Load-matched multi-evaporating pressure control in multi-split heat pumps for improving energy efficiency and thermal comfort

Multi-split heat pumps (MSHPs) are powerful tools for achieving carbon neutrality in the building sector. However, all the indoor units (IDUs) in MSHPs have the same evaporating pressure, causing overcooling and frequent on-off operations under varying loads. Thus, multi-evaporating pressure (MEP) control is essential for obtaining a matched capacity for each IDU with the zone load, thereby achieving high energy efficiency and thermal comfort. This study proposes a flow control valve (FCV)-based MEP system and quantitatively evaluates its performance advantages over conventional single-evaporating pressure (SEP) systems in MSHPs. A simulation model for MSHPs with the FCV-based MEP system was developed using Dymola TIL Library, and parametric and dynamic-load scenario-based analyses of MSHPs with MEP and SEP systems were conducted using the validated simulation model. Based on the parametric analysis performed under various part-load ratios (PLRs) and sensible heat ratios (SHRs), the MEP system improved the coefficient of performance (COP) by 3.59% and temperature control precision by 40 percentage points (%p), with the greatest gains at mid-PLRs (0.5–0.7) and high SHRs (0.8–1.0). Additionally, the dynamic-load scenario analysis revealed that the MEP system reduced the energy consumption by 4.7%–7.5% and improved the COP by 8.5%–10.7% while maintaining a temperature control precision of 90%. These results demonstrate that the FCV-based MEP system simultaneously improves the energy efficiency and thermal comfort of MSHPs under realistic multi-IDU operations.