Re: The chilling truth about cold horsepower

["Jerry Smith" <jerrytheplater at hotmail_com>]

Scott:

I called my HVAC vendor today to ask him about this question. He uses 1 HP = 
1 Ton Refrigeration =12,000 BTU/hr but also said that the HP rating is only 
used in the really big units. In our conversation he also stated that they 
use 3200 BTU/hr. as the heat generated by each 1 HP of electric motor that 
is operating when calculating heat loads in rooms to size them for air 
conditioning. This could be a rounded up figure from the 2450 BTU/hr to 
allow a safety factor for them. Could it be that the reference tables are 
using the 2450 BTU/hr conversion for 1 HP as the heat they generate when 
operating and not be referring to the output power of the motor?

I ask this because I also called a manufacturer of chillers today and spoke 
to someone in the Technical Service Department. I explained to him the 
problem I have in understanding the rating of their units compared to the 
conversion chart value of 2450 BTU/hr for 1 HP. When he understood the 
question he couldn't answer it. He put me on hold and asked an engineer who 
told him the chart is referring to the heat generated by the motor. He said 
if that motor were connected to a pump, just the action of the pump would 
generate 2450 BTU/hr in pumping the water. If you want to talk to them for 
yourself, email me privately and I will give you the telephone number and 
the name of the company.

I am confident that 1 Ton of Refrigeration = 12,000 BTU/hr because:
(2,000 lb. ice / 24 hr.)*(144 BTU / lb. ice, the Heat of Fusion for ice) = 
12,000 BTU/hr. This applies to the melting of ice at 32 F to water at 32 F, 
no change in temperature of the ice or water

When I was looking at various articles in the World Book Encyclopedia I read 
the one on Horsepower. In it it gave an example of the rating of gasoline 
engines. "Indicated Horsepower" is an estimate based on work done on the 
pistons by the gases produced by combustion. "SAE" Rating is another 
estimation method used. "Brake Horsepower" is not an estimate but a 
measurement of the power applied to the crankshaft. The example they gave 
rating the same engine resulted in 36.4 Indicated Horsepower, 19.6 SAE 
Horsepower, and 29 Brake Horsepower. The article also defined 1 Boiler 
Horsepower as the ability of a boiler to change 34.5 lbs. of water at 212 F 
into dry steam at 212 F in one hour. There is obviously more than one type 
of Horsepower depending where it is being used.

In a catalog, www.mcmaster.com, search for Liquid Chillers. They are on page 
438. I'd give you a link but I don't know how to do it. They rate the units 
they sell as Compressor Horsepower and BTU/hr. I don't know what is meant by 
Compressor Horsepower and if it is another type of Horsepower.

Well this is long and it is late.

Jerry Smith in Bloomingdale, NJ

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