McQuay OAC 003G Installation Manual
Installation and Maintenance Manual IM 777-4
Skyline Air Handler
Models OAC/OAH 003G – 090G
Group: Applied Air Systems
Part Number: IM 777
Date: May 2009
© 2009 McQuay International
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
General Information . . . . . . . . . . . . . . . . . . . . . . . 3
Receiving and Handling . . . . . . . . . . . . . . . . . . . . 3
Unit Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Installation Guidelines . . . . . . . . . . . . . . . . . . . . . 3
Mechanical Installation . . . . . . . . . . . . . . . . . . . . . . 4
Service Clearances . . . . . . . . . . . . . . . . . . . . . . . 4
Rigging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Curb Mounting and Unit Leveling. . . . . . . . . . . . . 4
Assembling Sections . . . . . . . . . . . . . . . . . . . . . . 5
Shipping Sections . . . . . . . . . . . . . . . . . . . . . . 5
Panels, Frame Channels, and Doors . . . . . . . . . . 7
Panel Removal . . . . . . . . . . . . . . . . . . . . . . . . 7
Frame Channel Removal . . . . . . . . . . . . . . . . 7
Access Doors and Panels. . . . . . . . . . . . . . . . 7
Fan Section Doors . . . . . . . . . . . . . . . . . . . . . 7
Injected-Foam Insulated Panels . . . . . . . . . . . 8
Field Mounting Junction Boxes and
Other Components. . . . . . . . . . . . . . . . . . . . . . . . 8
Duct Connections. . . . . . . . . . . . . . . . . . . . . . . . . 8
Dampers and Hoods . . . . . . . . . . . . . . . . . . . . . . 9
Mounting Actuators . . . . . . . . . . . . . . . . . . . . . . . 9
Face and Bypass Section Mounting. . . . . . . . . . 10
Piping Vestibules . . . . . . . . . . . . . . . . . . . . . . . . 10
Piping and Coils . . . . . . . . . . . . . . . . . . . . . . . . . 10
Water Cooling Coils . . . . . . . . . . . . . . . . . . . 10
Direct Expansion Coils . . . . . . . . . . . . . . . . . 10
Steam Coils. . . . . . . . . . . . . . . . . . . . . . . . . . 11
Water Heating Coils . . . . . . . . . . . . . . . . . . . 13
Drain Pan Traps . . . . . . . . . . . . . . . . . . . . . . . . . 13
Internal Isolation Assembly Adjustment . . . . . . . 14
Electrical Installation . . . . . . . . . . . . . . . . . . . . . . 16
Wiring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Operation Guidelines . . . . . . . . . . . . . . . . . . . . . . 17
Startup Checks . . . . . . . . . . . . . . . . . . . . . . . . . 17
Before Starting the Unit: . . . . . . . . . . . . . . . . . . 17
Fan Wheel Alignment . . . . . . . . . . . . . . . . . . 18
Operating Limits. . . . . . . . . . . . . . . . . . . . . . . . . 19
Fan Vibration Levels . . . . . . . . . . . . . . . . . . . . . 21
Vibration Causes . . . . . . . . . . . . . . . . . . . . . 21
Service and Maintenance . . . . . . . . . . . . . . . . . . . 22
Periodic Maintenance . . . . . . . . . . . . . . . . . . . . 22
Ball Bearing Lubrication. . . . . . . . . . . . . . . . . . . 22
Motor Bearings . . . . . . . . . . . . . . . . . . . . . . . 22
Fan Shaft Bearings. . . . . . . . . . . . . . . . . . . . 22
Fan Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
VM and VP Variable Pitch Key Type Sheaves 23
LVP Variable Speed Sheaves . . . . . . . . . . . 24
MVP Variable Speed Sheaves . . . . . . . . . . . 25
Fan Drive Belt. . . . . . . . . . . . . . . . . . . . . . . . 26
Front Load Filter Option. . . . . . . . . . . . . . . . . . . 28
Filter Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Coils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Winterizing Water Coils . . . . . . . . . . . . . . . . 29
Removing and Replacing Components . . . . . . . 29
Removing the Fan Section . . . . . . . . . . . . . . 29
Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Replacement Parts . . . . . . . . . . . . . . . . . . . . . . 31
Service and Warranty Procedure . . . . . . . . . . . . 32
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Warranty Return Material Procedure . . . . . . . . . 32
Check, Test, and Start Procedure Form . . . . . . . 33
Quality Assurance Survey Report. . . . . . . . . . . . 35
Introduction
OAH 003 G D A C
Model
OAH = Outdoor air handler
OAC = Outdoor air component
Nominal Unit Size
(nominal square foot of coil)
003, 004, 006, 008, 010, 012, 014, 017, 021, 025,
030, 035, 045, 055, 065, 080, 085, 090
Vintage of McQuay Air Handling Unit
Unit Cross Section
C = Standard unit cross section
M = Custom size cross section
Motor Location
A = Motor along side of fan housing
D = Motor downstream of belt drive plenum fan
F = Motor on inline fan
G = Motor downstream of direct drive plenum fan
T = Motor behind twin housed fans
Unit Type/Coil Position
B = Blow-thru cooling coil location
D = Draw-thru cooling coil location
H = Heating only
V = Vent only
Introduction
General Information
The system design and installation must follow accepted industry
practice as described in the ASHRAE Handbook, the National
Electric Code, and other applicable standards. Install this
equipment in accordance with regulations of authorities having
jurisdiction and all applicable codes.
