Direct Expansion Coils; Chilled Water And Hot Water Coils; Steam Inner Distributing Tube Coils; Piping - Carrier 39LA-25 Installation, Start-Up And Service Instructions Manual

DIRECT EXPANSION COILS

Rotate the coil in vertical plane and reinstall. Distributor must be
on downstream side of coil. (Refer to Fig. 58).

CHILLED WATER AND HOT WATER COILS

These coils can be rotated. If coil is rotated in vertical plane and
reinstalled with counterflow maintained, supply will be at the top
of the coil and return will be at the bottom. Ensure coil is continu-
ously vented and water velocity is maintained to prevent air
binding.
CAUTION
Chilled and hot water coils must not be rotated horizontally. If
coils are rotated horizontally, severe water blow-off will result.

STEAM INNER DISTRIBUTING TUBE COILS

Rotate in horizontal plane and reinstall. See Fig. 58.

PIPING

Direct expansion, chilled water, and hot water coils should always
be piped for counterflow. (Fluid should enter the coil at the leav-
ing-air side.) Steam coils must have the condensate connection at
bottom of coil.
To determine intervals for cleaning coils in contaminated air oper-
ations, pressure taps should be installed across the coils and
checked periodically. Abnormal air pressure drop will indicate a
need for cleaning the coils.
Annual maintenance should include:
1. Clean the line strainers.
2. Blow down the dirt leg.
3. Clean and check operation of steam traps.
4. Check operation of control valves.
5. Check the operation of check valves to prevent condensate
flowback.
6. Check operation of thermostatic air vents, if used. A float and
thermostatic trap will contain a thermostatic air vent. When
the bellows is ruptured, it will fail closed.
7. Check operation of vacuum breakers.
8. Check operation of the thermal protection devices used for
freeze-up protection.
9. Steam or condensate should not be allowed to remain in the
coil during the off season.This will prevent the formation and
build up of acids.
There are additional precautions and control strategies, as found in
various catalogs and in the ASHRAE Fundamentals Handbook
and in the Carrier System Design Guide — Piping Section, when
the entering-air temperature to the coil falls below 35°F. These
conditions occur when IDT coils are used for pre-heat and/or face
and bypass applications.
Freeze up protection:
1. Use a strainer in the supply line and the dirt leg ahead of the
trap.
DX AND ALL
WATER COILS
STEAM COILS
ONLY
Fig. 58 — Coil Rotation
2. Use a vacuum breaker in the return.
3. Do not use overhead returns from the coil. A floodback can
occur.
4. An immersion thermostat to control outdoor-air dampers and
the fan motor is recommended. This control is activated when
the steam supply fails or the condensate temperature drops
below a predetermined temperature, usually 120°F.
5. On low pressure and vacuum systems, the immersion ther-
mostat may be replaced by a condensate drain with a thermal
element. This element opens and drains the coil when the
condensate temperature drops below 165°F. Note the thermal
condensate drain is limited to 5 psig pressure. At greater coil
pressures they will not open.
In spite of the precautions listed above, a coil may still freeze up.
An oversize capacity coil, at partial load, with a modulating steam
control valve will occasionally freeze. Freezing occurs in the 20°F
to 35°F range of entering-air temperatures. A better installation
would be an undersize coil, with an on/off control valve with ther-
mostatic control in the outside air, set at 35°F air temperature, in-
stalled downstream of the first coil; or setting the minimum steam
pressure at 5 psig.

Filters

FILTER SECTIONS

See Table 18 for filter data. Filters are field-supplied.
Flat filter section can use 2 in. or 4 in. thick filters. The flat filter
section as shipped accepts 2 in. filters. Remove spacer in each fil-
ter track to provide the 4 in. space required to accommodate 4 in.
filters.
On all filter sections, filters are pushed into the track until they
touch the opposite side of the unit. Any remaining space is taken
up by the adjustable 2-piece sheet metal spacer. See Fig. 59 for
filter arrangements.
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