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dry-bulb temperature of entering primary air, oC dry-bulb temperature of leaving primary air, oC wet-bulb temperature of entering secondary air, oCt1 t2t s'Two stage or indirect/direct evaporative air conditioners combine both direct and indirectevaporative principles. In two-stage evaporative air conditioners, the first stage (indirect)sensibly cools the primary air (without increasing its moisture content) and the air isevaporatively cooled further in the second stage (direct) as shown in Fig.1(c). The dry-bulbtemperature of the supplied primary air can be reduced to 6 K or more below the secondaryair wet-bulb temperature (ASHRAE Handbook, 2004) without adding too much moisture. Astwo-stage evaporative coolers produce lower temperatures, they consequently require less airdelivery in comparison with the direct systems. Heidarinejad et al. (2009) experimentallystudied the cooling performance of two-stage evaporative cooling systems under the climateconditions of seven Iranian cities. It has been found that the saturation efficiency (as definedin equation 1 above) of the indirect/direct evaporative air conditioner varies in a range of108 111%. Also, over 60% energy can be saved using this system compared to a vapourcompression system. However, it consumes 55% more water in comparison with directevaporative cooling system for the same air delivery rate. Monitoring the electricityconsumption of evaporative and conventional refrigerated cooling systems in a smallcommercial building has demonstrated considerable energy savings and improved thermalcomfort with evaporative cooling (Saman, et al. 1995). Indirect evaporative cooling can alsobe used as a component of multistage air conditioning systems which may also includerefrigerated cooling stages. In such cases, the indirect evaporative cooling may be sufficientfor the provision of typical summer cooling requirements. The refrigerated stage operation islimited to peak demand days.Indirect evaporative air conditioners have been gaining more popularity in the market inrecent years. Recently, both Seeley International and Clear Solar have started marketingindirect evaporative air conditioners. Seeley has been developing such air conditioners for anumber of years. Clear Solar is marketing a product developed in USA by Coolerado.Both products produce air at conditions closer to refrigerated systems. Unlike conventional airconditioning units, they use no ozone-depleting chemicals and have mainly one energyconsuming component, the fan. The heart of both systems which sets them apart fromconventional evaporative coolers is a unique wetting system, a modular heat and massexchanger and the way the air flows through it.In 2008, Coolerado received a grant to build a solar-powered mobile demonstration coolerwhich brought Coolerado to the attention of a broader audience. The unit is outfitted with fourPV panels to power the cooler, and the cooler helps the solar array run at a lower temperatureand hence improved efficiency by about 15%.Seeley has drawn together its most innovative and energy efficient technologies and mergedthem with what it has been developing behind the scenes, over the past 14 years. The result isClimate Wizard, a product that incorporates a patented revolutionary heat exchanger whichensures that no moisture is added to the air entering the conditioned space, and at the sametime it maximises the effectiveness of all of the elements necessary to best facilitate the heatexchange process.8

Climate Wizard delivers significantly colder air than can be achieved by traditionalevaporative cooling. It delivers air at temperatures near, and at times, below, those producedby refrigerated air conditioning. According to the manufacturer, Climate Wizard uses up to 54%less energy than a fixed speed refrigerated system. Based on independent testing by theUniversity of South Australia, Climate Wizard is able to provide pre-cooled ―make-up air‖ tolarge commercial refrigeration plants, resulting in energy savings of up to 35%, and at times,even more. A Slim-line version for domestic applications, designed for installation against theouter walls of homes, has approximately the same footprint as a water heater. Air is deliveredthrough the space between the outer wall and the roof into the home and then through aconventional ducting system in the ceiling space, and into the rooms of homes. Ducting andfittings are the same dimensions as for traditional refrigerated systems.The main focus of this report is direct evaporative air conditioners as most units in current usewithin Australia are of this variety. However, the scope of the report also includes indirect andtwo-stage systems in view of their recent entry into the Australian market.A direct evaporative air conditioner is an enclosed metal or plastic box with louvers on thesides containing a fan or a blower with an electric motor, a number of cooling pads, a watercirculation pump to wet the cooling pads and a float valve to maintain a proper water level inthe reservoir. Fig. 2 illustrates the components in a typical evaporative air conditioner.Figure 2: Schematic diagram of the components of a typical direct evaporative air conditioner.Types of evaporative air conditioners range from portable units, window/wall units andducted units for residential and commercial use. Portable units cool one room at a time. Theyare fitted with legs and wheels and can be moved easily from room to room. A small pump isutilized to keep the cooling pads wet and water is needed to be periodically filled manually inthe internal water storage tank. Typical portable evaporative air conditioners are shown inFig.3. However, this report only examines plumbed units/systems and therefore the portable9

