Assuming that assigning the values to local variables is important,
something like the following might be used:

SELECT
@MAX_HEPE_OUT1 = COALESCE( MAX( CASE when Outputsource = 1 then Hepe
else <minvalue> end ),0),
@MIN_HEPE_OUT1 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT1 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT2 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT2 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT2 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT3 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT3 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT3 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT4 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT4 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT4 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT5 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT5 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT5 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT6 = COALESCE( MAX(CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT6 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT6 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT7 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT7 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT7 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
@MAX_HEPE_OUT8 = COALESCE( MAX( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@MIN_HEPE_OUT8 = COALESCE( MIN( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0),
@AVG_HEPE_OUT8 = COALESCE( AVG( CASE when Outputsource = 1 then
Hepeelse <minvalue> end ),0)
FROM #TMP2_UB_HEPE
WHERE
PMM_DATETIME BETWEEN @dINIT_DATE AND @dEND_DATE_AUX