*Article* **Experiments on Energy-Efficient Evaporative Cooling Systems for Poultry Farm Application in Multan (Pakistan)**

**Khawar Shahzad <sup>1</sup> , Muhammad Sultan 1,\* , Muhammad Bilal <sup>1</sup> , Hadeed Ashraf <sup>1</sup> , Muhammad Farooq <sup>2</sup> , Takahiko Miyazaki 3,4, Uzair Sajjad <sup>5</sup> , Imran Ali <sup>6</sup> and Muhammad I. Hussain <sup>7</sup>**


**Abstract:** Poultry are one of the most vulnerable species of its kind once the temperature-humidity nexus is explored. This is so because the broilers lack sweat glands as compared to humans and undergo panting process to mitigate their latent heat (moisture produced in the body) in the air. As a result, moisture production inside poultry house needs to be maintained to avoid any serious health and welfare complications. Several strategies such as compressor-based air-conditioning systems have been implemented worldwide to attenuate the heat stress in poultry, but these are not economical. Therefore, this study focuses on the development of low-cost and environmentally friendly improved evaporative cooling systems (DEC, IEC, MEC) from the viewpoint of heat stress in poultry houses. Thermodynamic analysis of these systems was carried out for the climatic conditions of Multan, Pakistan. The results appreciably controlled the environmental conditions which showed that for the months of April, May, and June, the decrease in temperature by direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and Maisotsenko-Cycle evaporative cooling (MEC) systems is 7–10 ◦C, 5–6.5 ◦C, and 9.5–12 ◦C, respectively. In case of July, August, and September, the decrease in temperature by DEC, IEC, and MEC systems is 5.5–7 ◦C, 3.5–4.5 ◦C, and 7–7.5 ◦C, respectively. In addition, drop in temperature-humidity index (THI) values by DEC, IEC, and MEC is 3.5–9 ◦C, 3–7 ◦C, and 5.5–10 ◦C, respectively for all months. Optimum temperature and relative humidity conditions are determined for poultry birds and thereby, systems' performance is thermodynamically evaluated for poultry farms from the viewpoint of THI, temperature-humidity-velocity index (THVI), and thermal exposure time (ET). From the analysis, it is concluded that MEC system performed relatively better than others due to its ability of dew-point cooling and achieved THI threshold limit with reasonable temperature and humidity indexes.

**Keywords:** poultry farms; air-conditioning; evaporative cooling systems; temperature-humidity index; temperature-humidity-velocity index

**Citation:** Shahzad, K.; Sultan, M.; Bilal, M.; Ashraf, H.; Farooq, M.; Miyazaki, T.; Sajjad, U.; Ali, I.; Hussain, M.I. Experiments on Energy-Efficient Evaporative Cooling Systems for Poultry Farm Application in Multan (Pakistan). *Sustainability* **2021**, *13*, 2836. https://doi.org/ 10.3390/su13052836

Academic Editors:

Muhammad Sultan, Yuguang Zhou, Redmond R. Shamshiri and Aitazaz A. Farooque

Received: 17 January 2021 Accepted: 25 February 2021 Published: 5 March 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

### **1. Introduction**

### *1.1. Background*

The agriculture sector of Pakistan contributes to about 21% of the gross domestic product (GDP) and absorbs 45.5% of the total labor strength [1]. The total share of livestock sector in agriculture covers about 11.4% of the agriculture gross domestic product and 53.25% of the value-added products [2]. Among the livestock sector, poultry contributed about 1.4% in overall gross domestic product (GDP) during (2017–18) [3]. It also employs directly/indirectly 1.5 million people [4]. Furthermore, the poultry meat production amounted to total 1.43 million tons in 2017–2018 which represented the 32.76% of the total meat production in the country. Keeping in view the economic importance of poultry, it is desirable to monitor the environmental condition for their control sheds where several flocks are brought up on yearly basis. A huge amount of capital is invested to raise the controlled structures. Therefore, minor risks either by labor or machine are vulnerable to poultry. Pakistan is recognized as a tropical country being along the equator on globe.

