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Re: The chilling truth about cold horsepower


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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