Re: Chilling truth

[Paul Sears <psears at nrn1_NRCan.gc.ca>]

	What a mess!  Let's start from square one and get away from
the obsolete units that caused the problem in the first place.

1 "ton" of chilling is 3.5 kW of chilling.

1 watt (W) is one Joule per second

1 BTU is 1055 Joules

1 horsepower is 746 W

1 boiler horse power is an even more obsolete unit and was in effect
the amount of heat applied to the boiler so that an engine could provide
1 horsepower.  Since boilers and engines had different efficiencies,
this could lead to problems.  I'm not touching that one again.

	A mechanical chiller works by moving heat from a low temperature
to a higher temperature.  The work applied by the motor appears as
heat in the heat output.  A chiller with a COP (coefficient of
performance) of 3 will use 1 unit of mechanical energy to remove
3 units of heat energy from the place to be chilled and will produce
3+1=4 units of heat energy at the place where heat is dumped.

	COP's depend heavily on the actual system and the temperatures
involved, but 3 to 4 is typical.  Note that COP is dimesionless.

	Convert everything to watts, and it's easy.

	Chiller efficiencies are sometimes reported as "SEER" instead
of COP.  The SEER is a ratio of heat removal in BTU/h to mechanical power in
watts.  Divide the SEER by (3600/1055 = 3.412) to get the COP.

	Why are we using nineteenth century units in the twenty-first
century????

-- 

Paul Sears
psears at nrn1_nrcan.gc.ca, 613-996-4171, facsimile / télécopieur 613-996-9400
Natural Resources Canada, 1, Haanel Drive, Nepean, Ontario K1A 1M1
Ressources naturelles Canada, 1, Haanel Drive, Nepean, Ontario K1A 1M1
Government of Canada / Gouvernement du Canada