Johnson Controls
5513350-JTG-1018
74
Controls (Continued)
DAT Setpoint Reset
The DAT setpoint reset feature provides six different meth-
ods of varying the DAT setpoint: fixed, OAT, RAT, zone tem-
perature, supply fan speed, and external control.
Fixed -
The DAT setpoint is a fixed value and does
not change in response to another signal. It can be
user adjusted from the default value over a BAS or
local UI.
OAT -
The DAT setpoint resets from DAT low setpoint
to the DAT high setpoint as the OAT varies from OAT
setpoint for low DAT to the OAT setpoint for high DAT
.
RAT -
The DAT setpoint resets from DAT low setpoint
to the DAT high setpoint as the RAT varies from the
RAT setpoint for low DAT to the RAT setpoint for high
DAT.
Zone Temperature -
The DAT setpoint resets from
DAT low setpoint to the DAT high setpoint as the zone
temperature varies from the setpoint for low DAT to the
setpoint for high DAT. If zone temperature becomes
unreliable, the unit reverts to DAT reset from RAT.
Supply Fan Speed -
The DAT setpoint resets from
DAT low setpoint to the DAT high setpoint as the fan
speed varies from the fan speed setpoint for low DAT
to the fan speed setpoint for high DAT.
External Control -
The DAT setpoint is controlled di-
rectly by a third party (BAS communication or voltage
signal). The hard wired DAT setpoint varies from DAT
low setpoint to DAT high setpoint as the input varies
from low value to high value.
Single Zone Variable Air Volume (SZVAV)
Mechanical Cooling
Zone Temperature Control -
The DAT setpoint re-
sets between low and high cooling setpoints based
on the zone cooling demand. The unit controls the
DAT by staging or modulating the compressors. The
supply fan runs at the minimum speed setpoint (ad
-
justable).
As the zone cooling demand increases and the DAT
controls to the low cooling setpoint, the supply fan
speed setpoint resets between minimum cooling
speed and 100% to maintain the zone temperature
setpoint.
Staged Temperature Control -
The unit can be
controlled by a standard two-stage cooling/heating
thermostat. Thermostat connections are hard wired
through BAS interface board: G, Y1, Y2, W1, W2.
Thermostat commands can also be communicated
by the BAS. The fan operates at minimum or maxi-
mum speed in occupied/unoccupied mode based on
the thermostat input.
Economizer
When free cooling is available, the outside air (OA) damper
modulates to maintain the mixed air temperature (MAT) at
the DAT setpoint. During the free cooling mode, if the OA
damper modulates to 100% open and cannot maintain the
DAT setpoint, the compressors energize to maintain the
DAT setpoint.
If the zone temperature exceeds the zone temperature set-
point, the OA damper is 100% open, and all cooling stages
are staged ON (or locked out due to compressor lockout),
then the supply fan speed shall modulate to maintain zone
temperature setpoint.
Satisfied
If the occupancy mode is occupied without a heating or
cooling demand, the supply fan runs at the minimum fan
speed.
Modulated Heating
The DAT setpoint resets between low and high heating set
-
points based on the zone heating demand. The unit con-
trols the DAT by modulating the heat (electric, gas, or hy
-
dronic). The supply fan runs at the minimum speed setpoint
(adjustable).
As the zone heating demand increases and the DAT con-
trols to the high heating setpoint, the supply fan speed set-
point resets between heating minimum speed and 100% to
maintain the zone temperature setpoint.
Staged Heating
The DAT setpoint resets between low and high heating set
-
points based on the zone heating demand. The unit con-
trols the DAT by staging the heat (electric or gas). The sup
-
ply fan runs at maximum capacity.
Unoccupied Mode
If the occupancy mode is unoccupied, the unit does not
operate in SZVAV mode but instead operates in to the fol
-
lowing manner: