Subject classification: 63.22.+m; 73.21.La; S8.11 Different types of electron (hole) ground energy level renormalization due to confined (L) and interface (I) phonons in a spherical quantum dot embedded in a semiconductor medium are investigated on the example of b-HgS/CdS nanoheterosystem. It is shown that for all QD sizes the shift of the ground energy level (D) is generally caused by the interaction of electron and confined phonons of the dot (L 0 ) and of the medium (L 1 ). The contribution of interface phonons (I + , I --) to the magnitude D is comparable with the contribution of L-phonons only at small QD radii (it is three times smaller). For all QD radii the interaction with all phonons through all states of the continuous spectrum gives a one order smaller contribution to D than the interaction through the states of the discrete spectrum. When the QD radius increases the I-phonon contribution decreases and the L-phonon one increases, consequently, the total shift becomes closer to its magnitude in bulk HgS crystal.