Heating system curve — dependence of the water temperature in the heating system on the outside air temperature.
The temperature of the water at the entrance to the heating system depends on the temperature of the outside air, that is, the lower the temperature of the outside air, the higher the temperature of the water should go into the heating system. The temperature schedule is selected during the design of the building's heating system, the size of the heating devices, the water flow in the system, and the diameter of the pipelines depend on it.
Two numbers are used to indicate the temperature graph, for example, 90-70°C — this means that at the calculated outside air temperature (for Kyiv -22°C), to create a comfortable air temperature inside the room (for housing 20°C), water with a temperature of 90°C should enter the heating system, and exit from it with a temperature of 70°C.
Temperature graphs are used when debugging and analyzing the operation of heating systems. So, for example, an overestimated water temperature at the exit from the heating system indicates a high flow of water through this branch of the heating system, and an underestimated one indicates a lack of flow.
Heating systems of buildings up to 10 floors built in the last century were designed for a heating schedule of 95-70°C, and in buildings with more floors, a schedule of 105-70°C was adopted. When calculating the heating systems of modern buildings, the temperature schedule is taken at the discretion of the designer and is most often 90-70°C or 80-60°C, although any other can be taken.