Tekmar Mixing Control 354 Data Brochure page 8

Settings
Step Six
Essential control settings
To obtain the best operation from a reset control, it is important to measure the system supply temperature as accurately
as possible. Whenever the control receives a heat demand signal, the system pump must be operated to maintain
continuous water flow across the supply temperature sensor. Whenever the control uses a boiler return sensor, the boiler
pump must also be operated to maintain continuous water flow across the boiler return sensor.
For specific application details refer to Brochures A 354.
A more detailed technical description of the effect of control settings on overall system operation is described in the tekmar Essay, E 002.
Heating Curve
As outdoor temperatures drop, heat losses from a space become greater and the heating system
supply water temperature must be raised to maintain a constant room temperature. The heating curve
value describes how many degrees the supply water temperature is raised for a one degree drop in
outdoor temperature. The supply temperature starts to increase when the outdoor temperature falls
below the WWSD point. To calculate the correct setting for the heating curve, use the following formula.
design supply temperature – room temperature
Heating Curve =
room temperature – design outdoor temperature
For example: • Design outdoor temperature = 5
• Room temperature = 70
• Design supply temperature = 160
160
Heating curve =
70
For more information regarding the Heating Curve, refer to page 2 of this
brochure. If the actual designed supply water temperature for a system
is unknown, a trial setting can be calculated using these typical supply
temperatures:
• Fan coils ...180° to 210°F (82° to 99°C)
• Baseboard convectors ...160° to 190°F (71° to 88° C)
• Hydronic radiant floors ...100° to 130°F (38° to 54°C).
Occupied temperature
When there is no room temperature feedback to the control, the Occupied dial setting determines the
starting point of the heating curve (WWSD point) and the heating curve setting will reset the water
temperature as described in the Heating Curve instructions above.
When an Indoor Sensor 074 is connected to the control, the Occupied dial setting becomes the actual
controlled temperature of the room. This valuable feature allows the control to compensate for an
incorrectly set heating curve or for unexpected internal heat gains or losses. If the room temperature
is too high or too low, the indoor sensor allows the heating curve to be shifted up or down accordingly.
When a tekmar Zone Control or RTU (Room Temperature Unit) is connected to the control, the RTU
setting becomes the controlled temperature and the Occupied dial becomes inactive.
Unoccupied temperature
The Unoccupied dial operates in the same way as the Occupied dial, but at a different temperature.
When the terminals UnO Sw — Com Sen (14 and 15) are shorted out, the control switches from
operating at the Occupied dial setting to operating at the Unoccupied dial setting. When a tekmar
Zone Control or RTU (Room Temperature Unit) is connected to the control, the RTU setting becomes
the controlled temperature and the Occupied/Unoccupied dials become inactive, making it necessary
to control Unoccupied temperatures at each individual zone.
Zone Control/Indoor Sensor switch
Set this selector switch to the "Indoor Sensor" position when a tekmar Indoor Sensor 074 or a tekmar
RTU is connected. The control will receive room temperature feedback from the room that has the
Sensor or RTU.
Set the switch to the "Zone Control" position when a tekmar Zone control is connected, the control
receives information from the Zone Control that allows the heating curve to be shifted so the supply
water temperature is hot enough to satisfy the requirements of the zone with the highest heat demand.
°
F (21
° °
°
F - 70 F
90 F
= = 1.4
° ° °
F - 5 F 65 F
° °
F (-15 C)
°
C)
° °
F (71 C)
WWSD
Point
90
(32)
8
0.4
Heating Curve
3.6 3.0 2.4 2.0
Heating
Curve
70 50 30 10
(21) (10) (-1) (-12)
Outdoor air temperature
70°F
(21°C)
35
(2)
Occupied
70°F
(21°C)
35
(2)
Unoccupied
Zone Control
External
(1 & 2)
Heat Demand
Permanent
Indoor Sensor
2.0
3.6
210
(99)
1.6
190
(88)
170
1.2
(77)
1.0
150
(65)
0.8
130
(54)
0.6
110
0.4
(43)
90
(32)
70
(21)
50°F
(10)°C
-10°F
(-23)°C
105
(41)
105
(41)
25% open
Boiler enabled
10% open