That is a rather hard Q to answer definitively. It could. Still other factors to consider:

1) How big is this terr? If large, you might need more than one fan or one strong fan.

2) How much light will be provided?

3) What kind(s) of orchids are you considering? [low light or high light lovers]

I don't have any experience with submersible heaters but from what I have read/heard, your water level might not be deep enough to use a heater. I also don't think you would really want a great deal of water to remain in the bottom area for any length of time -- molds and algae would flourish in such stagnant water.

Depending on room temp and the lights used, you very well might need any additiional heat source.

So agina, my thoughts are that this could work, but a bit more needs ironed out.

:)