Johnson Controls YORK YPC Series, Руководство по установке

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JOHNSON CONTROLS
55
17
FORM 155.17-N1
ISSUE DATE: 4/1/2013
SECTION 17 – COMBUSTION AIR REQUIREMENTS
Fresh air to support combustion, as well as to provide
adequate location ventilation, is of great importance.
All types of fuel require approximately 10 cubic feet
of standard air (sea level at 60°F) per 1000 BTUs fir-
ing rate, for the o ret i cal perfect combustion. In actual
practice, a cer tain amount of excess air (usually 20%
excess) is re quired to en sure com plete combustion.
As a general rule, 12 standard cubic feet (SCF) of air
are required for every 1000 BTU of fuel burned, but
this can vary sub stan tial ly with spe cif ic job con di-
tions. In ad di tion, air is lost from the equip ment room
through baro met ric damp ers, draft diverters, and simi-
lar venting de vic es. Outside air must be brought into
the room to make up for these losses.
Ventilation air should be brought in directly from the
outside whenever possible. Air supply openings of ad-
e quate size must be provided to the equipment room in
accordance with local codes and standards. The spe-
cific location and size should be sufficient to allow an
un ob struct ed flow of fresh air to the burner.
It is generally accepted that 1/2 square inch of free
air opening (for each gas or oil burner in the room)
per 1000 BTU/hr firing rate will be adequate. Under
no cir cum stanc es should the static pressure in the
equipment room become neg a tive (below atmo-
spheric pres sure).
Ju ris dic tion al au thor i ty re lat ing
to com bus tion air and equip ment room ven ti la tion re-
quire ments vary widely. In or der to make cer tain of
com pli ance, the con trol ling au thor i ties should be con-
sulted.
The following is standard field practice and should be
used as a minimum. All confined mechanical rooms
and spaces shall be pro vid ed with two permanent
openings: one com menc ing within 12 inches (30cm)
of the ceiling, and one com menc ing 12 inches (30cm)
from the floor.
Refer to Figure 27 on page 56 for different options.
1. If openings communicate with the outdoors
through vertical ducts, each opening must have
a min i mum free area of 1 square inch per 4,000
BTU/hr (5.5 cm
2
per kW) of the total input rating
of all equip ment in the me chan i cal room.
2. If openings communicate with the outdoors
through horizontal ducts, each opening must have
a minimum free area of 1 square inch per 2,000
BTU/hr (11cm
2
per kW) of the total input rating
of all equipment in the me chan i cal room.
3. If these openings directly communicate with the
outdoors (on an outside wall), each opening must
have a minimum free area of 1 square inch per
4,000 BTU/hr. (5.5 cm
2
per kW) of the total input
rating of all equipment in the enclosure.
If ducts are used, they shall be of the same
cross-sectional area as the free area of the
openings to which they connect.
LOUVERS AND GRILLS
In calculating free area, con sid er ation is to be given to
the blocking effect of louvers, grills and screens pro-
tecting the openings. Do not use screens which have a
mesh size smaller than 1/4" (6.3 mm).
If the free area through the design of louver or grill is
known, use it to calculate the size opening required
to provide the free area specified. If this value is not
known, the following rules of thumb may be used.
Wood lou vers and grills will have 20 - 25% free area
and met al lou vers and grills will have 60 - 75% free
area.