G.N. Tiwari

Modeling and optimal design of evaporative cooling system in controlled environment greenhouse

Abstract This communication deals with the development of a mathematical model for experimental validation of the thermal behavior in the greenhouse after evaporative cooling. Extensive experiments have been performed during July to October 2000 for an even span greenhouse of effective floor area of 24 m 2 and having a brick north wall. A parametric study involves the area of the cooling pad (height of cooling pad and greenhouse), mass flow rate and length of greenhouse. The optimum value of various parameters has also been determined. A computer program based on MatLab software has been used to predict the temperature profile as a function of various design parameters. The predicted room temperature of various zones shows fair agreement with the experimental values.

Thermal heating of controlled environment greenhouse: a transient analysis

In this paper, an attempt has been made to maintain the plant and room air temperature of a controlled environment greenhouse by using a thermal storage north wall and an integration of a ground air collector. An analytical expression for the plant and room air temperature, based on energy balances for each component, have been derived in terms of climatic as well as design parameters. Numerical computation have been performed for a typical cold day of Delhi, for various temperatures and thermal load levelling. It has been observed that: (i) there is a significant effect of the thermal storage north wall and the ground air collector on the plant and room air temperatures and (ii) thermal load levelling decreases with the increase of the isothermal mass in the case of heating and vice versa for cooling, as per expectations. Experimental validation has also been done for a similar type of greenhouse with movable insulation.

Modeling and optimal design of ground air collector for heating in controlled environment greenhouse

A mathematical model is devised to study the thermal behavior of a greenhouse while heating with a ground air collector (GAC). A computer program based on MatLab software has been used to predict the plant and room temperatures as a function of various design parameters of the ground air collector. Extensive experiments have been conducted during December 2000 to March 2001 for an even span greenhouse of effective floor area of 24 m2 with a GAC and having a brick north wall. The model was validated experimentally in the climate of Delhi for the winter season. A parametric study involves the area of the GAC, mass flow rate and heat capacity. The predicted plant and room temperatures show fair agreement with the experimental values.

Optimum distribution of insulation inside and outside the roof

Abstract The accurate prediction of the rate of heat flow through walls and roofs made of several layers of different materials is a problem of practical importance in the design of buildings and their associated air conditioning systems. In this paper we have investigated the optimum distribution of a given total thickness of insulation inside and outside the roof for achieving the maximum levelling in the heat flux entering through the roof. It is seen that this is achieved when the thicknesses of insulation inside and outside the roof are equal. The implications of this result in reducing the required capacity of air-conditioning plants have also been briefly discussed.

Evaluation of solar fraction on north partition wall for various shapes of solarium by Auto-Cad

In the present paper, the distribution of solar energy inside the uneven span solarium has been determined in terms of solar fraction on north partition wall by using Auto-CAD 2000 for New Delhi (28.5° latitude). This enables the prediction of its performance for passive heating. The concept has been extended to other shapes of greenhouses for cultivation of flowers during off-season. The other shapes included for study are even span, modified arch, vinery and modified IARI. They have similar floor area and height. Analysis has been made with the help of a model based on Auto-CAD 2000 for a typical day of each month of the year. It has been observed that the solar fraction plays an important role at low altitude for thermal heating of either a building or a greenhouse during winter months. It mainly depends on the shape and size of greenhouse and time of the nth day of the year. Based on the analysis it can be concluded that the modified arch shape greenhouse is suitable for thermal cooling through out the year. Uneven span shape greenhouse is most suitable for thermal cooling of living space in winter and heating in summer, in comparison to other shapes.

Periodic heat transfer with temperature dependent thermal conductivity

mean value of the surface temperature c”C], amplitude of the rtth harmonic of the surface temperature [“Cl ; specific heat of the medium [kJ/kg “C] ; =(-I)‘*; thermal conductivity of the medium at temperature A, [kJ/h m “C] ; thermal conductivity of the medium per unit temperature [kJ/h m “C*] ; number of harmonics; real part of the quantity; temperature of the medium [“Cl ; time [Ii]; vertical axis.

Experimental validation of thermal model of hybrid photovoltaic thermal (HPVT) double slope active solar still

Abstract A HPVT double slope active solar still was designed and fabricated to study their performance. In this paper thermal modeling of HPVT double slope active solar still with two fl at plate collectors connected to the basin of solar still has been carried out. Analytical expressions for yield, water temperature and condensing cover temperature have been derived as a function of climatic and design parameters on the basis of energy balance equations. The thermal model of distillation system has been validated with experimental data. It has been established that there are close agreement between theoretical and experimental results with coefficient of correlation varying from 0.872 to 0.965.

Exergy and Technoeconomic Analysis of Solar Thermal Desalination

Abstract The performance of any renewable energy system (RES) depends on the availability of the useful energy and exergy from the system; and the energy and exergy analysis of RES (optimization of the design and operating parameters) is essential for the minimum use of fossil fuel in order to preserve them for future generation. In exergoeconomic analysis, the mutual techniques of scientific disciplines (mainly thermodynamics) with economic disciplines (mainly cost accounting) are used in order to attain the overall optimal design of the RES. Basically, the main pillar of any implemented technique in the system is the life-cycle cost analysis (LCCA) of any system. It sets the constraints as well as gives an idea to approve or reject the system for the execution of technology.