The invention relates to a method for operating and/or monitoring an HVAC system (10), in which medium circulating in a primary circuit (26) flows through at least one energy consumer (11, 12, 13), the medium entering with a volume flow (φ) through a supply line (14) into the energy consumer (11, 12, 13) at a supply temperature (TV) and leaving the energy consumer (11, 12, 13) at a return temperature (TR) via a return line (15), and transferring heat or cooling energy to the energy consumer (11, 12, 13) in an energy flow (E). A considerable improvement in the operating behavior of the system is achieved by empirically determining the dependence of the energy flow (E) and/or the temperature difference (AT) between supply temperature (TV) and return temperature (TR) on the volume flow (φ) for the energy consumers (11, 12, 13) in a first step, and by operating and/or monitoring the HVAC system (10) according to the determined dependency or dependencies in a second step.