Ground Air Collector Research Articles

Thermal modeling aspects of solar greenhouse microclimate control: A review on heating technologies

Modeling of greenhouse microclimate is very important to maintain optimum inside environment during different stages of plant growth. To formulate an accurate thermal model, computation of precise solar radiation input and overall heat transfer coefficient is important as these affect the greenhouse energy and mass balance. Initially, we briefly review the modular studies related to solar radiation capture and overall heat transfer coefficient for greenhouse applications. Numerous thermal models have been developed to describe the microclimate of a greenhouse and validated at various locations, climates and crops. We review all these independent thermal models (static as well as dynamic) and discuss in detail the representative ones. In adverse winter climatic conditions, greenhouse has to be coupled with various active or passive heating systems to maintain the inside microclimate according to crop needs. We also review greenhouse thermal models integrated with heating/heat storage systems such as: rock-bed, phase change materials, earth-tube heat exchanger systems, all types of water heating systems (water thermal mass storage, heat-pipe heating system, shallow solar pond heating systems, geothermal based heating systems viz. ground source heat pump system, solar-assisted ground source heat pump system, aquifer coupled heat exchanger system), ground air collector system, north wall and thermal curtain, and soil heat exchanger system. Important aspects of each representative model such as: type, tool/program used for solution/simulation, input data used to run simulations, interactive components, parameters studied, assumption made, important model characteristics and results obtained are discussed at length. Based on the compiled information, a generalized procedure is devised to formulate greenhouse thermal model. Finally, based on the main characteristics and results of the study, some important conclusions are drawn and suggestions made for further studies.

Survey and evaluation of heating technologies for worldwide agricultural greenhouse applications

This paper reviews and evaluates all the available heating technologies for worldwide agricultural greenhouses and discusses the representative applications of each technology. Available information on the location, ground area, cover materials and performance of the greenhouses coupled with each technology such as water storage (including solar flat plate collectors, ground-source heat pumps and shallow solar ponds), rock bed storage, phase change material storage and earth-to-air heat exchanger system is collected and presented in detail. Using the collected information an attempt has been made to correlate the approximate storage volume or weight of the material required for a given greenhouse area for different storage media under various greenhouse cover materials. These relations can be of great importance to the potential users for the successful development of future applications. Apart from the above-mentioned technologies, a complete review and performance evaluation of other greenhouse heating technologies such as movable insulation, north wall storage, ground air collector and aquifer coupled cavity flow heat exchanger system is also presented. Heating potential (overall performance) of each system under different cover materials along with their advantages, limitations and suitability is also discussed.

Greenhouse heating and cooling using aquifer water

Abstract An aquifer coupled cavity flow heat exchanger system (ACCFHES) was designed using underground aquifer water for the heating as well as cooling of a composite climatic greenhouse. The performance of ACCFHES was experimentally evaluated for a full winter and a summer season. The ACCFHES makes use of constant temperature aquifer water (24 °C) available at an agricultural field through an irrigation tube well for heating in winter nights and cooling in summer days. The results showed that the average greenhouse room air temperature was maintained 7–9 °C above the outside air during extreme winter nights and 6–7 °C below the outside air in extreme summer days, and temperature fluctuations inside the greenhouse also decreased daily. The average relative humidity (RH) inside the greenhouse also decreased by 10–12% in the winter and increased by more than double in the extreme summer conditions as compared to the outside conditions. A comparison of economic feasibility of the ACCFHES coupled greenhouse was also conducted with conventional greenhouse and open field condition based on the yield of Capsicum annum. The ACCFHES was also compared economically with other existing heating/cooling technologies such as earth-to-air heat exchanger system (EAHES), ground air collector, evaporative cooling using foggers and fan & pad system in terms of net present worth (NPW) and pay back period. It was observed that the NPW of the ACCFHES coupled greenhouse was much higher as compared to the conventional greenhouse and open field condition. The payback period of the ACCFHES coupled greenhouse was the lowest among all other existing heating/cooling systems.

