Equithermal regulation

Equithermal regulation of the temperature in the room consists in setting the temperature of the heated water (by regulating the heat source) based on the outside temperature. At a lower outside temperature, a higher temperature of the supplied heated water is required in order to achieve a balance between the supplied heat and the heat losses of the room, so that the room temperature remains constant.

For a given room, it is possible to establish a system of so-called equithermal curves (also "heating curves"), which describe the mutual dependence of the temperature of the heated water, the room and the outside temperature.

Based on the required room temperature, it is possible to select a certain curve and regulate the temperature of the heated water according to the outside temperature. Of course, several basic questions immediately follow from the given description. What does it actually mean "is it possible to establish a system of equithermal curves?"
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The set of heating curves is determined both on the basis of the required temperature in the room (e.g. for the required temperature of 25°C) and also on the basis of knowledge of the lowest outdoor temperature that has ever been reached in the given area. A typical course of the dependence of the heated water temperature on the outside temperature, i.e. equithermal curves, is shown in Fig. 1.

This figure shows three equithermal characteristics for the required room temperatures of 25°C, 20°C and 15°C. The mentioned equithermal characteristics are implemented in the corresponding devices most often referred to as equithermal regulators. In these equithermal controllers, individual equithermal curves are implemented and most often denoted by certain numbers.