Thermal and ammonia concentration gradients in a rabbit barn with two ventilation system designs

Abstract

A B S T R A C TRabbit barns are of economic importance in central Mexico, where rabbit breeders use rustic buildings for production. In such barns, climate conditioning is mostly based on natural ventilation (NV) where the lack of a well-designed NV system may be a limiting factor. In this study, computational fluid dynamics was used to analyse the performance of the NV system in a 24 x 4 x 4.8 m typical Central Mexico rabbit barn with a density of 20 rabbits m -2 of cage. The barn included both side vents at 1.2 m in height from the ground. Results indicated exchange rates of 0.052 and 2.9 x 10 -4 m 3 m -2 s -1 when the wind direction was simulated as orthogonal and parallel to the side vents, respectively, suggesting the orthogonal direction favoured the exchange rate. However, such conditions produced an accumulation of ammonia underneath the rabbit cages. Thus, a design modification including a lower inlet vent was analysed. Such modification substantially decreased the concentration gradients of temperature and ammonia.Gradientes de temperatura e concentração de amônia em fazenda cunícula com dois sistemas de ventilação R E S U M O A produção de coelhos em sistemas intensivos é importante para a economia da região central do México, onde os criadores usam instalações rústicas para produção. O acondicionamento climático nesse tipo de instalação ocorre, basicamente, por ventilação natural; no entanto, a arquitetura desses galpões é fator limitante para uma ventilação eficiente. Neste trabalho foi usada Dinâmica Computacional de Fluido para analisar o desempenho da ventilação natural em um típico galpão de 24 x 4 x 4,8 m construído na parte central do México. Foi usada uma densidade de 20 coelhos m -2 para as simulações. O galpão tinha dois lados de ventilação de 1.2 m de altura desde o solo. Os resultados indicaram taxas de câmbio de 0,052 e 2,9 x 10 -4 m 3 m -2 s -1 quando se simulou a direção do vento em ortogonal e paralelo às saídas de ar resultando em zero de concentração sobre as gaiolas; porém uma acumulação de gás ocorreu abaixo das gaiolas devido a uma distribuição não uniforme do ar. Com base nos resultados foram realizadas modificações na arquitetura das instalações, incluindo a abertura de entrada de vento na parte inferior do galpão. Tais modificações permitiram diminuir, notoriamente, os gradientes de concentração térmica e amoníaco.

Natural Ventilation to Manage Ammonia Concentration and Temperature in a Rabbit Barn in Central Mexico

“…The experimental phase was carried out in a farm measuring 24 m long, 4 m wide, and 2.4 to 3.3 m high (Figure 1 The climate of the region, according to the Koeppen classification, is temperate humid or subhumid, subhumid prevailing, Cwb [29], with a mean annual temperature and humidity of 15.9 °C and 63.2%, respectively [30]. The hottest months are April, May, and June, with mean temperatures and relative humidity of 18.4 °C, 19.4 °C, 18.9 °C and 50.6%, 60.0%, 73.9%, respectively [27]. The facility had a total of 10 cages, each measuring 2 m × 2.4 m × 0.35 m, housing an average of 96 rabbits of a Californian breed in each cage for the purpose of meat production, maintaining a density of 20 rabbits mb −2 per cage (Figure 1).…”

“…The climate of the region, according to the Koeppen classification, is temperate humid or subhumid, subhumid prevailing, Cwb [29], with a mean annual temperature and humidity of 15.9 • C and 63.2%, respectively [30]. The hottest months are April, May, and June, with mean temperatures and relative humidity of 18.4 • C, 19.4 • C, 18.9 • C and 50.6%, 60.0%, 73.9%, respectively [27].…”

“…The boundary conditions (Table 2) were established based on previous work carried out in the same facility [27]. The values of temperature and wind speed and direction recorded by the climatic station outside the farm were used.…”

“…Computational fluid dynamics is governed by the Navier-Stokes equations, expressed in a group of partial derivatives as shown in Equation ( 1) [27,35].…”

“…Among the research studies that have been carried out using computational fluid dynamics are the following: in pig farms, air velocity analysis [11,12], temperature and heat stress studies [13,14], studies of ammonia emissions [15,16], and those focused on dust generation within the installations [3]; in cattle facilities, studies of heat transfer [17,18], ventilation rate [19], and extensive studies on air velocity and its influence on temperature, humidity, and heat transfer [20], as well as studies on the emissions of gases such as methane and ammonia, as well as CO 2 and N 2 O [1,7]; in bird houses, there have been studies that model the indoor climate and heat emissions [21][22][23] and simulations on air flow, temperature, humidity, and ammonia emissions [24][25][26]. However, in rabbit farms there have been few studies: one study performing simulations to determine the temperature gradient and ammonia concentration [27], and a study on the distribution of the air flow of the indoor environment in a rabbit facility [28].…”