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  1. #1
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    Freq drives on new chiller but not old? Problems?

    Our building is replacing an old Mcquay 800ton chiller with a trane 600 to accompany our two other trane cvhf570's and our trane 175ton. The big dog at corporate wants to put vfd drives on the new chiller. Our four trane cvhf pumps don't have vfd's. Will putting vfd's just on the new chiller cause surges in our other chillers that run balls to the wall?

  2. #2
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    It shouldn't.

    What kind of controls are staging the chillers?

    The other chillers don't really run balls out unless you have load, that's what the IGV's do, control capacity.

  3. #3
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    Its raining VFDs !!

    In general VFDs are a more efficient alternative to across the line starts but whether or not they actually modulate the frequency output depends on the application.

    If you maintain a constant flow they're still ecficient because of their soft start capabillities.

  4. #4
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    Quote Originally Posted by commtech77 View Post
    Its raining VFDs !!

    In general VFDs are a more efficient alternative to across the line starts but whether or not they actually modulate the frequency output depends on the application.

    If you maintain a constant flow they're still ecficient because of their soft start capabillities.
    I think he means on the compressor motor. In that case, the drive will ramp up and down with load, and parameters will be factory set, and perhaps field verified at time of start up. I believe Trane likes to modulate to maintain the chiller just below the surge boundary.

    As for water flow, there also real handy for setting max flow rate, much better then a tripple duty valve.

  5. #5
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    Quote Originally Posted by heatingman View Post
    I think he means on the compressor motor. In that case, the drive will ramp up and down with load, and parameters will be factory set, and perhaps field verified at time of start up. I believe Trane likes to modulate to maintain the chiller just below the surge boundary.

    As for water flow, there also real handy for setting max flow rate, much better then a tripple duty valve.
    He mentioned pumps in the first post.
    Also would it be up to the big dog at corporate to install VFDs on a chiller compressor motor?

  6. #6
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    your biggest problem will be in properly controlling the condenser water temperature. with vfd driven chillers, you will gain efficiency by lowering the tower water which will slow the compressor down. with trane's newest model, the oil pump motor is doubleshafted and has a refrigerant pump on the other end. this allows for motor cooling at lower condenser water temperatures and/or higher evaporator water temperatures.

    the problem comes in with your older chillers...do they have this type of oil/refriegerant pump? can they handle the lower condenser water temperatures? your BAS probably controls all of your towers to 1 set temperature...now there will have to be at least 2 temperatures...unless you have a common tower/sump system in which case you could be royally screwed. it is possible to have it work, however, i haven't seen a BAS person who can seem to understand how this all works and get it done.
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  7. #7
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    Mar 2003
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    VFD's on pumps is becoming a commonplace thing. It helps to prolong electrical and pump components by soft starting them, it also makes balancing easier, by setting your frequency reference, in lieu of choking back a triple duty on constant volume. By running at lower frequency, in lieu of sixty hertz, there are electrical efficiency gains as well.

    With repsect to the chiller itself, pretty much the same dela. Instead of running at sixty hertz and maintaining capacity control with IGV's, you ramp the speed of the centrif, saving energy and more closely matching the load. The problem comes into play when you try to run the old plant at new conditions.

    For example, trying to run cold condenser water on older chiller, in many cases, can cause issues. Also trying to do variable flow through am achine not designed for it can wreak havok on that machine. so yes, depending on your configuaration, it may be an issue, but there isnt nearly enough information provided to provide a strong argument.

  8. #8
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    Ya, I will try and provide more info once I hear wind of it. As for right now, we are all gritting our teeth at the thought of VFD's on just the pumps of the new chiller and not the old ones. Combining 2007 technology with 2012 technology is going to be tricky.

    I also don't feel our controls company is that up to date enough to make the programming work for the setup they are alotting.

    I will try and provide more info when I receive

  9. #9
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    Just so everyone's on the same page, are you talking about putting a vfd on the pump, or ordering a new chiller with a vfd on the compressor motor???

  10. #10
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    As I understand it, they just want VFD's on the Condenser Water and Chilled Water Pumps.

  11. #11
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    Quote Originally Posted by ZeroTolerance View Post
    As I understand it, they just want VFD's on the Condenser Water and Chilled Water Pumps.
    If you are going to run those pumps at 60hz then installing a VFD is going to be a waste of money.
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  12. #12
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    Quote Originally Posted by Dallas Duster View Post
    If you are going to run those pumps at 60hz then installing a VFD is going to be a waste of money.
    And a component that sometimea locks its self out in nuissance trips.

  13. #13
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    If we were going to run the pumps at 60Hz why would they want VFD's on them? The whole point of VFD's is efficieny reason being they want to put the pumps on them. Sorry, your answer isn't making sense to me. Please elaborate.

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