Heat pump assisted drying of flower bulbs

Within the agriculture sector, drying of food and flowering products is a required production step. Most companies use hot air dryers where the heat is obtained by combustion of natural gas. This paper proposes a heat pump assisted drying system as an alternative. Flower bulb carrying boxes containing just harvested products have been approximated as packed beds filled with spherical products. A heat pump is proposed which includes a cross flow heat exchanger and allows for recirculation of the drying air while maintaining its operating temperature and humidity at optimal conditions to guarantee the required drying rate while preventing damage of the product. Simulink is used to optimize the operating conditions of the system guaranteeing both the product quality and a low energy consumption. The heat pump has been sized to dry 10 flower bulb carrying boxes of about 800 kg each in 24 hours. The performance of the heat pump (170 kWh/day renewable electricity) is compared to the performance of conventional fossil fuel based drying systems (350 kWh/day fossil fuel). Understanding heat and mass transfer mechanisms during drying allows optimization of the heat pump design.