Hello Pam... I used to live in Tucson and now live in Wisconsin.
(Don't ask!) Anyway, I've had to face both issues...cooling and
heating uncooled or unheated spaces. I've set up a lot of temporary
studios in the last few years, carving out a small space for myself
in all kinds of interesting places, including a few garages.
Insulation is Numero Uno, and don't skimp on it! Garages usually
have flimsy doors but can be insulated...there are even kits these
days for doing the job. If you don't have to put the door up and
down, then you can superinsulate it and seal the bottom where heat or
drafts will happily enter. The rest of the room is insulated just
like a regular house. Find and kill drafts. Insulate around the
doors, windows, even the outlets...just like tightening up a house.
Every little thing they do to keep the outside air out will help.
I like to warm the place up with carpeting wherever I can get away
with it. It makes it feel cozier to me and helps with cold concrete
floors and helps to absorb a bit of noise.
If it's a multi-purpose garage, they can temporarily or permanently
create a small workroom with tarps (renters) or studwalls and then
heat or cool only that portion. I don't want drafts around my torches
so I like heating and cooling that does not blow large volumes of
air. I want my air warmed without burning all the oxygen in the room
so I use baseboard water heat instead of wood or direct gas or
electric heat. They make small electric baseboard type heaters that
are pretty efficient. I want to hear my music or nothing at all, so I
want to minimize any motor sounds. (How come I don't mind the banging
of hammers?). For cool air in dry climates, evaporative cooling made
me happy. In humid areas or during monsoon...nothing but a power
sucking air conditioner worked for me.
I think a comfortable workspace is essential and I would take the
opportunity to impress upon your students the necessity of making a
safe, efficient workspace that they are happy to be in. Have them
spend the money up front to make their space groovy so they can get
down to business. They can save money by creating a space only as big
as they really need to begin with and adding on later.