On the selection of shape and orientation of a greenhouse for composite climates

Five most commonly used single-span shapes of greenhouses such as even-span, uneven-span, vinery, modified arch and quonset type have been selected for comparison in a composite type of climate. The length, width and height (at the centre) are kept the same for all the shapes. The comparison is based on total solar radiation input (beam, diffused and ground reflected) to each shape through each wall, inclined surfaces and roofs. Total solar radiation is theoretically computed for each shape in east–west and north–south orientations and compared for each month of the year. The computed values for each shape are then introduced in a transient thermal model developed to compute the hourly inside greenhouse air temperature for the selected day of the year in each month. It is observed that the variation in greenhouse shape can cause up to 3.5–5.5 °C change in the inside air temperature during different hours of the day. Experimental validation of the model is carried out using the measured inside air temperature data (for a typical summer day) for an even-span greenhouse (in which capsicum is grown) at Ludhiana (31°N and 77°E), Punjab, India. The predicted and measured values are in close agreement. The results show that even-span or quonset shape in east–west orientation is the most suitable shape for year-round agricultural operations.     

On the selection of shape and orientation of a greenhouse: Thermal modeling and experimental validation

In this study, five most commonly used single span shapes of greenhouses viz. even-span, uneven-span, vinery, modified arch and quonset type have been selected for comparison. The length, width and height (at the center) are kept same for all the selected shapes. A mathematical model for computing transmitted total solar radiation (beam, diffused and ground reflected) at each hour, for each month and at any latitude for the selected geometry greenhouses (through each wall, inclined surfaces and roofs) is developed for both east-west and north-south orientation. Computed transmitted solar radiation is then introduced in a transient thermal model developed to compute hourly inside air temperature for each shape and orientation. Experimental validation of both the models is carried out for the measured total solar radiation and inside air temperature for an east-west orientation, even-span greenhouse (for a typical day in summer) at Ludhiana (31°N and 77°E) Punjab, India. During the experimentation, capsicum crop is grown inside the greenhouse. The predicted and measured values are in close agreement. Results show that uneven-span shape greenhouse receives the maximum and quonset shape receives the minimum solar radiation during each month of the year at all latitudes. East-west orientation is the best suited for year round greenhouse applications at all latitudes as this orientation receives greater total radiation in winter and less in summer except near the equator. Results also show that inside air temperature rise depends upon the shape of the greenhouse and this variation from uneven-span shape to quonset shape is 4.6 °C (maximum) and 3.5 °C (daily average) at 31°N latitude.     

Passive solar radiant system,SIRASOL. Physical–mathematical modeling and sensitivity analysis

When using passive solar heating systems, it is necessary to have available an Equator-facing facade on which to install them. Rooms without such a facade are not the best option for conventional passive solar heating systems. SIRASOL is a passive solar radiant system that captures solar energy and is to be installed in the ceiling of the room. This room must not necessarily have an Equator-facing facade. Solar energy heats up a metal sheet, which is the radiant panel, which transfers heat by long-wave radiation to the room below it. This paper presents a mathematical model and a sensitivity analysis. The mathematical model was used to analyze radiant panel temperature, radiant mean temperature, operative temperature and panel surface area. Results of the sensitivity study showed that when solar radiation rises (from 200 to 800 W) panel temperature increases from 36 °C to 92 °C, whereas variations in outside and inside air temperature have a negligible impact on the panel temperature. Thus, the use of SIRASOL is possible in locations with clear skies. Moreover, from panel temperature values we calculated mean radiant temperature and thereby the room’s operative temperature, which is proportional to the radiant panel area. When this area is 50% of the room’s floor area, operative temperature grows 3.1 °C higher than inside air temperature when solar radiation is 500 W/m². The analysis shows that a thermal asymmetry appears only when SIRASOL’s surface area to floor area ratio is higher than 32%.     

Parametric studies for heating performance of an earth to air heat exchanger coupled with a greenhouse

A thermal model has been developed to investigate the potential of using the stored thermal energy of the ground for greenhouse heating with the help of an earth to air heat exchanger (EAHE) system integrated with the greenhouse located in the premises of IIT, Delhi, India. Experiments were conducted extensively during the winter period from November 2002 to March 2003, but the model developed was validated against the clear and sunny days. Parametric studies performed for EAHE coupled with the greenhouse illustrate the effects of buried pipe length, pipe diameter, mass flow rate of air, depth of ground and soil types on greenhouse air temperatures. Temperatures of greenhouse air with the experimental parameters of EAHE were found to be on an average 7–8°C more in the winter than the same greenhouse without EAHE. Greenhouse air temperatures increase in the winter with increasing pipe length, decreasing pipe diameter, decreasing mass flow rate of flowing air inside buried pipe and increasing depth of ground up to 4 m. Predicted and measured values of greenhouse air temperature, which were verified in terms of root mean square of percent deviation and correlation coefficient, exhibited fair agreement. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal modelling and experimental validation of ground temperature distribution in greenhouse

