Once set these automatically adjust to the air temperature in the greenhouse and if it's hotter than you set it for it will open the vents to let the hot air out.
(the vents; to let; the hot air; out) (these; automatically adjust; to the air temperature in the greenhouse; T:Once set) (it; 's; hotter) (you; set; it; for it)
the vents these it you
to let automatically adjust 's set
the hot air out
to the air temperature in the greenhouse T:Once set
hotter
it for it