I/O MANUAL Horizontal/Modular/Vertical/Rooftop AHU 2015pg
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COMMERCIAL AIRE PRODUCTS 501 Terminal Road, Fort Worth TX 76106
Tel: 817-624-0820
AWG should be 35 inch/pound and 8 AWG should be 40 inch / pound wiring in heater.
6.) Review the proper size disconnect means and / or fusing has been applied to heater power supply
circuit Only qualified individuals experienced in proper installation of heating and cooling should
perform any start-up operations of HVAC systems.
Turn disconnect switch (s) to the on position. Energize heater circuit with thermostat to 100% rating of
heater KW rating. First start-up of heating element will burn off any element manufacturing oil that may
cause some smoke in the air system.
7.) Using proper measuring devices to measure voltage to heater, line voltage should be plus or minus
5% of heater rated voltage. Never operate 208V rated heater on 240V line voltage. Measure line 1 to
line 2 on single phase heaters and line 1 to neutral on 120V and 277V heaters.
On three phase heaters measure line 1 to line 3, line 2 to line 3 and line 1 to line 2 for proper line
voltage. Measure amp draw on supply conductors to heater disconnect switch or terminal block, for
proper amp draw with proper instruments. Amp draw must match heater data label with 100% heater is
energized; reading should be plus or minus 3%.
8.) Air flow over heating elements must be even across the face of the heater. Duct system must have
.08 minimum static pressure duct system 2
9.) Automatic reset will de-energize heater if heater is not installed to manufacturers duct installation
manual or low air flow/uneven air across face of element.
Correction must be made to operate heater. Manual reset will also de-energized heater if there is low or
uneven air flow over the heating elements. Air flow volume and / or reinstallation of heater must be
done before energizing heater.
10.) If heater has a control transformer it may have a breaker in the circuit. If transformer is shorted,
breaker will open the circuit. You must reset and find the cause of the short. If transformer has no
breaker, it may have an inline fuse. A short circuit will open the transformer. Transformer must be
replaced with an identical transformer.
11.) Air flow switch only proves that air flow exists, not that the minimum proper air flow does exist;
standard air pressure switch set-up is for positive air pressure system.
Heaters in negative air system must have air tubing to air pressure switch relocated to the open port of
the switch.
12.) After heater installation and operation has meet standards and heater data label, closed heater
panel door and energized heater circuit.
Minimum Air Flow Requirements Across the heaters
Each KW produces 3413 BTUH. Divide the total BTUH needed by 3413 to find the KW needed. Use the
chart below to find the minimum air flow required. You will need to know the maximum inlet
temperature of the heater. The outlet air from a Heat pump (sometimes 110 º F) would be the inlet air
to an auxiliary heater. You must also know the Kw per Sq. Ft. of the Minimum Duct Area (Kw/Sq. Ft.
MDA) for the heater. An example is worked out below:
EXAMPLE:
Using 12 KW Heater designed for minimum duct size 8” x 16” and being the only heat in
an area. You expect inlet air to the heater will be 77 º F Maximum.
8” x 16” divided by the .888 Sq. Ft. = 13.5 which is the Kw/Sq. Ft. MDA
Locate the 13.5 along the top side of the chart and from there draw a vertical line
downward until the 77 º F inlet air line is intersected. From point of intersection draw a
horizontal line to the left side of the chart to the answer of 800 FPM (Velocity) of air
minimum required over the heater.