A concept for reduced energy demand of greenhouses: the next generation greenhouse cultivation in the Netherlands

In high tech greenhouse cultivation like in The Netherlands, large amounts of fossil energy are used to optimize climate conditions like temperature and humidity. To achieve a more sustainable greenhouse horticulture, a considerable reduction in energy use is needed, but tradeoffs with production and quality are not acceptable. Therefore, we developed a novel cultivation system for tomato to meet the goal: reduction of the energy input by 40% from 1.3 to 0.75 GJ.m-2.y-1, maintaining a production level of 60 kg.m-2.y-1. This concept, the Next Generation Greenhouse Cultivation, is based on the intensified use of thermal screens combined with control of humidity, maximizing the use of the integration capacity of the crop, growing at high humidity, improved efficiency of CO2 supply by reduction of ventilation and the use of cooling combined with a heat pump and an aquifer. In this approach, the main element is the prolonged use of screens with a high insulating value (>70%) to reduce the energy demand, combined with a forced ventilation system that injects relatively dry outside air into the greenhouse. The maximal use of the integration capacity of the crop implies a strong relation between daily radiation sum and diurnal mean temperatures, and a large difference between night and day temperatures on sunny days. This reduces the energy input and ventilation rate. Growing at increased humidity, achieved by misting, reduces ventilation rates because of the increased enthalpy of the greenhouse air. When supplying CO2, reduced ventilation results in higher CO2 concentrations and hence a higher energy efficiency. Cooling can be used in combination with a heat pump and an aquifer to reduce the need for fossil fuel. This approach, in which proven technologies are combined, enables growers to implement the elements step by step, leading to an easy acceptance.