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


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.


25 thoughts on “Understanding IPLV/NPLV”

  1. A good discussion. However we have to be careful if we tell them energy savings based on IPLV. The considerations for the same can be: – Was chiller selected for 0.4% or 1% or 2% ASHRAE Conditions. If you select chiller for 2% ASHRAE conditions, how can you consider the given formula for IPLV with .01 for full load? This is erroneous, are you only going to not meet the conditions 98% of the time? What about record temperatures that even fall outside 0.4% and are many more as compared to what ASHRAE handbook suggests. For example, if I do bin hours for Austin and design a hospital for 0.4%, it tells me only 35 hours the ambient will be higher than what is given in ASHRAE, but when I look at for record year, it is more than 111 hours when our ambient temperatures fall out of ASHRAE limits? So one has to be careful about promising any energy savings based on IPLV using this formula. The consultant or Utility Cost Reduction Measure engineer or contractor has to make sure that bin hour methods are used and adjust IPLV or NPLV before committing any savings.
    – Similarly you have to look for record low temperatures and see if you will be able to return 120 F hydronic water during record low temperatures or how it will affect efficiency and internal temperatures or use of gas as fuel.

    Standardization based on sales literature also should be questioned unless factory tests are done and manufacturer guarantees such performance. I have seen with some manufacturers where the instrumentation or other reasons are pointed out, one has to be conservative in their design and sizing of equipment.

  2. any one tell me ..

    how to calcute the minimum inside temperature can be maintain with chilled water system @ evaporator side at 54 F (chilled water in) / 44 F (chilled water out).

    plz help me

  3. Can anybody tell me if some chiller is not delieverng capacity at 100% say requirement 325 TR delievering 310 TR.

    whether to consider part values w.r.t 325 or w.r.t 310.Please let us know.

  4. What is the definition of PPLV??? I have a chiller selection with 3 ratings, IPLV, NPLV and PPLV. I’m familiar with IPLV ans NPLV, not PPLV…

  5. IPLV & NPLV is depend on application of No of chiller Compressor to usage, EWT/LWT & Related to condensing in out temperature.Normally IPLV efficient almost at 100% at chilled water 44/54F & at 97F LWT condenser., not at Part load.

    For fact with use 1 unit bigger compressor capacity IPLV doesn’t real shown efficiency were within Part Load the compressor amp is not down due to a huge motor KW selected cause the RPM still remain at 2900 but chilled water is already reach 44/54F,IPLV & NPLV is depend on temperature were condenser temperature from 65F to 97F(100%)…

    With condensing Temperature from 65 to 97F… The table data shown is confuse.

    Condensing temperature for tropical area almost 87/97F consistent.. It can’t at 65F.

    Selected lower IPLV for Higher efficiency is good at only 100%,but must consider on application,usage of building, no of compressor.I think for good practice for energy saving multiple compressor is the answer not a single one.

  6. 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

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

  8. 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

  9. 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

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


  11. 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.

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

  13. 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?.



  14. 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.


    Amit Kumar

  15. Dear Bill,

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

  16. 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:


  17. 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.

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

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