Pruebas funcionales

The major types of ventilation system are; the tunnel ventilation system and the

conventional ventilation system. They both operate based on the static pressure (that is pressure difference between the inside and outside of the livestock building). This could be negative pressure, forcing air into the livestock building through the inlets; positive pressure, pushing air into the animal building through the mechanical fans; or neutral pressure, forcing air into and out of the animal building through mechanical fans

(University of Kentucky College of Agriculture, 2014). The two ventilation systems (tunnel and conventional) are designed to remove heat, moisture and contaminants from the broiler building. However, tunnel ventilation system, as a hot weather ventilation

approach, is majorly designed for providing desired air movement in the broiler occupied zones to relieve birds of heat stress (University of Kentucky College of Agriculture, 2014). Some mechanical ventilation systems and their performances are summarised in Table 2.4.

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Table 2.4: Evaluation of air velocities of different mechanical ventilation systems

Authors and years Ventilation system With/ without animals Comments

(Blanes-Vidal et al., 2007) Cross-ventilated No broiler chicken Fan combinations influenced air velocity variation in the building

Blanes-Vidal et al. (2010) Cross-ventilated With broiler chickens Fan size and ventilation rates affect air velocity Bustamante et al. (2012) Cross-ventilated No broiler chicken Fan combinations influenced air velocity variation in

the building

Bustamante et al. ( 2015) Tunnel-ventilated No broiler chicken Air velocity variations were significantly influenced by building sections, operating fans and height above the floor.

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2.4.1.1. Tunnel ventilation system

In the tunnel ventilation system (Figure 2.3), fans are located at one end and the inlets are placed at the opposite far end of the broiler building and air is drawn across the length of the broiler building to provide cooling for broiler chickens at an average static pressure of 12 Pa. (Bucklin et al., 2015; Czarick and Fairchild, 2008; Lacy and Czarick, 1992;

University of Kentucky College of Agriculture, 2014). Tunnel ventilation system is common in the tropical climate (warm regions) where mean annual temperature generally exceeds 25 ⁰C (Bhadhauria, 2014; Bustamante et al., 2015; Trewin, 2014). In broiler buildings, tunnel ventilation system usually produce an average air velocity of 1.5 to 3 m s-1 _{at the}

broiler level to prevent heat stress during hot weather periods (Bustamante et al., 2015; Lacy and Czarick, 1992).

Figure 2.3: Tunnel ventilation system (Big Dutchman, 2016)

Many studies have been carried out on the evaluation of the effectiveness of tunnel

ventilation system in providing cool environment for poultry birds. Bustamante et al. (2015) simulated the air velocity distribution in the tunnel ventilated broiler building in the

Mediterranean climate to evaluate the performance of the newly introduced tunnel

ventilation system over the existing (conventional) ventilation system using computational fluid dynamics (CFD). They indicated that the ventilation within the broiler building was not optimal as a result of dead zones and over ventilation at the ends of the tunnel ventilated broiler building. The performance of broiler chickens raised in a tunnel ventilated broiler building and the operation cost of the tunnel ventilation system were evaluated by Lacy and Czarick (1992). They reported that though the body weight of broiler chickens raised in the tunnel ventilated broiler building increased by 4.3 % compared to the birds raised in a conventional ventilated broiler building, the cost of electricity for running the tunnel ventilated building doubled the cost of running conventional broiler building. The stress

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conditions within the tunnel ventilated broiler building were spatially analysed by Miragliotta et al. (2006). They indicated that the stress zones are majorly located at the ends of the tunnel ventilated broiler building and that the highest bird mortality was recorded closer to the exhaust fans end. Similar report has also been indicated in the study carried out by Wheeler et al. (2003). They indicated that the microclimate of birds at the exhaust end was the warmest zone within the tunnel ventilated broiler building. It has been shown that birds raised in the tunnel ventilated broiler building tend to migrate towards the inlet area during hot periods which could result in lower performance of the birds and higher body condemnations as a result of overcrowding and poor litter quality (Czarick and Lacy, 1990; Lacy and Czarick, 1992).

2.4.1.2. Conventional ventilation system

The airflow exchange rate of conventional ventilation system in broiler buildings are determined based on the amount of the heat that is expected to be remove from the poultry building (University of Kentucky College of Agriculture, 2014). It has less operation cost compared to tunnel ventilation system (Lacy and Czarick, 1992). The available conventional ventilation systems are discussed below.

2.4.1.2.1. Cross ventilation system

In the cross ventilated broiler building (Figure 2.4), mechanical fans are installed on one sidewall while the inlets are on the other sidewall of the building (Bhadhauria, 2014). The fans could be equally spaced or arranged as a group of 2 or 3 (University of Kentucky College of Agriculture, 2014). Cross ventilation broiler building is usually about 10 m wide and is largely adopted in the hot and humid climate for removing heat during summer periods and contaminants during winter (Bhadhauria, 2014; Bustamante et al., 2013; University of Kentucky College of Agriculture, 2014). Due to high mortality and the heat stress of birds raised in the cross ventilated building, different studies have been carried out to evaluate the airflow within the cross ventilated broiler building. The ventilation efficiency of cross ventilated broiler building was explored by (Bustamante et al., 2013) to understand the air velocity distribution within the building using CFD. The ventilation rate of cross ventilated poultry buildings was evaluated by Calvet et al. (2010). The

homogeneousness of the indoor temperature and velocity in cross ventilated broiler buildings were evaluated by Wheeler et al. (2003) and they reported that almost half of the building exhibited air velocity less than 0.25 m s-1_{. The airflow within the cross ventilated}

broiler building was predicted using CFD by Blanes-Vidal et al. (2008). All the above studies have indicated that airflow within the cross ventilated broiler building was generally below (< 1.5 m s-1_{) the required mean air velocity in the broiler microclimate zones. As a}

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indoor heat during cold periods and not an appropriate ventilation system for providing cool environment for broilers during hot weather periods.

Figure 2. 4: Cross ventilation system (Big Dutchman, 2016)

2.4.1.2.2. Sidewall inlet and roof exhaust ventilation system

In this type of conventional ventilation system (Figure 2.5), automatically adjusted inlets are installed along the two sidewalls and the mechanical fans are mounted in the roof of the building. The fresh air is drawn through the inlet into the building using static pressure while the stale air is vertically expelled out of the building through the roof mounted fans into the atmosphere for better dispersal (AHDB, 2017; Hydor, n.d.). This ventilation system is mainly found in the United Kingdom (AHDB, 2017; Hydor, n.d.). As at when this literature review was written, the information on this type of ventilation system in the literature is scarce. Therefore, not much information could be provided here.

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Figure 2.5: Sidewall inlet and roof exhaust ventilation system