# Computational Modeling of the Thermal Behavior of a Greenhouse
## 4 Conclusions  
The results obtained from the simulation model developed in this paper have shown the effectiveness of EnergyPlus and DesignBuilder in assessing the thermal behavior of a greenhouse, as the air temperature inside the greenhouse followed a similar overall pattern when subject to approximately the same outside weather conditions. The case studies showed that the reference case configuration presents better thermal behavior for the same floor area. In the worst case, case study 3, the reduction in indoor air temperature goes from around 5 \({}^{\circ}\)C in January to 8 \({}^{\circ}\)C in July. Additionally, the east-west orientation allows a slight increase of the indoor air temperature by around 0.8 \({}^{\circ}\)C in January and reduction in July by around 1 \({}^{\circ}\)C. The number of greenhouse air changes per hour affects the indoor thermal conditions. The results for 15 January show that increasing the outdoor air input results in lower temperatures during the day, reaching an air temperature difference of 6.5 \({}^{\circ}\)C between the 0.2 ac/h case (reference case) and the 5 ac/h case. During the night, there is a reduced impact of the airflow rate on the variation of the temperature inside the greenhouse, due to the proximity between the indoor and outdoor temperatures. Better insulation, through lower emissivity covering material and usage of multiple layers of covering material, is capable of greatly increasing the greenhouse's solar energy absorption, resulting in much lower heating demands in colder regions and during the winter season. A three-layer cover solution of polyethylene film with an air gap of 13 mm allows obtaining the highest temperature of the greenhouse indoor air throughout the year, surpassing the reference case with a simple cover by 3.5 \({}^{\circ}\)C in January and 7.3 \({}^{\circ}\)C in July. The indoor air temperature of the greenhouse increases as well, reaching 2.9 \({}^{\circ}\)C in January and 5 \({}^{\circ}\)C in July, when the emissivity of the cover is reduced to 0.1 in relation to the reference case. The usage of a granite north wall can result in a considerably more constant temperature inside the greenhouse, due to its high thermal mass, although the sizing of this wall should be balanced with a careful airflow rate to limit the maximum air temperatures reached. In January, the minimum indoor air temperature of the greenhouse, reached at 08:00, is 3.6 \({}^{\circ}\)C above the reference greenhouse and 6.3 \({}^{\circ}\)C above the outdoor temperature regardless of the thickness considered for the wall. However, the July values show that the wall thickness affects the minimum and maximum values of the indoor air temperatures by about 2 \({}^{\circ}\)C when the wall thickness increases from 40 to 100 cm. If the aforementioned changes are introduced together in the greenhouse, the results for two locations with very different characteristics, Lisbon and Ostersund, show that a greenhouse located in Lisbon requires about three times less energy consumption to achieve the same indoor thermal conditions in January. Furthermore, the changes introduced allowed the energy consumption for the month of January to be reduced by 57% in Lisbon and by 43% in Ostersund with respect to the reference greenhouse. Conceptualization, P.D.S. and L.C.P. ; methodology, P.D.S. ; validation, P.D.S., L.C.P. and B.L. ; formal analysis, P.D.S. and B.L. ; investigation, P.D.S. and B.L. ; resources, P.D.S., L.C.P. and P.D.G. ; writing--original draft preparation, B.L. ; writing--review and editing, P.D.S., L.C.P. and P.D.G. ; visualization, P.D.S. and B.L. ; supervision, P.D.S. ; project administration, P.D.S., L.C.P. and P.D.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data used to support the findings of this study are available from the corresponding author upon request. P.D.G. and P.D.S.