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Periodic analysis is the best method to analyze any thermal system, even for a typical day, and the same thermal modeling can be extended for monthly performance without knowing the initial condition. A periodic thermal model for greenhouse integrated semi-transparent photovoltaic thermal (GiSPVT) system connected with earth air heat exchanger (EAHE) in terms of design, and climatic parameters have been developed. Based on the proposed periodic model, the effect of packing factor, mass flow rate of air flowing through EAHE, heat capacity of the plant on PV cell temperature, greenhouse air temperature, and plant temperature of GiSPVT system is investigated for harsh winter condition. Results indicate that it is economical to operate EAHE only during off sunshine hours. The value of both greenhouse and plant temperature increases with an increase in the mass flow rate of air flowing through EAHE. For a flow rate of 0.5 kg/s, the additional thermal energy supplied by the EAHE to the GiSPVT system increases plant and greenhouse air temperature by 4 °C and 5 °C, respectively. Moreover, electrical power of 11.74 kW has also been obtained to make the system self-sustained.

Non-destructive methods have been widely recognized for evaluating fruit quality traits of many horticultural crops and food processing industry. Destructive (analytical) test, and non-destructive evaluation of the quality traits were investigated and compared for ‘Red Rose’ tomato (Solanum lycopersicum L.) fruit grown under protected environment. Fresh tomato fruit at five distinctive maturity stages namely; breaker (BK), turning (TG), pink (PK), light-red (LR), and red (RD) were labeled and scanned using the handheld near infra-red (NIR) enhanced spectrometer at a wavelength range of 285–1200 nm. The labeled tomato samples were then measured analytically for flesh firmness, lycopene, β-carotene, total phenolic content (TPC) and total flavonoids content (TFC). The results revealed that quality traits could be estimated using NIR spectroscopy with a relatively high coefficient of determination (R2): 0.834 for total phenolic content, 0.864 for lycopene, 0.790 for total flavonoid content, 0.708 for β-carotene; and 0.679 for flesh firmness. The accumulation of Lyco and β-Car rapidly increased in tomatoes harvested between the TG and the LR maturity stages. Harvesting tomatoes at BK maturity stage resulted in significantly higher flesh firmness than harvesting at the later maturity stages. Tomato fruits had the lowest TPC and TFC contents at the earliest maturity stage (BK), while they had intermediate TPC and TFC levels at LR and RD maturity stages. NIR spectroscopic measurements of fruit firmness and lipophilic antioxidants in tomato fruit at various maturity stages were partially in accordance with those estimated by destructive (analytical) methods. Based on these findings, we recommend using non-destructive NIR spectroscopy as an effective tool for predicting tomato fruit quality during harvest stage and postharvest processing.

The use of synthetic antioxidants has been associated with serious concerns for human and environmental health. During ripening stages, tomato fruit is exposed to different abiotic stresses which not only influence its nutritional, mechanical, and functional properties at harvest, but also affect the quality and shelf life of the fruit during storage. This study investigated the pattern of changes in dietary antioxidants during various ripening stages of tomato fruit (cv. Red Rose) and their impact on storage behavior of the fruit during cold storage. Tomato fruits were harvested at mature green, breaker, turning, pink, light-red and red stages of maturity. Then, they were analysed for flesh firmness, soluble solids content, titratable acidity, total sugars, pH, dry matter content, lipophilic (lycopene, β-carotene, and total carotenoids), and hydrophilic (ascorbic acid, phenolic and flavonoids) antioxidants. Additional fruits were harvested at each maturity stage and divided into three equal lots, then were subjected to low-temperature (10 ± 1 °C) storage with 80 ± 5% RH, for 7, 14, and 21 days. Flesh firmness, and the levels of dietary antioxidants were analysed following the subsequent storage periods. The results revealed that the peak of hydrophilic antioxidants such as ascorbic acid, phenolic compounds, and flavonoids was between the ‘pink’ and the ‘light-red’ stages of fruit maturity. Whereas tomatoes harvested at the ‘red’ stage of maturity had the highest levels of lycopene and β-carotene. Both the stage of fruit maturity at harvest and duration of cold storage influenced flesh firmness, organoleptic and functional properties of ‘Red Rose’ tomato fruit. In conclusion, the results of the current investigation have practical implications in formulating foods with improved functional properties at processing industries.

Semi-transparent photovoltaic thermal (SPVT) greenhouse system combined with an earth air heat exchanger (EAHE) has been developed to make the system sustainable. The system is designed to cultivate plants in a hot climatic condition, where green net is provided, which bifurcates the enclosed space of the greenhouse into zone-1 and zone-2, and this green net cut the solar radiation incident on the plants. The influence of air changes in zone-1, mass flowrate of air flowing through EAHE, and packing factor on photovoltaic (PV) cell, air of the greenhouse, and the plant temperatures is investigated for a typical harsh summer day by using periodic model of these parameters. Furthermore, for a holistic performance assessment of this SPVT greenhouse, exergy, thermal load leveling, and decrement factor are evaluated. Results indicate that the optimum temperature range for plant growth (30 °C–37 °C) within the greenhouse can be achieved through a combination of ventilation in zone-1 and integration of EAHE. The temperature of plants reduced by 9 °C for 30 air changes in zone-1, and the temperature reduces further by 24 °C when EAHE having a flowrate of 0.5 kg/s is operated. The SPVT greenhouse system also generates 128 kWh of daily overall exergy that makes the system sustainable.

