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Waterheater:HeatPump Tank Storage Volume

asked 2019-10-23 13:23:42 -0500

Lindsey Gaunt's avatar

updated 2020-01-15 18:26:07 -0500

I'm investigating the impact of the storage volume of the tank attached to the Waterheater:HeatPump object in Openstudio v2.6. This exercise is to help inform the design team what size tank will help maximize the AWHP heating output, however, I'm seeing very little impact on the % annual DHW load met by the AWHP with varying tank sizes.

The table below shows the different scenarios I ran, and shows that the AWHP load met only increases with increased capacity and the tank size doesn't change results much.

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You can see from the images below that the system does seem to respond differently when a storage volume is present, however I'd expect the stored hot water from the AWHP to offset more of the backup gas water heating during peak hours. Any help is greatly appreciated

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answered 2019-12-20 11:23:10 -0500

Did you figure this out? Not sure if this is applicable, but the HP water heater is modeled as a mixed tank (not stratified). With a mixed tank, the instantaneous load will always be met simultaneously by the heat pump and supplemental heaters and not the stored capacity. Thermal storage, for the purpose of reducing peak demands, is better modeled using stratified tanks. Perhaps you could try putting a stratified tank after the HPWH?

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There are two objects in E+, WaterHeater:HeatPump:PumpedCondenser and WaterHeater:HeatPump:WrappedCondenser. The former can use either a mixed or stratified tank while the latter requires a stratified tank. This is explained in the E+ Input/Output reference.

shorowit's avatar shorowit  ( 2019-12-20 17:05:57 -0500 )edit

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Asked: 2019-10-23 13:23:42 -0500

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Last updated: Dec 20 '19