The scroll refrigeration compressor includes a sealed casing, stationary and moving volutes including spiral wraps engaged in one another and defining the variable-volume compression chambers, a delivery chamber defined by the plate of the stationary volute and the sealed casing, a heat shield disposed in the delivery chamber and dividing the delivery chamber into a first volume defined by the plate of the stationary volute and the heat shield and a second volume defined by the heat shield and the sealed casing, and at least one flow passage arranged to communicate the first and second volumes. The compressor further includes at least one bypass passage arranged to communicate the first volume with an intermediate compression chamber, and at least one bypass valve disposed in the first volume and movable between closing and opening positions for closing and opening the corresponding bypass passage.