A periodic analysis for daily and monthly variations of ground temperature with depths is presented both under greenhouse and bare surface conditions of Delhi and for bare surface condition in other climates of India in order to design an efficient earth to air heat exchanger for greenhouse system. Calculations were carried out for a typical winter and summer day of Delhi in year 2000. Predicted values of ground temperature at 1 m depth were in fair agreement with experimental values under both conditions. Ground temperatures at various depths inside greenhouse were found to be on an average 7–9°C and 3–6°C higher than bare surface for daily and monthly variations respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance analysis of direct solar dryer driven by photovoltaic thermal energy recovery and solar air collector for drying materials and electricity generation

The direct-type solar dryer is characterized by very simple construction, less maintenance, cost-effectiveness, and is easy to handle. The present study aims to enhance the performance of a direct-type solar dryer. To achieve this, the photovoltaic (PV) panels with thermal energy recovery and solar air collector were integrated with the direct-type solar dryer. In this study, the PV panels with thermal energy recovery and solar air collector were utilized as preheating units to raise the air temperature before entering the direct solar dryer. Moreover, the PV panels were utilized to drive the air blower. In this study, three incorporated models are suggested to study the performance of the solar dryer integrated with PV panels with thermal energy recovery and solar air collector. The model of each component was validated by the previously recorded empirical data. The results confirmed that the dual utilization of the PV panels with thermal energy recovery and solar air collector as a preheating unit raised the air temperature entering the direct solar dryer by the rate varying between 29°C and 42°C within the period 9:00 a.m.–4:00 p.m. Also, the moisture content of banana samples inside the direct solar dryer reduced from the initial value of 72% (wb) to the value of 33.4% (wb) within 7 h (9:00 a.m.–4:00 p.m.). During this operating period, moisture removal from the banana samples varied between 110 and 400 g/h.     

Efficiency of combined solar photothermal plants

The efficiency of a combined solar photothermal plant for electric and thermal energy generation has been evaluated with account for the daily variation of solar radiation and atmospheric temperature. It is shown that in the summer with the heat removal temperature 40°C it is possible to utilize additionally up to 50% of the solar radiation energy even in the absence of thermal insulation of receiver bottom.     

Numerical simulation of the airflow and temperature distribution in a lean-to greenhouse

In this paper, heat transfer and flow in a lean-to passive solar greenhouse has been studied. A mathematical model based on energy equilibrium and a one-dimensional mathematical model for the unsaturated porous medium have been founded and developed to predict the temperature and moisture content in soil and the enclosed air temperature in the greenhouse. On the condition that plant and massive wall is neglected, the air is mainly heated by the soil surface in the greenhouse, which absorbs the incident solar radiation. With increase in depth, the variation of the temperature and moisture content in soil decreases on account of ambient, and the appearance of the peak temperature in soil postpone. Solar radiation absorber, heat storage and insulation are the main effects of the north massive wall on greenhouse, which is influenced by the structure and the material. The specific heat capacity and thermal conductivity of wall material have a remarkable effect on the north wall temperature. The build-up north wall with thermal insulation material may be chosen for greenhouse. The temperature distribution and gas flow in greenhouse is influenced by the cover material of the inside surface of the north wall and the inclined angle of greenhouse roof. All results should be taken into account for a better design and run of a greenhouse.     

Effect of phase change material on passive thermal heating of a greenhouse

In this study, a periodic analysis of a greenhouse with combination of phase change material (PCM) and insulation as a north wall has been developed for thermal heating. The thermal model is based on Fourier analysis. Effect of distribution of PCM thickness on plant and room air temperature has been studied in detail. The plant and room air temperature have been evaluated with and without north wall. Numerical computations have been carried out for a typical winter day of New Delhi. On the basis of numerical results, it is inferred that (i) there is a significant effect of PCM north wall and heat capacity of plant temperature during off‐sunshine hour due to storage effect and (ii) the rate of heat flux inside greenhouse from north wall is maximum for least thickness of PCM. Copyright © 2005 John Wiley & Sons, Ltd.     

