Experimental Investigation of Desiccant Dehumidification Cooling

energies

Article Experimental Investigation of Desiccant Dehumidiﬁcation Cooling System for Climatic Conditions of Multan (Pakistan)

Muhammad Aleem 1, Ghulam Hussain 1,2, Muhammad Sultan 1,* , Takahiko Miyazaki 3,4,*, Muhammad H. Mahmood 1, Muhammad I. Sabir 2, Abdul Nasir 5, Faizan Shabir 1,6 and Zahid M. Khan 1

1 Department of Agricultural Engineering, Bahauddin Zakariya University, Multan 60800, Pakistan; [email protected] (M.A.); [email protected] (G.H.); [email protected] (M.H.M.); [email protected] (F.S.); [email protected] (Z.M.K.) 2 Agricultural Mechanization Research Institute (AMRI), Old Shujabad Road, Multan 60800, Pakistan; [email protected] 3 Faculty of Engineering Sciences, Kyushu University, Kasuga-koen 6-1, Kasuga-shi, Fukuoka 816-8580, Japan 4 International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 5 Department of Structures and Environmental Engineering, Faculty of Agricultural Engineering & Technology, University of Agriculture, Faisalabad 38000, Pakistan; [email protected] 6 Department of Agricultural Engineering, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan 64200, Pakistan * Correspondence: [email protected] (M.S.); [email protected] (T.M.); Tel.: +92-333-6108888 (M.S.) Received: 23 August 2020; Accepted: 20 October 2020; Published: 22 October 2020

Abstract: In this study, experimental apparatus of desiccant dehumidification was developed at lab-scale, using silica gel as a desiccant material. Experimental data were obtained at various ambient air conditions, while focusing the climatic conditions of Multan (Pakistan). A steady-state analysis approach for the desiccant dehumidification process was used, and thereby the slope of desiccant dehumidification line on psychrometric chart (φ*) was determined. It has been found that φ* = 0.22 in case of silica gel which is lower than the hydrophilic polymeric sorbent, i.e., φ* = 0.31. The study proposed two kinds of systems, i.e., (i) standalone desiccant air-conditioning (DAC) and (ii) Maisotsenko-cycle-assisted desiccant air-conditioning (M-DAC) systems. In addition, two kinds of desiccant material (i.e., silica gel and hydrophilic polymeric sorbent) were investigated from the thermodynamic point of view for both system types, using the experimental data and associated results. The study aimed to determine the optimum air-conditioning (AC) system type, as well as adsorbent material for building AC application. In this regard, perspectives of dehumidification capacity, cooling capacity, and thermal coefficient of performance (COP) are taken into consideration. According to the results, hydrophilic polymeric sorbent gave a higher performance, as compared to silica gel. In case of both systems, the performance was improved with the addition of Maisotsenko cycle evaporative cooling unit. The maximum thermal COP was achieved by using a polymer-based M-DAC system, i.e., 0.47 at 70 ◦C regeneration temperature.

Keywords: desiccant dehumidiﬁcation; silica gel; polymer; air-conditioning; Maisotsenko cycle; performance evaluation; Pakistan

Energies 2020, 13, 5530; doi:10.3390/en13215530 www.mdpi.com/journal/energies Energies 2020, 13, 5530 2 of 23

1. Introduction Air-conditioning systems (ACS) are mainly used to maintain a comfortable/favorable zone in a controlled environment by manipulating temperature and relative humidity. Heating, cooling, humidification–dehumidification and ventilation are some of the modes of the ACS which correspond to the climatic conditions and the required application of air-conditioning (AC) [1]. Depending upon the type of the AC application and the climatic conditions, multiple ACS modes could be applied [2]. In addition, different AC applications require particular ranges of temperature and relative humidity [3–6]. Conventionally, vapor compression air-conditioning (VCAC) systems are used to condition the environment, which primarily use hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) as refrigerant, endorsing environmental degradation and high energy consumption [3]. Consequently, the VCAC systems contribute to global warming (GW) due to carbon dioxide (CO2) emissions [7]. Alternatively, the heat driven adsorption/absorption-based environment friendly ACS are in practical use [2,8]. In ACS, 30–40% of overall energy is used by buildings throughout the world, i.e., approximately half of the total energy consumption [9,10]. In addition, heating, ventilation, and air-conditioning (HVAC) systems consume 50% of the entire building energy [11]. Therefore, environment friendly and least-energy-consumptive cooling systems are promising for AC. Evaporative cooling systems are environment friendly and least-energy-consumptive option for building AC load management. Evaporative cooling (EC) is a well-known and old cooling process that uses the water evaporation to lower the temperature of air. These cooling systems include direct evaporative cooling (DEC), indirect evaporative cooling (IEC), Maisotsenko cycle, i.e., M-cycle evaporative cooling systems (MEC) and M-cycle based indirect evaporative cooling (M-IEC) [7]. DEC is the simplest type of EC system in which the air comes into direct contact with water’s surface to decrease its temperature. It increases the humidity of the air by using the latent heat of water [12]. In term of temperature depression, DEC has around 70% to 95% effectiveness but the main downside of DEC is an excessive amount of humidification because the water vapors constantly disperse in the air till saturation occurs [13]. The IEC is a system in which heat and mass transfer takes place without adding moisture to reduce the temperature of primary/ambient air. The IEC system comprises of a dry channel and a wet channel. [14]. Cooling in wet channel has a psychrometric limitation to wet-bulb temperature (i.e., through direct evaporative cooling); therefore, the cooling in dry channel is dependent on (and is limited to) sensible heat transfer between the dry and wet channel (i.e., wet-bulb temperature of the air in wet channel). Hence, wet-bulb effectiveness (εwb) can be used to define the performance of the IEC system on the basis of sensible cooling. Therefore, the IEC system can reduce the temperature down to the wet-bulb temperature, and its wet-bulb effectiveness ranges from 0.5 to 0.65 [15,16]. The drawback of the IEC system is low wet-bulb effectiveness, as compared to the DEC system due to less sensible heat transfer between the channel walls [17]. However, the extract air from an air-conditioned environment can be used to perform DEC, to increase the wet-bulb effectiveness. Maisotsenko cycle (M-cycle) conception was proposed as early as 1976, by Maisotsenko and his colleagues in the Soviet Union, via patent numbers SU979796 and SU620745 [7]. M-cycle evaporative cooling (MEC) is a system in which ambient air is subjected to a thermodynamic process in which air-available psychrometric renewable energy is used to reduce the ambient air temperature. It extracts energy from the surrounding air by using the latent heat of evaporation phenomena [18]. Two thermodynamic processes create the cooling effect in the MEC system: evaporative cooling and heat transfer in which the ambient air almost approaches the temperature of dew point instead of the temperature of wet bulb [19–22]. M-cycle air-conditioning (MAC) systems provide sensibly cooled air and saturated hot air simultaneously [3,23,24]. In particular, the MAC system could potentially be capable of reducing energy consumption, and uses relatively less energy than the VCAC systems [25–27]. The MAC system is a dedicated outside air system which utilizes fresh ambient air to provide cool air unlike the VCAC which require mechanical energy [28–30]. The evaporative cooling with the VCAC system has been utilized in the literature, to attain the required level of AC [14,31–34]. Energies 2020, 13, 5530 3 of 23

In addition, several experimental and theoretical studies have been performed to achieve the necessary temperature and humidity conditions for evaporative cooling systems [35–42]. However, the key limitation of evaporative cooling technologies (DEC, IEC, and MEC) is that it cannot be effectively implemented in regions where the moisture content in the air is comparatively high [1,6]. Therefore, to overcome this limitation, evaporative cooling systems coupled with desiccant dehumidification units could be a viable AC option for such regions. Desiccant air-conditioning (DAC) system contains a dehumidifying component (desiccant) to dehumidify the process air. Owning to the difference in vapor pressure, a desiccant is a substance that can adsorb moisture from the air onto its surface. Desiccant materials are used in the AC system in both solid and liquid forms. Silica gel, activated aluminum composite adsorbents, and synthetic zeolite are widely used as solid desiccants. Lithium chloride (LiCl) and lithium bromide (LiBr) are liquid desiccants that are widely used. However, the major drawbacks of liquid desiccants are corrosiveness and crystallization [43,44]. Some recently developed composite materials that can perform even better are also available [45]. Due to their water attraction capability, the DAC systems are critical in applications where relative humidity (RH) control is mandatory. For humid climates, the DAC system is an energy-efficient and sustainable solution [3]. For temperature and humidity regulation, the DAC is incorporating desiccant dehumidification and evaporative cooling. The sensible and latent load of air can be treated simultaneously by the DAC system, which makes the DAC system versatile. The DAC is an environment-friendly technology, since it is free from CFCs, HCFCs (i.e., refrigerants). Therefore, the DAC contributes zero global warming (GW) and ozone depletion (OD). Additionally, the desiccant material used in the DAC system could easily be regenerated using low-grade waste heat or solar thermal heating source. In addition, via the desiccant dehumidification AC method, up to 5% and 30% energy consumption for heating and cooling, respectively, can be reduced by using the DAC systems as compared to the VCAC systems [3]. The general DAC applications include buildings, agriculture product storage, greenhouse AC, livestock AC [4,7,45–49] supermarkets, schools, cold warehouses, ice arenas, theaters, hotels, hospitals, automobiles [50], wet markets [51], drying grains [52], marine ships [53,54], and museums [55,56]. M-cycle supported DAC combines the characteristics of DAC and MAC. The M-DAC system attains two loads simultaneously. Latent load through the desiccant dehumidification process and sensible load through evaporative cooling [57–59]. M-DAC system is getting interested by the researchers and has been investigated in literature for humid climate [60–63]. In this research, a lab-scale open-cycle solid-silica-gel-based DAC experimental apparatus is locally developed. In literature, the DAC system comprises of desiccant blocks, rotor, or wheel that have a honeycomb like structure was used [4,64–67]. The significance of this research is that a solid-silica-gel-based DAC system was developed, at lab-scale, for the performance evaluation of the DAC system. In addition, this study offers researchers the opportunity to create their own solid-desiccant-based DAC systems at the lab-scale. According to Köppen–Giger climate classification, Multan has a warm desert climate. Concerning the climatic condition of Multan (Pakistan), the experimental data were obtained and analyzed. The experimental data were collected to evaluate the DAC system performance for such climatic conditions. The study proposed two kinds of systems: (i) standalone DAC system and (ii) M-cycle assisted DAC system. In addition, two kinds of desiccant material (i.e., silica gel and hydrophilic polymeric sorbent) are thermodynamically investigated for both system types, using the experimental data. The performance of the abovementioned systems is compared, and the feasibility of the systems is investigated on monthly basis by comparing dehumidification capacity, cooling capacity, and thermal coefficient of performance (COP) of the system.

