Development of a biomass-based system for nocturnal temperature and diurnal CO2 concentration control in greenhouses

Abstract

Greenhouses are productive systems characterized by an intensive but efficient use of primary resources. Such processes can receive important energy contributions from renewable sources, thereby helping to reduce external fossil fuel dependence, increasing the added horticultural production value and improving sustainability. It is well known that CO2 enrichment increases the photosynthesis rates in plants thus reducing environmental contamination. However, in countries with mild climates, the utilization of heating and CO2 is reduced due to the cost of traditional systems, along with lower heating requirements. The proposed system is a biomass-based boiler with CO2 recovery from flue gases. The advantages are twofold: firstly, the cost savings from using chipper fuel as pellets for heating; secondly, from the carbon dioxide stored during combustion being supplied during daylight hours inside the greenhouse for CO2 enrichment. A prototype of this plant has been installed in the “Las Palmerillas” Experimental Station. The whole design process is laid out in this work. The different components were sized by looking at the greenhouse climate in terms of energy inlets. Notice that in both control processes (nocturnal temperature and diurnal CO2 concentration), energetic efficiency is improved by reusing greenhouse organic material (biomass) from agricultural/industrial wastes, and CO2 generated from the heating system. Various tests were carried out and preliminary controllers are proposed for the optimal behaviour of the full-scale system.