TOO HOT!

After we built the greenhouse and it got to be summer, the interior temperature could skyrocket up to above 130 degrees F. The greenhouse has two ceiling vents that open automatically when the temperature is around 90 degrees and there is a passive vent at the bottom of the back wall for inflow. Despite these built-in features it gets too hot.

Kristin potting plants inside greenhouse.

I started by putting a cheap box fan pulling air in at the low vent…little improvement if any.

Next, I tried a more powerful fan at the low vent and still no appreciable improvement. The fan sat inside the greenhouse, up against the vent. Not air tight by any measure.

The next attempt was adding shade cloth with a 90% shade rating. This brought the peak temperature down to the mid 120 degrees. Still too hot.

Next, I replaced the inflow fan at the low vent with a purpose-built fan rated at 1597 CFM (Cubic Feet per Minute). This fan is installed air tight to the vent, pulling air into the greenhouse at the bottom. The fan is really intended to exhaust out, so I built this airtight box to have it sucking air in.

The interior of the greenhouse is about 90” x 113” x 80” which is 813,600 cubic inches which in turn converts to 470 cubic feet, To my mind, this means a 1600 CFM fan should replace the air in entire greenhouse around 3 times EVERY MINUTE!

Alas, the interior temp only dropped to 115-119 degrees in the heat of the day, even if the outside temperature was in the low 80’s. I was hoping for better.

Fan rating exaggerated? It feels like the fan is more like 300 CFM.

Air pressure inside the greenhouse decreases air flow?

Greenhouse Temperature Control

Partridge Peas (Chamaecrista fasciculata)