The primary need for ventilation of greenhouses is to prevent excessive rise of temperature in sunny days, and the other needs are to replenish the carbon dioxide and to lower an excessive level of humidity. In the design stage of a greenhouse equipped with natural ventilation, it is very useful if the natural ventilation rate can be calculated theoretically as a function of (i) greenhouse structures, (ii) arrangements of ventilators or other openings and (iii) wind speed and wind direction.
It is possible to estimate the ventilation rate from the pressure differences across openings and the resistances to air flow through openings. Pressure and discharge coefficients of openings for a single-span greenhouse with continuous side and ridge ventilators, and entrance/exit at gable end were determined experimentally. A one-fifteenth model was installed in a boundary layer wind tunnel for the experiments. The wind speed profile in the wind tunnel was adjusted to be the logarithmic profile with the roughness length of 0.067mm, which is a representative value observed often in nature. Based on the measurements of internal pressures and mean air speeds through openings, pressure and discharge coefficients were determined from the equations (10), (14) and (15).
The results are presented in Fig. 6, Table 1 and Fig. 7. Some noticeable features are as follows:
(1) All pressure coefficients across openings were not equal to those over surfaces at the ventilators closed, so that the calculation of ventilation rate should be based on the values for the ventilators open.
(2) Pressure coefficients of side ventilator were dependent only on wind direction, not on angle of opening. The maximum value of 0.3 was observed at the wind angles of 0-30° and the minimum value of -0.4 at the wind angles of 150-180°. It was assumed that the wind angle is 0° when the wind blows perpendicular to the ridge line facing the ventilator open.
(3) When only one side of ridge ventilators was open, pressure coefficients of the ventilator showed similar patterns to those of side ventilator, although the absolute values of them on the windward side increased slightly with increasing angle of opening. The minimum value of -0.4 was obtained at the wind angle of 135°
(4) When both ridge ventilators were open, pressure coefficients of the ventilators were negative at any wind angle and angle of opening, and dependent on both wind direction and angle of opening. The minimum value was -0.4 at the wind angle of 30° when the ventilators were positioned horizontally.
(5) Pressure coefficients of entrance/exit at gable end changed from -0.5 to 0.6 with the change of wind angle of 0 to 90° on the windward side, and on the leeward side they were -0.2 at the wind angles larger than 30°.
(6) Discharge coefficients of ventilators under windless condition were approximately 0.1, 0.4 and 0.6 at the angles of opening 10, 30 and 50°, respectively, and that of entrance/exit at gable end was 0.7. However, those values changed slightly with the differences in types and mounted positions of ventilators.
(7) Due to the influences of circumambient wind around the greenhouse, discharge coefficients changed with the change of wind direction and ν/V (mean air speed through opening to wind speed ratio). They reached the same values as those under windless condition with the increase of ν/V.
(8) Discharge coefficients of side ventilator and entrance/exit at gable end were independent of wind direction and ν/V.
(9) When only one side of ridge ventilators was open, discharge coefficients of the ventilator were dependent both on wind direction and ν/V at the angles of opening larger than 30°.
(10) When both ridge ventilators were open, discharge coefficients of the ventilators were notably dependent on wind direction and ν/V, and the maximum values were observed at the wind

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湖沼が周辺地域の自然や農業に及ぼす影響を知る手がかりとして, 湖沼周辺の局地気候に関する研究を開始し, 第1報では洞爺湖周辺の冬期の気温分布について報告したが, 今回は春から夏にかけての同地域の気候調査を行なった。1977年6月の観測は冬の観測と同様, 銅・コンスタンタン熱電対温度計のセンサーを自動車の屋根にとりつけ, 気温を記録しながら湖岸にそって周回し, 気温分布をしらべた。1978年4月～5月の観測では湖の北西岸の地域に6ケ所の観測点を設けて最高・最低気温を測定し, そのうち4観測点では気温を自記させた。得られた結果を要約すると次のごとくとなる。
(1) 湖周辺全体の気温分布は, 日中, 気温が水温より高いときには湖の風下で明瞭な低温域が見られ, 風上地域と約4℃の差があった。
(2) 湖の風下地域では湖岸から内陸に入るにともない気温は上昇したが, 約1.5kmまで湖の影響が見られた。
(3) 湖岸と内陸との気温差は風向により大きく異なり, 湖から吹く時は, 日中で約6℃の差が観測された。

