Tekmar Mixing Control 354 Data Brochure page 4

Outdoor temperature cold enough to require heating (cont.)
With Heat demand signal
The "Heat Demand" light will come on, the control will switch on the
pump, and calculate the desired supply temperature based on the
requirements of the Heating Curve.
The control will operate the actuating motor which positions the mixing
valve to deliver the correct supply temperature.
When positioning the mixing valve, the control uses the following control
actions;
(a) - Open the valve. The "Opening" light will come on and the control
will power the valve towards the fully open position.
(b) - Close the valve. The "Closing" light will come on and the control
will power the valve towards the fully closed position.
(c) - No valve movement. "Opening" and "Closing" lights are both off
and the valve remains in a fixed position.
Maximum Supply temperature operation
To provide a measure of protection to system components that may be damaged by
excessive heat, (eg. some types of plastic hydronic radiant floor tubing) this control has
a setting for Maximum Supply temperature. Maximum supply can be turned off by
rotating the dial fully clockwise.
When the supply temperature gets close to the setting on the Max. Supply dial, the Max
Supply light will come on an the control will begin closing the valve, in order to reduce
the temperature before it overshoots. The control will operate the valve to maintain the
temperature slightly below the Maximum.
The control may operate for a long time at the Maximum supply temperature if :
(a) - it is coming out of a deep setback or just starting up from a cold start.
(b) - an RTU (or Occupied dial when Indoor Sensor 074 is used) is turned up suddenly.
(c) - the maximum setting is too low for system design conditions.
Minimum Boiler Return temperature operation
To provide a measure of protection to boilers that may be damaged by low return water
temperatures, this control has a setting for Minimum Boiler Return temperature.
When the boiler return temperature gets close to the setting on the Minimum Boiler
Return dial, the "Min Return" light will come on and the control will begin closing the valve
in order to raise the boiler return temperature before it undershoots. The control will
operate the valve to maintain the boiler return temperature slightly warmer than the
Minimum Boiler Return temperature setting.
The control may operate for a long time at the Minimum Return temperature if:
(a) - it is coming out of a deep setback or just starting up from a cold start.
(b) - an RTU (or Occupied dial when Indoor Sensor 074 is used) is turned up suddenly.
(c) - the minimum setting is too high for system design conditions.
Notes on operation of Minimum Return and Maximum Supply functions
At times, the control may be trying to control both the Maximum Supply and Minimum Return temperatures (ie. when leaving a
deep setback). When this occurs, the control is programmed to give priority to the Minimum Boiler Return function, and only the
"Min. Return" light will be displayed.
When the control is in WWSD, the "Min. Return" and "Max. Supply" lights will not be displayed.
When using a Return Sensor for Minimum Boiler Return protection, it is essential that there always be water flow past the boiler
return sensor whenever there is a heat demand. See Brochure A 354.
Caution:
The tekmar Mixing Control 354 is an operating control and is not certified or intended for use as a primary safety device.
Under normal operating conditions, the control will provide excellent protection against excessive supply temperatures
and low boiler return temperatures, however, if failsafe protection against either of these conditions is essential then
separate certified safety limit devices should be employed.
(a)
Power
Heat Demand
WWSD
Unoccupied
Min. Return
Max. Supply
Pump
Boiler
Closing
Opening
4
(b)
Power
Heat Demand
WWSD
Unoccupied
Min. Return
Max. Supply
Pump
Boiler
Closing
Opening
Boiler light may also be on
Min. Return light may also be on
Max. Supply light may also be on
Unoccupied light may also be on
Power
Heat Demand
WWSD
Unoccupied
Min. Return
Max. Supply
Pump
Boiler
Closing
Opening
Opening or Closing
light may also be on
Boiler light may also be on
Unoccupied light may also be on
Power
Heat Demand
WWSD
Unoccupied
Min. Return
Max. Supply
Pump
Boiler
Closing
Opening
Opening or Closing
light may also be on
Unoccupied light may also be on
(c)
Power
Heat Demand
WWSD
Unoccupied
Min. Return
Max. Supply
Pump
Boiler
Closing
Opening
T est