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  1. #1
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    Chiller and Heat Recover Chiller Sequencing

    Hi,

    Did anyone encounter a proper technical guide where the staging of multiple chillers (parallel) in series with heat recovery chillers is discussed from a controls perspective?

  2. #2
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    Thread Starter
    Preferably a Variable Primary flow sequence.

  3. #3
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    I don't know if such guide exist.
    You need help figuring something?

  4. #4
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    Someone designed that system so i would think they have the operational specifications

  5. #5
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    Quote Originally Posted by HYP1278 View Post
    Someone designed that system so i would think they have the operational specifications
    Yes. I do have a general description of how the system is supposed to operate on a macro level. For example, the heat recovery chiller shall be no off if there is not enough heating and cooling demand simultaneously (duh! ). I have the manufacturer submittals as well taht give me an idea of on what basis the system was selected. Min max flows etc.
    However, I am interested in controls sequencing and guidelines like reset the chws temperature SP under low load condition to have better chiller efficiency.
    I did find some good literature from trane that covers the design considerations.

    Sent from my ONEPLUS A5010 using Tapatalk

  6. #6
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    If the chiller were built for heat recovery they should have a heating and cooling setpoint in their controller.
    All the chiller I know just need a permission to run and will automatically do the rest

    What type of chiller you have?
    Multistack or equivalent?
    What is your setup in more details

  7. #7
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    The setup consists of a heat recovery chiller (HRC) in series with two chillers (in parallel with each other). This type piping of HRC is refereed to as sidestream. The HRC has its on pumps and VSD, and would operate maintain a constant flow to the HRC. The CH1 & CH2 have multiple pumps (lead/lag/standby) and would towards variable primary flow. The pumps modulate to maintain a constant DP.

    The HRC by itself is not deigned to produce the CHWS temp design SP of the Pipe Mains, so I am assuming it is best to start with CH1 first, do the demand calculation and see if the HRC can be allowed come on.

  8. #8
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    (edited) What type of load you want to maintain on cooling side (process or comfort) and where do you send the heat recovered?
    If there's a demand for heat I'd start hrc until there is no more room to reject the heat.
    Chill water chiller only to help compensate on a big demand of cooling

  9. #9
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    The Heat Recovery Chiller is expected to operate all year round. During Summer there would be hot water demand for VAV reheat, DHW and Summing Pool. During Winter there will be cooling demand from Electrical Room.

    There is a Side stream filter on the CT side that runs all year round too regardless of the CT operation. It means that at least one of the CW Cir pump would be operating all the time and alteast one CH condenser iso valves would be open, to provide flow path, even though the chiller won't be on.

    It is not recommended to pump CW through the chiller when it is off, so the only option I see with this design is to run one of the CH all the time and use the HRC only if there is enough cooling and heating demand.

  10. #10
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    Quote Originally Posted by OnePlus View Post
    The Heat Recovery Chiller is expected to operate all year round. During Summer there would be hot water demand for VAV reheat, DHW and Summing Pool. During Winter there will be cooling demand from Electrical Room.

    There is a Side stream filter on the CT side that runs all year round too regardless of the CT operation. It means that at least one of the CW Cir pump would be operating all the time and alteast one CH condenser iso valves would be open, to provide flow path, even though the chiller won't be on.

    It is not recommended to pump CW through the chiller when it is off, so the only option I see with this design is to run one of the CH all the time and use the HRC only if there is enough cooling and heating demand.
    Why not run water to a stopped chiller?

    If your using another source for heating for your reheat your paying twice

  11. #11
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    Quote Originally Posted by patpinet View Post
    Why not run water to a stopped chiller?

    If your using another source for heating for your reheat your paying twice
    Well... The theory is that stopping the pumps would stop refrigerant charge migration to the condenser, which can create an inverted start situation that can lead to a fault condition.
    Given that running when the chillier is not running, the cooling towers would be off and we'd only be recirculating CW through the bypass valve, this recommendation can be ignored here. What do you think?

  12. #12
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    Refrigerant will migrate to the coldest place, depending on the type of chiller might or might not create a issue.
    Probably not.
    Like you said running hrc will save on cooling tower and reheat energy usage.

    I found some heat recovery doc on the web from carrier.

    You can try to Google for it.

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