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  1. #1
    What is the range of ideal condenser water temperature for a Chiller?

  2. #2
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    Depending on the Chiller. As low as 60 degrees to 82 degreees
    Old snipes don't die they just loose their steam

  3. #3
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    Ahhhh, here we go again.

    Condenser water temperature is a very debated topic in our industry.

    First of all, Snipe is right, I would just like to elaborate a little.

    Every "design" spec I've ever seen in my part of the country has been 85*.

    Now, stay with me on this.
    Every mfr manual I've ever read states that in order to save energy, operate machine with lower than design condenser water.

    The purpose of the design spec is to establish a most likely high end & nothing more.

    If you insist on operating your equip @ 85* all year long then you are leaving money on the table.
    You won't hurt the equip. & the power company will love you, but, you won't save on energy consumption.

    < What type of chiller do you have? >

    Operating entering condenser water in most cases can be as low as 20* above the leaving chilled water.

    A screw machine will require warm condenser water on start up, but once its on line, you can run it lower.

    The rules change a little on DX machines.

    You can go lower on machines with speed drives on the compressor.

    Lowering the condenser water is serious business, if you are relentless about it & you make every effort to keep it as low as you can at all times without exception, the payback will be huge.
    All my leon freaked out!

  4. #4
    Thank you Chiller Mekanic. That was very helpful.

    If I understand right, the condenser water (coming from a Cooling Tower) is used to efficiently remove the heat from the refrigerant, after it is compressed..right?

    The question in my head is how will this affect energy savings when the temperature is dropped from say, 75* to 70*.

    Does this increase the capacity of the refrigerant in the chiller to absorb heat - reducing the chiller runtime?

    But we are running the Cooling Tower Fans to reduce the Condenser Water Temperature. This consumes a lot of energy too..doesnt it? Same applies to DX Compressor(s).

  5. #5
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    chiller is basically right...but these assumptions are not always correct.

    lower entering cond water will lower head pressure and lower the kw/ton cost of running that chiller but...

    many chillers (esp centrifugals, but not only) use a fixed orifice design. when the pressure differential between the cond pressure and the evap pressure is reduced, so is cooling capacity, generally speaking.

    chillers are usually designed for specifications. the specs may not be right or best, but many chillers are internally designed based on these conditions. just changing things because it sounds good does not really mean that you will gain. it does not mean that it doesn't either...you just have to be careful.

    running down to 20F? no way. some centrifugals use the pressure differential to bring back oil and perform other operations (like motor cooling). if you have a lower cond pressure than evap pressure, how do you get any refrigerant flow?

    lower cond pressures do help. i am all for them, but only to a point. too far and you could start to create other problems. get with the manufacturers service techs to get the real skinny on your machine in your application.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  6. #6
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    Originally posted by scottbalan

    But we are running the Cooling Tower Fans to reduce the Condenser Water Temperature. This consumes a lot of energy too..doesnt it? Same applies to DX Compressor(s). [/B]
    It depends on the chiller, towers, and fans.

    When I was young my dad worked in a NH3 plant 149,000 tons of refrigeration. They had charted the KW vs head pressure. When the head reached a point they added a condencer fan.
    Old snipes don't die they just loose their steam

  7. #7
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    york with drive can go down to 15 degrees above chilled water temp and still return oil

  8. #8
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    Talking I didn't make any of this up, I promise.

    I got it all out of IOMs & brochures from the mfr of every chiller I've worked on.

    So if I'm only basically right, I'm not alone, that means the MFRs of the equip. are only basically right as well.

    Lowering the condenser water temp WILL increase capacity, not decrease.

    I know you factory guys are trained to "two step" but you shouldn't be so obvious.
    Make no mistake, lowering the condenser water temp will lower the KW consumption.
    If you have a R22 chiller with 85* ECW & 95* LCW. maybe your head pressure would be around 190PSI, if your suction is 68psi, your lift or delta P is 122PSI.
    If your ECW is 65* & LCW is 75*, maybe your head pressure would be around 140PSI, with a suction around 68PSI, your lift is now 72PSI.
    Thats a reduction by almost half!
    If you have a oil return problem in this range, you have a oil return problem.
    Raising cond wtr to "mask" a oil return problem is a very exspensive solution.

    I never said to run it down to 20*.

    I said down to 20* above the leaving chilled water.

    I also never said anything to indicate that the head pressure would or should be below the suction pressure.

    I also stated that the rules change some on DX chillers.
    To be more specific, most of the performance charts I've seen on DX chillers only went as low as 75* ECW.
    If in doubt, you can always lower the ECW slowly in small increments over several days of operation & watch the oil return, when you see a reduction, thats probably as low as you want to go.
    This is not to be confused with what I said about oil return on centrifugals & screws, this only applies to DX with recip or scroll compressors.
    If you have a screw in a DX machine, you can run it on the same principal as the flooded machines.(because of the seperator)

    As far as the cooling tower motors costing more to operate more, clearly they will.
    Once again, snipe is right.
    But, to elaborate again, (if I may) compare the FLA of the tower motor to the chiller motor & you will see that its usually better to wind out the towers to lower the amperage on the chiller motor.

