Satchwell IAC 600 - Page 17

Fi
g
.3
PRESET 3 – 3 Boiler Sequence Control (compensated) with a separate HWS System
Time re-synchronization
Pumps failed signal
Clear pumps failed
Pump 1
Pump 2
Boiler
1
High Limit Thermostat
(manual reset) and
burner controls.
*
Flow
Boiler
2
Boiler
3
Pumps Failed
Pump 2
Pump 1
Boiler 2
HWS
Valve
Backend
Valve 1
Supply
Backend Valve 3
HWS Sensor
Outside Sensor
Flow Sensor
Pump
Clear Pumps Failed
Connect to any IAC
isolated ground
terminal
Connect to any IAC 600
terminal
Note:–
The actual terminal block is a
double block running across
the bottom of the IAC. The
top (double height) block
contains terminals 1 to 33 and
the bottom (single height)
contains 34 to 41 and all of
the Ground and isolated
Ground terminals. Terminal
numbers run from left to right.
6
Ensure Terminal 2 is
earthed.
66
The 24Vac Supply must
be fused with a 2A fuse.
Terminal 5 is not used.
If an earth busbar is to be
used then it must be
connected to a single Ground
terminal on the IAC by a
single cable which should be
as short as possible and no
more than 150mm long. Earth
wire minimum 30/0.25
(1.5mm
2
) Stranded Cable.
Connect to any
IAC 600
terminal
HWS
Valve
Boiler 1
Time re-synchronization
Backend Valve 2
Boiler 3
TIME SCHEDULES
08:00 to 17:00
Connected to the compensator and HWS loops.
The time re-s
y
nchronization input will re-s
y
nchronize the IAC time to
midni
g
ht Monda
y
.
COMPENSATOR
Schedule OUTSIDE SUPPLY
080
10 50
20 20
The outside temperature value is fed into a look-up table. The result
is passed to the controller RPW input and is used to set the controller
set value.
Proportional Band 10
Inte
g
ral Action 300
Derivative Action 0
Ramp Time 60
Sample Time 10
BOILER/BACKEND VALVE
The lead boiler backend valve is alwa
y
s held open, with the others
bein
g
enabled on demand. The lead boiler rotates ever
y
100 hours.
The lead boiler is enabled when the control demand si
g
nal exceeds
25% with the second boiler and backend valve bein
g
enabled at 50%
and the third at 75%. There is a 5% h
y
steresis on all three steps.
The call for heat si
g
nal from the HWS is linked to the lead boiler to
ensure that the boiler fires if HWS is re
q
uired under low load
conditions.
PUMPS
Two pump outputs are supplied, Pump 1 normall
y
runs when the
controller is re
q
uestin
g
heat. In the event of pump 1 failin
g
to run, a
differential pressure switch si
g
nals the IAC which enables pump 2.
In the event of pump 2 failin
g
the "pumps failed" output is enabled. A
"clear pumps failed" input is supplied to enable the failed pumps to
be used once the
y
have been repaired or reset.
VALVE OPTIONS
Both the HWS and backend valve actuators ma
y
be 0 to 10Vdc or
24Vac driven, it should be noted however that valve operation in all
cases is purel
y
on/off and not modulatin
g
.
05/98 17 - 24 DS 2.951A