**6. Conclusions**

*hconva*−*abs*

*hcondtube*−*insulation*

*ρtube Stube Ctube*

= \_\_\_\_\_\_\_\_\_ <sup>1</sup> *δ* \_\_\_\_ *tube λtube* + *δ* \_\_\_\_\_\_ *insulation λinsulation*

AC systems investigated in the present chapter.

where *P* is the perimeter.

14 Sustainable Air Conditioning Systems

<sup>=</sup> *Nutube <sup>λ</sup>* \_\_\_\_\_\_\_*<sup>f</sup> Dh*,*tube*

**traditional ones**

following **Table 2**.

*dT*\_\_\_\_\_ *tube*

*dt* <sup>=</sup> *Scabs*−*tube hcondabs*−*tub*

+*Sctube*−*insulation hcondtub*−*insulation*

Re< <sup>2300</sup> <sup>⇒</sup> *Nutube* <sup>=</sup> 4.364 Re <sup>&</sup>gt; <sup>2300</sup> <sup>⇒</sup> *Nutube* <sup>=</sup> 0.023 Re0.8 Pr0.4

reached by the three proposed models under different climatic conditions.

**5. Comparative study of solar air-conditioning systems vs.** 

(*Tabs* − *Ttube*) + *Ptube hconvtube*−*insulation*

:the convective heat transfer coefficient between tube and circulating fluid (water)

The value of the Nusselt number *Nutube* depends on the Reynolds number *Re* as follows [48]:

The numerical values of the temperature and humidity show that the desired comfort is

**Table 1** summarizes the design values and the effectiveness of the three technologies of solar

From research studies reviewed in this chapter, we conclude that whatever the technology, solar AC systems have many environmental benefits compared with those that are driven by conventional vapor compression cycles. In fact, traditional AC systems operate with chlorofluorocarbons and hydrofluorocarbon refrigerants that impact on ozone depletion [49]. Hence, solar AC systems present an interesting solution to inhibit the harmful effects on the environment. It is observed that they significantly lower the emission of greenhouse gases into the atmosphere, achieve the desired comfort, and reach a considerable saving of energy of up to 80%. They also can be installed in all regions and operating under all climatic conditions. On the other hand, the solar air-conditioning can effectively mitigate peak load pressures occurred with the use of conventional air conditioners, thanks to the heat storage process. Indeed, the heat is especially stored when the solar irradiance is high and can be after harnessed when the solar radiation becomes deficient [50]. This fact ensures the continuous operation of the solar AC systems. In terms of COP, the thermal COP of a solar AC system is generally lower than those of a conventional AC system without decreasing the solar system performance. All these benefits make solar AC systems attractive and extensively integrated into modern buildings. This comparative study is illustrated in the

:conductive heat transfer coefficient between tube and insulation

(*Tinsulation* − *Ttube*) + *λtube Stube*

(*Tinsulation* − *Ttube*)

<sup>∂</sup><sup>2</sup> *<sup>T</sup>* \_\_\_\_\_*tube* ∂ *y*<sup>2</sup>

(10)

The solar AC systems reported in this chapter present an interesting worldwide solution to reduce the harmful effects (high energy consumption and pollution) of traditional AC systems. In fact, research studies revealed that absorption, adsorption, and desiccant systems allowed saving energy up to 80, 50, and 52%, respectively, thanks to the optimization of their designs at the level of using environmentally unfriendly refrigerants, investing in the free and clean solar energy to power them, as well as at the level of the choice of the components that comprise them. Therefore, these systems also reduced the pollution rate up to 95% (about 3000 kg of CO2 ), especially the absorption systems. In addition, their use is remarkably suitable in rural regions where the electricity is not available or its shortage is frequent. Some solar AC systems are also equipped with chilled or hot water tanks, which can be used in various activities (household, agricultural, and so on). However, their coefficient of performance is lower than 1 in most cases compared with the traditional AC systems that their coefficient can reach the value 3. Moreover, the installation and maintenance costs of the most solar AC systems are relatively high. They can reach up to \$ 29.000 and be paid back after at least 9 years. Hence, we can reach a long-term sustainability. Nonetheless, the design of these systems, especially adsorption and desiccant AC systems, is complex.

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