The reverse-cycle defrost strategy is not working properly in version 9.5 #132
Description
There's a bug in the way EnergyPlus models the reverse cycle defrost strategy in version 9.5. This seems to have a non-negligible impact on energy consumption and savings.
The bug has been fixed in more recent versions of EnergyPlus:
I ran two cases, HSPF_8p8_SEER_15_Std (baseline) and HSPF_9p0_SEER_16_Msr (measure), with run ID SFm&2&rDXHP&Ex&dxHP_equip, using model release D26v2024.12.07.02, in CZ01, across both version 9.5 and version 25.1.
The baseline case uses a single-speed HP with a resistive defrost strategy, while the measure case is a two-speed system with a reverse-cycle defrost strategy. In version 9.5, the simulated defrost power for the measure case appears to remain zero at all times, as shown in the plots below. In contrast, version 25.1 shows non-zero defrost power, indicating that this issue has been fixed. The variable DXGF EL2 HEATING COIL is the backup power.
These plots illustrate the defrost-related issue in version 9.5, although they may also reflect other HP or backup system updates introduced after version 9.5. However, those are not the focus of this issue.
Baseline, version 9.5
Measure, version 9.5
Baseline version 25.1
Measure version 25.1