2. Materials and Methods

2.1. Experimental Section An open-cycle lab-scale desiccant experiment system was set up. It contained a heater, fan, desiccant material, accessories, sieves, anemometer (BENETECH, GM816) with an accuracy of 1.5 m/s ± Energies 2020, 13, 5530 4 of 23

(5%) and range of 0.3–30 m/s, temperature sensor (UNI-T, UT330A) with an accuracy 2 ◦C (1.6%) Energies 2020, xx, x; doi: FOR PEER REVIEW ± 4 of 23 and range 40–80 C, relative humidity sensor (UNI-T, UT330A) with an accuracy of 5% (5%) and − ◦ ± range(5%) of 0–100%,and range and of 0–100%, pressure and sensor pressure (UNI-T, sensor UT330A) (UNI-T, with UT330A) an accuracy with an accuracy of 3 hpa of (0.8%) ±3hpa and(0.8%) range ± 750–1100and hPa, range respectively. 750–1100 hPa, A signiﬁcantrespectively. part A significant of the desiccant part ofsystem the desiccant is the arraysystem of is sieves the array because of the adsorbentsieves (desiccant because the material) adsorbent is placed (desiccant on it.material) The sieves is placed are contrived on it. The withsieves polyacrylic are contrived material with and mesh.polyacrylic A total of material 18 sieves and are mesh. used A for total the of desiccant 18 sieves systemare used and for werethe desiccant kept on system each other and inwere the kept form of a rectangularon each other block. in the Each form sieve of a has rectangular a dimension block. of Each 250 mmsieve has145 a mmdimension3 mm, of and250 mm about × 145 68 gmm of silica× × × gel is placed3 mm, over and eachabout sieve. 68 g of The silica total gel silicais placed gel usedover each in this sieve. experiment The total silica was approximatelygel used in this 1.22 kg. The pictorialexperiment representation was approximately of the experimental 1.22 kg. The pictoria setupl is representation shown in Figure of the1a. experimental setup is shown in Figure 1a.

Figure 1. Pictorial representation of (a) the experimental system, and (b) schematic representation of Figure 1. Pictorial representation of (a) the experimental system, and (b) schematic representation of the experimental system. the experimental system. Energies 2020, 13, 5530 5 of 23

As for as the experimental procedure is concerned, due to the high hydrophilic aﬃnity of desiccant material (adsorbent) and pressure gradients between adsorbent and ambient air vapors adsorb on the adsorbent surface for a period. At the point where the surrounding air is crossed into the desiccant unit, due to the release of heat from adsorption, it becomes dry and relatively hot. After a while, the adsorbent of the desiccant system becomes saturated and its adsorption capacity reduces. Therefore, adsorbent must require its regeneration. This is achieved by passing the warm air over the desiccant system. The hot air clears the moisture away from the adsorbent surface and the material gets regenerated. The schematic diagram of the experimental setup is shown in Figure1b. Therefore, the regeneration temperature for the regeneration of the adsorbent was set at 65–70 ◦C. The mass ﬂow rate of approximately 0.05 to 0.08 kg/s was transferred via the desiccant system inlet and outlet.

2.2. Data Processing The data on desiccant dehumidification were generated by the experimental apparatus for performance assessment of the DAC system. The dehumidification of ambient air takes place through the desiccant system and offers the outlet condition. The air conditions that passed through the heat exchanger (HX) and M-cycle cooling system are computed from Equations (1) and (2), respectively, given in the literature [4,48]. For completion of the cycle, the regeneration stream is provided to regenerate the desiccant. In the desiccant dehumidification process, the phase of water vapor changes from vapors to liquid and release equal heat of vaporization and condensation described as equivalent heat of adsorption. The equivalent heat of adsorption is calculated through Equation (6), and the total amount of water adsorption/desorption is determined by Equation (7) [68]. The enthalpy of the air is calculated by Equation (8) [69]. T = T εHX T T (1) 3,db 2,db − 2,db − 1,db T = T ε T T (2) 4,db 3,db − wb 3,db − 1,wb T = T εHX T T (3) 6,db 5,db − 2,db − 5,db X1 = X5 = X6 = X7 (4)

X2 = X3 = X4 (5) . qeq = m(hout h ) (6) − in ∆X = X Xout (7) in − h = 1.006Tdb + X(2501 + 1.86Tdb) (8) where the subscripts (1–7) represent the air state conditions, as shown in Figure2. Tdb, εHX, εwb, Twb, X, . qeq, m, hout, hin, Xin, and Xout represent dry-bulb temperature (◦C), effectiveness of heat exchanger taken as 0.9 [4], wet-bulb effectiveness taken as 0.6 [4], wet-bulb temperature (◦C), humidity ratio (g/kg-DA), equivalent heat of adsorption (W), mass flow rate of air (kg/s), air enthalpy at outlet side of desiccant system (kJ/kg), air enthalpy at inlet side of desiccant system (kJ/kg), humidity ratio at outlet side of desiccant system (g/kg-DA), and humidity ratio at inlet side of desiccant system (g/kg-DA), respectively. Ideally, for the duration of the dehumidification process, the dehumidification line slope on the psychrometric chart pursues an isenthalpic behavior. This means that the adsorption process is the same as the heat of water vapor condensation after the vapor stage to the liquid stage for the duration of the desiccant dehumidification. Although, via experimental results, it is concluded that the net adsorption heat is to some extent more than the ideal adsorption heat caused by the isosteric heat of adsorption [3,70]. The relationship between this behavior can be specified by Equation (9) [45]. The disparity among the actual slope of a line and ideal slope line on the psychrometric chart is mainly due to the kind of adsorption mechanism and adsorbent pair interactions. Consequently, it is intricate Energies 2020, 13, 5530 6 of 23 to stimulate the performance of desiccant precisely. As a result, the dehumidification line slope is experimentally developed, and several scenarios are explored to create a unique relationship for the desiccant dehumidification process. Equation (10) [68] specifies the slope of the actual or experimental dehumidification line. In addition, the cooling capacity, thermal COP of the standalone, M-cycle assisted DAC system and the amount of heat required to regenerate the desiccant are computed from Equations (11)–(14), respectively [6]. ∆ φ∗ = φh (9) Qst

X Xout φ = in − (10) ∗ T T db,out − db,in Qc = h h (11) 1 − 4 . ! mPA Cooling capacity (h1 h3) COP = . = − (12) m Heat input (h h ) RA 6 − 5 . ! mPA Cooling capacity (h1 h4) COP = . = − (13) m Heat input (h h ) RA 7 − 6 Q = m Cp(T T ) (14) inp RA 7 − 6 where the subscripts 1, 3, 4, 6, and 7 represent the air state conditions, as shown in Figure2. φ∗, ∆, Qst, . . φh, Xin, Xout, Tdb,out, Tdb,in, Qc, COP, mPA, mRA, Qinp, and Cp represent the slope of dehumidification line on psychrometric chart (-), heat of water vapor condensation (kJ/kg), isosteric heat of water vapor adsorption (kJ/kg), slope of enthalpy line on the psychrometric chart (-), humidity ratio at outlet side of desiccant system (g/kg-DA), humidity ratio at inlet side of desiccant system (g/kg-DA), dry-bulb temperature at outlet side of desiccant system (◦C), dry-bulb temperature at inlet side of desiccant system (◦C), cooling capacity (kJ/kg), coefficient of performance of the system (-), mass flow rate of process air (kg/s), mass flow rate of regeneration air (kg/s), heat input required for regeneration of desiccant block (kW), and specific heat capacity of air taken as 1.006 (kJ/kg-K), respectively. Uncertainty in the data can arise from multiple sources, including imprecise measurement from the sensor, design limitations, human error, inaccurate procedure, and other important factors. The uncertainty analysis is necessary because the magnitude of the model needs to be contemplated when interpreting the results of the model calculations. Uncertainty analysis is carried out to measure the uncertainty in calculating the variables (temperature, relative humidity, pressure, and air velocity) at the time of the experiment. In desiccant data, the uncertainty is resolved by the root of the sum of squares method by Equation (15) [71,72]. The total uncertainties (σt) during the measurement of air temperature, relative humidity and pressure is computed by Equation (16), as cited in the literature [73,74]. s !2 !2 !2 ∂R ∂R ∂R σR = α1 + α2 + ... + αN (15) ∂N1 ∂N2 ∂Nn q = 2 + 2 + 2 σt σsen σcalibr σdaq (16) where σR, α αN, R, N1 Nn, σt, σsen,. σ , and σ represent the total uncertainty in measuring 1 − − calibr daq the adsorption uptake, uncertainty in measuring different variables, a given function of independent variables, independent variables, total uncertainty in the measurement of temperature, relative humidity, and pressure (%), uncertainties of a sensor, uncertainty in calibration, and uncertainty associated with data-acquisition system, respectively. The uncertainties in sensor, calibration, and data acquisition are provided by the manufacturer. Therefore, the measurement uncertainties in temperature, relative humidity, pressure drop, and velocity are 2.6, 5.1, 1.6, and 5.1%, respectively. ± ± ± ± Energies 2020, 13, 5530 7 of 23

Energies 2020, xx, x; doi: FOR PEER REVIEW 8 of 23

Figure 2. Schematic representation of (a) standalone desiccant air-conditioning (DAC) system and (b) Figure 2. Schematic representation of (a) standalone desiccant air-conditioning (DAC) system and Maisotsenko(b) Maisotsenko cycle (M-cycle)-based cycle (M-cycle)-based DAC DAC system. system.

