In article ,
Lloyd at @the-wire. dot com wrote:
On Wed, 2 Sep 2009 17:49:21 -0400, "Nicholas
O. Lindan" wrote:

I have seen 'portable' air conditioners that use a hose that sticks
out the window - like a dryer hose - via an adapter panel. I thought
one of these with a blacked-out hose would make an ideal darkroom
airconditioner but Consumer Reports rated them badly. Anybody have
experience with these things.

September 4, 2009, from Lloyd Erlick,

Those things are on sale around here. It's
been an unususally cool summer, and I suppose
a lot of stock did not find buyers.

There is a problem with the single-hose models, which should be
pretty obvious if you think about how they work: they have an air
_exhaust__ but no intake, right? So where does the air they use to
cool the hot side of the freon coil come from?

The answer is, "inside your room". So they cause continual negative
air pressure in your room, and without it, they don't work. And what
_this_ means is that if your structure is really well sealed, they
cannot work at all, while if it's not, they pull in at least as much
hot air as they produce cold air!

It is a terrible loophole in the efficiency rating system for air
conditioners which permits these to exist at all. If they were rated
fairly, they would all fail the minimum-efficiency test and be banned
from the market.

The dual-hose models, on the other hand, work fine, if you can find
one that's not cheap junk from the lowest-bidding Chinese factory.
The dual-hose type, of course, uses _outside_ air which it pulls in
using one of the hoses to cool the hot side of the coil, just like
a normal window unit would.

You can replace the hoses with aluminum dryer hose, which is light
tight, and the unit should then work well in a darkroom. It can be
hard to find a small dual-hose unit. Frigidaire makes a 9,000BTU
model which A.J. Madison and some of the other national appliance
delivery chains carry. I have one and it's worked well so far.
But it does have some bright green lights on the control panel which
you will have to tape over, and also keep in mind the inside of that
aluminum hose is reflective and could give you a light leak if the
other end is in direct sunlight -- you might well want to paint
as much of the interior of the hose black at each end as you can
reach.

Like most units the Frigidaire has some vent slots to let the unit
pull exhaust air from the inside of the room like a single-hose
unit if the intake hose is blocked. I have taped these over on
other units without any trouble (they always pull some air from
the interior of the room if you don't but in a darkroom this
might actually give you some desirable exhaust air to carry
airborne contaminants out of the room).

I would not try to run a darkroom with positive-pressure ventilation.
It sounds good in theory, but a wet darkroom makes a lot of dirty
air which you really want out before it can irritate your mucus
membranes and your lungs. If anything, balanced airflow, with
fans for both intake and exhaust air, blowing across the sink,
would be the best way to go.

--
Thor Lancelot Simon
"Even experienced UNIX users occasionally enter rm *.* at the UNIX
prompt only to realize too late that they have removed the wrong
segment of the directory structure." - Microsoft WSS whitepaper