Installation and maintenance must be performed by qualified
personnel familiar with applicable codes and regulations and
experienced with this type of equipment. Sheet metal parts,
self-tapping screws, fins, clips, and such items inherently have
sharp edges; the installer should exercise caution.
CAUTION
Sharp edges and coil surfaces are a potential injury hazard.
Avoid contact with them.
ATTENTION
Les bords tranchants et les surfaces des bobines sont un
risque de blessure. Ne les touchez pas.
Receiving and Handling
1 Carefully check items against the bills of lading to verify
all crates and cartons have been received. Carefully
inspect all units for shipping damage. Report damage
immediately to the carrier and file a claim.
2 Skyline air handler units are constructed of galvanized or
painted steel and are inspected thoroughly before leaving
the factory. Take care during installation to prevent
damage to units.
3 Take special care when handling the blower section. All
fans are dynamically balanced before leaving the factory.
Rough handling can cause misalignment or a damaged
bearings or shaft. Carefully inspect fans and shaft before
unit installation to verify this has not happened.
Note: Screws, bolts, etc., for assembling sections are supplied
in a bag attached to each section. All necessary
gasketing is applied in the factory for section-to-section
mounting, unless the unit has a curb ready base. Units
require caulk sealant between sections.
Unit Storage
Store unit on a level surface. If air handling units are stored for
any period of time, periodically rotate the fan wheel to prevent
permanent distortion of drive components. In addition, grease
may settle in the lower part of the bearing, which can lead to
oxidation on the upper portion of the bearing surface. Keep the
fan bearings lubricated.
Nomenclature
Installation Guidelines
McQuay IM 777-4 3
Mechanical Installation
4 . 0 0 " b a s e r a i l e x t e n s i o n
W i d t h
3 0 . 0 0 "
4 . 0 0 "
W i d t h o f c o i l s e c t i o n
W i d t h o f
f a n s e c t i o n
3 0 . 0 0 "
H e i g h t
5 4 "
1 2 "
Mechanical Installation
Service Clearances
Rigging
In addition to providing adequate space around the unit for
piping coils and drains, access to at least one side of the unit is
always required to allow for regular service and routine
maintenance, which includes filter replacement, drain pan
inspection and cleaning, fan bearing lubrication, and belt
adjustment. Provide sufficient space—at least equal to the
length of the coil—on the side of the unit for coil removal. See
Figure 1 for servicing space requirements.
Maintain at least 54" of clearance in front of electrical power
devices. Electrical power devices that are mounted on the side
of the unit typically are up to 12" deep (Figure 2).
Figure 1: Servicing Space Requirements
Skyline air
assembled, or in modules of assembled sections.
handlers ship as separate sections, completely
The unit must
be rigged as it ships from the factory. Do not rig units after
assembly.
and
the corners of each shipping section.
Units are
provided with a factory-installed base rail
can be lifted using the 2" diameter lifting holes located in
To prevent damage to the
unit cabinetry, use spreader bars. Position spreader bars to
prevent cables from rubbing the frame or panels. Before
hoisting into position, test lift for stability and balance. Avoid
twisting or uneven lifting of unit.
Figure 3: Unit and Section Rigging
Figure 2: Service Clearance for Electrical Power Devices
Curb Mounting and Unit Leveling
Do not place a Skyline unit over an open curb unless it is
equipped with a curb-ready base. Installation instructions for
mounting units on a roof curb are provided in IM 770. For a
copy, contact your local McQuay representative or visit
www.mcquay.com. Make provisions under the unit to divert
any moisture from entering the building below.
