Crown TWZ065, Installation Instructions Manual

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34
Or
(Circulator Overrun) - Determines how long the Heating Circulator will operate after the call for heat ends. In some cases, this
can help reduce energy consumption by sending heat stored in the boiler out into the system. At the same time, caution should
be exercised before setting this value to something other than zero. Before doing so, verify that the system will permit flow (e.g.
flow is not completely cut-off by closed zone valves) and that the overrun will not cause overheating problems.
Circulator overrun is only possible on the heating zone controlled by T-T. The ZC Circulator will not over-run, even if it is used
as a second heating zone.
PP
(Thermal Purge Time) - Upon a call for heat, the boiler will prevent burner operation until either:
• The water temperature drops below the Thermal Purge Start Temperature (
St
) OR:
• The thermal purge time has passed
For some examples of this operation, see Table 12.6. If the “ZC” zone is used for space heating (ZC=Zr), this thermal purge
function will also keep the burner off at the beginning of a call from the thermostat connected to the “ZR” terminal in the manner
described above. If the “ZC” zone is being used for DHW (ZC=dh), the burners will immediately come on upon a call for DHW
as long as the water temperature is below the high limit setting.
Thermal purge is only invoked when a call for heat first appears and the boiler is not already firing. For this reason, if the boiler
is already firing in response to an call for heat, and a call for heat appears at the second zone, the boiler will continue to fire.
taBlE 12.6 EXaMPlEs OF tHErMal PurGE OPEratIOn
Example
#
Call for
Heat
From
Use of “ZC”
Zone
Thermal Purge Settings Boiler
Temp at
Begin
Call Boiler Behavior Time (
Pt
)
Start Temp
(
St
)
1 T-T N/A 2 min. 140F 130
• “C1-C2” Circulator starts
immediately
• Burner fires immediately
2 T-T N/A 2 min. 140F 150
• “C1-C2” Circulator starts
immediately
• Burner fires when either:
2 minutes have passed
OR
Temperature falls below 140
3 ZR DHW (
ZC
=
dh
) 2 min. 140F 150
• “ZC” Circulator starts immediately
• Burner fires immediately
4
Heat T’stat
on ZR
terminals
Heat (
ZC
=
Zr
) 2 min. 140F 150
• “ZC” Circulator starts immediately
• Burner fires when either:
2 minutes have passed
OR
Temperature falls below 140
5 T-T N/A 2 min. 145F 150
• “C1-C2” Circulator starts
immediately
• Burner fires when either:
2 minutes have passed
OR
Temperature falls below 145
6 T-T N/A 3 min. 140 150
• “C1-C2” Circulator starts
immediately
• Burner fires when either:
3 minutes have passed
OR
Temperature falls below 140