Aluminum removable pump box, it is designed to be removable in order to do maintenance to the pump and reinstall it again.
By insulating exterior HVAC duct with R8 insulation helps to maintain a constant temperature. In the same way, the aluminum jacketing prevents insulation does not get wet/damage by the rain.
Insulating pipes helps maintain constant temperature and prevents heat or cold loss. On the other hand, using pvc can work for many purposes that range from, weather barrier, color coding systems, and protecting insulation from getting damage.