Energy Resource

In a closed micropropagation system or a closed culture room, the exchanges of heat and radiative energy through the walls are minimal because thermally insulated walls are used. During the photoperiod, the lamps generate much heat, and thus cooling is necessary even during the winter in any places in the world. When the outside air temperature is higher than 25 C during the dark period, a minimum amount of cooling may be necessary to keep the air temperature of the culture room at around 25 C (during the summer in tropical, subtropical and temperate regions). However, greater cooling is necessary under such conditions if the culture room is not thermally well insulated. On the other hand, in cold climate regions where minimum outside air temperatures are regularly below zero, a heating, or air conditioning system with a minimum heating capacity, may be required if thermal transmission coefficient of the walls is higher than 0.1 W m-2 K-1. In hot climate regions, the heating system is not required even during the dark period in the winter if the walls are thermally well insulated. This is because a small but sufficient amount of heat is generated from equipments such as fans and pumps and from the plants.

In the closed micropropagation system, the cooling load of air conditioners during the photoperiod accounts for 95-99% of the total cooling load throughout the year. The rest (1-5%) is the cooling load due to heat transmission through the walls, warm air infiltration and the heat generated by equipment such as fans installed in the culture room. Thus, the cooling load of air conditioners during the dark period is negligibly small compared with that during the photoperiod. In a closed culture room equipped with a recently developed air conditioner, the electric consumption of air conditioner accounts for about 20-25% of the total electric consumption and that of lamps accounts for 75-80%. The percentage of electric consumption due to air conditioning will be higher than 25% when the thermal insulation of the walls is low, air infiltration is too much and/or the energy performance (Coefficient Of Performance, C.O.P.) of air conditioners is low.

Again, the use of natural or solar light for reducing electric consumption for lighting increases the electric consumption for cooling, the condensation of water at the inside surface of glass walls in the winter, and the heating load during the dark period in the winter. Furthermore, light intensity and air temperature fluctuate with time and their spatial variations in the culture room become significant. Therefore, the use of natural light for reduction in electricity cost cannot be practical in most cases.

On the other hand, use of solar energy for heating water for washing, autoclaving and other purposes is practical for reducing energy costs in micropropagation. Temperature of well or city water ranges between 15 and 30 C in most places and this can be raised to 50-70 C using a solar energy collector with a black-colored double layer panel through which the water flows. If water of 100 C is required then instead of heating the water of 25 C directly using fuel, if it is preheated to 70 C using the solar energy collector and then heated to 100 C using fuel, the fuel consumption is reduced by 67% [=100 (70-25)/(100-25) ].

In many cases, electric energy is used to obtain hot water and steam (110-115 C) for autoclaving. Then, the consumption of electric energy for autoclaving is considered to account for about 20% of the total electricity costs. However, hot water/steam can be obtained by using fuel other than electricity, and the cost of fuel is being about 30% of the cost of electricity. An autoclave driven with fuel instead of electricity is commercially available although it is not currently widely used. Its appearance, function and price are almost the same as those driven with electricity. If both fuel and solar energy are used for autoclaving instead of electricity, energy cost for autoclaving is reduced by 90% [100 - 0.3 x (100 - 67)].

It is also noted that autoclaving is not the only method for sterilization. In most cases, 70-80 C of water for 1-2 hours has the same effect as pressurized steam at 115 C for 15 min in terms of sterilization. This water can be obtained using a solar heater alone.

Current micropropagation systems have contributed greatly to the development of the micropropagation industry. However, we are regularly requested to provide improvements to the systems for further development of the industry. In this chapter, current micropropagation systems are reconsidered mainly from the viewpoint of environmental control engineering aiming at the production of high quality transplants with minimum use of resources and minimum release of pollutants. The two concepts discussed in this chapter for the improvement of current micropropagation systems are 'closed plant production system' and 'photoautotrophic micropropagation'. It is hoped that these two concepts will contribute to the initiation of discussion on the improvement of current micropropagation systems for producing high quality plants with minimum resources and environmental pollution.

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