How to Convert Between EER, SEER, COP & IPLV:
Formulas, Tables & Worked Examples

HVAC specifications routinely mix EER, SEER, COP, and IPLV — sometimes within the same bid document. If you cannot convert between them accurately, you risk comparing equipment on unequal footing, which the U.S. Department of Energy estimates can lead to 15–30% errors in lifecycle energy-cost projections^[1]. This guide provides the exact conversion formulas, quick-reference tables, and worked examples you need, plus the common pitfalls that even seasoned engineers overlook.

1. The Core Relationship: EER and COP

EER (Energy Efficiency Ratio) and COP (Coefficient of Performance) measure the same physical quantity — the ratio of cooling output to electrical input — but in different unit systems. The conversion is exact, not approximate^[2]:

The constant 3.412 comes from the unit equivalence 1 kW = 3,412.14 BTU/hr. Because this is a unit conversion (not an empirical correlation), it holds regardless of equipment type, refrigerant, or test conditions.

Quick Reference: EER ↔ COP Table

Need instant results? Use our free EER/COP/SEER Converter Tool — enter any value and get all metrics instantly.

2. Converting Between EER and SEER

Why SEER Is Always Higher Than EER

SEER (Seasonal Energy Efficiency Ratio) and EER are both expressed in BTU/W·h, but they measure fundamentally different things. EER is a single-point measurement at 95°F (35°C) outdoor temperature, while SEER is a weighted seasonal average across a range of outdoor temperatures from 65°F to 104°F, per AHRI Standard 210/240^[3]. Since equipment operates more efficiently at lower ambient temperatures, SEER values are always higher than EER for the same unit.

The Simplified Conversion

The most widely used approximation in the industry is:

This multiplier works reasonably well for single-speed equipment, where AHRI testing data shows SEER/EER ratios typically fall between 1.05 and 1.15^[4]. However, for variable-speed (inverter) systems, the ratio can be significantly higher — often 1.2 to 1.5 — because inverter compressors achieve dramatic efficiency gains at the part-load conditions that dominate the SEER test profile.

A More Accurate Formula

For single-speed units, the Pacific Northwest National Laboratory (PNNL) regression model provides a tighter estimate^[5]:

This quadratic correction accounts for the diminishing returns at higher SEER values: a SEER 21 unit does not have proportionally higher EER than a SEER 14 unit, because the extra SEER gains come from part-load efficiency that doesn't show up at the full-load EER test point.

Quick Reference: SEER ↔ EER Table

Notice how the gap between the two EER columns widens at higher SEER values. At SEER 25, the simple ÷1.12 method overstates EER by nearly 44%. For equipment selection decisions involving high-SEER inverter units, always request the manufacturer's tested EER rather than relying on conversion.

3. IPLV: The Part-Load Metric That Matters Most

Neither EER nor SEER captures how large commercial chillers perform under real operating conditions. ASHRAE research shows that commercial HVAC systems operate below 50% load for 60–70% of annual operating hours^[6]. IPLV (Integrated Part Load Value), defined by AHRI Standard 550/590, addresses this with a weighted four-point formula^[7]:

Where A, B, C, D are the efficiency values (COP or EER) at 100%, 75%, 50%, and 25% load respectively. The weighting reflects the load distribution of a typical North American commercial building — full load accounts for only 1% of operating hours.

IPLV to Full-Load COP: Rules of Thumb

There is no universal formula to convert IPLV back to full-load COP because the relationship depends entirely on the compressor type and control strategy. However, industry benchmarks provide useful guidance^[8]:

A 2022 study published in Energy and Buildings analyzed 847 chiller installations and found that buildings selecting equipment based on IPLV rather than full-load COP alone achieved 18–24% lower annual chiller energy consumption^[9].

4. SEER2: The 2023 U.S. Standard Update

Since January 2023, the U.S. Department of Energy requires all new residential HVAC equipment to be rated under SEER2 (and EER2), which uses a higher external static pressure (ESP) test condition — 0.5 in. w.g. instead of the previous 0.1–0.2 in. w.g.^[10]. This simulates more realistic installed duct conditions and results in lower numerical ratings:

For example, a unit previously rated SEER 16.0 would test at approximately SEER2 15.2 under the new protocol. When comparing equipment across the SEER/SEER2 boundary, engineers must normalize to the same standard — mixing SEER and SEER2 values in a side-by-side comparison will systematically penalize the SEER2-rated unit.

5. COP in kW/RT: The Chiller Metric

Large chiller specifications often express efficiency as kW/RT (kilowatts of input per refrigeration ton of cooling). This is the inverse of COP, converted to refrigeration ton units^[11]:

The constant 3.517 comes from the definition: 1 refrigeration ton (RT) = 3.517 kW of cooling. Lower kW/RT values indicate better efficiency (unlike COP, EER, and SEER where higher is better).

Quick Reference: COP ↔ kW/RT Table

For a deeper dive into cooling capacity unit conversions (BTU, kW, RT), see our BTU/kW/RT conversion guide.

6. Common Conversion Pitfalls

Pitfall 1: Comparing Across Different Test Standards

A COP of 6.0 tested under AHRI 550/590 (30°C entering condenser water) is not the same as COP 6.0 tested under EUROVENT conditions (35°C entering condenser water). The difference in test conditions alone can account for a 5–15% variation in the reported COP^[12]. Always confirm the test standard before comparing.

Pitfall 2: Conflating SEER and EER

A common error in equipment specifications is treating SEER and EER as interchangeable. They are not. A unit with SEER 20 and EER 13 will deliver COP 3.81 at peak design conditions (the EER-based value), not COP 5.86 (the SEER-based value). Using the SEER-derived COP for peak load calculations will lead to undersized electrical infrastructure.

Pitfall 3: Ignoring Auxiliary Power

Chiller COP typically includes only the compressor package. It excludes condenser water pumps, cooling tower fans, and chilled water pumps, which together consume 30–40% of total system power^[13]. A recent analysis by Lawrence Berkeley National Laboratory found that the "system COP" of typical chilled water plants is only 55–65% of the chiller nameplate COP^[14]. As Harvard Business Review noted in a 2023 analysis of commercial building decarbonization, "focusing solely on equipment-level efficiency while ignoring system-level performance is the single most expensive mistake in building energy management"^[15].

Pitfall 4: Overlooking Climate-Specific Performance

SEER is calibrated to a U.S. climate distribution that may not match your project's location. For tropical or subtropical climates (like Taiwan or Southeast Asia), the equipment spends more hours at high ambient temperatures where efficiency is lowest. CSPF (ISO 16358) or regional SEER calculations with location-specific bin data provide more accurate seasonal estimates^[16].

7. Master Conversion Table

For quick reference, here is a consolidated table of all HVAC efficiency metric conversion formulas:

Skip the math — use our EER/COP/SEER Converter Tool for instant conversions between all metrics, with automatic Taiwan energy rating classification.

Conclusion

Converting between EER, SEER, COP, and IPLV requires understanding not just the formulas but the test conditions behind each metric. The three exact conversions (EER ↔ COP, COP ↔ kW/RT) are simple unit math. The approximate conversions (EER ↔ SEER, SEER ↔ SEER2) depend on equipment type and operating profile. And IPLV cannot be meaningfully derived from a single full-load number at all — it requires actual part-load test data. When in doubt, request the manufacturer's full performance data at all four AHRI load points rather than relying on any single published metric. For a comprehensive explanation of what each metric means and how to use them for equipment selection, see our complete guide to HVAC energy efficiency metrics.