Original papers
Using CFD to assess the influence of ceiling deflector design on airflow distribution in hen house with tunnel ventilation

https://doi.org/10.1016/j.compag.2018.05.029Get rights and content

Highlights

  • Ceiling deflectors increase air speed in caged-hen occupied zone (CZ) effectively.

  • Indoor air speed change is linearly related to height and interval of deflectors.

  • Ceiling deflectors affect air speed variation trend along length direction of cage.

  • Air speed uniformity in CZ increases with height, decreases with deflector interval.

Abstract

Maintaining proper environment in hen house by mechanical ventilation is essential for the production. In order to fully mix the cold inlet air in winter with room air, the free space beneath ceiling of hen house is normally large. However, in summer, such a design is not optimal for tunnel ventilation that air is drawn into one end of the house and exhausted at the other end, i.e., a large portion of the ventilation air would pass through the free space under ceiling instead of caged-hen occupied zone (CZ), which leads to reduced air speed in CZ as well as wind chill effect. To solve this problem, application of deflectors beneath the ceiling was investigated by computational fluid dynamics (CFD) simulations. To assess the effect of deflectors, the indoor air speed and distribution with deflectors were compared to those without deflectors. The effects of heights (0.4 m, 0.55 m, 0.7 m, 0.85 m and 1 m) and intervals (6 m, 9 m, 12 m, 15 m and 18 m) of deflectors on air speed and distribution in CZ were analyzed. The CZ was modelled as porous media in simulations to reduce mesh numbers. The resistance coefficients in x, y and z directions were derived by pressure drop through CZ in a virtual wind tunnel with one cage of birds. The hen house model was validated by a set of field measurement data. A reasonable agreement was found between measured and simulated values (the relative difference is within 10%). The investigation showed that the deflectors could significantly direct airflow downwards and increase the air speed in CZ and aisle zone by 0.66 m s−1 and 0.91 m s−1, respectively, than those without deflectors, when deflectors were 1 m height with interval of 6 m. The average air speed changes in CZ were linearly related to the height and interval of deflectors. Along the length direction of cage, the variation trends of air speed were almost identical under different heights of deflectors, while under varied intervals, the air speed variation trends had significant difference. The uniformity of airflow distribution in CZ, which was defined as ratio of standard deviation of air speed to the mean, was increased by application of the deflectors. The uniformity was positively related to height and negatively related to the interval of deflectors.

Introduction

An appropriate indoor environment, e.g. air temperature, humidity, air speed and air quality in a hen house is crucial to the production performance, immune function and the welfare of hens (Mashaly et al., 2004). Thermoneutral zone for adult hens is generally from 18 to 24 °C (Hulzebosch, 2005). When the ambient temperature raises above the thermoneutral zone, hens will experience heat stress due to the decreased heat release between bodies and surroundings, which could diminish the feed consumption and conversion, body weight of hens and egg weight. Meanwhile, the mortality also increases (Freitas et al., 2017, Kocaman et al., 2006, Sterling et al., 2003). Below the thermoneutral zone, the birds need to consume extra energy to maintain normal body temperature and metabolic activities. This could decrease the feed conversion efficiency, body weight of hens, egg production and affects hens’ healthy condition (Campo et al., 2008, Ipek and Sahan, 2006). Whereas the excessively high or low ambient temperature, like in many regions in China where the maximum temperature is more than 35 °C in summer and the minimum is less than −20 °C in winter, mechanical ventilation systems with cooling and heating facilities are needed and the ventilation systems should be adjusted accordingly with seasons.

One of the most widely adopted ventilation strategies in hen houses in a region with cold winter and hot summer is to apply mix ventilation in winter and tunnel ventilation in summer. The mix ventilation consists of multiple sidewall inlets and a number of exhausted fans at a gable wall. To avoid cold air supply directly into caged-hen occupied zone (CZ), sidewall inlets with bottom hinged flaps are installed to direct the cold incoming air to the upper part of house and mix with warm air there before entry into CZ (Bjerg et al., 2002, Kwon et al., 2015). In summer, the tunnel ventilation that ventilating air is drawn into one end of the house and exhausted at the other end (Lott et al., 1998), is often applied to generate higher air speed that can increase the convective heat exchange between birds and ventilation air. The tunnel system is commonly used together with evaporation cooling pad installed behind the inlet when the outdoor temperature is high. Since after evaporation cooling, the inlet air is of low temperature and high humidity, it also needs to be directed to the upper part of house by bottom hinged flaps behind the cooling pad before entering the CZ (Xin et al., 1994). To ensure the proper mixing of the cold inlet airflow, a free space above the CZ remains in such a system. The free space, which has less resistance comparing with CZ, could allow a large portion of airflow passing through to the exhaust fans at the end of house. This will diminish the air speed in CZ. However, in tunnel ventilation, air speed is vital as it has a positive correlation with the cooling effect (Simmons et al., 2003). An air speed of between 2.29 m s−1 and 2.79 m s−1 would produce approximately a 5.5–6.6 °C wind chill effect (The University of Georgia, 1998) . To avoid the short-cut of air to the free spaces, installing deflectors under the ceiling was considered as a solution that could direct the airflow to CZ and increase the air speed in it.

