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IPLV - STULZ answers

The Integrated Part Load Value (IPLV) is based on the part-load efficiency of a chiller, which is calculated on the basis of the weighted percentage of the assumed operational hours of certain loads.

How is the IPLV calculated?

The formula focuses on four components (A, B, C, D) in which:

A: 1% of the time the chiller runs at 100% load

B: 42% of the time the chiller runs at 75% load

C: 45% of the time the chiller runs at 50% load

D: 12% of the time the chiller runs at 12% load

The reference points are then determined based on the Air Conditioning, Heating and Refrigeration Institute (AHRI) Standard 550-590. For this purpose, the Energy Efficiency Ratio (EER) of the system is examined per load.

Applicable here: the lower the IPLV value, the more efficient a chiller.


The IPLV is based on specified conditions as defined in AHRI Standard 550/590. So, not all the chillers are subject to the same standardised loads. In practice, two or more chillers are often installed, whereas the IPLV value is based on a single chiller.

In addition, the IPLV is not suitable for systems inside data centres. Data centres have systems requiring year-round cooling, whereas this value only relates to the period with outdoor temperatures from the highest temperature to approximately 7 °C (zero-load climate cooling according to AHRI).

Alternative: Non-Standard Part-Load Value (NPLV)

An alternative to the IPLV is the Non-Standard Part-Load Value (NPLV). This value reflects the energy efficiency of the chillers under circumstances that do not conform to the AHRI Standard but remain within the prescribed limits.

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