4. Results and Discussion The desiccant dehumidification performance on an experimental basis was inspected for different processes and regeneration air conditions. Figure 3 shows the experimental profile of ambient air conditions of Multan with desiccant dehumidification at a regeneration temperature of 70 °C. In Figure 3, the dynamic nature of the process and regeneration temperature of 70 °C is shown, Energies 2020, 13, 5530 8 of 23

3. Proposed DAC System The current study concentrates on two types of AC systems that involve a (i) standalone DAC system and (ii) M-cycle assisted DAC system. In addition, two adsorbents (i.e., hydrophilic polymeric sorbent and silica gel) were investigated. In this research, the overall performance of proposed DAC systems was investigated, and the feasibility of such systems was explored for the climatic conditions of Multan (Pakistan). A concise depiction of these systems is provided below.

3.1. Standalone DAC System Standalone DAC system contains a dehumidification unit coupled with a sensible heat exchanger (HX) and heating unit. There is no M-cycle cooling device that is solely use for the dehumidification of air. In Figure2a, a schematic representation of the standalone DAC system is provided. The DAC system is used for the dehumidification of the air and results in an increase in temperature near the regeneration temperature of the desiccant (i.e., conditions 1 and 2). Furthermore, the hot and dehumidified air passes through the sensible HX, which reduces the temperature of dehumidified air without affecting the humidity ratio near to the ambient air (i.e., condition 3). Consequently, ambient air (i.e., condition 4) is used for the regeneration of desiccant block. The air passes through the heat exchanger as a return air which transfers the heat of process air into the regeneration air, slightly raising its temperature without affecting the humidity ratio (i.e., condition 5). The regeneration air passes through a low-grade heating source, which further increases the temperature of the regeneration air (i.e., condition 6). This hot and relatively dry regeneration air passes through the desiccant block which desorbs the adsorbate (water vapors, i.e., condition 7), hence completing the cycle. The psychrometric representation of conditions 1–7 are shown in Figure2a.

3.2. M-Cycle-Based DAC System A typical M-cycle assisted DAC system, as shown in Figure2b, is intended for cooling and dehumidification of ambient air. The system consists of desiccant blocks with the inclusion of a flat plate heat exchanger, cooling device (M-cycle), and heat source for the regeneration of desiccant component. The DAC component is used to dehumidify the air, resulting in a rise in temperature near the desiccant’s regeneration temperature (i.e., conditions 1 and 2). Moreover, the hot and dehumidified air passes through sensible HX, which decreases the dehumidified air close to the ambient air temperature without affecting the humidity ratio (i.e., condition 3). In addition, the cooled air passes through the M-cycle cooling device which further decreases the temperature without affecting the humidity ratio (i.e., condition 4). Consequently, ambient air (i.e., condition 5) is used for the regeneration of desiccant block. The air is passed through a heat exchanger as a return air which transfers the heat of process air into the regeneration air, slightly raising its temperature without affecting the humidity ratio (i.e., condition 6). The regeneration air passes through a low-grade heating source which further increases the temperature of the regeneration air (i.e., condition 7). This hot and relatively dry regeneration air passes through the desiccant block, which desorbs the adsorbate (water vapors, i.e., condition 8), hence completing the cycle. The regeneration temperature differs according to the type of adsorbent, ambient conditions, and many other factors. A parametric analysis was performed to analyze the parameters affecting the regeneration temperature [3,75,76]. The psychrometric representation of conditions 1–8 are shown in Figure2b.

4. Results and Discussion The desiccant dehumidification performance on an experimental basis was inspected for different processes and regeneration air conditions. Figure3 shows the experimental profile of ambient air conditions of Multan with desiccant dehumidification at a regeneration temperature of 70 ◦C. In Figure3 , the dynamic nature of the process and regeneration temperature of 70 ◦C is shown, indicating that, after 240 min, ambient air entered the desiccant system on RH ~73–88% and departed Energies 2020, xx, x; doi: FOR PEER REVIEW 9 of 23 Energies 2020, xx, x; doi: FOR PEER REVIEW 9 of 23 indicatingEnergies 2020 ,that,13, 5530 after 240 min, ambient air entered the desiccant system on RH ~73–88% and departed9 of 23 indicating that, after 240 min, ambient air entered the desiccant system on RH ~73–88% and departed by RH ~38–59%. Figure 4 shows the impact on the amount of equivalent heat of adsorption at by RH ~38–59%. Figure 4 shows the impact on the amount of equivalent heat of adsorption at different regeneration temperatures. The 𝑞 increases with the increase in regeneration differentby RH ~38–59%. regeneration Figure 4 temperatures.shows the impact The on the𝑞 amount increases of equivalent with the heat increase of adsorption in regeneration at di fferent temperature; however, with respect to the time, it is decreased at both regeneration temperature. The temperature;regeneration temperatures.however, with Therespectq increases to the time, with it is the decreased increase at in both regeneration regeneration temperature; temperature. however, The line on the value of zero equivalenteq heat of adsorption shows the isenthalpic dehumidification. In linewith on respect the value to the of time, zero itequivalent is decreased heat at of both adso regenerationrption shows temperature. the isenthalpic The dehumidification. line on the value In of addition, the impact on adsorption heat with respect to the desiccant performance explored in the addition,zero equivalent the impact heat ofon adsorption adsorption shows heat with the isenthalpic respect to dehumidification. the desiccant performance In addition, explored the impact in the on literature [4]. literatureadsorption [4]. heat with respect to the desiccant performance explored in the literature [4].

80 100 80 Regeneration cycle Dehumidification cycle 100 Regeneration cycle DehumidificationInlet air RH cycle pointInlet (i) airin Fig.1aRH point (i) in Fig.1a 80 60 Inlet air T Outlet air RH 80 60 pointInlet (i) inair Fig.1a T pointOutlet (ii) in air Fig.1a RH point (i) in Fig.1a point (ii) in Fig.1a ) (%)

) 60 ℃ ( 60 (%) ℃ air

( Outlet air T air 40 Outlet air T air

T point (ii) in Fig.1a air

40 RH

T point (ii) in Fig.1a 40 RH 40 Outlet air RH Outlet air RH Outlet air T point (ii) in Fig.1a Outlet air T 20 point (ii) in Fig.1a Inlet air T point (ii) in Fig.1a 20 point (ii) in Fig.1a pointInlet (i) inair Fig.1a T 20 point (i) in Fig.1a 20 Inlet air RH pointInlet (i) airin Fig.1aRH 0 point (i) in Fig.1a 0 0 0 0 60 120 180 240 300 360 0 60 120 180 240 300 360 Time (min) Time (min)

Figure 3. Regeneration and dehumidification cycle profiles of the DAC system at 70 °C regeneration Figure 3. 3. RegenerationRegeneration and dehumidification and dehumidiﬁcation cycle profiles cycle proﬁles of the DAC of thesystem DAC at 70 system °C regeneration at 70 ◦C temperature. temperature.regeneration temperature. 2 2

1 1

Dehumidification cycle

(W) Dehumidification cycle 0 (W)

eq 0 q eq q Isenthalpic dehumidification -1 Isenthalpic dehumidification -1 Treg = 70°C Treg = 70°C Treg = 65°C Treg = 65°C -2 -2 0 15304560 0 15304560 Time (min) Time (min)

FigureFigure 4.4. ImpactImpact on on the the amount amount of equivalent of equivalent heat of adsorptionheat of adsorption at different at regeneration different temperatures.regeneration Figure 4. Impact on the amount of equivalent heat of adsorption at different regeneration temperatures. temperatures.Figure5 shows that the amount of adsorption of water vapor increases with the regeneration temperature.Figure 5 shows As reported that the by amount thermodynamic of adsorption laws, of total water water vapor adsorption increases equals with tothe the regeneration total water Figure 5 shows that the amount of adsorption of water vapor increases with the regeneration temperature.desorption at aAs certain reported regeneration by thermodynamic temperature. laws, The total dehumidification water adsorption cycle equals totothe the regeneration total water temperature. As reported by thermodynamic laws, total water adsorption equals to the total water desorptioncycle at a certain at a regenerationcertain regeneration temperature. temperatur The thermale. The COPdehumidification of the desiccant cycle system equals at di tofferent the desorptionregeneration at temperature a certain regeneration is also compared temperatur for thee. condition The dehumidification of T 37 C, Xcycle 25equals g/kg-DA to the by in ≈ ◦ in ≈ Energies 2020, xx, x; doi: FOR PEER REVIEW 10 of 23 Energies 2020, xx, x; doi: FOR PEER REVIEW 10 of 23 regeneration cycle at a certain regeneration temperature. The thermal COP of the desiccant system at Energies 2020, 13, 5530 10 of 23 regenerationdifferent regeneration cycle at a certain temperature regeneration is also tempercomparedature. for The the thermalcondition COP of T ofin ≈the 37 desiccant °C, Xin ≈ 25g/kg-DAsystem at different regeneration temperature is also compared for the condition of Tin ≈ 37 °C, Xin ≈ 25g/kg-DA by using 𝜀 =0.6 and 𝜀 =0.9. Figure 6a shows the system thermal COP at different regeneration by using 𝜀 =0.6 and 𝜀 =0.9. Figure 6a shows the system thermal COP at different regeneration usingtemperature.εwb = 0.6 Laterand theεHX analysis= 0.9. was Figure made6ashows with wet-bu the systemlb effectiveness thermal COP utilized at di rangesfferent from regeneration 0.6 to 1.3 temperature. Later the analysis was made with wet-bulb effectiveness utilized ranges from 0.6 to 1.3 temperature.to see the effect Later of thechanging analysis the was effectiveness made with of wet-bulb wet bulb eff onectiveness the system’s utilized thermal ranges COP from at 0.6different to 1.3 to see the effect of changing the effectiveness of wet bulb on the system’s thermal COP at different toregeneration see the effect temperatures. of changing Figure the eff ectiveness6b shows the of wetinfluence bulb onof thechanging system’s the thermaleffectiveness COP atof diwetfferent bulb regeneration temperatures. Figure 6b shows the influence of changing the effectiveness of wet bulb regenerationon the thermal temperatures. COP of the desiccant Figure6b showssystem. the influence of changing the e ffectiveness of wet bulb on on the thermal COP of the desiccant system. the thermal COP of the desiccant system. 12 12 Regeneraion cycle Dehumidification cycle Regeneraion cycle Dehumidification cycle

9 9

6 6 Treg = 65°C Treg = 65°C ΔX ΔX (g/kg-DA) Treg = 70°C ΔX ΔX (g/kg-DA) Treg = 70°C 3 3

0 0 0306090120150180 0306090120150180Time (min) Time (min)

FigureFigure 5.5. ImpactImpact of of regeneration temperature on netnet dehumidiﬁcation,dehumidification, forfor regenerationregeneration andand Figuredehumidiﬁcationdehumidification 5. Impact cyclecycleof regeneration ofof thethe DACDAC system.system.temperature on net dehumidification, for regeneration and dehumidification cycle of the DAC system.

