The effects of whitening and dust accumulation on the microclimate and canopy behaviour of rose plants (Rosa hybrida) in a greenhouse in Zimbabwe

Mashonjowa, Emmanuel; Ronsse, Frederik; Mhizha, Teddious; Milford, J. R.; Lemeur, Raoul; Pieters, Jan

doi:10.1016/j.solener.2009.09.004

Cited by 39 publications

(19 citation statements)

References 26 publications

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“…Therefore, external shading is strongly recommended for cooling the greenhouse air [2,3]. A traditional inexpensive shading method is spraying the outer surface of the greenhouse cover with an aqueous solution of hydrated Calcium oxide (Ca(OH) 2 ), a process that is called "whitening by slaked lime" [9,10]. Whitening the greenhouse cladding is used for reducing the solar heating load during summer, similar to shading by plastic nets.…”

Section: Introductionmentioning

confidence: 99%

“…For example, in [12], whitening reduced S i by 20%, and in [9] S i was reduced by 38% and T ai by 5 • C. In [13], whitening reduced T ai by 9.38 • C at around noon, and T ai was reduced by 32% and S i by 41% in [14]. In [10] whitening reduced S i by 22% and T ai by 0.8 • C, and in [15] whitening reduced S i by 30% and T ai by 4 • C. Unlike the whitening effects, the reduction in the transmitted solar radiation and the inside air temperature due to nets or screen shading depends on the type and color of nets, in addition to other meteorological factors. For example, deploying various types of nets, and having different colors and shading factors over naturally ventilated greenhouses reduced the daily average of the inside air temperature (T ai ) by 2-6 • C [16][17][18][19] and reduced the transmitted solar radiation by 30-50% [18,20,21].…”

Section: Introductionmentioning

confidence: 99%

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Predicting the Cooling Potential of Different Shading Methods for Greenhouses in Arid Regions

et al. 2019

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Shading greenhouses in a hot and sunny climate is essential to reduce the inside greenhouse air temperature. However, the type and location of nets need to be addressed properly to determine the shading method that provides a better cooling effect on the greenhouse air. This study was conducted to evaluate the effects of five different shading methods on greenhouse microclimates, and to investigate the cooling potential of each method. Four greenhouse models covered with 200-µm thick plastic film were used for the study: one was kept as control (C), one was whitened with slaked lime (L), and two were shaded with white and black nets (50% shading factor) deployed simultaneously at two locations, in contact (WC, BC) and at 20-cm distance from the cladding film (WD, BD). The microclimatic parameters were measured inside and outside the greenhouse models, and the cooling potential (CP) was predicted for each shading method. The results showed that the black net at 20-cm distance (BD) is desirable as it provides high CP with a reasonable solar radiation transmission. The maximum CP was estimated as 8.5 • C, 8 • C, 6 • C, 3.2 • C, and 2.1 • C for L, BD, BC, WD, and WC, respectively. Shading with white nets is not recommended because their cooling potential is very low. Based on these results, we developed correlations for predicting the CP for each shading method as a function of the transmitted solar radiation flux (S i ). These correlations depend on S i . Accordingly, they can be used for small greenhouses, whitewashed with a slaked lime of any concentration, or shaded with a black net having any shading factor.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Predicting the Cooling Potential of Different Shading Methods for Greenhouses in Arid Regions

et al. 2019

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“…This is accomplished by using commercial shading devices (curtains, clothes, or plastic nets). Shading the roof of a greenhouse is usually performed by various conventional methods such as: (i) whitening by spraying the exterior cover surface with an aqueous solution of hydrated calcium oxide [Ca(OH) 2 ] as in [5,6]; (ii) external shade cloths as in [7][8][9]; (iii) deploying fixed or movable refractive screens or curtains as in [10][11][12][13] and (iv) deploying fixed or movable plastic nets of various types and colors as in [14][15][16][17][18]. Whitening the roof is inexpensive; it can be used for reducing the heat load during summer.…”

Section: Introductionmentioning

confidence: 99%

“…Whitening the roof is inexpensive; it can be used for reducing the heat load during summer. However, it reduced the average greenhouse transmittance to solar radiation by about 50%; it is washed away if rains fall on the greenhouse and its shading density cannot be changed once applied [5,6].…”

