Laundry dryer of the type comprising a heat pump system having a refrigerant circuit for a refrigerant and comprising a process air circuit in communication with a laundry container suited for receiving laundry to be dried using process air, said refrigerant circuit comprising: a central processing unit, a refrigerant, a first heat exchanger for heating said process air and cooling said refrigerant, said first heat exchanger comprising a heat exchanger outlet for expelling the heated process air for said laundry container; a second heat exchanger for cooling said process air and heating said refrigerant; a refrigerant expansion device arranged in said refrigerant circuit between said first heat exchanger and said second heat exchanger; and a rotary or a scroll compressor arranged in said refrigerant circuit between said second heat exchanger and said first heat exchanger, said compressor comprising a compressor chamber and a compressor inlet where said refrigerant is sucked for said compressor chamber, characterized in that the product of the volume (Vd) of said compressor chamber and the refrigerant density at said compressor inlet in steady state condition of said heat pump system is comprised between 40 cm 3∗ kg/m 3 and 250 cm 3∗ kg/m 3; wherein the refrigerant density is calculated using the refrigerant temperature detected at the compressor inlet and/or the refrigerant pressure detected at the compressor inlet and/or at the evaporator inlet 23a; wherein the correlation between the refrigerant density and the detected values are stored as a function or as a table in a memory of the central processing unit; and wherein said steady state condition is a state condition reached by said heat pump system after a period of time (t1-t0) from its activation when thermodynamic conditions are substantially stable over time. a central processing unit, a refrigerant, a first heat exchanger for heating said process air and cooling said refrigerant, said first heat exchanger comprising a heat exchanger outlet for expelling the heated process air for said laundry container; a second heat exchanger for cooling said process air and heating said refrigerant; a refrigerant expansion device arranged in said refrigerant circuit between said first heat exchanger and said second heat exchanger; and a rotary or a scroll compressor arranged in said refrigerant circuit between said second heat exchanger and said first heat exchanger, said compressor comprising a compressor chamber and a compressor inlet where said refrigerant is sucked for said compressor chamber, characterized in that the product of the volume (Vd) of said compressor chamber and the refrigerant density at said compressor inlet in steady state condition of said heat pump system is comprised between 40 cm 3∗ kg/m 3 and 250 cm 3∗ kg/m 3; wherein the refrigerant density is calculated using the refrigerant temperature detected at the compressor inlet and/or the refrigerant pressure detected at the compressor inlet and/or at the evaporator inlet 23a; wherein the correlation between the refrigerant density and the detected values are stored as a function or as a table in a memory of the central processing unit; and wherein said steady state condition is a state condition reached by said heat pump system after a period of time (t1-t0) from its activation when thermodynamic conditions are substantially stable over time.