| Mechanical Specifications (cont.)
Airside Economizer (Optional)
Mixing box with controls shall be provided for use as an Airside Economizer. The
casing shall be fabricated from 16 gauge galvanized
steel. The exterior shall be painted beige with a one mil coat of paint. Parallel
blade dampers shall be fabricated from 16 gauge
galvanized steel and rotate on rustproof nylon bushings.
All controls including linkages and actuators shall be factory installed and adjusted. The economizer may be shipped
separately for field installation. An enthalpy sensor
shall be provided for field installation.
The airside economizer shall be controlled to maximize hours of free cooling.
When outdoor conditions are not suitable, the outside
air damper shall be opened to its minimum position. When outdoor conditions are
suitable, the damper position shall be modulated in
response to supply air temperature. The setpoint
of the enthalpy control and the minimum position of the outside air damper shall be adjustable. During economizer
operation, the compressors shall be enabled.
System Control (Optional)
Unit shall be provided with factory installed controls to interface with other components in the system to perform
Unoccupied Night Setback, Morning Warm-Up, and Occupied
Cooling. Contacts shall be provided to interface with Heat controls, VAV boxes,
Cooling Tower and Ventilation equipment. All setpoints
shall be adjustable. Temperature sensors for each heating setpoint and a switch to override Night Setback for 2 hours shall be
provided for field installation. (Choose one)
A) A factory mounted seven day programmable timer with a built-in rechargeable
battery back-up system shall be included to control the
unit operating mode. The timer shall be accessible without opening any unit panels.
B) A set of terminals shall be provided to control the unit operating mode.
The Unoccupied mode shall be initiated when the
connection between them is closed. Morning Warm-up shall be initiated when the connection is open.
Building Automation System (Choose one)
A) Unit shall be provided with the necessary controls to interface with a control system provided by others. Terminals
shall be provided for Auto/Off, Fan On-Ventilate, and
discharge air temperature setpoint inputs; and dirty filter and alarm outputs.
B) Unit shall be provided with factory mounted controls to operate as part of a complete Integrated Comfort™ system.
This system will control the operating mode of the
unit; monitor unit status and diagnostics; annunciate alarms; log unit run time and starts; log timed overrides; and produce
weekly and monthly reports for energy consumption,
timed overrides and temperatures.
Selection Procedure
Unit Capacities
1 Determine
entering air temperature dry bulb and wet bulb and
condenser water flow (gpm) or delta T and entering condenser water temperature.
2 Refer to Tables
31-1 through 83-1 to find gross total capacity and
gross sensible capacity and leaving water temperature or gpm of the unit that best meets capacity requirements.
3 Apply the cfm
correction factors from the capacity correction factor
tables to determine gross total and gross sensible capacities at desired cf m.
4 Multiply
condenser water delta T by the total capacity cfm
correction factor to determine new condenser water delta T.
5 Using design
cfm, determine static air pressure drops for
accessories from the air pressure drop tables. Add accessory static pressure drops to external supply and return static air
pressure drops. Use the total air pressure drop to
determine rpm and brake horsepower requirements from
the appropriate fan curve.
6 Calculate
supply fan motor heat by using the following equation:
Fan motor heat (MBh) = 2.8 x fan motor brake horsepower.
7 Determine net
total capacity and net sensible capacity by subtracting
fan motor heat from gross total capacity and gross sensible capacity.
8 Refer to Trane
psychometric chart to determine leaving air
temperatures. |
