tekmar 371 House Control User Manual
Page 8
8
PID Zone Temperature Control
The 371 operation is based on a 15 minute cycle. During every cycle
the control turns on each zone relay for a specific on time. The required
on time is calculated based on the PID response of the zone during the
previous cycles. If the zone needs more heat, the on time is increased,
and if the zone needs less heat, the on time is reduced. In order to
prevent short cycling, the 371 ensures that the zone relays remain on
or off for at least 3 minutes.
Zone Load Coordination
The 371 staggers the operation of the zones in order to achieve a
steady load on the boiler while minimizing boiler running time and
preventing boiler short cycling.
External Zone Control Input
Control of additional zones can be provided by connecting a tekmar
Zone Control to the 371. The zone control can be added to control
either boiler (hot water) or mixing (warm water) zones. If the
Zo DIP
switch is set to
Boiler, the 371 assumes the additional zones are on the
boiler (hot water) loop, and if the
Zo DIP switch is set to Mixing, the 371
assumes the additional zones are on the mixing (warm water) side of
the system.
The Zone Control signals to the 371 whenever one of its zones requires heat. Upon receiving a Zone Control heat demand, the 371
shifts the Heating Curve to satisfy the heating requirements of both its own zones and the zones connected to the Zone Control.
Zone Control Load Synchronization
The 371 monitors the heat demand signals from the Zone Control and synchronizes the start times of its own zones with those of
the Zone Control. More information on using a Zone Control with the 371 is provided in Application Brochures A 371.
Fast Acting Zone Valves or Zone Pumps
If the
Thermal Motor DIP switch is set to Off, the 371 assumes that fast acting electric
motor zone valves or zone pumps are connected to all zone relays. The mixing system
pump (P2) and / or boiler system pump (P1) is therefore turned on as soon as the first zone
relay is operated. One minute before the last zone relay is turned off, the 371 purges
the boiler.
Slow Acting Zone Valves with Thermal Motors
When the DIP switch is set to
Thermal Motor, the 371 assumes that slow acting zone
valves with thermal actuating motors are connected to all zone relays. With slow acting
zone valves, the 371 allows a 3 minute period for the first zone valve to open before the
mixing system pump (P2) and / or boiler system pump (P1) is turned on. The total
operating time for the zone relays is also increased by an extra 2 minutes. This helps
compensate for the longer opening versus closing time of the slow acting zone valves.
For one minute after the last zone relay is turned off, the 371 purges the boiler.
COOLING OPERATION
When the DIP switch on the 371 is set to
Zone 1 Cool, zone relay 1 can either be used to
enable an auxiliary cooling control system or to directly operate a central cooling unit.
Cooling Control (RTU is present)
If
Zone 1 Cool is selected and an RTU or Indoor Sensor is connected to terminals Com
Sen — RTU 1 (6 & 7), the 371 can directly control a central cooling system using zone
relay
1. If an RTU is used, the desired indoor temperature is set using the RTU dial down
to 73
°
F (23
°
C), but if an Indoor Sensor is used, the desired indoor temperature is fixed
at 77
°
F (25
°
C). Zone relay
1 is allowed to turn on once the heating zones in the 371 have
been satisfied for at least 45 minutes, and is turned off whenever any zone requires heat.
The 371 varies the on time of zone relay
1 over a 30 minute cycle. As the cooling load
increases, the on time of the zone relay increases. In order to prevent short cycling, the
371 ensures that zone relay
1 remains on or off for at least 3 minutes.
Cooling Enable (no RTU)
If
Zone 1 Cool is selected and there is no RTU or Indoor Sensor connected to terminals
Com Sen — RTU 1 (6 & 7), the 371 can enable an auxiliary cooling control through zone
relay
1. Zone relay 1 is turned on once the heating zones in the 371 have been satisfied
for at least 45 minutes, and is turned off whenever any zone requires heat.
2
27
1
26
25
Com
1-2
Cooling Enable
RTU
1
7
6
Com
Sen
C
NO RTU
2
27
1
26
25
Com
1-2
Cooling Control
RTU
1
7
6
Com
Sen
C
RTU
Off
Thermal Motor
Slow acting zone valve
Off
Thermal Motor
Fast acting zone valve
or zone pump
tekmar
Boiler or Heating System Control
LR 58233
E150539
LR 58233
E150539
tekmar
Zone Control
Relay On Time
Relay On Time
Relay On Time
Less Heat
More Heat
15 minute Cycle