McQuay IM 777-1, Skyline Maintenance Manual
Installation and Maintenance Manual IM 777-1
Skyline¥ Air Handler
Sizes 003–090
Group: Applied Air
Part Number: IM 777
Date: June 2005
© 2005 McQuay International
McQuay IM 782-1 1
Contents
General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Receiving and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Unit Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Installation Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Service Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Rigging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Curb Mounting and Unit Leveling . . . . . . . . . . . . . . . . . . . . . . 3
Assembling Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Access Doors and Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Injected-Foam Insulated Panels . . . . . . . . . . . . . . . . . . . 5
Field Mounting Junction Boxes and Other Components . . . . . 6
Duct Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Dampers and Hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Mounting Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Face and Bypass Section Mounting . . . . . . . . . . . . . . . . . . . . 7
Piping Vestibules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Piping and Coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Water Cooling Coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Direct Expansion Coils . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Steam Coils (see Figure 18 on page 10) . . . . . . . . . . . . . 9
Water Heating Coils . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drain Pan Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Internal Isolation Assembly Adjustment . . . . . . . . . . . . . . . . 12
Electrical Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Operation Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Startup Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Fan Wheel Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Operating Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Fan Vibration Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Vibration Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Service and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . 20
Periodic Service and Maintenance . . . . . . . . . . . . . . . . . . . . 20
Ball Bearing Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Fan Drive Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
VM and VP Variable Pitch Key Type Sheaves . . . . . . . 21
LVP Variable Speed Sheaves . . . . . . . . . . . . . . . . . . . . 21
MVP Variable Speed Sheaves . . . . . . . . . . . . . . . . . . . . 22
Fan Drive Belt Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
General Rules of Tensioning . . . . . . . . . . . . . . . . . . . . . 24
Tension Measurement Procedure . . . . . . . . . . . . . . . . . 24
Front Load Filter Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Filter Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Maintaining the Coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Winterizing Water Coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Removing and Replacing Components . . . . . . . . . . . . . . . . . 26
Removing the Fan Section . . . . . . . . . . . . . . . . . . . . . . . 26
Removing and Replacing the Coil . . . . . . . . . . . . . . . . . 27
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Warranty Return Material Procedure . . . . . . . . . . . . . . . . . . . 29
Replacement Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
McQuay and MicroTech II are registered trademarks of McQuay International.
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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, 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.
4 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.
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
OAH 003 G D A C
Model
OAH = Outdoor air handler
OAC = Outdoor 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
McQuay IM 777-1 1
Installation Guidelines
Service Clearances
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. See Figure 2.
Figure 1: Servicing space requirements
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
Figure 2: Service clearance for electrical power devices
1 2 "
5 4 "
Rigging
Skyline air
assembled, or in modules of assembled sections.
be rigged as it ships from the factory. Do not rig units after
assembly.
and
the corners of each shipping section.
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 the unit.
handlers ship as separate sections, completely
The unit must
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
3 0 . 0 0
"
H e i g h t
Figure 3: Unit and section rigging
2 McQuay IM 777-1
Installation Guidelines
S
t
a
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.
Uneven or distorted sections cause misfit or binding of the
doors and panels and improper draining of drain pans. See
Figure 4.
Figure 4: Leveling the unit
h i m s e c t i o n s u n t i l
h e y a r e s t r a i g h t
n d l e v e l
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 "
Assembling Sections
If the unit is shipped in more than one shipping section, rig
each section into position separately.
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
splice joint is insulated and provides an air-tight seal between
two sections once they are assembled together.
joint to seat into the mating gasket to provide an air seal.
was
splice joint
bent during shipping or rigging, restore it to its
original position. See Figure 7
To assemble shipping sections:
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. See Figure 5.
Shipping sections are
section. The
Align the splice
If the
.
Figure 5: Apply sealant to mating faces
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
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. See
Figure 7.
a To fasten two shipping sections together, 4 bolts are
needed (2 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.
– 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.
McQuay IM 777-1 3
Installation Guidelines
Figure 6: Remove vestibule lifting bracket
R e m o v a b l e
L i f t i n g B r a c k e t
Figure 7: Fasten bottom of section
Figure 8: Internal fastening
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 .
4
Check that the sealant is compressed between the mating
channels when the unit sections are joined. Touch up any
places where gaps are noted.
5 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.
6 Assemble the small splice plate at the top rail to secure the
sections together at the top. Use 5/16" bolts. See Figure 9.
3 / 8 x 1 " B o l t a n d N u t
Figure 9: Splice cap and splice plate
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
5 / 1 6 - 1 8 B o l t
5 / 1 6 - 1 8 N u t
S p l i c e
P l a t e
4 McQuay IM 777-1
Installation Guidelines
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.
Note – Opening fan section doors requires using a 1/2" socket
wrench, which satisfies ANSI standards and other codes
that require the “use of tools” to access compartments
containing moving parts or electrical wiring. See
Figure 10.
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 10. 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.
Figure 10: Opening fan section door
Do Not Rotate Cup
Jam
Nuts
View from inside doo r
OPEN
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:
• Check that adequate space is available inside the unit for
conduit or pipe routing.
• Do not locate holes in a panel that provides access to key
maintenance components such as filters and fan
assemblies.
• 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.
McQuay IM 777-1 5
Installation Guidelines
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 and watertight and
there is NO EXPOSED FOAM INSULATION.
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.
Figure 11: Cutting and sealing injected-foam insulated panels
Seal completely with silicone
Cut hole from both sides of panel
sealant or duct seal compound
inner panels. To maintain panel integrity, seal both ends with
an industrial/commercial grade silicone sealant or duct seal
compound.
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. See Figure 12
Figure 12: Discharge plenum
D i s c h a r g e
P l e n u m
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. See Figure 13.
Figure 13: Flashing over top panels and sides of units
.
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
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.
F l a s h i n g
D u c t
F l a s h i n g
D u c t
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 4, 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
6 McQuay IM 777-1
Installation Guidelines
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. See Figure 14.
Figure 14: Filler panel over the weather hood
Remove screws
and panel to access
damper control shaft.
Hood
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.
See Figure 15.
Figure 15: 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.
ATTENTION
La rotation maximale des colets est de 70°.
Le couple (torque) maximum de l’arbre est de 205po/lb.
Une plus grande rotation (ou torque) peut endommager
l’équipement.
E x h a u s t
I n t a k e
B a r r i e r
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.
McQuay IM 777-1 7
Installation Guidelines
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. See Figure 16.
Figure 16: Seal holes for piping—curb mounted units
Seal holes
cut for piping
For units with standard base rails, the vestibule is open to the
coil section; therefore, seal all holes to prevent air leakage.
Figure 17: Seal holes for piping—standard base rail units
Seal holes
cut for piping
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.
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 thermostatic expansion valve is supplied with the
unit, it 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.
8 McQuay IM 777-1
Installation Guidelines
Steam Coils (see Figure 18 on page 10)
Piping
•
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 that is
controlled individually trapped.
– 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.
• 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 777-1 9
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