The sky thermal irradiance (Rsky) is an important factor in meteorological, climatic, and energy balance studies. There are several empirical models for predicting Rsky; however, these are based on the meteorological parameters measured in non-arid climatic conditions and an empirical model for predicting Rsky in arid climates is unavailable. Therefore, this study presents two empirical models for predicting the Rsky under clear sky conditions, common in arid regions such as the Arabian Peninsula. One is based on the sky equivalent emissivity (esky-model) and the other on the sky equivalent temperature (Tsky-model). Meteorological parameters (i.e., air temperature, relative humidity, solar radiation, and downward Rsky) were measured over 3 years and used to develop and validate the proposed models. The results showed that the proposed esky- and Tsky-models had the highest predictive accuracy with a coefficient of determination of 0.86 compared with previously published models. In addition, the proposed esky- and Tsky-models resulted in low values of root mean square and mean absolute percentage errors (7.2 and 7.8 W·m−2 and 1, 2 %, respectively); they were able to precisely predict Rsky at any time in a clear arid climate compared with the prohibitive and time-consuming measurements.

This paper deals with the theoretical analysis of double slope solar still (DS) integrated with N identical evacuated tubular collectors (N-ETC-DS) on the basis of energy metrics. The analysis has been done considering four types of weather condition for each month of year for New Delhi climatic condition. Results of the proposed N-ETC-DS has been compared with DS integrated with N identical photovoltaic thermal (PVT) flat plate collectors (N-PVT-FPC-DS), DS integrated with N identical PVT compound parabolic concentrator collectors (N-PVT-CPC-DS) and conventional DS (CDS). It has been concluded that N-ETC-DS performs best on the basis of exergy based energy payback time, energy production factor and life cycle conversion efficiency followed by N-PVT-FPC-DS, CDS and N-PVT-CPC-DS.

In the present communication, N-partially covered photovoltaic thermal (PVT) collector integrated with compound parabolic concentrator (CPC) connected in series has been considered to evaluate the annual electrical gain, overall thermal energy and exergy by considering five different solar cell materials. In the present paper, concentration ratio (CR) is considered as Aa:Ar is 2. Following cases have been named as [case (i)]: mono crystalline silicon (c-Si) based solar cells/PV module, [case (ii)]: poly crystalline silicon (p-Si) based solar cells/PV module, [case (iii)]: amorphous silicon (a-Si) based solar cells/PV module, [case (iv)]: cadmium telluride (CdTe) based solar cells/PV module and [case (v)]: copper-indium-gallium-selenide (CIGS) based solar cells/PV module. The electrical efficiency for considered all five cases of N PVT-CPC collector have been compared on hourly basis and further, monthly thermal and electrical gains have been obtained for a year by numerical computation. The mass flow rate and number of collector of PVT-CPC collector have been optimized. Numerical computations have been carried out for all weather conditions at New Delhi, India. It has been observed that proposed case (i) has been found to be better than other other proposed cases from electrical, an overall thermal energy and exergy based on annual performance.

Huge quantities of palm tree residues are available annually in Saudi Arabia, they are often disposed of by burning, leading to large environmental pollution and health problems. Enclosed composting may be a successful method for utilizing these residues. Effective composting in a rotary bioreactor depends on the composting materials and the frequencies of the rotation&ndash, aeration process. Here, we attempted to determine the optimal method for composting these residues in a bioreactor. Four identical pilot-scale bioreactors (D1&ndash, D4) were used. The respective aeration&ndash, rotation frequencies were continuous (D1), and 20 min per 1 h (D2), 2 h (D3), and 3 h (D4), the rotation speed of the bioreactors was 3 rpm. Three periods were analyzed, their names and their respective lengths for D1, D2, D3, and D4 were as follows: the lag period was 10 h for each, the mesophilic periods were 13, 14, 89, and 231 h, and the thermophilic periods were 0, 55, 71, and 17 h. The peak compost temperatures (Tc, max) for D1, D2, and D3 were 65.2, 57.2, and 46.9 &deg, C, and were achieved at 36, 71, and 108 h of operation, respectively. In D1, Tc quickly declined after reaching Tc, max due to limited microbial activity at Tc &gt, 60 &deg, C. In D2, a Tc of 50&ndash, 57.2 &deg, C was maintained for 61 h, and the highest organic matter degradation (OMD) of 0.30 was achieved. During the composting period, the carbon to nitrogen (C/N) ratio and moisture contents (MC) remained in the optimal ranges for microorganisms and did not affect the composting process. The results indicated that combined aeration&ndash, rotation for 20 min every hour (D2) gave the best results for composting palm tree residues, it ensured the hygiene safety of the end product, and it also consumed less power for aeration and rotation than D1.

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-&micro, m 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 &deg, C, 8 &deg, C, 6 &deg, C, 3.2 &deg, C, and 2.1 &deg, 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 (Si). These correlations depend on Si. 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.

In arid regions, limitation of protected cultivations in greenhouses is mainly due to the overheating of the inside air during hot and long summer seasons. The greenhouse accumulates around 10 MJ m-2 of heat energy per day; this requires an expensive, energy consuming cooling system to remove the heat and to achieve favorable conditions for crop growth. Cooling greenhouses are facing several challenges in arid regions due to the excessive solar irradiance, extremely high ambient air temperature, as well as water scarcity and salinity. A new concept (net-house) as a naturally-ventilated alternative agricultural structure, covered with low-cost, plastic nets was introduced. The proposed net-house does not require cooling and ventilation systems, and provides a uniform distribution of solar radiation and a suitable environment for crop growth and the production costs will be significantly decreased.

