Honeywell SDC Service Manual page 133

SDC / DHC
EN2H-0221GE51 R0812
Combined operation for 2-stage heat generators
• As long as just one stage can meet the heat demand (stage II
inactive), stage I is switched according to switching
differential I.
• As soon as stage 2 is needed to meet the heat demand,
switching differential I takes over the switching on and off of
stage II and switching differential II takes over the switching of
stage I.
a Switch-off level stage I
b Switch-off level stage II
c Switch-on level stage II
d Switch-on level stage I
e Swap of switching
differential
f Theoretical progression
with stage I alone
1) Temperature drop becomes slower after every switch-off of
stage II, as stage I provides support.
2) Switch-on level stage II is no longer reached, temperature is
reached from stage I.
3) Temperature drops due to increased heat demand under
switch-on level stage II.
Hydraulic Components
g Area 1 high use (start-up),
coverage of heating demand at
full load (burner stages I and II)
h Area 2 low use, coverage of
heat demand with partial load
(burner stage I only)
i Area 3 increased use,
coverage of heating demand at
full load (both burner stages)
x Boiler temperature
y Time
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