units will be excluded from the discussion. Window/wall evaporative air conditioners aremounted through exterior windows or walls and they can cool larger areas than the portableunits. A window evaporative unit is presented in Fig. 4. Ducted evaporative air conditionersmake up the vast majority in use in Australia. They are usually mounted on the roof and thecooled air is delivered through ducts to each room in the building. Fig. 5 shows residentialroof ducted evaporative air conditioners with different profiles. Both window/wall and ductedunits have a water bleeding system to control the water salinity under a certain level.Figure 3: Portable evaporative air peac/ConvairPEAC.html).10

(b)(c)(a)Figure 4: (a) Window evaporative air conditioner; (b) View from cooled space; (c) View from ing/window/default.aspx)Figure 5: Residential roof ducted evaporative air conditioners with different profiles.1.2 Suitability for use in AustraliaUsing the Australian summer design conditions, Tables 1 and 2 include the estimates of theperformance parameters of direct and indirect evaporative air conditioners. The parametersinclude the outlet temperature, relative humidity and cooling capacity for 8 Australianlocations.11

Table 1: Performance of direct evaporative air conditioners at some Australian locationsAIRAHDesignConditionsAir conditionerSupplyConditionsCooling Capacity(kW)Based on10 000 m3/hrair flowDry Bulb( C)Wet Bulb( C)Dry BulbTemperature( .547.515.1Sydney31.119.821.561.818.8The first two columns of Table 1 show the AIRAH design conditions of the dry and wet bulbtemperatures for eight cities in Australia. The dry bulb temperatures of the air leaving thedirect evaporative air conditioner are presented in the third column. The temperatures of theair leaving the direct evaporative air conditioner can be calculated from Eqn. 1, based on theassumption that the saturation efficiency of the direct evaporative air conditioner is 85%. Therelative humidity of the air leaving the evaporative air conditioner is also included in the table.Based on a nominal volume flow rate of 10,000 m3/hr for the air conditioner, the coolingcapacity of the direct evaporative air conditioner is computed based on Eqn. 3 below. Table 1shows that despite the relatively low temperatures achieved by direct evaporative airconditioners, the low cooling capacity and high humidity produced in the tropical andsubtropical regions (Darwin, Brisbane) make their use impractical. However, comfort coolingconditions (temperature and relative humidity) and high cooling capacities are achievable inall other Australian locations having relatively cool and/or dry summers.One option for extending the climatic regions where evaporative cooling is effective is the useof indirect or 2 stage indirect/direct evaporative cooling. The use of a heat exchanger to coolthe outside air without humidifying it by making use of indirect evaporative cooling systemswas developed in Australia in the 1960s and 1970s; plate heat exchangers were manufacturedand marketed (Pescod, 1968 & Pescod, 1979). From the manufacturing view point, the mainchallenge of the system is the size and cost of the heat exchanger required to achieve goodeffectiveness and low pressure loss. Work has been done at the University of South Australia12

to develop low cost heat exchangers optimised for heat recovery as well as indirectevaporative cooling purposes (Saman & Kilsby, 1999).Both indirect evaporative air conditioners which have recently been introduced into theAustralian market are based on multistage indirect evaporative cooling and achieve lowertemperatures without increasing the air humidity, thus enabling them to compete directly withrefrigeration systems. Consequently less air is required for producing the required coolingcapacity in comparison with direct systems.Table 2: Performance of indirect evaporative air conditioners at some Australian locationsAIRAHDesignConditionsAir conditionerSupplyConditionsCooling Capacity(kW)Based on2 000 m3/hr air flowDry Bulb( C)Wet Bulb( C)Dry Bulb ( 46.2Sydney31.119.817.081.95.7The first two columns of Table 2 show the AIRAH design conditions of the dry and wet bulbtemperatures for eight major cities in Australia. The dry bulb temperature and relativehumidity of the air leaving the indirect evaporative air conditioner are presented in the thirdand fourth columns. The temperatures of the air leaving the indirect evaporative airconditioner is calculated from Eqn. 2, based on the assumption that the direct evaporativesaturation efficiency is 125%. With the wet and dry bulb temperatures of the air leaving theevaporative air conditioner determined, the relative humidity of the air leaving the evaporativeair conditioner can then be computed. Based on a reduced nominal volume flow rate of 2,000m3/hr, the cooling capacity of the indirect evaporative air conditioner is computed based onEqn. 3 below.13

