No abstract

Crop drying, especially maize drying, occurs at low external air temperatures, which are lower than the extract air temperature. Therefore, using heat exchangers, to recover thermal energy from the extract air to preheat the cold and dry external air, results in a significant reduction in the primary energy demand for crop drying. The measurements of air parameters in the crop dryer, with a drying capacity of 19 Mg/h of maize, confirm the assumptions undertaken for the production of the heat recovery system. We apply the cross-counter-flow surface heat exchanger system to provide a significant improvement in the efficiency of crop drying. We perform the analysis of the thermal energy recovery system operation. Our results indicate the influence of the drying air set-point and the crop specific humidity on the efficiency of energy recovery from the exhaust air. We performed our measurements at different drying air temperature set-points and different crop relative humidity.

Abstract. Under certain conditions, a HVAC system may consume less energy, provided that the initial response to the increasing heat gains is the increase in the airflow, while cooling is delayed. This ensures that the energy for cooling and reheat is reduced, while the fan power increases. Note that it is difficult to develop the following approach in the standard sequential control algorithms. On the other hand, the use of more complex algorithms than standard sequential algorithms is generally not encouraged because of the increase in the complexity of the control system and its resistance to respond to the varying parameters of a HVAC system. In this work, therefore, to avoid the following complications, the Intake Power Optimization algorithm is proposed. The Intake Power optimization algorithm is compared to the two sequential algorithms: Air conditioning and Airflow priority. To create the reference point enabling comparisons of the three strategies, the optimal control was established using the Nelder-Mead method. It is shown that the Intake power optimization algorithm provides a better control than the sequential algorithms and almost exclusively performs the optimal control actions. As an aside, the results indicate that the same heat gains, however, evenly distributed between rooms may contribute to the significant reduction of the energy demand.

Past experiences of excess energy consumption and malfunctioning controls introduced prejudice when considering dual-duct ventilation systems during design stages. Modern technologies, however, can be used to improve performance and control of dual-duct systems, thus making these a sensible and safe design option. In the paper, we discuss challenges associated with setting the warm and cold supply air temperatures and how these set-points affect the airflows. We present limitations in temperature settings, due to instantaneous room thermal conditions and the individual design temperature requirements. Portions of warm and cold air (the ratio of these in the ventilating airflow) affect the transport costs of ventilating airflow. In many cases, rational control of warm and cold air temperature set-points, in a yearly cycle, enables distribution of similar portions of warm and cold air within the system. Even airflows in warm and cold air installations minimise the overall flow resistance, so that the air transport costs are minimal. Simultaneously, apart from minimising the energy for air transport, the primary energy demand for air treatment should be controlled and minimised.