Greenhouse With an Integrated Nir Filter and a Solar Cooling System

Abstract

The scope of this paper is a new greenhouse design that incorporates both a filter for rejecting near infrared radiation (NIR) and a solar cooling system. Cooled greenhouses are an important issue for the combination of high global radiation and high outdoor temperatures. As a first measure, this study prevents heat entering the greenhouse by applying a NIR-reflective cover material. The special spectral selective properties of these materials will block up to 50% of the outside solar energy from entering the greenhouse, which will reduce the cooling capacity required. The second measure is the introduction of a solar driven cooling system. When the NIR reflecting coating is designed as a parabolic or circular shaped reflector integrated in the greenhouse, the reflected solar energy received by a PV cell at the focus delivers sufficient electric energy to drive a fan and pad cooling system. The excess energy can be used for desalination and/or energy supply. Parameters related to typical climate conditions and energy flows are presented. INTRODUCTIONIn the northern countries, with colder winter climate conditions, energy saving is an important issue. Moreover during summer cooling is needed by natural ventilation to remove excess energy. In the southern countries with higher global radiation and higher outdoor temperatures during summer, cooling of greenhouses is even more important (Stanghellini, 1987). With the novel greenhouse design presented in this paper, cooling can be combined with energy supply. First developments applying linear Fresnel lenses were presented by Jirka et al. (1999) and Tripanagnostopoulos et al. (2004). Fraas et al. (2001) presented an illumination system with glass fibres. A schematic setup of the new design with a spectral selective mirror is depicted in Fig. 1. The advantage of this system is a very homogeneous and high illumination level in the greenhouse. The basic setup is an integrated NIR filter with a parabolic or circular shape that will focus the NIR radiation. First of all, it will prevent high radiation load during a period with high outdoor temperatures. Secondly, the focused radiative energy can be transformerd into electrical energy. This can be used, for example, for cooling the greenhouse with a pad and fan system and/or can be supplied for external use.

Greenhouse Cooling by Nir-Reflection

“…Future studies should investigate whether it is possible to use the reflected NIR energy by storing this energy or using it for other processes. First ideas have been developed by Sonneveld et al (2006). Verlodt, I. and Verschaeren, P. 1997 …”

Innovative Technologies for an Efficient Use of Energy

“…Runkle et al, 2002;GarciaAlonso et al, 2006;Hemming et al, 2006c) and may be applied either as greenhouse cover or as screen material. The use of this NIR energy and its conversion into electric power to run a pad and fan cooling system is an example of combined passive and active cooling to be used in the future (Sonneveld et al, 2006).…”

“…In an attempt to combine greenhouse production with electricity production in stead of warm water production, Sonneveld et al (2006 and described a system with a parabolic NIR reflecting greenhouse cover. This cover reflects and focuses the NIR radiation on a specific PV cell or solar collector to generate either electricity or steam.…”

Solar Energy Delivering Greenhouse With an Integrated Nir Filter

“…The designed spectral reflection of this film is given in Figure 3.This film shows a total NIR reflection in the area of 750-2500 nm of 97% combined with a PAR reflection (400-700nm) of only 7%. Implications for the climate conditions in greenhouses with a NIR reflecting film are given by Hemming et al (2005) and Sonneveld et al (2006).…”

“…A computer simulation of the thermal balances of a greenhouse (Sonneveld, 2006) was used to predict the implications for the climate inside a greenhouse. When NIR radiation is reflected by the special selective covering material, a reduced heat load remains, which will result in a better climate in the case of high global radiation.…”