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Thismakes thecontrol of theof thedehumidification
device
simple when u sing t he enthalpy ordifferential
enthalpy sensor.
The
enthalpy sensor ordifferential
enthalpy sensor isinstalled onthe
equipment
todetermine
economizer
operation.
Thehigh enthalpy
signal from the enthalpy sensor ordifferential
enthalpy sensor can
beused t oturn ontheoutdoor airmoisture removal device a ny
time fresh a irisrequired forthe space.
The energy recovery device s hould besized f ormaximum latent
and sensible
conditioning
atmaximum
ventilation
onadesign day.
A calculation
forleaving-air temperature
onalowambient, low
ventilation dayshould a lso bedone t odetermine
the mixed-air
temperature
of thereturn and pre-conditioned
outside air.The
design should p roduce anairtemperature
somewhat
near r oom
conditions to prevent reheat of theair mixture. Theenergy
recovery
device should beinterlocked
withthe heat toturn offthe
device when i nthe heat mode.
Operating
Sequence
Cooling_ Units Without Economizer
When the thermostat
calls for one stage of cooling,
Y1 and G are
energized.
The
indoor-fan
contactor
(IFC)
and
compressor
contactor
C.AI
and outdoor-fan
contactors
(OFC1
and OFC2
when outdoor
temperature
is above LTS setting)
are energized
and
the
indoor
fan motor,
compressor(s)
or AI,
and
outdoor
fans
controlled
by OFCI
are started.
If the outdoor
temperature
is above
the
setting
of the
low
temperature
switch,
the
outdoor
fans
controlled
by OFC2 are also started.
If more
cooling
is required,
the thermostat
will call for a second
stage
of cooling,
energizing
Y2.
This
in
turn
energizes
the
compressor
contactor
C.BI.
The second
stage
compressor
BI is
then started.
Heating_
Units
Without
Economizer
When
the
thermostat
calls
for
one
stage
of heating,
WI
is
energized.
The thermostat
must be configured
such that the blower
output
(G) is energized
when
there is a Wl
call for heating.
The
indoor-fan
contactor
(IFC)
and first stage electric
heat contactor(s)
are energized
and the indoor-fan
motor,
and first stage
electric
heater are started.
If additional
heating
is required,
the
thermostat
will call for a
second
stage
of heating,
energizing
W2. This
will energize
the
second
stage of electric
heat.
Cooling_
Units
With
EconoMi$er
IV
When
free
cooling
is not
available,
the
compressors
will
be
controlled
by the zone thermostat.
When free cooling
is available,
the
outdoor-air
damper
is modulated
by the
EconoMi$er
IV
control
to provide
a 50 ° to 55°F
mixed-air
temperature
into the
zone.
As
the
mixed-air
temperature
fluctuates
above
55 ° or
below
50°F,
the dampers
will be modulated
(open
or close)
to
bring the mixed-air
temperature
back within control.
If
mechanical
cooling
is
utilized
with
free
cooling,
the
outdoor-air
damper
will maintain
its current
position
at the time
the compressor
is started.
If the increase
in cooling
capacity
causes
the mixed
air temperature
to drop below 45 °F, then the outdoor-air
damper
position
will be decreased
to the minimum
position.
If the
mixed-air
temperature
continues
to fall, the outdoor-air
damper
will
close.
Control
returns
to
normal
once
the
mixed-air
temperature
rises above 48°F.
If optional
power
exhaust
is installed,
as the outdoor-air
damper
opens
and closes,
the power
exhaust
fans will be energized
and
deenergized.
If field-installed
accessory
CO2
sensors
are connected
to the
EconoMi$er
IV control,
a demand
controlled
ventilation
strategy
will begin
to operate.
As the CO2 level in the zone increases
above
the CO2 set point,
the minimum
position
of the damper
will be
increased
proportionally.
As the CO2 level decreases
because
of the
increase
in fresh air, the outdoor-air
damper
will be proportionally
closed.
Table 8 - CO 2 Sensor
Standard
Settings
SETTING
1
2
3
4
5
6
7
8
VENTILATION
ANALOG
EQUIPMENT
OUTPUT
RATE
OUTPUT
(cfm/Person)
0-10V
Proportional
Any
4-20 mA
Interface
w/Standard
2-10V
Building
Control
Proportional
Any
7-20 mA
System
0-10V
Exponential
Any
4-20 mA
Economizer
Health & Safety
Parking/Air Intakes/
9
Loading Docks
Proportional
Proportional
Exponential
Exponential
Proportional
Proportional
0-10V
15
4-20 mA
0-10V
20
4-20 mA
0-10V
15
4-20 mA
0-10V
20
4-20 mA
0-10V
--
4-20 mA
0-10V
--
4-20 mA
CO2
CONTROL
RANGE
(ppm)
0-2000
0-2000
0-2000
0-1100
0-900
0-1100
0-900
0-9999
0-2000
OPTIONAL
RELAY SETPOINT
(ppm)
1000
1000
1100
1100
900
1100
900
5000
700
LEGEND
PPM i
Parts Per Million
RELAY
HYSTERESIS
(ppm)
50
50
50
50
50
50
50
500
50
33
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