1 (a) 1.8 1 (b) Treg = 50°C (a) 1.8 (b) Treg = 50°C 0.8 1.5 Treg = 60°C 0.8 1.5 TregTreg = =60°C 70°C 1.2 TregTreg = =70°C 80°C 0.6 1.2 Treg = 80°C 0.6 0.9 0.4 0.9 0.4 0.6 Thermal COP (-) COP Thermal ThermalCOP (-) 0.6

0.2 (-) COP Thermal ThermalCOP (-) 0.3 0.2 0.3 0 0 0 50 55 60 65 70 75 80 0 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 50 55Regneration 60 65temperature 70 (°C 75 ) 80 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 Wet bulb effectiveness (-) Regneration temperature (°C ) Wet bulb effectiveness (-)

FigureFigure 6.6. ComparisonComparison ofof thermalthermal coecoefficientfficient ofof performanceperformance (COP)(COP) atat ((aa)) wet-bulbwet-bulb eeffectivenessffectiveness = = 0.6;0.6; Figure 6. Comparison of thermal coefficient of performance (COP) at (a) wet-bulb effectiveness = 0.6; andand ((bb)) didifferentfferentwet-bulb wet-bulb e effectivenessffectiveness against against di differentfferent regeneration regeneration temperatures. temperatures. and (b) different wet-bulb effectiveness against different regeneration temperatures. FigureFigure7 7 shows shows the the experimental experimental evaluation evaluation of of the the slope slope of of the the dehumidification dehumidification line line at at di differentfferent regenerationregenerationFigure 7 shows temperatures. temperatures. the experimental In In Figure Figure7 evaluation, the 7, φthe* does ϕ of* notthdoese fluctuateslope not offluctuate the considerably dehumidifi considerably forcation the 3600 linefor s.atthe Therefore,different 3600 s. * regenerationtheTherefore, experimental the temperatures. experimental value of the In valueφ *Figureis utilizedof the 7, ϕthe for* is ϕ simulatingutilized does fornot thesimulating fluctuate desiccant theconsiderably dehumidification desiccant dehumidificationfor the process. 3600 s. Therefore,process. the experimental value of the ϕ* is utilized for simulating the desiccant dehumidification process. Energies 2020, 13, 5530 11 of 23 Energies 2020, xx, x; doi: FOR PEER REVIEW 11 of 23

0.6 Dehumidification cycle Mahmood et al. [68] 𝜙∗ ≈ 0.31 0.5 Treg = 60°C

0.4

(-) 0.3 𝜙∗

0.2

This study 0.1 𝜙∗ ≈ 0.22 Treg = 70°C

0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Time (s)

Figure 7. Experimental evaluation of the slope of the dehumidification line at different Figure 7. Experimental evaluation of the slope of the dehumidification line at different regeneration regeneration temperatures. temperatures. The slope φ* = 0.22 has been utilized to stimulate the performance of standalone silica-gel-based The slope ϕ* = 0.22 has been utilized to stimulate the performance of standalone silica-gel-based DAC and silica-gel-based M-DAC systems. Likewise, hydrophilic polymer sorbent-based standalone DAC and silica-gel-based M-DAC systems. Likewise, hydrophilic polymer sorbent-based standalone DAC and hydrophilic-polymer-based M-DAC desiccant systems performance are also related using DAC and hydrophilic-polymer-based M-DAC desiccant systems performance are also related using φ* = 0.31 [68]. The simulation has been applied on an hourly (13 July), daily, and monthly basis for the ϕ* = 0.31 [68]. The simulation has been applied on an hourly (13 July), daily, and monthly basis for climatic condition of Multan (Pakistan) by 20-year average data occupied from Meteonorm software, the climatic condition of Multan (Pakistan) by 20-year average data occupied from Meteonorm to evaluate the dynamic performance of proposed DAC systems. Figure8 shows the thermodynamic software, to evaluate the dynamic performance of proposed DAC systems. Figure 8 shows the performance of (a) silica-gel-based standalone DAC system and (b) standalone polymer-based DAC thermodynamic performance of (a) silica-gel-based standalone DAC system and (b) standalone system on an hourly, daily, and monthly basis for the climatic conditions of Multan. Figure8a,b show polymer-based DAC system on an hourly, daily, and monthly basis for the climatic conditions of that inlet ambient air temperature varies from 28.3 ◦C (1:00 a.m.) and progressively increases to 37 ◦C Multan. Figure 8a,b show that inlet ambient air temperature varies from 28.3 °C (1:00 a.m.) and (3:00 p.m.) and then decreases to 28 ◦C (12:00 a.m.), at the same time inlet relative humidity, frequently progressively increases to 37 °C (3:00 p.m.) and then decreases to 28 °C (12:00 a.m.), at the same time shifting from 51% to the maximum value of 97% during the whole day. Furthermore, the change inlet relative humidity, frequently shifting from 51% to the maximum value of 97% during the whole in temperature and relative humidity after dehumidification varies from 45 to 48 ◦C, 21% to 29%, day. Furthermore, the change in temperature and relative humidity after dehumidification varies and 43 to 46 ◦C, for silica-gel-based and polymer-based DAC system, respectively. The daily inlet from 45 to 48 °C, 21% to 29%, and 43 to 46 °C, for silica-gel-based and polymer-based DAC system, ambient temperature and relative humidity vary from 27 to 38 ◦C and from 56% to 93%, respectively, respectively. The daily inlet ambient temperature and relative humidity vary from 27 to 38 °C and throughout the month. The change in relative humidity and temperature after dehumidification ranges from 56% to 93%, respectively, throughout the month. The change in relative humidity and from 19% to 35%, 45 to 48 ◦C, and 43 to 45.5 ◦C, in both silica-gel-based and polymer-based DAC temperature after dehumidification ranges from 19% to 35%, 45 to 48 °C, and 43 to 45.5 °C, in both systems, respectively. Likewise, monthly temperature and relative humidity variation are displayed silica-gel-based and polymer-based DAC systems, respectively. Likewise, monthly temperature and for both silica- and polymer-based DAC systems. relative humidity variation are displayed for both silica- and polymer-based DAC systems. Energies 2020, 13, 5530 12 of 23

Energies 2020, xx, x; doi: FOR PEER REVIEW 12 of 23

Silica-gel based DAC system (This study) Polymer based DAC system [68]

T_in T_out RH_in RH_out

(a)50 100 (b)50 100

40 83 40 83

30 66 30 66 Hourly based 20 49 20 49 RH (%) RH (%) 10 32 10 32 Temperature (°C) Temperature Temperature (°C) Temperature 0 15 0 15 1:00 5:00 9:00 13:0017:0021:00 1:00 5:00 9:00 13:0017:0021:00 Hours Hours 50 100 50 100

40 83 40 83

30 66 30 66 Daily based 20 49 20 49 RH (%) RH (%) 10 32 10 32 Temperature (°C) Temperature Temperature (°C) Temperature 0 15 0 15 1 4 7 1013161922252831 1 4 7 1013161922252831 Days Days 50 75 50 75

40 60 40 60

30 45 30 45 Monthly based 20 30 20 30 RH (%) RH (%) 10 15

Temperature (°C) Temperature 10 15 Temperature (°C) Temperature

0 0 0 0

FigureFigure 8.8. Thermodynamic performance performance of of (a )(a silica-based) silica-based standalone standalone DAC DAC system, system,and (andb) polymer-based (b) polymer- DACbased system DAC system on an hourly, on an daily,hourly, and daily, monthly and basis monthly for the basis climatic for the condition climatic of Multancondition (Pakistan). of Multan (Pakistan). Figure9 shows the thermodynamic performance of (a) silica-gel-based DAC system coupled withFigure M-cycle 9 coolingshows the system, thermodynamic and (b) polymer-based performance DACof (a) systemsilica-gel-based coupled withDAC M-cyclesystem coupled cooling systemwith M-cycle on an hourly,cooling daily,system, and and monthly (b) polymer-ba basis, forsed the DAC climatic system conditions coupled of with Multan. M-cycle In Figure cooling9, hourlysystem temperatureon an hourly, ranging daily, and from monthly 22 to 28 basis,◦C, at for a relative the climatic humidity conditions of 80–88% of Multan. for silica-gel-based In Figure 9, M-DAChourly temperature system, and ranging temperature from 22 ranging to 28 °C, from at a 22relative and 27 humidity◦C, at a of relative 80–88% humidity for silica-gel-based of 69–84% forM- polymer-basedDAC system, and M-DAC temperature system. ranging Figure9 fromshows 22 daily and temperature27 °C, at a relative ranging humidity from 21 toof 3169–84%◦C, at for a relativepolymer-based humidity M-DAC of 76–93% system. for silica-gel-basedFigure 9 shows M-DACdaily temperature system, and ranging temperature from 21 ranging to 31 from°C, at 21 a torelative 30 ◦C, humidity at a relative of 76–93% humidity for ofsilica-gel-based 71–90% for polymer-based M-DAC system, M-DAC and temperature system. Similarly, ranging proﬁlesfrom 21 ofto 30 °C, at a relative humidity of 71–90% for polymer-based M-DAC system. Similarly, profiles of monthly temperature and relative humidity for silica-gel-based and polymer-based M-DAC systems are also shown in Figure 9. These results display that polymer-based M-DAC system provides more Energies 2020, 13, 5530 13 of 23 monthly temperature and relative humidity for silica-gel-based and polymer-based M-DAC systems are also shown in Figure9. These results display that polymer-based M-DAC system provides more cooling and less relative humidity as compared to silica-based M-DAC system, which is better than the standalone DAC system for the climatic conditions of Multan, Pakistan, especially for July (i.e., heavy rainfall season, resulting in suﬀocation) [77,78].

