The chilling truth about cold horsepower

["S. Hieber" <shieber at yahoo_com>]

Aquarium chiller manufacturers seem to equate 1 hp, a
commonly used unit of measurement for the capacity of their
chillers, with 12,000 BTU/hr.  Although, one must admit
that some of them follow a rather loose set of arithmetic
rules. 

What's interesting to me is that every engineering
reference I've been able to dig up equates 1 HP to 2540
BTU/hr (give or take a few BTU).

The reference works and engineering tables do commonly
equate 1 hp to 12,000 tons regfrigeration, but not 12,000
BTU/hr.  Tons Refrigeration is a still used but somewhat
antiquated standard of measure for chilling capacity,
having originated as a measure of the amount of ice a
device could produce in a fixed period.

Can anyone steer me in the right direction here?  Are there
two different kinds of British Thermal Units, one of them
being used only by refigeration manufacturers?

There's some pretty whacky standards of measurement in this
world (gasoline antiknock ratings are a great example) so I
wouldn't be surprised to learn that I'm just missing a
piece of the formula here.

Scott H., not sweating the small stuff, but curious.

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