Understanding IPLV/NPLV

By: John Fabian

The Integrated Part Load Value (IPLV) is a performance characteristic developed by the Air-Conditioning, Heating and Refrigeration Institute (AHRI).  It is most commonly used to describe the performance of a chiller capable of capacity modulation.  Unlike an EER (Energy Efficiency Ratio) or COP (coefficient of performance), which describes the efficiency at full load conditions, the IPLV is derived from the equipment efficiency while operating at various capacities.  Since a chiller does not always run at 100% capacity, the EER or COP is not an ideal representation of the typical equipment performance.  The IPLV is a very important value to consider since it can affect energy usage and operating costs throughout the lifetime of the equipment.  Energy codes such as ASHRAE Standard 90.1 specifies minimum values for the equipment.

The IPLV is calculated using the efficiency of the equipment while operating at capacities of 100%, 75%, 50%, and 25%.  For the purpose of chiller equipment, the operational conditions are shown in Table 3 of AHRI Standard 550/590-2003.  A water cooled chiller, for example, is required to run at a 44ºF evaporator LWT with a flow rate of 2.4 gpm/ton.  The condenser EWT will vary depending on the part load capacity utilizing a 3.0 gpm/ton flow rate.  If a chiller is designed to operate at different conditions than specified in Table 3, including lower water temperature or different flow rate, the efficiency is called a NPLV (non-standard part load value).  Both of these ratings can be calculated using the following equation:

IPLV (or NPLV) = 0.01A+0.42B+0.45C+0.12D

Where:

A = COP or EER @ 100% Load

B = COP or EER @ 75% Load

C = COP or EER @ 50% Load

D = COP or EER @ 25% Load

The derivation of this equation is extensive and includes various assumptions which create a lengthy discussion.  For more information refer to Appendix D, AHRI 550/590-2011.

 

Posted in CTTC, History, Technical Article
20 comments on “Understanding IPLV/NPLV
  1. quyume says:

    1. the evaporator side at 54 F (chilled water in) / 44 F (chilled water out).On the condenser side in both the modes 100 F (condenser water in)/90 F (condenser water out).

    2. the evaporator side at 54 F (chilled water in) / 44 F (chilled water out).On the condenser side in both the modes 95 F (condenser water in)/85 F (condenser water out).

    which option give more efficiency ? what is the basic of selecting condenser for better efficiency?
    pls let me know

  2. bharat bhushan says:

    i have to select one chilling machine from two having IPLV 0.33 and .49, which one is more efficient. please suggest.
    thanks

  3. yasin says:

    thanks

  4. Sagar says:

    Can any one let know the formula or thumb rule for pressure drop for evaporator and condenser for 300 TR water cooled screw chiller with 7/12 degree Celsius & 32/36 degree Celsius. Thanks

  5. The ASHRAE NPLV based on COP = 3.517/(NPLV based on Kw/ton) since

    NPLV based on Kw/Ton = 1/((.01/A’)+(0.42/B’)+(0.45/C’)+(o.12/D’))

    Where A’ = kw/ton at 100% capacity
    B’ = kw/ton at 75% capacity
    C’ = kw/ton at 50% capacity
    D’ = kw/ton at 25% capacity

  6. COP = 12000/(Kw/ton x 3412) = 3.517/(kw/ton)

    1 Ton = 12000 Btu/hr per ton

    1 Kw = 3412 Btu/hr

  7. E Tolentino says:

    Kw/Ton = 12000/COP x 3412) = 3.517/COP

  8. RAMON says:

    No logro entender los conceptos IPLV NPLV PARA QUE SIRVEN

  9. Wasfi says:

    Lower kW/ton that means higher efficiency,IPLV and NPLV both are the reciprocal of COP or efficiency.

    Regards

  10. Glen says:

    Amit, I would leave the chiller water temperture at a constant 44 degrees and use a mixing valve to control the higher temperature water for your chilled beams. You will also be better off if you can keep the condenser water below design. However you can’t go too long. I would speak to your rep because depending on your chiller low condenser water temp can cause issues.

  11. Ray Hickey says:

    IPLV or IEER (newest)
    The lower the kw/ton or the higher the EER equals the highest efficiency.

  12. Hernando says:

    In the IPVL, the coefficients are specific for each climatic zone conditions?.

    These are the percentage of time that the chiller operate at each load?.

    Analizing the indoor and outdoor temperature can I derive these coefficients?.

    Regards,

    Nando

  13. Amit Kumar says:

    Dear All,

    Very Good Morning,

    In one of my projects I am facing one difficulty. Here I have to use chiller in two modes i.e Mode (1)on the evaporator side at 60.8 F (chilled water out) / 68 F (chilled water in) and Mode (2)on the evaporator side at 54 F (chilled water in) / 44 F (chilled water out).On the condenser side in both the modes 96 F (condenser water in)/89 F (condenser water out). Now my question is that in both the modes can we use the same in /out temp in condenser end or we have to modulate the same to get the desired temp at diffrent modes of the screw chiller ?
    Mode(1)of chiller is being used to feed chilled water to the chilled beams and Mode(2)is used to feed chilled water to the AHUs for conventional system.
    And how does tower relief will help to get the desired result without effecting much on the efficiency end ?
    Outside wet bulb temp is 83 F.
    Mode(1)generates 160 TR and Mode(2)generates 240 TR.
    What is the minimum temp the condenser should go to get the desired result ?
    Can anyone please help regarding the above issues ? I will be available on the below mentioned mail and contact no.

    Regards,

    Amit Kumar
    mail.voltas@gmail.com
    +919910498934

  14. Calvin Li says:

    Dear Bill,

    Will the weighting of the COP of the formula be changed for different geographic area? Where could these weighting be found?

  15. Bill says:

    Robert, yes, water conditions will affect part load performance. Contact your local rep to get chiller efficiency curves for your particuliar application. At a minimum, they will need to know your design conditions: Capacity, entering and leaving CW Temp, entering and leaving condenser temp, and % glycol in either evap or condenser loop (if any). If you are wondering about an existing chiller, you’ll want to provide the model and serial number too.

    Another important factor is if you want the analysis done using tower relief, which lowers the tower temperature as the chiller unloads. This assumes the chiller unloading typically coincides with lower OA wet bulb temperatures. There are AHRI standard values that are typically used for tower relief.

    Here’s a link to a document that explains AHRI tower relief, along with additional info on IPLV / NPLV:

    http://trane.com/commercial/library/vol281/en_28-01.pdf

  16. Robert says:

    will the leaving chilled water temperature(LCHT) and the entering condensing water temperature (ECWT) affect the part load performance? if yes, what are the other neccesary data to get chiller curve?

    I am more interested in chiller curves. Hope you can help me.

  17. Bill says:

    The units for IPLV are KW/Ton, which is (energy input / energy output). Thus Lower IPLV = Higher Efficiency!

  18. FAYAZ says:

    yes, the higher the value of IPLV, the better the efficiency.

  19. Hans Viggaard says:

    The higher IPLV, the more energy efficient.

    Hans

  20. Bruce says:

    Concerning IPLV, the higher the value indicate better efficiency or poorer?

    Thanks,
    Bruce

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