful environmental effects. In theMiddle East and particularly in the United Arab Emirates, it seemsthat there is a high potential for using solar air conditioning schemes.This paper will outline a suitable solar-assisted desiccant coolingtechnology. By defining the performance term of solar desiccant airconditioning, some effective parameters on system cooling behavior,such as solar irradiation and humidity, are considered.Anillustrative example will be presented to show that exploiting solardesiccant cooling system is feasible in the United Arab Emirates. Theexample is for an occupied residential home in Abu Dhabi.According to the geographical and meteorological data of this city,solar gains, infiltration gains, internal gains, and convective coolingload for the assumed building is evaluated first. Then by using totalsensible cooling load and latent heat, total cooling load is calculated.Lastly two appropriate existing solar desiccant cooling plants areoffered to provide the required total cooling load for studied home.Keywords— air conditioning, solar cooling, desiccant airconditioning, air conditiong systems.and put further tension on government budgets (3). Moreoverbecause of environmental impacts of fossil fuel, alternativeenergies such as solar energy are certainly required, ifpractical air conditioning technology is accessible andattainable (4). Reducing high power spending in the UAE (5)is one of the main motivations for advancing solar energytechnology. It may have an effect on the ecosystem, globalwarming, and human health. It can influence the economy ofthe country.The United Arab Emirates is positioned as one of the mainenergy consumers in the world. Its energy use goes beyondglobal development levels. It is rising with a mean rate of 10%yearly, more than twice the global growth rate of 4% (5). Higheconomic growth, rising population, and a relatively lowenergy cost in this country during the past decades haveincreased energy consumption (6). Economic developmentand improvement in quality of life are two results of energyexpansion programs (1). According to data on economicgrowth, life standards, and the number of emigrantsparticipating in the workforce during the two last decades, it ispredicted that the population of the UAE will double by 2015(2). These trends and predictions strongly suggest increasingdemand for energy consumption. Moreover it illustrates thatthe UAE will be challenged to "fulfill its share in the worldenergy market (3).I. INTRODUCTIONTemperature and humidity control of indoor air is definedas the main aim of air conditioners. In a typical roomthere are five categories of main loads for air conditioningsystems. Conduction from walls and windows, solar loadsfrom windows, and conditioning of ventilation air are the mostimportant ones. In addition there are sensible and latentinternal loads from persons, equipment, artificial lighting, andplants (1). The United Arab Emirates has long hot and humidsummers and temperate climatic conditions for about half of ayear. Air conditioning for a comfortable indoor environment istherefore indispensable. Because air conditioning is one of thebiggest power users in the UAE (2), different energyconservation measures should be implemented.Electrically driven cooling systems have been utilized andcommonly found in homes, offices, industrial facilities andtransportation. Continuous growth in electricity demand willnecessitate considerable investments over the coming yearsMona Shaery, Heriot Watt University, Dubai Campus, EPS, United ArabEmiratesSarim Al-zubaidy, Military Technological College, Muscat, Oman(e-mail:sarim.alzubaidy@gmail.com)Fig. 1 Flowchart of factors which encourage getting aidfrom renewable energy resourcesAs illustrated in Fig. 1, in addition to rapid economic growth,hot and humid climatic conditions increase energy demandand consumption due to the need for increased airconditioning (4).II. UAE CLIMATEThe United Arab Emirates, UAE (5), is one of the majoroil-producing countries in the Middle East. Its overall area isabout 84,000 km2. It is located in latitude of 22.5-26 Northand longitude of 51-56 East (6). The UAE has a semiaridclimate and quite low precipitation. The monthly average,
