IPLV and NPLV are part-load efficiency metrics for liquid chillers, while COP and EER describe efficiency at defined operating conditions. SEER, SEER2 and APF are seasonal metrics used for particular air-conditioning or heat-pump product categories and regional test procedures. These values are not interchangeable unless the equipment scope, test standard, units and rating conditions are the same.
For a project comparison, request the full certified selection鈥攏ot one efficiency number. GESON engineers need the required cooling load, leaving and entering fluid temperatures, flow, fluid or glycol concentration, design ambient or condenser-water temperatures, electrical supply and destination country.
IPLV vs NPLV: the short answer
| Metric | What it represents | Best use | Main limitation |
|---|---|---|---|
| IPLV | Integrated part-load performance at the standard rating conditions and weighting method defined by the applicable chiller standard | Comparing covered chillers on a common standardized basis | It is not a prediction of a specific building or process plant |
| NPLV | Non-standard part-load performance calculated for stated project or non-standard conditions using the standard’s prescribed method | Comparing selections at defined project conditions | Values are comparable only when inputs and calculation basis match |
| COP | Useful heating or cooling effect divided by power input on a consistent energy-unit basis | Full-load or point-performance comparison at stated conditions | System boundary and rating conditions must be stated |
| EER | Cooling capacity divided by electric input, commonly expressed in Btu/(Wh) in US practice | Point efficiency for covered air-conditioning equipment | Units and test procedure differ from dimensionless COP |
| SEER / SEER2 | Seasonal cooling efficiency under a specified regional test procedure | Covered unitary and residential/light-commercial air conditioners | Not a general industrial-chiller rating |
| APF | Annual performance factor under a specified regional product standard | Covered air conditioners or heat pumps in markets that use APF | Product scope and regional standard must be identified |
What is COP?
Coefficient of performance is a ratio of useful thermal output to power input. For cooling:
Cooling COP = net cooling capacity 梅 power input
Both quantities must use consistent units, normally kW of cooling divided by kW of input. A COP of 5.0 therefore means 5.0 kW of useful cooling per 1.0 kW of the stated power input鈥攏ot 500% electrical efficiency.
The system boundary matters. A compressor-only ratio is not the same as a packaged-chiller COP that includes defined auxiliaries. Pumps, cooling-tower fans and other plant equipment may be outside the chiller rating. Always ask whether the value is net or gross and which electrical loads are included.
What is EER, and how is it related to COP?
Energy efficiency ratio is cooling capacity divided by electrical input at stated test conditions. In US practice, EER is commonly reported as Btu/h of cooling per watt. When both metrics refer to the same equipment boundary and operating point, conversion is possible:
EER [Btu/(Wh)] 鈮� 3.412 脳 cooling COP [W/W]
Do not convert a published EER to COP until you verify that capacity, input power, auxiliary loads and rating conditions are identical. A water-cooled chiller selection at one condenser-water temperature cannot be compared directly with an air-cooled unit tested at another outdoor temperature.
What are SEER, SEER2 and APF?
SEER and SEER2 are seasonal cooling metrics for equipment covered by the applicable US Department of Energy test procedures. SEER2 reflects the current test procedure for covered products; it is not simply a new label for every chiller efficiency calculation.
APF is an annual performance metric used under particular regional standards for specified air-conditioner and heat-pump categories. Its heating and cooling treatment, climate assumptions, load profile and included power depend on that standard. An APF number from one product category or market should not be used to rank an industrial process chiller.
What is IPLV?
Integrated part-load value summarizes chiller performance at multiple load points under the standard rating method. The applicable edition of AHRI 550/590 (I-P) or AHRI 551/591 (SI) defines the covered equipment, rating conditions, test method, efficiency expression and integration procedure.
IPLV is useful because many comfort-cooling chillers operate below design load for substantial periods. It gives specifiers a common comparison basis, but it does not reproduce a project’s weather, load duration, chilled-water reset, condenser-water reset, fouling, pumping energy, sequencing or process schedule.
What is NPLV?
Non-standard part-load value applies the prescribed part-load methodology to stated non-standard or project conditions. It can be more relevant than IPLV when a building or process has different leaving-fluid temperatures, condenser conditions or operating requirements.
