AbstractThe present study is concerned with the thermal indoor environment and HVAC system energy consumption of a detached, one- story, single family, plus-energy house during a cooling season. The house was located in Denmark and it has been used as a full- scale experimental facility for one year. The house was cooled by a floor cooling system and was ventilated with a mechanical ventilation system. Different operative temperature set-points and different ventilation rates were tested. Operative temperature at a representative location inside the occupied zone was used as an indicator of the thermal indoor environment. For the energy consumption of the HVAC system, air-to-brine heat pump, mixing station and controller of the radiant floor, and the air handling unit were considered.The measurements were analyzed based on the achieved indoor environment category (according to EN 15251:2007), overheating hours (according to DS 469:2013) and the energy consumption. Operation and switchover of the heating and cooling system during the transition periods (i.e. May and September) proved to be a challenge. Overheating was a significant problem. Decreasing the operative temperature set-point (of the floor cooling system) and increasing the ventilation rate provided a better thermal indoor environment but with increased energy consumption. The thermal indoor environment and energy performance of the house can be improved with decreased glazing area, increased thermal mass, installation of solar shading, adjustment of the orientation of the house, and natural ventilation.