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Internal Shading System: Cooling and Winter Insulation
Internal shading system: summer cooling plus winter night insulation with aluminised reflective fabric and full open-close control.
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TEL：+86 191 5068 3942
- Features
The Internal Shading System: Two Jobs From One Screen
An internal shading system is mounted inside the greenhouse, below the roof and above the crop, and it is asked to do two opposite jobs. In summer it blocks part of the solar radiation before that energy reaches the plants and the floor, which lowers the air temperature and the cooling load. In winter, drawn at night, the same layer holds a cushion of still air under the roof and slows heat escaping upward, so the heating demand drops. That double duty is why the screen is built as a movable layer with a full opening and closing stroke instead of fixed netting.
The surface decides which job the screen does best. Where the fabric carries an aluminised or aluminium foil reflective face, part of the incoming radiation is reflected back toward the roof instead of being absorbed, and at night the low-emissivity metal face slows radiative heat loss from the crop to the cold roof. A plain woven screen absorbs more of what it intercepts and keeps more light, so it suits houses where light is the limiting factor. Because it sits indoors, it is shielded from wind, hail and snow load, so a lighter fabric and finer control can be used here than outside.
Driving the Screen: Motor, Shaft, Pull Lines, Roller and Curtain Rods
The travelling parts are the family of parts that appears in the equipment list: the gear motor, the drive shaft, the pull screen lines, the screen-line roller, the curtain rods and the connecting fittings. A gear motor at the head of the bay turns the drive shaft; the shaft carries the pull screen lines that run out across the house; the roller and the curtain rods keep the fabric travelling straight; the connecting fittings tie each rack back to the structure under the gutter. The lay-out is arranged so one stroke gathers the screen into a compact package at the ridge or gutter, leaving the crop and roof vents clear.
Three details are fixed at drawing stage: the number of drive shafts and their spacing along a long bay, whether the screen is divided per span or runs across the whole house, and where the package parks when the screen is open. Brackets and slide parts should be specified for the same corrosion class as the frame, so that a hot-dip galvanized structure is not fitted with untreated hardware. For the frame itself the reference standards are ISO 9223 and BS EN ISO 14713-1, with class C2 to C5 taken according to the local atmosphere.
How Far to Close: Opening Ratio and Light Loss
An internal screen is rarely an all-or-nothing device. Working on the opening ratio, the usual positions are about one third closed on a hazy day, roughly half closed at midday, and fully closed only in a heat wave or around solar noon. Light loss is not proportional to the closing ratio: a partly drawn screen still shades what is under it, while the open part of the house lets a large share of the light through, so a half-closed screen costs far less light than a half-open fabric suggests.
Two rules make this easier to manage. Set the position by measuring at crop level with a light meter rather than trusting the percentage on the control panel, because ridge height, crop and roof material all change the result. And always leave enough of the roof open for air to move when the vents are working; if the screen covers the vents, the temperature curve of the house shows the stagnation at once. Open-field screening and its fabric grades are a separate subject, covered on the page about shade net specifications from 65% to 90%.
Shading Against Humidity: the Trade-off Nobody Avoids
The same layer that keeps radiation out also slows the movement of air and water vapour. A screen closed across a whole bay creates a still space under it, and in a heavily irrigated house the humidity can rise until condensation forms on the leaves and the inner roof face. That is the real trade-off of internal shading: the more area you close, the better the temperature control and the smaller the natural exchange of moisture.
The usual answers are to keep the screen slightly open while the vents are closed and the crop is wet, to run the screen in steps so the house can be aired between positions, and to choose a screen with an anti-drip construction where dripping onto the crop would be a problem. In winter the night screen is drawn only when the outside temperature asks for it, because a closed screen under a cold roof is also the classic place for condensation to start. Where a project needs strong dehumidification on top of shading, the airflow side of that train is designed with it, as described on the pages about exhaust fan airflow matching and wet curtain cooling systems, the companion decisions to a shading screen.
Tension and Routing: Where an Internal Screen Fails
Most problems with an internal screen show up as fabric trouble rather than drive trouble, and almost all of them come from tension and routing. The pull lines have to be adjusted so the fabric is equally tight on both sides of the bay; a screen tight on one side and slack on the other folds unevenly, rubs the curtain rods and starts to fray at the edges within a season. Slack fabric also sags, collects condensation and can touch the crop, the lamps or a heating pipe below.
Routing is planned like a service run. Lines stay parallel along the bay, supported so they cannot sag into the roof glazing or a vent opening, and routed clear of lamps, sprinkler lines and any hot pipe. The screen ends its travel without touching the structure, and the open package is clear of the vents and of any maintenance walkway; a change of direction halfway along a bay is the one thing a screen cannot tolerate. The two photographs above show both ends of the system, the reflective screen and its drive hardware parked at the ridge and the same kind of fabric drawn out over the crop. Related items from our greenhouse equipment range are listed under greenhouse accessories and assist equipment. Bozong Greenhouse has been building and equipping greenhouses for above 35 years. If you need to ask a question and get some help to find the best greenhouse for you, then just call us on +86 191 5068 3942 OR send E-mail to sales@cngreenhouses.com
Frequently Asked Questions About Internal Shading
Q1: Is an internal shading system useful in winter, or only in summer?
A1: Both. In summer it cuts the radiation that would heat the crop and the floor; in winter, drawn at night, the fabric and the still air below it reduce the heat escaping through the roof.
A1: Both. In summer it cuts the radiation that would heat the crop and the floor; in winter, drawn at night, the fabric and the still air below it reduce the heat escaping through the roof.
Q2: What does the aluminium foil face on the screen change?
A2: It sends part of the incoming radiation back toward the roof instead of absorbing it, and at night its low emissivity slows radiative heat loss. A plain woven screen absorbs more and keeps more light.
A2: It sends part of the incoming radiation back toward the roof instead of absorbing it, and at night its low emissivity slows radiative heat loss. A plain woven screen absorbs more and keeps more light.
Q3: Which parts are included inside the roof?
A3: The gear motor, the drive shaft, the pull screen lines, the screen-line roller, the curtain rods and the connecting fittings. Shaft number and parking position come from the greenhouse drawing.
A3: The gear motor, the drive shaft, the pull screen lines, the screen-line roller, the curtain rods and the connecting fittings. Shaft number and parking position come from the greenhouse drawing.
Q4: How far should the screen be closed on a bright summer day?
A4: About half closed as the normal working position, about one third on a hazy day, fully closed only in a heat wave or around solar noon, with part of the roof left free for air.
A4: About half closed as the normal working position, about one third on a hazy day, fully closed only in a heat wave or around solar noon, with part of the roof left free for air.
Q5: Can the screen stay closed all night in a humid climate?
A5: Not without checking. A screen closed across the bay traps water vapour, which is where condensation and leaf disease start. Keep it slightly open, run it in steps or use an anti-drip screen.
A5: Not without checking. A screen closed across the bay traps water vapour, which is where condensation and leaf disease start. Keep it slightly open, run it in steps or use an anti-drip screen.
Q6: Can an internal shading system be added to an existing greenhouse?
A6: Yes, if the structure can carry the brackets for the curtain rods and the drive and there is space at the ridge or gutter for the gathered screen. Send us the span width, bay length, gutter height and vent positions and we will propose a lay-out. More background on shading and protected cultivation is published by HortWeek.
A6: Yes, if the structure can carry the brackets for the curtain rods and the drive and there is space at the ridge or gutter for the gathered screen. Send us the span width, bay length, gutter height and vent positions and we will propose a lay-out. More background on shading and protected cultivation is published by HortWeek.
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