Crown Boiler 24-07 User Manual
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ASHRAE Fundamentals for the area closest to
the installation. This value has a default of 10°F,
and is adjustable between –60ºF to 32ºF.
e. WWSD – The Warm Weather Shut Down feature
is used only when the outdoor reset feature
is selected. (OUTDR DESIGN = ON) If the
outdoor temperature rises above the WWSD
value, WWSD will be displayed. If a demand
for heat is generated when the control is in the
WWSD mode, the boiler will be disabled. The
default for the WWSD is 70ºF, but is adjustable
from 35ºF to 100ºF.
f. MIX MIN – This represents the minimum mix
target supply temperature when the outdoor reset
feature is selected. (OUTDR DESIGN = ON)
This is the lowest temperature the controller is
allowed to use as a MIX TARGET temperature.
During mild conditions, if the RTC calculates a
MIX TARGET below the MIX MIN, the target
will be adjusted to match the MIX MIN setting.
g. MIX MAX – This represents the highest
temperature allowed as the MIX TARGET
temperature when the outdoor reset feature is
selected. (OUTDR DESIGN = ON) If the RTC
calculates a MIX TARGET higher than the MIX
MAX, the MIX TARGET will take the value of
the MIX MAX. Typically, this is set between
200ºF and 220ºF. The temperature must be set
below the lowest permissible temperature for
any system related component affected by boiler
supply water.
h. OPEN DELAY – This value represents the
number of seconds required for the actuator to
open through 90 degrees of rotation. Leave in
default value of 50 seconds.
i. BOIL MIN – This is the minimum boiler return
temperature allowed. The minimum value has
been set to 135ºF, adjustable to as high as 230ºF.
The RTC will control the diverting valve while
maintaining a minimum BOIL MIN temperature.
Setting should remain at 135ºF unless a higher
minimum boiler temperature is required.
j. BOIL MIN DELAY – This represents the time
(in seconds) required for warm-up during an
initial cold start. This prevents the counter
from including cold start warm up time in the
total boiler operation time below 135ºF. This
grace period is provided for every heat demand
cycle until 135ºF has been sensed at the return
sensor. Once the return sensor has sensed a
return temperature reading of 135ºF, after the
heat demand cycle has initiated, the grace period
is terminated. The warm up time includes a 90
seconds of pre-purge time. Use the values in
Table V for the correct application.
k. PUMP DELAY – Pump delay represents the
time (in seconds) for pump purge (boiler
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circulator purge) after a heat demand cycle. This
minimizes the amount of boiler temperature
overshoot at the end of a boiler cycle. During
the pump purge the diverting valve will
continue to operate and prevent low return water
temperatures from entering the boiler. At the
end of the pump purge period the diverting valve
will be immediately closed. The default PUMP
DELAY is set to 30 seconds.
l. UNITS – The temperature units can be changed
to either Fahrenheit or Celsius. The default
temperature unit is Fahrenheit.
4. ERROR MESSAGES – Error messages are shown
on the LED display. The function in error will be
shown as a black background label in the LED.
Most of the errors indicate an open or short circuit,
connected to the RTC. The RTC Installation and
Maintenance Manual identifies common errors.
Cycle through the error messages and repair as
required.
a. Return Sensor Error – If the return water
temperature sensor has been damaged or omitted,
the BOIL item will be displayed as either a
“short” or “open” circuit. This will force the
mixing device (i.e. 3-way valve) to run at a
fixed 30% open position. The system may not
receive enough heat nor will it be fully protected,
however a significant change will be obvious to
occupants and/or operators.
b. Operation Below Minimum – If the return sensor
has been damaged or omitted, and the return
water is allowed to return to the boiler below
135ºF, the BOIL MIN field will be displayed
along with ERR. The failure must be identified
and repaired immediately since the boiler
has been operating in a condition that fosters
premature boiler failure.
5. COMPONENT EXERCISE - The RTC will exercise
Table V: Boil Min Delay Settings