maximum, minimum, and average relative humidity trends inAbu Dhabi in 1994 is illustrated in Figure 2 (1).Fig. 2 Maximum, minimum, and average relative humidity,Abu Dhabi, 1993 (1)energy can be applied to provide electricity for coolingsystems by means of photovoltaic cells. Moreover it can beused to supply heat for thermal driven cooling systems. Thereare many possible processes for converting solar radiation intocooling. Figure 3 (5) gives an overview of these processes.Solar air conditioning (SAC) can be categorized into closedand open cycle systems. Closed cycle systems have thermallymotivated chillers which provide cooled water. Chilled wateris utilized in air handling units to produce cooled anddehumidified air. Chilled water may also be used ininstallations such as fan coils or chilled ceilings. A requiredelement in all chilled water systems is heat rejection (7).Open cycle systems provide complete air conditioning bydelivering cooled and dehumidified air. Water, as therefrigerant of this cycle, has direct contact with theatmosphere. The most widespread open system is thedesiccant cooling system with a rotating dehumidificationwheel (7).Throughout the year, clear sky conditions predominate inUAE as table 1 illustrates, the clearness index for Abu Dhabi(capital of UAE) varies from 0.54 to 0.66 and its annualaverage is reported 0.58.Table 1 Monthly averaged insolation clearness index ofAbu Dhabi, K(0-1), NASA Surface meteorology and solarenergy, 22-year average (ref 2)In Abu Dhabi, 24.43 N, 54.45 E, NASA surfacemeteorology and solar energy has issued monthly averagetemperatures for the city and these are shown in Table 2.Table 2 Monthly average temperature of Abu Dhabi at 10mabove the surface of the earth (C), 22-year average ref 3)Fig. 3 Outline on physical methods to change solar radiationinto cooling or air conditioningSolar air conditioners are relatively expensive, but solarassisted cooling systems have a comparatively low cost (2).Figure 4 (3) expresses the differences between solar selfdirected and solar assisted systems in detail.In warm seasons, as air temperature rises, the need for airconditioning increases, resulting in increased energy demand.At the same time, growing demand for sea water desalinationalso increases energy demand (1) which puts further stress onthe energy reserves of the country. Air conditioning is a mainsource of electric energy consumption in the United ArabEmirates. For instance in Al-Ain city, 60% of the summerpeak load in the housing section is devoted for airconditioning (3).III. SOLAR COOLING SYSTEMFig. 4 Diffrences between solar self- directed and solarassisted systemsUsing solar energy for cooling purposes is an attractiveapproach to solving the growing energy demand issues. SolarSolar Desiccant air conditioners use a desiccant (either liquidor solid) to dehumidify incoming air. During this process, the
air is dried and heated. The air then flows to a heatexchanger/recovery where it is cooled by the outgoing airfrom the air conditioned premises. In some configurations, thecooled dry air is then humidified and evaporatively cooledfurther before entering the premises. Return air is firsthumidified which lowers the temperature due to evaporativecooling before entering the heat exchanger/recovery. Therelatively hot, dry incoming air after dehumidification iscooled while the cooler outgoing air is heated in the heatrecovery process. From the heat recovery process, theoutgoing air is further heated by auxiliary means and thisheated air is used to regenerate the desiccant before exiting tothe environment. In the solar assisted process, some of theauxilliary heat is provided by solar collectors which bringsolar heated water to a liquid to air heating coil. Thus, duringthe hottest part of a day, when air conditioning demand is at itsgreatest, the solar collectors are also providing the hottestwater to the process. This thus appears to be an efficient useof the climatic conditions found in Abu Dhabi to reduce theenergy demands of air conditioning. Two water/solution heat exchangersOne solution/solution heat exchanger: It is used todecrease the amount of external heating and coolingrequired.One air/air heat exchangerIV. THE COOLING UNIT OPERATIONFigure 7 below highlights psychrometric