tekmar 371 House Control User Manual
Page 7
7
MIXING OPERATION
The 371 can supply a lower water temperature to part of the heating
system by varying the speed of an injection pump or modulating a mixing
valve. See Essay E 021 for more information. An outdoor reset strategy
is used with indoor temperature feedback from each of the mixing zones.
Boiler Protection
When the boiler is fired and the boiler supply temperature is below the
Min. Boiler Supply dial setting, the 371 turns on the Minimum Boiler
light and reduces the heating load on the boiler. During this warm up
period, the mixing device is operated at low outputs and some of the
zones may be prevented from operating.
System Maximum Supply / Setpoint Supply
The 371 has a
Max. Supply dial that can be used to set an upper limit
to the mixed supply water temperature. If this supply water tempera-
ture approaches the
Max. Supply dial setting, the 371 turns on the
Maximum Supply light and reduces the speed of the injection pump or
closes the mixing valve.
If the
Setpnt DIP switch is set to Mixing and setpoint operation is required, the 371 controls
the variable speed injection pump or the mixing valve in order to increase the mixed
supply water temperature to the
Setpnt dial setting.
DOMESTIC HOT WATER (DHW)
The DHW tank requests heat from the 371 through a DHW Demand. Whenever 120 V (ac)
is applied to the
DHW Dem (23) terminal on the 371, the control registers a DHW Demand
and turns on the
DHW Demand light. An aquastat, setpoint control or other switching device
can be used to generate a DHW Demand by wiring the line voltage signal through the
switching device and into the
DHW Dem terminal.
The 371 does not turn on the boiler system pump (P1) when DHW is required, therefore
piping a DHW tank to operate through a zone valve will increase wiring complexity.
DHW Supply Temperature
During DHW operation, the 371 targets a boiler water temperature of at least 180
°
F (82
°
C).
DHW Priority
The 371 is designed to provide DHW priority at all times. When a DHW demand is present, the control closes the contacts between
Power L — DHW Pmp (4 and 22) and turns on the DHW pump. The boiler system pump (P1) and the boiler zone relays are turned
off until the boiler water temperature is greater than 170
°
F (77
°
C).
DHW Post Purge
When the DHW Demand is removed and none of the zones require heat, the 371 turns off the boiler but continues to run the DHW
pump. This purges some residual heat from the boiler. The 371 allows a maximum Post Purge time of 4 minutes. If the boiler supply
temperature drops below 150
°
F (66
°
C) or below the
Min. Boiler Supply dial setting, the 371 stops the DHW Post Purge.
DHW Mixing Purge
If some of the zones require heat, the 371 performs a DHW Mixing Purge. During the Mixing Purge period, the 371 simultaneously
operates the DHW and heating systems. The 371 allows a maximum Mixing Purge period of 2 minutes for fast acting zone valves
and pumps and a longer purge period for thermal motor zone valves. The actual length of the purge period is dependent on the boiler
supply water temperature. At the end of the Mixing Purge period, the
DHW Pmp relay is turned off but the system pumps (P1 and
P2) and zone relays continue to operate.
DHW Setback
The
DHW during UnOcc. DIP switch selects whether DHW setback is desired while the
371 is in UnOccupied mode. If the
DHW during UnOcc. DIP switch is set to Off, the DHW
Demand is ignored during the UnOccupied period. However, if
Optimum Start is selected,
the 371 will respond to the DHW Demand in the last hour of the UnOccupied mode. This
will generally ensure that the DHW storage tank is up to temperature by the time the
Occupied period begins. If the DIP switch is set to
DHW during UnOcc., the 371 responds
to the DHW Demand at all times.
ZONING OPERATION
The 371 can directly control the temperature of up to 5 heating zones. In order to measure
the indoor temperature, each zone requires either an Indoor Sensor or a Room Tempera-
ture Unit (RTU). With an RTU the desired zone temperature is set using the RTU dial, but
with an Indoor Sensor the desired zone temperature is fixed at 72
°
F (22
°
C).
boiler
sensor
injection
pump
Maximum
Supply
Setpoint
Demand
OR
Max. Supply / Setpnt
120
170
°
F
220
boiler
sensor
M
mixing valve
70
Indoor Sensor
RTU
Off
DHW during
UnOcc.
23
DHW
Dem
DHW
Demand
4
L