Section: Introductionmentioning

confidence: 99%

Radiometric Characterization, Solar and Thermal Radiation in a Greenhouse as Affected by Shading Configuration in an Arid Climate

et al. 2015

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Abstract:Shading the greenhouses is necessary in summer to reduce the solar radiation load. This however generates a considerable amount of thermal radiation heat load that needs to be removed via cooling systems. This study aimed to evaluate the effect of different shading configurations on the solar and thermal radiation in a greenhouse. Nets at four different locations were employed to shade the roof and side-walls of a polycarbonate, mechanically ventilated greenhouse. The spectral radiative properties of all these plastic materials were measured in short and long wave spectrum bands. The net solar and thermal radiations and air temperature were measured outside and inside two identical shaded and unshaded greenhouses. The results showed that external roof-shading is desirable, as it reduced the generated thermal radiation in the greenhouse by 21% and 15% during the day and night time, respectively and reduced the greenhouse air temperature during the day. The internal shading (roof and side walls) is undesirable, since it drastically increased the generated thermal radiation in the greenhouse by 147% and strongly increased the greenhouse air temperature during the day. Shading the side-walls is not recommended because it significantly reduces the transmitted solar radiation in the morning and afternoon (when the outside irradiance is low) and is useless at around noon when the outside irradiance is extremely high.

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“…Previous studies conducted in Japan [13] and in the Mediterranean region [14,15] demonstrated that an adequate level of shading mitigates excessive temperature rises in greenhouses in summer, improving crop growth and quality [16,17]. Conventionally, nets [14,15,18] and reflective coatings [18,19] have been used as practical and reasonable methods for greenhouse shading. Sunlight on the canopy is moderated properly by virtue of the reflection of partial solar irradiance to the outside using these simple shading methods.…”

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confidence: 99%

Electrical Energy Producing Greenhouse Shading System with a Semi-Transparent Photovoltaic Blind Based on Micro-Spherical Solar Cells

Yano

Cossu

et al. 2018

Energies

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An increasing population and limited arable land area endanger sufficient and variegated food supplies worldwide. Greenhouse cultivation enables highly intensive plant production and thereby enables the production of abundant fresh vegetables and fruits. The salient benefits of greenhouse cultivation are supported by ingenious management of crop environments, assisted by fossil fuel and grid electricity supplies. To reduce dependence on traditional energy resources, various studies have investigated exploitation of renewable energies for greenhouse environment management. Among them, solar photovoltaic (PV) technologies are anticipated to feed electrical energy to greenhouse appliances for microclimate control. This study proposes a venetian-blind-type shading system consisting of semi-transparent PV modules as blind blades based on micro-spherical solar cell technology to achieve greenhouse shading and electricity production concurrently. In response to the solar irradiance level, the PV blind inclination was altered automatically using a direct current (DC) motor driven by electrical energy generated by the PV blind itself. The PV blind was operated continuously during a five-month test period without outage. Moreover, the PV blind generated surplus electrical energy of 2125 kJ for blind system operations during the test period. The annual surplus energy calculated under the present experimental condition was 7.8 kWh m −2 year −1 , suggesting that application of the PV blind to a greenhouse roof enables sunlight level control and electrical appliance operations in the greenhouse with a diminished fuel and grid electricity supply, particularly in high-insolation regions.Energies 2018, 11, 1681 2 of 23 produces carbon dioxide emissions, the amounts of which should be reduced in the agricultural sector [2]. Under these circumstances, various studies have been conducted to use renewable energy for managing greenhouse crop environments [3,4]. Among them, solar photovoltaics (PVs) are expected to feed electricity to appliances that are used for greenhouse environment management [5].Deploying PV arrays on the sunny ground beside a greenhouse is the simplest and most effective mode of electrical energy generation. For instance, fan and pad cooling systems in Saudi Arabia [6] and in Arizona [7], a fog cooling system in Malaysia [8], and heat pump systems in Italy [9,10] were operated with power from ground-mounted PV arrays. Nevertheless, installing PV arrays partially on a greenhouse roof might be preferred if the PV panels are intended as shading materials. Shading is a fundamentally important practice for greenhouse cultivation in high-insolation regions, such as Spain [11] or Saudi Arabia [12]. Previous studies conducted in Japan [13] and in the Mediterranean region [14,15] demonstrated that an adequate level of shading mitigates excessive temperature rises in greenhouses in summer, improving crop growth and quality [16,17]. Conventionally, nets [14,15,18] and reflective coatings [18,19] have been used as practical ...

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The effects of whitening and dust accumulation on the microclimate and canopy behaviour of rose plants (Rosa hybrida) in a greenhouse in Zimbabwe

Cited by 39 publications

References 26 publications

Predicting the Cooling Potential of Different Shading Methods for Greenhouses in Arid Regions

Predicting the Cooling Potential of Different Shading Methods for Greenhouses in Arid Regions

Radiometric Characterization, Solar and Thermal Radiation in a Greenhouse as Affected by Shading Configuration in an Arid Climate

Electrical Energy Producing Greenhouse Shading System with a Semi-Transparent Photovoltaic Blind Based on Micro-Spherical Solar Cells

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