Experimental investigation on pyramid solar still with single and double collector cover—Comparative study

Sun radiation is the heat energy source for solar still. That should be utilized maximum for increasing the evaporative rate at the top surface of the brine. The pyramid shape solar still (PSSS) can receive solar input radiation from all four directions. In this research, the top layer of conventional pyramid shape solar still (CPSSS) is covered with air‐packed cover and analysed the effect in the modified still after air packed in between the two glasses, finally, that result is compared with the CPSSS. The air inside the two glasses will be receiving maximum radiation and retain in it. It can be used as top side insulation and which can ensure the maximum insulation for heat energy inside the PSSS. The CPSSS and air‐packed pyramid shape solar still (APPSSS) were fabricated and experimented. The experiments were conducted at an ambient condition of the Chennai, Tamil Nadu (12.9416°N, 80.2362°E). The CPSSS gives good yield at evening when an increase in wind velocity. The APPSSS gives a lower performance as compared to the CPSSS due to the air‐packed cover.     

Global solar radiation estimation from measurements of visibility and air temperature extremes

Solar radiation is the main source of energy for the survival of life and its associated activities. It is important to know accurate solar radiation value in areas such as agricultural activities, solar energy systems, heating, and meteorology. In this study, we present a model for the estimation of solar radiation value with other meteorological parameters in cases where solar radiation cannot be measured or not available. This model is based on the relationship between solar radiation and measured air temperature and visibility extremes. As is known, the incident global solar radiation is attenuated by clouds, aerosols, ozone layer, water vapor, etc.. In the model, the attenuation of the solar radiation is expressed by dew point temperature, visibility, and the maximum and minimum air temperatures. Dew-point temperature refers to the effect of water vapor on solar radiation, air temperature extremes are used to signify cloudiness. Visibility also gives the effect on the attenuation of solar radiation by air pollutants and aerosols in the model. The model was applied to the data taken from meteorological stations in Turkey. Error analysis was performed and compared with the models in the literature and satisfactory results were obtained.

Abbreviations H: Daily total global solar radiation, units of MJ ? m^?2 ? day^?1; H₀: Extraterrestrial solar radiation, units of MJ ? m^?2 ? day^?1; H_m: Measured daily total global solar radiation, units of MJ ? m^?2 ? day^?1; H_c: Calculated daily total global solar radiation, units of MJ ? m^?2 ? day^?1; T_min: Daily minimum temperature, units of °C; T_max: Daily maximum temperature, units of °C; RH: T_dew: Relative humidity, units of %rh; Dew-point temperature, units of °C     

Formulation and validation of a mathematical model of the microclimate of a greenhouse

A mathematical model MICroclimate of GREENhouse (MICGREEN), consisting of set of algebraic equations, was developed. The equations were written for four components of the greenhouse viz. cover, inside air, canopy surface and bare soil surface. It was assumed that the greenhouse air is well mixed, thermal properties of materials of construction do not change with time and solar radiations pass through cover without absorption. The values of dimensions and material properties of the greenhouse constructed at the Research Farm of Department of Soil and Water Engineering, Punjab Agricultural University, Ludhiana were put in these equations. The inputs to the model are ambient air temperature, solar radiations on normal surface, solar radiations on earth's surface, temperature of the soil under canopy and temperature of the soil at a depth of 6 cm. A computer program was written in C++ language. The equations were solved using Gauss–Seidal Iteration method. The outputs of the model are greenhouse cover temperature, inside air temperature, canopy temperature and bare soil temperature. The relative humidity of the inside air is predicted from the predicted inside air temperature with the help of psychrometric chart. To validate this model, experiments were conducted on greenhouse to obtain data during winter as tomato crop was being grown. The results of computer model were compared with the experimental results and agreement was found between the measured and predicted values.     

日光温室加内保温幕的试验

减少夜间通过前屋面的散热是日光温室节能的关键。文章对室内前屋面下设置保温幕的试验温室(有幕温室)与相同结构的不设保温幕的对比温室(无幕温室)的温度环境进行了测试比较。测试结果显示:内保温幕的设置有效地抑制了夜间通过前屋面由于温差引起的散热,并提高了晴天夜间室内的温度。     

Optimum Tilt Angle for Solar Collectors

A solar collector is required to absorb solar radiation and transfer the absorbed energy into a heat transfer fluid with a minimum of heat loss. In assessing the performance of a collector, it is therefore important not only to determine its ability to absorb solar radiation but also to characterize its heat losses. The ability of a collector to absorb solar radiation is largely determined by its optical and geometric properties. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation in tilt angle affects the amount of solar radiation reaching the collector surface. In this study, a mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. It is found that the optimum tilt angle changes between 0° (June) and 61° (December) throughout the year. In winter (December, January, and February) the tilt should be 55.7°, in spring (March, April, and May) 18.3°, in summer (June, July, and August) 4.3°, and in autumn (September, October, and November) 43°. The yearly average of this value was found to be 30.3° and this would be the optimum fixed tilt throughout the year.     