Climate change causes an increase in frequency, duration, and magnitude of heat events [5,6]. Tropical countries are susceptible to hot and humid weather conditions [7]. In Pakistan, there is a cycle of four seasons giving temporal variations. Summer and winter reach the intense weather conditions. Over this course of time, temperature hits above 40 ◦C and the corresponding mark of relative humidity drops below 20% in plain areas during summer. Poultry birds are susceptible to environmental conditions. It is advisory to control these factors that adversely affect the production and welfare of broiler chickens. Heat stress is the major contributory force to affect the fate of these broilers. Poultry birds are homoiothermic in nature and have the ability to control the body temperature throughout the year whereas, the thermoregulatory mechanisms are efficient only in the range of thermo-neutral zones (27.5–37.7 ◦C) [8,9]. The current study consists of the applicability of evaporative cooling systems in the ambient conditions of Multan, Pakistan. To maintain the thermal comfort in a poultry farm, air-conditioning is necessary [10,11]. Figure 1a,b shows the dry-bulb temperature (DBT) and relative humidity (RH) variation for Multan (Pakistan) throughout the year. It is found from the literature that the temperature higher than 25 ◦C causes heat stress in poultry [12]. This study comprises the poultry thermal comfort under the ambient conditions of Multan, Pakistan. The suitable relative humidity ranges from the efficiency of the poultry farms and the chickens get affected by this temperature-humidity index (THI) [13]. Once these situations reach poorly managed controlled houses for poultry, the mortality rate per flock increases.

Pursuing this trend, growth of chickens is depressed, and heavy economic loss is incurred. High temperatures can be absorbed by the poultry birds to some extent but may go negatively when summer conditions turn severely warm with low humidity in ambient air.

### *1.2. Heat Stress and Poultry Air-Conditioning*

Heat stress is a key problem affecting both the health and performance of the poultry [14]. The chickens try to maintain their body temperature in between the thermo-neutral zone but it is a condition where chickens are unable to maintain the balance between the heat production and heat loss [15]. If the controlled temperature exceeds this zone, heat must be lost in some way by poultry birds. Chickens have no sweat glands. Naturally, a human body has pores on the skin through which moisture loss occurs by specific glands balancing the ambient weather conditions. Unlike humans, chickens are deprived of such sweat glands. Weight gain in chickens gradually goes on with increasing age. During summer, the body heat of poultry birds is also exalted causing raised temperature [16]. At this point, there are two ways: either reduce feed intake by bird or provide optimal weather conditions inside controlled sheds. At 29.4 ◦C (85 ◦F), chickens start panting [17]. Figure 2a shows the temperature/humidity heat stress index for chickens which combines the air temperature with the relative humidity to analyze that how increasing humidity affects the thermal comfort zone. Panting is a natural process for heat dissipation in bodies of poultry

birds. Analogous to humans, this process maintains metabolic heat balance for chickens. As a result of this phenomenon, water intake is increased to avoid dehydration. Figure 2b illustrates the temperature zones of poultry birds which states that the optimum poultry bird's growth can be obtained by maintaining the desired temperature and humidity zones inside the poultry house. During panting, high values of temperature and humidity pose a serious problem. As the chickens lose moisture heat of the body to their surroundings for attaining thermal comfort. But high humidity in ambient hot air hinders the functioning of this process [18]. It also affects the productive and reproductive performance as well as the economic traits and the welfare of poultry [19,20].

**Figure 1.** Illustration of (**a**) dry-bulb temperature, and (**b**) relative humidity variation (on hourly basis) for the ambient conditions of Multan, Pakistan.

**Figure 2.** Heat stress effects on poultry birds. (**a**) Illustration of temperature-humidity index (THI) for chickens, reproduced from [21,22], and (**b**) diagram of temperature zones for broiler chickens representing lower, upper, and maximum temperature, reproduced from [23].

The activity and position of broiler chickens in broiler houses if monitored and controlled could potentially lead to ameliorate conditions for health, energy consumption, and welfare of these birds [14]. This research focused on controlling chamber environment for broilers on micro-scale to understand their attributes. Broiler chickens transmit heat flow from their body surface to maintain thermal equilibrium with the environment. The surface temperature of birds can be directly related to the flow of blood in their body. Any change in ambient temperature can be felt through the blood flow in birds near the skin. Climate in poultry houses is a combination of dry air and humidity. Poultry litter is affected when moisture and relative humidity is increased above 70% in room/poultry house. In a result, ammonia (above 70 ppm) production increases which affects bird's health and reduces growth [24–26].

The optimum control of these two parameters guarantees the safety and welfare of broiler chickens. Broiler chickens maintain their body temperatures through sensible (change in body surface temperature) and latent (release of moisture from body in while exhaling) heat emissions. It is suggested that the comprehensive study of metabolic functions be conducted to understand the heat production in poultry birds. Figure 3 illustrates the effects of heat stress on behavioral changes. Chickens under heat stress conditions spend less time in feeding and more in drinking, wings are lifted and less moving. The panting signs are also observed [15]. Physiological changes include the oxidative stress, acid base imbalance, respiratory alkalosis, and changes in cecal microbial profile. Heat stress is correlated with the cellular oxidative stress which causes severe health disorders, lower growth rates and economic losses [16,17]. The heat stress causes production changes by increasing the weight of the chickens and decreasing the quality and quantity of eggs. The mortality rate also increases due to heat stress [18]. *Sustainability* **2021**, *13*, x FOR PEER REVIEW 5 of 23 by increasing the weight of the chickens and decreasing the quality and quantity of eggs. The mortality rate also increases due to heat stress [18].

