Semi-arid regions are frequently subject to major temperature changes during a 24 h period, which may drastically affect greenhouse indoor climates. In order to improve energy management of these buildings, numerical tools have been developed to predict the evolution of the inside climatic conditions. However, most of the available models neither take account of the transmittivity variation through the day nor of differences between wall temperatures. In the present paper, a model for predicting the thermal and water behaviour inside an unheated agricultural green-house is presented. The energy balance method is applied to each element: cover, indoor air and soil surface. Specific modules have been developed to calculate heat transfer coefficients for the cover of the greenhouse as well as heat transfer through the subsoil. These modules have been integrated in the TRNSYS environment. Radiative transfers and view factors were also calculated. The simulations predict two main parameters under transient conditions: the indoor air temperature and the indoor humidity in response to the outside conditions. These parameters were validated with fair agreement from experiments conducted in a monospan greenhouse located in Batna (6.11° E, 35.33° N). Based upon the results of the simulations and the measurements it was also concluded that firstly, the transmittivity was not constant in time and varied with surface orientation; and secondly, vertical surface temperatures were different during the daytime while the temperature difference between roof surfaces remained insignificant. The evolution of humidity was not correctly reproduced by the model, probably because the effects of condensation and variation of soil water content were not properly included in the equations.

Crop cultivation in greenhouses under semi-arid climatic conditions is subject to various stresses, in particular during the winter season at night, when the interior air is poorly controlled, leading to prolonged periods of low temperature. The aim is then to evaluate and control the heat exchanges of the enclosure in order to prevent low indoor air temperatures and reduce the thermal load of the greenhouse. The objectives of this study are to investigate the convective and radiative heat exchanges at the cover in order to establish new correlations for the convective heat transfer coefficients in semi arid regions. The climatic parameters were measured inside and outside a closed empty glasshouse without crop, for three different nights during the winter season in the semi-arid land of Algeria. A physical model for analysing the convective heat transfers was implemented, and new correlations were established, parameterised, calibrated and validated thoroughly. A significant difference was observed between the correlations obtained by this study and the models obtained for other greenhouse designs under different climatic conditions. Results show that the convection mode along the inside wall of the cover is free turbulent. Conversely, the convection mode along the outside greenhouse cover remains forced turbulent. A consistent performance of the correlations was observed, both in the calibration and validation stages.

Heat transfer by convection occurs in various domains such as atmospheric flows, exchangers, passive air conditioning, etc.…For example, in passiveair conditioning, theheat transfer rateat alateral wallof an enclosure can be enhanced if the surface is not flat. Indeed, it is well known that a rough surface allows increasing the heat transfer. Such rough surface can be obtained with the use of protuberances on walls. The purpose of this study is to investigate, numerically in 2D, the effect of rough surfaces at the vertical walls on heat and mass transfers in an enclosure. As boundary conditions, the vertical walls of this enclosure are subject to a uniform heat flux and horizontal walls are supposed to be adiabatic. The numerical modeling, used by us, is briefly described below. The rough surfaces are described as sinusoidal profiles which are transformed, using a homotopic transformation, into a flat plate. Governing equations are discredited using the finite volume method and the resolution is obtained by the THOMAS algorithm. The coupling of the velocity and pressure fields is achieved using the SIMPLE algorithm. The effect ofthe formofprotuberances, and the imposed heat flux at a vertical wall, on streamlines and temperature fields has been considered. The first obtained results are in agreement with previous experimental and numerical results, showing thus that our modeling is accurate. The first results are a validation of code are in agreement with previous experimental, numerical, and software Fluent showingthat our model is accurate

The aim of this work is to analyze the thermal performance of a greenhouse exposed to semi-arid conditions by investigating experimentally the heat transfers occurring through the walls and ground. A closed unheated Venlo greenhouse without crop in the area of Batna (southern Mediterranean basin) was considered. The study focuses on the effects of (i) the thermal inertia of the soil, (ii) the radiative losses through the cover, and (iii) the convection mode and flow regime on the heat transfer coefficients. Experiments were conducted from January to March 2008 under clear or cloudy skies, and low or high wind velocities. From the results, it is concluded that the heat stored in the ground of the greenhouse represents a significant heat source which can compensate the energy losses through the walls, especially during a night preceded by a high diurnal insulation. This process can maintain an average inside - outside temperature difference during the night within the range [1.59-2.81] K. Results also show that the radiation losses are the main component of the energy losses of the greenhouse, mainly through the outside wall surface of the cover. Conversely, the radiative heat exchange along the inner wall represents the main heat supply to this wall. The convection mode inside the greenhouse induced by the air movement seems to play a significant role on the convective exchange coefficient inside the greenhouse. These coefficients both inside and outside the greenhouse were estimated and analyzed, and a good agreement with the models reported in the literature was found. This study could help growers define and adapt their heating strategy to avoid undesired low temperatures which may damage their crops at night.