Approximating DOAS to AHUs in EnergyPlus

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It depends on the system configuration but I have done this a few different ways, none of which are perfect. These are the steps I generally take:

1. Represent DOAS heating and cooling using components on the outdoor air path of each AHU. Say that the DOAS provides air at 70 F. You can put a heating coil and a cooling coil on the AHU outdoor air path (before the OA mixer) and apply scheduled setpoint managers to the outlet node of each coil, each set to 70 F. In this same way, you could apply ERV, evap cooling, etc.
2. The tricky part is correctly capturing the fan energy. I have tried a few ways to do it and can think of at least one other, but none of them are perfect. I have added the DOAS fan power as a process load but then you don't capture its fan heat at all, and this approach really only works well for a CAV DOAS. For a VAV DOAS I have represented the DOAS fan by applying a relief fan to each AHU (such that the flow through the fan is always equal to the OA intake, as long as you don't have exhaust fans affecting the flow balance, even if you have DCV applied). Again, however, fan heat is not captured. I haven't tried this, but you could also increase the W/cfm of the AHU supply fans to represent the fan heat added by the DOAS, but the exact amount of heat getting added will vary with a variable speed supply fan, and the heat is really getting added to the wrong place (after the OA mixer, as opposed to before). So, the bottom line is you probably can't capture the DOAS fan heat correctly no matter what you do, unless there's some other way I haven't thought of.