Performance assessment of a heat pump and a concentrated photovoltaic thermal system during the wood drying process

Abstract

Wood drying is an unavoidable step to bring to the market products with higher added value. Achieving drying under certain economic conditions requires calculating the drying cost with great precision while minimizing energy consumption. Conventional dryers with very high heating power are useful, but their energy consumption and greenhouse gas emissions remain too high. This work aims to propose a water/air heat pump powered by a concentrated photovoltaic thermal as a new hybrid solution for carrying out the drying process of softwood. The drying system consists of four main units, a drying chamber, a Closed Feed Air Heater, a water/air heat pump and a concentrated photovoltaic thermal. The study is based on the establishment of energy and mass balances in the drying system. The governing equations of the drying model are solved using the finite difference method. A perfect agreement is obtained between experimental and numerical results. The results show that the electrical energy consumption ratio using a heat pump as the main heater device fluctuates between 29 and 52 kWh.m−3. The coefficient of performance also ranges from 3.91 to 7.2. The results show that a decrease of the heat pump set temperature from 75 to 65 °C improves the coefficient of performance at least 17%. The combined use of heat pump and concentrated photovoltaic thermal system has the effect of reducing the energy consumption ratio up to 86%. The effect of parameters such as optical efficiency, concentration ratio and evaporator air temperature on drying performance is investigated. The results show that the heat recovered at the Closed Feed Air Heater increases as the temperature of air leaving the dryer increases. A decrease in optical efficiency from 0.9 to 0.65 increases the electrical energy consumption ratio by 73%. An increase in the aperture area from 100 to 150 m2 also improves electricity production and drying capacity by 45 and 27%, respectively. The drying capacity has known an increase of about 43% by increasing the mass flow rate from 0.6 to 1 kg.s−1. Finally, the combined use of a heat pump and a concentrated photovoltaic thermal can reduce significantly the electrical energy consumption and improve thermal performance of drying systems throughout the year.