Magic Aire HHA Series, Инструкция по установке, эксплуатации и обслуживанию

Страница: 29 / 66

035-000029-001 Page 29 HHA IOM 1.4 10/11/2021
Following the piping diagrams in Fig. 7-11,
make all connections while observing the fol-
lowing precautions:
• Install a drip line and trap on the pressure
side of the inlet control valve. Connect the drip
line to the return line downstream of the return
line trap.
• To prevent scale or foreign matter from enter-
ing the control valve and coil, install a 3/32-in.
mesh strainer in the steam supply line up-
stream from the control valve.
• Provide air vents for the coils to eliminate
noncondensable gases.
• Select a control valve according to the steam
load, not he coils supply connection size. Do
not use an oversized control valve.
• Do not use bushings that reduce the size of
the header return connection. The return con-
nection should be the same size as the return
line and reduced only at the downstream trap.
• To lift condensate above the coil return line
into overhead steam mains, or pressurized
mains, install a pump and receiver between the
condensate trap and the pressurized main. Do
not try to lift condensate with modulating or on-
and-off steam control valves. Use only
15-degree check valves, as they open with a
lower water head. Do not use 45-degree or
vertical-lift check valves.
• Use float and thermostatic traps. Select the
trap size according to the pressure difference
between the steam supply main and the return
main.
• Load variations can be caused by uneven
inlet air distribution or temperature stratifica-
tion.
• Drain condensate out of coils completely at
the end of the heating season to prevent the
formation of acid.
Coil Freeze-Up Protection
STEAM COILS — When used for preheating
outdoor air in pressure or vacuum systems, an
immersion thermostat to control outdoor-air
damper and fan motor is recommended. This
control is actuated when steam supply fails or
condensate temperature drops below an estab-
lished level, such as 120 to 150 F. A vacuum
breaker should also be used to equalize coil
pressure with the atmosphere when steam
supply throttles close. Steam should not be
modulated when outdoor air is below 40 F.
On low-pressure and vacuum steam-
heating systems, the thermostat may be re-
placed by a condensate drain with a thermal
element. This element opens and drains the
coil when condensate temperature drops below
165 F. Note that condensate drains are limited
to 5 psig pressure.
INNER DISTRIBUTING TUBE STEAM COILS
— The inner distributing tube (IDT) steam coil
used in the HHA air handling units has an inner
tube pierced to facilitate the distribution of the
steam along the tube's length. The outer tubes
are expanded into plate fins. The completed
assembly includes the supply and condensate
header and side casings which are built to slant
the fin/tube bundle back toward the condensate
header. The slanting of the assembly ensures
that condensate will flow toward the drains. This
condensate must be removed through the return
piping to prevent premature failure of the coil.
The fin/tube bundle is slanted vertically for hori-
zontal airflow coils, and horizontally for vertical
airflow coils.
IDT Steam Coil Piping — The following piping
guidelines will contribute to efficient coil opera-
tion and long coil life:
1.
Use full size coil outlets and return piping to
the steam trap. Do not bush return outlet to
the coil. Run full size to the trap, reduce at
the trap.
2. Use float and thermostatic (F & T) traps only
for condensate removal. Trap size selection
should be based on the difference in pres-
sure between the steam supply main and
the condensate return main. It is good prac-
tice to select a trap with 3 times the conden-
sate rating of the coil to which it is connect-
ed.
3. Use thermostatic traps for venting only.
4. Use only 1/2-in., 15-degree swing check
valves installed horizontally, piped open to
atmosphere, and located at least 12 in.
above the condensate outlet. Do not use 45
-degree, vertical lift and ring check valves.
5. The supply valve must be sized for the max-
imum anticipated steam load.
6. Do not drip steam mains into coil sections.
Drip them on the pressure side of the con-
trol valve and trap them into the return main
beyond the trap for the coil.
7. Do not use a single trap for two or more
coils installed in series. Where two or more
coils are installed in a single bank, in paral-
lel, the use of a single trap is permissible,
but only if the load on each coil is equal.
Where loads in the same coil bank vary,
best practice is to use a separate trap for
each coil. Variation in load on different coils
in the same bank may be caused by several
factors. Two of the most common are une-
ven airflow distribution across the coil and
stratification of inlet air across the coil.
8. Do not try to lift condensate above the coil
return into an overhead main, or drain into a
main under pressure with a modulating or
on/off steam control valves. A pump and
receiver should be installed between the coil
condensate traps and overhead mains and
return mains under pressure.
9. Use a strainer (3/32-in. mesh) on the steam
supply side, as shown in the piping dia-
grams, to avoid collection of scale or other
foreign matter in the inner tube distributing
orifices.
INSTALLATION-Piping (cont’d)