Figure 9. Thermodynamic performance of (a) silica-based DAC system with M-cycle unit, and (b) polymer-based DAC system with M-cycle unit on hourly, daily, and monthly basis for the climatic condition of Multan (Pakistan). Energies 2020, 13, 5530 14 of 23

Figure 10 shows the temperature and relative humidity proﬁle of average year data for the climatic condition of Multan (Pakistan). Figure 11 shows the monthly performance of the investigated systems (i.e., standalone silica-gel-based, standalone polymer-based, M-cycle-based silica-gel-based, and M-cycle-based polymer-based DAC systems) on psychrometric chart plots. Energies 2020, xx, x; doi: FOR PEER REVIEW 14 of 23

Figure 10. Temperature and relative humidity profile of test reference year for the climatic condition Figure 10. Temperature and relative humidity proﬁle of test reference year for the climatic condition of of Multan (Pakistan). Multan (Pakistan).

FigureFigure 12 12aa shows shows the the monthly monthly profileprofile ofof thethe dehumidificationdehumidification capacity capacity of of silica-gel-based silica-gel-based and and polymer-based DAC system at 70 °C regeneration temperature for the climatic conditions of Multan polymer-based DAC system at 70 ◦C regeneration temperature for the climatic conditions of Multan (Pakistan). Moreover, the monthly profile of the dehumidification capacity of the polymer-based and (Pakistan). Moreover, the monthly profile of the dehumidification capacity of the polymer-based silica-gel-based DAC systems at different regeneration temperatures are shown in Appendix A and silica-gel-based DAC systems at different regeneration temperatures are shown in AppendixA Figure A1. Results from Appendix A Figure A1 conclude that the desiccant dehumidification capacity Figure A1. Results from AppendixA Figure A1 conclude that the desiccant dehumidification capacity increases with the increase in regeneration temperature. Figure 12b shows the monthly profile of the increasescooling withcapacity the increaseof silica-gel-based in regeneration and polyme temperature.r-based M-DAC Figure systems12b shows at a the 70 monthly°C regeneration profile of thetemperature cooling capacity for the of climatic silica-gel-based conditions and of Multan polymer-based (Pakistan). M-DAC In Figure systems 12b, the at cooling a 70 ◦C capacity regeneration of temperaturethe polymer-based for the climaticM-DAC system conditions is higher of Multan than the (Pakistan). silica-gel-based In Figure M-DAC 12b, system. the cooling Moreover, capacity the of themonthly polymer-based profile of M-DAC the cooling system capacity is higher of sili thanca-gel-based the silica-gel-based and polymer-based M-DAC system. M-DAC Moreover, systems at the monthlydifferent profile regeneration of the coolingtemperatures capacity is shown of silica-gel-based in Appendix A and Figure polymer-based A2. M-DAC systems at differentFigure regeneration 12c shows temperatures the monthly is profile shown of in heat Appendix input requiredA Figure for A2 the. regeneration of silica-gel- andFigure polymer-based 12c shows DAC the monthly system profileat 70 °C of regenera heat inputtion required temperature. for the According regeneration to Figure of silica-gel-and 12c, the polymer-basedpolymer-based DAC DAC system system at 70 requires◦C regeneration more heat temperature. input for its According regeneration to Figure throughout 12c, the polymer-basedthe year, as DACcompared system to requires the silica-gel-based more heat input DAC forsystem its regeneration at 70 °C regeneration throughout temperature. the year, asAdditionally, compared tothe the silica-gel-basedmonthly profiles DAC of system the heat at 70input◦C regenerationrequired at di temperature.fferent regeneration Additionally, temperatures the monthly are given profiles in of theAppendix heat input A Figure required A3. at Figure different 12d shows regeneration the mont temperatureshly profile of arethermal given CO inP Appendixof polymer-basedA Figure and A3 . Figuresilica-gel-based 12d shows thestandalone monthly DAC profile and of M-DAC thermal system COP ofs. polymer-basedAccording to Figure and silica-gel-based 12d, the polymer-based standalone DACstandalone and M-DAC DAC and systems. M-DAC According system possess to Figure higher 12 thermald, the polymer-basedCOP (i.e., 0.24, 0.47 standalone in May) at DAC 70 °C and regeneration temperature, as compared to the silica-gel-based M-DAC system (i.e., 0.21, 0.36 in May) M-DAC system possess higher thermal COP (i.e., 0.24, 0.47 in May) at 70 ◦C regeneration temperature, respectively. Additionally, the monthly profiles of thermal COP of silica-gel-based and polymer- as compared to the silica-gel-based M-DAC system (i.e., 0.21, 0.36 in May) respectively. Additionally, based M-DAC systems at different regeneration temperatures are given in Appendix A Figure A4. the monthly profiles of thermal COP of silica-gel-based and polymer-based M-DAC systems at different regeneration temperatures are given in AppendixA Figure A4. Energies 2020, 13, 5530 15 of 23 Energies 2020, xx, x; doi: FOR PEER REVIEW 15 of 23

Figure 11. Psychrometric representation of monthly profile for (a) standalone silica-gel-based DAC system, (b) standalone polymer-based DAC system, (c) silica- Figure 11. Psychrometric representation of monthly proﬁle for (a) standalone silica-gel-based DAC system, (b) standalone polymer-based DAC system, gel-based M-DAC system, and (d) polymer-based M-DAC system. (c) silica-gel-based M-DAC system, and (d) polymer-based M-DAC system. Energies 2020, 13, 5530 16 of 23

Energies 2020, xx, x; doi: FOR PEER REVIEW 16 of 23

Figure 12. Monthly profile of (a) dehumidification capacity, (b) cooling capacity, (c) heat input, and Figure 12. Monthly proﬁle of (a) dehumidiﬁcation capacity, (b) cooling capacity, (c) heat input, (d) thermal COP for proposed AC systems. and (d) thermal COP for proposed AC systems.

5. Conclusions5. Conclusions In the present study, a lab-scale open cycle silica-gel-based experimental apparatus was set up In the present study, a lab-scale open cycle silica-gel-based experimental apparatus was set for desiccant air-conditioning (DAC). The experiments were performed at the various process and upregeneration for desiccant air air-conditioning conditions for the (DAC).climatic Thecondition experiments of Multan were (Pakistan). performed Consequently, at the various a steady- process andstate regeneration analysis approach air conditions was used for for the the desiccant climatic dehumidification condition of Multanprocess of (Pakistan). the system. Thereby, Consequently, a steady-statethe slope of analysisthe dehumidification approach was line usedon the for psyc thehrometric desiccant chart dehumidification was examined for process identifying of the the system. Thereby,actual thedesiccant slope ofdehumidification the dehumidification process linebased on on the experimental psychrometric data chart which was are examined found, ϕ for* = identifying0.22. theThis actual value desiccant is lower dehumidification than the slope of the process hydrophilic based onpolymeric experimental sorbent, data ϕ* = which 0.31, available are found, in theφ* = 0.22. Thisliterature. value is This lower study than proposed the slope two of kinds the hydrophilicof AC systems polymeric that include sorbent, the standaloneφ* = 0.31, DAC available system in the literature.and Maisotsenko-cycle-based This study proposed DAC two (M-DAC) kinds of system. AC systems In addition, that two include kinds the of adsorbent standalone (i.e., DAC silica system gel and hydrophilic polymeric sorbent) were thermodynamically investigated for both system types, and Maisotsenko-cycle-based DAC (M-DAC) system. In addition, two kinds of adsorbent (i.e., silica using experimental data and associated results. The study aimed to explore the optimum AC system, gel and hydrophilic polymeric sorbent) were thermodynamically investigated for both system types, as well as optimum adsorbent (desiccant) material for building AC application. The performance of usingproposed experimental AC systems data and and adsorbent associated materials results. were The in studyvestigated aimed in perspectives to explore theof dehumidification optimum AC system, as wellcapacity, as optimum cooling capacity, adsorbent and (desiccant) thermal COP. material The results for building showed ACthat application. the hydrophilic-polymeric- The performance of proposedbased sorbent AC systems has a better and adsorbent performance, materials as compared were to investigated silica gel. The in dehumi perspectivesdification of dehumidificationcapacity of capacity,hydrophilic cooling polymeric capacity, sorbent and thermal (i.e., desiccant COP. The material) results showed is greater that than the hydrophilic-polymeric-basedthe silica gel at 70 °C sorbentregeneration has a better temperature. performance, In the as case compared of propos to silicaed AC gel. systems, The dehumidification the results show capacitythat the M-DAC of hydrophilic system has a better performance, as compared to the standalone DAC system. Accordingly, the polymeric sorbent (i.e., desiccant material) is greater than the silica gel at 70 ◦C regeneration temperature. In the case of proposed AC systems, the results show that the M-DAC system has a better performance, as compared to the standalone DAC system. Accordingly, the maximum thermal COP was obtained by a standalone DAC system (i.e., 0.36) and M-DAC system (i.e., 0.47) at a 70 ◦C regeneration temperature. Energies 2020, 13, 5530 17 of 23

Author Contributions: Conceptualization, M.A., G.H., and M.S.; data curation, M.A. and G.H.; formal analysis, M.A., G.H., M.S., M.H.M., and F.S.; funding acquisition, M.S. and T.M.; investigation, M.A., G.H., T.M., M.H.M., M.I.S., A.N., and F.S.; methodology, M.A., G.H., T.M., and M.H.M.; project administration, M.S.; resources, M.S.; software, M.A., G.H., M.H.M., and F.S.; supervision, M.S.; validation, M.S. and T.M.; visualization, T.M. and Z.M.K.; writing—original draft, M.A. and G.H.; writing—review and editing, M.S., T.M., M.I.S., A.N., and Z.M.K. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: This work is part of the Ph.D. research of Ghulam Hussain (second author). This research work was carried out in the Department of Agricultural Engineering, Bahauddin Zakariya University, Multan, Pakistan. This research was funded by Bahauddin Zakariya University, Multan, Pakistan, under the Director Research/ORIC grant entitled “Thermodynamic Evaluation of Low-Cost Air-Conditioning Systems for Various Applications”, awarded to Principal Investigator Muhammad Sultan. Conﬂicts of Interest: The authors declare no conﬂict of interest.

