tekmar 365 Mixing Control - Manual (Page 11)

Copyright © D 365 - 06/00 11 of 16
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 Brochure A 365.
A more detailed technical description of the effect of control settings on overall system operation is described in the tekmar Essay, E 002.
Settings
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.
Heating Curve
0.4
2.0
3.6
design supply temperature – room temperature
room temperature – design outdoor temperature
Heating Curve =
For example: • Design outdoor temperature = 5
°
F (-15
°
C)
• Room temperature = 70
°
F (21
°
C)
• Design supply temperature = 160
°
F (71
°
C)
Heating curve = = = 1.4
160
°
F - 70
°
F
70
°
F - 5
°
F
90
°
F
65
°
F
For more information regarding the Heating Curve, refer to page 2 of this
brochure. If the design 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).
Outdoor air temperature
Supply water temperature
50
(10)
30
(-1)
10
(-12)
-10 °F
(-23) °C
110
(43)
70
(21)
70
(21)
90
(32)
210
(99)
170
(77)
150
(65)
130
(54)
190
(88)
3.6 3.0 2.4 2.0 1.6
0.8
0.4
1.0
0.6
90
(32)
50 °F
(10) °C
Heating
Curve
WWSD
Point
1.2
Occupied temperature
When there is no room temperature feedback to the control, the Occupied dial setting determines the starting point
of the Heating Curve. This starting point becomes a fixed WWSD point.
When an Indoor Sensor 074 is connected to the control, the Occupied dial setting becomes the actual controlled
temperature of the room. This allows the control to compensate for unexpected internal heat gains or losses. If
the room temperature is too high or too low, the indoor sensor shifts the Heating Curve up or down accordingly.
Except when there is an external heat demand, when a Zone Control or RTU (Room Temperature Unit) is
connected, the RTU dial(s) set the desired room 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 (13 and 14) are shorted together, 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(s) becomes the controlled temperature and the
Occupied/Unoccupied dials become inactive. Unoccupied temperatures must be controlled at the zones.
Indoor Sensor/Zone Control 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.
Setpoint/Reset switch
When this selector switch is in the "Setpoint" position, the control will operate the system to maintain
the supply water temperature at the setting of the "Max./Setpoint" dial.
When the switch is in the "Reset" position, the Heating Curve is active, and the "Max./Setpoint" dial
becomes an override to the Heating Curve, limiting the maximum allowable water temperature.
Occupied
35
(2) 105
(41)
70 °F
(21 °C)
Unoccupied
35
(2) 105
(41)
70 °F
(21 °C)
Zone Control
Boiler on when 25% open
External Heat Demand
Setpoint
1 2 3 4
Reset Permanent Heat Demand
Indoor Sensor 1 2 3 4
Boiler on when 10% open
150 °F
100 200
Max./Setpoint
Zone Control
Boiler on when 25% open
External Heat Demand
Setpoint
Reset
1 2 3 4