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  1. #1

    VFD on condensor pumps

    I know this is a broad question but we have installed VFD's on our condensor pump's as a going green save engery program and I am concerned that with less water flow it will damage the chiller's ? Is this really going to save money I thought full flow would be a better to get the heat load out of the building an the VFD on the chiller would back down on load demand and save money better than backing down a pump motor. Opinion's welcome Thanks

  2. #2
    Join Date
    Aug 2009
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    Some older chillers don't take variable flow through the condenser side well. If the chiller is newer, variable condenser flow is a good method for saving energy. Some manufacturer's don't want the condenser inlet temp to drop below 80.

    I put a VFD on the chilled water and condenser water side for all new chiller designs. I also put VFD's on the cooling tower fans. I put a three way valve on the condenser system to bypass the tower(s) in order to maintain at least 80 degrees on the condenser inlet.

    Did anyone check with the chiller manufacturer about variable condenser flow before you installed the VFD's?

  3. #3
    Join Date
    May 2012
    Location
    California
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    223
    Really need more info on you system, but if you have drives now they most likley opened your triple duty valves to 100% and at lower loads depending on control system they lower the flow to a point at lower load conditions. Is your building automation controling the drives now?

  4. #4
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    Ive got a building that runs VFDs on the CW pumps. Flow is set at start up according to manufacturer specs and pump speed is constant.

    VFD's give you a soft start option as opposed to across the line which is more effecient. Other than that I cant think of any other reason they would use VFDs on CW pumps.

  5. #5
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    I bet its for soft start and if thats the case its not enough justification for using a VFD on a CW pump.

  6. #6
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    Quote Originally Posted by brewidus View Post
    Some older chillers don't take variable flow through the condenser side well. If the chiller is newer, variable condenser flow is a good method for saving energy. Some manufacturer's don't want the condenser inlet temp to drop below 80.

    I put a VFD on the chilled water and condenser water side for all new chiller designs. I also put VFD's on the cooling tower fans. I put a three way valve on the condenser system to bypass the tower(s) in order to maintain at least 80 degrees on the condenser inlet.

    Did anyone check with the chiller manufacturer about variable condenser flow before you installed the VFD's?

    Flow would be constant with tower fan and bypass controlling temperature. You have seen a chiller that utilizes variable flow through the condenser inclusing tower fan and bypass ?

  7. #7
    Join Date
    May 2012
    Location
    California
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    We have many chillers with varible flow throught the condenser. Ussaly done on a chiller with a VFD. Low loads lower condeser water temp lower flow and the VFD on the chiller will run at much lower speed.

  8. #8
    Join Date
    Jan 2011
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    1,147
    Quote Originally Posted by Brewidus
    I put a three way valve on the condenser system to bypass the tower(s) in order to maintain at least 80 degrees on the condenser inlet.
    I understand that some manufacturers desire warmer condenser water, but 80 F is too warm even for brands like Trane if you want to take advantage of variable speed on the chiller. Years ago I spoke with a Trane engineer and he told me the 80-85*F number wasn't necessary. As I recall he said the condenser water needed to be 16*F warmer than entering chilled water.

    VSDs on condenser water pumps make sense in a "Hartmann Loop" (variable primary chilled water flow). Surprisingly enough not only do they slow the condenser water flow under light loads, but they raise the CW temperature as well. I thought that counterintuitive. My mantra had always been "the colder the better". Under light load conditions I have seen a York chiller run at 37-39 Hz with 73 F entering condenser water.

  9. #9
    Join Date
    Feb 2012
    Location
    utah
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    I run most of my machines at 70-80 condenser temp with no problems. generally (if capable) I let the chiller run the tower and pumps to whatever temp the machine wants, which hovers around 75. as far as drives on the pumps it allows one to give the machine the exact gpm without balancing valves with the bennifit of soft start. I always try to include them.

  10. #10
    Join Date
    Jan 2011
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    1,147
    Quote Originally Posted by nigue
    I run most of my machines at 70-80 condenser temp with no problems.
    Perhaps you don't have York chillers with VSD. You won't get near the performance those chillers are capable of if you keep the condenser water between 70-80*F.

  11. #11
    Join Date
    Apr 2012
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    17
    On a side note has anyone ever noticed while physically amping a load with a vfd on it that the line sides(inlet to the drive)amperage is lower than the loads(outlet of the drive)side.Could it be because of the capacitor storage banks?I have ABB drives.

  12. #12
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    The current out put is chopped and taken from peak amperage values.

    Compare line to amps displayed on VFD. Some amprobes can not accurately measure motor amp draw.

  13. #13
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    Its by definition not a consistent cycling of polarity and waveform. I m surprised your amprobe didnt just go blank and then flash a little icon of a hand giving you the finger.

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