A.J. Both, E. Reiss, D.R. Mears, W. Fang
Design of greenhouse environmental control systems are typically specified to meet anticipated extreme weather conditions. The control strategy will typically operate the equipment to maintain specified set points. For a heating system that has adequate maximum capacity and a modulated rate of heat delivery, the set point will be closely tracked. Similarly, a modulated cooling system can closely track set points until ambient temperature and radiation conditions exceed the total capability of the cooling system. A shade system, with no precise modulation of shade level, will cause crop canopy light levels to vary between set points. Multiple layers of shade material that are independently controlled can reduce, but not eliminate variability. A simple spreadsheet simulation can be a useful tool for design. The database needed is an hourly record of dry bulb temperature, wet bulb temperature and solar radiation. Using the database, the design parameters of the greenhouse, and its environmental control systems, internal conditions can be calculated for each hour. The deviations of achieved conditions from desired set points can be evaluated both in terms of magnitude and frequency. This is of particular interest in selecting a shading system for a crop where control of light level at the crop canopy as well as crop temperature is important. A single shade system will over shade the crop whenever solar radiation is under the maximum design point but over the initial closing set point. This over shading can be significantly reduced by having multiple independent shade systems that will provide finer control. A number of possible designs for a greenhouse and environmental control system to grow orchids in central New Jersey and Taiwan have been evaluated. The results provide the designer with information on the impact of design options on the predicted performance over the entire growing season or year.
Both, A.J., Reiss, E., Mears, D.R. and Fang, W. (2005). DESIGNING ENVIRONMENTAL CONTROL FOR GREENHOUSES:. Acta Hortic. 691, 807-814
DOI: 10.17660/ActaHortic.2005.691.99
cooling, evaporative cooling, greenhouse, heating, shading

Acta Horticulturae