Some standard content:
ICS65.040.30
Machinery Industry Standard of the People's Republic of China
JB/T10297-2001
Design regulation on greenhouse heating system
Design regulation on greenhouse heating systemPublished on 2001-06-22
China Machinery Industry Federation
Implementation on 2001-10-01
JB/T10297—2001
This standard is one of the greenhouse series standards formulated for the first time. This series of standards includes: 1. Greenhouse structure design load
2. Greenhouse ventilation and cooling design specifications
3. Greenhouse engineering terms
4. Multi-span greenhouse structure
5. Sunlight greenhouse structure
6. Wet curtain cooling device
7. Greenhouse heating system design specifications
8. Greenhouse electrical wiring design specifications
9. Greenhouse control system design specifications
Among the above standards, the first two are national standards, and the rest are industry standards. This standard is a newly formulated industry standard.
This standard is proposed and managed by the National Agricultural Machinery Standardization Technical Committee. The drafting unit of this standard: Environmental Engineering Equipment Research and Development Center, China Academy of Agricultural Mechanization Sciences. The main drafter of this standard: Wan Xuesui.
This standard was first issued in June 2001.
1 Scope
Machinery Industry Standard of the People's Republic of China
Design regulation on greenhouse heating systems
Design regulation on greenhouse heating systems JB/T10297—2001
This standard specifies the calculation method of greenhouse heat load, establishes the basic principles for designing various greenhouse heating systems, and provides equipment installation and configuration guidelines.
This standard applies to the design of heating systems for greenhouses that require heating (including solar greenhouses, single-span greenhouses and multi-span greenhouses). 2 Definitions
This standard adopts the following definitions.
2.1 Greenhouse heating greenhouse heating is the engineering technology that uses heating methods to increase the temperature of air, bed soil, floor, nutrient solution and substrate in a greenhouse. 2.2 Conductive heat loss Conductive heat loss Heat loss through the enclosure structure (including surrounding walls, doors, windows and roofs, etc.) in a greenhouse, including heat loss caused by long-wave radiation, conduction and convection.
Heat transfer coefficient heat transfer efficiency 2.3
The amount of heat transferred through a unit area of material when the temperature difference on both sides of the light-transmitting covering material is 1K per unit time. The direction of heat transfer is from the high-temperature side to the low-temperature side, and the heat transferred includes long-wave radiation, conduction and convection. 2.4 Parmeation heat loss parmeation healoss The heat loss caused by the exchange of indoor and outdoor air due to the gaps in the greenhouse enclosure structure. 2.5 Heat loss to soil heat loss to soil
The heat lost by conduction from the ground.
Central heating centarheating
The method of using a boiler as a heat source and water or steam as a heat medium, and the heat medium is transmitted through a pipeline to heat the greenhouse at the radiator (pipe). Central heating is mostly used in large greenhouses.
2.7 Air heating
Using hot air blowers (fuel oil, gas) and hot air furnaces (coal or other solid fuels) as heat sources, the heated air is sent to the greenhouse through a heat exchanger to increase the temperature of the air in the greenhouse in the form of hot air. 2.8 Hotbed
Protected cultivation facilities that use artificial methods to increase the ground temperature of crop cultivation beds. Commonly used for seedling cultivation and low-temperature seasonal crop cultivation. 2.9 Hot floor
The heating device is buried in the floor, and the heat is dissipated to the space through the floor. This method is suitable for greenhouses where potted containers are directly placed on the floor.
Approved by China Machinery Industry Federation on June 22, 2001, implemented on October 1, 2001
3 Calculation of heat load
Indoor design temperaturet
JB/T10297—2001
Generally speaking, the maximum heating load of a greenhouse occurs at the coldest night in winter. Different crops, different varieties, and different growth stages have different requirements for ambient temperature. Table 1 shows the suitable temperature range of common greenhouse fruit plants. Table 1
Suitable temperature range of common greenhouse fruit plants
Tomatoes
Daytime temperature
Nighttime temperature
100mm deep soil temperature
Under normal circumstances, the indoor design temperature can be selected within the suitable temperature range at night. The specific value should be determined based on the local fuel price, heating cost, market conditions and sales price of plant products, and after economic benefit calculation. The indoor design temperature shall not be lower than the lowest temperature at night.
