The subject of my thesis was to design a system of ventilation, heating and cooling of an administrative building, located in Liptovsky Mikulas. The proposal began when determining the marginal requirements for the state of the indoor environment. Further, heat gains and heat losses of the building were calculated, on the basis of which we designed the required amount of incoming air, and we also determined the need for heat and cold for the space.According to the quantity of necessary air, we have oversized the appropriate air handling unit, the end distribution elements for the air inlet and outlet, and we have over-sized the air-conditioning pipeline to connect the entire system.Last but not least, we have designed a system for cooling and heating the building, using internal VRV cassette units with a heat and cool source external condensing unit.As some heat gains and heat losses will cover the incoming air, we have designed a reversible air-water heat pump as a heat and cold source for the air-conditioning unit.