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understanding refrigeration

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  • understanding refrigeration

    I have seen glycol chillers described by horsepower and by tons. What is being referred to by a "4 ton glycol chiller"? Is that the weight of the chiller itself? Also, if I am trying to determine what size glycol chiller I will need, should I be more concearned about horsepower or tons? In a nutshell, I need to chill six 7bbl tanks. Also, should a 200 sq. ft. walk in be a separate chilling system?

  • #2
    A ton of refrigeration is 12,000 btu/hr, if I remember right. A 4 ton would probably be a 5 hp chiller or so.

    I would go with a different refrigeration system for your cooler, makes it less complicated and a cold room manufacturer could give you an exact quote.
    Linus Hall
    Yazoo Brewing
    Nashville, TN


    • #3
      Hi Charles,

      Basically, the "Tons" specification of a refrigeration system (generally the compressor/condensor side) is derived from the old days and is a comparison to the cooling effect of ice. I believe this was how much cooling capacity you got from 2,000 lbs of ice melting over a 24 hour period. It equates to 12,000 BTU/hr of cooling capacity, or 288,000 BTUs/day.

      A BTU (British Thermal Unit) is the energy required to cool or heat 1 Lb of water by 1 Degree F. There is an equation between BTUs and horsepower, and that is 1hp = 2,546 BTU/hr. As I stated before, there is also a relationship between refrigeration tons and BTUs, and that is BTU/hr capacity = refrigeration tons x 12,000. To equate refrigeration tons and horsepower, it is Hp = refrigeration tons x 4.716.

      These, of course, are all calculations used for sizing and equating, and your milage may vary based on road conditions.

      Example: A 3 hp compressor assembly will produce about .636 tons of refrigeration, or be able to remove about 7,638 BTUs/hr of heat from your system.

      Why do we use "tons of refrigeration"? I seems a little antiquated to me............kinda like measuring people's weight in "stones" or similar. The real deal in all this is BTUs/hr and horspower. Based on some rudimentary calculations, you can approximate your heat load based on how much heat is generated during fermenation, how fast you want to "crash" a tank (drop its temperature), and how low you want to go temperature wise. There's a few other considerations in there, but using those, to calculate BTUs/hr, and deriving your horsepower, which the sizes the motor(s), which will then give you your electrical requirement.


      • #4
        In the big world of HVAC/R (heating ventilating air conditioning refrigeration) you can kind of divide refrigeration systems as either "air conditioning" or "refigeration". Air conditioning of course refers to a system to cool air, and refrigeration systems of course cool your walk ins, freezers, food processing etc.

        As stated previously, 12,000BTU/HR equals one TON of refrigeration. And yes it is derived from the BTU capacity of melting (or freezing) 2000 lbs of ice in a 24 hour period.

        BTU/HR is a kind of a generic rate of heat transfer. Any device designed to move heat will have a BTU/HR (or it metic equivalent) rating.

        In general, the Tonnage of a machine refers to the capacity a refrigeration system to move XYZ btus/hr at a certain set of conditions.

        An air cooled radiator, will have a rating in BTU/HR, but it really doesn't make sense (though it may be mathematically correct) to state the capacity in tons.


        Back in the day, when refrigeration compressor were "open drive" you had two pieces, a motor, and a compressor. It may even be belt driven, and looks like a garden variety air compressor. These used standard electic motors that were rated in horsepower.

        Now, most refrigration compressors are hermetic or semihermetic (the motor is internal to the compressor) and horsepower doesn't apply as well.

        So like Tons, Horsepower is a rating of the INPUT power of the machine. The BTU/HR output will vary.

        The previous post provide a conversion from BTU/HR to Horsepower, but it wasn't really accurate realtive to this case. BTU/HR and HP are both units of power, so you can convert one to another. But, that Horsepower to drive a refrieration compressor, and the BTU/HR you get out that compressor are not convertible. It is derived from the thermodynamic properties of the refrigerant.

        HP-TONS-BTU/HR relationship.

        A given refrigeration (or A/C) system has an output capacity that veries with the operating conditions. For an air cooled chiller, those conditions are the temperature of the water, and the temperature of the ambient air. If we keep the ambient air the same, the capacity goes DOWN as the water temperature goes DOWN.

        Now in general, a 5 TON refrigeration systems, used for air conditioning for comfort cooling, requires a 5 HP compressor. How convenient. Becuase air conditioning systems are designed around a very narrow criteria, this 1 ton = 1 HP varies very little. So if one A/C guy is talking to another, they can use tons (yeah I just installed a 5 ton system), and they know what each other is talking about.

        In the refrigeration world, there are so many different applications, and the conditions very so much, that the refrigeration system tonnage is less cut and dry.

        For example, you have a beer cooler that needs to remove 12,000 BTU/HR of heat.

        Then you also have a freezer that needs to remove 12,000 BTU/HR of heat.

        To say that they both need a 1 ton system, would be inaccurate. The freezer actually needs a more power compressor to move the same number of BTU's. And will therefore cost more.

        So horsepower, gives a more accurate description of the physical size, cost, and power of the compressor.

