Convective and ventilation transfers in greenhouses, Part 1: the greenhouse considered as a perfectly stirred tank
In this paper, the characterization and modelling of the most relevant convective transfers contributing to the elaboration of the greenhouse climate are reviewed. Convective transfers include heat and mass transfers between air and solid surfaces (walls, roof, leaves) along with air, heat, water vapour and tracer gas transfers to or from the inside air. Adopting the assumption that the greenhouse is a perfectly stirred tank, the specific characterization methods associated with this approach are reviewed. The perfectly stirred tank approach requires the assumption of uniform temperature, humidity and CO2 content inside the greenhouse and uses a 'big leaf model to treat the plant canopy and describe the exchanges of latent and sensible heat with inside air. The simulation of the ventilation processes associated with this simplified approach is based on the Bernoulli equation and on the experimental determination of semi-empirical parameters by means of air exchange rate measurements. The techniques used to measure temperature and air exchange rates measurements pertaining to the whole greenhouse volume are presented. A complete panorama of the studies in relation to the transfer coefficients between the different surfaces together with the ventilation performances of various greenhouse types are also presented. This paper is the first part of a review of the convective transfers in greenhouses and in the second paper, a similar study based on the approach of the distributed climate is presented. (C) 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.