For units without roof curb mounting, place the equipment on
a flat and level surface. Where surface irregularities exist, shim
the base of the unit at one or more points along the length of
the rails to prevent distortion or sagging of the support rails.
Uneven or distorted sections cause misfit or binding of the
doors and panels and improper draining of drain pans
(Figure 4).
4 McQuay IM 777-4
Mechanical Installation
S h i m t o p r e v e n t
d i s t o r t i o n i f w i d t h
i s o v e r 1 0 8 "
S h i m s e c t i o n s u n t i l
t h e y a r e s t r a i g h t
a n d l e v e l
1 / 4 " d i a m e t e r
b e a d c e n t e r e d
i n f a c e o f
c l e a r a n c e
U s e S p l i c e
J o i n t a s a
g u i d e
R e m o v a b l e
L i f t i n g B r a c k e t
Figure 4: Leveling the Unit
Assembling Sections
If the unit is shipped in more than one shipping section, rig
each section into position separately. Shipping sections are
provided with a connection splice joint attached on the leaving
air side of the shipping section that seals against the frame
channel on the entering-air side of the adjoining. The splice
joint is insulated and provides an air-tight seal between two
sections once they are assembled together. Align the splice
joint to seat into the mating gasket to provide an air seal. If the
splice joint was bent during shipping or rigging, restore it to its
original position (Figure 8).
2
Pull sections together to fasten. Use straps and a ratchet
to help pull the sections together securely. Apply sealant
to any gaps that may admit moisture.
3 Fasten base rails together first using the 3/8"-16 × 5"
bolts located in the splice kit provided with the unit
(Figure 7).
a To fasten two shipping sections together, four bolts
are needed (two on each side of the unit). The bolts
are run from one base rail into the other and fastened
with a nut. Complete each section bottom and top
before attaching additional sections.
b If desired, shipping sections for non curb-ready units
can be fastened together internally. To fasten
internally, run field-provided #10 sheet metal screws
or drill screws (4" long, maximum) through the
interior frame channel of one unit into the splice joint
of the neighboring section.
c Handle units with curb-ready bases and vestibules so
the lifting bracket can be removed after the unit is
placed on the curbing.
Note: Remove the lifting bracket that projects inward over
the curbing. Save the self tapping screws. When the
adjacent section is placed in position, use self
tapping screw to secure the bases together.
Figure 6: Remove Vestibule Lifting Bracket
Shipping Sections
Figure 5: Apply Sealant to Mating Faces
McQuay IM 777-4 5
1 Caulk all assembly joints of the unit—Before joining the
sections, apply at least 1/4 inch diameter bead of sealant
to the mating faces of the cabinet. Use the splice joint as
a guide for applying the sealant (Figure 5).
Mechanical Installation
A
S p l i c e C o l l a r
m u s t b e a l i g n e d
t o s e a l t o g a s k e t .
5 / 1 6 - 1 8 N u t
S p l i c e
P l a t e
5 / 1 6 - 1 8 B o l t
S l i d e S p l i c e C a p o n
a n d b e n d e n d s d o w n
Figure 7: Fasten Bottom of Section
“D”
Gasket
3/8" x 1" Bolt and Nut
d A length of “D” gasket is attached to each section
(Figure 7). This gasket MUST be installed to the unit
base section.
IMPORTANT
The gasket is to be installed in an arc shape with the ends
lower than the center, so that any moisture that may reach the
gasket will be drained to the outside of the unit.
e Handle units with curb-ready bases and vestibules so
the lifting bracket can be removed after the unit is
placed on the curbing.
Note: Remove the lifting bracket that projects inward over
the curbing. Save the self tapping screws. When the
adjacent section is placed in position, use self
tapping screw to secure the bases together.
Figure 8: Internal Fastening
1 Check that the sealant is compressed between the mating
channels when the unit sections are joined. Touch up any
places where gaps are noted.
2 After sections are seated tightly together, slip the splice
cap over the top panel flanges. Bend the ends of the
splice cap down to secure in place (Figure 9).
3 Assemble the small splice plate at the top rail to secure
the sections together at the top. Use 5/16" bolts
(Figure 9).
Figure 9: Splice Cap and Splice Plate
6 McQuay IM 777-4
Mechanical Installation
Remove panel
to remove frame
Remove any
panel screws that
engage frame
OPEN
View from inside door
Jam
Nuts
Do Not Rotate Cup
Panels, Frame Channels, and Doors
Panel Removal
To remove a side or top panel, remove the flat head Torx 30
fasteners along the sides of the panel. Lift off the panel after
removing all fasteners.
