Lay out greenhouse fans and see how fast the air moves across the floor at crop height: where it sits still, where it's on target, and where it's too windy.
About this tool: HAF, VAF, heaters, exhaust fans and how much air is enoughAir Speed Map
Floor to roof, gutter and peak averaged.
Hover or tap the map to read the air speed at a spot.
Right-click a fan for more. Shift-click to pick several. Keys: Delete removes what's picked, D copies it, R turns it, [ and ] turn it a little, arrows move it, N picks the next one, Ctrl+Z (⌘Z on a Mac) undoes.
Hover or tap the side view to read the air speed at a height.
Colors are air speed at the top of the crop, including any bench. Lines with arrows show the path the air takes, and where they stop, the air has stopped too. Around a VAF fan, they show its air spreading out across the floor.
The shares cover the whole floor at crop height, aisles included. It works out how the fans' push, the walls and the drag of the crop and roof shape the air. It assumes the vents are shut, as at night, and leaves out heaters and exhaust fans. Advanced adds them. Heaters count only for their blower, not the warm air rising off them, and open vents only let in what the exhaust fans pull. Wind through vents is left out. It leaves out benches and gable shapes. Check it with an anemometer held at the top of the crop.
Fans
The size and airflow above go on the next fans you add or lay out. Use the airflow printed on your fan's label: two fans the same size can differ by half.
| Fan | Type | Size (in) | Airflow (CFM) | Speed (%) | Height (ft) | From end (ft) | From side (ft) | Direction |
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Saved Plans
A plan saves the house, the fan settings and everything on the map. Saving under a name you already used updates that plan, and so does Update with current.
Would a 3D model be worth the development effort to you? It would show the whole house from any angle, with the air speed at any height.
Thanks. That helps decide what to build next.
Glossary
Every leaf has a thin layer of still air on its surface. Water vapor and CO2 have to cross it, so the stiller the air, the slower a leaf transpires and takes in CO2. Moving air thins that layer, and most of the gain comes by about 0.2 m/s (40 ft/min).
The map's target is 0.2 to 0.5 m/s (40 to 100 ft/min) at the top of the crop. Air at fan height moves faster than that. The crop slows the air near it, so canopy air often runs at about half the speed of the stream under the trusses.
Still air stays humid around the leaves. Leaf surfaces cool below the air at night and collect dew, which is how botrytis and downy mildew get started. Transpiration slows, and with it calcium, which only moves in the water stream. That shows up as tipburn and blossom-end rot even when there's plenty of calcium in the feed. VPD looks fine on the sensor but the leaf sits in a wetter pocket than the sensor reads.
Above about 0.5 m/s (100 ft/min), small parasitic wasps released for biocontrol can't fly a straight course. Above about 1 m/s (200 ft/min), leaves can lose water faster than the roots replace it, so plants close their stomata and growth slows. Tender seedlings and cuttings dry out and get battered, and plants stay short and tough. Hard wind also blows CO2 and sprays away before they do any good. Keep seedlings and cuttings at the low end of the target.
Horizontal airflow fans hang above the crop and blow along the length of the house. Half point one way down one side and half point back up the other, so the whole air mass turns in a slow loop. The common rule is 2 CFM of fan for every square foot of floor, a little more for tall crops or hanging baskets. Put the first fan 10 to 15 ft from an end wall, the next ones 30 to 50 ft apart, and hang them above head height, with clear air between the fan and the crop tops.
A fan pulls in as much air as it pushes out, but it pulls from every side at once, so the pull is weak and only reaches a few fan widths. The push is a narrow jet that carries for dozens. That's why where a fan points matters so much more than where it sits.
Fans pointed at each other collide and cancel. Fans all pointed the same way push air into the far wall instead of looping it. Fans bunched at one end stir that end and leave the rest still. Fans spaced too far apart let the stream cut across to the return side early, leaving dead air past the turn. Corners where the loop turns are always a little slower. In a wide house, run one loop for every 30 ft or so of width.
Vertical airflow fans hang high and blow down. The air hits the crop, spreads out across it, and rises again between fans, which mixes warm air from the roof down into the crop. They suit tall, dense crops and houses with energy curtains. Hung too low or too fast, they blast the plants right under them, so pick a larger, slower fan and hang it higher.
A tube jet is a fan blowing into a clear plastic tube that runs the length of the house, with holes along both sides. In winter it draws a little cold outside air through a shutter, mixes it with warm house air, and jets it out along the whole house so no plant sits in a cold draft. Many houses also run it from the heater to spread heat. It moves less air across the floor than HAF fans do. Summer cooling is the exhaust fans' job.
Advanced maps tubes. Pick one and enter its size, length, fan airflow, number of holes, hole size and how far down the holes aim. The map treats each hole as a small jet out the side, with the fan's air shared evenly. Holes at about 4 and 8 o'clock aim 30° down, so their air reaches the crop beside the tube. That holds when the holes add up to 1.5 to 2 times the tube's cross-section, the range in the ASAE greenhouse standard. Outside it, the planner warns you, because the air won't come out evenly.
Advanced has a speed for each fan, for variable speed fans and controllers. Airflow drops in step with speed, so a fan at 50% moves half its label airflow. Its push drops faster, to a quarter, because the air also leaves the fan slower.
A unit heater is a fan with a burner. While it runs, its blower pushes air like an HAF fan, so aim it along the loop, not against it. Turn heaters off to see the house on a mild night. The map counts the blower only, and the warm air rising off a heater is left out.
Exhaust fans pull air out through a wall and open vents let the same amount back in, so air crosses the whole house from the vents to the fans. Summer cooling needs about 8 CFM per square foot of floor. Put the vents on the wall across from the fans, keep fans no more than 25 ft apart, and don't put a vent next to a fan or the air goes straight from one to the other. With every vent shut, exhaust fans pull against the house and move little air.
Advanced adds a side view: a slice down the length of the house, floor to roof, along the dashed line on the map. It shows how far down into the crop the air reaches, VAF air landing and spreading, and warm air from heaters rising to the roof. The fastest air runs at fan height. Inside the crop it slows toward the floor, so the lower leaves of a dense crop sit in stiller air than the tops. The map works out the air across the house as one layer, then puts the heights back with known shapes for wind in a crop, jets and warm air, so the heights in the side view are rough.
Hold a vane or hot-wire anemometer at the top of the crop in a grid of spots down the house, with vents in their usual position. A strip of tissue or a soap bubble works too. If it barely drifts, the air there is still.
Sources: fan sizing and placement from UMass and UConn Extension; exhaust fans and vents from NGMA; canopy speed targets from HortiDaily and Kitaya et al.; the flow model from depth-averaged flow research. Full list: sources.