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Thread: Package Chiller Configuration: Hot/Cold Reservoir vs Single Well

  1. #1
    Join Date
    Jun 2015
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    Dallas
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    Package Chiller Configuration: Hot/Cold Reservoir vs Single Well

    We are a brewery in planning and I am currently researching our options for packaged chillers for our cellar. I have broadly seen two different configurations and I was just wondering what are the advantages/disadvantages of having a separate hot and cold reservoir for the chiller circuit as opposed to having one single larger reservoir?

  2. #2
    Join Date
    Oct 2005
    Location
    Caldwell, ID
    Posts
    5
    My favorite answer; "It depends."

    The difference between single reservoir vs. a dual tank hot/cold system has more to do with the pumping system. The tank design is a byproduct of the pump layout and not the other way around.

    There are two common ways to run a pump system for a brewery:

    (keep in mind I am sticking to generalities and there are minor variations from mfg to mfg)

    1. Single Pump Loop-

    These systems have a single reservoir (or two piped in parallel but it acts like one). There is one pump that draws from the reservoir, pumps water to the brewery, returns to the chiller and enters the chiller evaporator, leaves the evaporator (now colder than it entered the chiller) and then dumps into the tank, then goes to the pump and in a big loop.

    Often times a redundant pump is supplied in parallel as a backup. To keep the pressure from rising too high as tanks shut down, and prevent loss of flow to the chiller, a pressure relief bypass valve is often installed at the chiller. This will open when the pump discharge pressure exceeds the setting of the bypass valve.


    In these systems, there is just one tank.

    2. Dual pump loop-

    There are one or two tanks in this scenario. For sake of discussion at this point, assume there are always two tanks. Also, a single tank with a baffle that splits the tank into hot and cold sections is functionally equivalent to a two tank system.

    One tank is the "hot" tank. The return from the brewery enters this tank. The other is the "cold" tank. The cooled water leaving the evaporator goes into the cold tank.


    There are at least two pumps in the chiller. One pump is for the evaporator. Goes by many names; evaporator pump, chiller pump, recirculating pump, primary pump.

    The second pump delivers the glycol to the brewery. This pump also goes by many names; system pump, process pump, secondary pump.

    On a two tank system, the primary pump draws the water from the hot tank, delivers it to the evaporator where it is cooled. From there is drains into the cold tank. The secondary pump draws water from the cold tank and delivers it to the brewery. This ensures that the coldest water is delivered to the brewery, and the hottest water enters the evaporator. This keeps the chiller efficiency up.

    You can also do a dual pump system with one tank. The primary pump draws water from the tank, pumps it through the evaporator and it returns to the tank. The secondary draws water from the tank as well, pumps it to the brewery, then it returns to the same tank. If the single tank doesn't have a baffle, they have to be piped very carefully. Basically if the primary pump inlet and outlet are close to each other on the tank, the primary pump "short circuits" which leads to really low temperatures across the evaporator, robbing capacity and efficiency. On the secondary side if this happens, you can make cold glycol all day long, but the secondary pump can't pick it up. So the pumps have to be piped in such a way that the primary pump suction is near the return from the brewery, and the secondary pump suction is near where the evaporator dumps into the tank.


    So to summarize:
    Single pump loop- Only uses one tank. Can't use two tanks.
    Dual pump loops- Can use both.

    So what is better? No single answer.

    Single Loop/Single Tank-
    Pros-
    • Cheaper. One pump, simpler piping
    • Easier/cheaper to do redundancy. Add one pump and you have 100% backup.
    • Always ensures the warmest water enters the evaporator.
    • Expansion is pretty simple as you just tap into one tank.



    Cons-
    • The brewery pressure drop and the chiller pressure drop are in series so they are additive. Not only do you have a higher pump discharge pressure, but the return line pressure will always "see" the chiller pressure drop. This is in the 5-10 psi range depending on flow rates. This may be a problem if your tanks have a 10-15 pressure rating. The tanks will never see less than this pressure. There lots of other piping design problems that low psi rated tanks cause, this is just one. But it is a big one.
    • It is more difficult to do a variable speed pumping system. It is possible, but tricky to setup.
    • Flow issues in the brewery cause flow issues in the chiller, since they are all connected. If the pump too small, and can't flow to the brewery, it won't flow through the chiller right either.


    Dual Loop/Dual Tank (hot/cold configuration)

    Pros
    • The flow rates through the brewery can fluctuate like crazy but if doesn't effect the flow through the chiller evaporators.
    • Pressure drop across chiller does not "touch" the brewery. Important for low pressure rated tanks.
    • Simple to do a variable flow system
    • Accommodates (almost required actually) system with multiple evaporators.


    Cons
    • More complex as you are dealing with the flow of two pumps.
    • Twice as many mechanical seals to leak!
    • Total added pump HP is often (not always) higher. If the secondary pump is constant flow, the total consumed power is often higher.
    • More expensive. 2 x 5HP pumps costs far more than 1 10HP pump.
    • Redundancy is way more expensive as four pumps would be needed. There may not be space for four pumps.




    What we do:

    JTS builds both single pump single tank systems and dual pump dual tank systems. For breweries/wineries/distilleries, the break for us is roughly 30 tons and up is dual pump dual tank and single pump for 30 ton and lower (we have an overlap between two models at 30 tons).

    Our chillers are sold through tank and brewhouse manufacturers (mostly QTS in Wisconsin), so we are generally walking into a "known" situation as far as pump requirements, and their tanks are all rated for 75 psi. And most of those chillers are less than 30 tons. Those are all 1 pump 1 tank systems.

    Our larger chillers tend to be made of multiple modules with multiple evaporators so it is advantageous for us to do the dual pump loop thing, and then the dual tank follows suit.


    For others chiller suppliers as well, as you get smaller the dual loop and tank system starts to cost more than its value.

    I hope this helps.Thanks for reading this far.

    Jeff Johnson
    Johnson Thermal Systems, Inc.

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