If the exact crop is unknown, the indoor design temperature of greenhouses for several major crop categories can be taken according to Table 2. Table 2 Recommended indoor design temperature values
Tropical crops
Ordinary flowers
Thermophilic fruits and vegetables
Ordinary leafy vegetables
Cold-region turf
If the indoor design temperature cannot be determined based on Tables 1 and 2, please consult agricultural and horticultural experts and determine it based on the specific crop category, variety, and the growth stage at which the crop is controlled in the severe winter. Outdoor design temperature to
For greenhouses used for 20 years, it is recommended to take the average of the coldest day temperature in the past 20 years as the outdoor design temperature value. If there is no recent local meteorological statistical data, the outdoor design temperature values in major cities in northern my country can be taken as the values listed in Table 3. Table 3 Outdoor design temperature t, recommended value
Harbin
Karamay
Shijiazhuang
Lianyungang
Urumqi
For greenhouses that are not used all year round, different outdoor design temperature values can be selected according to the weather conditions of the specific season of use. 2
3 Heat transfer loss Q
JB/T10297—2001
The heat transfer loss 9 through the greenhouse enclosure structure can be calculated by formula (1): EujA,(ti-to)
Where:
Heat transfer loss of greenhouse enclosure structure (including walls,
translucent roof, opaque back slope and doors and windows, etc.), W; heat transfer coefficient of the jth enclosure structure (see Table 4), W/(m2·K): surface area of the jth enclosure structure, m;
number of enclosure structures;
indoor design temperature, ℃;
outdoor design temperature, ℃.
The heat transfer coefficient u of commonly used enclosure structure materials is listed in Table 4. The heat transfer coefficient u is the reciprocal of thermal resistance. For multi-layer composite envelope structures, =
-total thermal resistance of the envelope structure, m2·K/W:
where: R
S-thickness of the i-th layer of envelope material, m;
heat transfer coefficient u can be calculated by formula (2):
人—thermal conductivity of the i-th layer of envelope material
文 (see Table 5), W/(m·K):
number of envelope structure layers.
Heat transfer coefficient of commonly used enclosure materials u
Single-layer glass
Double-layer glass
Single-layer polyethylene film
Double-layer inflatable plastic film
Glass fiber reinforced plastic (FRP) corrugated boardPolycarbonate hollow (PC) board, 6mm
Polycarbonate hollow (PC) board, &mm
Polycarbonate hollow (PC) board, 10mm
Polycarbonate hollow (PC) board, 16mm
Polycarbonate hollow (PC) board,| |tt||Glass fiber reinforced plastic corrugated board,
16mm,
three-layer wall
PMMA solid board, 4mm
corrugated cement asbestos board
brick wall, 240mm
brick wall, 370mm
brick wall,
earth wall (rammed), 1000mm
air layer, 50-100mm
Note: The infrared absorption film of the new product can reduce heat loss, but considering the safety factor, no reduction is made in the actual calculation. (1)
W/(m2·K)
JB/T10297—2001
Table 5 Thermal conductivity of common composite wall materials^ Wall materials and filling materials
Solid clay brick wall
Asphalt glass wool felt
Glass wool board
Slag wool (loose)
Slag wool products (board, brick, pipe)
Asphalt slag wool felt
Boiler slag
Expanded perlite powder (dry, loose)
Expanded vermiculite
Asphalt vermiculite board
Cement vermiculite Slate
Polystyrene foam board
Straw mud plastering
Mortar mud plastering
Permeation heat loss Q2
0.03-0.04
0.027-0038
0.035~0.045
0.03-0.04
Q045-0.06
0.07-0.09
W/(m·K)
Strictly speaking, the heat loss caused by the air penetrating through the gaps and the exchange of indoor and outdoor air includes sensible heat and latent heat. However, the environmental conditions for heat load calculation basically occur in the early morning of the cold winter season, and the latent heat exchange is limited, which can be ignored in engineering calculations. Therefore, the infiltration heat loss can be calculated by formula (3):
Q=0.5k wind VN (tt.)
Where: 92
Infiltration heat loss, W:
V greenhouse air volume, m;
N—air changes per hour (see Table 6), h-: k wind speed—wind factor (see Table 7).
Wind speed factor k is listed in Table 7.
Infiltration heat loss increases with the increase of wind speed. Table 6 Recommended values of ventilation times N per hour
Covering method
Single-layer glass, unsealed gaps
Single-layer glass, sealed gaps
Double-layer glass
Single-layer plastic film
Double-layer inflatable plastic film
Rigid board
..............
