35
3. After coil is drained:
Method I
—
Connect line with a service valve and union
from upper nozzle to an antifreeze reservoir. Connect a
self-priming reversible pump between the low header
connection and the reservoir.
Method II
—
Make connection to auxiliary drain valves.
4. Fill reservoir with any inhibited antifreeze acceptable to
code and underwriter authority.
5. Open service valve and circulate solution for 15 minutes;
then check its strength.
6. If solution is too weak, add more antifreeze until desired
strength is reached, then circulate solution through coil
for 15 minutes or until concentration is satisfactory.
7. Remove upper line from reservoir to reversible pump.
Drain coil to reservoir and then close service valve.
8. Break union and remove reservoir and its lines.
9. Leave coil flanges or coupling open and auxiliary drain
valves open until spring.
AIR DRYING METHOD OF COIL PROTECTION (Unit
and coil must be level for this method.)
1. Close coil water supply and return main valves.
2. Drain coil as described in procedures for Antifreeze
Methods of Coil Protection.
3. Connect air supply or air blower to inlet header connec-
tion and close its drain connection.
4. Circulate air and check for air dryness by holding mirror
in front of open vent in outlet header drain connection.
Mirror will fog if water is still present.
5. Allow coil to stand for a few minutes; repeat Step 4 until
coil is dry.
PIPING — Direct expansion, chilled water, and hot water
coils should always be piped for counterflow. (Fluid should
enter the coil at the leaving-air side.) Steam coils must have the
condensate connection at bottom of coil.
To determine intervals for cleaning coils in contaminated air
operations, pressure taps should be installed across the coils
and checked periodically. Abnormal air pressure drop will indi-
cate 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 conden-
sate 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 forma-
tion and build up of acids.
There are additional precautions and control strategies, as
found in various catalogues and in the ASHRAE Fundamentals
Handbook and in the Carrier System Design Guide — Piping
Section, when the entering-air temperature to the coil falls be-
low 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.
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 acti-
vated 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
thermostat 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 thermostatic control in the
outside air, set at 35 F air temperature, installed downstream of
the first coil; or setting the minimum steam pressure at 5 psig.
Filters
FILTER SECTIONS — Open or remove filter panel to re-
place old filter with a new filter. See physical data tables for fil-
ter data.
Lubrication
MOTORS — Lubricate in accordance with nameplate at-
tached to motor or with manufacturer’s recommendations
included with motor.
BEARINGS
Fan Bearings — Lubricate fan bearings in accordance with
manufacturer’s recommendations included with blower.
