Update

Justin My experience is on cooling side only, we have little use for heating on the DCS we have modelled. It would depend if you particular target in mind for the small building and/or are you planning on using the DCS to justify its good energy performance? I would suggest targeting efficent features in the small building (required anyway to prove it complies with ASHRAE) Then I would recommend considering using the default COP of 4.4 for the whole DCS plant as a starting point. If you do a really detailed model and have very efficent plant you can have a higher COP by around another 10-15% . If that makes a big difference to your overall strategy then look at it in more detail. But from experience I would stick with the defaults in concept stage and for LEED points evaluation. Only model in detail to develop up the detailed plant selections and control strategies to justify upgrading the DCS plant if you need to justify further changes to improve its efficency. As for software we use TAS or IES for the buldiling and cooling loads. For the DCS simulation we use a very complex computer program otherwise known as excel with 8760 rows and hourly calculations.