Understanding IPLV: Integrated Part Load Value Explained (AC, Chillers)

IPLV or Integrated Part-Load Value is a metric used for adequately assessing the energy efficiency of chillers and air conditioners in realistic conditions.

The key metric that we use for the energy efficiency of any HVAC appliance is COP (Coefficient Of Performance). Supplementary metrics include EER, SEER, CEER, and HSPF ratings.

Where does IPLV fit in?

EER rating, for example, gives you the energy efficiency of an air conditioner when operating at 100% cooling output. It’s a simple metric but it lacks to describe how an AC unit actually performs in practical conditions. That’s because an AC might be running at 100% cooling output less than 5% of the time. What about other times?

Here is where the IPLV comes in. IPLV is used to describe the practical energy efficiency of chillers and air conditioners at different (more realistic) loads. IPLV is calculated not only at 100% output, but also at 25%, 50%, and 75% output.

Note: EER and COP are, by definition, subgroups of IPLV. We talk about IPLV EER and IPLV COP.

Essentially, Integrated Part Load Value is a weighted average of these 4 loading points. That means that you can assess the energy efficiency at part-loads (25%, 50%, 75%); hence the ‘Part-Load’ in IPLV.

How do you actually calculate IPLV? Here’s the formula:

IPLV Formula

IPLV is calculated as a weighted average of 4 loading points. The calculation presumes that a chiller or air conditioner operates (you will find the equation below):

  • 12% of the time at 25% load (D in the equation).
  • 45% of the time at 50% load (C in the equation).
  • 42% of the time at 75% load (B in the equation).
  • 1% of the time at 100% load (A in the equation).

Here is the full IPLV formula:

IPLV = 0.01A + 0.42B + 0.45C + 0.12D

We always use this equation to calculate IPLV. The key part is how do you actually measure how much is the realistic 25%, 50%, and 75% load:

How Is IPLV Measured?

Measurement of cooling loads at these 4 points is generally measured by AHRI, according to the existing standard AHRI standards.

When AHRI measures the loads at 25%, 50%, and 75%, they simply input the measurements in the weighted-average IPLV equation and calculate the IPLV.

Now, measuring these loads is not always possible. That’s why not every air conditioner or chiller has a specified IPLV value.

The issues that prevent IPLV from being adequately measured include:

  • Variations in distribution system design.
  • Different climate conditions.
  • Unpredictable temperature variations.
  • Difficulty of keeping the load constant at 25%, 50%, or/and 75%.

Despite these issues, we still want to measure the realistic load and consequent energy expenditure of air conditioners and chillers.

That why when we can’t measure IPLV adequately (with sufficiently low measurement error), we use two other values to assess energy efficiency more precisely: NPLV and SPLV.

You can read a similar explanation of what NPLV or Net Part-Load Value is here. To fully understand all of these metrics, it’s advisable that you educate yourself about SPLV or Specific Part-Load Value here as well.

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