Nomenclature

ACS air-conditioning systems AC air-conditioning COP coefficient of performance Cp specific heat capacity of air (kJ/kg-K) DAC desiccant air-conditioning DEC direct evaporative cooling EC evaporative cooling GW global warming h enthalpy of air (kJ/kg) HCFCS hydrochlorofluorocarbons HFCS hydrofluorocarbons HVAC heating, ventilation, and air-conditioning HX heat exchanger IEC indirect evaporative cooling MEC Maisotsenko cycle evaporative cooling MAC Maisotsenko cycle-based air-conditioning M-DAC Maisotsenko cycle based desiccant air-conditioning M-IEC Maisotsenko cycle-based indirect evaporative cooling N1 Nn independent variables in measuring uncertainty − OD ozone depletion Qc cooling capacity (kJ/kg) qeq equivalent heat of adsorption (W) Qinp heat required for regeneration of desiccant (kW) Qst isosteric heat of water vapor adsorption (kJ/kg) RH relative humidity (%) T temperature (◦C) VCAC vapor compression air-conditioning X humidity ratio (g/kg-DA) ∆X difference in humidity ratio (in–out) (g/kg-DA) φh slope of enthalpy line (-) φ∗ slope of dehumidification line (-) ε effectiveness (-) σ uncertainties (-) . m mass flow rate of air (kg/s) σR total uncertainty in adsorption uptake α α uncertainty in measuring different variables 1 − N σt total uncertainty (%) Energies 2020,, xx,, x;x; doi:doi: FORFOR PEERPEER REVIEWREVIEW 18 18 of of 23 23

𝛼 −𝛼 uncertainty in measuring different variables 𝜎 total uncertainty (%) Energies 2020, 13, 5530 18 of 23 Subscripts

Subscriptscalibr calibration calibrdaq data calibration acquisition system daqdb dry data bulb acquisition system dbin inlet dry condition bulb inout outlet inlet condition condition outPA process outlet air condition PARA regeneration process air air RAreg regeneration regeneration air regsen sensor regeneration sen sensor wb wet bulb wb wet bulb Appendix A Appendix A

Silica-gel based M-DAC system (This study) Polymer-based M-DAC system [68]

Treg = 50°C Treg = 55°C Treg = 60°C Treg = 65°C Treg = 50°C Treg = 55°C Treg = 60°C Treg = 65°C

Treg = 70°C Treg = 75°C Treg = 80°C Treg = 70°C Treg = 75°C Treg = 80°C 18 18 (a) (b) 15 15

12 12

9 9

6 6 Dehumidification (g/kg-DA) Dehumidification Dehumidification (g/kg-DA) Dehumidification Dehumidification (g/kg-DA) Dehumidification 3 (g/kg-DA) Dehumidification 3

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

FigureFigure A1. A1.Dehumidiﬁcation Dehumidification capacity capacity of of ( a(a)) silica-gel-based silica-gel-based DAC DAC system system and and ( b(b)) polymer-based polymer-based DAC DAC systemsystem at at di differentﬀerent regeneration regeneration temperatures. temperatures.

Silica-gel based M-DAC system (This study) Polymer-based M-DAC system [68]

Treg = 50°C Treg = 55°C Treg = 60°C Treg = 65°C Treg = 50°C Treg = 55°C Treg = 60°C Treg = 65°C Treg = 70°C Treg = 75°C Treg = 80°C Treg = 70°C Treg = 75°C Treg = 80°C

32 32 (a) (b) 28 28

24 24

20 20 (kJ/kg) (kJ/kg) (kJ/kg) (kJ/kg) c c c 16 c Q Q Q Q 16

12 12

8 8

4 4

0 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

FigureFigure A2. A2.The The cooling cooling capacity capacity of of ( a(a)) silica-gel-based silica-gel-based M-DAC M-DAC system system and and ( b(b)) polymer-based polymer-based M-DAC M-DAC systemsystem at at di differentﬀerent regeneration regeneration temperatures. temperatures. Energies 2020, 13, 5530 19 of 23 EnergiesEnergies 20202020,, xxxx, , x;x; doi:doi: FORFOR PEERPEER REVIEWREVIEW 19 19 of of 23 23

Silica-gelSilica-gel based based M-DACM-DAC systemsystem (This(This study)study) Polymer-basedPolymer-based M-DACM-DAC systemsystem [68][68]

TregTreg = = 50°C50°C TregTreg = = 55°C55°C TregTreg = = 60°C60°C TregTreg = = 65°C65°C TregTreg = = 50°C50°C TregTreg = = 55°C55°C TregTreg == 60°C60°C TregTreg = = 65°C65°C TregTreg = = 70°C70°C TregTreg = = 75°C75°C TregTreg = = 80°C80°C TregTreg = = 70°C70°C TregTreg = = 75°C75°C TregTreg == 80°C80°C

1212 1212 (a)(a) (b) (b) 1010 1010

88 88

66 66

Heatinput(kW) 4 Heat input (kW) input Heat 4 Heatinput(kW) 4

Heat input (kW) input Heat 4

22 22

00 00 JanJan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec JanJan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

FigureFigure A3.A3. HeatHeat input input required required for for ( (aa)) silica-gel-basedsilica-gel-based DAC DAC system system and and ((bb)) polymer-basedpolymer-basedpolymer-based DACDAC systemsystem atat didifferentdifferentﬀerent regenerationregenerationregeneration temperatures. temperatures.temperatures.

Silica-gelSilica-gel based based M-DACM-DAC systemsystem (This(This study)study) Polymer-basedPolymer-based M-DACM-DAC systemsystem [68][68]

TregTreg = = 50°C50°C TregTreg = = 55°C55°C TregTreg = = 60°C60°C TregTreg = = 65°C65°C TregTreg = = 50°C50°C TregTreg = = 55°C55°C TregTreg = = 60°C60°C TregTreg = = 65°C65°C

TregTreg = = 70°C70°C TregTreg = = 75°C75°C TregTreg = = 80°C80°C TregTreg = = 70°C70°C TregTreg = = 75°C75°C TregTreg = = 80°C80°C 0.80.8 0.80.8 (a)(a) (b)(b) 0.70.7 0.70.7 0.60.6 0.60.6 0.50.5 0.50.5 0.40.4 0.40.4 0.30.3 0.30.3 Thermal(-) COP Thermal(-) COP Thermal(-) COP Thermal(-) COP 0.20.2 0.20.2 0.10.1 0.10.1 00 00 JanJan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec JanJan Feb Feb Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec

FigureFigure A4. A4. A4. Thermal ThermalThermal coefficient coefficient coeﬃcient of of performance performance of performance of of ( (aa)) silica-gel-based silica-gel-based of (a) silica-gel-based M-DAC M-DAC system system M-DAC and and ( system(bb)) polymerpolymer- and (basedbasedb) polymer-based M-DACM-DAC systemsystem M-DAC atat differentdifferent system regenerationregeneration at diﬀerent regeneration temperatures.temperatures. temperatures.

