Air Monitor OAM II User guide

Precision Airflow Measurement
An ON
I CON Brand
Precision Airflow Measurement
An ON
I
CON Brand
OAM II
Outdoor Airow Measuring System
Application Guide

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 2 onicon.com
0
500
1000
1500
2000
2500
3000
0.000 0.500 1.000 1.500 2.000 2.500
3.000
Velocity SFPM
Total Pressure Drop In wc
Required Fixed Inlet Total Pressure Drop Graph
1.00(25.40)
.90(22.86)
.80(20.32)
.70(17.78)
.60(15.24)
.50(12.70)
.10(2.54)
.09(2.29)
.08(2.03)
.07(1.78)
.06(1.52)
.40(10.16)
.30(7.62)
.20(5.08)
.05(1.27)
.04(1.02)
.03(.76)
.02(.51)
.01(.25)
100 (30) 200 (61) 300 (91)
400 (122) 500 (152) 600 (183) 700 (213) 800 (244) 900 (274)
1000 (305) 2000 (610) 3000 (914)
4000 (1219) 5000 (1524) 6000 (1829) 7000 (2134) 8000 (2438) 9000 (2743)
10,000 (3048)
INTAKE
EXHAUST
PRESSURE DROP
Air Velocity in feet and (meters) per minute through Free Area
Ratings do not include the effect of a bird screen
Static Pressure Drop in inches w.g. and (mm)
Example of a louver pressure drop graph
Blowing dust and debris, moist air and low ow velocities are just some of the
problems commonly associated with outdoor airow measurement. These
conditions can be very challenging when trying to accurately measure the
amount of outdoor air entering a building using thermal or Pitot style airow
elements. Air Monitor’s OAM II Outdoor Airow Measurement System is
specically designed to provide accurate airow measurement in this
challenging application.
Each OAM II consists of a dedicated transmitter with a built-in barometric
pressure sensor, reference temperature sensor(s) and uni-sensor ow element(s).
The system oers exceptional performance in this dicult but extremely
important airow measurement application.
There are three dierent OAM II congurations. Each oers distinct advantages
for some of the most common outdoor airow applications. This guide
presents an overview of airow inlet types, OAM II congurations, and system
components. Consider the following when selecting an outdoor airow
measurement system.
What is the airow inlet type?
There are a variety of inlet types. The most common inlets incorporate
architectural louvers or packaged roof top units with single or multiple rain
hoods. The OAM II utilizes the static dierential pressure eld created by the air
entering and moving through the xed inlet. The dierential pressure required
to achieve accurate airow measurement is indicated in the graph below. Refer
to the louver manufacturer’s published pressure drop data to conrm it is
adequate to meet your application requirements.
What is the airow inlet size/geometry?
Many systems are large enough or shaped such that they will require multiple
uni-sensors connected in parallel to eectively average total airow through
the inlet. Minimum/Economizer (split) inlets may also require multiple sensors.
What is the best OAM II conguration for my applications?
The OAM II is available in three dierent factory congurations based on your
inlet type. Each conguration is optimized for a specic airow application. A
detailed description of each conguration is provided on the next page.
SECTION 1.0
INTRODUCTION

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 3 onicon.com
Inlet Types
System Congurations
Inlet Types
System Congurations
Single
System
Min/Econ
(Split)
Dual
System
Single
System
Min/Econ
(Split)
Dual
System
LOUVERED INLET RAIN HOOD INLET
SINGLE
√
SINGLE
√
SPLIT
√
SPLIT
√
MULTIPLE INLETS OF
EQUAL AREA
√
DUAL
√
FREE INLET DUCTED INLET
SINGLE
√
EXPANDED METAL
√
DUAL
√
STATION
√
SECTION 2.0
CONFIGURATIONS
The OAM II can be factory congured to operate in three dierent modes.
Single Channel, Single System Airow Measurement – This conguration
provides airow measurement from 150 to 2400 FPM. It is ideal for measuring
highly variable airow in a single inlet.
Minimum/Economizer (Split) Airow Measurement – The Min/Econ
conguration provides combined airow measurement for separate minimum and
economizer inlets. The OAM II is an eective tool for measuring this commonly
used inlet conguration.
Dual Channel, Dual System Airow Measurement – The dual channel
conguration provides two separate airow measurements in one transmitter. Ideal
for built-up systems that provide outdoor air to multiple locations.

