Allow sub-timestep DHW draw events (for HPWHs)

[shorowit]

General Summary

Residential heat pump water heaters typically have both a heat pump and electric backup resistance heating. The electric backup resistance heating is used for short duration, high flow rate draws that are not captured by EnergyPlus unless short timesteps are used. Requiring that EnergyPlus use short timesteps for everything (all heat transfer calculations) just to obtain more accurate HPWH energy consumption is overkill and comes with a steep runtime performance penalty; thus this significant effect is often overlooked.

Detailed Description

Previously NREL modified the stratified tank model (that underpins the HPWH model) to use a partial analytical solution for the tank system of ODEs and use adaptive internal sub timesteps, bringing a 10x improvement in runtime performance. If schedule objects in EnergyPlus were refactored so that shorter hot draw events (relative to the overall EnergyPlus timestep) data was made available to the stratified tank model, HPWH energy consumption could be more accurately modeled without compromising EnergyPlus runtime.

Possible Implementation

No response