diagram for theprocesses. The processes of evaporative cooler (state 3–state4), the cooling coil (state 3–state 4'), and a heat exchangercooler (state 2–state 3) are all shown. It must be noted that incase of replacing the cooling coil by an evaporative cooler, themoisture content will be slightly increased.Figures 5 and 6 below illustrate the solid desiccant coolingunit and liquid desiccant system.Figure 7 Psychrometric diagram demonstrating the principleof desiccant coolingV. HISTORICAL REVIEWFigure 5 System using desiccant wheelFigure 6 System using liquid desiccantAs shown in Figure 6, the liquid desiccant cooling systemsusually have 6 main components: An air dehumidifier (absorber): The mission of thispart is to eliminate the damp of the inlet air byproviding contact with scattered liquid desiccant.A solution regenerator (desorber): In this section theweak solution from dehumidification part isregenerated to a satisfactory concentration (close tothe desiccant’s first concentrationThe first rotary silica gel desiccant cooler was invented byMiller and Fonda (6) although lack of information preventedappreciating the potential of desiccant dehumidifiers. In 1935,Hausen initiated the earliest concept of desiccant cooling.After that Shipman in 1936, Fleisher in 1939, Larriva in 1941and Altenkrich in 1941 and 1944 attempted to expanddesiccant cooling schemes commercially, however they didnot succeed (6).In 1955, Pennington attained the first patent for a desiccantcooling system (1). This scheme contains a rotary heatexchanger that included solid desiccants and thereforefunctioned as an adiabatic regenerative dehumidifier. It took inambient air and adsorbed the moisture in it. When the air wassensibly and evaporatively cooled, then it entered into thetrained room. The return air was initially cooled evaporatively.Then it passed to a sensible heat exchanger to recuperate theheat of adsorption from the supply air. Next it was heated by alow grade thermal energy resource for regenerating thedesiccant. Coefficient of performance (COP) for this cycle ispredicted near 0.8-1 (2). Simultaneously Lof studied atriethylene glycol solution for dehumidifying the air (3).Dunkle (1965) built a solid desiccant dehumidification andcooling rotary wheel (4). A few year later, in 1968, Mutersenhanced Pennington's cycle by the using parallel passages
concept. Actually Munters environmental cycle (MEC) is asuperior version of the Pennington (ventilation) cycle. Whenthe desiccant system was incapable of satisfying the coolingneed, the backup vapor compression system was used. Studiesdemonstrate that the desiccant cooling scheme had the abilityto cover the cooling load by itself, so such backup was notrequired (5).Maclaine-cross and Banks (1972) built up an analogousmethod to predict the joined heat an quid desiccant cooling scheme and a solid desiccant coolingplant is offered in the second one.Sample 1:Figure 9 (1) shows a two-stage solar liquid desiccant (LiCl)cooling scheme supported by CaCl2 solution. It has beendesigned by SJTU, Tsinghua University and Shanghai JiaoTong University. Its design dehumidification capacity is 3kW. Assessment has been done on a two-stage liquiddesiccant cooling unit driven by 65–70 C hot water. Thethermal COP is about 0.7. To evaluate the liquid desiccant’senergy storage capacity, the liquid desiccant concentrationvariance was increased to 5%.Sample 2:Figure 10 (3) shows new research work on solar desiccantcooling in SJTU. It concentrates on a hybrid energy system.Solar air collector and gas boiler are both used to achieve soliddesiccant cooling, heating and hot water supply. The hybridenergy system would require 10 m2 solar collectors, to provideFig. 9 scheme of the solar powered two-stage liquid desiccantcooling systemFig. 10 The hybrid energy systemCURSORY ECONOMIC VIEWMany economic benefits are outlined in detailed economicevaluation of desiccant cooling system. It seems that byapplying this technique the operating cost, capital costs andmaintenance costs (10) are reduced. Adding solar collectorsdecreases costs, too. If they are installed near the air
