I forgot to add, the window is south facing.

Sounds like paradise for plants. There are many orchids which would like your conditions. You don't mention where this building is...what State, zone.

Dendrobiums, Cattleyas like high light, warm temps. Certain Dends need cooler temps, you would need to research. There are others but might require cooler temps and more humidity.

This is a good beginning:

Here is a link that might be useful: American Orchid Society

Thanks! I am in Chicago, zone 5, so in the winter there are many cloudy days but thanks to the window it seems enough still gets through.

It sounds like you have good conditions, as Jane says. Three feet from the window would be okay for phals and phaphs and other low light orchids, but not for sun lovers like cattleyas, dendrobiums, oncidiums, and so on. They would need to be closer to the window.

Don't worry about the 90 degrees, most orchids can tolerate that temp and even more for brief periods. Here in NJ the temps often go over 100, and as long as the orchids are kept hydrated, they come through fine.

As for the reverse osmosis water, you would need a fertilizer with all the micro and macro nutrients in it since the RO water is almost pure and has nothing in it. (Dyna-Gro was developed for hydroponics and is one you should consider, Jack's Classic is another, and there are MSU formulas out there also).

Don't worry so much about the humidity, that can be dealt with fairly easily. Light is the most important consideration, and it appears you have that already. A low light lover can be kept back from the window a bit, light lovers closer to the window. With the temps you have, you should be looking for an intermediate-to-warm temperature loving orchid.

It sounds as if your conditions are predominantly low (by natural standards) light, in which case my recommendation would be Phalaenopsis. Another plant, closely related, which does very well in such conditions is Doritis. It is smaller than Phal and very easy to flower, often hybridized as Doritaenopsis or "Mini-Phal". It looks very good on an office desk, as it doesn't take up too much space. When happy it will flower 2 or 3 times a year with long lasting blooms. Needs only about 1 hour of sun a day - Ian.

While I agree with all of the statements above, I want to caution you that not all dendrobiums love bright light. Most do, but I have one that I do not believe was doing so well under T5 fluorescent lights. At least so far, based on other conditions (water, temp, etc), I believe this dendrobium does not like bright light. The leaf color is fading and it doesn't appear as vibrant. Otherwise it is healthy and produced a spike with buds. Unfortunately, I have no idea what type of dendrobium I have, as it was one of those on-sale Orchids from either Lowes or Home Depot.

Sarah