In this paper gray-box models of the residential heating, ventilation and air conditioning (HVAC) system were developed. The HVAC system comprises of several subsystems such as energy recovery ventilator (ERV), air handling unit (AHU), buffer tank (BT), radiant floor heating (RFH) system, zone and ground source heat pump (GSHP) whose models can be identified separately and combined to obtain the model of the full system. The parameters of the subsystem models were identified from the data measured from the instrumented TRCA Archetype Sustainable House (TRCA-ASH) HVAC systems located at Kortright Centre for Conservation in Vaughan, Ontario, Canada. Individual subsystem models were combined to obtain the full system model which replicates the performance of the existing HVAC system and provides the cost estimate for running the HVAC system. Existing HVAC system uses ON/OFF controllers for zone temperature and BT temperature control. The ON/OFF controllers were integrated into the full scale system model and energy estimates were calculated for the operation of primary and secondary components (e.g., GSHP, fans and pumps). This model can be used to further investigate the effects of more advanced controllers (e.g., PID, model predictive control-MPC) and energy conservation strategies (e.g., set-point reset, passive/active thermal energy storage) in the simulation before implementing on the existing HVAC system. (C) 2014 Elsevier Ltd. All rights reserved.