Experimental and economic study of a greenhouse thermal control system using aquifer water

Abstract Underground aquifer water is used for thermal control (heating as well as cooling) of a greenhouse in which chilli and capsicum are grown. Year round performance of the designed system is experimentally evaluated and presented. The designed system utilizes the constant temperature aquifer water available on the ground surface at around 24 °C (year round) in the agricultural field through deep tubewell used for irrigation purposes for heating a greenhouse in winter nights and cooling in summer days. Experimental performance of the designed system is tested during a full winter as well as for summer conditions. To enhance the efficiency of the system and to improve relative humidity during extreme summer conditions, a simple evaporative cooling process is also added within the same designed system. The experimental results show that the average greenhouse room air temperature is maintained 7–9 °C above ambient during winter nights and 6–7 °C below ambient in summer days besides decreasing the daily temperature fluctuations inside the greenhouse. Improvement in the average relative humidity during extreme summer conditions is also observed. Technoeconomic analysis of the greenhouse integrated to the designed aquifer coupled cavity flow heat exchanger system (ACCFHES) is also conducted based on the yield of capsicum and chilli crops and compared with those of the greenhouse without any thermal control system and the open field condition yields. An economic comparison of the ACCFHES has also been made with other existing thermal control technologies such as the earth air heat exchanger system, ground air collector, evaporative cooling using foggers and a fan and pad system.

06/00771 Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse: Ghosal, M. K. et al. Energy and Buildings, 2005, 37, (6), 613–621.

06/00771 Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse: Ghosal, M. K. et al. Energy and Buildings, 2005, 37, (6), 613–621.

06/00244 Modeling and comparative thermal performanceof ground air collector and earth air heat exchanger for heating of greenhouse: Ghosal, M> K. et al. Energy and Buildings, 2005, 37, (6), 613–621

06/00244 Modeling and comparative thermal performanceof ground air collector and earth air heat exchanger for heating of greenhouse: Ghosal, M> K. et al. Energy and Buildings, 2005, 37, (6), 613–621

Modeling and comparative thermal performance of ground air collector and earth air heat exchanger for heating of greenhouse

The potential of using the stored thermal energy of ground for space heating has been investigated with the help of two buried pipe systems, i.e., ground air collector and earth air heat exchanger, integrated with the greenhouse located in the premises of Indian Institute of Technology, Delhi, India. The total length of the buried pipes in both the arrangements was kept same for making a comparative study. A complete numerical model has been developed to predict and compare their thermal performance for choosing a suitable heating method in the composite climate of India. Experiments were conducted extensively during winter period from November 2002 to March 2003, but the model was validated against the clear and sunny days. Performance of these two arrangements was compared in terms of thermal load leveling and total heating potential. Temperatures of greenhouse air with ground air collector were observed to be 2–3 °C higher than those with earth air heat exchanger. The temperature fluctuations of greenhouse air were also less when operated with ground air collector as compared to earth air heat exchanger. Predicted and computed values of greenhouse air temperatures in both the systems exhibited fair agreement. Finally ground air collector was chosen as a suitable option for heating of greenhouse in the above climate.

03/02040 Modeling and optimal design of ground air collector for heating in controlled environment greenhouse: Jain, D. and Tiwari, G. N. Energy Conversion and Management, 2003, 44, (8), 1357–1372

03/02040 Modeling and optimal design of ground air collector for heating in controlled environment greenhouse: Jain, D. and Tiwari, G. N. Energy Conversion and Management, 2003, 44, (8), 1357–1372

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 m 2 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.

Off-season cultivation of capsicums in a solar greenhouse

SYNOPSIS The use of solar energy for growing capsicums in pots and in the ground has been studied both under a controlled environment in a solar greenhouse (IIT model) and in an open field during August 2000 to March 2001. Cooling arrangements (natural, forced convection, shading, evaporative cooling) and heating methods (ground air collector, movable insulation during the night) have been employed during the pre-winter and winter periods respectively to maintain the protected environment in the greenhouse. The effects of a north brick wall and the use of movable insulation during the night in the winter months to reduce heat loss from the greenhouse have been incorporated to study the efficacy of the greenhouse. The average height, weight and yield per plant of the greenhouse crop were higher than those of the open field.

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.

EFFECT OF THERMAL STORAGE ON CROP DRYING SYSTEM: A PERIODIC ANALYSIS

This communication presents the periodic analysis of a ground air collector with reflector and crop drying chamber. The effect of thermal storage, collector length, depth of the plane of heat retrieval, the flow rate on the useful energy gain and crop temperature has been studied. Numerical computation has been carried out for the typical day of the month of June and December for Delhi climatic conditions. It is observed that there is a significant phase shift 10-12 h due to storage effect.

Thermal analysis of a ground air collector

In the present paper a mathematical model for a ground air collector is presented. The collector consists of a metallic duct buried in the ground whose top surface is blackened and suitably glazed. The air flows through the metallic duct and is heated. The model takes into account the time dependence of various performance parameters. Numerical calculations carried out for a typical set of parameters show that an air temperature, varying between 44°C and 38°C, at a depth of 0.3 m can be obtained, corresponding to a variation in ambient air temperature of 43—30°C. The results indicate that the system stores substantial amounts of energy and can also be used for night operation.