Crown Boiler 24-03 用户手册

49

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 

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