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The purpose of this study was to determine and compare the performances of conventional and heat pump systems for cooling open and closed loop (confined) greenhouse systems. A dynamic simulation model was developed and validated to predict energy and mass exchanges 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, CO2 enrichment, ventilation, variable shading, and the use of night curtains in open and confined greenhouse environments. Variable shading, ventilation and evaporative cooling provided cooling in the conventional system. In the heat pump systems, however, gas fired heat pump units provided cooling. Outputs of the simulation 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, transpiration, energy and CO2 use and fixation in the greenhouse. This study concluded that the heat pump system performed very well with a variable shading system meeting the cooling requirements of both open and confined greenhouse systems.

HEAT PUMP COOLING AND GREENHOUSE MICROCLIMATES IN OPEN AND CONFINED GREENHOUSE SYSTEMS