Frame Channel Removal
Frame channels that run the length of the unit along the top can
be removed to allow access to both the side and top of the unit.
To remove the frame channel, first remove the side panel(s).
Once the side panel is off, remove the flat head Torx 30
fasteners in the corner of the frame channels. Then pull the
frame channel out the side. Remove any panel screws that are
within one inch of the of the frame since they are engaged into
the gasketed flange of the frame (Figure 10).
Figure 10: Removing Panel Screws
that require the “use of tools” to access compartments
containing moving parts or electrical wiring. See
Figure 11.
1
Remove padlock if one is present.
CAUTION
Sharp edges and coil surfaces are a potential injury hazard.
Avoid contact with them.
ATTENTION
Les bords tranchants et les surfaces des bobines sont un
risque de blessure. Ne les touchez pas.
CAUTION
DO NOT attempt to rotate the cup. Damage to the unit will
occur.
ATTENTION
NE PAS tenter de faire tourner la cuvette (cup). Ceci va
dendomagger l’unité.
2 Insert 1/2" socket into cup and rotate 1/4 turn clockwise
as shown in Figure 11. If the cup and handle are on the
left side of the door, rotate 1/4 turn counterclockwise.
3 Rotate the door handle 1/4 turn clockwise and then 1/4
turn counterclockwise to release any internal pressure or
vacuum and open the door. If the cup and handle are on
the left side of the door, rotate the door handle 1/4 turn
counterclockwise and then 1/4 turn clockwise.
4 To prevent air leakage, tighten the door panels by
adjusting the jam nuts.
Access Doors and Panels
For routine maintenance, access normally is obtained through
access doors or by removing side panels. Removing all flat
head fasteners along the sides of a panel allow it to be
removed.
Fan and filter sections are always provided with a service door
on one side of the unit. If requested on order, doors can be
provided on both sides of the unit. Optional service doors are
available for most section types and are provided based on
customer request.
Fan Section Doors
Note: Opening fan section doors requires using a 1/2" socket
wrench, which satisfies ANSI standards and other codes
Figure 11: Opening Fan Section Door
McQuay IM 777-4 7
Mechanical Installation
D i s c h a r g e
P l e n u m
Injected-Foam Insulated Panels
Skyline air handlers now are furnished with double-wall,
injected-foam insulated panels. Foam panels are stronger,
more rigid, and lighter than panels with fiberglass insulation.
The insulation R-value is improved to 13. However, foam
insulation can burn when exposed to flame or other ignition
sources and release toxic fumes. Take care in cutting and
sealing all field-cut openings in these panels.
Panel Cutting Procedure
1 Determine the number and location of holes required for
electrical conduit, piping, and control wiring as follows:
a Check that adequate space is available inside the unit
for conduit or pipe routing.
b Do not locate holes in a panel that provides access to
key maintenance components such as filters and fan
assemblies.
c Do not locate where the conduit or piping blocks
airflow or obstructs hinged access doors.
2 Once a proper location is determined, drill a small pilot
hole completely through the panel. Then use a sharp hole
saw or a saber saw and cut from each side of the panel.
3 Seal the double-wall panel on each side with an
industrial/commercial grade silicone sealant or duct seal
compound. It is extremely important to seal each panel
hole or penetration securely so it is airtight, watertight,
and so that there is no exposed insulation.
Figure 12: Cutting/Sealing Injected-Foam Insulated Panels
Seal completely with silicone
Cut hole from both sides of panel
Prop 65—Substances in fuel or from fuel combustion can cause personal injury or death,
and are known to the State of California to cause cancer, birth defects or other reproductive harm.
sealant or duct seal compound
Field Mounting Junction Boxes and Other Components
For field mounting 4" × 4" or smaller junction boxes to the
standard panel exterior, use a minimum quantity of four, 3/16"
diameter pop rivets. Do not use self-tapping drill screws.
They will not tighten nor secure properly and panel
damage can occur.
If larger, heavier components require mounting on unit panels,
use through-bolts with flat washers through both outer and
inner panels. To maintain panel integrity, seal both ends with
an industrial/commercial grade silicone sealant or duct seal
compound.
WARNING
Flame and smoke can cause equipment
damage, severe personal injury, or death.
Before operating unit, seal all piping and
wiring holes on both inner and outer panels
with an industrial grade silicone sealant or
duct seal compound. Do not use a cutting
torch or expose panel to fire. Panel
damage can occur.
