Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
It sounds like you're trying to model a boiler that provides hot water to a storage tank, is this correct? If the water heater is providing the energy to heat the water, not a boiler, it should be on the supply side of the plant loop, not the demand side.
If you're trying to model a passive storage tank, there is a way to do this but it's not fully supported by OpenStudio 1.5.0. A work around would be to set the capacity of the water heater to zero to ensure all of the energy comes from the boiler or heat exchanger.
The two inputs I use most often to control DHW energy usage are the "Use Flow Rate Fraction schedule" and " Peak Use Flow Rate".
This video is a good resource on creating DHW systems in openstudio.
