Performance of Greenhouse Coupled to Earth-Tube-Heat-Exchanger in Closed-Loop Mode

An experimental greenhouse coupled to an Earth Tube Heat Exchanger (ETHE) in closed-loop mode has been installed at Kothara (23o 40N 72o 38E), India. Area is hot and extremely arid. ETHE is used to warm the greenhouse in winter nights and cool it in hot days. The saw-tooth house is of 6 m span, 20 m length and has ridge height of 3.5 m. ETHE consists of eight ms pipes, each of 20 cm dia and 20 m long. A centrifugal blower powered by 7.5 hp motor moves the air through the system. Volume flow rate of air is 7200 m3 per hour, which makes for about 20 air changes per hour. ETHE was able to heat the house easily from 9oC to 22-23oC in half hour in the cold winter nights. Opening of side and ridge vents from 11 A.M. to 4 P.M. and fogging at hourly interval kept the house below 34oC till the end of February. Operation of the ETHE became necessary from April. Operation of ETHE reduced the temperature by 7oC below the ambient. ETHE offers the advantage that it uses no water which is scarce. Results of the first cropping trial showed that tomato yield was 2.7 times the open field yield in this area, and water used for irrigation nearly 34% less than that used in open field.