ReferencesReferences

1.1. Sultan:Sultan,Sultan: M.; M.; Miyazaki, Miyazaki, T. T. Energy-Efficient Energy-EEnergy-Efficientfficient Air-Conditioning Air-Conditioning Systems SystemsSystems forfor Nonhuman Nonhuman Applications. Applications. RefrigerationRefrigeration 20172017.[,, doi:10.5772/intechopen.68865.doi:10.5772/intechopen.68865.CrossRef] 2.2. Sultan,Sultan, M.T.;M.T.; Miyazaki,Miyazaki, T.;T.; Saha,Saha, B.B.;B.B.; Koyama,Koyama, S.S. Steady-stateSteaSteady-statedy-state investigationinvestigation ofof waterwater vaporvapor adsorptionadsorption forfor thermallythermally driven driven adsorption adsorption based based greenhouse greenhouse air-conditioning air-conditioning system. system.system. Renew.Renew. EnergyEnergy 20162016,, 8686,, 785–795, 785–795.785–795, doi:10.1016/j.renene.2015.09.015.[doi:10.1016/j.renene.2015.09.015.CrossRef] 3.3. Sultan,Sultan, M.; M.; El-Sharkawy, El-Sharkawy, I.I.; I.I.; Miy Miyazaki,Miyazaki,azaki, T.; T.; Saha, Saha, B.B.; B.B.; Koyama, Koyama, S. S. An An overview overview of of solidsolid desiccantdesiccant dehumidificationdehumidificationdehumidification andandand air air conditioningair conditioningconditioning systems. systems.systems.Renew. Renew.Renew. Sustain. Sustain. EnergySustain. Rev. EnergyEnergy2015 , 46Rev.Rev., 16–29. 20152015 [,CrossRef, 4646,, 16–29,16–29,] 4. doi:10.1016/j.rser.2015.02.038.Sultan,doi:10.1016/j.rser.2015.02.038. M.; Miyazaki, T.; Koyama, S.; Khan, Z.M. Performance evaluation of hydrophilic organic polymer 4.4. Sultan,sorbentsSultan, M.;M.; for Miyazaki,Miyazaki, desiccant T.; air-conditioningT.; KoKoyama,yama, S.;S.; Khan,Khan, applications. Z.M.Z.M. PerformancePerformanceAdsorpt. Sci. evaluaevalua Technol.tiontion2017 ofof hydrophilichydrophilic, 36, 311–326. organicorganic [CrossRef polymerpolymer] 5. sorbentsSultan,sorbents M.; forfor I El-Sharkaw, desiccantdesiccant I.;air-air- Miyazaki,conditioningconditioning T.; Saha, applications.applications. B.B.; Koyama, Adsorpt.Adsorpt. S. Experimental Sci.Sci. Technol.Technol. Study 20172017 on,, Carbon3636,, 311–326,311–326, Based Adsorbentsdoi:10.1177/0263617417692338.doi:10.1177/0263617417692338. for Greenhouse Dehumidification. Evergreen 2014, 1, 5–11. [CrossRef] 5.6.5. Sultan,Mahmood,Sultan, M.;M.; M.H.;II El-Sharkaw,El-Sharkaw, Sultan, M.; I.;I.; MiyazakMiyazak Miyazaki,i,i, T.; T.; Saha, Koyama,Saha, B.B.;B.B.; S. Koyama,Koyama, Desiccant S.S. Air-Conditioning ExpeExperimentalrimental StudyStudy System onon Carbon forCarbon Storage BasedBased of AdsorbentsFruitsAdsorbents and Vegetables: forfor GreenhouseGreenhouse Pakistan Dehumidification.Dehumidification. Preview. Evergreen EvergreenEvergreen2016, 3 20142014, 12–17.,, 11,, 5–11,5–11, [CrossRef doi:10.5109/1495157.doi:10.5109/1495157.] 6.6. Mahmood,Mahmood, M.H.;M.H.; Sultan,Sultan, M.;M.; Miyazaki,Miyazaki, T.;T.; Koyama,Koyama, S.S. DesiccantDesiccant Air-Air-ConditioningConditioning SystemSystem forfor StorageStorage ofof FruitsFruits andand Vegetables:Vegetables: PakistanPakistan Preview.Preview. EvergreenEvergreen 20162016,, 33,, 12–17,12–17, doi:10.5109/1657381.doi:10.5109/1657381. 7.7. Mahmood,Mahmood, M.H.;M.H.; Sultan,Sultan, M.;M.; Miyazaki,Miyazaki, T.;T.; Koyama,Koyama, S.;S.; Maisotsenko,Maisotsenko, V.S.V.S. OverviewOverview ofof thethe MaisotsenkoMaisotsenko cycle—Acycle—A wayway towardstowards dewdew pointpoint evaporativeevaporative cooling.cooling. Renew.Renew. Sustain.Sustain. EnergyEnergy Rev.Rev. 20162016,, 6666,, 537–555,537–555, doi:10.1016/j.rser.2016.08.022.doi:10.1016/j.rser.2016.08.022. Energies 2020, 13, 5530 20 of 23

7. Mahmood, M.H.; Sultan, M.; Miyazaki, T.; Koyama, S.; Maisotsenko, V.S. Overview of the Maisotsenko cycle—A way towards dew point evaporative cooling. Renew. Sustain. Energy Rev. 2016, 66, 537–555. [CrossRef] 8. Cheng, F.; Li, Y.; Zhang, X.; Li, X. Effect of different absorbents on actual performance of the absorption air-conditioning system based on capacitive deionization regeneration method. Appl. Therm. Eng. 2020, 172, 115130. [CrossRef] 9. Caliskan, H.; Dincer, I.; Hepbasli, A. Exergetic and sustainability performance comparison of novel and conventional air cooling systems for building applications. Energy Build. 2011, 43, 1461–1472. [CrossRef] 10. Zhan, C.; Duan, Z.; Zhao, X.; Smith, S.; Jin, H.; Riffat, S. Comparative study of the performance of the M-cycle counter-flow and cross-flow heat exchangers for indirect evaporative cooling—Paving the path toward sustainable cooling of buildings. Energy 2011, 36, 6790–6805. [CrossRef] 11. Pérez-Lombard, L.; Ortiz, J.; Pout, C. A review on buildings energy consumption information. Energy Build. 2008, 40, 394–398. [CrossRef] 12. Xuan, Y.; Xiao, F.; Niu, X.; Huang, X.; Wang, S. Research and application of evaporative cooling in China: A review (I)—Research. Renew. Sustain. Energy Rev. 2012, 16, 3535–3546. [CrossRef] 13. Kashif, M.; Sultan, M.; Khan, Z.M. Alternative Air-Conditioning Options for Developing Countries. Eur. J. Eng. Res. Sci. 2017, 2, 76–79. [CrossRef] 14. Matsui, K.; Thu, K.; Miyazaki, T. A hybrid power cycle using an inverted Brayton cycle with an indirect evaporative device for waste-heat recovery. Appl. Therm. Eng. 2020, 170, 115029. [CrossRef] 15. Duan, Z.; Zhan, C.; Zhang, X.; Mustafa, M.; Zhao, X.; Alimohammadisagvand, B.; Hasan, A. Indirect evaporative cooling: Past, present and future potentials. Renew. Sustain. Energy Rev. 2012, 16, 6823–6850. [CrossRef] 16. Sultan, M.; Niaz, H.; Miyazaki, T. Investigation of Desiccant and Evaporative Cooling Systems for Animal Air-Conditioning. Low Temp. Technol. 2020.[CrossRef] 17. Maheshwari, G.; Al-Ragom, F.; Suri, R. Energy-saving potential of an indirect evaporative cooler. Appl. Energy 2001, 69, 69–76. [CrossRef] 18. Pandelidis, D.; Anisimov, S. Numerical analysis of the heat and mass transfer processes in selected M-Cycle heat exchangers for the dew point evaporative cooling. Energy Convers. Manag. 2015, 90, 62–83. [CrossRef] 19. Enteria, N.; Mizutani, K. The role of the thermally activated desiccant cooling technologies in the issue of energy and environment. Renew. Sustain. Energy Rev. 2011, 15, 2095–2122. [CrossRef] 20. Pandelidis, D.; Anisimov, S.; Worek, W.M. Comparison study of the counter-flow regenerative evaporative heat exchangers with numerical methods. Appl. Therm. Eng. 2015, 84, 211–224. [CrossRef] 21. Lin, J.; Wang, R.; Li, C.; Wang, S.; Long, J.; Chua, K.J. Towards a thermodynamically favorable dew point evaporative cooler via optimization. Energy Convers. Manag. 2020, 203, 112224. [CrossRef] 22. Arun, B.; Mariappan, V.; Maisotsenko, V.S. Experimental study on combined low temperature regeneration of liquid desiccant and evaporative cooling by ultrasonic atomization. Int. J. Refrig. 2020, 112, 100–109. [CrossRef] 23. Anisimov, S.; Pandelidis, D.; Jedlikowski, A.; Polushkin, V. Performance investigation of a M (Maisotsenko)-cycle cross-flow heat exchanger used for indirect evaporative cooling. Energy 2014, 76, 593–606. [CrossRef] 24. Delgado, J.M.P.Q.; de Lima, A.G.B.; da Silva, M.V. Numerical Analysis of Heat and Mass Transfer in Porous Media; Springer: Berlin/Heidelberg, Germany, 2012. [CrossRef] 25. Khalatov, A.; Karp, I.; Isakov, B. Prospects of the maisotsenko thermodynamic cycle application in ukraine. Int. J. Energy Clean Environ. 2011, 12, 141–157. [CrossRef] 26. Anisimov, S.; Pandelidis, D. Heat- and mass-transfer procesess in indirect evaporative air conditioners through the maisotsenko cycle. Int. J. Energy Clean Environ. 2011, 12, 273–286. [CrossRef] 27. Tertipis, D.; Rogdakis, E. Maisotsenko cycle: Technology overview and energy-saving potential in cooling systems. Energy Emiss. Control. Technol. 2015, 2015, 15. [CrossRef] 28. Anisimov, S.; Pandelidis, D.; Danielewicz, J. Numerical analysis of selected evaporative exchangers with the Maisotsenko cycle. Energy Convers. Manag. 2014, 88, 426–441. [CrossRef] 29. Chua, K.; Chou, S.; Yang, W.; Yan, J. Achieving better energy-efficient air conditioning—A review of technologies and strategies. Appl. Energy 2013, 104, 87–104. [CrossRef] Energies 2020, 13, 5530 21 of 23

