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The correct way to model in-unit HPWH is with a stratified tank model that exchanges air with the zone it is in. Until the most recent release of EnergyPlus, the stratified tank model was agonizingly slow, making it nearly unusable for the sort of parametric analysis one may want to do with the "create typical building" measure.

The workaround in openstudio-standards is to instead model a HPWH as an electric water heater, but adjust the part load efficiency curve with a constant efficiency equal to rated annual HPWH COP. So it runs as fast as a basic mixed electric water heater, but accounts for the annual COP difference. This is fine for most modeling projects. However, if you want to model the dehumidification, cooling, and heating impacts of a HPWH in your zone, you need the full stratified tank model. There is a separate residential BeOpt measure which adds it if you are interested.

The correct way to model in-unit HPWH is with a stratified tank model that exchanges air with the zone it is in. Until the most recent release of EnergyPlus, the stratified tank model was agonizingly slow, making it nearly unusable for the sort of parametric analysis one may want to do with the "create typical building" measure.measure. The most recent EnergyPlus version is a little better, and we may update openstudio-standards to use the stratified tank model in the future.

The workaround in openstudio-standards is to instead model a HPWH as an electric water heater, but adjust the part load efficiency curve with a constant efficiency equal to rated annual HPWH COP. So it runs as fast as a basic mixed electric water heater, but accounts for the annual COP difference. This is fine for most modeling projects. However, if you want to model the dehumidification, cooling, and heating impacts of a HPWH in your zone, you need the full stratified tank model. There is a separate residential BeOpt measure which adds it if you are interested.