Refrigeration plant for refrigeration and air conditioning comprising at least a first set of compressors whose inlets for the plant refrigerating fluid are connected to a common first inlet collector means and whose outlets are connected to a common first outlet collector means connected to a first pipe provided with a set of shunt means (26, 27) for the refrigerating fluid each one assigned to insert or isolate from said first pipe a respective first heat exchanger (28, 29) assigned, in the state of insertion along the first pipe, to transfer to a secondary fluid the heat of the refrigerating fluid cooling or condensing the latter; said first pipe is also provided with a first branch having a first valve means for opening and closing the first branch that is connected to the first pipe between the first outlet collector means and the shunt means (26, 27); the first branch is connected to the first inlet collector means by a first pressure regulating valve and a first way of a second heat exchanger with the refrigerating fluid of a second branch connected to the first pipe closely downstream to one of the first heat exchangers and connected to the first inlet collector means through a second pressure regulating valve and through the second way of the second heat exchanger; said first pipe further comprises, downstream to one of the first heat exchangers, a connecting portion connected to the outlets of the second heat exchanger, and said first pipe further comprises a second closing valve means for end closing the portion or for the one way flow of the fluid and it comprises a third pressure regulating valve and, downstream to the latter, a third exchanger assigned, in a flow condition of the refrigerating fluid along the said portion of the first pipe, to transfer heat from a secondary fluid to the refrigerating fluid cooling the secondary fluid; the second closing valve means is downstream to said third exchanger and said plant further comprises control means for a programmed actuation of said compressors, shunt means (26, 27), valve means (31, 41), regulating valve (33, 37, 38) and each of the active element of the plant; said control means being programmed at least for a first operation in which the shunt means (26, 27) and the first valve means allow the flow of the refrigerating fluid compressed by the first set of compressors through at least one of the first heat exchanger, through both the first and second pressure regulating valves (33, 37) and both ways of the second heat exchanger to the first inlet collector means and for a second operation in which the shunt means (26, 27) and the first valve means route the refrigerating fluid compressed by the first set of compressors to transit through at least one of the first heat exchangers (28, 29), the third pressure regulating valve, the third exchanger and the second valve means up to the first inlet collector means; said plant is characterized in that it further comprises a second set of compressors whose outlets are connected to the first outlet collector means and whose inlet for the plant refrigerating fluid are connected to a common second inlet collector means fed by the refrigerating fluid by a second pipe having a connection means that connects it to the first pipe downstream to the first heat exchanger and upstream to the third pressure regulating valve; from said connection means the second pipe has a first pressure regulator means, it passes through a first way of a fourth exchanger and it flows into a receiver - separator means from which it outflows from the outlet for the refrigerating fluid in the liquid state and it proceeds to feed a set of users (53, 54) at normal temperature and/or low temperature flowing through them then it flows in the second inlet connector means; an outlet for the steam of the receiver - separator means is connected to the second inlet connector means through a second pressure regulator means and the second way of the fourth exchanger; downstream to the connection means and upstream to the first pressure regulator means, the second pipe passes through a first way of a fifth exchanger; an outlet for the steam of the receiver - separator means is connected to respective shunt means actuated by the control means to connect said outlet to the second valve means directly or through the second way of the fifth exchanger.