**Figure 3.** Heat stress effects on the poultry behavioral, physiological, production and neuroendocrine changes, reproduced from [18]. **Figure 3.** Heat stress effects on the poultry behavioral, physiological, production and neuroendocrine changes, reproduced from [18].

With the increasing ambient temperature, the mortality rate increases. The high levels of temperature not only affect the production performance but also hinders the immune function in poultry [27,28]. To achieve the desired conditions for poultry, many cooling systems have been developed and thus controlled air-conditioning has become necessary. Air conditioning systems specifically evaporative cooling pads alone, or in combination with nozzles are studied in literature [19,20,29,30]. Figure 4 illustrates the With the increasing ambient temperature, the mortality rate increases. The high levels of temperature not only affect the production performance but also hinders the immune function in poultry [27,28]. To achieve the desired conditions for poultry, many cooling systems have been developed and thus controlled air-conditioning has become necessary. Air conditioning systems specifically evaporative cooling pads alone, or in combination with nozzles are studied in literature [19,20,29,30]. Figure 4 illustrates the schematic of a typical EC-based poultry air-conditioning.

**Figure 4.** Schematic diagram of typical poultry air-conditioning for thermal comfort.

Air-conditioning happens to be an integrated process which transports the ambient air into the conditioned space with optimal parameters of thermal environment for the occupants [19,20,29,31]. In this way, it controls and maintains the temperature, relative humidity, and air movement, in the conditioned space within the predetermined limits either for thermal comfort or product processing. For poultry birds, thermal environment is of prime significance. The optimal mixture of temperature and relative humidity gives

schematic of a typical EC-based poultry air-conditioning.

crine changes, reproduced from [18].

by increasing the weight of the chickens and decreasing the quality and quantity of eggs.

**Figure 3.** Heat stress effects on the poultry behavioral, physiological, production and neuroendo-

With the increasing ambient temperature, the mortality rate increases. The high lev-

els of temperature not only affect the production performance but also hinders the immune function in poultry [27,28]. To achieve the desired conditions for poultry, many cooling systems have been developed and thus controlled air-conditioning has become

The mortality rate also increases due to heat stress [18].

schematic of a typical EC-based poultry air-conditioning.

**Figure 4.** Schematic diagram of typical poultry air-conditioning for thermal comfort. **Figure 4.** Schematic diagram of typical poultry air-conditioning for thermal comfort.

Air-conditioning happens to be an integrated process which transports the ambient air into the conditioned space with optimal parameters of thermal environment for the occupants [19,20,29,31]. In this way, it controls and maintains the temperature, relative humidity, and air movement, in the conditioned space within the predetermined limits either for thermal comfort or product processing. For poultry birds, thermal environment is of prime significance. The optimal mixture of temperature and relative humidity gives Air-conditioning happens to be an integrated process which transports the ambient air into the conditioned space with optimal parameters of thermal environment for the occupants [19,20,29,31]. In this way, it controls and maintains the temperature, relative humidity, and air movement, in the conditioned space within the predetermined limits either for thermal comfort or product processing. For poultry birds, thermal environment is of prime significance. The optimal mixture of temperature and relative humidity gives birth to temperature-humidity-index (THI). It is the thermal comfort that enhances health of occupants in any conditioned space [32–34]. DEC, IEC, and MEC systems are performing better as compared to vapor compression systems in terms of saving primary energy and providing desired environmental conditions. Poultry control sheds employ direct evaporative coolers for summer cooling. Evaporative cooling systems are developed and installed to meet air-conditioning requirement in poultry houses. The efficiency of these systems makes them cost effective and acceptable to user end. Poultry control sheds are chambers which are conditioned on the principle of direct evaporative cooling system. Heat production by poultry birds is ejected out of the system with reduction in temperature.

> The objectives of this study include the understanding of poultry air-conditioning requirements for poultry birds based on heat and moisture production, calculating heat stress per bird and THI index to assess the desired evaporative cooling systems under the climatic conditions of Multan, understanding the effects of sensible and as well as the latent heat production in poultry birds and evaluation of evaporative cooling systems i.e., direct evaporative cooling (DEC), indirect evaporative cooling (IEC), Maisotsenko-Cycle evaporative cooling (MEC) for the poultry environment in terms of THI and THVI.