This study is to describe the degradation behavior of the optical constants (refractive index $$ \bar{n} $$ and extinction coefficient $$ \bar{\sigma } $$ ) of PE-LD sheets during exposure to an arid climate. Values of $$ \bar{n} $$ and $$ \bar{\sigma } $$ are used to determine the solar radiative properties of any PE-LD cover at any time without the need of measurements. Different greenhouse models were covered with PE-LD films and exposed for 1 year to an arid climate, and values of $$ \bar{n} $$ and $$ \bar{\sigma } $$ were investigated. Exposing films to the arid climate for 1 year increased the values of $$ \bar{n} $$ from 1.58 to 2.86 and $$ \bar{\sigma } $$ from 3.86 to 8.1 mm−1, resulting in a decrease in transmittance from 0.42 to 0.12. Two correlations for predicting the degradation rate of $$ \bar{n} $$ and $$ \bar{\sigma } $$ for PE-LD covers were developed.

Rotary drum composters are used to produce high-quality, pathogen-free compost without weed seeds. Insulation is usually applied to small-scale composters to warm up the composted materials and enhance metabolic reactions to produce stable and mature compost within a short time. However, the relationship between the composter size and the heat loss rate is still unclear. In this study, the relationship between the composter size (designated as the ratio of surface area to volume, As/V) and heat loss was analyzed and identified. To show the effect of insulation on the composting performance, two identical rotary drum bioreactors (each of As/V = 9) were used to compost tomato plant residues, one insulated and the other kept without insulation. Results showed that insulation increased the overall resistance against heat loss from the bioreactor from 0.37 (m2 °C W−1) to 1.12 (m2 °C W−1), quickly increasing the compost temperature, and a temperature of 55⁻67 °C could be achieved and remained for three days. Therefore, mature, stable, well-aged, and high-quality compost was obtained. In the non-insulated bioreactor, the compost temperature did not exceed 37 °C; this caused a decline of microbial activity and the composting process temperature was only in the mesophilic range, leading to a high risk of the existence of weed seeds and pathogens in the final immature compost. Insulation is necessary for laboratory-scale and small pilot-scale bioreactors (As/V ≥ 6), because heat loss is high as As/V is high, whereas it is not necessary for commercial full-scale bioreactors (As/V ≤ 4), because heat loss is minor as As/V is low. For larger pilot-scale bioreactors (As/V: 4⁻6), insulation cost must be considered when comparing the impact of energy saving on the composting process.

The work concerns experimental and theoretical studies of building integrated semitransparent photovoltaic/thermal (BiSPVT) system. The analytical expressions for temperature dependent electrical efficiencies of the system have been established. It concerns a roof integrated semitransparent mono crystalline silicon (c-Si) PV with two options: (i) with air duct or (ii) without air duct. An experiment has been performed on a specially designed proto-type c-Si BiSPVT set up built in Indian Institute of Technology, New Delhi, India. Theoretically calculated results using derived expressions have been validated with experimentally measured thermal and electrical parameters for both cases. A fair agreement between theoretically calculated and experimentally measured values is observed. The characteristic curves, energy and exergy analysis have also been performed particularly under cold climatic conditions of Srinagar, India. Further, to maximize the electrical and thermal efficiencies, BiSPVT system has been optimized for various design parameters as cross sectional area of air duct, duct height, fluid flow velocity, packing factor and number of air change. Without air duct, the efficiency (ηm) and the average room temperature (Tr) are found to be 12% and 25 °C respectively, whereas with air duct the BiSPVT systems inflicted the efficiency (ηm) and temperature (Tr) to be 13.11% and 10.1 °C respectively.

Food is necessity for human being. As the world population is increasing, it is very difficult to fulfil everyone's need of food. One of the alternatives of this problem is the preservation of crops, vegetable and fruits when it is available in abundant amount. Drying is one of the best methods to preserve agricultural products for long time but it requires lot of energy. As availability of electricity per capita in developing and under developed countries is very less, thus the electricity uses for heating purpose cannot be economically and environmentally justified option. So entrapment of thermal energy from solar radiation may be the best option for drying. Solar energy can be utilized for drying in different ways namely open sun drying and closed drying (direct and indirect). Open sun drying have various disadvantages like contamination of dust particles, bacteria in crop, decolouration of the product after drying etc. To overcome these problems greenhouse drying or closed drying has been developed. This review is an attempt to explore different types of drying systems was developed across the world. Further different thermal modelling, mathematical modelling and performance evaluation on the basis of characteristic curve have been discussed. One of the thermal modelling has been discussed in detail to evaluate heat transfer coefficient, heat absorbed and moisture evaporate with experimental validation to give practical exposure to the researchers.