1.3 Market share of evaporative air conditionersThere are currently four major local evaporative air conditioner manufacturers: Air GroupAustralia Pty Ltd, Carrier Australia Pty Ltd, Climate Technologies Pty Ltd and SeeleyInternational Pty Ltd. The evaporative air conditioners that are currently available in Australiatogether with their key available specifications (such as type, energy input, water bleedingsystem, fan and pad type, supply flow rate, control system and evaporation efficiency) arelisted in Appendix 1.Figure 6 shows the national penetration of air conditioners and the number of air conditioners(including refrigerated and evaporative) utilised in residential houses in Australia from 1994to 2008 (ABS, 2008). Penetration is the proportion of households having a particular type ofair conditioner. The refrigerated air conditioners refer to the reverse cycle and cooling onlyrefrigerated air conditioners, non-ducted or ducted. Between 1999 and 2008, there has been asharp increase in penetration and the number of refrigerated air conditioners. The penetrationrose from 34.7% in 1999 to 66.4% in 2008, which is nearly double in 10 years. The number ofevaporative air conditioners slowly increased from 0.41 million in 1994 to 1.03 million in2005, before slightly decreasing between 2005 and ion60.050.04.00040.03.00030.02.000Penetration (%)Units 00020022004200620080.02010YearFigure 6: National penetration and number of air conditioners (ABS, 2008)Fig. 7 illustrates some trends in the share of installed stock of air conditioners which are of theevaporative variety, both by state and nationally. The share of evaporative air conditionersreached a peak (27.4%) in 1999 and gradually went down to 18.6% in 2008. Also, for most ofthe states, the evaporative air conditioner share decreased since 1999. However, evaporativeair conditioners are still popular in suitable climatic zones – Western Australia, AustralianCapital Territory, Victoria and South Australia where their market share is around 30%.However, the general trend is a clear reduction of market share in the face of competitionfrom refrigerated systems. The raw data for Figs. 6 and 7 is listed in Appendix 2.14

Evaporative air conditioner share traliaFigure 7: Evaporative air conditioners percentage share of all installed domestic air conditioners bystate and nationally (ABS, 2008).Refrigerated air conditioner sales in Australia had a distinct increase over the past 25 yearsfrom less than 100,000 units per year in 1980 to more than 900,000 units a year in 2006(Energy Efficient Strategies, 2008). The market is large and complex and at present there arearound 200 brands. The vast majority of domestic refrigerated air conditioners are imported.The annual sales figure of rooftop evaporative air conditioners is approximately 60,000 unitsand this figure has been reasonably stable over the last 5 years. Most of the residential ductedevaporative air conditioners sold in Australia are manufactured domestically.Despite the lower energy consumption of evaporative air conditioners in comparison withother cooling systems, and improvements in the quality of products produced by theAustralian evaporative air conditioning industry, there is a general trend of a shrinking marketshare. This is partly possibly a result of the competition provided by internationalrefrigeration system manufacturers and suppliers, particularly in marketing their products, aswell as cost advantages associated with larger scales production.1.4 Types of heating systems1.4.1 Reverse Cycle Air ConditionersRefrigeration air conditioners shift heat from one location to another, using a compressor andtwo heat exchangers linked by a refrigeration circuit. As electricity is required to operate thecompressor and fans which take the heat from the environment, they are the most efficientform of electric heating. Unlike electrical resistance heaters which at most convert allelectrical input into heat (efficiency approach 100%), the heating output provided by a reversecycle air conditioner may be 3 to 6 times the electrical energy consumed by the system.Refrigeration air conditioners are available as ―cooling only‖ units, or ―reverse cycle units‖15

which provide both cooling and energy efficient heating. There are a number of differenttypes of refrigeration air conditioners available:window/wall units which are used for individual rooms or small open plan areas.non-ducted split systems which are used for individual rooms or small open plan areas.These differ to the above in that the 2 heat exchangers are separated, one being locatedindoors and the other outdoors.ducted systems (usually of the split type) which are used for large open plan areas or thewhole floor of a building.multi-split systems, which have more than one indoor unit with more than one independentindoor controls, with only one condenser unit located outside.chillers which cool water as opposed to air. The cold water is then piped around the hometo cool the air with the use of heat exchangers.

Evaporative air conditioners can be categorised as direct, indirect, two- and multi-stage. Direct evaporative air conditioners are the most popular in the market. As shown in Fig.1 (a), outside air is drawn through wetted filter pads, where the hot dry air is cooled and humidified through water evaporation.