COVERAGE OF REJECT HEAT IN THE DUTCH GREENHOUSE INDUSTRY *)

In the Dutch greenhouse-industry energy is intensively used for heating the crops.
The major part of the growers uses one or more gasboilers to produce heat.
A small part uses reject heat in combination with a gasboiler.

The environmental policy plan aims at an improvement of the energy-efficiency and the CO₂-emission.
This can be realized by using reject heat.
A power station converts fuel into electricity.
Beside electricity heat can be produced.
The total-efficiency of the power station by the combined production of electricity and heat will be higher than by separate production.
The reject heat can be used in greenhouses.
Fuel saving is the result.

The reject heat has been used for a part of the heat demand in de greenhouse: called the base-load.
Next to it a gasboiler is used for the peak-load for the crop and the production of CO₂. The coverage is the percent of reject heat in the total heat demand.
The height of the coverage influences strongly the fuel-savings.

During a year a great number of measurements were done on 45 individual holdings to determine the coverage of heat on practice.

The results showed that de mean coverage per holding is 57%. The differences between the holdings are big and various from 25% to 100%.

The differences are caused by various factors.
These are:

• the capacity of the heat source

• the cooling down of the water which transports the reject heat (delta t_p (°C))

• the quantity of gas used for CO₂-enrichment

• the heat intensity (heat use per m²)

The practical meaning of the results are that an increase of the capacity and the delta t_p causes an increase of the coverage.
An increase of the quantity of gas used for CO₂-enrichment and heat intensity have a decreasing effect on the coverage.

European Seminar New Technologies for the Rational Use of Energy in Greenhouse Horticulture in Northern Europe

B.J. van der Sluis, K.R. Nawrocki

https://doi.org/10.17660/ActaHortic.1992.312.14