In this paper, the design and fabrication of photovoltaic thermal integrated greenhouse system (PVTIGS) for biogas heating has been done for climatic condition of IIT Delhi, India. PVTIGS can also be used for a number of applications like generating electricity, space heating, enhancing production of biogas, crop cultivation and crop drying, etc. Thermal modelling of proposed system (PVTIGS) without load has been developed based on energy balance equations. Further, with the help of thermal modelling the solar cell temperature, room temperature and solar cell efficiency have been calculated for a typical clear day of May. Experimental validation have been done on the basis of correlation coefficient ( r ) and root mean square percentage deviation ( e ) and found to be in fair agreement between theoretical and experimental values. Effect of packing factor, mass flow rate of air below module, absorptivity (degradation effect) and transmittivity (dusting effect) on thermal load levelling have been discussed. Electrical energy has been calculated and validated with experimental values. Further, thermal energy and overall thermal energy have been evaluated and found to be 11.18 kW h and 12.76 kW h respectively for a clear day without load.

In present communication, an experimental study has been carried out to evaluate the performance of series connected photovoltaic thermal (PVT) water collector in terms of overall thermal energy gain and overall exergy gain. Earlier developed theoretical model has been validated by performing the experiment in a clear sky day, hazy day and partially cloudy day for New Delhi climatic condition. It was found that theoretical results were in good agreement with experimental results. The annual energy gain, exergy gains, CO2 mitigation, energy matrices and carbon credit of the system have also been discussed. The energy pay-back time was found to be 1.50 and 14.19 years on overall thermal energy and exergy basis respectively. Carbon credits earned in a year were Rs. 6321.70 for overall thermal energy gain and Rs. 667.30 for overall exergy gain. For 30 years of life time, cost of one unit of electricity was estimated to be Rs. 1.53 on overall thermal energy basis however it was Rs. 14.45 on overall exergy basis.

This paper presents the life cycle cost analysis of passive solar stills by incorporating the effect of energy payback period. Exergoeconomic and energy matrices have been evaluated for climatic condition of New Delhi. The annual exergy, yield and energy have been calculated considering the four climatic conditions for each month of year. The kW h per unit cost based on exergoeconomic parameter has been found to be 0.144 kW h/Rs. and 0.137 kW h/Rs. for single and double slope passive solar stills respectively. It is inferred that single slope solar still performs better than double slope solar still based on annual exergy analysis.

The transmitted radiation into the conventional net-houses is very low in the early morning and late afternoon that may not fulfill the crop growth requirements. To solve this problem, two types of net-house models (polygon and curved-arch net-houses) were newly designed, each having seven surfaces made up of different net types. The spectral radiative properties of 32 nets were examined and three nets were selected to cover the surfaces of each model. The two designs showed high transmittance in the morning and afternoon, and low at around noon (U shape). The polygon style was scaled-up and an experiential net-house was constructed with a floor area of 28 m2. An evaporatively-cooled greenhouse with a floor area of 28 m2 was used for comparison; each floor was planted with 500 potted Chrysanthemum plant. The results showed that the PAR and microclimate in the net-house and cooled greenhouse were similar. The net-house reduced water consumption by 13 kg m−2 day−1 in summer and by 0.94 kg m−2 day−1 in winter; and reduced electric energy consumption by 0.26 kw-h m−2 day−1 in summer and by 0.18 kw-h m−2 day−1 in winter compared to the greenhouse.

A hybrid photovoltaic–thermal (PVT) greenhouse solar dryer under mixed mode has been proposed and different parameters have been evaluated for climatic condition of Indian Institute of Technology, New Delhi (28_350N, 77_120E, 216 m above MSL), India. Further thermal modelling has been developed for the PVT greenhouse dryer by considering different parameter namely crop, greenhouse and solar cell temperatures, etc. Numerical computations have been done with the help of program made on MATLAB 2013a and the results are validated with experimental values. Characteristic curves have been developed for drying and system efficiency with experimental validation. Further, an overall thermal energy and exergy have been calculated. Theoretical and experimental values of overall thermal energy found to be 1.92 kW h and 2.03 kW h respectively. It can be seen that there is good agreement between theoretical and experimental value with r = 0.98 and e = 10.76. Further validation has also been done for energy and exergy of PVT dryer.

This paper deals with the experimental studies and performance analysis of partially covered hybrid photovoltaic thermal (PVT) flat plate collector (FPC) solar still. The thermal model of the system has been developed. The data have been collected for the composite climate condition of New Delhi. The experimental results have been compared with theoretical results. It has been observed that there is a fair agreement between the experimental and theoretical values with the correlation coefficients varying between 0.97 and 0.99. The coefficient of determination varies between 0.94 and 0.98. The annual productivity has been found to vary between 120.29% and 883.55%. The thermal, exergy and overall thermal efficiency have been evaluated. It has also been observed that the proposed system is self sustainable and it can meet potable water requirement as well as electricity requirement.

In this paper, a new design of a glazed and an unglazed inverted absorber partially covered photovoltaic thermal compound parabolic concentrator (PVT-CPC) water collector has been proposed. The performance of proposed systems has been compared with partially covered inclined and horizontal PVT-CPC water collector systems for constant mass flow rate mode. Analytical expressions for the outlet fluid temperature (Tfo1) and electrical efficiency of the proposed systems have been derived and presented. Based on the analytical thermal model, a software program has been developed in MATLAB 2010a to determine the outlet fluid temperature, electrical efficiency, thermal energy, electrical energy and overall exergy efficiency of the systems. The results showed that the glazed inverted absorber partially covered PVT-CPC water collector system exhibited higher values of instantaneous thermal efficiency. Further, the glazed inverted absorber partially covered PVT-CPC system is more suitable for higher thermal energy. However, the partially covered inclined PVT-CPC water collector is more favourable for electrical energy requirements. Further, the inverted absorber partially covered PVT-CPC system is cost effective.

