Hi Waseem,
I think it'll help if you think about the solution if you draw the above schematic including the EnergyPlus loops. I would start with:
- Put the biomass boiler on the supply side of a loop ("Biomass Loop")
- Your "Buffer Tank" should be a "WaterHeater:Mixed" or "WaterHeater:Stratified" object. It's source nodes should be on the demand side of "Biomass Loop" and the use side nodes should be on the supply side of "HW Loop"
- Your gas boilers could also be on the supply side of "HW Loop". Set the loop load distribution scheme to "Sequential" and put the gas boilers after the water heater in the PlantEquipmentList.
The above would operate as follows:
- biomass boiler operates to maintain temperature in the water heater
- when there is a load, the temperature in the water heater is drawn down
- if the water heater gets too cold to satisfy the load, the gas boilers are called on
- the gas boilers are never used to heat the water heater
If you want to use the gas boilers to heat the water heater directly, you'll have to get more creative.