Ground heat loss 93
JB/T10297—2001
Wind speed factor k Wind chase
Wind force level
Below level 4 wind
Level 5 wind
Level 6 wind -
Level 6 wind +
Level 7 wind
The speed of heat dissipation from the greenhouse ground is related to the distance between the calculation point and the outer protective structure. In engineering, the land of the greenhouse can be divided into three areas according to the distance from the outer protective structure. The heat loss of different areas is calculated according to their respective heat transfer coefficients and areas, and then the sum is obtained to obtain 9303
Where: 9
Ground heat loss, W:
u,A,(t-to)
Ground heat transfer coefficient of the i-th zone (see Table 8), W/(m2·K): Area of the i-th zone, m2
Table 8 Ground heat transfer coefficient u
Distance from calculation point to external protective structure
3.6 Greenhouse heat load Q
The greenhouse heat load is calculated using formula (5):
Q=9+Q+Q
Central heating system
W/(m2·K)
Central heating systems can be divided into two types according to the heat carrier medium: steam and hot water. Steam or hot water from a heat source (e.g., boiler, geothermal well, etc.) flows through standard black tube (ungalvanized tube) or round fin tube radiators (natural convection), or through radiators consisting of various radiators (e.g., airfoil and column types) (forced convection), distributing heat to the greenhouse and raising the indoor temperature. 4.1 Calculation of the number of radiators
The number of radiators (number of pieces or meters) required for a greenhouse can be calculated using formula (6): n=(Q/q)β,β,β3
Wherein: n-
required number of radiators (or meters), unit: piece or m; Q—greenhouse heat load, W;
unit (per piece or per meter) heat dissipation of radiator, W/piece or W/m; (6)
JB/T10297—2001
β, a set of correction factors for the number of pieces (column type) or length (flat tube type and plate type) (see Table 9); β, a branch pipe connection form correction factor (see Table 10); β-flow correction factor (see Table 11). Table 9 Correction factor β for number of assembled pieces or length
Number of assembled pieces for column type
Radiator type
Four-column type
M-H132 type
Radiator type
Column type, wing type
Flat tube type
4.2 Installation suggestions
Top in and bottom out
Assembly length of plate type and flat tube type
≤600
Correction factor β for branch pipe connection form,
Top in and bottom out
Bottom in and bottom out
Flow correction factor B
Bottom in and top out
≥1000
Bottom in and top out
4.2.1 The most commonly used method of distributing heat for central heating in greenhouses is natural convection, using standard black tubes or round wing tubes for heat dissipation. You can also use the forced convection distribution method, using column-type and wing-type diffusers to radiate. 4.2.2 If the greenhouse is a single-span temperature with a span (or width) of less than 9m, standard black tubes or round wing tubes can be arranged along the side walls. If the span exceeds 9m, some heat dissipation pipes can be added between crops (or under the racks). 4.2.3 If steam is used as the heating medium, due to the high temperature, the heat dissipation surface must be at least 0.3m away from the plant body. 4.2.4 The heat dissipation pipes of multi-span greenhouses are generally set along the outer walls and under the gutters. If needed, some heat dissipation pipes can be added under the cultivation racks or between crop rows.
4.2.5 If natural air circulation is not enough to produce a sufficiently uniform temperature at the height of the crop, necessary horizontal air circulation fans should be added. After the black tube is painted with silver powder paint, the heat dissipation efficiency is reduced by about 15%. 4.2.6
5 Hot air heating system
Working principle
By burning different fuels (such as oil, natural gas, coal, etc.), heat is released, and the surrounding air is heated through the heat exchanger, and then the hot air is sent to the greenhouse by the blower, so that the temperature around the crops is appropriate and uniform. Usually, the burner that burns oil or gas is small in size, and together with the heat exchanger, blower, controller, etc., it forms a hot air blower, which can be installed in the greenhouse. However, the flue gas after combustion often contains harmful gases (such as nitrogen and sulfur oxides, tar, etc.), so it needs to be led to the outside by a flue. The combustion chamber of coal-fired combustion is large in size and has high smoke, and is generally installed outside the greenhouse. Only the heated air is sent to the greenhouse by the blower. The air temperature at the outlet of the blower should generally be controlled within the range of 60~80℃.
