Culture bed heating comparison between electric wire and hot water generated from pellet boiler in asparagus forcing production
2018
Zeng, J. | Kumano, T. | Yamagata, S. | Kamide, M. | Fujii, M. | Araki, H.
Domestic fresh asparagus are in great demanded in Japan from late autumn to winter. However, the oil or electric heating system for the asparagus culture may be the cause of high costs and CO2 emission. An alternative heating system, instead of oil or electricity, is desirable in today's low carbon society. The heating system using wood pellets consists of three components: 1) a pellet boiler, 2) hot water storage tanks and 3) an asparagus cultural bed in a plastic house. The cultural bed was covered with a plastic sheet every night and during the day under cloudy conditions. The temperature, electric power and flow volume were measured continuously in three cultural beds i.e., 1) electric wire for soil-heating, 2) hot water heating (soil), 3) hot water heating (soil and air). Pellets were automatically supplied to the pellet boiler. The pellet boiler warmed the water more than 50°C on a daily basis in two hot water storage tanks. The hot water circulated when the soil temperature of the culture bed and air temperature inside the tunnel decreased below 20 and 15°C, respectively. All of the three heating systems could maintain the soil temperature to 15-20°C averagely in mid-winter. Even when the outside temperature fell to -10°C, the air temperature inside the plastic house was kept to around 0-5°C at night. Our results showed that the electric wire-heating system supplied the lowest caloric value while the hot water-heating system supplied more caloric value for asparagus production in the winter. The soil and air-heating system had the greatest harvest. There was no significant difference between the spear yield by soil-heating and electric wire-heating in winter production. Effective systems will be discussed from the view point of spear yield, required energy for heating and CO2 emission.
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