Hello all,

I am currently working to create an energy model for an addition to be made to a hospital and am unsure how to go about modelling the heating system. New air handling units provide ventilation to the addition, however the boiler is outside of the LEED system boundary. Is it acceptable to exclude the existing building from an energy model of the addition? If so, what is the method of approximating the efficiency of such a system? If not, is the boiler to be modeled as a scaled down version of the existing boiler or a full sized model with an estimated "dummy load" applied to approximate the existing building?

A full building model may be required due to the boiler's use in both the existing building and the addition as well as the local electric utility's use of a declining block power rate. Based on ASHRAE 90.1 Appendix G, Table G3.1 Section 2 these issues preclude excluding the existing building from the model. 

Thank you,

Eddie