Determination of maximum ventilation and evaluation on the performance of the cooling system for commercial pig houses in different climate zones

Abstract: Ventilation systems can move the stale air out of the building and draw the fresh air in, serving to preserve the optimum living conditions. It can be widely recognized as an effective way to relieve the strong impacts of heat stress on the health and behavior of pigs under the ventilation systems of a house in summer. The maximum ventilation of pig houses can often be assumed to design the ventilation systems. A cooling pad system with high performance has also been widely used in pig houses in China. However, the cooling performance of the pad system can be significantly reduced under a high humid environment, particularly for the diverse climate types. Furthermore, a variety of environmental factors can lead to the different performances of ventilation fans and cooling pad system under specific climatic conditions over the large geographical regions of China. A reasonable configuration of fans and cooling pad systems is very essential to the climate control for the pig houses in summer. In this study, a novel VBA model of the maximum ventilation and cooling pad operation was developed to predict the indoor environment under different climate types and operating conditions using the CIGR energy and mass balance. According to the 'Code for Thermal Engineering Design of Civil Buildings', the typical cities were selected as the study areas from different climate zones of China, including Changchun (severe cold), Beijing (cold), Wuhan (hot summer and cold winter), Nanning (hot summer and warm winter), and Guiyang (mild). The environmental data of five cities were collected from the weather database. A pig house in a dimension of 110 m×15 m×3 m was set up as a model case. Firstly, a systematic analysis was made to determine the ratio of heat transfer to the ventilation and heat dissipation of the envelope structure. Then, a relationship equation was established for the maximum ventilation and the heat dissipation under various ventilation rates in commercial pig houses. Five parameters were finally selected to evaluate the performance of the cooling pad system with the maximum ventilation in the study areas, including the duration of the cooling pad system, the duration at the indoor temperature above 27 ℃, the proportion of time below 27 ℃, the average decrease of temperature, and the average increase of the relative humidity, after the cooling pad system. The results showed that the building envelope presented less effect on the heat exchange in the pig houses when the outdoor temperature reached 30℃. The sensible heat production of the pigs was almost equal to the ventilation and heat dissipation. Therefore, the maximum ventilation rate was closely related to the sensible heat production of the pig herd. The operation time of the cooling pad system was longer than that in the nursery, according to the indoor prediction using the VBA model. There was a similar tendency on the duration of indoor temperature higher than 27 ℃ with the cooling pad system. The duration of the cooling pad system was ranked in the order of Nanning>Wuhan>Beijing>Guiyang>Changchun. The duration of indoor temperature higher than 27 ℃ with the cooling pad system was ranked in the order of Nanning> Wuhan> Beijing > Guiyang> Changchun. The average decrease of temperature after the cooling pad system was ranked as Beijing> Changchun> Wuhan> Nanning> Guiyang, while the average increase of relative humidity was Beijing> Changchun> Wuhan> Nanning> Guiyang. The proportion of time at the indoor temperature below 27 ℃ was Changchun> Beijing> Guiyang> Wuhan > Nanning. Therefore, the temperature of the pig house with the cooling pad system was basically lower than the high-temperature limit in Changchun, Beijing, Guiyang, but additional cooling was still necessary for Nanning and Wuhan. Different operation schemes were also recommended for the cooling pad systems in five major climate zones. The finding can provide a strong reference to predict the summer microclimate in commercial pig houses with the cooling pad systems.