conditioner equipment. In addition to the simplifying theinstallation, the costs will be lessened. Energy storage can bealso accomplished by using intense desiccants instead of hotwater to reduce more cost. In usual payback of the desiccantcooling scheme is in less than eight years with no governmentfinancial support (10).CONCLUSIONSolar-assisted desiccant cooling system is a noveltechnology in air conditioning systems. Owing to the highsolar energy potential in the United Arab Emirates, it seemsthat using solar desiccant air conditioners may be anappropriate choice to reduce cooling demands especially inhot summer periods. In this project, an attempt has been madeto explain the importance, advantages, and viability of usingthis system in the UAE. This work introduces solar assisteddesiccant air conditioners, and illustrates a potentiallyeffective technique to address UAE's environmental interest ofa healthier and greener country. Primary energy savings forproperly designed solar desiccant cooling cycles is about 2050%. This fact implies reduction in air pollution andconsumption of conventional energy resources. As this workhighlights, solar desiccant cooling technology usesenvironmentally friendly refrigerants such as water . Anotherattractive point which is stated in this study is that the solardesiccant air conditioner can control the humidity of spaces. Itis therefore suitable for the high level of moisture found in theUAE during summer. This will assist in preventing mold andbacteria growth in buildings (3).This study demonstrates that exploiting the solar desiccantcooling system is theoretically feasible and possible in theUnited Arab Emirates. The scheme design should be carefullyexamined for local use based on climatic conditions. There isalso a need for practical knowledge on design, control andoperations of this technology in the local environment of theUnited Arab Emirates. Although the initial cost of thistechnology is high, the likelihood is that the payback periodwould be reasonable considering that energy savings areestimated to be between 20% and 50%. As evidence of this, arobust market for solar air conditioners is developing. It hasbeen reported that the market for solar cooling systems grewby 26% in the EU in 2005. Future studies should focus oncost benefit analysis taking into consideration initial capitalcosts, long term operating and maintenance costs as well asenvironmental benefits resulting from a reduction in carbonfootprint, a reduction in the use of potentially dangerouschemicals, as well as other benefits. It is recommended thatthe cost of energy for these studies be based on global markettrends and not on government subsidized energy costs.VII. NOMENCLATUREQa*aThe mean convective cooling load (W)QThe alternating component of the convective cooling load (W )QkThe total sensible cooling load to the air node (W )Qsg The cooling load due to windows and blinds (W )Qv Cooling load due to infiltration (W)Q fa The mean fabric gain to the air node (W )Qrad The radiant component of the mean internal gain (W )Qcon The convective component of the mean internal gain (W )*The convective component of the swing in internal gain (W )Qcon*QradQ*faFcyFcuThe radiant component of the swing in internal gain (W )The swing in fabric gain to the air node (W )The room admittance factor with respect to dry resultanttemperatureThe room conduction correction factor with respect to dryresultant .asp?id 1000&mid 9, Accessed on 25 May2009. "The district cooling market heats up”. Danish Board of DistrictHeating -DBDH-Sustainable energy. 17 June 2008.[2] www.solaterm.eu/publications/know-how transfer/expert missions/2solar-cooling-context-and-overview.pdf, Accessed on 25 May 2009.2"Solar Cooling and Air-Conditioning”. Fraunhofer-Institute for solarenergy systems, Dep. Thermal Systems and Buildings, Tunis, Dec 2nd– 4th, 2008 W. Strunk Jr., E.B. White, The Elements of Style, fourthed., Longman, New York, 2000.[3] http://www.eduvinet.de/servitec/henninge.pdf , Accessed on 29 May2009. Dr. Hans-Martin Henning. “Air Conditioning with Solar Energy”Fraunhofer-Institute for Solare Energiesysteme, Barcelona, October 3,2000.[4] http://www.sciencedirect.com, Accessed on 3 June 2009. Electricalpower supply and utilization, Fuel and Energy Abstracts. March 2006,page 102.