実測による温室暖房負荷係数の決定
1972 年 27 巻 3 号 p. 93-98
詳細
1972 年 27 巻 3 号 p. 93-98
In order to calculate the heat requirement per unit floor area for greenhouse heating design, a simple equation has been derived (eq. 1), and its constant has been defined as heating load coefficient(K). Suppose that r% of the total heat loss from the greenhouse is transferred into the soil, the heating load coefficient results in 100kt/(100-r) and the total heat requirement is given by eq. 6, where Kt is the sum of thee overall heat transfer coefficient of the greenhouse wall (k) and the heat transfer coefficient due to ventilation (hven). These coefficients, the over-all heat transfer coefficient of the greenhouse wall and the heat transfer coefficient due to ventilation are expressed by eqs. 3 and 4, respectively.
In the present field experiment, two identical greenhouses, one is east-west oriented and the other is north-south have been used. Both of them were heated by circulating hot water.
The heat balance analysis of the greenhouses shows that 50% of the total heat loss from the greenhouse is due to radiation, 20% due to convection from the outside surface to the outside air, 20% due to ven tilation, and 10% due to conduction into the soil in approximate values. It is also shown that the over-all heat transfer coefficient of the greenhouse wall is constant (k=4.8) and would not be affected by the fluctuation of the outside weatherconditions, and the heat transfer coefficient due to ventilation is a linear function of the outside wind speed(eq. 7).
The ratio of the heat loss into the soil to the total heat loss of the greenhouse given as percentage is presented in Fig. 5. In order to evaluate the heating load coefficient, the value of r must be determined. In the present study, the value of 10 is adopted for fail safe. Consequently, the heating load coefficient of the greenhouse is determined as a linear function of outside wind speed, i. e., eq. 10. Using eqs.1 and 10, the stochastic evaluation of the heat requirement of the greenhouse is demonstrated in relation to outside wind speed and daily minimum temperature in Figs. 6a and b. In the same figure, the heat requirement lines are indicated by the group of hyperbolic curves.
