DRAWING THE SHEET —
DRAWING THE SHEET —
ENVIRONMENTAL SYSTEMS — THE CLIMATE DECISION
Active ventilation pulls outside air through a wet wall and runs it the length of the house. With VPD control the house stays sealed while an AC system we engineer holds your crop's setpoint. One question below sorts most operations.
ONE QUESTION · NO FORM · THE RIGHT BUILD LINK AT THE END
OUTSIDE
WARM · TURBULENT · WHAT THE FANS PULL FROM
SCROLL — WATCH THE AIR SETTLE
INSIDE
COOL · LAMINAR · HOLDS THE NUMBER
THE STEEL STARTS COOL
Cool Lock™ white steel absorbs about 69% less solar heat than bare galvanized, so the frame adds less heat for either system to remove.
SOURCE — NASA PUBLICATION 1121 · WHY THE STEEL IS WHITE
14-FT SIDEWALLS
The hot layer stratifies above your canopy, and the fan-to-wet-wall air path gets a full cross-section to move through.
TALK IT THROUGH FIRST
A Greenhouse Expert walks the climate choice with you before you spend anything.
01 — THE TWO PATHS
PATH ONE — ACTIVE VENTILATION
Exhaust fans on the door end pull outside air through the wet wall at the back, and evaporation cools it on the way in. It prices as one line in the build tool, sized to your length. Evaporative cooling works toward the outside air's wet-bulb temperature, so it bites hardest in dry heat and loses power as the air turns humid.
PATH TWO — VPD CONTROL
The house stays sealed. A large AC system we supply controls temperature and humidity together and sits inside a tight band hour by hour, through a July afternoon and a wet night. It is engineered to your crop, so it prices in your quote.
The test: on your hottest, most humid design day, can outside air pulled through a wet pad still hold the temperature and humidity your crop needs?
If it can, buy active ventilation and keep the difference. When the answer is no and your margin rides on that number, you size a VPD system.
SOURCE — UMASS EXTENSION / ACES / GPN
02 — THE NUMBER, IN PLAIN ENGLISH
Vapor pressure deficit, measured in kPa, rolls temperature and humidity into one number the plant feels. 70% humidity at 65°F and 70% humidity at 85°F put different loads on the same leaf, and VPD reads both rooms honestly.
In the right band the stomata stay open, so the plant keeps pulling water and nutrients while it takes in CO₂. Drift too low and moisture sits on the tissue until mold moves in. Run too high, and the stomata close to save water while growth stalls.
Lettuce selling as healthy and marketable rarely chases that number. Contract-grade flower loses a harvest to one humid night, so for that crop the band is the whole job.
03 — WHAT EACH PATH COSTS
ACTIVE — THE OPEN BOOK
$4,000 AT 60 FT + $500 PER 20 FT BEYOND, PER BAY
One price covers the fans, the wet wall, the vents, and the circulation fans, sized to your length. On a 30×100 bay it runs $5,000, priced to the dollar in the build tool. On your meter it draws fan energy, a fraction of a full climate system's load.
VPD CONTROL — THE HONEST ANCHOR
≈ $100,000 FOR THE CLIMATE SYSTEM ALONE, ON A STANDARD 30×100
That figure is a standard system. Yours is engineered to your crop and stage targets in your quote, and that work takes more input and more time. Weigh it against the crop one humid night can take. The VPD page walks the whole system.
04 — WHO EACH TOOL IS FOR
ACTIVE VENTILATION IS THE RIGHT CALL IF —
VPD CONTROL IS THE RIGHT CALL IF —
A leafy-greens grower in a dry valley hears it from us straight: buy the active-ventilation package and keep the rest of the money.
05 — CHOOSE
Answer the one question that settles most cases and leave with the right build link.
Answer it the way your worst week goes. If the active-ventilation package holds your numbers, we'd rather you keep the money.
THE DECISIVE QUESTION
On your hottest, most humid design day, can outside air pulled through a wet pad still hold the temperature and humidity your crop needs?
IF YOU'RE WEIGHING IT ON CLIMATE
LEAN ACTIVE WHEN —
Dry heat. Evaporative cooling drops the most degrees where humidity is low
LEAN VPD CONTROL WHEN —
Your design day is hot and humid
IF YOU'RE WEIGHING IT ON CROP
LEAN ACTIVE WHEN —
Leafy greens, cool-season veg, hardy ornamentals, nursery and bedding stock
LEAN VPD CONTROL WHEN —
High-value fruiting, propagation, disease-sensitive crops, cannabis
IF YOU'RE WEIGHING IT ON QUALITY BAR
LEAN ACTIVE WHEN —
Healthy and marketable, seasonal, weather-tolerant
LEAN VPD CONTROL WHEN —
Contract-grade consistency, max yield per square foot, year-round
Still split? Disease usually decides it. When one humid night of bud rot or powdery mildew costs more than the climate equipment, size the VPD system. Otherwise buy the active-ventilation package and bank the difference.
06 — WHY YOU CAN TRUST THIS PAGE
01 — EVERY CLAIM CARRIES ITS SOURCE
University extension bulletins from UMass and Auburn sit behind the evaporative figures, and PE-authored HVAC studies sit behind the dehumidification load. The references ride with the sections they support.
02 — REAL PRICES WHERE WE HAVE THEM
Active ventilation is a book line in the build tool, and the VPD system prices exactly in your engineered quote.
03 — THE SAME BUILDING UNDER BOTH
Either path rides on the same PE-stamped structure, engineered to your county's wind and snow loads.
RELATED — WHY THE STEEL IS WHITE · THE WIND-RATING DECISION · THE FULL PRICE BOOK
07 — GOOD QUESTIONS
Active ventilation pulls outside air through the wet wall with exhaust fans and cools toward the outside air's wet-bulb temperature. VPD control keeps the house sealed while a large AC system holds temperature and humidity inside your crop's band through any weather.
Ask this: on your hottest, most humid day of the year, can outside air pulled through a wet pad still hold the temperature and humidity your crop needs? If it can, buy active ventilation. When your margin rides on a number that day refuses to give you, size the VPD system.
Yes. The structure is sealed by design and engineered to your wind and snow loads either way, so a later change is a climate-equipment purchase. A Greenhouse Expert can phase it with you.
No. Cannabis is the most common case because the margins and the disease risk both run high. High-value fruiting crops, propagation, and disease-sensitive crops hold a VPD setpoint for the same physics.
Active ventilation is one priced line in the build tool, sized to your length. The VPD system is ours to supply and engineered to your crop and stage targets, so it lands in your quote.
Answer the chooser above and leave with the right build link.