Boxoffice-March.04.1950

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and sides of this rectangle are less than
four times the ceiling height. Therefore,
one large diffuser will satisfactorily handle
the section from balcony to stage and will
be placed at the center of the 57x45-foot
ceiling area.
We have one more theatre section to
consider; the projection booth. Here is a
volume of 2,940 cubic feet. Using the two
rules, we see that one diffuser placed in
the center of the 14x21 projection room
ceiling will be adequate.
SELECT TYPE AS WELL AS NUMBER
Having determined the location and
number of diffusers needed for the 600-
seat theatre, it is now necessary to select
the proper types and sizes. The total air
volume of all areas to be conditioned is
100,140 cubic feet. Since the air conditioning
equipment handles 18,000 cubic feet
of air every minute, the air will be changed
every 5.56 minutes or about 10.8 times every
hour.
Turning to a manufacturer's table, we
can quickly select the proper unit recommended
for high rates of air change, and
good for large cooling temperature differentials.
It is now necessary to determine maximum
neck velocity for use with this diffuser
under the four types of locations
In our case-history theatre. By checking
the table which shows the type of diffuser
chosen we find that Curve C covers
areas under theatre balconies and calls for
a maximum neck velocity of 1,075 feet per
minute (fpm) for the diffusers here when
placed 10 feet above the floor. Curve D,
for areas over balconies, indicates 1,375
fpm maximum neck velocity for ceiling
units at 14-foot height over the balcony,
1,500 fpm maximum neck velocity for the
ceiling unit that is 24 feet above the floor,
and 1,280 fpm maximum neck velocity for
the unit in the projection room.
DETERMINE REQUIREMENTS
Before selecting the required size of the
type of the diffuser chosen, it is necessary
to find how many cubic feet of aii- each
diffuser must handle every minute ( cfm
i
Under the balcony the volume of the enclosure
is 33x45x10 feet or 14,850 cubic
feet. Since the system changes the air
10.8 times every hour, the two diffusers
under the balcony must pass 1,335 cfm
apiece.
For the section over the balcony the
volume is 20,790 cubic feet. Since the system
changes air 10.8 times every hour, the
two diffusers over the balcony must pass
3,740 cfm, or 1,870 cfm apiece.
In the area from balcony to stage the
volume is 61,560 cubic feet. The single
diffuser for this section must pass 11,100
cfm. Finally, in the projection room the
single diffuser must pass 530 cfm.
Fi-om tables prepared by the Anemostat
Corp., it is now possible to determine the
necessary size of diffuser to deliver 1,400
cfm 11,335 cfm calculated requirement)
with a neck velocity of 1,000 fpm (maximum
allowable 1,075 fpm). The table also
shows this size unit can take care of a
radius of diffusion from 8 to 17 feet at
1,000 fpm neck velocity. Each diffuser
under the balcony serves an area 22V2X33
feet, thus the radius from the diffuser to
the nearest side wall is 11 "A feet and to
the farthest wall is 16 y2 feet—this is within
the specified limitations.
Again using this table for the diffusei's
over the balcony, the same size diffuser
will deliver 1,870 cfm (calculated requirement)
at 1,343 fpm neck velocity (interpolated)
which is under the maximum allowable
neck velocity calculated (1,375
fpm). The table also shows this size unit
can take care of a radius of diffusion from
9 to 20 feet at 1,300 fpm neck velocity.
Each diffuser over the balcony serves an
area 22'/2x33 feet, thus the radius from
the diffuser to the nearest side wall is llVi
feet and to the farthest wall is 16% feet
again within the specified limitations.
EMPLOY LARGER UNIT
Applying the table to selection of the
diffuser over the theatre section from balcony
to stage, a larger unit will deliver
11,810 cfm at 1,500 fpm neck velocity.
Calculated requirement was 11,100 cfm at
PIAN VIEW AT AUOITOSIUM CEIUNG
a neck velocity not to exceed 1,500 fpm.
Allowable radius of diffusion is from 26 to
53 feet at 1,500 fpm neck velocity. Actual
measurements between walls is 22 '/a feet
which is within the requirements.
In the projection room we find that the
proper diffuser will deliver 545 cfm (530
cfm calculated requirement) with a neck
velocity of 1,000 fpm. The table shows that
this unit can take care of a radius of
diffusion from 5 to 11 feet at 1,000 fpm
neck velocity. This diffuser actually
serves an area of 14x21 feet, thus the
radius from the diffuser to the nearest side
wall is 7 feet and to the farthest wall is
10 ('2 feet—this is within the specified requirements.
BASE SYSTEM ON DIFFUSER NEEDS
From the very simple steps outlined, it
should be quite obvious to theatremen
that they can take pencil in hand and can
do a bit of figuring themselves before
calling in the air conditioning experts.
True, many other problems must be solved
before final plans can be drawn, but once
the diffusers are selected and placed, then
the rest of the system is designed to fit
this picture.
Many attractive decorative effects can
be worked out by accommodating lighting
and air diffusion needs through use of
combination units. Other stimulating* architectural
motifs can be developed by
surrounding the diffuser unit with cove
lighting construction.
Choice of proper air diffusers is a vital
step in laying out a new system or in
eliminating troubles in old installations.
With this basic know-how, theatre owners
and operators can approach the problem
with increased understanding of proper
equipment requirements.
=15
2 T,pt AH 1 Aremoito ,
diHuicri 16" n«l dcom.,
40" outer cone d>om Copoolr
1400 UNOEI lAlCONT
BOXOFFICE March 4, 1950