## 2 Materials and Methods  
The numerical TRNSYS model was based on a real case geometry of four interconnected single-floor offices, partitioned by interior walls, and the data collected from monitoring these offices. The offices and the model itself have an area of 108 m\({}^{2}\), with the orientation of the facade being 15\({}^{\circ}\) SW, and represent a small part of the fifth floor of an office building in Ljubljana, Slovenia (46\({}^{\circ}\)40\({}^{\circ}\)N, 14\({}^{\circ}\)31\({}^{\circ}\)E). (Figure 1a) The location has a typical mixed climate, with some continental and Mediterranean characteristics, i.e., warm summers and moderately cold winters. These four offices were the subject of an extensive retrofit of the building envelope, the installation of water-filled ceiling heating/cooling panels, the installation of mechanical ventilation (with recuperation) and the renovation of the electrical system. The ceiling panels were designed as large metal sheets over the copper piping, covering roughly 60% of each office ceiling slab (Figure 1b) with no thermal insulation layer. In the product specification the cooling power was 80-90 W/m\({}^{2}\) per 10 K, whereas the heating power was 60-70 W/m\({}^{2}\) per 10 K of the temperature difference. Since the temperature difference in the offices can reach up to 7 K in the cooling mode, and up to 14 K in the heating mode, the power of the panels in the cooling mode can be as high as 63 W/m\({}^{2}\), while in the heating mode it can reach 91 W/m\({}^{2}\). The HVAC system was installed as a separate and autonomous energy system with its own solar power supply, and as such was equipped with sensors, metering devices and other supporting monitoring equipment. The ceiling heating/cooling panels were equipped with calorimeters to measure the amount of energy delivered to each office and with inlet/outlet temperature sensors. Also, the inlets and outlets of the mechanical ventilation system for transport of the tempered air in each office were equipped with electronic volume regulators and temperature sensors. All the office systems were designed to be managed by the newly installed building management system (BMS). The purpose of the BMS is to collect the measured values and give commands to each part of the system according to the measured values and logic (schedules) that are built in. As in the real offices, the geometry of the TRNSYS model involved four main zones and an unconditioned title above them as a surplus fifth model zone. Each of the four office zones in the model was subdivided into five equal horizontal layers, each containing one thermal node. A total  
Figure 1: (**a**) Office 2 of premises which were the basis for modeling; (**b**) schematic floor plan of the offices with the radiation ceiling panels indicated by the brighter rectangles. of 20 air thermal nodes were implemented. The system of nodes in the simulations was harmonized with the installation of the measurement locations of the air temperature in each of four offices, which consisted of five vertically installed temperature sensors arranged over the height of the room. This enabled a direct comparison between the measured and simulated air temperatures with the similarly distributed thermal nodes in the model without any ambition to run the heating/cooling system or evaluate the user's thermal comfort. The model was completed using a TRNSYS Type 56 block [11] with an identical structure of the building elements and indoor furnishings to the real offices. The main construction material of the building elements was concrete, with the exception of the internal walls, which were made of a lightweight gypsum sandwich or brick. The facade and the ceiling of the unheated attic were thermally insulated (U\({}_{\mathrm{facade}}\) = 0.28 W/(m\({}^{2}\)K), U\({}_{\mathrm{ceiling}}\) = 0.18 W/(m\({}^{2}\)K)).