    Since the plug was made to contact a factory tech, I'll make a plug to call a reputable "independent" contractor.
    Look for one that is associated with the "chiller group".

    I have several friends that have gone to work for the MFRs over the years, most of them have done a good job of keeping it real, but its always a bummer when one of them starts in with the MFRs propaganda.

    None of this just "sounds good".

    But it will save energy.

    I promise!









    [Edited by chiller mekanik on 11-30-2006 at 11:45 PM]
    All my leon freaked out!

  9. #9
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    Reset ECWT w/wet bulb

    Originally posted by scottbalan
    Thank you Chiller Mekanic. That was very helpful.

    If I understand right, the condenser water (coming from a Cooling Tower) is used to efficiently remove the heat from the refrigerant, after it is compressed..right?

    The question in my head is how will this affect energy savings when the temperature is dropped from say, 75* to 70*.

    Does this increase the capacity of the refrigerant in the chiller to absorb heat - reducing the chiller runtime?

    But we are running the Cooling Tower Fans to reduce the Condenser Water Temperature. This consumes a lot of energy too..doesnt it? Same applies to DX Compressor(s).
    One of the better methods to strike a balance between entering condenser water temperature (ECWT) and tower fan usage is to set up the towers with a reset schedule based upon outdoor air wet bulb temperature and tower design approach temperature. If the towers have VFD's on the fan motors, this is a very good method.

    Tower design approach (if known) is the difference between wet bulb temperature and temperature of water leaving the tower at design conditions stated by the tower's manufacturer. The closer the tower sump water temp (essentially ECWT) is to wet bulb, the more efficient the tower is...to a point. If you try to get close to wet bulb on a day with high outdoor wet bulb temps, the fans will be running like crazy, using lots of energy.

    I'll use my towers as an example, which have a design approach of 7 degrees at 95 degrees dry bulb air entering tower, 78 degrees wet bulb air entering , 85 degrees leaving water temperature. The towers use VFD's on the blowers and a bypass for low ambient temperature operation. In summer, as outdoor air wetbulb temperatures rise, the ECWT setpoint is automatically reset 7 degrees above this temperature to maintain tower design approach as closely as possible. This means the fans run only at the speed necessary to maintain the ECWT setpoint. On hot days they may run full speed. As wet bulb temperatures drop, the ECWT setpoint is lowered simultaneously, resulting in cooler water delivered to the condenser barrel at the chiller.

    The overall object of this method is to strike a balance between condenser water temperature relief (concurrently a relief of condenser barrel head pressure/compressor lift) and cooling tower fan relief. Without it, the only other way is to run the tower fans harder to maintain a lower ECWT. You will see improved efficiency at the chiller, but at the expense of increased power consumption at the tower fan motors.

    You don't always get optimum ECWT with this method because load and wet bulb temps always vary. But if the reset is automatic, such as a DDC or BMS doing the logic, then the reset is occuring constantly. Any improvement in wet bulb temperatures will be seen at the tower and system instantly and compensated for, rather than waiting for an operator to catch it and then make an ECWT setpoint adjustment manually.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #10
    Thank you shop hound.

  11. #11
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    Re: I didn't make any of this up, I promise.

    Originally posted by chiller mekanik
    Make no mistake, lowering the condenser water temp will lower the KW consumption.

    If you have a oil return problem in this range, you have a oil return problem.
    Raising cond wtr to "mask" a oil return problem is a very exspensive solution.

    I never said to run it down to 20*.

    I said down to 20* above the leaving chilled water.

    I also never said anything to indicate that the head pressure would or should be below the suction pressure.

    i also said the kW will drop. sorry about the 20F thing...i missed the last part. my wording about the head pressure being below the suction pressure was also based on 20F thing. sorry about that again.

    i do not claim to run the head pressure up to get the oil back. i do claim that dropping the head pressure can cause more oil to be pushed out into the system (esp. in centrifugals). this can cause refrigerant side tube fouling and that can cause an increase in kW/ton (vs. no oil fouling). every chiller is different. i have some chillers that can run down to 5 psi difference in cond/evap pressures without problems. others lose oil below 80F entering cond water. every chiller is different. whatever you choose to do, do it slowly.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  12. #12
    Join Date
    Dec 2006
    Posts
    23
    Originally posted by snipe70e
    Depending on the Chiller. As low as 60 degrees to 82 degreees

    Yes you are right......in my country we design 75 to 85 entering water temp, as long as the Approach is within 3-7F, everything will be OK...

    Renan

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