Cropping in Arid-Area Greenhouse

In hot, arid regions, yields are usually low and unstable. Greenhouse technology can stabilize and improve yields. But its adoption is impeded by the requirement of large amounts of water for cooling. Evaporative cooling is the most common method. Arid Area Greenhouse (AAG) is being developed for hot arid regions, particularly to reduce or eliminate the water needed for cooling. To achieve this, AAG employs earth-tube-heat-exchanger (ETHE) and static vents for environmental control. A prototype was installed in 2002 in an arid region, at village Kothara (ƒ� 23�X 14 N, ƒ� 68�X 45 E, at 21 m a.s.l.) for study. The single span saw-tooth greenhouse is 20 X 6 X 3.5 m. The ETHE is buried 3m deep directly below and coupled to it in closed-loop mode. ETHE is made of a bundle of eight mild steel pipes arranged in two tiers. Each pipe is 23 m long and 20 cm diameter. ETHE provides 20 air changes per hour. Initial cost of ETHE (material, fabrication, transport and installation) was $ 5000, nearly equal to that of greenhouse excluding instrumentation. There are three continuous closable vents - two along the base of long sides and one along the ridge. A retractable shading cover is provided over the roof. The aim was to determine (a) the extent to which ETHE and natural ventilation meet the need for environmental control and the associated costs (b) the extent to which productivity is increased, cropping season extended. By summer of 2007 five rounds of cropping have been done. ETHE was able to heat the greenhouse easily from 9�XC to 22-23�XC in half hour in the cold winter nights. Static ventilation along with shading was effective for day time control till February keeping the temperature about 34�XC inside. Subsequently, ETHE was operated. It limited the greenhouse temperature to 36-37�XC with top shaded and crop inside. If grid supply is steady it is operated for five-six hours in the day. House is closed in May-June. Yield of tomato has been close to 2 times that of the open-fields in the province. Water used was 44% of that used in open-field. The water used was mostly for plants, only a small part was for supplementary cooling using foggers. ETHE and static vents hold promise as environmental control device for greenhouses in hot arid regions. There is need to reduce installation cost by substituting plastic pipes for metal. It is also necessary to develop a more easily scalable design than the present one.

Development and Some Applications of Earth Tube Heat Exchanger in Gujarat

This write-up describes the development and some applications of earth tube heat exchangers in Gujarat. Work outlined here was delivered as Nanubhai Amin Memorial Lecture at Electrical Research and Development Association, Vadodara as part of Technology Day, 11 May 2004.

Harvesting dew to supplement drinking water supply in arid coastal villages of Gujarat

Shortage of drinking water is chronic, sever and widespread in Kutch - a hot and very arid region. It is specially acute in coastal villages where surface sources dry up rapidly and groundwater is not potable. Many of these are listed as “no source” villages and are supplied water on tanker-trucks daily from long distances. The conventional efforts to conserve and augment water resources are all in place. But one potential resource - dew - had remained unnoticed. The possibility that it may also be a supplementary resource was first noticed in the summer of 2001 when it was observed that dew condensed frequently on a plastic- clad greenhouse in Kothara, a village 15 km from the coast. That led us first, to carry out systematic measurement, and then to develop practical ways to harvest dew for human use. Measurement at Kothara was followed by measurements at two other locations along the coast - Panandhro and Mithapur. Data showed that dew occurred over an eight-month season (October- May) spanning the entire dry part of the year. Quantity was more in summer months than in winter. Dew water was found potable and safe. In the next three years development of dew harvest systems was carried out, prototypes were made and tested. After successful field trial three models were launched. The key component of the systems is the condenser, made of thin plastic film which can harvest 15 – 20 mm of dew water in the season. Condenser cools itself by radiative exchange with sky, without the use of any external energy. Working installations have been made on large roofs and on open ground. While the devices are specifically engineered to condense dew, these routinely harvest rain as well. These are being promoted as “dewrain” harvest systems that deliver useful but varying amount of water through all the months of the year.

