Chap that is conserving energy, a small-minded type (6)
I believe the answer is:
meanie
'a small-minded type' is the definition.
(I've seen this before)
'chap that is conserving energy' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'conserving' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mca).
'man'+'ie'='manie'
'manie' placed around 'e' is 'MEANIE'.
(Other definitions for meanie that I've seen before include "nasty person" , "nasty type" , "Nasty piece of work?" , "Unkind person (informal)" , "Stingy person (informal)" .)