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1. The author proposed the model of diurnal course of air temperature which is required to analyze a crop growth. The relationship between air temperature (x) and time (t) is shown by the following “modified sine-curve (MS-curve)”,
x=f(t, A, B, H, k)=(B-A)sin²(πt/2H)+A+k(B-A)sin²(πt/H),
for |k|≤1/4 (1)
where A is the minimum air temperature, B the maximum one, H the period between emergence times of A and B, and k the modification coefficient which shows the ratio of deviation from sine-curve.
The two models of diurnal course of air temperature were devised from MS-curve. The one is “two-half cycle model” which simulates the rising course of the air temperature in a day by the half cycle of x=f(t, A₁, B, H, k₁) and the descending course by that of x=f(24-t, A₂, B, 24-H, k₂). The other is “one-half cycle model” which expresses the mean diurnal variation of air temperature by the half cycle of x=f (t, A, B, 24, k_m). In these equations, A₁ and A₂ are the morning minimum air temperature and that of the next day, and k₁ and k₂ are the modification coefficients to the periods A₁ to B and B to A₂, respectively, k_m is the daily mean modification coefficient shown by k_m={k₁H+k₂(24-H)}/24.
2. The air temperature in 1968-1977 at Morioka in Japan was analyzed using these models. The following seasonal values were obtained;
k₁=-0.01-0.08, k₂=-0.20-0.10, k_m=-0.13-0.05,
H=8.4-10.0 hours, and t_A=4.2-5.5,
where t_A is the emergence time of minimum air temperature. It was found that k₁ and k₂ values investigated for instance at Sapporo, Tokyo and Fukuoka were roughly similar to those values at Morioka. Then, the emergence time periods of classified air temperature, which were calculated from the reverse function of MS-curve using these coefficient values, agreed very well with the observed values.
3. The daily mean air temperature θ_m which is estimated from the integration of MS-curve is shown as follows;
θ_m=(A+B)/2+k_m(B-A)/2. (2)
On the other hand, the daily mean air temperature θ_n which is obtained from the observations of several times a day is shown as follows;
θ_n=(A+B)/2+l_m(B-A), (3)
where (A+B)/2 is the average air temperature and l_m the coefficient of diurnal range of air temperature to convert (A+B)/2 into θ_n. The convenient equations of k_m and θ_m at Morioka were obtained from Eq. (2). Eq. (3), and the values observed at intervals of three hours as shown below,
k_m=2l_m-0.034, and (4)
θ_m=(A+B)/2+(l_m-0.017)(B-A). (5)

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The relation between the radiation and the temperatures on greenhouses is studied from a view of the heat budget on this paper. The radiation exchange of the outside of greenhouses is expressed by equation (11) or (14), and of the inside by eqs. (12), (15) or (16). The equations (11), (12) and (16) assume that the intensity of the atmospheric radiation does not change by the altitude, and eqs. (14) and (15) are introduced without the assumptions. The absorptivity and transmissivity of plastic films for the atmospheric radiation differ from these for the black body radiation. The equations (14), (15) and (16) are introduced, taking account of this fact. Table 4 and Fig. 2 show the measured values and calculated ones from these equations. At a cloudy night, the calculated values from eq. (12) fit the measured, and at a fine night from eq. (16) do. By use of the modified values of coefficients which are shown on Table 5, eq. (12) fits both at cloudy and fine nights as shown in Fig. 3. The equations (52) and (53) are derived from eqs. (11), (12) and the heat budget equation (10) and these can give the relations between heat fluxes and temperatures on greenhouses. By use of these equations, the relation between the over-all heat transfer and heating load can be shown like the equation (56).

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