WARNING
La fumée et les flammes peuvent
endommager le matériel et causesr des
blessures graves ou la mort.
Avant d’utiliser le dispositif, obturer tous les
trous de passage de tubulures et de fils
ménagés dans les panneaux intérieurs et
extérieurs au moyen d’une pâte à base de
silicone ou d’un mastic d’étanchéite â
conduits de qualité industrielle.
Ne pas se servir d’un chalumeau coupeur ni
exposer les pannequx à une flamme nue
pour ne pas risquer de les endommager.
The unit frame channel is another excellent location for
securing heavier components; self-tapping screws are not
acceptable. Ensure that the location permits the full operation
of all access doors and panels and does not interfere with other
vital components.
Duct Connections
Use flexible connectors on the outlet and inlet duct
connections of all units. Do not position down flow fans over
air ducts that are routed down into the building. Use a
discharge plenum when bottom connections are necessary
(Figure 13).
Figure 13: Discharge Plenum
8 McQuay IM 777-4
Mechanical Installation
F l a s h i n g
D u c t
F l a s h i n g
U n i t t o p
p a n e l
F l a s h i n g
D u c t
F l a s h i n g
Remove screws
and panel to access
damper control shaft.
Hood
E x h a u s t
I n t a k e
B a r r i e r
If the unit has a top mixing box or economizer damper or a top
duct connection, field fabricate and install flashing to divert
moisture from the connection. The flashing must lap over the
standing seams of the top panels. The flashing also must lap
over the side edges of the unit (Figure 14).
Figure 14: Flashing Over Top Panels and Sides of Units
Dampers and Hoods
Side dampers may be provided in the mixing box and
economizer sections of units. When dampers are provided, a
removable panel is located above the weather hood to provide
access to the damper drive shaft. Other access may be
available depending on the specific construction of the unit
(Figure 15).
Figure 15: Filler Panel Over the Weather Hood
Figure 16: Field-Installed Barrier Between Hoods
Mounting Actuators
The installing contractor is responsible for the mounting of all
field-installed actuators. No provisions are made for the
location of these actuators due to the number of options and
arrangements available and the variety of specific applications.
Typically, actuators are mounted inside the cabinet. Provide
proper support for the actuator to avoid excessive stress in the
cabinet, linkage, or damper shafts.
Note: Damper blades are at full flow when open to 70 degrees.
Do not open blades further than 70 degrees.
Fresh air and return air dampers can be linked together and
driven from the same actuator if the dampers are the same size.
If the dampers are different sizes, they must be driven by
separate actuators and controlled appropriately. Exhaust
dampers are always driven by a separate actuator.
A typical rotary electric actuator can handle up to 40 sq. ft. of
damper. For pneumatic actuators, allow 5 in-lb per square foot
of damper area.
CAUTION
Maximum damper rotation is 70°. Maximum shaft torque is 205
inches/pound. Greater rotation or torque can cause equipment
damage.
La rotation maximale des volets est de 70°. Le couple (torque)
maximum de l’arbre est de 205po/lb. Une plus grande rotation
(ou torque) peut endommager l’équipement.
ATTENTION
When units are ordered with exhaust hoods and intake hoods
adjacent to each other, install a field-supplied barrier to
prevent recirculation of exhaust air into the intake openings.
(Figure 16).
McQuay IM 777-4 9
Mechanical Installation
Seal holes
cut for piping
Seal holes
cut for piping
Face and Bypass Section Mounting
Internal and external face and bypass sections are mounted
together using the instructions for horizontal components and
do not require additional instruction. Skyline air handlers are
provided with a bypass duct that is integral to the unit
construction and requires no field assembly.
Face and bypass dampers may or may not be linked together.
When dampers are placed before a single bank of coils, they
always are linked together and require a single actuator. When
dampers bypass a stacked or staggered coil, the dampers are
not linked and require multiple actuators.
Face and bypass dampers have a torque requirement of
10 in-lbs per square foot of damper face area.
Piping Vestibules
For units that include a piping vestibule, cut the openings for
routing the field piping as required in the field. Carefully seal
passages cut through the panels to prevent air leakage. A
single metal thickness pan is provided in the bottom of the
curb-mounted vestibule. The pan can be removed if necessary.
If holes are cut into the pan for a piping passage, seal the holes
to prevent moisture leakage (Figure 17).
Figure 17: Seal Holes for Piping—Curb Mounted Units
Piping and Coils
When designing and installing piping:
• Follow applicable piping design, sizing, and installation
information in ASHRAE handbooks.
