tekmar 365 Mixing Control - Manual (Page 2)

Copyright © D 365 - 06/00 2 of 16
Shifting the Heating Curve
(a) Manually, at the control:
The Occupied and Unoccupied dials on this control can shift the WWSD
point up or down from 35 to 105
°F (2 to 41°C).
(b) Automatically, using room temperature feedback:
In addition to a Supply Sensor and an Outdoor Sensor, this control can use
a tekmar 2k RTU, 10k Zone Control or 10k Indoor Sensor to provide room
temperature feedback for added comfort and system flexibility.
The control still calculates a desired supply temperature based on the
Heating Curve setting and the outdoor temperature.
If the air temperature in the room is too cold, the control will shift the Heating
Curve (and WWSD point)
up, which raises the supply temperature until the
room warms up again.
If the air temperature in the room is too warm, the control will shift the
Heating Curve (and WWSD point)
down, which lowers the supply tempera-
ture until the room cools down.
Correct setting and shifting of the Heating Curve... the key to More Comfort and Energy Savings.
Heating Curve
As outdoor temperatures get colder, heat losses from a building increase, requiring the addition of more heat to prevent the indoor
air temperature from also getting colder. This tekmar reset control measures the outdoor temperature and as the outdoor
temperature gets colder, it balances the heat loss by making the heating supply water hotter.
The Heating Curve is used to calculate how hot to make the supply water at different outdoor temperatures. It is the number of
degrees the supply water temperature is raised for each degree that the outdoor temperature falls.
Setting the Heating Curve
Two examples of how the Heating Curve works are given in the following illustration.
—With a 2.4 Curve, the supply water temperature is raised 2.4 degrees for every degree of outdoor temperature drop.
If WWSD point = 70
°F and Outdoor temperature = 30°F, then Supply temperature = 166°F
—With a 0.6 Curve, the supply water temperature is raised 0.6 degrees for every degree of outdoor temperature drop.
If WWSD point = 70 °F and Outdoor temperature = 30°F, then Supply temperature = 94°F
To provide heat to the building, this control turns on the system pump and starts the injection pump (or opens the mixing valve),
delivering heat at the low output required by the Heating Curve near the WWSD point. If the outdoor temperature rises above the
WWSD point, the control shuts the system off again, and because the system was operating at a low heat output level, overheating
and temperature swings in mild weather are avoided.
When the system is operating near the WWSD point and the building is too cold; the WWSD point should be raised.
When the system is operating near the WWSD point and the building is too warm; the WWSD point should be lowered.
• If the Heating Curve selected is too low; the heating system will not be
able to raise the supply temperature high enough to keep the room
temperature warm during colder weather.
• If the Heating Curve selected is too high; too much heat is delivered and
the building will overheat during colder weather.
Warm Weather Shut Down (WWSD)
At warm outdoor temperatures, the indoor space of a building gains heat
from the outdoors; additional heat is not required, and if the heating
system is running (even on standby), enough excess heat can be
produced to overheat the building, causing discomfort and wasting
valuable energy.
This control turns off the system pump and injection pump (or closes a
mixing valve), when the outdoor temperature is above the WWSD point.
As outdoor temperatures get colder, there comes a point where the heat
gain turns into heat loss; the heat loss causes the indoor temperature to
fall below the comfort level, and the heating system must be turned on to
start delivering heat.
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
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
90
(32)
50 °F
(10) °C
Heating
Curve
WWSD
Point
will
shift
up and
down
with
shift of
Heating
Curve
1.2
UP
DOWN
UP DOWN
Parallel Shift of Heating Curve
0.6
A very cool room temperature can shift the curve far enough up to bring the control out of WWSD at warm outdoor temperatures.
A very warm room temperature can shift the curve far enough down to put the control into WWSD at cool outdoor temperatures.
Refer to the tekmar Essays E 001 and E 002 for more detailed information regarding control strategy and integration of control functions.
Outdoor Reset Strategy