**6.4 Multi-span glass greenhouses**


The ratio between the glass (cooling) surface and the multi-span greenhouse total volume is such that can cut the heating costs, but are hard to ventilate through vents (windows). In such cases, it is necessary to install a special ventilation system (including fans as well) that allows good indoor air exchange and circulation (**Figure 2**).

#### **Figure 1.**

*The 21st century multi-span greenhouses with a clearly defined road network and the meticulously kept weedless lawns (The Netherlands).*

#### **Figure 2.**

*Multi-span greenhouses, ancillary structures, and a weather station on one of the production complex ancillary buildings (Serbia).*

A modern greenhouse weather station usually consists of instruments that in regular intervals measure some of the weather parameters that are significant for the greenhouse crop production. Such instruments may include an anemometer, a wind vane, a thermometer, a hygrometer, a barometer, then sensors for measuring rainfall, solar radiation (direct and diffuse solar radiation). The obtained data are used locally for arranging the greenhouse production. Also, the data can be sent, in a special computer format, to the World Meteorological Organization (WMO) to help build a model for weather forecasting all over the world. WMO is a specialized UN agency and is dedicated to international collaboration and cooperation between the countries in terms of climate conditions control on this planet of ours, as well as making a model for the horticultural production monitoring and control.
