4.1. Direct evaporative cooling (DEC)

Figure 5. Working principle of conventional vapor compression air-conditioning (VAC) systems.

104 Refrigeration

Direct evaporative cooling [46, 49] (DEC) is the fundamental sense of typical evaporative cooling conception in which water vapors continuously evaporate into air until condition of air saturation arises. Therefore, cooling effect is produced by means of heat of water

Figure 6. Ambient air conditions of Multan and Fukuoka archetypally for summer season. Each point represents hourly value (average) for 24 h in a day.

vaporization as shown in Figure 7(a). The process can be realized from the fundamental equation of air enthalpy given by Eq. (1) [29].

$$h\_a = 1.006 \ T\_a + w \left(2501 + 1.86 T\_a\right) \tag{1}$$

where ha represents enthalpy of moist air [kJ/kg], Ta represents dry-bulb temperature [�C] and w represents humidity ratio [kgw/kgDA]. It is worth mentioning that the term 1.006 Taexpresses specific enthalpy of dry air, whereas the term w (2501 + 1.86Ta)embodies specific enthalpy of saturated water vapors. In DEC system, enthalpy of the inlet and outlet air streams remains constant, thus cooling limit of DEC system is ambient air wet-bulb temperature. Hence, isenthalpic cooling potential of DEC will be function of ðTinÞdb � ðTinÞwb. For insight of DEC, inlet and outlet air conditions are described by Eqs. (2)–(5).

$$((T\_{out})\_{db} \ge (T\_{in})\_{wb} \tag{2}$$

$$\text{RH}\_{\text{out}} > \text{RH}\_{\text{in}} \tag{3}$$

$$
\omega\_{\rm out} > \text{ } \varpi\_{\rm in} \tag{4}
$$

$$h\_{out} = \; h\_{in} \tag{5}$$

where h and w represent enthalpy of moist air [kJ/kg] and humidity ratio [g/kgDA], respectively. Subscripts in, out, db, and wb represent inlet, outlet, dry-bulb, and wet-bulb, respectively. Similarly, wet-bulb effectiveness εwb [–] of the DEC systems can be written as:

Energy-Efficient Air-Conditioning Systems for Nonhuman Applications http://dx.doi.org/10.5772/intechopen.68865 107

$$(\varepsilon\_{wb})\_{DEC} = \frac{(T\_{in})\_{db} - (T\_{out})\_{db}}{(T\_{in})\_{db} - (T\_{in})\_{wb}} \tag{6}$$

Figure 7. Direct evaporative cooling (DEC) system: (a) schematic representing the fundamentals and thermodynamic principle; and (b) system performance for nonhuman AC applications for Multan and Fukuoka, where each legend point represents hourly value (average) of a day.

Performance of DEC system is analyzed for Multan and Fukuoka cities, archetypally for summer season. Results are expressed on psychrometric chart for εwb= 0.95, in order to highlight its applicability for nonhuman AC applications as shown in Figure 7(b). It can be observed for both cities that the DEC system cannot provide required conditions for "tobacco softening" and for "storage of fruits & vegetables." On the other hand, DEC can support/assist conventional AC unit for "optical lens grinding" and "animals' AC" for Multan and Fukuoka climates, respectively. Similarly, all the nonhuman AC applications can be examined for DEC system applicability using Figure 7(b).

### 4.2. Indirect evaporative cooling (IEC)

vaporization as shown in Figure 7(a). The process can be realized from the fundamental

Figure 6. Ambient air conditions of Multan and Fukuoka archetypally for summer season. Each point represents hourly

where ha represents enthalpy of moist air [kJ/kg], Ta represents dry-bulb temperature [�C] and w represents humidity ratio [kgw/kgDA]. It is worth mentioning that the term 1.006 Taexpresses specific enthalpy of dry air, whereas the term w (2501 + 1.86Ta)embodies specific enthalpy of saturated water vapors. In DEC system, enthalpy of the inlet and outlet air streams remains constant, thus cooling limit of DEC system is ambient air wet-bulb temperature. Hence, isenthalpic cooling potential of DEC will be function of ðTinÞdb � ðTinÞwb. For insight of DEC,

where h and w represent enthalpy of moist air [kJ/kg] and humidity ratio [g/kgDA], respectively. Subscripts in, out, db, and wb represent inlet, outlet, dry-bulb, and wet-bulb, respectively.

Similarly, wet-bulb effectiveness εwb [–] of the DEC systems can be written as:

ha ¼ 1:006 Ta þ w ð2501 þ 1:86TaÞ ð1Þ

ðToutÞdb ≥ ðTinÞwb ð2Þ

RHout > RHin ð3Þ

wout > win ð4Þ

hout ¼ hin ð5Þ

equation of air enthalpy given by Eq. (1) [29].

value (average) for 24 h in a day.

106 Refrigeration

inlet and outlet air conditions are described by Eqs. (2)–(5).

Increase in product air humidity is the key limitation of typical DEC system; therefore, indirect evaporative cooling (IEC) system can be employed for constant absolute humidity [49]. As no moisture is added in the air by IEC, it enables hygiene air quality. Fundamentals and thermodynamic principle of IEC system is expressed by the schematic diagram shown in Figure 8(a). Referring to Figure 8(a), the IEC cooling is achieved by combination of two thermodynamic processes: (i) isenthalpic cooling by water vapor evaporation into the air, that is, DEC process (wet-channel) and (ii) sensible heat transfer from process (i) (dry-channel). As the cooling effect is based on water vapor evaporation, the cooling limit of IEC is also wet-bulb temperature. Thus, the cooling potential of IEC will be function of ðTinÞdb � ðTinÞwb, similar to DEC. In addition of DEC efficiency parameters, the net efficiency of IEC device is influenced by air-flow ratio and heat transfer between dry and wet channels. For insight of IEC, inlet and outlet air conditions along with wet-bulb effectiveness are expressed by Eqs. (7)–(11).

$$(T\_{out})\_{db} \succeq (T\_{in})\_{wb} \tag{7}$$

$$\text{RH}\_{\text{out}} > \text{RH}\_{\text{in}} \tag{8}$$

$$
\omega\_{\rm out} = \varpi\_{\rm in} \tag{9}
$$

$$h\_{out} < \ h\_{in} \tag{10}$$

$$(\varepsilon\_{wb})\_{IEC} = \frac{(T\_{in})\_{db} - (T\_{out})\_{db}}{(T\_{in})\_{db} - (T\_{in})\_{wb}} \tag{11}$$

Figure 8. Indirect evaporative cooling (IEC) system: (a) schematic representing the fundamentals and thermodynamic principle; and (b) system performance for nonhuman AC applications for Multan and Fukuoka, where each legend point represents hourly value (average) of a day.

It can be observed from Eqs. (2)–(11) that the numerical value of outlet temperature by DEC and IEC units will be identical for same effectiveness; however, humidity makes the difference in cooling performance. In this regard, IEC system performance is investigated for summer season of Multan and Fukuoka cities for nonhuman AC applications as shown in Figure 8(b) for εwb = 0.95. According to the results, "tobacco softening" and "storage of fruits & vegetables" cannot be entertained by IEC system for both cities. On the other hand, unlike DEC, the IEC can provide optimum conditions for "animals' AC" for Fukuoka city. In addition, IEC can support/assist conventional AC system for the industrial AC process of "optical lens grinding" for Multan. Similarly, rest of the nonhuman AC applications can be examined by Figure 8(b).