        If two reefer guys are talking, one working on a ultra low temp sperm cooler, and another on a walk-in, one could say to the other " I installed a XYZ Horsepower compressor" and they could understand each other.

        To make things even more confusing, chillers are kind of a redhead stepchild in the industry. Most rate their chillers in tons, some in HP. Pro Refrigeration calls everything by HP, but they have come from a refrigeration backgound. A true air conditioning chiller, like something from Trane, won't even have HP listed anywhere on the data sheet.

        Most chiller ratings are based on 44 F chilled water. That is the American Refrigeration Insitute rating standard. So a 5 ton chiller will do 60,000 BTU/HR @ 44F water in a 95 F ambient. This same chiller will do about 60% of that , around 36,000 BTU/HR with 30 F glycol in the same ambient.

        If you see a chiller, with a hermetic compressor, running R22, you can figure that the brewery capacity will be about 60% of the nominal rating. Check the manufacturers specs to be sure.

        When I was designing and selling chillers for my former employer (Schreiber engineering) I came up with a a Low temp line designed for brewery and pharmaceutical applications. I would took our 500AC (5 ton air cooled chiller) and created a 500AC-LT. The regular chiller would do 5 tons @ 44F, but the LT chiller would do 5 tons @ 28 F. It was a 9 HP chiller. I thought it was a great idea but it just confused everybody. People would say my 5 ton was too expensive.

        Now I build chillers for refrigeration and air conditioning. My R-404a chiller used for brweries are rated in HP, and the R-22 chillers go by tons.

        So, should you be more interested in HP or tons. Neither really, you need to know the BTU/HR OUTPUT at the temp glycol you want to run.

        I would use a separate system for your cooler. It will give you more reliablity, and is usually more efficient.

        It is hard to answer the "how big a chiller do I need" question without more information. It depends on your management, process, plans for expansion, as it does the # of bbls. I usually have a brewery guy that I sell my chillers through size them anyway. What a copout, eh?

        Sorry for the ramble, you question was just hard to answer in short order.

        Have fun.

        Johnson Thermal Systems


        • #5
          Hey, Jeff............great write-up, Buddy.


          • #6
            My two cents: Once you figure out what you need, spend a few buck more to oversize the unit. Fermentation will be your likely equipment bottleneck as you grow, and it's nice to have the extra cooling capacity.



            • #7
              Absorption Chiller vs. Compressor Chiller?

              Since we are on the topic of chillers, does anyone have experience with absorption type chillers? I came across one... and had never heard of one before. What are the differences? Do they have the same end result?


              • #8
                Abosorption refrigeration systems replace the compressor with an aborber and a generator.

                You have a mixture of two chemicals (usually lithium bromide and water) that boil off at different rates. You boil off the refrigerant, condense it with air or a nother water sources, run it into an evaporator, and then it is aborbed back into the abosrbent in the absorber.

                This is what an RV fridge does.

                Most absorbption systems of notable size can't produce water less than 35 or 40 F. The theoretical absorption cycle if way less efficient than the vapor compression (compressor systems). They really only make sense if you have some waste heat or fuel source. Or if you don't have 3 phase power.

                The other problem is that there are no domestic manufacturerers of absorption chillers. I only know of a couple people who make them in a microbrewery size. Arkla-Servel. These are no longer made in the states, they are made in Italy. I have not heard super good things about them in terms of reliability. Arkla builds a 5 ton, and when you buy a 10, 15 or 20 ton you get 2, 3, or 4 of the 5 tons factory assembled on a skid.

                They run off of natural gas or propane.

                They are also more expensive per ton(hp) than a vapor compression system.

                There are also things called ADsorption chillers. Those are really neat. And REALLY expensive. They are also HUGE in size. Made buy an outfit in Japan.

                Did you buy that $4700 7 ton?

                Johnson Thermal Systems


                • #9
                  re: absorption chillers

                  My local Trane outfit has a 5 ton absorption chiller for $1500. It's brand new...they had it sitting in the warehouse and didn't know what it was. Do you think it's a good option?


                  No I didn't buy the 7 ton chiller... The shipment date pushed out to mid-January and he wasn't able to provide any specifications on the unit. So, I need one sooner and I'm not really comfortable about buying a chiller without specs..



                  • #10
                    Without seeing any specs, it sounds like a smokin' deal.

                    You probably already have a pretty good size gas service, so it may save you a bit of operating cost, hard to say.

                    Make sure it is AIR COOLED -(or you'll need a cooling tower)
                    Make sure it can go to the temp you want, on a hot day. Their capacity falls of real fast in high ambients.

                    If it doesn't go cold enough, you might be able to hook up with a regular chiller in series or something.

                    Give me a call 208-697-0713 if you have any questions. I won't try to sell anything. I have an engineer in the area (San Jose) who may be able to meet with you. Let me know.

                    Johnson Thermal Systems


                    • #11
                      re: absorption chiller

                      well it looks like this model of absorption chiller only goes down to 37 F.

                      I may use it in a series with another chiller.

                      Absorption technology seems to be very cool. There are absorption units that will go down to the correct temp., but they are very $$$$.

                      thanks for input.

                      anyway...still looking for a 7 ton chiller...