In the present study, the thermal energy balance equations have been taken for N partially covered photovoltaic thermal–compound parabolic concentrator collectors ( N -PVT–CPC) connected in series. An analytical mathematical expression for N th outlet water temperature ( T foN ) and efficiency of solar cell at N th collector ( η cN ) have been derived in terms of climate and design parameters. Numerical computations have been carried out for two Indian climatic condition namely (a) January (winter) and (b) June (summer), respectively. Effect of number of PVT–CPC collectors connected in series, mass flow rate and the percentage of PV coverage on various temperatures, an overall thermal energy and overall exergy have been carried. It has been observed that an overall exergy of proposed system is maximum for winter condition due to less thermal losses.

In hot and sunny regions, extensive solar radiation transmitted into greenhouses makes it essential to select a greenhouse cover with specific characteristics. Reflection and diffusion are the most important properties of covers for reducing solar heating load and scattering solar beams for better growth of plants. Three types of plastic films that are commonly used for covering greenhouses in arid climate were selected for this study. These were reflective-diffusive (RDF), diffusive (DF), and locally produced (CF) films. The films were used to cover three identical twin-span greenhouse models; the radiation components, air temperature (Ti), and relative humidity (RHi) were measured in each model. Transmission of solar radiation through each cover was characterized by determining: (i) The beam that is diffused during transmission, and (ii) the unscattered beam that is transmitted directly through the film. The results show that the diffuse radiation transmitted through the DF, RDF, and CF covers was enhanced, respectively by 77%, 85%, and 109% as a result of diffusing 34%, 33%, and 43% of the transmitted beam radiation by the DF, RDF, and CF covers, respectively during transmission. The diffusive nature of the tested covers increased the ratio of diffuse to direct beam radiation (D/B) from 0.3 outside the greenhouse to 0.77, 0.69, and 0.95 inside a greenhouse covered with DF, RDF, and CF, respectively. At around noon, the CF cover decreased Ti by about 5−10 °C and increased RHi by about 3%−5% compared to those under the DF and RDF covers. However, DF and RDF covers showed almost similar effects in Ti and RHi. The low-price CF cover showed higher diffusive-radiative properties than DF and RDF covers and can serve effectively in arid climate as an alternative covering material.

Plastic films are widely used to cover greenhouses in arid regions. Unlike predicting the total radiative properties of films, predicting the deterioration behavior of the spectral radiative properties is quite difficult during the service life of the films. These properties should be of great interest for crop morphogenesis studies. This study was to investigate the degradation behavior of spectral transmittance, $$ \tau_{\lambda } $$ , and reflectance, $$ \rho_{\lambda } $$ (in the solar spectrum range), of a 200 µm thick, LDPE film-covered greenhouse model that was exposed for 1 year to an arid climate. Every 30 days, $$ \tau_{\lambda } $$ and $$ \rho_{\lambda } $$ were measured for six samples taken from the six surfaces of the greenhouse cover and averaged to obtain the cover properties. Based on the collected data, nonlinear correlations (each as a function of the wavelength, λ, and the exposure time, t) were obtained to predict $$ \tau_{\lambda } $$ and $$ \rho_{\lambda } $$ at any time during the service life of the cover under such climatic conditions. Results showed that 1 year exposure drastically reduced the spectral and total transmittance of the cover film to global and PAR solar radiation by about 32 % and increased the spectral and total reflectance by about 19 % compared to new film. Degradation of the radiative properties of the film did not affect the light quality or the transmission ratios of light into the greenhouse. The transmitted PAR was reduced from 115 W·m−2 to 27 W·m−2 after 1 year exposure.

In the present paper, the earlier developed model for wall window has been modified for rooftop window. The model has been validated for dynamic behavior by considering the hourly measured both direct and diffuse components of the sunlight and skylight under clear sky conditions. It can be used to predict the Daylight Illuminance Ratio (DIR) and daylight at a given point in living space. The annual energy saving from rooftop window has been estimated for different climatic locations in India. It has been observed that highest DIR was always along the line normal to the rooftop window and decreases as we go away from the normal line in all directions. It was found that, for increasing aperture to floor area ratio, the energy saving potential increases. The minimum annual energy saving was found to be 65.74 kW h/m2 for Srinagar whereas the maximum was 77.10 kW h/m2 for Bengaluru. The monthly average value of model exponent (p) has been computed as 1.25. Hence, the present model can be used to design building for optimum daylighting at a given point inside living space.

This paper presents an exergoeconomic and enviroeconomic analyses of partially covered photovoltaic thermal (PVT) flat plate collector (FPC) integrated solar distillation system known as PVT-FPC active solar distillation system. The analysis is based on experimental studies for composite climatic condition of New Delhi. The hourly thermal, exergy, electrical, overall exergy and overall thermal efficiency have been evaluated and the results have been compared with the results obtained by earlier researchers. It has been observed that the proposed PVT-FPC active solar distillation system can meet the daily requirement of potable water as well as DC electrical power during sunshine hours.

