Cooling and heating of greenhouse in arid area by earth tube heat exchanger

Abstract

Adoption of greenhouse technology in hot and arid areas in north-west India is impeded by lack of good quality water. Besides irrigation, evaporative cooling uses large amounts. Provision of natural ventilation and coupling the house to earthtube-heat-exchanger (ETHE) is being tried as alternative measures for environmental control, specially cooling. The experimental facility, located in arid region at Kothara (ϕ 23° 14 N, λ 68° 45 E, at 21 m a.s.l.), is a single span saw-tooth greenhouse (20 X 6 X 3.5 m) coupled in closed- loop to ETHE buried 3m deep directly below. ETHE provides 40 air changes per hour. For natural ventilation, there are three continuous (closable) vents - two along the base of long sides and one on the roof. 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 the yields increase and cropping season extended. ETHE was able to heat the greenhouse easily from 9°C to 22-23°C in half hour in the cold winter nights. Natural ventilation along with roof shading was effective for day time control till February keeping the temperature about 34°C inside. Subsequently, ETHE was operated. It limited the greenhouse temperature to 36-37°C with top shaded. ETHE and natural ventilation hold promise as environmental control measures. There is need to reduce installation cost of the ETHE. A more easily scalable design than the present one is also desirable.