Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Please note that the boilers.idf document you linked to clearly states: "For the curve below, specify EnteringBoiler for the Efficiency Curve Temperature Evaluation Variable". According to that, the second independent variable is return water temp, not supply water temp, for this boiler performance curve.
As you note, data is available for plenty of units, so you will be better off if you create your own curve.
Bear in mind as you are creating a performance curve: consider the range of independent variables that will occur in the simulation. Unless your RWTs will span between 240F and 40F, you do not necessarily have to encompass the entire range of the ASHRAE handbook diagram in order get good results for a particular simulation.
| | 2 | No.2 Revision |
Please note that the boilers.idf document you linked to clearly states: "For the curve below, specify EnteringBoiler for the Efficiency Curve Temperature Evaluation Variable". According to that, the second independent variable is return water temp, not supply water temp, for this boiler performance curve.
I agree with you that it would be really helpful for the boilers.idf example file to be improved, as I think that's where new comers would tend to look for an initial starting point.(I did this myself, as you have done, and found the curve data to be difficult to justify. Now that I understand from @rraustad the source of these data, it seems understandably not that great. It is not clear what the "part load efficiency [%]" values in the Viessmann Fig. 9 graph represent - they exceed 100% for many conditions.)
As you note, data is available for plenty of actual units, so you will be better off if you create your own curve.
Bear in mind as you are creating a performance curve: consider the range of independent variables that will occur in the simulation. Unless your RWTs will span between 240F and 40F, you do not necessarily have to encompass the entire range of the ASHRAE handbook diagram in order get good results for a particular simulation.
