## 3 Materials and Methods
### Research Methodology  
To determine the design cooling load for the AC system, heat produced (HP) by the birds and their THI is required. [PERSON] (2000) [43; 44] model is used to calculate the HP (sensible and latent) per bird for climatic conditions of Multan. Figure 5 represents an illustration of integration of EC systems into a poultry house and sensible and latent heat load generated by a poultry bird. Heat production in birdschanges with respect to their body weight [45]. The birds grow muscles over time due to consuming more energy produced from feed intake [46]. As a result, more heat is released. Heat production (_HP_) in poultry birds is governed by Equation (13) given in the literature [26].  
\[HP=60.64+0.04 LW \tag{13}\]  
where HP represents heat production from poultry birds (W/kg) and LW represents the live weight of poultry birds (g).  
Sensible and latent heat production per bird is calculated using the [PERSON] (2000) model given by Equations (14) and (15), respectively [43; 44].  
\[Q_{t}=9.84m_{a}^{3}(4.10^{-5}(20-T_{db})^{3}+1) \tag{14}\]  
\[Q_{s}=0.83Q_{t}(0.8-1.85e^{-7}(T_{db}+10)^{4}) \tag{15}\]  
where \(Q_{t}\) and \(Q_{s}\) represent total and sensible heat productions (J/s), respectively, and \(m_{a}\) represents the mass of live birds (kg) and \(T_{db}\) represents dry-bulb temperature (\({}^{\circ}\)C).  
The temperature-humidity index (_THI_) is a linear combination of dry-bulb temperature and wet-bulb temperature. THI has been established to evaluate the effect of the thermal environment on thermoregulatory status of poultry birds [47]. Equation (16) governs THI for broilers [47].  
\[THI=0.85T_{db}+0.15T_{wb} \tag{16}\]  
where THI represents temperature-humidity index (\({}^{\circ}\)C), and \(T_{wb}\) represents wet-bulb temperature of air (\({}^{\circ}\)C). The wet-bulb temperature for poultry birds is calculated by Equation (17) [48; 49].  
\[\begin{array}{ll}T_{wb}=T_{db}tan^{-1}&\left[0.151977+(RH+8.313659)^{\frac{1 }{2}}\right]+tan^{-1}(T_{db}+RH)\\ &-tan^{-1}(RH-1.676331)+0.00391838~{}RH^{\frac{3}{2}}tan^{-1}(0.023101~{}RH) \\ &-4.686035\end{array} \tag{17}\]  
where RH represents relative humidity of air (%).  
THI has been developed based on body temperature responses instead of production responses [47]. Based on physiological parameters such as: body temperature, respiration rate, or pulse rate, heat production, or production performance, THI equations describe the importance of \(T_{db}\) and \(T_{wb}\) for a  
Figure 5: Scheme of temperature and humidity control system(s) in a typical poultry shed for maintaining the thermal comfort of poultry birds.  
range of animals including poultry birds and cattle [50]. However, THI fails to integrate the effect of air velocity (\(V\)) on animal thermal comfort [50]. Effects of air velocity on body temperature of poultry birds is accounted for by integrating V into THI [27]. Due to the nonlinear nature of V, the asymptotical function is considered [50]. Consequently, the temperature-humidity-velocity index (THVI) is used in this study for homeostasis (i.e., ability of an animal to maintain constant internal conditions in the face of fluctuating external conditions) of birds [27]. With increase in velocity up to a certain point (i.e., 1.2 m/s), optimum thermal comfort for poultry birds inside a poultry can be achieved [50]. THVI is calculated by Equation (18) given in the literature [27].  
\[THVI=V^{-0.058}\ THI \tag{18}\]