Modine Manufacturing VFV Installation And Service Manual page 9

SEQUENCE OF OPERATION
Hot Water and Chilled Water (2-Pipe) with
Valve Control
Units with valve control to provide heating and cooling on
a single water coil (2-pipe system) and not using Carel
controls shall use a spring-return, normally open modulating
valve operated by a proportional signal (2-10VDC) or a tri-
state (24VAC) signal. Units with Carel controls shall use a
modulating control valve with a proportional signal. On a call
for heating or cooling (depending on the season), the valve
shall open proportionally based on how many degrees the room
temperature is from the setpoint. The adjustable proportional
band on the Carel controller is set to a default 1˚F (example:
valve is 50% open when room temperature is 0.5˚F from
setpoint). If for any reason the supply air temperature drops
below 55˚F (adjustable), the water valve shall modulate open to
maintain 55˚F. On 2-pipe units not having Carel controls or not
connected to a network, an optional aquastat is recommended
to prevent inadvertent changeover of heating/cooling modes.
Hot Water and Chilled Water (2-Pipe) with
Face & Bypass Control
Units with face and bypass control to provide heating and
cooling on a single water coil (2-pipe system) shall modulate
the face & bypass damper via a spring return actuator,
controlled by a proportional signal (2-5.5V). The face &
bypass damper regulates the amount of return air and outside
air passing through the water coil. On a call for heating
or cooling (depending on the season), the damper shall
open proportionally based on how many degrees the room
temperature is from the setpoint. The adjustable proportional
band on the Carel controller is set to a default 1˚F (example:
damper is 50% open when room temperature is 0.5˚F from
setpoint). When the damper is in full bypass position (2V),
all return and outside air bypasses the water coil. When the
damper is in full face position (5.5V), all return and outside air
passes through the water coil. If for any reason the supply air
temperature drops below 55˚F (adjustable), the water valve
shall open (if equipped) and the face and bypass damper shall
modulate to maintain 55˚F.
2-Position Control Valves
Optional spring-return, 2-position control valves can be used to
control the end of cycle flow on both chilled and hot water coils.
On a chilled water coil, a normally closed valve is used. On a
hot water coil or 2-pipe changeover system, a normally open
valve is used.
The 2-position valve used on a chilled water coil shall open on a
call for cooling when the outside air temperature is greater than
55˚F (adjustable). When the outside air temperature is less than
55˚F, the valve should remain closed and free cooling shall be
utilized. The 2-position chilled water valve shall be closed when
the 2-position hot water valve is open (when equipped). The
valve is controlled by a 24VAC digital output.
The 2-position valve used on a hot water coil shall open on a
call for heating. The valve shall always open when the outside
air temperature drops below 40˚F. This is to prevent the coil
from freezing or nuisance tripping of the freeze stat. The
2-position hot water valve shall be closed when the 2-position
chilled water valve is open (if equipped). The valve is controlled
by a 24VAC digital output.
The 2-position valve used on a 2-pipe changeover system shall
operate like the 2-position chilled water valve in cooling mode,
and like the 2-position hot water valve in heating mode.
Condensate Pump (Optional)
On units equipped with a condensate pump, the pump shall
begin to run once the condensate reaches a set level. The
pump comes with an internal safety switch that can be wired
either normally open or normally closed. The safety switch shall
be wired such that the chilled water valve closes when it trips.
On Carel units, the switch shall be wired normally closed into
a digital input of the controller. If the unit is also equipped with
a condensate pan float switch, both switches shall be wired in
series.
Condensate Pan Float Switch (Optional)
On units equipped with a condensate pan float switch, the
normally closed switch shall be wired such that the chilled
water valve closes or the outdoor condensing unit is disabled
(DX Cooling Models Only) upon tripping. On Carel units, the
switch shall be wired normally closed into a digital input of the
controller. If the unit is also equipped with a condensate pump,
both the condensate pump limit switch and condensate pan float
switch shall be wired in series.
CO Sensor (Optional)
2
An optional CO sensor with a range of 0-2000 ppm producing
2
an output signal of 4-20mA is available to modulate the outside
air damper. If equipped, the outside air damper shall modulate
open proportionally to compensate for the CO
room. On Carel units, if the CO
(adjustable), the damper shall remain at its normal minimum
position. If the CO level increases above 800 ppm, the
2
damper begins to open according to the proportional band.
The proportional band is set to a default of 200 ppm and is
adjustable. Using the default, once the CO
ppm, the damper shall be at its maximum ventilation position.
14-500.5
levels in the
2
level is 800 ppm or less
2
level reaches 1000
2
9