When designing an air-conditioning cooling and heating source system, what do the COP and IPLV indicators each reflect? Which one should be given priority during equipment selection?
I am an HVAC expert. The COP (Coefficient of Performance) and IPLV (Integrated Part Load Value) of an air-conditioning cooling and heating source system are core indicators for measuring equipment energy efficiency, and they directly relate to system operating energy consumption, initial investment, and long-term operating costs. In actual engineering, many designers easily confuse the meanings of the two, causing equipment selection to deviate from actual needs. Below I will provide a detailed analysis based on standards and experience.
First, COP reflects the energy efficiency of equipment under **full-load conditions**. According to Article 8.2.2 of GB 50736-2012 "Design Code for Heating Ventilation and Air Conditioning of Civil Buildings," the nominal working condition coefficient of performance (COP) of chillers should meet the energy efficiency limit values; for example, the COP of water-cooled screw units under standard working conditions should not be lower than 5.0 (energy efficiency grade 1). It mainly guides the energy consumption evaluation of equipment on extreme design days (such as summer peak load) and is the basis for factory calibration and energy efficiency certification of equipment.
IPLV, however, reflects the integrated energy efficiency of equipment under **part-load** conditions. According to Part 1 of GB/T 18430.1-2007 "Water Chilling (Heat Pump) Packages Using the Vapor Compression Cycle," IPLV is calculated by weighting the energy efficiency at four typical load points (100%, 75%, 50%, 25%), reflecting the energy efficiency performance during actual operation when the system is under part load most of the time. For example, actual measurements from a certain project show that for about 70% of the year the load rate is between 40% and 70%, and IPLV can more truly reflect annual operating energy consumption.
During equipment selection, **IPLV should be the primary criterion, with COP as secondary**. The reasons are as follows:
1. **Actual operating characteristics**: Air-conditioning systems operate at full load for only 1%-5% of the year and under part load most of the time. If selection is based only on COP, the equipment may have low energy efficiency under part load (for example, the COP of a fixed-frequency unit may drop by 30% at 50% load), while equipment with high IPLV (such as variable-frequency centrifugal chillers) can maintain high efficiency by adjusting compressor speed.
2. **Standard orientation**: Article 8.2.3 of GB 50736 explicitly requires that "the integrated part load value of chillers shall meet the current national standards." In green building evaluation, IPLV is a key indicator (for example, the "Green Building Evaluation Standard" GB/T 50378 requires IPLV not lower than 5.5).
3. **Economy**: A hotel project compared two schemes: Scheme A selected variable-frequency units with COP=6.0 and IPLV=5.5; Scheme B selected variable-frequency units with COP=5.8 and IPLV=7.0. In the first year of operation, Scheme B saved about RMB 150,000 in electricity costs (based on the local electricity price of RMB 0.8/kWh). Although the initial investment was 10% higher, it could be recovered in 2 years.
**Engineering case**: An office building in East China has a design cooling load of 5,000 kW. The original design selected three fixed-frequency screw chillers with COP=5.8 and IPLV of only 4.5. Through optimization, we changed to two variable-frequency centrifugal chillers (COP=6.2, IPLV=7.2) plus one small screw chiller (COP=5.5). In actual operation, the energy efficiency of the variable-frequency units remained stable below 80% load, annual operating energy consumption was reduced by 22%, and equipment wear caused by frequent start-stop was avoided.
**Summary**: During equipment selection, priority should be given to using IPLV to guide equipment selection and ensure high efficiency under part load; at the same time, COP should be used to verify whether energy efficiency meets the standard under full-load conditions, avoiding insufficient equipment efficiency under extreme conditions. The above are reference opinions. The actual situation of the project still needs further comprehensive evaluation and implementation in combination with specific working conditions, site conditions, and other factors.