[5] http://www.sciencedirect.com, Accessed on 3 June 2009. Abdul RazakF. Al-Faris. The demand for electricity in the GCC countries. EnergyPolicy 30 (2002) 117-124.[6] http://www.irbdirekt.de/daten/iconda/CIB8395.pdf, Accessed on 29May 2009. Kwong Fai Fong and Tin Tai Chow. Application Potentialof Solar-assisted Desiccant Cooling System in Sub-tropical Hong Kong.Building Energy and Environmental Technology Research Unit.Division of Building Science and Technology. City University of 1/res001 20.doc, Accessedon 3 June 2009. Ahmed Okeil, Mohammed Assem and Ahmed Rashid.Urban Density and Energy Efficiency in City Planning: Case Study ofAl Ain City. Department of Architectural Engineering. United ArabEmirates University.[8] Mona Shaery, 2009, “Solar Desiccant Air Conditioning System and ItsPerformance in the United Arab Emirates”. MSc dissertation, HeriotWatt University, Dubai campus.[9] http://www.sciencedirect.com, Accessed on 3 June 2009. Haris Doukas,Konstantinos D. Patlitzianas, Argyris G. Kagiannas, John Psarras.Renewable energy sources and rationale use of energy development inthe countries of GCC: Myth or reality?. Renewable Energy 31 (2006)755-770[10] http://www.ead.ae/en/?T 4&ID 2025, Accessed 3 June 2009. Meena SJanardhan. Fuel-rich UAE sends green signals. Environment AgencyAbu Dhabi. 8 August 2006[10] Electrical power supply and utilization, Fuel and Energy Abstracts,March 2006, page 102(http://www.sciencedirect.com, Accessed on 3 June 2009)Mona Shaery completed her Master degree (MSc-Energy) from Heriot WattUniversity, Dubai campus. She remains active in the field.Sarim Al-Zubaidy is presently the Vice-Dean for Academic Affairs atMTC, Muscat. He acted as project supervisor for the first author during herundertaking of the master degree at Heriot Watt University, Dubai campus.
Figure 5 System using desiccant wheel functioned Figure 6 System using liquid desiccant As shown in Figure 6, the liquid desiccant cooling systems usually have 6 main components: An air dehumidifier (absorber): The mission of this part is to eliminate the damp of the inlet air by providing
HL Heatless Desiccant Dryers Ingersoll Rand heatless desiccant dryers thoroughly capture moisture in the compressed air produced as it is directed through the online desiccant-filled dryer tower of the dryer. As the desiccant in this tower adsorbs water from the air, the desiccant in the dryer
removes water vapor directly from the air. The air to be dried passes through the desiccant wheel and the desiccant removes the water vapor directly from the air and holds it while rotating. As the moisture-laden desiccant passes through the regeneration sector, the water vapor is transferred to a heated airstream, which is exhausted
from the air, the desiccant in the dryer’s Selecting An Ingersoll Rand Desiccant Dryer off-line tower is purged of moisture and readied for use. The basic difference in the three technologies is the manner in which moisture is desorbed from the desiccant, also known as regeneration. Heatles
lower, a desiccant dryer is the most effective solution. The Ingersoll-Rand ThermoSorb dryer uses twin columns filled with desiccant beads to dry the compressed air. Tiny pores within the desiccant beads trap moisture and remove it permanently from the compressed air supply. The temperature of File Size: 1MB
The Munters DryCool HD desiccant dehumidifier provides significant drying capability in a small package. The unit utilizes a refrigerant circuit in conjunction with a heat reactivated desiccant wheel to provide efficient drying capability. Due to the capabilities of the desiccant wheel, the unit can continue to
Munters offers a choice of six desiccant wheels – Titanium silica gel, lithium chloride, GTR, HPX, HCR and molecular sieve. For more than 50 years, Munters has conducted extensive research and development to improve the desiccant wheel. Munters six desiccant options provide the widest
based upon time, dew point, bed moisture load or a combination of these. All of these dryers have filtration on the inlet to keep water and oil from damaging and contaminating the desiccant. An additional filter on the outlet catches the desiccant dust that is generated from the constant movement of the desiccant beads against one another
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