Most of thermal models used to estimate the natural ventilation of greenhouses ( m ˙ a ) use an average value for the cover transmittance (τc) to estimate the input solar energy to the greenhouse. These models failed to predict m ˙ a at low solar radiation flux due to the spatial variation of τc in the greenhouse and the thermal inertia of soil. This study is to develop and validate a thermal model predict m ˙ a precisely. All modes of energy were treated, under the unsteady state conditions, at the outer surface of the cover to avoid the sources of error. The required parameters were measured for a naturally ventilated glasshouse. The predicted values of m ˙ a were in the range between 0.36 kg s−1 and 1.65 kg s−1 and showed good accordance with measured and simulated values in the literature. The results also confirmed that outside wind at a speed m ˙ a and the temperature difference of air between inside and outside the greenhouse (ΔT) is the main driving force of ventilation. A correlation between m ˙ a and ΔT was provided, it can be used to estimate m ˙ a that required to maintain the air temperature in the greenhouse at a desired level.

In the present paper, daylight factor model (DFM) has been developed for daylight aperture which has been experimentally validated for east oriented wall window under clear sky condition. The correlation coefficient (r) and the root mean square percentage error (e) are in the range of 0.96–0.99 and 5.1–7.9%, respectively. It has been seen that there is a close agreement between modeled and measured values. The annual average daylight factor (DF), sky component (SC) and internally reflected component (IRC) values for the room were determined to be 1.8%, 1.2% and 0.6%, respectively. It is observed that the south oriented window has maximum DF while it is minimum for north oriented window. It is also concluded that the window in the upper position allows higher illuminance of the rooms compared to a wall window toward the bottom of the room.

In the present study the series combination of N PVT water collectors, partially covered with photovoltaic module, in two different configurations namely case A: Photovoltaic module at lower portion; case B: Photovoltaic module at upper portion, have been analyzed. Analytical expressions for instantaneous thermal efficiency and temperature dependent electrical efficiency have been derived. The performances of both configurations have been compared on thermal efficiency basis and temperature dependent electrical efficiency basis. It has been concluded that at moderate mass flow rate, for large number of PVT water collectors connected in series both cases give nearly same results.

Determining convective heat is essential for analyzing energy exchange with shading nets. Unlike solar and thermal radiation, the convection (Qn−a) and the convective coefficient (hn−a) have never been estimated or measured for plastic nets. In this study, an energy balance was applied to a horizontal net under outdoor conditions to predict Qn−a and hn−a. Therefore, the net was tacked onto a wooden frame; energy balance was applied below and above the net surfaces and above a black substrate underneath the frame. The wind speed (V), net-air temperature difference (ΔT), downward and upward solar and thermal radiation fluxes were measured, on sunny days, below and above the net to be used for solving the energy balance equations. Accordingly, the time dependence of Qn−a and hn−a were investigated. Nets with different porosities and colors were used. For each net tested, hn−a was expressed as a function of V and ΔT. The results showed that hn−a depends mainly on the texture structure of the net rather than its color or porosity. Therefore, a similar net texture would have nearly the same hn−a value. These expressions can be used to estimate hn−a for nets having similar texture structures, different colors, and different porosities.

The PV research community and industry has major focus on the new advancement and improvement on power efficiency of PV systems. An attempt has been made to model and optimize the parameter of hybrid single channel photovoltaic thermal (PVT) module. In this paper it has been observed that there are many parameters that affect the electrical efficiency of a hybrid single channel PVT module like thickness of the glass and tedlar, temperature of the inlet flow, and solar cell temperature. All equations for solar cell and thermal collector have been derived. By using genetic algorithms (GAs), thermal efficiency and electrical efficiency of the system may be optimized. All the parameters that are used in genetic algorithms are the parameters that could be changed, and the non changeable parameters, like solar radiation cannot be used in the algorithm. It has been observed that the GAs are very efficient technique to estimate the design parameters of hybrid single channel PVT module.

In this paper, an analytical expression for characteristic equation of a partially covered photovoltaic thermal compound parabolic concentrator (PVT-CPC) water collector system similar to Hottel–Whillier–Bliss (HWB) equation of flat plate collector has been derived. The derivation is based on basic energy balance equation for each component of partially covered PVT-CPC water collector system. The analytical result of proposed partially covered PVT-CPC water collectors [case (i)] has been compared with [case (ii)]: fully covered PVT-CPC water collectors; [case (iii)]: conventional CPC water collectors and [case (iv)]: partially covered PVT water collectors. It is observed that (a) an overall exergy efficiency of partially covered PVT-CPC water collector (25%PV) system is maximum and (b) an instantaneous thermal efficiency of conventional CPC water collector system [case (iii)] is maximum as compared to other cases.

To determine the energy transfer through a plastic net-covered structure, the temperature of the net ( T n ) is an essential parameter. The perforated nature of nets and the effects of solar and thermal radiation, during the daytimes, make it is impossible to measure T n correctly by using most types of thermometer. Therefore, T n has never been theoretically estimated or experimentally measured in the presence of solar and thermal radiation. In this study, T n was simulated by determining the emissive power of the net ( E n ) and the net emittance ( e n ). To determine E n and e n , the net was tacked onto a wooden frame; thermal radiation balance was applied below and above the net surfaces and above the substrate underneath the frame. The downward and upward thermal radiation fluxes were measured below and above the net to be used in the simulation. A simple measuring method was proposed to predict T n using a thermocouple junction of 0.3 mm in diameter (copper constantan, type-T) inserted into the net texture. The measured values of T n were in agreement with those predicted by the simulation. The mean absolute difference between the measured and the simulated values of T n ranged from 0.75 °C to 1.9 °C for all the nets tested. For nets with low porosity, the inserted junction should keep exposing to the surrounding environment. However, for nets with high porosity, the inserted junction should be shielded from radiation to improve measurements in the correct direction.

