THE REQUEST: COLLECTIVE CIRCULATION SYSTEM. For the collective heating, conditioning, cooling and hot water system of this hotel, a group was supplied consisting of 6 main multistage centrifugal electric pumps with a vertical axis type NKVE, 4 DPH-E twin circulators with a DIALOGUE device and energy class A certification, and 2 CPE circulation pumps with in-line outlets, which, thanks to the use of the HYDRODRIVER, adapts automatically to the various requests of the system, maintaining constant differential pressures.