This article discusses the comparison of simulated and experimental data for a solar heat supply system based on flat collectors integrated into an office building to meet the need for heat. A new design of a flat solar collector has been developed, in which thermal insulation occurs in a heat-insulating transparent double-glazed window. Also, to reduce the radiation on the surface of the heat receiver, a selective coating was used to prevent heating from infrared radiation. The TRNSYS model has been developed and tested on experimental data and then used for optimization purposes. Temperature data for a flat solar collector were determined using the commercial software package CFD (Computational Fluid Dynamics) ANSYS FLUENT 19.0. The numerical analysis of temperature data confirmed the accuracy of the results obtained as a result of experimental analysis. The results showed that using solar energy strongly depends on the collector area and storage volume. The proposed approach can be used to optimize the design of solar heat supply systems.