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Innovative Solutions _______ January 2006
In this issue
-- Feature Article: Definition of Refrigeration Horsepower
-- On a Personal Note:
-- On the Lighter Side:
-- Article Policy

Welcome to the January 2006 edition of Innovative Solutions, the monthly newsletter from Innovative Thermal Solutions. If you find this information interesting or useful, please share it with your friends and colleagues.

Word count approx. 1000
Reading time approx. 4-5 minutes.

This week’s feature article is based on some research I did while putting together a presentation I’ll be giving at the ASHRAE technical conference in Chicago next week. I thought it might be interesting to define a refrigeration capacity term we all use, but nobody seems to know what it really means – Refrigeration Horsepower.

Feature Article: Definition of Refrigeration Horsepower
With the introduction of refrigerating machines in the first half of the 20th century, the new refrigeration industry was faced with a challenge. What recognizable measurement for "coldness" could be easily understood by the public?

Refrigerating machines and air conditioners moved heat and therefore could be rated in terms of BTU's per hour. The British Thermal Unit ( BTU ) is defined as the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit from 58.5 to 59.5 degrees Fahrenheit. That is a very good engineering definition, clearly and precisely defined.

But, to the general public, "BTU's" were used in the measurement of something hot like a heater or boiler. "Coldness" was generally perceived to be something entirely different than heat!

Most consumers were used to iceboxes and cold storage ice warehouse facilities were common. So, in a stroke of marketing genius, the recognizable measurement for "coldness" was defined as a relationship to melting ice! Melting ice at 32 degrees Fahrenheit requires 144 BTU's per pound to become liquid at 32 degrees Fahrenheit. The Refrigeration Ton was defined as the heat absorbed by one ton of ice (2000 pounds) causing it to melt completely by the end of one day (24 hours).

Therefore: 1 Refrigeration Ton = 2000 Pounds x 144 BTU per Pound / 24 hours = 12,000 BTU's per Hour

The idea of Refrigeration Ton made it easier to sell equipment. The machine's capability could be compared to a quantity of ice. Imagine a salesperson trying to persuade a customer that a new-fangled "refrigerator" is equivalent to an icebox holding several hundred pounds of ice! "And just more ice deliveries!" Today, the term is still in common use. The capacity of most air conditioners is nearly always described in terms of the Refrigeration Ton. Note that the Refrigeration Ton is defined as BTU's per hour which is work units divided by time units. Work done in a time frame is defined as power. Therefore, the Refrigeration Ton can be related directly to other definitions of power such as watts. 1 Refrigeration Ton = 3,515 Watts

But, to throw in some industry jargon, refrigeration capacity as opposed to air-conditioning capacity is often referred to as horsepower rather than tons. So what is the definition of “refrigeration horsepower”? I called the vice president of engineering at three different compressor manufacturers and asked where the term refrigeration horsepower came from. The good news is I got the same answer from all three of them. The bad news is they just laughed, said I was the first person who had asked and they really didn’t know.

But I can tell you what it isn’t. It isn’t the simple conversion of Ton to horsepower. As a simple power unit conversion 1 Ton equals 4.72 horsepower. Refrigerating horsepower isn’t mechanical horsepower. It isn’t the power input to the compressor. In fact, it isn’t a well defined engineering unit of measure at all.

I was able to track down a refrigeration engineer who graduated from college and started work the year I was born. He knew what was meant by refrigeration horsepower. The generally accepted definition is:
High Temperature refrigeration, 1 Hp = 12,000 Btu/hr (1 Ton)
Medium Temperature refrigeration, 1 Hp = 8,000 Btu/hr
Low Temperature refrigeration, 1 Hp = 4,000 Btu/hr

These definitions will help you identify approximate compressor or system capacities as sometimes listed in various manufacturers’ catalogs. However my general advice is


Air-conditioning and refrigeration capacity is correctly defined as Btu/hr or watts, depending on whether you are using I-P or SI units.

On a Personal Note:
I went to the Detroit Auto Show this week. This is the second time I’ve gone in the 10 years that I’ve lived in Michigan. It just seems that if I live this close I should go every few years. Overall, I just don’t find looking at so many beautiful, expensive automobiles all that interesting anymore. But a couple of things struck me as noteworthy. First, I remember when station wagons were called station wagons. They weren’t downsized SUVs and they certainly weren’t “crossovers”. I understand the marketing reason; no one wants to buy a station wagon anymore. But give me a break, if it looks like a station wagon and drives like a station wagon, it’s a station wagon. And what’s with these huge trucks that hold 6 people and don’t have enough cargo area to haul a single bail of hay? I’d like to see them load a stack of 4’ x 8’ plywood in one of those monsters – it isn’t going to happen. Who needs to take 6 people to the lumber yard to get plywood and sheet rock anyway?

On the Lighter Side:
And speaking of the auto show-

At a nursing home in Miami, Florida, a group of seniors were sitting around talking about all their ailments.

"My arms have gotten so weak I can hardly lift this cup of coffee," said one.

"Yes, I know," said another. "My cataracts are so bad I can't even see my coffee."

"I couldn't even punch out the chad at election time, my hands are so crippled," volunteered a third.

"I can't turn my head because of the arthritis in my neck," said a fourth, to which several nodded weakly in agreement.

"My blood pressure pills make me so dizzy!" exclaimed another.

"I guess that's the price we pay for getting old," winced an old man as he slowly shook his head. The others nodded in agreement.

"Well, count your blessings," said one woman cheerfully, "and thank God we can all still drive."

Article Policy
© 2006 Innovative Thermal Solutions. All Rights Reserved. You are free to use material from the Innovative Solutions newsletter in whole or in part, as long as you include complete attribution, including live web site link. Please also notify me where the material will appear.

The attribution should read: "By Bob Utter of Innovative Thermal Solutions. Please visit Bob's web site at for additional articles and resources on engineering services and new product development." (Make sure the link is live if placed in an eZine or in a web site.)

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