Humidity control for swine buildings in cold climate - Part I : modelling of three control strategies

Lambert, M., Lemay, S.P., Barber, E.M., Crowe, T.G. and Chenard, L. 2001. Humidity control for swine buildings in cold climate Part I : Modelling of three control strategies. Canadian Biosystems Engineering/Le genie des biosystemes au Canada 43: 5.29-5.36. A steady state computer model has been developed to evaluate the benefits of temperature-humidity control (THC) systems over temperature control (TC) systems in swine buildings under coldclimate conditions. This model simulated a full-scale grower/finisher pig room, commercial equipment, and control systems. The comparison of heating/ventilating control systems was based on average temperature, energy demand, and fluctuations of relative humidity (RH) and carbon dioxide (CO2) concentrations. For THC systems, proportional (P) and proportional-integral-derivative (PID) controls were simulated. Based on simulation results, a TC system provided effective RH control, as long as the minimum ventilation rate was adequately set and adjusted throughout the growth period. In THC control, decreasing the setpoint from 80 to 70% RH doubled energy requirements. Overall, PID control, compared to P control, provided a lower relative humidity and CO2 concentration. However, differences were less than 2.5% and the energy required was higher. Simulations indicated that the optimum strategy would be THC with P control, a 75% RH setpoint, and a proportional band of 5% RH. Un modele informatique en regime permanent a ete developpe dans le but d’evaluer les avantages d’un systeme de controle de la temperature et de l’humidite (THC) comparativement a un systeme de controle de la temperature (TC) dans les porcheries sous des conditions de climat froid. Ce modele simule une chambre de croissance-finition munie d’equipements commerciaux et de systemes de controle. La comparaison des systemes de controle, THC et TC, a ete basee sur les resultats obtenus pour la temperature moyenne, la demande energetique, l’humidite relative (HR) et la concentration de CO2. Pour les systemes THC, des controles proportionnel (P) et proportionnelintegral-derive (PID) ont ete simules. Les resultats de simulation ont montre que le systeme TC fournit un controle efficace de la HR si l’on considere que le taux de ventilation minimal est integre au controleur adequatement et qu’il est ajuste pendant la periode de croissance. Pour le controle THC, lorsque la valeur de consigne est abaissee de 80 a 70% HR, les besoins energetiques pour le chauffage sont doubles. De maniere generale, pour une meme consigne de HR, le controle PID a maintenu l’humidite et les concentrations de CO2 a des niveaux plus bas comparativement au controle P (difference de moins de 2,5 %) tout en ayant des besoins energetiques plus eleves. Selon les resultats de simulation, la strategie de controle optimale est la THC, avec l’utilisation d’un controleur P programme pour maintenir une consigne de 75% HR avec une bande proportionnelle de 5%. INTRODUCTION