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.

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