035-000029-001
Page 41
HHA IOM 1.4 10/11/2021
SERVICE—Winter Shutdown (cont’d)
Method II
— Make connection to auxiliary drain
valves.
4.
Fill reservoir with any inhibited antifreeze
acceptable to code and underwriter authori-
ty.
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 circu-
late solution through coil for 15 minutes or
until concentration is satisfactory.
7.
Remove upper line from reservoir to reversi-
ble 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 PROTEC-
TION (Unit and coil must be level for this meth-
od.)
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 connection and close its drain con-
nection.
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 coun-
terflow. (Fluid should enter the coil at the leav-
ing-air side.) Steam coils must have the conden-
sate connection at bottom of coil.
To determine intervals for cleaning coils in con-
taminated air operations, pressure taps should
be installed across the coils and checked peri-
odically. Abnormal air pressure drop will indicate
a need for cleaning the coils.
Steam Systems
Annual steam system maintenance should in-
clude:
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 pre-
vent condensate flowback.
6.
Check operation of thermostatic air vents, if
used. A float and thermostatic trap will con-
tain a thermostatic air vent. When the bel-
lows is ruptured, it will fail closed.
7. Check operation of vacuum breakers.
8. Check operation of the thermal protection de-
vices 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 catalogues and in
the ASHRAE Fundamentals Handbook 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 appli-
cations.
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 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 thermostat may be replaced by a con-
densate drain with a thermal element. This ele-
ment opens and drains the coil when the conden-
sate 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 tempera-
tures. 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 tempera-
ture, installed downstream of the first coil; or set-
ting the minimum steam pressure at 5 psig.
Filters
FILTER SECTIONS — Open or remove filter
panel to replace old filter with a new filter. See
physical data tables for filter data.
Содержание HHA Series
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