Note: Descriptions are shown in the official language in which they were submitted.
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Air~to-air heat_exchangers and machine and method for the
manufacture thereof
Field of the Invention
This invention relates to heat exchangers for
transferring heat from one air ~low to another, to cores
for such heat exchangers and to a machine and a method for
manufacturing such cores.
Background to the Invention
The modern trend in the construction of buildings is
to make them more and more air tight, in order to be able
to achieve better control over the interior environment
particularly the temperature and humidity thereof.
However~ utilisation of oxygen by inhabitants of the
building and other factors rendering the air stale, such
as noxious gases given off by furnishing or odours
generated in kitchens or bathrooms, usually necessitate
the building being provided with some form of ventilation,
preferably forced ventilation. If stale air is to be
evacuated ~rom the building, it must be replaced by fresh
air coming in from the exterior. In those regions of the
world experiencing cold winters, such incoming fresh air
is often much colder than the stale air being evacuated, a
fact that places an added burden on the building's heating
system. The need to heat the incoming air up to the
o~
'~P--2 -
inte~ior temperature may involve heating it as much as 20
to 40C. Evacuation of the stale air at a relatively
elevated temperature clearly represents a ma~or waste of
heat.
s For these reasons, heat exchangers have been developed
for the purpose of transferring at least some of the heat
in the stale air as it leaves the building to the colder
incoming fresh air. This diminishes the extent to which
further heat needs to be supplied to the fresh air by the
heating system of the building and generally renders the
entire heating operation more efficient.
In this connection, it should be explained that the
term "building" will be used herein for convenience to
refer to any space that is required to be force ventilated,
whether it be a large multi-unit building, an individual
apartment or other subdivision of a larger building, a
house, warehouse, shop, store or even a moving structure
such as a ship, train or the like. The present invention
is applicable to any such structures that are provided
with forced ventilation and internal heating (or cooling)
to maintain a temperature difference between the interior
and the exterior. The foregoing reference to cooling
envisages use of a heat exchanger according to the present
invention to employ air evacuated from an air conditioned
space to precool hotter incoming air.
Summary of the Invention
The invention provides in a method for forming a heat
exchange core from thin metallic sheets having edge Elanges
projecting peripherally therefrom, a procedure for joining
a pair of such sheets together in spaced apart, parallel,
aligned orientation by forming joints from flanges of said
pair of sheets along a pair of opposite edges thereof, said
procedure comprising (a) clamping each pair of sheet edges
to be joined against top and bottom surfaces of a mandrel
located between said edges with the flanges projecting in
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spaced, parallel planes beyond an edge surface of the
mandrel into a work area; and (b) moving a series of tool
surfaces along each said work area in the longitudinal
direction of said sheet edges; (c~ the leading tool
surfaces acting to bend a Eirst flange so that an inner
portion thereof is bent to lie at right angles to the
sheets against the edge surface of the mandrel and an
outer portion thereof lies parallel to and against an
inner portion of the second flange; (d) the subsequent
tool surEaces acting to bend an outer portion of the
second flange around the end of the outer portion of the
first flange to lie against such outer por~ion of the
first flange and hence form an assembly in which said
outer portion of the first flange is sandwiched between
the two portions of the second flange; and (e) the final
tool surfaces acting to bend such assembly to lie against
the inner portion of the first flange and thus co~plete a
substantially air tight joint that is mechanically inter-
locked against relative movement of the sheets in both
2Q directions transverse to the direction of extent of such
joint.
The invention also consists of a machine for orming
a heat exchange core from thin metallic sheets having edge
flanges projecting peripherally therefrom, said machine
comprising on each side thereof (a) an elongated inner
mandrel for receiving on opposite surfaces thereof a pair
of sheet edges to be joined in spaced apart, parallel,
aligned orientation with their flange projecting beyond an
edge of the mandrel into a work area; (b) an elongated
3~ slide assembly extending generally parallel to said inner
mandrel and including a bottom mandrel; (c) tool means
slidably mounted in said slide assembly; (d) means for
holding said inner mandrel and said slide assembly in a
clamped condition with the bottom mandrel aligned with
said inner mandrel; (e) means for clamping one of said
;.,
- 2b -
pair of sheet edges against one of said inner mandrel
surfaces and the other oE said sheet edges between the
other inner mandrel surface and the bottom mandrel with
said flanges pro]ecting into the work area; (f) means for
moving said tool means along said slide assembly through
said work area; (g) said tool means including first
surfaces shaped for bending a first flange at right angles
to cause an inner portion thereof to lie against the edge
of the mandrel and an outer portion thereof to lie parallel
to and against an inner portion of the second flange,
second surfaces shaped for bending an outer portion
of the second flange around the end of the outer port:ion
of the first flange to lie against such outer portion of
the first flange and form an assembly in which said outer
portion of the first flange is sandwiched between the two
portions of the second flange and further surfaces shaped
for bending said assembly to lie against the inner portion
of the first flange and thus complete a substantially
air-tight joint that is mechanically interlocked against
relative movement of the sheets in both directions
transverse to the direction of extent of such joint.
,
To enable the various aspects of the present invention
to be understood, embodiments thereof are described below
in association with the accompanying drawings. These
embodiments are set forth merely by way of example,
however, and it is to be understood that the invention in
its broad scope is not limited to the specific details
thereof, but only as defined in the appended claims.
