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PKG-SVX029A-EN
Waterside Economizer Option
The waterside economizer option takes advantage of
cooling tower water to either precool the entering air to aid
the mechanical cooling process or, if the water temperature
is low enough, provide total system cooling. Waterside
economizing enables when the unit’s entering water
temperature is below the unit’s entering mixed air
temperature by a minimum of 4°F plus the economizer’s
approach temperature. The approach temperature default
is 4°F. Waterside economizing disables when the unit’s
entering water temperature is not below the unit’s entering
mixed air temperature by at least the water economizer
approach temperature. The approach temperature defaults
to 4°F. The economizer acts as the first stage of cooling. If
the economizer is unable to maintain the supply air
setpoint, the unit control module brings on compressors as
required to meet the setpoint.
The waterside economizer includes a coil, modulating
valves, controls, and piping with cleanouts. The coil
construction is ½-inch (13 mm) OD seamless copper tubes
expanded into aluminum fins. The evaporator and
economizer coils share a common sloped (IAQ) drain pan.
Drain pan options are either galvanized or stainless steel,
and are insulated and internally trapped.
The tubes are arranged in a staggered pattern to maximize
heat transfer. The coil has round copper supply and return
headers with removable clean-out and vent plugs.
Figure 16. Waterside economizer flow control
Heat Mode
The BAS HEAT option supports remote heat (hot water coil
or electric heat).
When the SWUD Operating Mode is set to BAS HEAT, the
unit controller ends any Cooling Mode operation
(Mechanical and/or Water Side Economizer) and
transitions to control Discharge Air Temperature to the BAS
HEAT setpoint temperature. The unit controller does this by
opening and closing the heating ball valve or staging the
electric. The Fan Array is controlled normally to maintain
static pressure to the Static Pressure Setpoint.
If the Discharge Air Temperature exceeds 104°F a
Manually Resettable High Discharge Air Temperature
Diagnostic is annunciated.
Dirty Air Filter Sensor Option
A factory installed differential pressure sensor senses the
pressure differential across the filters. When the differential
pressure exceeds a user selectable setting will display a
diagnostic. The unit will continue to run until you replace
the air filters.
Supply Air Static Pressure High Limit
During normal operation, the Supply Air Static is monitored.
If at any time the static pressure exceeds the software high
static limit (defaulted at 2.0 inches from the factory) the unit
will immediately shut down and generate a diagnostic.
In order for the unit to resume operation, the Alarm Reset
must be toggled from the TD-7. The software high static
limit can be user adjusted at the TD-7.
Airside Components
Two-Position Damper Interface
Units with two-position damper ventilation interface are
equipped with the necessary control sequences to allow
opening of a two-position outdoor air damper to deliver
ventilation air to the return air stream of the unit.
When the unit is in the occupied mode and the supply fans
are running, a binary output will turn on sending 24 Vac to
the two-position damper to allow ventilation air into the unit.
Airside Economizer Interface with OA
Reference
Units with airside economizer interface are equipped with
the necessary control sequences to allow using outside air
for the first stage of cooling, in occupied or unoccupied
mode and when ambient conditions are favorable for
economizing. Inherent in the unit controller is the ability to
suppress the setpoint below the normal unit setpoint. This
allows the building to improve comfort levels when
possible, and at the same time, optimize building
mechanical cooling operation for peak operating efficiency.
An outside air temperature and relative humidity sensor are
field sourced and installed.
Economizer operation enables when the outside air
enthalpy is less than 25 BTU’s/lb. (adjustable 19 to 28
BTU’s/lb). During occupied mode, the outside air damper
opens to 15 percent (adjustable 0 to 50%) for ventilation
purposes. An analog 2 to 10 Vdc output is provided to
modulate the field-provided and installed damper
actuators.
Airside Economizer Interface with
Comparative Enthalpy
Units with airside economizer interface and comparative
enthalpy are equipped with the necessary control
Operating Principles
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