Needs For Ventilation - Fujitsu UTZ-BD035B Technical Manual

4-2. NEEDS FOR VENTILATION

4-2-1. OBJECTIVES AND EFFECTS OF VENTILATION
 EFFECTS OF VENTILATION
Ventilation is not simply designed to exhaust stale air. It also
has deodorizing, dust removal, dehumidification, and room
temperature adjustment functions, in addition to exchanging
air.
(1) Ventilation function
Ventilation supplies fresh air required to sustain our
normal breathing and exhausts stale air; as well as
supplies oxygen required for combustion and prevents
imperfect combustion.
(2) Deodorizing function
A ventilation fan can quickly exhaust unpleasant odor
derived from various sources, and create comfortable
environment.
(3) Dust removal function
Dust floating in the air may accompany invisibly tiny various
harmful bacteria, etc. Dust and dirt should thus be exhausted
from room to create hygienic and comfortable environment.
(4) Dehumidification function
Humidity in a house is not limited to the bathroom. Moisture is
also emitted from human bodies and combustion appliances.
Particularly, in recent years, heating in a highly airtight
structure has caused dew condensation, resulting in mold
growth and even damaging floors and walls, etc. Eliminating
interior humidity through ventilation will create comfortable and
healthy conditions for both human bodies and buildings.
(5) Room temperature adjustment function
At summer nights, ventilation accompanied by refrigeration
air conditioning can eliminate warm room air by the
ventilator, and let in cool outdoor air. Circulation-type
ventilators can also maintain the room temperatures,
realizing highly efficient heating in winter.
 EFFECTS OF STALE AIR ON
BUILDING

Stains on interior surfaces
Brand new white ceilings, walls, furniture, and decorative items
may turn yellowish in a year or two, due to tar contained in
cigarettes and floating dust.

Beware of humidity
Humidity emitted from one human body is said to amount to
about two liters a day. In highly airtight modern structures, in
addition to bathrooms, which are almost always humid, many
places can remain highly humid, such as living rooms, closets,
storerooms, and under-floor areas, etc. If left unattended,
mold and ticks will soon appear, and the wood may be more
likely to be rotted. In addition, heating will also accelerate dew
condensation, which may further damage portions behind walls
and floors, which are not readily visible.
 NEEDS FOR AIR SUPPLY
Ventilation is to exchange indoor air with outdoor air. When
ventilation is performed by a ventilating fan (generally for the
exhausting function), if air inlet is limited (in a room or a building),
the capabilities of the ventilator may be greatly reduced, or the
indoor pressure may be lowered, causing drafts and noises, as
well as making it difficult to open or close doors.

Sizes and locations of inlets
(1) Sizes of air inlets
Required sizes of inlets may vary, depending on the sizes of apertures
and openings of the buildings. The effective opening area (cm
be 0.7 times the ventilation airflow (m
pressure difference set at 10Pa.
Effective opening area αA(cm
As a reference, the following computation formulas are proposed
in the ventilation/air-conditioning engineering standards.
αA= 0.68V - S αA' (in the case of
αA= 0.39V - S αA' (in the case of
αA: Effective opening area (cm
V: Effective ventilation air volume (m
S: Gross floor area of a building (m
αA': Air-tightness of a building (cm
A ventilating fan has an exhaust capability specified in the catalog,
for which, however, the amount of air exhausted by the fan needs to
be supplied from the inlet.
In other words, if the air-inlet is small, sufficient air cannot be
supplied indoors, resulting in insufficient ventilation capacities. The
air-inlet should generally be larger than the installation area for the
ventilation fan. As the inlet area gets bigger, the air velocity there
will be reduced, making it less uncomfortable for people near it.
Air-inlet
Fig. 2-1 Fig. 2-1
Fig. 2-1
For a large room, air-inlets should For a large room, air-inlets should
For a large room, air-inlets should
be dispersed and as far distanced be dispersed and as far distanced
be dispersed and as far distanced
from the ventilating fans as possible, from the ventilating fans as possible,
from the ventilating fans as possible,
so that air can be ventilated evenly. so that air can be ventilated evenly.
so that air can be ventilated evenly.
A good example A good example
A good example
Ventilating fans should also Ventilating fans should also
Ventilating fans should also
be dispersed. be dispersed.
be dispersed.
Fig. 2-3 Fig. 2-3
Fig. 2-3
(2) Locations of exhausts (ventilation fans) and air-inlets
In the case of general ventilation, air-inlets should be located as
far detached from ventilating fans as possible. On the other hand,
in the case of local ventilation, the air-inlet should be as close
to the ventilating fans to minimize any effects to the surrounding
areas.
(3) In bathrooms,...
When ventilating fans are installed in bathrooms, etc., air-inlets should
always be installed (except for simultaneous exhaust/supply systems).
Otherwise, ventilating air volumes may be reduced, or the sealing
water may be disrupted in shallow traps, causing the sewage stench
to flow into the room.
(4) In rooms where half-enclosed combustion apparatus are used
In a cold region, when a stove with a chimney is installed without
proper air-inlets, and ventilation fan is put into operation, the chimney
may function as an air-inlet and let the exhaust into the room, causing
a dangerous situation.
- (01-20) -
3
/h), with the internal and external
2
) = 0.7 x airflow (m
Pmax = 10Pa)
Pmax = 30Pa)
2 ) of dedicated inlets
3
/h)
2
)
2 2
/m )
Ex- Ex-
Ex-
haust haust
haust
Smooth airflows Smooth airflows
Smooth airflows
Slow air supply Slow air supply
Slow air supply
velocity velocity
velocity
Air-inlet
Fig. 2-2 Fig. 2-2
Fig. 2-2
Air-inlet Air-inlet Many portions of the Many portions of the
Air-inlet Many portions of the
room remain unven- room remain unven-
room remain unven-
tilated. tilated.
tilated.
A bad example A bad example
A bad example
Air-inlet Air-inlet
Air-inlet
A good ex- A good ex-
A good ex-
Air-inlet Air-inlet
Air-inlet
ample ample
ample
2
) should
3
/h)
Ex- Ex-
Ex-
haust haust
haust
Fewer Fewer
Fewer
portions portions
portions
of the of the
of the
room room
room
remain remain
remain
unventi- unventi-
unventi-
lated. lated.
lated.