Greenhouse
热门新闻
A greenhouse is a controlled environment that captures sunlight, traps heat and shields crops from wind, rain, pests and temperature extremes. The structure you select determines how much light reaches the canopy, how quickly heat is lost, how effectively the space can be ventilated and how the building will behave under local wind and snow loading.
The frame is the skeleton for every downstream system, including the covering, gutters, vent rails, shading screens, irrigation rails and heating pipes. Decisions about span layout, column spacing and ridge height therefore have to be made before equipment is specified. Too many columns block light and reduce usable floor area; too few columns leave the frame unable to carry vent rails or drifting snow.
Modern growers work mainly with three structural families: single-span houses, multi-span Venlo houses and glasshouses built around a rigid welded frame. Each family can be clad in film, polycarbonate or glass, and each can support soil, substrate or hydroponic production. This guide compares the families, their materials and the criteria for choosing between them.
A single-span greenhouse is a freestanding building with one continuous roof from eave to ridge, typically eight to twelve metres wide and forty to sixty metres long. Its advantages are simplicity, low capital cost per square metre and a short erection time. Because there are no internal gutters, rainwater usually runs to the ground rather than being captured, which reduces rain shadow over the crop but also removes a free water source for irrigation.
Tunnel greenhouses use a semicircular or multi-hoop frame covered with polyethylene film. They are common in mild and warm climates where the main objectives are frost protection, wind shelter and modest temperature buffering rather than precise climate control. Low tunnels, sometimes framed in bamboo or treated timber, extend the season outdoors and are used for nursery stock, seedlings and short crop cycles.
Limitations should be recognised early. Film loses transmission over time and must be replaced every one to three seasons. Curved roofs have less usable vertical clearance than a gabled house, so height and equipment mounting are restricted. Continuous ridge or side vents are harder to achieve without sophisticated mechanisms, and frames with few braced bays collect snow unevenly, which shortens structural life in cold climates.
Multi-span construction links several narrow bays that share gutters, so there is no side wall between them. This removes a large share of the opaque wall area and therefore increases light transmission and reduces heat loss. It also concentrates the structure into a smaller number of columns, which lowers the foundation cost per square metre and simplifies the layout of internal roads, benches and service pipes.
The Venlo configuration is the most widely used modern system for vegetable production. A Venlo unit combines narrow bays, typically between six and eight metres, with a gable roof, small gutters at each bay edge and a valley between neighbouring bays. Gutter heights commonly fall between four and six metres and ridge heights between six and eight metres, giving enough clearance for high-wire crops, overhead lighting rails and pipe heating in the gutters.
Multi-span houses are also the easiest to automate. Continuous roof vent sections can be motorised across several bays, external shading screens can be drawn across the entire roof, and fertigation rail systems can run the full length of the house. The trade-off is that each column carries a much higher load, so foundations, column spacing and wind bracing must be calculated for the local code rather than copied from a generic drawing.
Sawtooth greenhouses are distinguished by a raised roof section on one side of each bay. Opening that raised section allows warm air to escape as the cooler air enters from the side vents, giving natural ventilation without powered fans. This layout suits regions with high daytime temperatures and relatively low humidity, and it is common in southern Europe, North Africa and parts of Asia.
Glasshouse structures use a rigid welded steel frame with trusses or girders, aluminium glazing bars and glass panes. Typical venlo glasshouses use spans of six to eight metres with gutter heights of four and a half to six metres, while wide single-span glasshouses can reach twelve metres or more with higher ridges. The frame carries heavier dead load than a film house and is usually specified for larger vent openings and more glazing hardware.
Glass offers the highest light transmission and the longest service life, but it also creates the largest heat load, so these houses are normally paired with a full heating, cooling and humidity control system. Modern glasshouse practice increasingly relies on diffuse light and careful energy management, because the same solar gain that produces high yields in winter becomes a cooling problem in summer.
Frame material selection depends on span, cladding type and local corrosion exposure. Galvanized steel is the default for multi-span structures because its torsional stiffness keeps long buildings square and lets the frame resist lateral wind loads. Hot-dip galvanized members are used where the frame must carry heavy glazing or where humid, salty air would attack a lighter coating.
| Frame material | Typical application | Maintenance focus |
|---|---|---|
| Galvanized steel | Multi-span and Venlo houses | Inspect welded joints and touch up coating damage |
| Hot-dip galvanized steel | Glasshouses and heavy glazing | Check drainage paths and fixings for corrosion |
| Aluminium | Glazing bars, vent rails, ladders | Clean surfaces and check seals and gaskets |
| Bamboo or treated timber | Low tunnels and nursery houses | Replace warped members and treat against rot |
Foundations must reach below the local frost line and resist overturning from wind. Screw piles, driven piles and concrete strip footings under the column line are the usual options; isolated pads work only where the load path is short and clearly braced. On any site, surface drainage is as important as the foundation. A gently graded floor, a gravel layer or a geotextile-protected base keeps standing water away from the greenhouse, while perimeter drains or a soakaway manage roof runoff from the gutters.