Physical Characteristics of Some Vegetables Grown in Ahmedabad Region

Physical dimensions, mass, shape and bulk density of vegetables grown around Ahmedabad have been determined. Measurements were carried out on samples at the farm immediately after harvest. Pattern underlying one of the characteristic dimensions has been identified. Statistical distribution that best described the pattern in all cases was found to be two parameter Weibull. Use of cluster analysis was illustrated in case of okra to determine the number of relatively homogenous groups into which the produce can be separated. Results may be useful to those working on unit technology and technology systems for fresh produce.

Design of Greenhouse Irrigation System at Kothara

In this paper we present the details of fertigation system for greenhouse at Kothara (Kutch). Two separate alternatives--Drip and Sprinklers--have been examined.

Soil Temperatures Regime at Ahmedabad

A 3-m deep temperature probe was installed at the campus of Indian Institute of Management, Ahmedabad in August, 1999. Probe has five resistance type device PT 100 sensors, mounted at 1-m interval. It was put in to the ground up to depth of 3-m. First sensor is at 3-m depth, second at 2-m depth, third at 1-m depth, fourth just 2 cm below the surface and the fifth 1-m above ground. Temperatures from all the sensors were noted one day on each month for a year. Readings were noted at hourly interval. In this paper, the results are presented. Motivation for this work was the need to know the diurnal and seasonal variation of temperature in deeper layers of soil in order to determine the level suitable for installation of earth tube heat exchangers.

Modeling and Simulation of Condensation on Plastic Condenser Cooling under Night Sky

The Kutch region of north-west India is hot and semiarid, chronically short of drinking water. Dew forms frequently in the areas near the coast, over a span of eight-month (October- May) coinciding with the entire dry part of the year. Dew water is potable and safe. Dew harvest systems - devices to condense and collect dew - have been developed which could be installed on building roofs (condenser-on-roof), open ground (condenser-on-ground) and on frames (condenser-on-frames). The key component is the condenser, made of thin plastic film insulated underneath, which cools at night by radiative exchange with cloud-free sky. Condensation occurs when the film cools to or below the dew point of the surrounding air and humidity level is high - upwards of 85%. Over the season of eight months, 15 – 20 mm of dew water can be harvested. In this region where rainfall is very erratic and in normal years only 300 mm, harvested dew water can be an appreciable supplement. It can also be a small but critical supply for plants in nurseries. Design principle of efficient dew condenser is discussed and dew water collection in some recently installed working systems reported.

Performance of Single Pass Earth-Tube Heat Exchanger: An Experimental Study

A single pass earth-tube heat exchanger (ETHE) was installed to study its performance in cooling and heating mode. ETHE is made of 50 m long ms pipe of 10 cm nominal diameter and 3 mm wall thickness. ETHE is buried 3 m deep below surface. Ambient air is pumped through it by a 400 w blower. Air velocity in the pipe is 11 m/s. Air temperature is measured at the inlet of the pipe, in the middle (25 m), and at the outlet (50 m), by thermisters placed inside the pipe. Cooling tests were carried out three consecutive days in each month. On each day system was operated for 7 hours during the day and shut down for the night. Heating tests were carried out at night in January. Test results are presented in summary form for each month. Detailed analysis is presented for two months only -- May for cooling and January for heating. ETHE cools the ambient air in May by as much as 14oC. It heats the ambient air in January nights also by similar amount.

Fourier Representation of Climatic Data of Kothara-Kutch

Fourier series representations of some climatic variables were developed using data from the site of an experimental greenhouse at Kothara (Kutch). Hourly data was averaged over a month to yield a profile of an average day of that month. That was put through harmonic analysis to determine Fourier coefficients . Analytical expressions would be useful to those working on modelling.

SolCafe : A Solar Cooking Facility for Schools and Small Catering Business in Hot Arid Areas

A solar cafeteria, termed, SolCafe was designed and commissioned at a residential school of hundred children in Kothara-Kutch. In this paper we present the experience of its first year of operation. Cooking modules of the caf� consists of two large box type solar cookers. One cooker has an aperture of 0.5 m2 and the other 1m2. Cookers are of front-loading type. Installation permits the cook to operate from indoors without having to go in the sun. One year of experience has shown that the cookers are easy to use. The only maintenance needed was regular cleaning of glass covers. Such facilities can also be useful to small catering business in hot arid areas.