5.2 Installation suggestions
5.2.1 The outlet of the air blower is usually designed to supply air in the horizontal direction. For greenhouses less than 20m in length, two hot air blowers can be installed at the opposite corners of the greenhouse diagonal, each blowing warm air toward the opposite end wall in a direction parallel to the side wall. For greenhouses longer than 20m but less than 40m, it is difficult for hot air blowers alone to blow warm air far away, which is not enough to obtain good air circulation. It is recommended to add two circulation fans in the middle of the greenhouse, one on each side, to relay air supply. If the greenhouse length is greater than 40m, the number of circulation fans needs to be increased. In the direction of circulating air flow, the distance between the two fans should not be more than 30 times the diameter of the fan impeller. The circulation fan should be between 4.5 and 6.0m away from the end wall. 5.2.2 For longer greenhouses, perforated plastic film hoses or cloth pipes can also be used at the outlet of the hot air blower to supply air to the room to improve the air circulation and temperature uniformity of the entire greenhouse. The hose is generally made of polyethylene plastic film or cloth, extending horizontally in the greenhouse and hanging on the frame. Exhaust holes are punched out on both sides of the hose axis to send warm air to the greenhouse. The spacing of the exhaust holes along the axis is generally between 0.3 and 1.0 m. The air flow rate at the hose inlet is about 5.1 to 6.1 m/s. The total area of the exhaust holes should not be less than 15 to 2.0 times the cross-sectional area of the hose. 5.2.3 The installation height of the circulating fan and the circulating hose should generally be 0.6 to 0.9 m higher than the crop canopy height. The circulating fan should be equipped with a protective cover to prevent the operator from touching the moving parts such as the impeller and being injured. The length of the circulating hose should not exceed 50 m. Too long will affect the uniformity of air distribution. For greenhouses with a width of less than 9 m, one air supply hose is enough. If the greenhouse width is greater than 9 m, more than two circulating air supply hoses must be installed.
5.2.4 When the burner is not working, start the matching air supply fan and circulation fan to improve the air circulation in the greenhouse, eliminate condensation on plant leaves, and avoid damage to crops caused by mold. 5.2.5 In the horizontal air circulation system of the multi-span greenhouse, the circulation path can go down from one span and return from the other span. In a single-span greenhouse, the installation of the circulation fan should make its axis parallel to the length of the greenhouse and the distance from the side wall is 1/4 of the width of the greenhouse. The airflow goes down along one side wall and returns from the other side wall. 5.2.6 The selection of the circulation fan should provide a total flow rate of 0.01m/s of air flow per square meter of ground. The fan speed should be adjustable so that the local air velocity near the crop canopy does not exceed 1.0m/s. 6 Hotbed
6.1 Type and scope of application
In order to promote seed germination, proliferation and crop growth, it is necessary to provide the most suitable temperature in the plant root zone, so the soil of the crop cultivation bed must be heated, which is the hotbed. According to the heat source, commonly used hotbeds include electric hotbeds and water-heated hotbeds. 6.2 Electric hotbed
6.2.1 Structure
The width of the electric hotbed is generally 1~2m, and the bed length is determined according to the length of the greenhouse. There are pools with a width of 150~200mm and a height of 100~200mm built around it. A 50mm thick insulation layer is laid at the bottom of the bed. The insulation material can be polystyrene foam board, crushed slag or crushed straw. The electric heating wire is laid back and forth along the length of the bed at a certain interval and straightened. It must not be curled or crossed and overlapped to avoid leakage or short circuit accidents. Both ends of the electric heating wire should be led out from the same bed end through external wiring to facilitate connection with the power supply and controller. The joints of the external wiring and the power line should be well insulated and buried under the soil together with the heating wire. The thickness of the soil should be uniform. Generally, the soil thickness of the seedling hotbed is 50mm; the soil thickness of the transplanting hotbed is 100mm7
The soil thickness of the leafy vegetable cultivation hotbed is 150mm. 6.2.2 Selection of heating wire
JB/T10297—2001
The rated voltage of domestic heating wires is 220V, and the rated power of each heating wire is 400W, 600W, 800W and 1000W. The length of each heating wire is about 90~120m. 6.2.3 The total power of the hotbed P can be calculated according to formula (7): P-Sp-LWp
Wherein: P-
Total power of the hotbed, W
Hotbed area, m:
Hotbed power density, W/m2, the value range is generally 80~120Hotbed length, m;
WHotbed width, m.
6.2.4The bed width of each heating wire w
According to the specifications of the selected heating wire, wW=Q(pL)
Wherein: w
The bed width of each heating wire, m;
Q——Rated power of the heating wire, W.
6.2.5 Adjacent spacing of electric heating wires D
D = w/([(L line = -w)/ L)+ 1)
Where: D
Adjacent spacing of electric heating wires, m
The length of a heating wire, m.
