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11UH-PRC001-EN
Selection
Procedure
Trane Propeller Unit Heaters
Both Model S and Model P Propeller
Unit Heaters are ideally suited to such a
wide variety of installations that there
can be no hard and fast rules regulating
their selection.
In determining the type and size of the
units for any building, the following
points are generally considered:
BTU Requirements
While the choice of units depends upon
several important factors, the total Btu
requirement is usually determined first.
In calculating heat loss, methods as
recommended by the ASHRAE Guide
may be used, or any other procedure
which is known to be acceptable.
Type of Building
Once the total Btu requirement is known,
the type of building together with its
architecture and its purpose is
considered.
In the many cases where a combination
of space characteristics is found, a
combination of Model S and Model P
Unit Heaters may be used to create the
most satisfactory heating system.
The Model P Unit Heater has the natural
ability to tap the reservoir of heated air
which collects at the ceiling level and
return it to active service in the floor
zone.
The Model P can be used on either high
or low ceilings. From high mounting
positions the Model P will allow ample
clearance for moving objects and can
project heat down into occupied areas
regardless of obstacles which would
restrict the flow of air from horizontal
units.
From low mounting positions the Model
P, with proper diffusion, can be used
without disturbing nearby occupants
with direct blasts of high velocity heated
air, or requiring return lines so low as to
leave insufficient head room.
The superior horizontal action of the
Model S, on the other hand, is ideal for
creating a wiping effect of warm air
along exposed walls which neutralizes
drafts at their source, beaming heat
down narrow aisles and production
lines, and blanketing large windows,
doors and other points of high heat loss.
Spacing of Units
It is the usual practice to divide the
building into areas with like exposures,
or in relation to heat load distribution
desired.
In general, Model S Unit Heaters may
be selected for buildings where direct
horizontal air currents are desired and
where there are no obstacles to
interrupt the flow of air from the
heaters.
Model P Unit Heaters are successfully
used where high or low mounting
heights are required and should
ordinarily be specified with diffusers,
depending upon the mounting height
and application.
Mounting Heights
The
maximum
effective mounting
height is determined by the outlet
temperature of the air, the outlet
velocity, the cfm for which the heater is
designed, and if a diffuser is used – the
setting of its blades.
The higher the outlet temperature of
the air, the more difficult it is to force it
down into the living zone.
The cfm also affects the mounting
height as a large volume of air will
travel farther than a small volume
under the same initial conditions of
temperature and velocity.
In the preliminary planning stages, it is
well to remember that the lowest
possible mounting height is desirable in
order to get the most heat down to the
floor line and to allow the greatest
possible diffusion adjustment to
provide tailor-made distribution for
each area.
In providing for the use of diffusers
please remember, adjustment of a
Louver Cone Diffuser to deflect the air
toward the horizontal immediately
lowers the mounting height limit.
Adjustment for lateral deflection with
the Louver Fin Diffuser shortens the
distance of throw.
Diffusion
The use of Trane Louver Cone or
Louver Fin Diffusers influences the
selection of units in two principal ways:
First: It is seldom necessary to install
oversized heaters to extend the
maximum effective mounting height of
the Model P or the distance of throw of
the Model S. Conversely, Trane Diffusers
enable extremely low mounting since the
adjustable blades direct heat where it is
wanted without creating uncomfortable
hot spots near the units.
Second: After the original selection has
been made, units may be located with
confidence because adjustments in heat
distribution are possible to
accommodate future changes or
unforeseen draft conditions.
Air Changes
Better diffusion and more even
temperatures can be maintained in a
heated space when the rate of air
recirculation through the heaters is
relatively high. For buildings where large
numbers of people are engaged, it is
desirable to provide for a greater number
of air changes than for sparsely occupied
areas.
A greater number of small units are used
where wide diffusion and even
temperatures are necessary. A few
centrally located units of large capacity
would be used where there are few
occupants.
Comfort Conditions and Economy
Air circulation, diffusion and spacing of
units are closely related to economy and
comfort in the selection of unit heaters.
The more units used to provide the
required number of Btu’s, the more
comfortable will be the conditions for
personnel. On the other hand, a few
large units can be selected to provide
plenty of heat at low first cost, but may
be slower in response and thorough
distribution of heat.
Here again, adjustable diffusion
equipment can go a long way toward
saving the buyer first cost expense while
still providing completely satisfactory
comfort conditions.