Articles
Quantifying energy saving by screens – the role of humidity transport
Article number
1426_66
Pages
479 – 486
Language
English
Abstract
The application of new energy saving cultivation techniques in Dutch greenhouses heavily relies on using one or more movable screens.
Screens affect greenhouse climate by thermal radiation, air and humidity exchanges between the lower and upper part of the greenhouse compartment separated by screens.
Thus, screens affect the sensible and latent heat exchange and therefore the insulation value of the greenhouse, they have an important role in energy saving.
The objectives of this project are to quantify screen properties by standardised measurements: thermal properties (transmissivity and emissivity for thermal infrared radiation), air transport properties (sensible heat losses) and humidity transport characteristics (latent heat losses). All energy flows around screen materials are analysed, the overall potential energy saving is then calculated dynamically yearround.
The project aims to quantify the energy loss through dry and wet screens materials with different properties with special emphasis on humidity transport and the consequences for humidity control by different control strategies.
Screen property measurement and energy calculation results are given for four materials.
It is shown that a single screen typically saves ~25-30% of energy compared to no screen in a tomato crop.
A screen with optimised properties having no/low air and humidity permeability and low TIR transmissivity and emissivity, can even save ~40%. An increasing humidity setpoint from 80 to 90% RH saves 40% more energy, using screens more intensively at the beginning and end of the day by increasing the closure setpoint from 0 to 50 W m‑2 saves 10-15%. Double/ triple screens add 25-40% energy saving compared to a single screen of the same material.
Results further show that highest energy savings can be reached with a triple screen with optimised properties, with high RH setpoints (90%), more screen hours (up to 100 W m‑2) and a mechanical dehumidification for humidity control.
Screens affect greenhouse climate by thermal radiation, air and humidity exchanges between the lower and upper part of the greenhouse compartment separated by screens.
Thus, screens affect the sensible and latent heat exchange and therefore the insulation value of the greenhouse, they have an important role in energy saving.
The objectives of this project are to quantify screen properties by standardised measurements: thermal properties (transmissivity and emissivity for thermal infrared radiation), air transport properties (sensible heat losses) and humidity transport characteristics (latent heat losses). All energy flows around screen materials are analysed, the overall potential energy saving is then calculated dynamically yearround.
The project aims to quantify the energy loss through dry and wet screens materials with different properties with special emphasis on humidity transport and the consequences for humidity control by different control strategies.
Screen property measurement and energy calculation results are given for four materials.
It is shown that a single screen typically saves ~25-30% of energy compared to no screen in a tomato crop.
A screen with optimised properties having no/low air and humidity permeability and low TIR transmissivity and emissivity, can even save ~40%. An increasing humidity setpoint from 80 to 90% RH saves 40% more energy, using screens more intensively at the beginning and end of the day by increasing the closure setpoint from 0 to 50 W m‑2 saves 10-15%. Double/ triple screens add 25-40% energy saving compared to a single screen of the same material.
Results further show that highest energy savings can be reached with a triple screen with optimised properties, with high RH setpoints (90%), more screen hours (up to 100 W m‑2) and a mechanical dehumidification for humidity control.
Publication
Authors
S. Hemming, V. Mohammadkhani, M. Raaphorst, F. de Zwart
Keywords
greenhouse, energy consumption, humidity control, air permeability, radiometric properties, emissivity, tomato
Groups involved
- Division Precision Horticulture and Engineering
- Division Greenhouse and Indoor Production Horticulture
- Working Group Nettings in Horticulture (subgroup of Protected Cultivation in Mild Winter Climates)
- Working Group Light in Horticulture
- Working Group Organic Greenhouse Horticulture
- Working Group Vegetable Grafting
- Working Group Modelling Plant Growth, Environmental Control, Greenhouse Environment
- Working Group Protected Cultivation, Nettings and Screens for Mild Climates
- Working Group Computational Fluid Dynamics in Agriculture
- Working Group Design and Automation in Integrated Indoor Production Systems
- Working Group Mechanization, Digitization, Sensing and Robotics
- Working Group Greenhouse Environment and Climate Control
- Division Landscape and Urban Horticulture
- Commission Agroecology and Organic Farming Systems
- Division Vegetables, Roots and Tubers
- Working Group Vertical Farming
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