Pub shortly working to conserve energy (8)
I believe the answer is:
hostelry
'pub' is the definition.
(thesaurus)
'shortly working to conserve energy' is the wordplay.
'working' indicates an anagram.
'to conserve' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'shortly' with letters rearranged gives 'hostlry'.
'hostlry' placed around 'e' is 'HOSTELRY'.
(Other definitions for hostelry that I've seen before include "Inn (arch., joc.)" , "Lodging house" , "Holy rest (anag.)" , "Old word for an inn" , "Old name for inn" .)