VAV-SVX07F-EN 43
Calibration, Operation Modes, and Control
• Stage 1; energizes when the space temperature falls below the active heating setpoint and
minimum airflow requirements are met. When the zone temperature rises above the active
heating setpoint by 0.5°F (0.28°C), stage 1 is de-energized.
• Stage 2; energizes when the space temperature is 1°F (0.56°C) or more below the active
heating setpoint, and is de-energized when the space temperature is 0.5°F (0.28°C) below the
active heating setpoint.
• Stage 3; energizes when the z
one tem
perature is 2°F (1.11°C) or more below the active heating
setpoint, and de-energizes when the space temperature is 1.5°F (0.83°C) below the active
heating setpoint.
When reheat is de-energized, the
coo
ling Airflow Minimum Setpoint is enforced. Refer to Table 9,
p. 41 and Table 10, p. 42.
Hot Water Heat
Two types of control of hydronic heat are supported:
• ON/OFF
Refer to on/off electric heat for
opera
tion. The main difference with ON/OFF hot water heating
is the control of a two position hot water valve instead of the contact energizing an electric heat
strip. Refer to Table 9, p. 41 and Table 10, p. 42.
• Modulating
Proportional hot water reheat uses 3-wire,
fl
oating-point-actuator technology. It is enabled if
there is no valid supply air temperature and disabled if the supply air temperature is greater
than the configured reheat enable setpoint.
When the space requires cooling, the
air valve modulates between Airflo
w Setpoint Maximum
and Airflow Setpoint Minimum, to maintain space temperature at the active cooling setpoint;
and the water valve is closed. When the cooling load has decreased to the point where the air
valve has reached Airflow Setpoint Minimum, space temperature is allowed to drift downward,
in the deadband between the active cooling setpoint and active heating setpoint.
When the space temperature drops be
low the ac
tive heating setpoint, the air valve opens to the
Airflow Setpoint Reset Minimum Local Heat and the reheat valve modulates to maintain space
temperature at the active heating setpoint. Control of the water valve uses a separate
proportional plus integral control loop, and its position is dependent on the degree that the
space temperature is below the active heating setpoint and the amount of time that the space
temperature has been below the active heating setpoint.
If the discharge air temperature re
aches the Discharge Air Temperature Design Setpoint, the air
valve opens further and modulates between Airflow Setpoint Reset Minimum Local Heat and
Airflow Setpoint Reset Maximum Local Heat to maintain space temperature at the active
heating setpoint, while the water valve modulates to maintain discharge air temperature at the
Discharge Air Temperature Design Setpoint. (See Figure 6, p. 41.) If the air valve reaches Airflow
Setpoint Rese
t Maximum Local Heat, the water valve opens further and modulates to maintain
space temperature at the active heating setpoint, while the air valve remains at Airflow Setpoint
Reset Maximum Local Heat.
An additional ON/OFF remote heat
output is available and energized when the water valve
is
driven 100% open and de-energized when the water valve reaches 50% open.
When reheat is de-energized, the cooling Ai
rflow
Minimum Setpoint is enforced.
Note: Steam is not
supported.
Fan-Powered Units
The UC400 controllers provide the following three (3) fan options when in space temperature
control mode:
• One-speed ON/OFF series fan
To Next Page
Loading...
