Generally speaking, heat source capacity of HVAC system is designed by maximum thermal load calculation method. Considering peak thermal load of the buildings emerge only a few days throughout the year especially in highly insu-lated buildings, heat source tend to deteriorate its performance due to partial load operation. The purpose of this study is to propose new design method for highly insulated buildings. Firstly, operational state of existing HVAC systems in Hokkaido during winter was clarified. Second, case studies on operational state of heat source and indoor temperature using EPS-r were carried out.
