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Thermal energy use in greenhouses

the influence of climatic conditions and dehumidification

Maslak, Katarzyna (2015). Thermal energy use in greenhouses. Alnarp : Sveriges lantbruksuniv.
ISBN 978-91-576-9289-4
eISBN 978-91-576-9290-0
[Licentiate thesis]

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Abstract

In the North European greenhouses, energy use for climatization accounts for a significant share of the operational costs. Air temperature and humidity are important factors whose control is crucial for assuring high productivity and limited use of energy.

The objective of this thesis was to examine the use of thermal energy in greenhouses and to investigate the impact of a number of climate parameters on that use. A specific goal was to compare the measured use of energy for heating with the values simulated employing a model developed in Powersim software and, by means of the model, to determine the amount of energy necessary for dehumidification of a tomato greenhouse. Another specific goal was to employ the experimentally obtained performance values for a rotary heat exchanger to estimate the potential energy savings when heat exchanger is used for dehumidification of a greenhouse.

Indoor and outdoor climate data were collected in three greenhouses located in southern Sweden, two with tomatoes and one with ornamental plants. The use of thermal energy in a tomato greenhouse was first measured and then modelled in Powersim for different levels of transpiration, i.e. for a leaf index area (LAI) of 3.5 and 4.0 m²/m². The impact of wind under no-sunlight conditions and at different outdoor temperatures was investigated. The performance of the heat exchanger operating at high humidity levels was tested in a series of measurements.

The study showed that the use of thermal energy in greenhouses with tomatoes was significantly higher than in the greenhouse with ornamental plants. Further, the amount of energy used increased together with the wind speed. The reduction of the wind speed by 50% could result in energy savings of 4-10%. The use of thermal energy as obtained in the Powersim simulations was fairly similar to the measured values, especially when the modelling was for higher transpiration levels. However, it was concluded that further work on the model is needed. The simulations indicated that 23-29% of thermal energy in a greenhouse was used for dehumidification purposes. It was experimentally shown that thermal and moisture efficiencies of the heat exchanger employed in the study were about 70% and 45%, respectively. Further, it was found by modelling that the usage of such a heat exchanger in the investigated greenhouse resulted in the energy savings of 15-17%.

Authors/Creators:Maslak, Katarzyna
Title:Thermal energy use in greenhouses
Subtitle:the influence of climatic conditions and dehumidification
Year of publishing :March 2015
Number of Pages:68
Papers/manuscripts:
NumberReferences
IMaslak, K. & Nimmermark, S. (2014). Thermal energy use in three Swedish greenhouses – the outdoor temperature-dependent variation and the influence of wind speed under no-sunlight conditions. Agricultural Engineering International: CIGR Journal, 16(3), 43-54.
IINimmermark, S. & Maslak, K. (2014). Measured energy use in a greenhouse with tomatoes compared to predicted use by a mechanistic model including transpiration. Agricultural Engineering International: CIGR Journal. (Accepted 2014-11-28).
IIIMaslak, K. & Nimmermark, S. (2015). Modelling and simulation of thermal energy use in a greenhouse – dehumidification by ventilation and heat exchange. (Manuscript).
Place of Publication:Alnarp
Publisher:Department of of Biosystems and Technology, Swedish University of Agricultural Sciences
ISBN for printed version:978-91-576-9289-4
ISBN for electronic version:978-91-576-9290-0
Language:English
Publication Type:Licentiate thesis
Full Text Status:Public
Agris subject categories.:F Plant production > F01 Crop husbandry
P Natural resources > P05 Energy resources management
Subjects:(A) Swedish standard research categories 2011 > 2 Engineering and Technology > 201 Civil Engineering > Building Technologies
(A) Swedish standard research categories 2011 > 2 Engineering and Technology > 207 Environmental Engineering > Energy Systems
Agrovoc terms:greenhouses, energy consumption, lycopersicon esculentum, ornamental plants, humidity, humidity control, heating, temperature, models
Keywords:greenhouses, energy use, humidity, dehumidification, modelling
URN:NBN:urn:nbn:se:slu:epsilon-e-2543
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-e-2543
ID Code:12037
Faculty:LTV - Fakulteten för landskapsarkitektur, trädgårds- och växtproduktionsvetenskap
Department:(LTJ, LTV) > Department of Biosystems and Technology (from 130101)
(VH) > Department of Biosystems and Technology (from 130101)
Deposited By: Katarzyna Maslak
Deposited On:07 Apr 2015 11:11
Metadata Last Modified:14 Apr 2015 21:54

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