Geothermal water-to-water heat pump is used as a device that uses the accumulated heat of groundwater and with the help of electricity converts thermal energy depending on the needs of the designed architectural object into energy needed for the heating or cooling system. For the purpose of groundwater abstraction, a well water system is used, which consists of two pumping wells that should be at least ten meters apart and one abyssal well. In this paper, calculations and heat balance for water - water heat pump for production and business building are made. The production and business building with a usable area of 3029 m2 for which it is necessary to design the GViK system is located in the economic zone of the city of Varaždin. According to the standard HRN EN 12831, heat losses amounting to 197.4 kW in the heating temperature regime of 55/45 °C were calculated, and according to the VDI 2078 standard, heat gains amounting to 291.2 kW in the temperature regime 7/12 °C were calculated. Passive cooling is designed for the needs of the production hall in the amount of heat gains of 58.5 kW and the passage of cold water in the mode of 16/19 ºC. For ventilation of the production plant and storage, air-conditioning chambers with a capacity of 20000 m3/h for the production plant and 6000 m3/h for the storage with associated ducts for air outlet and supply have been designed. For separate units of the office part of the building, designed ventilation devices with an air recuperator and a duct system were calculated. Ventilation of sanitary facilities is performed by small silent fans with a delay in the start of work. For year-round cooling of technical rooms, the project envisages cooling with mono-split air conditioners with a capacity of 3.6 kW for the GRO room and 5 kW for the server room. The basic task and goal of any heating, ventilation and air conditioning system is to provide thermal conditions (thermal comfort) in which the users of the space feel comfortable. In order to achieve this task, based on the conceptual design of the heating, ventilation and air conditioning system according to the given space, it is necessary to make a quality construction with emphasis on space insulation, precise heat balance calculations and make the right choice of equipment.