STUDY OF THE THERMAL ENVIRONMENT AND MARGINAL EFFECTS OF A SUNKEN SOLAR GREENHOUSE

Cheng, Weiwei; Wang, Changchao; Wang, Yu; Cheng, Mengjun; Qiao, Penhui; Liu, Zhonghua

doi:10.1590/1809-4430-Eng.Agric.v44e20230168/2024

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Scientific Paper • Eng. agríc. 44 • 2024 • https://doi.org/10.1590/1809-4430-Eng.Agric.v44e20230168/2024 copy

STUDY OF THE THERMAL ENVIRONMENT AND MARGINAL EFFECTS OF A SUNKEN SOLAR GREENHOUSE

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

A sunken solar greenhouse is a unique structure used in China that has good thermal performance and a low cost. To explore the thermal environment and the marginal effect area under the trellis membrane in a sunken solar greenhouse, daytime heat absorption and nighttime exothermic models of the greenhouse were established based on existing theories and hypotheses. An experimental study of the three-dimensional thermal environment of a solar greenhouse was also conducted in the Jinzhong Basin of Shanxi Province. The daytime heat absorption model described how the internal thermal environment of the greenhouse changes in three dimensions, while the nighttime model calculated the amount of heat released at night. The results showed that the rate of change in the maximum temperature difference along the height direction in the greenhouse was 13 times that along the vertical direction, and three times that along the horizontal direction. We also observed that the marginal effect area under the membrane varied over time and by month. The minimum value of the marginal effect area occurred at the middle cross-section, spanning the middle position of the greenhouse, and the maximum height was 2.7 m. The results of this study can provide theoretical guidance and experimental data for the thermal environment of greenhouses of the same type in the Jinzhong Basin of Shanxi Province, thus providing a basis for environmental regulation and low-temperature margins in greenhouses.

microclimate; mathematical modelling; theoretical modelling; thermal comfort; environmental quality

Parameter
S_QZ	Amount of direct solar radiation received at a spatial point Q (W/m²)
Q_S	Amount of solar scattered radiation received at a spatial point Q inside the greenhouse (W/m²)
S'₁	Direct solar illumination passing through the atmosphere to the outer surface of the greenhouse membrane (W/m²)
S_Qs	Solar scattered radiation illuminance passing through the atmosphere to the outer surface of the greenhouse membrane (W/m²)
Θ	Angle of incidence of daylight
T₁	Direct light transmission rate of the film at different roof angles (%)
T₂	Scattered light transmittance of the film at different roof angles (%)
T_z0	Transmittance of a dry, clean, new covering material to direct light radiation at an incidence angle of 0°
γ₁	Loss of shading of the greenhouse structural materials
γ₂	Loss of light transmission of the covering material due to deterioration
γ₃	Loss of light transmission due to dust contamination and droplets of condensation
H_aze	Haze of the covering material (%).
η	Influence coefficient of point scattering
$(\int z d x + \int \int 1 / 2 d y d z) \times L$	Volume of the greenhouse (m³)
x, y, z	Coordinate values of point Q (m)
b	Length of the upper bottom of the northern soil trapezoidal wall (m)
D	Sunken depth of the greenhouse (m)
W,L,H	Span, length and ridge height of the sunken solar greenhouse (m)
A_S	Floor area of the greenhouse (m²)
q	Heat per unit area (w/m²)
a	Heated area correction factor
q	Reflectance of indoor sunlight

Parameter
Q	Conduction heat loss (W)
μ_j	Heat transfer coefficient of the maintenance structure (W/m²⦁K)
A_j	Area of the enclosed structure (m²)
t₁	Temperature of the inner side of the plastic film of the solar greenhouse (K)
t₂	Outdoor temperature (K)
Φ	Heat flow (W)
μ	Convective heat transfer coefficient (W/m²⦁K)
A	Area of the greenhouse floor (m²)
T_g	Ground temperature or back wall surface temperature (K)
T_f	Ground air temperature or back wall air temperature (K)
△Q_a	Indoor nighttime heat loss（W）
△Q_s	Nighttime heat release from soil (W)
△Q_w	Nocturnal heat release from walls (W)
△Q_c	Crop heat release at night (W)
$Δ Q_{I a - O a}$	Nighttime heat exchange between indoor and outdoor gases (W)
△Q_c	Soil area of the greenhouse (m²)
$\frac{d T_{s i}}{d t}$	Rate of change in the temperature of the lower surface of the soil in the greenhouse with time, constant value (K/s)
$\frac{d T_{s i}}{d t}$	Rate of change in the air temperature at the upper surface of the soil interior with time, constant value (K/s)
A_wn, A_we, A_ww	Areas of the walls on the north, east and west sides of the greenhouse, respectively (m²)
$\frac{d T_{w n}}{d t}, \frac{d T_{w e}}{d t}, \frac{d T_{w w}}{d t}$	Surface temperatures of the walls on the north, east and west sides of the greenhouse velocity of change with time (K/s)
$\frac{d T_{g n}}{d t}, \frac{d T_{g e}}{d t}, \frac{d T_{g e}}{d t}$	Rate of change of surface temperatures of the walls on the north, east and west sides of the greenhouse with time (K/s)
$\frac{d T_{out}}{d t}$	Rate of change of outdoor gas temperature with time, as a constant value (K/s)

