  While the grand canonical partition function Z_{GC}(mu) with chemical
potential mu explicitly breaks the Z_3 symmetry with the Dirac determinant, the
canonical partition function at fixed baryon number Z_C(B) is manifestly
Z_3-symmetric. We compare Z_{GC}(mu=0) and Z_C(B=0) formally and by numerical
simulations, in particular with respect to properties of the deconfinement
transition. Differences between the two ensembles, for physical observables
characterising the phase transition, vanish with increasing lattice size. We
show numerically that the free energy density is the same for both ensembles in
the thermodynamic limit.
