Greenhouse Thermal Effectiveness to Produce Tomatoes Assessed by a Temperature-Based Index

Abstract

This study proposed an indicator to calculate the regional thermal potential from the local temperature. A probabilistic function curve generalized as a complementary error function (erfc) was used to assume the temperature curve follows the normal distribution and considered only the portion of the curve where the appropriate temperatures for the crop are located (wi). The Greenhouse Thermal Effectiveness (GTE) index was calculated using (a) the data of measured temperature (outside) and simulated values from inside of the greenhouse, and (b) the normal temperature data from five meteorological stations. Estimations of GTE using average daily temperature (°C) throughout the year indicate that, with an annual mean temperature of around 14 °C, the GTE is 2798 degree units and inside the greenhouse its value goes up to 5800. May is when the highest temperatures occur and when the highest amount of GTE units can be accumulated. The range of temperatures in the analyzed stations were from 13 to 21 °C and the GTE calculated per year was from 2000 to 7000. The perspective will be to calculate if this energy will be enough to grow tomatoes (or other crops) without extra energy for heating or cooling. If more energy may be needed, estimating how much would be the next step.

Keywords

• computational fluid dynamics
• greenhouse heat requirements
• heating degree day
• greenhouse energy use