Preferred FlexFit 110 - Page 81

Parameters 4-73
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
PP
AA
RR
AA
MM
EE
TT
EE
RR
SS
Finally, parameter "P3.5.1 T27 Options" can cause a CFH based of a 120 V contact closure to terminal 27.
See "Figure 4 – 5 Call for Heat Logic" for a owchart of the call for heat logic, and see below for a description of the parameters
mentioned above.
Figure 4 – 5
Boiler Outlet
Rate Local SP
CFH Start Deviation
CFH Stop Deviation
CFH Terminal
DHW, Rate PID Override SP
(if T27 Options = DHW w/SP Override)
SP Deviation CFH
OR
Whichever
is greater
Set-point
CFH Local Mode
4-20 mA SP
Modbus SP
(40048)
Local or Remote
Remote Modulation
L
R
Modbus CFH
(00274 or 49539 bit 1)
CFH Remote Mode
Remote or
Local CFH
Local or Remote
LR
DHW CFH
(with or without
SP Override)
Warm Standby w/ LFH CFH
T27 Options
Call For Heat
Deviation from
Set-point CFH
Start when
boiler outlet < (SP - CFH start dev)
Stop when
boiler outlet > (SP + CFH stop dev)
OR
Modbus Warm
Standby Enable
(00275 or 49539 bit 2)
Not Used
(CFH is always active)
Call for Heat Logic
P3.4.1 cFh local Mode
Menu > Optional Features > Local/Remote Mode Password Level: Technician Restricted? No
Determines the FlexFit Call for Heat (CFH) logic in local mode.
Options: Not Used: Local mode CFH is not used.
CFH Terminal: CFH is based on a 120 V contact closure to terminal 17.
SP Deviation: CFH is based on the boiler outlet deviation from the current setpoint. This is based on steam pressure
or water temperature.
Error Check If "P3.1.1 Local Firing Rate Control Source" equals 135 Ohm Demand or 4-20 P7810 Demand, then "CFH Local
Mode" cannot be set to SP Deviation.
P3.4.2 cFh Start deVIatIon
Menu > Optional Features > Local/Remote Mode Password Level: Operator Restricted? No
This determines the amount of deviation from setpoint needed to start a Call for Heat (CFH) sequence.
Options: -50.0 to 500.0 [Default 5.0]
The boiler starts when the boiler outlet drops below the current setpoint by this amount for more than 2 seconds.
Note
"CFH Start Deviation"
and "CFH Stop Devi-
ation" are ignored if
neither "P3.4.1 CFH
Local Mode" nor "P3.4.5
CFH Remote Mode" are
set for SP Deviation.