Dynamic Modeling of Microclimate and Environmental Control Strategies in a Greenhouse Coupled with a Heat Pump System

The purpose of this study was to develop and validate a dynamic simulation model to be employed in accurate prediction of microclimate in a greenhouse as a function of dynamic environmental factors. The model has options to evaluate the effects of location, time of the year, orientation, single and double polyethylene glazings, conventional and heat pump heating and cooling systems, open and confined greenhouse systems, CO2 enrichment, variable shading, and the use of night curtains. Conventional gas furnace and evaporative cooling, respectively, provided heating and cooling in the conventional system. In the heat pump systems, gas-fired heat pump units provided both heating and cooling. The heat pump systems were operated both as an open and a completely confined system. Outputs of the simula­ tion model included both temporal and vertical distribution of air, leaf, floor and cover temperatures, CO2, relative humidity, solar radiation, and photosynthetically active radiation in addition to the dynamics of photosynthesis, respiration, transpira­ tion, energy and CO2 use and fixation. Comparison of experimental and predicted results showed that the compared microclimatological parameters were in fairly good agreement. The greenhouse model developed in this study is useful for ecologists, plant scientists, and engineers to evaluate individual or combined effects of various forcing functions on the enclosed environment and plant responses; and to develop control strategies for different parameters. INTRODUCTION Accurate prediction models for greenhouse and plant growth performance can be used as a design tool and in economic feasibility analyses as well. A dynamic analysis is required for more accurate prediction and control of greenhouse thermal environments. In addition to experimental tests, efforts have been made to predict the greenhouse environment under both steady state and transient conditions. Some reported work on greenhouse models and thermal performance tests include the work of Chandra et al. (1981), Glaub and Trezek (1981), Kindelan (1980), Navas et al. (1998), Pita and Vargues (1998), and Rijsdijk and Hauter (1993). The purpose of this study was to develop and validate a dynamic simulation model to be employed in accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors such as solar energy, outside temperatures and moisture levels, plant moisture and energy exchanges and heat removal or storage. This article deals with the model development, validation and preliminary simulation results.