Options/Accessories; Economizer Sequences; Dry Bulb Changeover; Single Enthalpy Changeover - York DC180 Installation Manual

5120416-XIM-C-0216
Check all connections for leaks when piping is completed using
a soap solution. NEVER USE A FLAME.
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warning exactly could result
in serious injury, death or property damage.
Never test for gas leaks with an open flame. use a
commercially available soap solution made specifically
for the detection of leaks to check all connections. A fire
or explosion may result causing property damage,
personal injury or loss of life.
Vent And Combustion Air
Two vent hoods and a combustion air hood (with screens) are
shipped attached to the blower housing in the blower
compartment. For units with factory installed VFD option, the
hoods and accompanying hardware are shipped inside the
gas heat section. These hoods must be installed to assure
proper unit function. All hoods must be fastened to the
outside of the gas heat access panel with the screws
provided in the bag also attached to the blower housing.
The screen for the combustion air intake hood is secured to
the inside of the access panel opening with four fasteners and
the screws used for mounting the hood to the panel. The top
flange of this hood slips in under the top of the access panel
opening when installing. Refer to Vent and Combustion Air
Hood Figure 17.
Each vent hood is installed by inserting the top flange of the
hood into the slotted opening in the access panel and securing
in place.
The products of combustion are discharged horizontally
through these two screened, hooded vent openings on the
upper gas heat access panel.
Vent Air
Outlet Hoods
Combustion Air
Intake Hood
Figure 17: Vent and Combustion Air Hood
22

Options/Accessories

Electric Heat
Electric heaters are available as a factory-installed option.
These heaters mount in the heat compartment with the
heating elements extending into the supply air chamber. All
electric heaters are fused and intended for use with single
point power supply.
Economizer/Motorized Outdoor Damper Rain Hood
The instruction for the optional economizer/motorized damper
rain hood can be found in the rain hood kit. Use these
instructions when field assembling an economizer rain hood
onto a unit. The outdoor and return air dampers, the damper
actuator, the damper linkage, the outdoor and return air divider
baffles, and all the control sensors are factory mounted as part
of the "Factory installed" economizer option.
Power Exhaust/Barometric Relief Damper and Rain Hood
The instructions for the power exhaust/barometric relief damper
and rain hood can be found in the rain hood kit. The exhaust
fan, all supporting brackets, angles, and the wiring are factory
installed as part of the power exhaust option.

Economizer Sequences

Several functions can drive the economizer, including: minimum
position, free cooling, economizer loading, and minimum
outdoor air supply.
Economizer Minimum Position
The economizer minimum position is set during occupied mode
when outside air is not suitable for free cooling. The position of
the damper is set proportionally between the "Economizer
Minimum Position and the Economizer Minimum Position Low
Speed Fan" set points, in relationship to the VFD output
percentage. On a constant volume single speed supply fan
system both set-points should be set to the same value.
Free Cooling
Four types of free cooling options are available: dry bulb
changeover, single enthalpy, dual enthalpy changeover, and
Slotted Openings in
Auto.
Access Panel

Dry Bulb Changeover

For dry bulb economizer operation, the outside air is suitable for
free cooling if the outside air temperature is 1°F below the
Economizer OAT Enable Setpoint and 1°F below the Return Air
Temperature.
Free cooling is no longer available if the outside air temperature
Gas Heat
Access Panels rises above either the Economizer OAT Enable setpoint or the
return air temperature.

Single Enthalpy Changeover

For single enthalpy economizer operation, the outside air is
suitable for free cooling if the outside air enthalpy is at least 1
Johnson Controls Unitary Products