Trane LPC, Инструкции по установке и эксплуатации

Страница: 77 / 110

LPC-SVX01C-EN 77
Operation
sequence of
operation
Entering water temperature
sampling
This sequence applies to controllers
configured for space temperature
control.
If configured for space temperature
control, the controller can sample the
entering water condition for air-handling
units with a single hydronic coil. The
entering water temperature is important
for reliable heating and cooling control.
The entering water temperature must be
at least 5ºF above the space temperature
for hydronic heating and 5ºF below the
space temperature for hydronic cooling
for satisfactory capacity control.
Three-way valve applications
When using three-way control valves, the
central water supply flows continuously
to the unit valve and is either directed
through the coil or bypassed around the
coil. Because water flow is continuous,
the entering water temperature sensor
can be installed on the pipe where the
flow rate is constant. For both three-way
valves and bleed lines, continuous water
flow when combined with proper sensor
location gives a continuous and reliable
measurement of the entering water
temperature.
Note: Entering water sampling (also
referred to as purge) is not required for
three-way valve applications.
Two-way valve applications
The AH540/541 controller offers a control
solution for two-way valve applications.
The entering water temperature
sampling function (purge) periodically
opens the two-way valve to allow
temporary water flow, producing a
reliable entering water temperature
measurement.
When water flows normally and fre-
quently through the coil, the controller
does not initiate the entering water
temperature sampling function because
the water temperature measurement is
valid for determining the entering water
condition. During unit startup or
changeover, the controller determines its
ability to deliver heating or cooling. The
controller initiates the entering water
temperature function to determine if the
entering water temperature is adequate
for delivering the desired heating or
cooling. The measurement must indicate
that the water is warm enough to heat
the space or cool enough to cool the
space.
When the controller initiates the entering
water temperature sampling function, the
controller turns Off the supply fan and
opens the hydronic valve for no more
than the maximum sampling time while
measuring entering water temperature.
An initial stabilization period is allowed to
open the valve to a configured position
(50% default) and to flush the piping.
When this temperature stabilization
period has expired, the controller
compares the entering water tempera-
ture to the effective space temperature
(either hard-wired or communicated) to
determine if it can be used for the desired
mode. The controller continues to
compare the entering water temperature
to the effective space temperature for the
maximum sampling time.
Whenever the entering water tempera-
ture is warmer than 110°F, the controller
assumes the entering water temperature
is hot because it is unlikely the coil would
drift to a high temperature unless the
actual temperature was very high. If the
entering water temperature is not usable
for the required space demand, the
controller closes the water valve and
starts the supply fan until the next
sampling period (configurable). If the
controller determines the entering water
temperature is adequate for heat or
cooling, it resumes normal heating/
cooling control and effectively disables
entering water sampling until it is
required.
Entering water temperature sampling is
disabled when:
• Unit configuration is dedicated heating
and cooling or two-pipe changeover
without purge (three-way valve
application).
• Entering water temperature is
communicated to the controller.
• For cooling, entering water
temperature is less than five degrees
colder than the space temperature or
greater than 110°F.
• For heating, entering water
temperature is greater than 5º warmer
than the space temperature.
Face-and-bypass damper
operation
This sequence applies to both space
temperature control and discharge
air temperature control.
The face-and-bypass damper modulates
a percentage of air to the face of the heat
coil and around the coil (bypass) to
maintain the supply air temperature
setpoint. The air passing through the hot
water coil is mixed with the air bypassing
the coil to produce a desired discharge air
temperature.
The Tracer AH540/541 controller sup-
ports face-and-bypass operation for low
outdoor temperature heating modes of
operation only. During low outdoor
temperatures, when the outdoor air
temperature is lower than the face-and-
bypass heat modulation setpoint, the
heating valve is fully opened and the
face-and-bypass damper is used for
heating to prevent the coil from freezing.
During economizer cooling operation,
when outdoor temperature is less than
the face and bypass heat modulation
setpoint, the face-and-bypass damper is
full bypass.
The face-and-bypass heat modulation
setpoint is the outdoor air temperature
(40°F default, configurable) at which the
controller changes over to face and
bypass heating operation. The face-and-
bypass heat modulation setpoint can be
changed using the Rover service tool.
When the outdoor air temperature is
greater than 3°F above the face-
andbypass heating modulation setpoint,
the hydronic heating valve is modulated
to maintain discharge air temperature.
The face-and-bypass damper is
positioned for full face air flow. When the
outdoor air temperature is less than the
face and bypass heating modulation
setpoint, the controller fully