|Authors: ||I. Schuch, D. Dannehl, L. Miranda-Trujillo, T. Rocksch, U. Schmidt|
|Keywords: ||semi-closed, solar energy, heat pump, cooling, COP, collector efficiency|
2009 to 2014, the joint research program ZINEG is carried out in Germany.
Its main aim is to reduce the consumption of fossil fuels and hence the CO2 emissions up to 90% for production in greenhouses.
At Humboldt University the research is focused on using a greenhouse system as solar thermal collector with above-ground heat storage.
During the tomato production in 2011, a seasonal energy efficiency ratio (SEER) of 5.1 and a heating seasonal performance factor (HSPF) of 4.4 was achieved using an electrically-driven heat pump utilized for cooling and heating in the collector greenhouse.
Approximately half of the solar irradiation was stored into an insulated rainwater-tank.
This corresponds to 1.76 GJ/m2. Twenty percent of this solar energy was collected by condensation (originally latent heat) on finned pipes in the roof zone.
For heating the collector greenhouse, about 0.53 GJ/m2 of the stored heat was re-used.
That means that additional heat might be exported or the cooling surface area can be reduced to one-third.
Furthermore, the solar thermal collector greenhouse achieved a primary energy consumption of 147.6 MJ/m2 (considering a full re-use of the stored heat). Simultaneously, the conventional greenhouse achieved a primary energy consumption of 767.1 MJ/m2. That means that the consumption of non-renewable energies (fossil fuels) is reduced up to 81% with the collector system.
In further studies an economic assessment regarding energy-saving in semi-closed greenhouses should be performed to estimate the potential of such facilities.
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