Hourly model for predicting year-round temperature and relative humidity of the environment in laying hen houses

Abstract: Laying hen house is an important part of livestock industries, particularly with an intensification scale of over 70% in China. Appropriate indoor temperature and relative humidity are also critical to the health of birds, production performance, and egg quality, further fully exploiting the excellent genetic features of modern laying hens. An automatic control system is, therefore, necessary to precisely predict the dynamic changes of indoor temperature and relative humidity for laying hen houses. An evaporative cooling pad system is the most popular used to increase the accuracy of the prediction model in laying hen houses in summer. However, most currently-used prediction models usually fail to consider the cooling variation of the evaporative cooling pad system. Particularly, it is also lacking to consider the humidified impact on the indoor temperature and relative humidity in laying hen houses. In this study, a novel hourly model was created to predict the annual indoor temperature and relative humidity, as well as its variation in laying hen houses. A mathematical model of cooling efficiency was also adopted to consider the quantitative influence of the evaporative cooling pad system on the indoor thermal and humid environment. A field experiment was then conducted to verify the model in Handan, Hebei Province of China in July 2019. Twenty-six points of indoor temperature and relative humidity were set for the field measurement. A hot-wire anemometer was utilized to monitor the airflow rate of exhaust fans. Meanwhile, an outdoor meteorological station was installed on the roof to continuously record the climatic parameters. Moreover, two cases were carried out in Wuhan City and Harbin City of China to evaluate the performance of the prediction model, thereby analyzing the influence of different climate conditions on the indoor environment of laying hen houses. Finally, the prediction model was used to clarify the difference of heat transfer in the steady and dynamic state for the building envelope on the indoor thermal and humid environment of laying hen houses. The accuracy of the prediction model was obtained between the constant and variable evaporative cooling efficiencies. The results demonstrated that the predicted values of indoor temperature and relative humidity were consistent with the field measured ones. Specifically, the overall average error of indoor temperature was 0.67 ℃, and the average error of indoor relative humidity was 3.1%. It was found that there was no temperature delay in summer and only one hour delay in winter. Temperature attenuation presented 0.36 ℃ in summer and 1.02 ℃ in winter, indicating a negligible effect due to the thermal inertia of the enclosure. The variation of dynamic cooling efficiency was contributed to the higher accuracy of the prediction model in the evaporative cooling pad system. For example, the predicted error of temperature reduced from 1.4 ℃ to 0.67 ℃, and the error of relative humidity from 5.4% to 3.1%, when the cooling efficiency was fixed at 80%. Consequently, this finding can provide potential theoretical guidance for building design and thermal environment control of laying hens houses, and further improve the production performance of laying hens.