Advancements in Indirect Evaporative Cooling Systems through Novel Operational Configuration

*Muhammad Ahmad Jamil, Muhammad Wakil Shahzad, Ben Bin Xu, Muhammad Waqar Ashraf, Kim Choon Ng, Nida Imtiaz and Haseeb Yaqoob*

### **Abstract**

Rising global temperature has triggered the cooling demand in the last three decades with growing predictions for the future. The use of conventional energyintensive and high global warming chemical-based cooling systems is working in a loop, increasing the global warming rate, emissions, and cooling system inventory. Therefore, the development of an innovative cooling system with high energy efficiency, low monetary cost, and environmentally sustainable. The indirect evaporative cooling-based systems have shown potential to serve the purpose because of low energy consumption, absence of energy, and cost-intensive equipment like compressors and water-based operation. A novel indirect evaporative cooler based on an innovative operational configuration is proposed, fabricated, and tested experimentally. The Proposed system has several advancements compared to the conventional indirect evaporative coolers like high operational reliability, low maintenance, and better control of the processes in the system. The study shows that the proposed system can achieve a temperature drop of as high as 14°C. The maximum cooling capacity of the system is calculated as 110 W, and the cooling performance index of 28. The performance of the cooler improves with increasing outdoor air temperature which makes it suitable for diverse climatic conditions. Moreover, the proposed design offers several benefits due to novel operational configurations by addressing limitations in the earlier systems.

**Keywords:** advanced evaporative cooler, humidity-controlled cooling, cleaner air conditioning, sustainable development, cooling systems

#### **1. Introduction**

A remarkable surge in the global energy demand has been seen in the recent past because of an exponential rise in population, urbanization, and economic growth [1]. Moreover, the improving lifestyle is also contributing significantly to the energy consumption to maintain human comfort [2, 3]. The worldwide energy demand is estimated to rise to 850 quadrillions Btu by 2050 from merely 500 quadrillions Btu in 2010 indicating around a 50% rise in 4 decades [4]. Particularly, the situation is alarming for developing countries that will face a tremendous surge of around 71%in the energy demand compared to the developed countries with 18% [5, 6]. Building energy consumption is of critical importance in the overall energy consumption scenario because of the major share and diverse necessary activities [7]. The common among these are human thermal comfort, cleaning, cooking, food preservation, lightening, etc. Despite the wide range of activities taking place in buildings, the overall energy consumption can be classified into 6 different types as shown in **Figure 1** [8, 9]. For commercial and residential buildings, the energy consumption is as follows: heat ventilation and air conditioning 36–40%, lighting 12–20% hot water supply 9– 13%, electronics 8–15%, refrigeration 5–7%, cooking 4–5% and others 8–18% [10, 11].

Meanwhile, the demand for air conditioning is also increasing continuously and the global air conditioner inventory is expected to cross 5600 million by 2050 from merely 1600 million units reported in 2016 [12]. The corresponding energy consumption and emission are also expected to surge to 6200-Terawatt hour and 170 Gigatons by 2050 [13]. The use of conventional vapor compression chillers is one of the major reasons for these high energy demands. This is because these systems have very low energy efficiency, which is low efficiency, and involve high global warming potential refrigerants for cooling [14]. Meanwhile, their performance has not seen any considerable improvement in the last 30 years with a stagnant coefficient of performance (COP) of 3–4. This is because of rigid temperature lifts (5 to 7°C) across the evaporator and condenser which require a high input energy compressor [15]. Moreover, high global warming potential chemical refrigerants are used for compression and expansion in the system for cooling with high chances of leakage due to elevated pressure operation. These problems cannot be abandoned in conventional operational schemes. So, an innovative system is required to achieve a breakthrough in the cooling sector [16].

**Figure 1.** *Building energy consumption distribution [8–10].*

*Advancements in Indirect Evaporative Cooling Systems through Novel Operational… DOI: http://dx.doi.org/10.5772/intechopen.107305*

One of the lucrative options for the above-mentioned problems emerged is the indirect evaporative cooling system [17]. It uses a water-based cooling mechanism and does not involve any hazardous chemical refrigerant [18]. Moreover, it does not involve any high energy consumption compressor. Rather these systems use fans for air movement through the system and pump for water supply [19, 20]. In these systems, the hot outer air is cooled using cold wet air (water-air mixture) in two different channels. The channels are separated by thermally conductive impermeable walls which only allow heat exchange between the air streams without any moisture exchange. Therefore, these systems produce cold dry air using air and water through evaporation [21, 22].

These systems have been extensively studied by the research community from an experimental and theoretical viewpoint. For instance, multipoint air injection in IECs improved the cooling performance by achieving an additional 2 to 3°C temperature drop by achieving COP as high as 78 for cooling [23]. Likewise, the enhancement of heat transfer plates through protrusion was reported to enhance the IEC performance achieving wet bulb efficiency up to 85% [24, 25]. Chua et al. [26] investigated a feltassisted IEC with a cross-flow heat exchanger and showed that the cooler can achieve wet bulb efficiency of 90%. Similarly, Duan et al. [27] developed a compact heat exchangers based counter flow IEC. They reported the performance characteristics of the system in terms of wet bulb efficiency up to 107%, cooling capacity up to 8.5 kW, and energy efficiency ratio up to 20. They also improved the system efficiency and energy efficiency ratio by 30% and 40%, respectively by enhancing plates with corrugations [28]. Similarly, finned channel-based systems have also shown promising performance with wet bulb efficiency as118–122% and dewpoint effectiveness of 75– 90% [29]. Cui et al. [30] investigated the hybrid air conditioning system with IEC and reported the COP as 14.2 for cooling.

Besides experimental studies, the theoretical analyses of IEC systems have also shown considerable performance improvements through design and operational modifications. For instance, Oh et al. [31] studied the effect of purge configuration on regenerative type IEC performance. They reported the maximum cooling performance at 35% purge ratio with a dew point efficiency of 58% and cooling capacity of 59 W. Similarly, Pandelidis et al. [32] showed that the performance of regenerative IEC systems can be improved through additional perforations, particularly at higher air flow rate ratio > 45%. Riangvilaikul et al. [33] showed that the Polyurethane based IEC system showed promising performance by achieving dewpoint efficiency of 65– 87% and the wet bulb efficiency 106–109%. Wang et al. [34] optimized a dewpoint regenerative type IEC based on the entropy principle. The optimal values for velocity, heat exchanger length, channel gap, and airflow rate ratio were reported as 1.0 m/s, 1–1.75 m, 3-5 mm, and 30–40%, respectively. Jradi et al. [35] optimized the dew point cooler for maximum wet bulb efficiency of 112%, and dewpoint efficiency of 78%. The optimal channel gap and heat exchanger length under considered operating conditions were reported as 5 mm and 500 mm, respectively. Similarly, Adam et al. [36] optimized the cross-flow IEC and reported the supply air temperature as 24°C and wet bulb efficiency as 92%. and TPA,o = 24°C. Some other efforts include the study of the effects of condensation in the dry channel [37], wettability enhancement in the wet channel [38], and improving heat transfer characteristics of heat exchangers [39].

The literature review shows that indirect evaporative coolers are a capable substitute for compression cooling systems because of promising performance from temperature drop, efficiency, and COP. Therefore, an innovative indirect evaporative cooler with a novel operational configuration is proposed and tested experimentally.

The proposed system has several advancements like simple construction, separate control for the air-water mixing process, fewer maintenance requirements, and better control of sensible and latent heat transfer processes. The current study analyzes a generic cell of the system which can be used to develop the design metrics for commercial-scale expansion of the proposed idea.
