T H E S M A R T S O L U T I O N F O R E N E R G Y E F F I C I E N C Y
Vertical DOAS
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c l i m a t e m a s t e r . c o m
The total air fl ow of a ClimateMaster 20-ton through
30-ton system should be checked by measuring the air
pressure drop across only the reheat coil as shown in
Figure 2. Note: Port #1 is measuring the internal cabinet
pressure downstream of the evaporator (high side)
and port #2 is added to the discharge duct in the fi eld,
downstream of the reheat coil (low side).
A Magnehelic® or inclined manometer with a range
of 0.0-1.0 inch water column will work well for this.
ClimateMaster DOAS units feature an adjustable blower
sheave to simplify air balancing. Utilize the following
procedure to determine system airfl ow:
1. Check the condition of the air fi lters and coils. Assure
that they are clean.
2. Check for any obvious restrictions in the ductwork.
3. Drive the outdoor air damper open, start the supply
air blower and energize the fi eld-installed exhaust air
blower by turning on the “occupied” switch.
4. Use a Magnehelic® or inclined manometer to
measure the air pressure drop across ports #1 and #2.
Refer to Figures 1 & 2 to determine your unit cabinet
confi guration and the air sampling port locations.
Compare this value to the value printed on the air fl ow
label on the side of the DOAS unit.
5. Change the air fl ow, if necessary, by adjusting the
motor pulley or any balancing dampers in the fi eld-
installed ductwork.
Always measure the current draw of the blower motor
after you make any changes to the air fl ow quantity. If
the motor draws more than its FLA rating but the total
air fl ow is still low, check the resistance of the ductwork.
Verify that all grilles and dampers have been opened
and that there are no sudden turns or restrictions in the
ductwork.
Duct System Installation
Duct System Installation -
Duct design and installations
should conform to the latest ASHRAE and SMACNA
low velocity duct standards Undersized, restrictive
ductwork with abrupt turns or transitions can decrease
the effi ciency and the moisture removal capacity of
your DOAS unit. Size the ductwork for an acceptable air
pressure drop at the airfl ow volume of your DOAS unit.
Use neoprene fl ex connectors when you attach ductwork
to the DOAS unit to prevent transmission of excess
vibration and noise.
Select the grilles, registers and diffusers for low static
pressure loss, required throw distance, and the specifi ed
CFM rating. You can fi nd this information in most grille
manufacturer’s catalogs. If you are installing the grilles in
a corrosive environment, choose components made from
anodized aluminum.
If you must install ductwork in an unconditioned area, use
fi berglass duct wrap with vapor barrier facing. You must
install the outdoor air intake away from any sources of
airborne contamination such as exhaust fans or plumbing
vents. You can use galvanized sheet metal ducts for
most applications. However, you should use aluminum
or stainless steel ducts for extreme applications such as
chemical-laden environments.
Unit Air Flow -
Each ClimateMaster DOAS unit is
designed to operate at a specifi ed air fl ow rate. System
air fl ow must be checked prior to troubleshooting the
refrigeration circuit to assure that such problems are not
actually caused by improper unit air fl ow.
Problems with excessive airfl ow include:
• Reduction in moisture removal capacity.
• High amperage draw by the blower motor.
• Water carry over from evaporator coil.
• Excessive unit noise levels.
Problems with inadequate airfl ow include:
• Violation of ventilation codes.
• Risk of evaporator coil freezing.
• Possibility of premature compressor failure.
Determining System Air Flow -
The total air fl ow of a
ClimateMaster 4-ton through 15-ton system should be
checked by measuring the air pressure drop across both
the evaporator and reheat coil between port #1 (low side)
and port #2 (high side) as shown in Figure 1.
WARNING!
WARNING! - Disconnect power before adjusting blower. Failure
to disconnect power could result in death or serious injury.
