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49
Demand Controlled Ventilation —
Demand Controlled Ventilation (DCV) function requires a
space air CO
2
sensor be connected to the W7220
controller. The CO
2
sensor provides a 2 to 10 vdc signal
proportional to the space CO
2
level. This sensor is
available as a factory--installed option (located in the
unit’s return air plenum) or as a field--installed accessory.
See Fig. 1 for model number nomenclature; check
Position #9 for codes E, F, G or H indicating a
factory--installed CO
2
sensor. The W7220 automatically
recognizes the connection of this sensor and self--enables
the DCV function after the Configuration period.
VENTILATION FOR PEOPLE
VENTILATION FOR SOURCES
INCREASING VENTILA
TION
VENTMAX
VENTMIN
100
700
INSIDE OUTSIDE CO
2
DIFFERENTIAL
C12167
Fig. 51 -- DCV Single--Speed System Setpoints
DCV With Single--Speed Fan System:
During DCV, the
outside air damper modulates between two user
configurations depending upon the signal level of the
space or return air CO
2
sensor representing the space
occupancy level. The lower of these two positions is
referred to as the Minimum IAQ Damper Position
(designated VENTMIN) while the higher is referred to as
Economizer Minimum Position (designated MINIMUM
POSITION or VENTMAX). The VENTMIN position
should be set to an economizer position that brings in
enough fresh air to remove contaminants and CO
2
generated by sources other than people; this airflow rate is
designated Va. The VENTMAX should be set to an
economizer position that brings in enough fresh air to
remove contaminants and CO
2
generated by all sources
including people at the design condition for maximum
space occupancy; this airflow rate is designated Vbz.
DCV With Two--Speed Fan System:
Ventilation codes
require that the same ventilation rates (Vbz and Va,
expressed as CFM) be provided regardless of supply fan
speed. When the supply fan speed is reduced, the internal
static pressure in the unit’s return plenum also decreases.
If the same outside air damper position is retained, the
airflow rate through the OA damper decreases below the
Va and Vbz levels. To restore ventilation rates to design
levels, the damper positions VENTMIN and VENTMAX
must be automatically adjusted when the fan speed
changes. The W7220 provides this function when it is
configured for 2--speed fan operation through a second set
of damper position setpoints.
During operation at High fan speed, the damper setpoint
limits are designated VENTMIN H and VENTMAX H.
Damper operation is same
as described under
Single--Speed Fan above.
During operation at Low fan speed, the damper setpoint
limits change to VENTMIN L and VENTMAX L. These
settings are higher than the comparable High speed
settings and cause the outside air damper to open more to
allow the same Va and Vbz airflow rates to be admitted to
the space.
Adjust the DCV setpoints VENTMAX H and VENTMAX L
with supply fan speed in High speed and Low speed
respectively to provide the design load ventilation airflow
rate Vbz by measuring outside air temperature, return air
temperature and supply air temperature. Make damper
position adjustments with at least 10
_
F temperature
difference between the outdoor and return--air temperatures.
VENTILATION FOR PEOPLE
VENTILATION FOR SOURCES
INCREASING VENTILA
TION
VENTMAX H
VENTMIN H
100
700
INSIDE OUTSIDE CO
2
DIFFERENTIAL
VENTILATION FOR PEOPLE
VENTILATION FOR SOURCES
INCREASING VENTILA
TION
VENTMAX L
VENTMIN L
100
700
INSIDE OUTSIDE CO
2
DIFFERENTIAL
HIGH SPEED FAN
LOW SPEED FAN
C12168
Fig. 52 -- DCV 2--Speed System Setpoints — Same Ventilation CFM at Both Speeds
Summary of Contents for WeatherExpert 48LC
Page 5: ...5 C13057 Fig 2 Unit Dimensional Drawing 14 Size Unit Sheet 1 of 3 ...
Page 6: ...6 C13058 Fig 2 cont Unit Dimensional Drawing 14 Size Unit Sheet 2 of 3 ...
Page 7: ...7 C13059 Fig 2 cont Unit Dimensional Drawing 14 Size Unit Sheet 3 of 3 ...
Page 8: ...8 C13032 Fig 3 Unit Dimensional Drawing 17 and 20 Size Units Sheet 1 of 3 ...
Page 9: ...9 C13033 Fig 3 cont Unit Dimensional Drawing 17 and 20 Size Units Sheet 2 of 3 ...
Page 10: ...10 C13034 Fig 3 cont Unit Dimensional Drawing 17 and 20 Size Units Sheet 3 of 3 ...
Page 11: ...11 C14106 Fig 4 Unit Dimensional Drawing 24 and 26 Size Units Sheet 1 of 3 ...
Page 12: ...12 C14107 Fig 4 cont Unit Dimensional Drawing 24 and 26 Size Units Sheet 2 of 3 ...
Page 13: ...13 C14108 Fig 4 cont Unit Dimensional Drawing 24 and 26 Size Units Sheet 3 of 3 ...
Page 17: ...17 C13054 Fig 8 Roof Curb Details 14 Size Unit ...
Page 18: ...18 C13055 Fig 9 Roof Curb Details 17 and 20 Size Units ...
Page 19: ...19 C13056 Fig 10 Roof Curb Details 24 and 26 Size Units ...
Page 27: ...27 a48 9336 Fig 26 48LC 14 26 Electro mechanical Control Wiring Diagram ...
Page 28: ...28 a48 9337 Fig 27 48LC 14 26 RTU Open Control Wiring Diagram ...
Page 29: ...29 a48 9338 Fig 28 48LC 14 26 SystemVut Control Wiring Diagram ...
Page 31: ...31 a48 9339 Fig 30 Typical Power Wiring Diagram SystemVut Controls 48LC 26 208 230V Shown ...
Page 58: ...58 a48 9340 Fig 55 Typical EconoMi erR X Wiring Diagram ...