Simulation of the energy balance of a greenhouse
1973
Kimball, B.A.
The energy balance of a greenhouse was simulated with a digital computer program. The fluxes of solar radiation were calculated from sun angle equations and the optical properties of the greenhouse walls and vegetation. The thermal radiative, sensible, latent, and conductive heat fluxes were modeled by mathematical equations in terms of unknown temperatures and vapor pressures. Provision was made for the introduction of externally imposed heating or cooling fluxes. Energy balance equations were then developed for various locations in the greenhouse where the sum of the fluxes at that location should be zero. The equations were solved by an iterative procedure to obtain the unknown temperatures and vapor pressures. Measurements of temperatures and radiation fluxes were obtained in a glass greenhouse to provide physical data with which to compare values predicted by the model. The greenhouse was alternatively: (1) evaporatively cooled and not shaded, (2) not cooled and not shaded, and (3) cooled and shaded, each treatment lasting one day. The observed and predicted values agreed closely for each of these extremely different treatments. It is concluded that the model can accurately predict the heating and cooling requirements of a greenhouse for a wide range of greenhouse properties and environmental conditions.
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