The deflectors under the ceiling have been employed to decrease the cross section area of a broiler house, which can increase the local air speed in animal occupied zone (AOZ) (Mostafa et al., 2012). Similarly, ceiling deflectors have also been investigated in low-profile cross-ventilation (LPCV) cow house to divert airflow into the AOZ (Harner and Smith, 2008, Harner et al., 2009, Lobeck et al., 2011). Harner and Smith found that with deflectors, the air speed in AOZ increased from 0.9 to 1.3 m s−1 to 2.7–3.6 m s−1 during the summer. Dairies had better lay-down rates as well as a corresponding increase in milk production (Harner and Smith, 2008). Deng et al. added deflectors under ceiling and over headlocks in cattle house, which increased the air speed of AOZ by 52.8% comparing to that without deflectors (Deng et al., 2014). Chen et al. arranged deflectors of 2 m height with 6 m intervals in the beef cattle barn and the air speeds in AOZ were improved by 0.3–0.6 m s−1 (Chen et al., 2017). Ikeguchi et al. investigated the airflow pattern in LPCV and found that the most suitable installation location of deflectors was 9.5 m from the inlet sidewall and the height was 2.5 m (Ikeguchi et al., 2015). However, the literature concerning the application of deflectors with varied heights and intervals in the caged-hen house with tunnel ventilation is limited.

Recently, computational fluid dynamics (CFD) has been regarded as a powerful and versatile tool to study the airflow pattern and gas emission in livestock house with mechanical ventilation (Bustamante et al., 2017, Fidaros et al., 2017, Li et al., 2017, Wu et al., 2012b). Comparing with the field and wind tunnel experiment, CFD is time and economic saving, feasible to fully control the external factors and experimental variables. Also, rather than the limited measurement points in tests, it is more convenient for CFD to obtain all relevant environmental information within the simulation zone and the airflow pattern could be analyzed quantitatively and qualitatively. Nonetheless, the accuracy of the simulations is of controversial unless the validation and verification are made (Rong et al., 2016).

This study investigated the effect of ceiling deflectors with different heights and intervals on air speed in a parental breeding hen house with CFD. The objectives of this study were: (1) investigating the feasibility of deflectors to direct airflow from ceiling zone to CZ and aisle zone; (2) studying the influence of deflectors on air speed distribution inside the house; (3) evaluating the effects of varied heights and intervals of deflectors on indoor air speed, air speed variation trend and distribution in CZ.

Section snippets

Materials and methods

Some field measurements were done in an existing farm to validate a CFD model, and then the performance of deflectors was evaluated using CFD.

The resistance coefficients of CZ

Fig. 4a revealed the static pressure distribution in the model of virtual wind tunnel with inlet velocity of 2.5 m s−1 in x direction. When treating CZ as porous media, through Eq. (1), the resistance coefficients were obtained by regression between static pressure drops (Δpx, Δpy and Δpz) and inlet velocities (vx, vy and vz) in x, y and z directions (Fig. 4b). The viscous resistance coefficients are 7461.11 m−2, 22.2 m−2 and 8400 m−2, the inertial resistance coefficients are 0.675 m−1, 1.54 m−1

Conclusions

This paper investigated the effect of deflectors on air speed and distribution in CZ. The deflectors with various heights and intervals were researched by CFD to quantify the air speed distribution. The following conclusions could be drawn:

  • (1)

    The deflectors could significantly increase ventilation efficiency by directing airflow from ceiling zone to CZ and aisle zone. The air speeds in CZ and aisle zone were increased by 0.66 m s−1 and 0.91 m s−1, respectively, than those without deflectors, when

Acknowledgement

Thanks to China Scholarship Council (CSC) for the scholarship (201606350035) of Qiongyi Cheng for the Ph.D. study in Denmark and the research grant of National Innovation Foundation/Advanced Technology Foundation Denmark, New hot climate ventilation system for poultry and pigs (j.nr. 17-2013-3).

References (39)

Cited by (33)

  • CFD study on the impacts of geometric models of lying pigs on resistance coefficients for porous media modelling of the animal occupied zone

    2022, Biosystems Engineering
    Citation Excerpt :

    Wu et al. (2012) concluded that the animal occupied zone could be treated as porous media when determining the air exchange rate in a naturally ventilated dairy cattle building. Cheng, Li, et al. (2018) investigated airflow in a hen house using CFD simulation by simplifying the caged-hen occupied zone into porous media. Porous media modelling in CFD simulations requires the inputs of the resistance coefficients of the inertial and viscous terms in the relationship between air speed and pressure drop of the porous media region.

  • Study on the air resistance of pigs in groups based on open-source CFD code: Influence of stocking density and live weight

    2022, Biosystems Engineering
    Citation Excerpt :

    Thus, different turbulence models need be evaluated to establish an accurate numerical model. Since it is extremely difficult to obtain the experimental data for the pressure drop of groups of animals to validate the simulation model, regular geometry instead of animal models has been used in some studies (Li et al. (2019); Cheng, Li, et al. (2018)). Thus, tube bundles where there are available experimental data and empirical equations are used to provide reference data for evaluating numerical model performance.

View all citing articles on Scopus
View full text