### **2. Evaporative Cooling Systems**

Many types of cooling systems are available to provide cool air for commercial or domestic purpose. Since the ancient times, evaporative cooling systems (EC) are used for cooling the ambient air by evaporating water droplets into the air. Evaporation of water is a process in which heat of the ambient air is absorbed and water vapors are imparted to it. In this process, only the latent load is achieved by providing humidity into the ambient air. Whereas the total heat (enthalpy) gets negligible change. Evaporative cooling generally lies on the conversion of sensible heat into the latent one. The main work is accomplished by the water in EC systems. The heat and mass transfer in EC systems occurs on account of temperature and vapor pressure deficits. On the other hand, vapor compression air-conditioning (VCAC) systems employs CFCs or HCFCs which are environmentally harmful being the major exploiters of ozone layer depletion [10,31]. In this regard, increasing research efforts have been made in designing low cost and environmental friendly technologies; specifically EC techniques have been demonstrated effectively [35–37]. Energy consumption is also lower in EC systems as compared to the VCAC [38]. When ambient air is passed through any water steam directly or indirectly, it gets cooled with the effect of water evaporation into the air [20,31,39]. EC system is generally employed in hot and relatively dry climates [7]. On the contrary, humid environment is not suitable for evaporating cooling systems as air is already saturated. The evaporating cooling system can be categorized into DEC and IEC with respect to the interaction of water with air. A new system called M-cycle evaporative cooling (MEC) has also been introduced to get a cool fresh air. Figure 5 shows the laboratory-scale models for DEC, IEC, and MEC systems, respectively. These systems were developed in Agricultural Engineering Department Bahauddin Zakariya University Multan, Pakistan. The experimental setup uses 6.5 L/min water pump for all three developed systems and a standard anemometer for air flow rate (i.e., average 1.7m/s). Standard temperature and moisture sensor (H2) with an experimental uncertainty of ±1 ◦C temperature and ±2% RH was used in the experimental setup. Experimental data were collected for a time span of a typical meteorological year and thermodynamic analyses were carried out for poultry air-conditioning. Under the climatic conditions of Multan city, these systems can be employed to achieve certain results which were further optimized to obtain THI and THVI values. Figure 6 illustrates the schematics of typical evaporative cooling with DEC, IEC, and MEC. EC system is an environment friendly and energy saving technology [40]. In terms of thermal comfort, this system can be a suitable option in hot and arid climates as the relative humidity lies in between the 60 and 70%. This system altogether meets the thermal comfort needs of the occupant, being environmentally friendly [41]. The effectiveness of EC system is indicated by wet-bulb and dew-point effectiveness [31]. In this system, ambient air is directly brought in contact with water stream to lower down the temperature and increase relative humidity [19,20,29,31,42].

## *2.1. Direct Evaporative Cooling (DEC)*

It is the easiest and oldest type of EC system in which ambient air is brought in direct contact with air stream to reduce the temperature [38]. The continuous evaporation of water vapors (adiabatic process) causes a cooling effect up to a saturation point in which enthalpy of air remains same, whereas the humidity ratio increases throughout the process [31,44]. These water streams are brought from metal or plastic tubes commonly known as "pads" as their boundary walls. The ambient air is showered with water and thus, it gets cooled and humidified. The water stream is injected with the help of motor and from the top of the wall water droplets are drawn downward with the gravity force and capillary action. The ambient temperature is potentially reduced to its wet bulb temperature at wet-bulb effectiveness of 75–95% [31,45]. Figure 6 shows the working principle of DEC system. In dry climates, DEC system works with 80% efficiency as reported in [38].

### *2.2. Indirect Evaporative Cooling (IEC)*

It is a system in which heat and mass transfer phenomenon takes place without the addition of moisture and works on the principle of sensible cooling [44]. In this system, cooling effect is produced by isenthalpic cooling in the wet channel and sensible heat transfer in the dry channel [44]. In IEC systems, product air passes over the dry side while the working air passes over the wet side. In case of DEC, the conditioned air is obtained but with an increased relative humidity level [46]. To achieve the constant absolute humidity, the IEC systems are desired. Figure 6 shows the working principle of an IEC system. IEC system can reduce the temperature up to the wet-bulb temperature at wet-bulb

effectiveness of 50–65% [47]. The humidity ratio of the inlet and outlet air remains same while the enthalpy of the outlet air decreases in an IEC system [44]. system is indicated by wet-bulb and dew-point effectiveness [31]. In this system, ambient air is directly brought in contact with water stream to lower down the temperature and increase relative humidity [19,20,29,31,42].

**Figure 5.** Laboratory-scale models for direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and Maisotsenko-Cycle evaporative cooling (MEC) systems, reproduced from author's work [43]. **Figure 5.** Laboratory-scale models for direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and Maisotsenko-Cycle evaporative cooling (MEC) systems, reproduced from author's work [43].