		Line number
		1	2	3	4	5	6
y-coordinate		0	1.2	4.2	7.2	10.2	North Wall
Height of measuring point	1	1.5 (+)	2.1 (+)	3.6 (+)	4.5 (+)	4.8 (+)	4.5 (+)
	2	1.2 (−)	1.8 (−)	3.3 (−)	4.2 (−)	4.5 (−)	3.9 (−)
	3	0.9 (−)	1.5 (−)	3 (−)	3.9 (−)	4.2 (−)	3.3 (3)
	4	0.6 (+)	1.2 (+)	2.4 (−)	3.6 (−)	3.6 (−)	2.7 (−)
	5	0.3 (−)	0.6 (−)	1.8 (+)	3 (+)	3 (+)	2.1 (1.8)
	6	0 (+)	0.3 (−)	1.2 (−)	2.4 (−)	2.4 (−)	1.5 (−)
	7	-	0 (+)	0.6 (−)	1.8 (+)	1.8 (+)	0.9 (−)
	8	-	-	0.3 (−)	1.2 (−)	1.2 (−)	0.3 (+)
	9	-	-	0 (+)	0.6 (−)	0.6 (−)	-
	10	-	-	-	0.3 (−)	0.3 (−)	-
	11	-	-	-	0 (+)	0 (+)	-

Cross section
Line number	Height from indoor floor (m)	1	2	3	4	5	6	7
1	0	1.2	1.8	2.4	3.2	3.4	4.5	−
	0.6	−2.3	0.8	1	1.9	2	2.5	1.6
	1.5	−1.2	0.3	0.5	0.2	0.6	1.5	1.9
2	0	1.7	−	−	2.8	3.4	4	4.2
	1.2	−0.4	0	1.3	2.2	2.5	2.8	3.5
	2.1	−0.2	0.3	0.9	2	2.2	2.4	2.2
3	0	3.4	2.9	4.3	4.2	4.3	5	6.8
	1.8	0.7	0.4	1.2	2	2.3	2.8	2.6
	3.6	0.2	0	1	1.7	2.5	2.3	2.6
4	0	2.8	3.2	4.2	6	4.5	4.7	4.3
	1.8	2.4	1	1.3	2.6	2.5	3.1	3
	3	0.6	0.7	1.2	2.3	2.5	2.9	3
	4.5	0.4	0.5	0.9	2.3	2.5	2.9	2.7
5	0	2	−	4.5	6	5.8	5.8	4.6
	1.8	1	−	1.6	2.6	3.2	3.3	4
	3	0.7	1.1	1.4	2.3	3.1	3.3	3.3
	4.8	−	−	1.2	2.3	3	3.2	3.2
6	0.3	3.8	2.9	4.1	4	5.3	4.9	5
	1.8	3.1	3.4	4.9	−	6.4	6.2	4.7
	3	1.5	1.6	2.4	−	4.4	4.6	4
	4.5	1.3	1.5	2	3.1	3.9	3.9	4.2

Line no.	Marginal curve position	Fitting function
1	Marginal effect curve equation for trellis	$T = 0.9433 z^{2} - 2.3626 z + 4.2601$
1	Equation for soil marginal effect curve	$T = - 1.1204 z^{2} + 1.3672 z + 2.6863$
2	Marginal effect curve equation for trellis	$T = - 0.0629 z^{2} - 0.0024 z + 3.3119$
2	Equation for soil marginal effect curve	$T = 0.0241 z^{2} - 0.2049 z + 3.4151$
3	Marginal effect curve equation for trellis	$T = - 0.0593 z^{3} + 0.5192 z^{2} - 1.5135 z + 4.6135$
3	Equation for soil marginal effect curve	$T = - 0.1983 z^{3} + 1.4328 z^{2} - 3.3233 z + 5.6388$
4	Marginal effect curve equation for trellis	$T = - 0.0909 z^{3} + 0.7953 z^{2} - 2.2195 z + 5.1864$
4	Equation for soil marginal effect curve	$T = - 0.0977 z^{3} + 0.8856 z^{2} - 2.528 z + 5.4603$
5	Marginal effect curve equation for trellis	$T = 0.136 z^{2} - 1.02 z + 5.409$
5	Equation for soil marginal effect curve	$T = 0.1465 z^{2} - 1.0935 z + 5.5179$
6	Marginal effect curve equation for trellis	$T = - 0.1026 z^{2} - 0.0728 z + 6.4288$
6	Equation for soil marginal effect curve	$T = - 0.0057 z^{2} - 0.5449 z + 6.9252$

Associação Brasileira de Engenharia Agrícola SBEA - Associação Brasileira de Engenharia Agrícola, Departamento de Engenharia e Ciências Exatas FCAV/UNESP, Prof. Paulo Donato Castellane, km 5, 14884.900 | Jaboticabal - SP, Tel./Fax: +55 16 3209 7619 - Jaboticabal - SP - Brazil
E-mail: revistasbea@sbea.org.br

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[1] *Corresponding author. Shanxi Agricultural University, College of Urban and Rural construction/Taigu, China. E-mail: lzh6175305@163.com |