The covering determines how much light enters, how much heat is retained and how much the grower must spend on climate control. Two properties dominate the choice: solar transmission, which drives photosynthesis, and thermal transmittance, which drives heating cost. Diffuse light also matters, since it penetrates more evenly through the canopy and reduces hot spots on upper leaves.
| Covering | Light transmission | Typical service life | Key note |
|---|---|---|---|
| Float glass, 4 mm | About 80 to 85 percent | Twenty years or more | Highest light, highest heat load, highest cost |
| Twin-wall polycarbonate, 8 to 16 mm | About 75 to 82 percent | Ten to fifteen years | Good insulation and diffusion, yellows over time |
| Polyethylene film, 150 to 200 micron | About 85 to 90 percent | One to three seasons | Lowest cost, replaced regularly, best diffusion |
| Anti-condensation film | About 85 percent | One to three seasons | Channels condensation away from the crop |
| Diffuse etched glass | About 70 to 75 percent | Twenty years or more | Even light, reduced scorch risk |
In practice, film is often chosen where light transmission and cost dominate, polycarbonate where insulation and impact resistance matter, and glass where the crop value and long payback justify the investment. Wherever condensation forms, it falls onto the crop and raises disease pressure, so anti-condensation treatment and correct ridge and gutter detailing are standard specifications.
Dimensioning a greenhouse starts with the crop and the climate. Tall crops need ridge clearance and rail height, wide canopies need span width to avoid shading patterns, and low winter light makes every avoidable shadow costly. Loads are then layered: dead load from structure and cladding, live load from maintenance and equipment, wind pressure on the windward wall and roof, and snow drifting against gutters and valleys.
| Parameter | Typical range | Design note |
|---|---|---|
| Single-span width | Eight to twelve metres | Wider spans need deeper trusses and stronger columns |
| Multi-span bay width | Six to eight metres | More bays mean more gutters and more column lines | Gutter height | Four to six metres | Set by crop height and pipe heating capacity |
| Ridge height | Six and a half to eight metres | Higher ridges increase volume but also wind load |
| Column spacing | Four to six metres | Tighter spacing reduces deflection, raises steel weight |
| Wind and snow | Per local building code | Drifting snow at valleys often governs the design |
Site selection completes the structural picture. A level, well-drained site with unobstructed airflow and access for delivery vehicles reduces foundation cost. Orientation should place the ridge so that shadow lines fall between crop rows rather than across them, and the structure should avoid being funnelled between tall neighbouring buildings. Every house also needs room for service corridors, plant, water treatment and power distribution.
A sound selection starts with the crop profile and the local climate, not with a preferred structure. Write down the target yield, the planting and harvest dates, the summer peak temperature and the winter design temperature, then choose the covering and the heating approach that deliver that combination. A structure that cannot hold temperature on the coldest night of the year is a poor investment regardless of its appearance.
Finally, evaluate the whole system rather than the frame alone. Frame, covering, vents, screens, irrigation, heating, cooling, storage and handling facilities must be designed as one environment with compatible dimensions and a single control strategy. Suppliers able to deliver a complete integrated house reduce the interface risk that otherwise dominates the first operating season.
A single-span house has one roof covering the entire width, with no internal gutters, so it is cheaper per square metre and quicker to build. A multi-span house joins several narrow bays that share gutters, which cuts wall area, increases light transmission, lowers the number of columns and makes continuous ventilation and shading easier to install, but requires heavier foundations and more complex roof detailing.
Not automatically. Glass gives the best light transmission and lasts the longest, but it also produces the largest heat load and the highest purchase and maintenance cost. Film and polycarbonate are frequently the better economic choice in mild climates or for short cycles, and in many regions the crop and energy prices decide the outcome more than the covering alone.
Span width and column spacing are dictated by the crop, the wind and snow loads and the size of the equipment to be hung from the frame. Start with the standard bay widths used by your supplier, then confirm them against the structural calculations for your site, since any change in span, height or cladding alters the load path and therefore the column and foundation design.
A complete package normally includes the frame, covering, gutters and downpipes, vent and screen drives, doors, foundations and drainage, and the control cabinets. It also normally includes the internal growing equipment and the supporting facilities, meaning heating plant, cooling, irrigation and fertigation, water treatment, storage, packing, transport and electrical distribution, all sized to work with the structure.
相关文档
