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The Greenhouse as a Solar Collector
The Integrated Greenhouse project is designed to make the most efficient use of the Green Greenhouse as a solar collector.
As with all glasshouses, over the course of the day, the Green Greenhouse will warm up naturally as it traps the heat of the sun. Radiation waves from the sun are short and pass through glass with ease. However, after heating surfaces in a greenhouse these convert into long wave radiation, which cannot easily travel back through the glazing. Consequently, an increasing volume of solar radiation is trapped within the greenhouse and it warms up inside. This process is called passive solar collection. It heats surfaces inside the greenhouse, such as rocks, concrete or volumes of water during the day and these release their stored heat back into the greenhouse at night.
Averaged out over the course of a year, a greenhouse will gain more than enough heat for its needs. But, as the level of solar radiation reaching a greenhouse fluctuates across the year, with the majority concentrated during summer months, much of this annual heat is traditionally released via ventilation during the summer, to keep internal temperatures at an appropriate level. In contrast, during the winter and overnight a greenhouse does not collect or store enough heat, particularly for exotic species or commercial horticulture, so additional energy sources (usually in the form of fossil fuels) are required to heat the greenhouse at these times.
To make best use of the seasonal fluctuation in solar collection and reduce reliance on fossil fuels, the Green Greenhouse is being constructed in conjunction with a Vertical Soil Heat Exchanger (VSHE). The VSHE system will harvest excess summer heat arising from solar gain, thereby cooling the greenhouse on warm, sunny days, and will store this for seasonal and overnight heating of the greenhouse and associated building spaces.
The amount of heat passively collected by the Green Greenhouse over the course of a year will vastly exceed the quantity required by the Integrated Greenhouse buildings complex during winter months and overnight. As such, only a proportion of the excess solar gain will be stored within the ground source system (sufficient to supply heating needs) and ventilating windows will be required to maintain optimum greenhouse temperatures. The use of shading screens to reduce solar collection will render one-side, top-roof ventilation sufficient for this purpose.
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