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 4 onicon.com
OUTDOOR AIR
CONTROL DAMPER
AIR
FLOW
VOLU-o/OAM II
UNI-SENSOR
LOUVERED INLET
BIRD SCREEN
Install the uni-sensor as close to the center of the inlet as possible. The distance
between the tip of the uni-sensor and the edge of the fully open damper blade
should be at least 2”. See drawing below.
Louvered Inlets:
Install the uni-sensor on the front face of the louver. The louver size and
shape will determine the number of sensors required for the inlet. If the louver
manufacturer, model number, net free area and free area velocity vs. pressure
drop information is provided, Air Monitor will factory characterize the OAM II
transmitter. This will eliminate the need for eld characterization.
The louver depth will dictate the length of the uni-sensor probe (louver depth
+ 2”). Standard probe lengths are available in 1” increments.
SECTION 3.0
INLET TYPES

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 5 onicon.com
OAM II STATION
Rain Hood Inlets:
The inlet must produce the required pressure drop (as shown in the graph on
page 2) in order to accurately measure the airow through the inlet. The use of
expanded metal across the inlet or an airow station provided by Air Monitor
will greatly simplify the installation process and eliminate the need for eld
characterization. If an OAM II Airow Station is used, it can be sandwiched
between the rain hood and the AHU’s OA damper.
Minimum/Economizer (Split) Inlets:
In the installation below, two inlets separately provide minimum and
economizer outside airows to a single air handler. The OAM II, operating in a
dual channel, single system conguration would provide both individual and
totalized airow rate information.

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 6 onicon.com
OAM II STATION
AIR
FLOW
Ducted Inlets:
OAM II Stations or expanded metal screens installed in ducts should be located
such that there is no interference upstream or downstream that would intrude
into the OAM II station casing or into the area where the uni-sensor is installed.
WITH OAM II STATION
PLENUM
PLENUM INLET
WITH OAM II STATION
PLENUM
PLENUM INLET
UNI-SENSOR
MOUNTED ON
EACH INLET
SIGNALS
MANIFOLDED
TOGETHER
Plenum Inlets:
When mounting an OAM II station directly to a damper casing, conrm
there is sucient clearance between the fully open damper blades and
the uni-sensor probe. If required, an extended case OAM II Station can be
provided in order to achieve the required 2” minimum distance.
Multiple Inlets:
Uni-sensors installed on each inlet are connected via manifolds or tees to
provide averaged sensor signals to the transmitter. The area of each inlet
should be identical for best results, and inlet dampers must operate in unison.
OAM II STATION

OAM II APPLICATION GUIDE
Air Monitor Corporation 800.AIR.FLOW Page 7 onicon.com
OAM II Station (shown with a single uni-sensor)
OUTSIDEAIR MONITOR
VOLU-flo/OAM ll
UNI-SENSOR
FLANGE
EXPANDED METAL
TEMPERATURE
SENSOR
LOW PRESSURE PORT
HIGH PRESSURE PORT
Inlets with an Aspect Ratio >6:1 & Inlets with an Area >30 ft2:
Inlets with an aspect ratio >6:1 require the use of multiple uni-sensors spaced
at equidistant intervals. For example: A 2’ x 30’ louvered inlet has an aspect
ratio of 15:1. Use three equally spaced sensors serving 2’ x 10’ areas to reduce
the aspect ratio to 5:1 for each sensor. Another example; if a unit has a 7’ x 12’
inlet, three sensors are required with each covering a 7’ x 4’ area.
OAM II Stations are built to order and are delivered fully assembled. The number
of sensors provided varies based on the size and shape of the station. When
multiple OAM II stations are provided for a single system, only one station will
include an RTD temperature sensor.
OAM II Stations are built using attened galvanized or stainless steel expanded
metal with 63% open (free) area, 0.05” thickness, and 0.50” SWD x 1.25” LWD x
0.096” strand width. The ow and pressure drop characteristics of this expanded
metal is fully dened. This simplies the installation as the airow station is
provided fully characterized from the factory.
SECTION 4.0
AIRFLOW STATIONS

Precision Airflow Measurement
An ON
I CON Brand
1050 Hopper Avenue • Santa Rosa, CA 95403 • USA
(P) 800.AIR.FLOW • www.airmonitor.com
DOC-0001939
OAM II APPLICATION GUIDE
February 2019
The uni-sensor is constructed of 316 stainless steel and is resistant to
corrosion caused by salt and most other airborne corrosives. It combines an
outside reference (high pressure) sensor and an inlet airow (low pressure)
sensor into one assembly. They are provided with probe lengths that match
the clearance requirements of the inlet where they will be installed.
Uni-sensors are ideal for retrot installations because they are easily
mounted to a variety of existing inlet types.
IMPORTANT NOTE
Air Monitor’s OAM II system is provided with an easy-to-use eld
characterization program. Test and balance ow data is entered,
automatically adjusting the factory OAM II response curve. Field
characterization is recommended for those installations where the inlet
type is not fully dened at the factory.
SECTION 5.0
AIRFLOW SENSORS