Hi,

I took this thread off of "sci.engr.heat-vent-ac" and "alt.hvac";
hopefully it will calm down a bit. It seems to be added to
"alt.energy.homepower", so I'll continue it there as well. If anyone is
just starting on this thread, I'm trying to come up with a way to make
an AC that works without a window, yet works better than those portable
units (I already own one, and I don't like it). There are "split" AC
systems pre-made, but I'm starting to think they aren't appropriate for
an apartment, even if money was not an issue. Upon moving out, the
refrigerant circuit would have to be dismantled. I'm not sure if
store-bought units provide valves to contain the refrigerant when doing
this; otherwise the refrigerant would have to be completely drained and
refilled every time. Additionally, they're fairly expensive, and though
building one is simple in principle, I might instead pursue another
route, which Nick just suggested.

Warning: This is a rather long post.

---------------

In reply to Nick's previous message:

That would actually be like a cross between two types of AC's: split
and portable units. It would be just like the portable unit in that the
compressor and the entire refrigerant circuit stays inside. Except
instead of using a fan and an air duct to remove the heat outdoors, it
would use a water circuit. And instead of discharging the exhaust right
out a window, like a portable unit, it would have a "second half"
outdoors, like a split unit. The nice thing about such a unit would be
that the exhaust "duct" could just be two thin, flexible hoses. If such
a unit was commercially produced (or should I say producable?), it
could have many applications. There are many people who work in
temporary locations, and use portable AC's. But a lot of these people
just point the AC at their immediate work area, and let the hot air
blast out the back. Usually this is because it's too inconvenient or
impractical to duct the hot air through their workplace. With smaller
water hoses, this wouldn't be as much of a problem. Don't get me wrong,
lugging around a swimming pool of tubing wouldn't allow for
portability, but I address an alternative later in the post.
Additionally, for temporary use, they could just plug into any cold
water supply and drain.

In order to get my store-bought portable unit to operate acceptably, I
need to use an enormous hose (bigger than the manufacturer supplied),
or else it will overheat and automatically shut off. Even in a very
small room, with the exhuast only having to go a foot or two. The
exhaust duct is ugly, and it is extremely hot. If the duct was more
than 10 feet or so, I bet the net result of using the portable AC would
be to heat the room, due to the heat radiating from the duct.

To add to Nick's idea:

What about using a second (smaller) compressor for the water circuit?
If the water was allowed to evaporate as it hit the hot coils, its
cooling ability would be much more efficient than if it stayed liquid
and just absorbed a small amount of heat as it passed. The compressor
would then pressurize the steam, lowering its boiling point, and it
would cool through the tubing Nick just mentioned, where it would
condense. There could then be a resevoir of water, to ensure that the
water in the next part of the tubing was almost entirely in the liquid
phase. Then it would go through some small flexible tubing to the
indoors, and cools the coils again. The pressure in various stages of
the tubing could be regulated somewhat by adjustable valves.

For me, a 6 foot pile of piping isn't that bad in the first place; I
never use my porch. But it would be nice to reduce that size, if
possible.

Some people might argue that having two compressors would reduce the
efficiency of the total system by a factor of about 1/2 purely because
of having double the number of compressors. However, where the water
compressor is doing "extra" work, the regular AC doesn't have to work
as hard, because its hot coils would be cooler. There would still
energy losses due to more moving parts, the viscocity of the water,
etc... The net efficiency would surely go down, and maybe it would go
to less than 1/2 its original value. It's just a question of whether it
goes to an acceptable level. People who buy portable units expect to
pay more for the units, and paying more for electricity is expected
too. The units are usually only bought because the user is unwilling to
go without AC, but the choice of AC units is limited by the
environment. Generally the application is temporary, and my case is no
exception (I won't live here very long). I have to guess that my
store-bought portable AC has an efficiency of 1/4 of even a cheap
window unit. A similar efficiency would be fine.

Also, I *do realize* a purely water-based AC would NOT work well
(alone). I am definitely not suggesting anything like that. Here, the
water is just transferring heat from a very hot coil to the less hot
outdoor air. The water would do that naturally, without a compressor
involved. It is NOT causing a SEPERATION of heat between two resevoirs;
ie: adding heat to the hotter side. And I realize that the water would
probably never been cooler than either the indoor or outdoor air. It
would only be cooler than the hot coils of the AC, and that's all that
matters. The phase changes between liquid and vapor would simply be to
absorb and release lots of energy quickly.

If such a unit was made commercially, the only benefit over a standard
portable AC would be having a thinner, flexible exhaust circuit. That
alone would open up possibilities. But for me, it would also mean that
I wouldn't have to cut into any refrigerant circuits. Which means not
having to worry about properly containing the refrigerant, getting a
vacuum pump, soldering the joints, putting more refrigerant back in
without letting in air/moisture, getting the pressure right, the list
goes on...

----------------------

Now, we had some arguements in the other newsgroup about making versus
buying, "reinventing the wheel", etc. Personally, I think it's more
like "building a wheel" to a certain specification. There will always
be some people who try to do things that they are destined to fail at,
and others who run away from anything challenging. Either extereme
isn't desirable. As far as that topic goes, I think it's best to just
leave it at that. But just for the record, if someone made a portable
AC unit approximately 20,000 BTU which had the design I described above
(with flexible, insulated water tubing), I would probably buy instead
of build. But that's besides the point, because I've never seen such a
thing.