To protect humans from heat stress risks, thermal comfort and heat stress potential were evaluated under arid environment, which had never been made for such climate. The thermal indices THI, WBGT, PET, and UTCI were used to evaluate thermal comfort and heat stress. RayMan software model was used to estimate the PET, and the UTCI calculator was used for UTCI. Dry and wet bulb temperatures (Td,Tw), natural wet bulb temperature (Tnw), and globe temperature (Tg) were measured in a summer day to be used in the calculation. The results showed the following. (i) The thermal sensation and heat stress levels can be evaluated by either the PET or UTCI scales, and both are valid for extremely high temperature in the arid environment. (ii) In the comfort zone, around 75% of individuals would be satisfied with the surrounding environment and feel comfortable during the whole day. (iii) Persons are exposed to strong heat stress and would feel uncomfortable most of the daytime in summer. (iv) Heat fatigue is expected with prolonged exposure to sun light and activity. (v) During the daytime, humans should schedule their activities according to the highest permissible values of the WBGT to avoid thermal shock.

Thermal sensation and heat stress were evaluated in a plastic greenhouse, with and without evaporative cooling, under arid climatic conditions in Riyadh, Saudi Arabia. Suitable thermal comfort and heat stress scales were selected for the evaluation. Experiments were conducted in hot sunny days to measure the required parameters (i.e., the dry and wet bulb temperatures, globe temperature, natural wet bulb temperature, and solar radiation flux) in the greenhouse. The results showed that in the uncooled greenhouse, workers are exposed to strong heat stress and would feel very hot most of the day time; they are safe from heat stress risk and would feel comfortable during night. An efficient evaporative cooling is necessary during the day to reduce heat stress and to improve the comfort conditions and is not necessary at night. In the cooled greenhouse, workers can do any activity: except at around noon they should follow a proposed working schedule, in which the different types of work were scheduled along the daytimes based on the heat stress value. To avoid heat stress and to provide comfort conditions in the greenhouses, the optimum ranges of relative humidity and air temperature are 48–55% and 24–28°C, respectively.

The perforated nature of nets makes it impossible to measure the thermal radiative properties (emittance, εn, transmittance, τn, and reflectance, ρn) correctly by using any measuring device under natural conditions. In this study, a theoretical model was developed and validated to predict εn, τn, and ρn precisely by solving the model equations simultaneously. The net was tacked onto a wooden frame; thermal radiation balance was applied below and above the net surfaces and above a black substrate underneath the frame. The downward and upward thermal radiation fluxes were measured below and above the net to be used as input parameters to the simulation. Nets with different porosities (ϕ) and colors were used for the study. The results showed that the estimated εn ranged from 0.41 to 0.82 and τn ranged from 0.16 to 0.55 for the nets tested, whereas the reflectances were very low (ρn≤0.08). The color and porosity together affect the properties of the net. Even though under equilibrium conditions of a net with the surrounding environment, the emittance of the net is equal to its absorptance. However, the absorbed thermal radiation by the net dose not equal to the emitted radiation and the difference is a convected heat.

The long-wave radiative properties of a plastic shading net are essential to determine the thermal performance of a particular structure covered with this net. Nets are non-homogeneous, three-dimensional and semi-transparent materials, and therefore the radiative properties of a net cannot be measured in a laboratory using instruments designed for homogeneous materials. In addition, net radiometers cannot be used to measure these properties directly due to radiation emitted from the net surfaces. No suitable technique is presently available for determining the long-wave properties of shading nets. This paper describes a simple method for determining the total hemispherical long-wave radiative properties (i.e., transmittance, reflectance and absorptance or emittance) of nets. Nets with colors, porosities, texture type and nominal shading factors that are most commonly used in hot regions were selected for testing. The measurements were performed under equilibrium conditions (i.e., nighttime, steady-state and uniform sky thermal irradiance). The results show that the behaviors of plastic nets under thermal radiation conditions were different from those of translucent homogeneous materials. Net temperature and porosity were more important than texture type and color in determining transmittance and reflectance. The net temperature drop at night (6–10.5 °C) caused shrinkage in the net. This resulted in a decrease in porosity, which in turn caused a decrease in transmittance and an increase in reflectance. For the nets tested, transmittance decreased from 1.2% to 6.3% per 1 °C decrease in temperature. The reduction in transmittance was equal to the increase in reflectance. Emittance of the net depends on net temperature, color, porosity and texture type, although, at low temperature, none of these effects was significant.

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria, not on scientific considerations because parameters used to characterize the different types of nets is not available. Solar radiation transmission is the most important parameter characterizing nets. A simple measuring method is presented and used to quantify global, diffuse and direct beam solar radiation transmission trough seven plastic shading nets. Nets with colors and nominal shading factors that are most commonly used in the Arabian Peninsula were selected for the study. The results showed that the behaviors of the plastic nets and their radiative properties under solar radiation conditions were similar to translucent materials. Accordingly, investigating equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets similar to translucent materials is possible. Determining these constants can help to predict the radiative properties of the net without the need of measurements. Solidity and color of the net had significant effects on the radiative properties. The shading factor of a plastic net depends on the time of the day and on the design and meteorological parameters. Daily integral of the shading factor, solidity and the total radiative properties are appropriate parameters describing a net whereas, nominal shading factors provided by the producers cannot be used.

