From: ems@Apple.COM (Mike Smith)
Newsgroups: sci.energy
Subject: Re: Thermal Energy Storage (was Re: SOLAR efficiency)
Date: 2 Oct 92 02:09:47 GMT
Distribution: na
Organization: Apple Computer Inc., Cupertino, CA

In article <1992Sep21.173522.9358@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes:
>The most recent EPRI Journal has an interesting article on Thermal
>Energy Storage (cold storage) systems for large buildings.  A summary:
>
>Cold TES systems have been installed on about 4,000 large buildings in
>the US, representing a displaced peak load of more than 400 MW.  This
>is still a small fraction of the possible market for large buildings,
>however.

We looked at such a system for our Cray.  (We had an XMP-48 that used
massive quantities of chiller water.)  Using ice storage was a big win
for us.  Make ice at night, cool with it during the day.

Fortunately or not, we also found that upgrading to an air cooled 
YMP-232 not only solved a shortage of memory, but the saving in 
utility costs (both electricity and water) was so great changing 
to the YMP that we could no longer justify the ICE system ...

YUP, conservation by improved technologies was the winner...  we even
got a $197,000 rebate check from PG&E for our concervation efforts!
(That should give you an idea how much power we were using and how 
much water had to evaporate to cool the machine ...)

I STILL liked the ice system (which we cristened the ICE BUCKET option
internally) ... Someday I may build a little one at home.  It was rather
trivial technology...

>Modern TES systems can actually be more efficient than conventional
>chillers (without thermal storage), for several reasons:

I THINK that our numbers said about a 30% savings.  Whatever it was
exactly, I remember is was a real big win...

>  -- They run constantly, rather than cycling on/off.
>  -- They run an night, when it is cooler.

These too accounted for most of the gain in our model.

>  -- Because they produce lower temperatures than conventional
>     chillers, the air moved during the day is colder, and
>     so less air flow is required.

We were chilling water, so this didn't enter...

>A new material called "slippery ice" has boosted efficiency.  By
>mixing calcium magnesium acetate into the water, ice forms throughout
>the solution and does not stick to the refrigerant coils in the
>storage tank.  This slush can also be pumped through distribution
>lines, where it has about 4 times the heat capacity of chilled water.

Where were you a hear ago?  One of the technical issues we were
looking at was how to make ice in the Ice Bucket while not having 
the chiller water freeze in the pipes ...

>Elsewhere, I read that a utility is now using an ice-based TES system
>to boost the capacity and efficiency of a combustion turbine.
>Combustion turbines lose capacity in hot weather (it requires more
>work to compress enough hot air); precooling the air can add 25% to
>the capacity of the turbine.  The ice is produced off-peak with
>cheaper baseload power.

Nifty!  A way to turn natures cold air into electric power!

>This suggests to me the interesting possibility of using ice ponds as
>seasonal thermal energy storage systems, in conjunction with
>combustion turbines.  I don't know if that would be economical.  

Even if it isn't economical now, it is an interesting way to 'harvest'
seasonal heat variations ...

>Ice ponds, you may recall, are created by spraying water from a nozzle
>into cold winter air; slush is formed and falls into a pond, where it
>accumulates.  The pile is covered with straw + aluminized plastic for
>insulation.  Meltwater is drawn off for cooling.

Or maybe all that snow in the snow belt could be bulldozed into a pile
for storage ...

Buffalo, NY, may have a feature after all!

-- 
E. Michael Smith  ems@apple.COM

"Nothing can keep an argument going like two persons who aren't
sure what they're arguing about."   O.A.Battista
Newsgroups: sci.energy,talk.environment