tekmar 279 Steam Control - Manual (Page 7)

7 of 24 © 2010 D 279 - 05/10
Heating Cycle - Cycle Length Section D
The Adjust menu includes a setting called Cycle that
determines how often the heating system will run. During
each heating cycle the boiler is turned on once, and the
boiler is turned off once. Each building has a natural heat up
and a cool off rate. This is determined by many factors such
as the size and length of runs in the steam heating system,
the size and mass of the radiators, and the heat loss of the
building. The factory default is 60 minutes. When using
optional Indoor Sensors, an automatic setting is available
that allows the control to learn the natural temperature
swing of the building. If the optional Indoor Sensors are
not used, then the only method of adjustment is trial and
error by the installer. The control is designed to operate on/off steam boilers or
steam valves. These systems can only produce heat at
a fixed rate (on = 100%, off = 0%). In order to match the
heat loss of the building, the steam heating system must
be cycled on and off. To determine the boiler on time, the
control uses the percent on time required by the heating
curve and multiplies this by the heating cycle time. While
operating in the heating cycle, the Status field will have a
pointer indicating Heat Cycle.
Example: When the outdoor temperature is 32°F (0°C), the
heating curve may determine a 50% on time is required. If the
heating cycle is 60 minutes, then the boiler on time is: Boiler On
Time Per Heating Cycle = 0.5 x 60 minutes = 30 minutes.
60 minute cycle
Boiler On
Boiler On
Boiler Off
30 minutes
on time
30 minutes
on time
30 minutes
off time
30 minutes
off time
60 minute cycle
30 minutes
on time
30 minutes
on time
30 minutes
off time
30 minutes
off time
30 minute cycle
Off On Off On Off
On Off
On Off On
Boiler
Operation
Boiler Off
15 minutes
on time
15 minutes
on time
15 minutes
off time
15 minutes
off time
15 minutes
on time
15 minutes
on time
15 minutes
off time
15 minutes
off time
30 minute cycle 30 minute cycle 30 minute cycle
15 minutes
on time
15 minutes
on time
15 minutes
off time
15 minutes
off time
15 minutes
on time
15 minutes
on time
15 minutes
off time
15 minutes
off time
Off On
Boiler
Operation
50% On Time With a 60 Minute Heating Cycle
50% On Time With a 30 Minute Heating Cycle
Lockout Differential Section E
The Adjust menu includes a setting called Lockout Differential.
When a condensate return sensor is present, a lockout
differential can be set to ensure that any remaining steam
in the system condenses and the condensate has time to
return to the boiler. This increases the efficiency of the system
by removing the latent heat of the steam remaining after
the burner is shut down, and lengthening the cycle so that
remaining heat is allowed to radiate into the building.
The lockout differential is the number of degrees the
condensate return sensor temperature must fall below the
steam established setting before the control can operate
the heating system for the next cycle. During the lockout
differential, the heating system is held off, and the Status
field will have a pointer indicating Lockout Differential. The
factory default is a 25°F lockout differential.
There is no exact method to set the Lockout Differential for
a particular building; it is a process of trial and error. If the
building tends to over heat, the lockout differential should
be increased to allow the steam system to cool down further
before starting the next cycle. If the building tends to under
heat, the lockout differential should be decreased to allow
the next heating cycle to start sooner.
45 minutes off time 45 minutes off time
Boiler Off Boiler On Boiler Off
Steam established - start cycle
Steam established
temperature setting
Condensate
Return Temperature
30°F Lockout
Differential Setting
E
s
ta
b
li
s
h
in
g
S
te
a
m
(w
a
rm
-u
p
p
e
ri
o
d
)
Establishing Steam
(w
arm-up period)
L
o
c
k
o
u
t
P
e
ri
o
d
Lock
out P
e
riod
E
s
ta
b
li
s
h
in
g
S
te
a
m
(w
a
rm
-u
p
p
e
ri
o
d
)
Establishing Steam
(w
arm-up period)
L
o
c
k
o
u
t
P
e
ri
o
d
Lock
out P
e
riod
Steam Established
on on
off off
Boiler On
Boiler
Operation
220°F -
210°F -
200°F -
190°F -
180°F -
170°F -
160°F -
150°F -
140°F -
15 minutes
on time
15 minutes
on time
60 minute cycle 60 minute cycle
Steam established - start cycle