The passive solar heated school in wallasey. IV. An observational study of the thermal response of a passive school building

An observational study on the Wallasey School has demonstrated its ability to maintain in most conditions of climate an equitable indoor climate both in regard to daily mean temperatures and daily variations, through use of solar gain and heat from the lights, and the appropriate control of ventilation. During occupied periods, air temperatures are usually between 17°C in winter and 23°C in sunny summer periods. The room provides a mainly ‘cold wall’ environment. The observational data and a series of model estimates have been compared. The general level of temperature within the building is known to depend strongly on ventilation rate, but since ventilation rate was not measured, steady-state comparisons as such are not possible. The observed and estimated temperature profiles for air and various surfaces including that of the furnishings during a very sunny period are in broad agreement. Analyses of the transient response of the structure in winter conditions has demonstrated a long response time (several days) describing the response of the enclosure, and a shorter response time of about half a day which describes the rate of settlement of internal temperature differences which may be initially present. Evidence is presented indicating low values for the convective heat transfer coefficient. An autocorrelational technique demonstrates that the thermal ‘memory’ of the classroom is much longer in winter than in summer. The response of the room during occupied and unoccupied periods is broadly similar, but conditions are rather more variable during occupation.     

Potential for large-scale solar collector system to offset carbon-based heating in the Ontario greenhouse sector

In the Ontario greenhouse sector the misalignment of available solar radiation during the summer months and large heating demand during the winter months makes solar thermal collector systems an unviable option without some form of seasonal energy storage. Information obtained from Ontario greenhouse operators has shown that over 20% of annual natural gas usage occurs during the summer months for greenhouse pre-heating prior to sunrise. A transient model of the greenhouse microclimate and indoor conditioning systems is carried out using TRNSYS software and validated with actual natural gas usage data. A large-scale solar thermal collector system is then incorporated and found to reduce the annual heating energy demand by approximately 35%. The inclusion of the collector system correlates to a reduction of about 120 tonnes of CO₂ equivalent emissions per acre of greenhouse per year. System payback period is discussed considering the benefits of a future Ontario carbon tax.     

Short-term thermal performance of a built-in solar storage for frost prevention in a greenhouse

Built-in solar storage is an alternative to the traditional solar collectors. This paper explores the possibility of utilizing such solar stores for frost prevention in greenhouses. In the study, two identical NE–SW orientated greenhouses with 50 m² ground area were erected. The total ground area and volume of the water stores used in the solar greenhouse were about 6·4 and 5·4% of the total ground area and volume of the greenhouse. The short-term results showed that at times when the air temperature in the control greenhouse dropped below 0°C, it was about 3·5°C in the solar greenhouse, and sometimes this difference was more than 4·5°C. The average fraction of solar energy storage by the stores was 0·26 for a four day period. © 1998 John Wiley & Sons, Ltd.     

ANFIS modelling of a natural convection greenhouse drying system for jaggery: an experimental validation

The aim of the current research work is to generate an adaptive-network-based fuzzy inference system (ANFIS) model so as to forecast the jaggery temperature, the greenhouse air temperature and the moisture evaporation for drying of jaggery inside the greenhouse for natural convection mode. The experiment was conducted separately for 0.75 and 2.0 kg of jaggery pieces having dimensions of 0.03×0.03×0.01 m³ for complete drying. The jaggery was dried in a roof-type even span greenhouse with a floor area of 1.20×0.78 m². An ANFIS model was developed in MATLAB software so as to calculate the jaggery temperature, the greenhouse air temperature and the moisture evaporated and was also used to forecast the thermal performance of the greenhouse on the basis of solar intensity and ambient temperature. This model was experimentally validated. It was shown that the analytical and experimental results for jaggery drying are in good agreement.     

Evaluation of solar fraction (Fn) for quonset type empty greenhouse: an experimental validation

In this study, the experiments were conducted from December 2000 to November 2001 to evaluate solar fraction (F_n) for quonset type empty greenhouse. Solar radiation was measured at different points inside and outside the greenhouse weekly once. The model based on Auto-CAD 2000 has been used for a given solar altitude and azimuth angles. Calculations have also been carried out for a typical day of each month of the year. It is observed that the solar fraction obtained by using Auto-CAD 2000 are very close to the value determined by using experimental observations and its value is more during winter months. Copyright © 2002 John Wiley & Sons, Ltd.     

温室内太阳净辐射分配及计算

针对温室内存在气体辐射问题,应用辐射相关知识,推导出温室各内表面对太阳净辐射的吸收份额,并给出了温室内气体吸收率的计算方法。针对睛天和阴天的不同太阳辐射特性,提出了相应的理论计算方法,为温室内能量计算提供了理论依据。