A heating, ventilation and air conditioning (HVAC) system for an indoor space (10a,10b) of a building, the HVAC system comprising: a heat pump system configured to supply heat or cold to the indoor space (10a,10b), the heat pump system comprising a refrigerant circuit, a ventilation system configured to supply outdoor air to the indoor space (10a,10b), the ventilation system comprising a ventilation unit configured to draw outdoor air from the outside of the building and an air duct connected to the ventilation unit for guiding the outdoor air to the indoor space (10a,10b), a utilization-side unit provided in an indoor space (10a,10b), the utilization-side unit comprising a utilization-side heat exchanger directly or indirectly connected to the refrigerant circuit and configured to exchange heat with the indoor air of the indoor space (10a,10b), an air outlet in fluid communication with the air duct and an outlet valve for adjusting the amount of outdoor air flowing through the air outlet into the indoor space (10a,10b), at least one sensor (44,46) for detecting a parameter of the indoor space (10a,10b) and a control unit configured to control the outlet valve based on the parameter detected by the sensor (44,46), characterized in that the utilization-side unit comprises a housing, the housing defining a ventilation compartment and an air conditioning compartment, the utilization-side heat exchanger being accommodated in the air conditioning compartment and the air outlet and the outlet valve being accommodated in the ventilation compartment so that the outdoor air is flowable into the indoor space (10a,10b) without flowing through the utilization-side heat exchanger. a heat pump system configured to supply heat or cold to the indoor space (10a,10b), the heat pump system comprising a refrigerant circuit, a ventilation system configured to supply outdoor air to the indoor space (10a,10b), the ventilation system comprising a ventilation unit configured to draw outdoor air from the outside of the building and an air duct connected to the ventilation unit for guiding the outdoor air to the indoor space (10a,10b), a ventilation unit configured to draw outdoor air from the outside of the building and an air duct connected to the ventilation unit for guiding the outdoor air to the indoor space (10a,10b), a utilization-side unit provided in an indoor space (10a,10b), the utilization-side unit comprising a utilization-side heat exchanger directly or indirectly connected to the refrigerant circuit and configured to exchange heat with the indoor air of the indoor space (10a,10b), an air outlet in fluid communication with the air duct and an outlet valve for adjusting the amount of outdoor air flowing through the air outlet into the indoor space (10a,10b), a utilization-side heat exchanger directly or indirectly connected to the refrigerant circuit and configured to exchange heat with the indoor air of the indoor space (10a,10b), an air outlet in fluid communication with the air duct and an outlet valve for adjusting the amount of outdoor air flowing through the air outlet into the indoor space (10a,10b), at least one sensor (44,46) for detecting a parameter of the indoor space (10a,10b) and a control unit configured to control the outlet valve based on the parameter detected by the sensor (44,46), characterized in that the utilization-side unit comprises a housing, the housing defining a ventilation compartment and an air conditioning compartment, the utilization-side heat exchanger being accommodated in the air conditioning compartment and the air outlet and the outlet valve being accommodated in the ventilation compartment so that the outdoor air is flowable into the indoor space (10a,10b) without flowing through the utilization-side heat exchanger.