• Observe all local codes and industry standards.
• Do not apply undue stress at the connection to coil headers;
always use a backup pipe wrench.
• Support pipework independently of the coils.
Water Cooling Coils
Note: Use glycol in water coils for outdoor air handlers. Power
failures and other mechanical issues can expose coils to
freezing temperatures.
• Water supply, water return, drain, and vent connections
extend through the end panel of the coil section. All
connections are labeled on the end panel.
• Water supply and water return connections are typically
male NPT iron pipe.
• When installing couplings, do not apply undue stress to the
connection extending through unit panel. Use a backup
pipe wrench to avoid breaking the weld between coil
connection and header.
• Follow recommendations of the control manufacturer
regarding types, sizing, and installation of controls.
For units with standard base rails, the vestibule is open to the
coil section; therefore, seal all holes to prevent air leakage.
Figure 18: Seal Holes for Piping—Standard Base Rail Units
Direct Expansion Coils
• The coil distributor and suction connection extend through
the end panel of the coil section.
• Check nozzle in distributor for proper tonnage.
• When a (field supplied) thermostatic expansion valve is
located outside the unit and connected directly to the
distributor (except on units with piping vestibules). Do not
apply heat to the body of the expansion valve.
• The thermostatic expansion valve must be the external
equalizer tube type. Connect the 1/4-inch diameter external
equalizer tube provided on the coil to the connection on the
expansion valve.
• Use care when piping the system, making sure all joints are
tight and all lines are dry and free of foreign material. For
typical refrigerant piping, see condensing unit product
manual.
10 McQuay IM 777-4
Mechanical Installation
Steam Coils
Piping (see Figure 19)
• Steam supply and steam return connections typically are
male NPT iron pipe and are labeled on the end panel of coil
section. Connections extend through the coil section end
panel.
• When installing couplings, do not apply undue stress to the
connection extending through unit panel. Use a backup
pipe wrench to avoid breaking the weld between coil
connection and header.
• Support piping independently of coils and provide adequate
piping flexibility. Stresses resulting from expansion of
closely coupled piping can cause serious damage.
• Do not reduce pipe size at the coil return connection. Carry
return connection size through the dirt pocket, making the
reduction at the branch leading to the trap.
Coils
• Pitch all steam coils in units toward the return connection.
• Do not drip supply mains through the coil.
• Do not attempt to lift condensate when using modulating or
on/off control.
• Install vacuum breakers on all applications to prevent
retaining condensate in the coil. Generally, connect the
vacuum breaker between the coil inlet and the return main.
The vacuum breaker should be open to the atmosphere and
the trap design should allow venting of large quantities of
air.
Traps
Note: Do not place steam traps outdoors.
• Size traps in accordance with the manufacturers’
recommendations. Make sure the required pressure
differential is always available. Do not undersize.
• Use float and thermostatic or bucket traps for low pressure
steam. On high pressure steam, use bucket traps. Use
thermostatic traps only for air venting.
• Use bucket traps for on/off control only.
• Locate traps at least 12 inches below the coil return
connection.
• Multiple coil installation—individually trap each coil or
group of coils.
• Coils in series—use separate traps for each coil, or a bank of
coils.
• Coils in parallel—a single trap can be used, but an individual
trap for each coil is preferred.
• Do not attempt to lift condensate when using modulating or
on/off control.
• With coils arranged for series airflow, use a separate control
on each bank or coil in the direction of airflow.
Valves
• Do not use modulating steam valves on high pressure
systems.
• Properly size modulating valves. Do not undersize.
• Avoid freezing conditions (entering air temperatures below
35°F).
• McQuay strongly recommends 5JA, 8JA, 5RA and 8RA
coils.
• Supply 5 psi steam to coils at all times.
• Do not use modulating valves. Provide control by face and
bypass dampers.
• Consider using two or three coils in series with two position
steam control valves on the coil or coils that handle 35°F or
colder air. Use a modulating valve on the downstream coil to
provide the desired degree of control.
• Thoroughly mix fresh air and return air before it enters the
coil. Also, to obtain true air mixture temperatures, properly
locate temperature control elements.
• As additional protection against freeze-up, install the trap
sufficiently below the coil to provide an adequate
hydrostatic head to remove condensate during an
interruption in the steam pressure. Estimate three feet for
each 1 psi of trap differential required.
• On startup, admit steam to coil ten minutes before admitting
outdoor air.
• Close fresh air dampers if steam supply pressure falls below
the minimum specified.
McQuay IM 777-4 11
Loading...