An NPLV must never be presented without its inputs. Two suppliers can produce different-looking NPLV figures simply by using different condenser-water temperatures, outdoor temperatures, fluid properties, flow assumptions or control limits.
Why old IPLV formulas can be misleading
Search results often reproduce weighting factors and temperature schedules from older ARI or AHRI editions. Standards and product scopes change. Mixing an old arithmetic expression, current performance data and an unstated unit basis can produce a plausible but invalid answer.
Use the edition required by the specification or destination market. If a tender cites AHRI 550/590 or 551/591, obtain the actual edition, confirm whether efficiency is expressed as COP or kW/ton, and follow its current equation and rating conditions. Do not combine a COP-weighted formula with a kW/ton-weighted formula: one is a higher-is-better metric, while the other is lower-is-better.
Can IPLV predict annual chiller energy?
No. Multiplying IPLV by full-load capacity and annual hours is not a reliable annual-energy calculation. Annual energy requires a time-based model or bin analysis that matches the actual load and operating conditions.
At minimum, a defensible estimate should include:
- Hourly or binned cooling-load profile;
- Leaving and entering chilled-fluid temperatures;
- Outdoor dry-bulb for air-cooled equipment or condenser-water temperature for water-cooled equipment;
- Part-load limits, staging, variable-speed behavior and cycling;
- Chilled-water and condenser-water pump power;
- Cooling-tower fan and water-treatment loads where applicable;
- Fluid type and glycol concentration;
- Fouling, altitude and heat-exchanger pressure-drop assumptions;
- Standby units, redundancy and plant sequencing.
How engineers should compare chiller efficiency
- Fix the duty. Use the same net cooling load, leaving/entering fluid temperatures, flow and fluid composition.
- Fix the heat-rejection condition. State design outdoor dry-bulb for air-cooled chillers or entering condenser-water temperature and flow for water-cooled chillers.
- Fix the boundary. Confirm which fans, pumps and controls are included in input power.
- Request point data. Compare full-load and relevant part-load capacity, input power, COP or kW/ton at the same conditions.
- Check the standard. Record the rating standard and edition; use certified data where certification is required.
- Model the plant. For operating-cost decisions, include auxiliary energy and the site’s actual load profile.
Chiller selection information for a comparable quotation
| Input | Why it changes capacity or efficiency |
|---|---|
| Application and process | Defines load behavior, contamination risk and reliability requirement |
| Required net cooling load | Sets the useful capacity at the actual duty |
| Entering/leaving fluid temperature | Changes evaporating conditions and compressor lift |
| Flow and allowable pressure drop | Determines heat-exchanger and pump selection |
| Water or glycol type/concentration | Changes heat capacity, viscosity, pressure drop and freeze protection |
| Design ambient or condenser-water condition | Changes condensing pressure and available capacity |
| Operating hours and load profile | Determines which part-load points matter economically |
| Power supply and destination country | Controls electrical design, applicable codes and rating requirements |
| Redundancy and control interface | Affects staging, standby capacity and system integration |
Frequently asked questions
Is IPLV higher or lower better?
It depends on the reported efficiency unit. Higher is better when IPLV is expressed as COP or another output-per-input ratio. Lower is better when it is expressed as kW/ton. Confirm the unit, standard edition and conditions.
Is NPLV always more accurate than IPLV?
No. NPLV can better match stated project conditions, but only if those inputs represent the real system. It is still a standardized part-load summary, not a complete annual plant simulation.
Can COP be compared across different chilled-water temperatures?
Not directly. Leaving-fluid temperature, entering-fluid temperature, condenser condition, flow, fluid properties and included auxiliaries must be aligned before comparing COP.
Does IPLV include pumps and cooling towers?
Do not assume it does. Chiller ratings use a defined package boundary. Project energy analysis should add external chilled-water pumps, condenser-water pumps, cooling-tower fans and other auxiliaries where they are outside that boundary.
Which metric should be used for an industrial process chiller?
Start with net capacity and input power at the actual process conditions. Use COP or kW/ton at matched duty points. IPLV or NPLV may supplement the comparison when the equipment and operating profile fit the applicable standard, but neither replaces process-load analysis.