my wife just had green house built 16x20 ft i would like to control the tempeture in the greenhouse with the help of
a exhaust fan about 4000cfm would a vfd work and how do i controll the speed with a stat ?the motor would be about 0.5hp any one know what is the best way to do this
Thanks
jack

Probably the easiest way is just a regular stat with a relay.

Get an automated light [window] opener, it works for free. A fan will remove plant food, [ good old carbon dioxide ] and force entry of a plethora of disease spores and spider-mites, apart from the cost of running a fan. A timed/sensed watering distibutor/mats will be better way to improve your glasshouse. I use bagged compost, not soil, and use it to pot flowers up the next year, third year as a soil improver. My little 8x6 produced 13 cantaloupe melons this year, plus 2 cucumbers a week and more tomatoes than we could eat. Best of luck next year and good eating!