30. Anisimov, S.; Pandelidis, D. Numerical study of perforated indirect evaporative air cooler. Int. J. Energy Clean Environ. 2011, 12, 239–250. [CrossRef] 31. Kojok, F.; Fardoun, F.; Younes, R.; Outbib, R. Hybrid cooling systems: A review and an optimized selection scheme. Renew. Sustain. Energy Rev. 2016, 65, 57–80. [CrossRef] 32. Noor, S.; Ashraf, H.; Sultan, M.; Khan, Z.M. Evaporative cooling options for building air-conditioning: A comprehensive study for climatic conditions of Multan (Pakistan). Energies 2020, 13, 3061. [CrossRef] 33. Duan, Z.; Zhao, X.; Zhan, C.; Dong, X.; Chen, H. Energy saving potential of a counter-flow regenerative evaporative cooler for various climates of China: Experiment-based evaluation. Energy Build. 2017, 148, 199–210. [CrossRef] 34. Liu, Y.; Yang, X.; Li, J.; Zhao, X. Energy savings of hybrid dew-point evaporative cooler and micro-channel separated heat pipe cooling systems for computer data centers. Energy 2018, 163, 629–640. [CrossRef] 35. Farmahini-Farahani, M.; Delfani, S.; Esmaeelian, J. Exergy analysis of evaporative cooling to select the optimum system in diverse climates. Energy 2012, 40, 250–257. [CrossRef] 36. Lin, J.; Bui, D.T.; Wang, R.; Chua, K. On the exergy analysis of the counter-flow dew point evaporative cooler. Energy 2018, 165, 958–971. [CrossRef] 37. Alklaibi, A. Experimental and theoretical investigation of internal two-stage evaporative cooler. Energy Convers. Manag. 2015, 95, 140–148. [CrossRef] 38. Fikri, B.; Sofia, E.; Putra, N. Experimental analysis of a multistage direct-indirect evaporative cooler using a straight heat pipe. Appl. Therm. Eng. 2020, 171, 115133. [CrossRef] 39. Khalajzadeh, V.; Farmahini-Farahani, M.; Heidarinejad, G. A novel integrated system of ground heat exchanger and indirect evaporative cooler. Energy Build. 2012, 49, 604–610. [CrossRef] 40. Chauhan, S.S.; Rajput, S. Experimental analysis of an evaporative–vapour compression based combined air conditioning system for required comfort conditions. Appl. Therm. Eng. 2017, 115, 326–336. [CrossRef] 41. Duan, Z.; Zhao, X.; Liu, J.; Zhang, Q. Dynamic simulation of a hybrid dew point evaporative cooler and vapour compression refrigerated system for a building using EnergyPlus. J. Build. Eng. 2019, 21, 287–301. [CrossRef] 42. Zhou, S.; Gong, L.; Liu, X.; Shen, S. Mathematical modeling and performance analysis for multi-effect evaporation/multi-effect evaporation with thermal vapor compression desalination system. Appl. Therm. Eng. 2019, 159, 113759. [CrossRef] 43. Fekadu, G.; Subudhi, S. Renewable energy for liquid desiccants air conditioning system: A review. Renew. Sustain. Energy Rev. 2018, 93, 364–379. [CrossRef] 44. Qi, R.; Dong, C.; Zhang, L.-Z. A review of liquid desiccant air dehumidification: From system to material manipulations. Energy Build. 2020, 215, 109897. [CrossRef] 45. Sultan, M.; Miyazaki, T.; Koyama, S. Optimization of adsorption isotherm types for desiccant air-conditioning applications. Renew. Energy 2018, 121, 441–450. [CrossRef] 46. Mahmood, M.H.; Sultan, M.; Miyazaki, T. Experimental evaluation of desiccant dehumidification and air-conditioning system for energy-efficient storage of dried fruits. Build. Serv. Eng. Res. Technol. 2019, 41, 454–465. [CrossRef] 47. Sultan, M.; Miyazaki, T.; Mahmood, M.H.; Khan, Z.M. Solar assisted evaporative cooling based passive air-conditioning system for agricultural and livestock applications. J. Eng. Sci. Technol. 2018, 13, 693–703. 48. Niaz, H.; Sultan, M.; Khan, A.A.; Miyazaki, T.; Feng, Y.; Khan, Z.M. Study on evaporative cooling assisted desiccant air conditioning system for livestock application in Pakistan. Fresenius Environ. Bull. 2019, 28, 8623–8633. 49. Kashif, M.; Niaz, H.; Sultan, M.; Miyazaki, T.; Feng, Y.; Usman, M.; Shahzad, M.W.; Niaz, Y.; Waqas, M.M.; Ali, I. Study on Desiccant and Evaporative Cooling Systems for Livestock Thermal Comfort: Theory and Experiments. Energies 2020, 13, 2675. [CrossRef] 50. Nagaya, K.; Senbongi, T.; Li, Y.; Zheng, J.; Murakami, I. High energy efficiency desiccant assisted automobile air-conditioner and its temperature and humidity control system. Appl. Therm. Eng. 2006, 26, 1545–1551. [CrossRef] 51. Lee, S.H.; Lee, W.L. Site verification and modeling of desiccant-based system as an alternative to conventional air-conditioning systems for wet markets. Energy 2013, 55, 1076–1083. [CrossRef] 52. Ismail, M.; Angus, D.; Thorpe, G. The performance of a solar-regenerated open-cycle desiccant bed grain cooling system. Sol. Energy 1991, 46, 63–70. [CrossRef] Energies 2020, 13, 5530 22 of 23

53. Guojie, Z.; Chaoyu, Z.; Guanghai, Y.; Chen, W. Development of a New Marine Rotary Desiccant Airconditioning System and its Energy Consumption Analysis. Energy Procedia 2012, 16, 1095–1101. [CrossRef] 54. Zhu, J.; Chen, W. Energy and exergy performance analysis of a marine rotary desiccant air-conditioning system based on orthogonal experiment. Energy 2014, 77, 953–962. [CrossRef] 55. Ascione, F.; Bellia, L.; Capozzoli, A.; Minichiello, F. Energy saving strategies in air-conditioning for museums. Appl. Therm. Eng. 2009, 29, 676–686. [CrossRef] 56. Ascione, F.; Bellia, L.; Capozzoli, A. A coupled numerical approach on museum air conditioning: Energy and fluid-dynamic analysis. Appl. Energy 2013, 103, 416–427. [CrossRef] 57. Daou, K.; Wang, R.; Xia, Z. Desiccant cooling air conditioning: A review. Renew. Sustain. Energy Rev. 2006, 10, 55–77. [CrossRef] 58. La, D.; Dai, Y.; Li, Y.; Wang, R.; Ge, T. Technical development of rotary desiccant dehumidification and air conditioning: A review. Renew. Sustain. Energy Rev. 2010, 14, 130–147. [CrossRef] 59. Mei, L.; Dai, Y. A technical review on use of liquid-desiccant dehumidification for air-conditioning application. Renew. Sustain. Energy Rev. 2008, 12, 662–689. [CrossRef] 60. Saghafifar, M.; Gadalla, M. Innovative inlet air cooling technology for gas turbine power plants using integrated solid desiccant and Maisotsenko cooler. Energy 2015, 87, 663–677. [CrossRef] 61. Gao, W.; Cheng, Y.; Jiang, A.; Liu, T.; Anderson, K. Experimental investigation on integrated liquid desiccant–Indirect evaporative air cooling system utilizing the Maisotesenko—Cycle. Appl. Therm. Eng. 2015, 88, 288–296. [CrossRef] 62. Amer, O.; Boukhanouf, R.; Ibrahim, H.G. A Review of Evaporative Cooling Technologies. Int. J. Environ. Sci. Dev. 2015, 6, 111–117. [CrossRef] 63. Miyazaki, T.; Nikai, I.; Akisawa, A. Simulation analysis of an open-cycle adsorption air conditioning system—numeral modeling of a fixed bed dehumidification unit and the maisotsenko cycle cooling unit. Int. J. Energy Clean Environ. 2011, 12, 341–354. [CrossRef] 64. Yaningsih, I.; Mahmood, M.H.; Wijayanta, A.T.; Miyazaki, T.; Koyama, S. Experimental Study on Dehumidification Technology using Honeycomb Desiccant Block. Evergreen 2018, 5, 11–18. [CrossRef] 65. Kabeel, A. Solar powered air conditioning system using rotary honeycomb desiccant wheel. Renew. Energy 2007, 32, 1842–1857. [CrossRef] 66. Yaningsih, I.; Wijayanta, A.T.; Miyazaki, T.; Koyama, S. Analysis of heat and mass transfer characteristics of desiccant dehumidifier system with honeycomb configuration. Appl. Therm. Eng. 2018, 144, 658–669. [CrossRef] 67. Wrobel, J.; Ma, X.; Schmitz, G.; Grabe, J. A Desiccant Assisted Air Conditioning System with Use of Geothermal Energy. In Proceedings of the World Geothermal Congress, Bali, Indonesia, 25–30 April 2010. 68. Mahmood, M.H.; Sultan, M.; Miyazaki, T. Solid desiccant dehumidification-based air-conditioning system for agricultural storage application: Theory and experiments. Proc. Inst. Mech. Eng. Part A J. Power Energy 2019, 234, 534–547. [CrossRef] 69. ASHRAE. Handbook of Fundamentals; American Society of Heating, Refrigerating and Air-Conditioning Engineers. Inc.: Atlanta, GA, USA, 2013. 70. Sultan, M.; El-Sharkawy, I.I.; Miyazaki, T.; Saha, B.B.; Koyama, S.; Maruyama, T.; Maeda, S.; Nakamura, T. Water vapor sorption kinetics of polymer based sorbents: Theory and experiments. Appl. Therm. Eng. 2016, 106, 192–202. [CrossRef] 71. Esen, H.; Inalli, M.; Esen, M. Technoeconomic appraisal of a ground source heat pump system for a heating season in eastern Turkey. Energy Convers. Manag. 2006, 47, 1281–1297. [CrossRef] 72. Holman, J.P. Experimental Methods for Engineers; McGraw-Hill: New York, NY, USA, 2012. 73. Hepbasli, A.; Akdemir, O. Energy and exergy analysis of a ground source (geothermal) heat pump system. Energy Convers. Manag. 2004, 45, 737–753. [CrossRef] 74. Uçkan, I.; Yılmaz, T.; Hürdo˘gan,E.; Büyükalaca, O. Experimental investigation of a novel configuration of desiccant based evaporative air conditioning system. Energy Convers. Manag. 2013, 65, 606–615. [CrossRef] 75. Panaras, G.; Mathioulakis, E.; Belessiotis, V. Proposal of a control strategy for desiccant air-conditioning systems. Energy 2011, 36, 5666–5676. [CrossRef] Energies 2020, 13, 5530 23 of 23

76. Sultan, M.; Miyazaki, T.; Saha, B.B.; Koyama, S.; Kil, H.-S.; Nakabayashi, K.; Miyawaki, J.; Yoon, S.-H. Adsorption of Difluoromethane (HFC-32) onto phenol resin based adsorbent: Theory and experiments. Int. J. Heat Mass Transf. 2018, 127, 348–356. [CrossRef] 77. El-Agouz, S.A.; Sathyamurthy, R.; Manokar, A.M. Improvement of humidification–dehumidification desalination unit using a desiccant wheel. Chem. Eng. Res. Des. 2018, 131, 104–116. [CrossRef] 78. Zhang, J.; Ge, T.; Dai, Y.; Zhao, Y.; Wang, R. Experimental investigation on solar powered desiccant coated heat exchanger humidification air conditioning system in winter. Energy 2017, 137, 468–478. [CrossRef]

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