IMPROVED HEATING TECHNIQUES FOR GREENHOUSES USING LOW EXERGY FROM REJECT HEAT SOURCES

In the mid-1980s, 66 ha of greenhouses were built close to a power station with a cooling tower in the Cologne area, Germany.
Since then, reject heat has been used to operate them, so as to profitably cultivate tomatoes, cucumber and floriculture plants.
Unfortunately, the energy costs have increased throughout the years.
In order to minimize those costs, a feasibility study has been conducted to project a new horticultural park for reject-heat-operated greenhouses.
As the best solution, this study has found that 30 ha of greenhouses should be connected to the cooling towers of an improved power plant fuelled by brown coal.
The heating equipment has been redesigned for the new greenhouses to reduce the electrical charges for the direct-heat distribution of the 26°C water flow.
The heat-generation costs are calculated as follows: capital expenditures for heating pipelines, and capital expenditures for enlarged heating systems in the greenhouses, plus the running cost for pumps and fans.
The rejected-heat utilization has been compared on economic basis to different heating techniques, such as conventional light oil, natural gas, or hard coal burning, and different heat pump configurations.
Next, the primary-energy efficiencies of these techniques and the greenhouse gas emissions have been quantified.
The use of reject heat by a direct use of low-temperature water in enlarged air heaters has turned out to be the most favourable of all assessments.
Now only the infrastructure of the market and the enormous capital expenditures for large new greenhouses with heat supply are keeping the German growers from its realization.

International Symposium on High Technology for Greenhouse System Management: Greensys2007

B. von Elsner

low-temperature heating, waste heat, heat pump, heat generation costs, primary energy efficiency, greenhouse gas emission, cumulated energy demand

https://doi.org/10.17660/ActaHortic.2008.801.82