ACG CERTIFIED COMMISSIONING AUTHORITY EXAMINATION
APPENDIX
For Use with Exam Questions 85 – 100 only
Table of Contents
Design Sequence Of Operation
Figure 1 --
BAS Approved Submittal Drawing
Figure 2 --
Design Airflow Drawing
ACG CERTIFIED COMMISSIONING AUTHORITY EXAMINATION
DESIGN SEQUENCE OF OPERATION
FOR TYPICAL DUAL DUCT AIR HANDLING UNIT
System Description
The unit is designed as a heating-cooling, dual duct, variable volume air handling system. The unit consists of a
single supply fan, with coils located in a blow thru configuration. Each unit is provided with a minimum
amount of pretreated outside air. These systems shall supply air to dual duct air terminal mixing boxes.
The unit shall function as a complete system and shall normally operate 24 hrs/day (the unit does not require
occupied-unoccupied operation). In addition to the normal operating mode, the unit shall be provided with an
emergency smoke control operating mode. In building areas requiring smoke compartmentalization, each AHU
has been zoned to serve one smoke compartment (in some locations, the AHU will serve two smoke
compartments).
The AHU shall be enabled thru the building automation system (BAS).
Interlocking
Recirc pump shall be interlocked with supply fan.
Outside Air Control
Outside air shall be measured and controlled using a pressure-independent single duct, air terminal unit. Flow
shall be constant volume (FA). Refer to air terminal unit schedule. The air terminal unit shall close off outside
air flow when the AHU is not operating.
Fan Control
Each unit shall be furnished with a variable frequency drive (VFD). Fan shall start with VFD at low speed. The
BAS shall monitor the hot deck static pressure (HDP) and the cold deck static pressure (CDP). A static pressure
controller and its duct mounted static pressure sensors shall modulate the supply fan VFD to maintain the static
pressure setpoint (FA) from the static pressure sensor requiring the most air volume. Static pressure setpoint
shall be reset based on demand.
Unless otherwise shown, static pressure sensors PE-5 and PE-2 shall be located 2/3 down the most hydraulically
remote duct. One sensor shall be in the hot deck and one sensor shall be in the cold deck duct. Upon failure of
the static pressure signal, the fan speed shall be controlled to maintain the lower limit static pressure setpoint.
Test and balance shall give to the BAS contractor setpoints for the required hot deck (HDSP) and cold deck
(CDSP) static pressures.
Temperature Control
The hot deck temperature shall be sensed by an averaging sensor, TE-5. Cold deck temperature shall be sensed
by averaging sensors, TE-3 and TE-4. After proof of fan status, the temperature loops shall be enabled. The
ACG CERTIFIED COMMISSIONING AUTHORITY EXAMINATION
BAS shall modulate the hot deck control valve to maintain hot deck discharge air setpoint of 95 deg F (FA).
The BAS shall reset the hot deck setpoint (HDSP) based upon outside air temperature. See following schedule.
Outside Air Temperature
Hot Deck Supply Temperature Setpoint
30 Deg F
70 Deg F
95 Deg F
80 Deg F
The BAS shall modulate the chilled water control valve to maintain air setpoint, TE-3, of 52 Deg F (FA). The
BAS shall modulate the hot water reheat control valve (N.C.) to maintain air setpoint, TE-4, of 54 Deg F.
Recirculation pump shall run continuously. The BAS shall have the capability to reset the cold deck setpoint
(CDSP). Reset shall be based upon the return air temperature (TE-2) and return air humidity (HE-1) or owner
specified reset based upon the cooling requirements of the air terminals.
Dehumidification Control
Relative humidity in the return air duct shall be monitored by the BAS. Provide return air humidity sensor to act
as a high limit override. If return air relative humidity exceeds 60%, reset cold deck discharge air temperature
downward to maintain 60% RH. Provide a low limit cold deck discharge air temperature of 50 Deg F.
Safeties
The BAS shall monitor the discharge static pressure sensor. Upon a high static condition above setpoint
(CDSP), the VFD control signal shall be overridden to limit discharge static pressure.
Alarms
An alarm shall be generated at the BAS workstation if any of the following incidents take place during normal
operating mode.
1.
2.
3.
4.
Discharge air temperature falls below 45 Deg F or above 65 Deg F for more than 5 minutes when the AHU
is operating.
The filter differential pressure switch exceeds 1.5” WG for 10 minutes
The VFD Hand-Off-Auto switch is not in Auto
Supply fan commanded value does not match status proof condition
Smoke Mode
For AHUs serving compartmentalized areas of the building, refer to Drawing MB6.002. For AHUs listed
below, duct mounted smoke detectors shall automatically stop the supply fan on detecting the presence of
smoke.
AHU-AC-3-04
AHU-AC-3-05
AHU-AC-3-06
AHU-AC-3-07
AHU-AC-1-01
AHU-AC-P1-01
AHU-AC-P1-02
AHU-AC-P1-03
Figure 1 BAS Approved Submittal Drawing