マイコン制御による炊飯エネルギーの節減

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(1) 従来の電気炊飯器を用いて米飯を炊く場合，蒸発量を見込んであらかじめ米飯に必要な量以上の水を加えなければならない。特に大型炊飯器で少量炊飯する場合は，昇温が急速であるため吸水時間が充分に確保できない。それを補うためと，澱粉がα化するのに必要な温度を所要時間保持するために，白米重量の10～40％の水を余分に加える。この水を蒸発させるための熱エネルギーは消費電力量のうち非常に大きな部分を占めていた。（2）電気炊飯器の内鍋内の蒸気温度が95℃以下では蒸発量も僅少であり，それ以上の温度で蒸発が激しくなる。95℃になったとき内鍋内を密閉し，蒸気の温度を100℃に維持するように電力を制御すれば鍋内の圧力は理論的にも <special>1.91kgf/cm2</special> （0.117MPa）を超えることはない。この程度では圧力鍋のような構造とする必要もな〈，水蒸気の放散は僅少である。（3）マイコンを利用した電力の制御によって米粒の吸水時間の調節と沸騰時の水分の蒸発を抑制した場合，炊飯に必要な米飯温度（98℃以上20分間）を十分に保持しても消費電力量は通常の炊飯方法に比較して大巾に小さくなった。（4）マイコン制御による炊飯では普通型炊飯器と比較して熱効率は19％～14％向上し，電力消費量は25％～35％節減できる。そのうち保温構造等の改善によるものは熱効率において2％向上し，電力節減率は5％程度であった。（5）大型炊飯器で少量炊飯する場合，米飯粒の中心部に硬さが残ることが多いが，マイコン制御によってこの間題は解消し，同時に電力量の大巾な節減が可能となる。When rice is cooked in an ordinary ricecooker, more water must be added than necessary to offset quantity of rice is cooked in a large cooker, water absorption time cannot be surfficiently assured, as the temperature increases rapidly. To supplement water absorption and maintain the temperature needed for making alphastarch, 10％ to 40％ more water than weight of the rice must be added. The thermal energy to evaporate this extra volume of water accounts for a very large portion of the electric energy consumed. ・Electric power needed rice cooking can be sharply reduced by controlling it in accordance with the quantity of rice and the progress of cooking, and by holding down evaporation to the minimum. Such control can be managed easily using a microcomputer（hereinafter referred to as MC control）. ln a comparison of eleetricity consumed by rice cookers available on the market with one using MC control, the energy saving effect has been determined. In ordinary type rice cookers, water evaporation during cooking is great. When the capacity of the cooker and electric power are fixed, the ratio of water evaporation to rice weight increases inversely to the quantity of rice. Thus the initial water addition ratio （weight of additional water／weight of the rice）must be increased. For rice cooking, i. e., to completely make alphastarch in grains, it is necessary to have grains sufficiently swollen with water and kept at 98℃ or above for 20 minutes. When steam temperature inside the pan of thecooker is below 95℃, there is little evaporation, but evaporation increases when the temperature is above 95℃. With the pressure rice cookers available on the market, steam at 100℃ or above is liberated vigorously through the safety valve, making the pressure inside the pan at or over <special>1.24 kgf/cm2</special>（0.122MPa）. If electric power is used to close the inside tightly steam temperature therein becomes 95℃ and steam temperature is maintained at 100℃, the inner pressure of the cooker does not exceed <special>1.19kgf／cm2</special>（0.117MPa）. Thus, in this case a pressure pan is not required, and almost no liberation of steam is expected. First, a certain definite maximum power <special>P0</special>is loaded, and with a thermosenser fixed under the lid of the inside pan, steam temperature <special>θ2</special>is detected. Then, according to the time required to raise the temperature from 40℃to 46℃, <special>t2-t1</special>, the amount of rice to be cooked is judged. Accordingly, time for water absorption and heating <special>Ts</special>, electric power for boiling <special>Pi</special>, time for heating and maintenance <special>Tm</special>, time for settling by its own heat <special>Tn</special>, are read from the table. When <special>θ2</special> reaches 50℃, electric power for water absorption and heating is fixed at <special>P1</special>. After <special>Ts</special>, it is fixed to <special>Pi</special> to accommodate the quantity of rice. The valve is closed when <special>θ2</special>is at 95℃, and when <special>θ2</special>is at 98℃, clectric power for maturing is fixed at <special>P2</special>. The thermosenser in contact with the bottom of the inside pan determines the temperatuer at the bottom of the pan <special>θ8</special>. When <special>θ8</special> is at 110℃, the heat maintenance power is fixed at <special>P3</special>. When <special>P2</special>is about 200W and <special>θ8</special> rapidly increases above 110℃, all water has been absorbed by the rice grains and the rice throughout the pan has reached 100℃. With a large quantity, the temperature of the rice after switching off <special>P2</special> declines gradually, so that electric power for heat maintenance <special>P3</special> is not necessary. However with 500 grams or less rice, even if the cooker is well insulated, it cools down rapidly. Thus, ideally, about 60W of <special>P3</special>, will have to be loaded for <special>Tm</special> min. to keep rice temperature <special>θ5</special> not far below 98℃. When <special>θ8</special> reach 100℃, the rice temperature has already been kept at 98℃ or above for longer than 2 minutes. Therefore the sufficient total of <special>Tm</special> and <special>Tn</special> after switching off the electricity <special>P2</special> ia 18 minutes. When water absorption time of grains is adjusted and evaporation of boiling water is controlled by a microcomputer, electricity consumption is greatly reduced over the ordinary way of cooking, even with a well maintained cooking temperature. The ratio of minimum energy needed for rice cooking to consumption of clcetrycity is expressed by thermal efficiency η in fig 13. With MC control, thermal efficiency is generally improved. The energy saving rate of a cooker under MC control is compared with that of a popular type rice cooker on the market in fig 12. Only about 5% of electricity can be saved by thermal insulation, but a sharp reduction of energy can be expected by holding down watere evaporation. This is especially effective when a small quantity of rice is cooked. Thermal efficiency is improved by 14% （M = 291gr) - 19% （M = 1164gr） compared with the ordinary type cooker, and 25% （M = 1164gr) - 35% （M = 291gr） of electric energy can be saved. In that case thermal efficiency is improved 2% and electric energy is reduced by 5% upon remeodelling of thermal insulation. Generally rice cooked by this means was fairly acceptable. When a small quantity of rice is cooked in an ordinary large cooker, the center of the graines occasionally rermains uncooked. This can be solved by properly controlling electric power, which also makes possible electric energy conservation.

マイコン制御による炊飯エネルギーの節減

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