Your plants NEED either a fresh supply of CO2
, and exceptionally good aircooled or watercooled shades, (which either requires a vent fan or very large tanks of water for the latter) or you can just exchange the air with an exhaust fan.
There is no "optional" ventilation, most plant rooms will skyrocket in temp and humidity levels unless the air is regularly exchanged. Using HID
lamps you should move all the air out within 5 minutes, under 1 is better if you can.
regulation and equipment is hard and expensive. To reasonably set yourself up and supply the plants with the required co2, and this isn't taking into account the heat and humidity generated by the plants, you'll have to work out a way to remove that too, cost upwards of 1000 bucks more like 2. There are some products out there like sodium bicarbonate mixed with muriatic or other acids, which when you add water releases co2, but the amounts required for reasonable levels, as well as the fact that it's going to be gone almost instantly, with any reasonable ventilation, makes it kinda pointless except maybe for clones or small motherplants. Even then it's not economical to make a real dent in the levels above 300ppm.
So yeah, I'd suggest thinking a little laterally, and trying to vent the hot, humid air from the growing space out and away, (smell will be an issue) and have some kind of intake down low to allow fresh, preferably cool and clean air through the grow space. This is really hard to emphasise, but fresh air for temp/humidity reduction and co2 levels is one of those major limiting factors, meaning that you could have everything else perfect, with no ventilation, the plants will never produce, and will suffer greatly for it.
You'll work it out I'm sure.
Considered just keeping a small seedling box @ home with minimal ventilation via a small computer fan, then planting outdoors somewhere as a guerilla grow? That way you won't be risking your olds necks either.