tekmar 374 Universal Reset Control - Manual (Page 8)

© 2009 D 374 - 03/09 8 of 36
Boiler Mass
The boiler mass setting allows the installer to adjust the control to the thermal mass of the type of heat sources used in the
application. If the heating system is causing the boiler(s) to be staged on and off in rapid succession, a higher boiler mass
setting will result in a decrease in the amount of cycling. Conversely, if the system is slow to respond to heat requirements, then
decreasing the boiler mass setting will increase the response rate by staging the boilers at a faster rate.
Lo (1)
The Lo setting is selected if the boiler(s) that is used has a low thermal mass. This means that the boiler(s) has a very small
water content and has very little metal in the heat exchanger. A boiler that has a low thermal mass comes up to temperature
quite rapidly when fired. This is typical of many copper fin-tube boilers. The Lo mass setting provides a fast staging rate of
on / off boiler stages.
Med (2)
The Med setting is selected if the boiler(s) that is used has a medium thermal mass. This means that the boiler(s) either has
a large water content and a low metal content or a small water content and a high metal content. This is typical of many
modern residential cast iron boilers or steel tube boilers. The Med mass setting provides a moderate staging rate of on / off
boiler stages.
Hi (3)
The Hi setting is selected if the boiler(s) that is used has a high thermal mass. This means that the boiler(s) has both a large water
content and a large metal content. A boiler that has a high thermal mass is relatively slow in coming up to temperature. This is typical
of many commercial cast iron and steel tube boilers. The Hi mass setting provides a slow staging rate of on / off boiler stages.
Time
Boiler #2 Fires
Boiler #1 Fires
Stage Delay
Boiler Contact Closes
Fire
Delay
Fire
Delay
Boiler #1
Boiler #2
1 2
720 hours 672 hours
2 1
672 hours 720 hours
STAGING
The control operates up to two on / off boiler stages (or one low / high fire) in order to provide the required supply temperature. After
a stage is turned on in the firing sequence, the control waits for a minimum time delay. The minimum time delay is adjustable using
the Stage Delay setting. After the Stage Delay has expired, the control examines the control error to determine when the next stage
is to fire. The control error is determined using Proportional, Integral and Derivative (PID) logic.
Proportional – compares the actual supply temperature to the boiler target temperature. The colder the supply water temperature,
the sooner the next stage is turned on.
Integral – compares the actual supply temperature to the boiler target temperature over a period of time.
Derivative – compares how fast or slow the supply water temperature is changing. If the supply temperature is increasing slowly,
the next stage is turned on sooner. If the supply temperature is increasing quickly, the next stage is turned on later, if at all.
ROTATION
The control’s Equal Run Time Rotation function is fixed at 48 hours. The
firing order of the boilers changes whenever one boiler accumulates 48
hours more running time than the other boiler. After each rotation, the
boiler with the least running hours is the first to fire and the boiler with
the most running hours is the last to fire. This function ensures that both
boilers receive equal amounts of use. When the
Rotate / Off DIP switch
is set to the Off position, the firing sequence always begins with boiler
one and then boiler two.
Note: When using a single two-stage boiler, ensure that the Rotate / Off
DIP switch is set to Off.
Resetting the Rotation Sequence
To reset the rotation sequence, set the Rotate / Off DIP switch to
the Off setting for 5 seconds and then return the DIP switch to the
Rotate setting.
FIRE DELAY
The Fire Delay is the time delay that occurs between the time that the
control closes a stage contact to fire a stage and the burner fires for
that stage.
Stage Delay
The stage delay is the minimum time delay between the firing of stages.
After this delay has expired the control can fire the next stage if it is
required. This setting can be adjusted manually or set to an automatic
setting. When the automatic setting is used, the control determines
the best stage delay based on the operation of the system.