  We have studied hybrid superconducting micro-coolers made of a double
Superconductor-Insulator-Normal metal tunnel junction. Under subgap conditions,
the Andreev current is found to dominate the single-particle tunnel current. We
show that the Andreev current introduces additional dissipation in the normal
metal equivalent to Joule heating. By analyzing quantitatively the heat balance
in the system, we provide a full description of the evolution of the electronic
temperature with the voltage. The dissipation induced by the Andreev current is
found to dominate the quasiparticle tunneling-based cooling over a large bias
range.
