Your map has to have env cubemap entities spread across the map, you compile to hdr, then in the game you must use the following commands in the game console before loading the map: sv_cheats 1, mat_specular 0 (disables reflections), mat_hdr_level 2 ( puts the game in hdr mode), map cbe_fullmetalbunker_v7 (to open the map), buildcubemaps(builds reflections), disconnect (to exit the map), mat_hdr_level 0 (puts the game without hdr), map cbe_fullmetalbunker_v7(to reopen the map), buildcubemaps, disconnect, done!

mat_specular 1 (turn reflections back on) and here you can test your map using mat_hdr_level 2 to view it with hdr and mat_hdr_level 1 to view it without hdr.

Some tips to avoid problems is that if you change the name of the map, do it before doing the reflections using "save as...". Once you build the reflections you should not change the name of the map. And you should build the reflections before packaging custom content (if your map has it).

https://developer.valvesoftware.com/wiki/Cubemaps