TranSystems Corporation - LGM Construction

501070099 Federal Express Oakland Sort Expansion Issued for Bid 10/11
1. The RTU will enable cooling or heating to maintain discharge air temperature setpoint
(adj). The RTU will control the supply fan VFD to maintain duct static pressure setpoint
(adj). The outdoor air damper will open to the minimum setpoint.
E. Discharge Air Temperature Reset Control:
1. The discharge air temperature setpoint, adjustable (55°F-65°F), will be reset based on
either the outside air temperature or zone average temperature. The minimum discharge
air setpoint will be set at 55ºF (adj). The discharge temperature sensor will prevent the
discharge air temperature from falling below the minimum discharge air setpoint (adj). If
the discharge air temperature continues to fall, the discharge temperature sensor will act
as a low discharge temperature limit, a low temperature alarm will be annunciated, and
the unit will shut down. If the discharge temperature rises above the high limit setpoint
the sensor will act as a high discharge temperature limit and will keep the unit running, a
high temperature alarm will be annunciated.
a) Outdoor Air Temperature Reset:
The discharge air temperature setpoint will be adjusted based on the outside air
temperature and the cooling load of the building.
b) Zone Temperature Reset:
The discharge air temperature setpoint will be adjusted based on the
temperature of the critical zone(s).
F. Discharge Duct Static Pressure Control:
1. Reference Duct Static Pressure Optimization in section 4.01 “ROOFTOP/VAV SYSTEM
CONTROL”
G. Economizer Control:
1. The mixed air sensor will measures the dry bulb temperature of the air leaving the
evaporator coil while economizing. When economizing is enabled and the unit is
operating in the cooling mode, the economizer damper is modulated between its
minimum position and 100% to maintain the zone temperature at the economizer
setpoint. The economizer setpoint is (ESP) derived from the cooling and heating setpoints
(CSP and HSP) so that ESP is the higher of CSP – 1.5°f or HSP + 1.5°f. If the mixed air
temperature starts to fall below 53°F, the economizer starts to close, at 50°F, the damper
will be at minimum position. Compressors will be delayed from operating until the
economizer has opened to 100% for 5 minutes.
H. Supply Fan Operation:
a) Reference Dry Bulb:
Outside air (OA) temperature is compared with a reference dry bulb point. The
economizer is enabled when OA temperature is less than reference dry bulb
point. The economizer is disabled when OA temperature is greater than
reference dry bulb point + 5.0°F.
1. The supply fan will be enabled while in the occupied mode and cycled on during the
unoccupied mode. A differential pressure switch will monitor the differential pressure
across the fan. If the switch does not open within 40 seconds after a request for fan
DIRECT DIGITAL CONTROL SYSTEM 15900-23