IPLV and NPLV calculator
Enter a chiller’s efficiency at 100%, 75%, 50% and 25% load and get the weighted part-load figure defined by ANSI/AHRI Standard 550/590 — in kW/ton, COP and EER at once. Compare two machines and see which load point actually decides the answer. Free, no sign-up, nothing leaves your browser.
Calculate IPLV from four load points
The weighted part-load figure defined by ANSI/AHRI Standard 550/590.
Enter the four efficiencies produced on the standard condenser-relief trajectory. That is what makes an integrated value comparable between manufacturers.
Machine X
Efficiency at each load point, in kW/ton.
Machine Y
Efficiency at each load point, in kW/ton.
The ranking flips
Machine X is 6.1% better at full load, which is the figure a datasheet comparison settles on. On the standard’s own weighting, Machine Y is 10.3% better. Full load carries a weight of 0.01 here; half load carries 0.45.
How Machine X’s IPLV is made up
| Load | Weight | Efficiency | Term (w / x) | Share of the result |
|---|---|---|---|---|
| 100% | 0.01 | 0.540 kW/ton | 0.018519 | 1.0% |
| 75% | 0.42 | 0.520 kW/ton | 0.807692 | 43.9% |
| 50% | 0.45 | 0.535 kW/ton | 0.841121 | 45.7% |
| 25% | 0.12 | 0.700 kW/ton | 0.171429 | 9.3% |
The share column is each point’s fraction of the weighted sum — how much of the final figure that load point decides. Full load decides roughly one percent of it.
These four efficiencies come from a machine’s certified capacity and power map, read at the load points and condenser conditions you are rating against. MileSoft’s chiller selection software produces them, the full-load figure and both part-load values from one traversal of that map, so a reviewer who recomputes any one of them from the others finds them consistent.
See it run on your own machine dataThe method
What the weights are actually saying
The part of the standard that decides the number.
A chiller is sized for a design day and then spends almost none of its life there. The integrated part-load value exists because of that gap: instead of one number at full load, it combines efficiency at four load points, weighting each by the share of operating hours AHRI 550/590 attributes to it.
Those weights are 0.01 at 100% load, 0.42 at 75%, 0.45 at 50% and 0.12 at 25%. Half load carries forty-five times the weight of full load. A selection process that ranks machines on full-load kW/ton is not making a small approximation — it is optimising for a condition the equipment almost never occupies, and the standard that governs the rating says so in its own arithmetic.
The combination is harmonic rather than arithmetic when efficiency is expressed in kW/ton, because kW/ton is an inverse quantity: a plain average of it would overweight the efficient points. Expressed as COP or EER, where higher is better, the identical result comes from the ordinary weighted mean. The calculator computes in kW/ton and converts, so all three units always agree.
IPLV vs NPLV
IPLV vs NPLV: one equation, two sets of conditions
The distinction is misread more often than any other part of the rating.
The integrated value applies the standard’s own condenser-relief trajectory, which is exactly what makes it comparable across manufacturers. The non-standard part-load value applies the identical weighted formulation at the project’s actual condenser-water and ambient conditions.
The difference is frequently taken to be one of rigour, as though the non-standard value were the less official number. It is the reverse: the integrated value is the comparison metric and the non-standard value is the prediction. A plant with limited condenser relief — a dry cooler in a hot climate, or a constant-temperature condenser loop — will not realise the integrated value, and quoting it as an energy forecast overstates what the plant will do.
Report both, and name which one the project should be judged on. That is the difference between a compliant submittal and a useful one.
Limitations
What this calculator cannot tell you
Where the arithmetic stops and engineering judgement starts.
- It does not produce the four efficiencies. Those come from the machine’s certified capacity and power map, interpolated at the load points and condenser conditions being rated. No free page can derive them without that map — which is why this tool takes them as inputs rather than guessing at them.
- The weights describe an average single chiller. They are specific to AHRI 550/590’s model of one machine’s load profile, and should not be applied to a plant with an atypical profile without re-deriving them. Multi-chiller plants stage differently, and the best machine for one staging arrangement is not necessarily the best for another.
- A weighted figure is not an hourly simulation. AHRI 550/590 itself cautions that a comprehensive hourly analysis remains the most accurate predictor for a specific installation. The non-standard value is a defensible middle position between a single point and a full simulation, not a substitute for one.
- Part-load reasoning does not generalise everywhere. It applies to equipment whose duty varies and whose efficiency is non-linear in load — chillers, large direct-expansion plant, heat pumps. For constant-duty process cooling, full-load rating is the correct basis.
FAQ
IPLV and NPLV questions
The ones that come up in selection reviews.
How is IPLV calculated?
What is the difference between IPLV and NPLV?
Why does the 50% load point carry the most weight?
Can a chiller with worse full-load efficiency have a better IPLV?
Which number should a project be judged on?
Is this calculator free?
Related
Where this fits
The method in full, and the software that produces the inputs.
- Part-load efficiency, NPLV, and why full-load kW/TR is the wrong metric — the full method paper, with the derivation, the worked examples this calculator is preloaded with, and the standards it rests on.
- MileSoft Chiller Selection Software — produces full-load efficiency, the four-point part-load table and both part-load values from one traversal of the certified map.
- HVAC Lifecycle Cost Analysis — where a part-load figure turns into an owning cost over the plant’s life.
- Standards glossary — AHRI 550/590, its SI counterpart 551/591, and the other standards cited across MileSoft’s HVAC software.