The radiative properties of several plastic shading nets were measured under natural solar radiation conditions. We found that the plastic nets behave as homogeneous translucent materials (e.g., plastic film, plastic sheets, and glass). Based on this behavior, we suggest that it is possible to treat plastic nets as translucent materials and to characterize them with equivalent optical constants (i.e., equivalent refractive indexes,neq, and equivalent extinction coefficients,σeq). Here a physical model to determineneqandσeqof plastic nets was described in analogy to homogeneous translucent materials. We examined three groups of nets based on their color (black, black-green, and beige). Each group consisted of nets with four or five different porosities. Nets of each group had almost the same texture structure. For each group, we derived an equation forneqas a function of the net porosity and determined an average value forσeq. Once values ofneqandσeqwere determined, the solar radiative properties of a net could then be calculated fromneqandσeqfor any incident angle of solar beam radiation without the need of measurements. The present model was validated by comparing the calculated with the measured radiative properties of three nets at different incident angle of solar beam radiation. The calculated radiative properties reasonably agreed with measured values.

For a greenhouse thermal analysis, it is essential to know the energy partition and the amount of solar and thermal radiation converted into sensible and latent heat in the greenhouse. Factors that are frequently needed are: efficiency of utilization of incident solar radiation (π), and sensible and latent heat factors (η and δ). Previous studies considered these factors as constant parameters. However, they depend on the environmental conditions inside and outside the greenhouse, plants and soil characteristics, and structure, orientation and location of the greenhouse. Moreover, these factors have not yet been evaluated under the arid climatic conditions of the Arabian Peninsula. In this study, simple energy balance equations were applied to investigate π, η and δ; energy partitioning among the greenhouse components; and conversion of solar and thermal radiation into sensible and latent heat. For this study, we used an evaporatively cooled, planted greenhouse with a floor area of 48 m2. The parameters required for the analysis were measured on a sunny, hot summer day. The results showed that value of π was almost constant (≅0.75); whereas the values of η and δ strongly depended on the net radiation over the canopy (Rna); and could be represented by exponential decay functions of Rna. At a plant density corresponding to a leaf area index (LAI) of 3 and an integrated incident solar energy of 27.7 MJ m−2 d−1, the solar and thermal radiation utilized by the greenhouse components were 20.7 MJ m−2 d−1 and 3.74 MJ m−2 d−1, respectively. About 71% of the utilized radiation was converted to sensible heat and 29% was converted to latent heat absorbed by the inside air. Contributions of the floor, cover and plant surfaces on the sensible heat of the inside air were 38.6%, 48.2% and 13.2%, respectively.

Plastic nets with opaque threads are frequently used for shading agricultural structures under high solar radiation conditions. A parameter that is often used to define a net is the net porosity (Π). Value of Π is usually estimated by one of three methods: image processing, direct beam transmittance, or solar radiation balance (hereafter radiation balance). Image processing is a rather slow process because it requires scanning the net sample at high resolution. The direct beam transmittance and radiation balance methods greatly overestimate Π because some of the solar radiation incident on the thread surfaces is forward scattered and add a considerable amount of radiation to that transmitted from the net pores directly. In this study, the radiation balance method was modified to estimate Π precisely. The amount of solar radiation scattered forward on the thread surfaces was estimated separately. Thus, the un-scattered solar radiation transmitted from the net pores directly, which describes the net porosity, Π could be estimated. This method, in addition to the image processing and the direct beam transmittance methods were used to estimate Π for different types of nets that are commonly used for shading structures in summer. Values of Π estimated by using the proposed method were in good accordance with those measured by the image processing method at a resolution of 4800 dpi. The direct beam transmittance and the radiation balance methods resulted in overestimation errors in the values of Π. This error strongly depends on the color of the net. The estimated errors were +14% for a green net and +37% for a white net when using the radiation balance method, and were +16% and +38%, respectively, when using the direct beam transmittance method. In the image processing method, a resolution of 2400 dpi is sufficient to estimate Π precisely and the higher resolutions showed no significant effect on the value of Π.

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. Different varieties of these nets are commercially available. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria and not on scientific considerations because essential information used to characterize the different types of nets is not available. In order to replace expensive measuring facilities that use artificial lighting to investigate the radiative properties of plastic shading nets, a simple method was presented to investigate these properties under global, diffuse and direct beam solar radiation conditions. Measurements were performed on clear sunny days, (December 28, 2008–February 10, 2009). Nets with colors and shading factors that are most commonly used in hot regions were selected for the study. The results showed that the behaviors of the plastic nets under solar radiation conditions were similar to those of translucent materials. Accordingly, it is possible to (i) treat plastic nets as translucent materials and (ii) investigate the equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets as functions of the net solidity, texture type and color. Solidity and color of the net had significant effects on the radiative properties and the effect of color was much more than the effect of solidity. The shading factor of a plastic net, is a function of the daytime, depends on several design and meteorological parameters, so it cannot be used to describe a net. However, the net solidity together with color, and the daily integrals of the shading factor and of the radiative properties are appropriate parameters for describing a net.