6.3 Water-heated hotbed
Water-heated hotbeds generally use hot water at 35~40℃ as the heating medium. Let the hot water circulate through a rigid polyethylene (PE) pipe, polyvinyl chloride (PVC) pipe, chlorinated polyvinyl chloride (CPVC) pipe, polybutylene pipe or ethylene propylene rubber (EPDM) hose with a diameter of about 13mm to transfer heat to the bed soil of the hotbed. In order to improve the uniformity of the bed soil temperature, the water supply pipe and the return pipe should be connected in series to form a loop so that the temperature gradient of the front water supply pipe and the temperature gradient of the return pipe compensate each other. The distance between the water supply pipe and the return pipe is about 100mm. Polystyrene insulation boards should be laid under the water pipes to ensure that most of the heat is directed to the root zone of the crop. A layer of wet sand is laid on the pipes, covered with a perforated plastic film to retain moisture in the sand, and then the soil is laid to further improve the uniformity of the soil temperature. Hot water can come from a central heating system or from a separate water heater.
7 Heated floor
7.1 OverviewWww.bzxZ.net
In greenhouses where potted crops are grown, if the pots and containers are placed directly on the floor, laying heated floors is the best heating method. This heating device does not occupy ground area and space and does not hinder any operations in the greenhouse. Heated floors are particularly suitable for greenhouses with low heat requirements, such as wintering greenhouses for shrubs such as rhododendrons. In greenhouses with heated floors, the capacity of the main heating system can be reduced accordingly.
7.2 Low-temperature radiant electric heating film floor
Low-temperature radiant electric heating film is a new type of energy-saving, high-efficiency, and pollution-free electric heating material. The electric heating film is made of conductive special ink and metal carrier strips printed and hot pressed between two layers of insulating poly film. When powered on, the maximum temperature of the working surface of the electric heating film is 40~60℃, and most of the energy is transmitted by radiation.
The number of electric heating films depends on the floor area and power density to be heated. Usually, when designing hot floors, the power density is taken as 45~50w/m.
During construction, a layer of 25~50mm thick self-extinguishing polystyrene foam insulation board (or glass fiber wool felt, rock wool, etc.) should be laid on the ground first, and the electric heating film should be flattened. The diaphragms should be connected with special connection cards and insulated wires with plastic insulation covers. It is recommended to use PVC single-strand copper wire with a cross-section of 4mm for the branch line connecting the electric heating film, and use an insulated single-strand copper wire with a cross-section of 6mm? for the power line. The electric heating film can only be cut along the shear line to prevent the ink strip from being cut off, resulting in no heat and leakage. One end of the current-carrying strip at the cut end is connected to the connection card and the wire, and the other end needs to be sealed with a waterproof insulating tape with a temperature resistance of more than 90°C in a dry environment. After completing the above treatment, except for the power line, all the electric heating films, connection cards, and connecting wires can be paved with cement, tiles or other floor materials according to general construction methods. The electric heating film is best to be close to the floor decoration material to avoid forming air thermal resistance and affecting thermal efficiency. The electric heating film has the same lifespan as the building and is suitable for permanent building heating. For temporary buildings, it is not recommended to use electric heating film. Drilling and nailing are prohibited on the floor where the electric heating film has been installed. 7.3 Water-heated floor
The working principle of the water-heated floor is similar to that of the water-heated hotbed. It also uses 35~40℃ hot water as the heating medium. The difference is that the hot water circulation pipeline is buried under the floor. The circulation pipeline usually uses polyethylene (PE) pipes, polyvinyl chloride (PVC) pipes or polybutylene pipes with a diameter of about 20mm. The flow rate of water in the pipe is about 0.61~0.91m/s. Generally, each circuit should not exceed 120m in length, with a pipe center distance of 300mm, which can provide 47W power for each square meter of cement floor. If an independent water heater is used to provide hot water, the size of the water heater can be selected according to the power density of 47W/m. 9
Mechanical Industry Standard
Design Specification for Greenhouse Heating System
JB/T10297-2001
Published and issued by the Mechanical Science Research Institute
Printed by the Mechanical Science Research Institute
(No. 2 Shouti South Road, Beijing: Postal Code 100044)*
Format 880X12301/16 Printing Sheet 3/4
4 Word Count 20000
First Edition in September 2001
First Printing in September 2001
Print Quantity 1-500
Price 1200 Yuan
2001-137
Mechanical Industry Standard Service Network: http/AvwwJB.ac.cn
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