Comment by rcxdude

You can get a COP of ~3-4 out of regular TECs, but only at pretty low temperature differences. That's the killer, fundamentally the TEC material itself is thermally conductive and heat really wants to flow back the other way, so no matter how well it moves the heat, it winds up fighting against the heat load generated by itself. A refrigerant based heat pump works much better because the heat basically only moves in the direction the refrigerant itself is moving.