Mechanical Specifications
Return Air
General
Return air options shall include 100 percent modulating return fan and 100 percent modulating return with direct space building pressurization control. Return fans shall be either standard or low airflow.
100 Percent Modulating Return Fan
A single width plenum fan with airfoil blade shall be mounted on a shaft with fixed sheave drive. The fan shall be dynamically balanced for the operating envelop and tested in factory before being installed in unit. The plenum fan shall be test run in unit as part of unit test. Fan operating envelop rpm shall be below first critical speed. Fan shaft shall be mounted on two grease lubricated ball or roller bearings designed for
100 Percent Modulating Return Fan with Statitrac™ Control Option
A single width plenum fan with airfoil blade shall be mounted on a shaft with fixed sheave drive. The fan shall be dynamically balanced for the operating envelop and tested in factory before being installed in unit. The plenum fan shall be test run as part of unit final run test. Fan operating envelop rpm shall be below first critical speed. Fan shaft
mounted on common base to allow consistent belt tension with no relative motion between fan and motor shafts. The entire assembly shall be completely isolated from unit with
Fresh Air
General
Three outside air options: 0 to 25 percent motorized controlled outside air,
Demand Control Ventilation
The fresh air damper position shall modulate in response to a CO2 sensor in the conditioned space, in order to minimize the unit energy consumption, yet simultaneously meet the ventilation requirements of ASHRAE Std 62.1.
Fresh Air Measurement
A factory mounted airflow measurement station (TRAQ) shall be provided in the fresh air opening to measure airflow. The airflow measurement station shall measure from 15 to 100 percent of unit airflow. The airflow measurement station shall adjust for temperature variations.
0-100 Percent Modulating Economizer Option
Operated through the primary temperature controls to automatically utilize OA for “free” cooling. Automatically modulated return and OA dampers shall maintain proper temperature in the conditioned space. Economizer shall be equipped with an automatic lockout when the outdoor high ambient temperature is too high for proper cooling. Minimum position control shall be standard and adjustable at the Human Interface Panel or with a remote potentiometer or through the building management system. A spring return motor shall ensure closure of OA dampers during unit shutdown or power interruption. Mechanical cooling shall be available to aid the economizer mode at any ambient. Standard economizer dampers shall have a leakage rate of 20 cfm/ft^2 at 1.0 in W.C. pressure difference.
Low Leak and Ultra Low Leak Economizer Dampers Option
Low leak dampers shall be provided with chlorinated polyvinyl chloride gasketing added to the damper blades and rolled stainless steel jamb seals to the sides of the damper assembly. The low leak dampers shall have a leakage rate of 10 cfm/ ft^2 (AMCA Class 2) at 1.0 in W.C. pressure difference.
Ultra low leak damper will have added sealing under the jam seals and in the frame. The ultra low leak dampers shall have a leakage rate of 4 cfm/ft^2 (AMCA Class 1) at 1.0 in W.C. pressure difference.
Note: Based on testing completed in accordance with AMCA Standard 500D.
shall be mounted on two grease lubricated ball or roller bearings designed for
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