tekmar 370 House Control - Manual (Page 8)

Copyright © D 370 -06/99 8 of 20
DHW Priority −−−−−−−−−−−−−− −−−−−−−−−−−−−− −−−−−−−−−−−−−− −−−−−−−−−−−−−− −−−−−−−−−−−−−−
The DHW system can be given priority over the 370 heating operation by setting the DIP
switch to
DHW Priority. The operation of the control during DHW Priority depends primarily
on whether the control is used in boiler reset or mixing reset. If the DIP switch is set to Boiler,
the zone relays are turned off when a DHW Demand is received. If the DIP switch is set to
Mixing, the variable speed injection pump is turned off when the control receives a DHW
Demand.
DHW Mixing Purge
When the DIP switch is set to DHW Priority and some zones require heat, the 370 performs a DHW Mixing Purge once the DHW
Demand is removed. During the Mixing Purge period, the 370 simultaneously operates the DHW and heating systems. The 370
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 / Vlv relay is turned off but the system pump and zone relays continue to operate.
DHW Post Purge
    
When the DHW Demand is removed and none of the zones require heat, the 370 turns off the boiler but continues to run the DHW
pump or system pump and DHW valve. This purges some residual heat from the boiler. The 370 allows a maximum 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 370 stops the
DHW Post Purge.
DHW Setback
    
The DHW During UnOcc. DIP switch selects whether DHW setback is desired while the
370 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 370 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 370 responds
to the DHW Demand at all times.
ZONING OPERATION
The 370 can directly control the temperature of up to 4 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 70
°F (21°C).
PID Zoning Logic
    
The 370 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 370 ensures that the zone relays remain on
or off for at least 3 minutes.
Zone Load Staggering     
The 370 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 (Maximum of 6) to the 370. The Zone Control signals to
the 370 whenever one of its zones requires heat. Upon receiving a
Zone Control heat demand, the 370 turns on its system pump and
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 370 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 370 is provided in Application Brochures A 370.
Note In order for the 370 to provide the most efficient operation, the warmer zones (RTU dials set higher) should be connected
to the 370 and the cooler zones (RTU dials set lower) should be connected to the Zone Control(s).
Relay On Time
Relay On Time
Relay On Time Less Heat
More Heat
15 minute Cycle
70
Indoor Sensor RTU
tekmar
Boiler or Heating System Control
LR 58233 E150539 LR 58233 E150539
tekmar
Zone Control
Off
DHW during UnOcc.
DHW Priority
Off
Operation