Trane RT-DS-10 - Manual (Page 33)

33
Controls CV Units Only
VAV Units Only
Morning Warm-up (MWU)
Morning warm-up control (MWU) is
activated whenever the unit switches
from unoccupied to occupied and the
zone temperature is at least 1.5°F
below the MWU setpoint. When MWU
is activated the VAV box output will be
energized for at least 6 minutes to drive
all boxes open, the inlet guide vanes
are driven full open, and all stages of
heat (gas or electric) are energized.
When MWU is activated the
economizer damper is driven fully
closed. When the zone temperature
meets or exceeds the MWU setpoint
minus 1.5°F, the heat will be staged
down. When the zone temperature
meets or exceeds the MWU setpoint
then MWU will be terminated and the
unit will switch over to VAV cooling.
CV Units Only
Sequence of Operation
1
Occupied Zone Temperature Control
Cooling/Economizer
During occupied cooling mode, the
economizer (if provided) and primary
cooling are used to control zone
temperature. If the enthalpy of outside
air is appropriate to use “free cooling,”
the economizer will be used first to
attempt to satisfy the cooling zone
temperature setpoint; then primary
cooling will be staged up as necessary.
On units with economizer, a call for
cooling will modulate the fresh air
dampers open. The rate of economizer
modulation is based on deviation of the
zone temperature from setpoint, i.e.,
the further away from setpoint, the
faster the fresh air damper will open.
First stage of cooling will be allowed to
start after the economizer reaches full
open.
Note that the economizer is allowed to
function freely only if ambient
conditions are below the enthalpy
control setting or below the return air
enthalpy if unit has comparative
enthalpy. If outside air is not suitable
for “economizing,” the fresh air
dampers drive to the minimum open
position. A field adjustable
potentiometer on the Unitary
Economizer Module (UEM), Tracer or a
remote potentiometer can provide the
input to establish the minimum
damper position.
At outdoor air temperatures above the
enthalpy control setting, primary
cooling only is used and the outdoor
air dampers remain at minimum
position.
If the unit does not include an
economizer, primary cooling only is
used to satisfy cooling requirements.
Heating
Gas Heating
When heating is required the UCP
initiates the heating cycle by energizing
the K5 relay, heating relay(s), and the
ignition control module(s). The K5 relay
brings on the combustion fan motor.
The ignition control module(s) begin
the ignition process by preheating the
hot surface ignitor(s). After the hot
surface ignitor is preheated the gas
valve is opened to ignite first stage. If
ignition does not take place the ignition
control module(s) will attempt to ignite
2 more times before locking out. When
ignition does occur the hot surface
ignitor is de-energized and then
functions as a flame sensor. The UCP
will energize the supply fan contactor
45 seconds after the initiation of the
heat cycle. If more capacity is needed
to satisfy the heating setpoint, the UCP
will call for the second stage of heat by
driving the combustion blower motor
to high speed.
When the space temperature rises
above the heating setpoint, the UCP de-
energizes the K5 relay, the heating
relays, and the ignition control module,
terminating the heat cycle.
Electric Heating
When heat is required, the UCP
initiates first stage heating by
energizing the first stage electric heat
contactor. The first stage electric heater
bank(s) will be energized if the
appropriate limits are closed. The UCP
will cycle first stage heat on and off as
required to maintain zone temperature.
If first stage cannot satisfy the
requirement, the UCP will energize the
second stage electric heat contactor(s)
if the appropriate limits are closed. The
UCP will cycle second stage on and off
as required while keeping stage one
energized.
The supply fan is energized
approximately 1 second before the
electric heat contactors. When the
space temperature rises above the
heating setpoint, the UCP de-energizes
the supply fan and all electric heat
contactors.
Supply Air Tempering
This feature is available only with
TRACER or with systems using
programmable zone sensors (CV only
with economizer). For gas and electric
heat units in the Heat mode but not
actively heating, if the supply air
temperature drops to 10°F (-12.2°C)
below the occupied zone heating
temperature setpoint, one stage of heat
will be brought on to maintain a
minimum supply air temperature. The
heat stage is dropped if the supply air
temperature rises to 10°F (-12.2°C)
above the occupied zone heating
temperature setpoint.
Auto Changeover
When the System Mode is “Auto,” the
mode will change to cooling or heating
as necessary to satisfy the zone cooling
and heating setpoints. The zone
cooling and heating setpoints can be as
close as 2°F (-16.7°C) apart.
Unoccupied Zone Temperature Control
Cooling and Heating
Both cooling or heating modes can be
selected to maintain Unoccupied zone
temperature setpoints. For Unoccupied
periods, heating or primary cooling
operation can be selectively locked out
at the remote panels or TRACER.