Brief Description of Drawings
In the drawings:
Figure 1 is a plan view of a sheet for use in a heat
exchanger core;
Figure 2 is an enlarged fragment of the sheet of
Figure l;
Figure 3 is a fragmentary view of a pair of dies
illustrating how such a sheet can be made;
Figure ~ is a perspective view of the main working
parts of a machine for constructing a core from a series
of such sheets;
Figure 5 is a diagrammatic plan view of the main
elements of the machine of Figure 4;
Figure 6A is a diagrammatic end view of one side of
the machine, taken on the line 6A-6A in Figure 5, but with
the parts in a relaxed condition;
Figure 6B corresponds to Figure 6A with the parts in a
clamped position;
Figure 7A is an underside perspective view of a tool
employed in the machine of Figure 5;
Figure 7B is an underside view of the tool as seen
looking from the right hand side of Figure 7A;
Figure 7C is a side view taken on 7C-7C in Figure 7B;
Figure 7D is a rear view taken on 7D-7D in Figure 7C;
Figure 8A to 8F are a series of end views showing
successive actions of the tool in operation of the machine;
Figure 9 is an almost completed core;
Figure lOA is an end view of a corner piece of such
core as seen at lOA-lOA in Figure lOB;
Figure lOB is a section on lOB-lOB in Figure lOA;
Figure 11 is a diagram illustrating from the side one
manner of constructing the core;
Figure 12 is a diagram taken on the line 12-12 in
Figure 11;
Figure 13 shows an alternative to Figuee 11;
Figure 14 is a perspective view showing the core
mounted in a frame;
Figure 15 is a cut-away perspective view showing the
manner in which this frame can be engaged in a housing of
a heat exchanger;
Figure 16A is a plan view of such a heat exchanger,
illustrated diagrammatically and with the top of the
housing removed to show the internal parts;
Figures 16B and 16C are similar front and back views
with the outer housing panels largely cut away, taken
respectively on lines 16B-16B and 16C-16C in Figure 16A;
Figures 16D and 16E are similar end views taken
respectively on lines 16D-16D and l~E-16E in Figure 16B,
the outer housing panel being partly cut,away in,Figure
16D;
Figure 17A is a front view of an alternative
construction of heat e~changer,
Figure 17~ is the construction of Figure 17A
substantially with the front panel removed; and
Figures 17C, 17D and 17E are respectively sections on
lines 17C-17C, 17D-17D and 17E-17E in Figure 17B.
Description of the Preferred Embodiments
The heat exchanger core is made up of a series of
comparatively thin sheets of a suitable metallic material
having good thermal conducting properties, preferably
aluminum. Except for the end sheets which will be planar,
each sheet will preferably be formed with an array of
oppositely directed nodules. Figure 1 shows such a sheet
10 formed with nodules 11.
~ 89~ 2
As shown in Figure 3, which illustrates fragments of
a pair of dies 12a and 12b for forming such a sheet 10,
nodules lla project in one direction out of the plane of
the sheet, while nodules llb extend oppositely. Figure 2
shows how these nodules lla and llb are arrayed alternately
in rows and columns. While the exact shape and arrangement
of these nodules can vary, it is convenient to make them
by the dies 12a, 12b which will produce for each ncdule a
convenient central circular portion 13a surrounded by a
frusto-conical portion 13b.
The main body of the sheet 10 is square, the distances
X in Figure 1 being equal to each other. In addition, the
sheets 10 include peripherally projecting flanges 14 and
15 of unequal dimensions Y and z respectively. The plane
sheets 10' tFigure 9), for use at the ends of the core,
are provided with the larger flanges 15 but not with the
smaller flanges 14. In practice, of course, all the
sheets are stamped out of stock by dies (not shown) that
simply remove the corner pieces of metal.
Figures 4, 5, 6A and 6B illustrate a machine 20 for
forming heat exchanger cores from a series of such sheets.
For simplicity the bed plate of the machine has been
mostly omitted, only the main working parts being shown.
The machine is symmetrical about a front to rear centre
line and hence only the right hand side will be described
in detail.
Extending along each side of the machine 20 there is a
forming block slide assembly 21 that is pivoted to the bed
plate about a vertical axis 22 at the rear of the machine.
Rotation of the slide assembly 21 about the axis 22 in the
two directions indicated by the arrows A is controlled
principally by a fluid operated, e g. pneumatic, cylinder
23 that moves a wedge element 24 between a fixed member 25
and an inclined surface 26 secured to the assembly 21. ~he
assembly 21 acts as a slide for front to back travel of a
forming block 27 that carries a forming tool 28 later to
be described in detail. Travel of the block 27 is
controlled by the piston of a fluid operated cylinder 29.
An inside mandrel 30 is pivoted to the bed plate about
a vertical axis 31 for limited movement in the directions
of arrows B and can be forced in counter-clockwise rotation
by a fluid operated cylinder 32 whose piston carries a
wedge element 33 engaging an inclined surEace 34 secured
to the mandrel 30. As best seen in Figure 6A, beneath the
mandrel 30 there is a fixed block 35 secured to the bed
plate of the machine. This block acts as a stop for a
further block 36 secured to the underside of the mandrel 30.
The block 35 also has a projecting portion 35' which
acts as a stop for the slide assembly 21 and serves to
house a spring 37 that tends to urge the slide assembly
away from the block 35, i.e. counter-clockwise abo~lt the
axis 22. Figure 6A shows this relaxed condition, while
Figures 5 and 6B show the clamped condition achieved when
the cylinders 23 and 32 are actuated and both the slide
assembly 21 and the inner mandrel 30 are pressed firmly
against the block 35 ~35').
With the machine parts in the relaxed condition, the
operator slides a first pair of sheets horizontally into
the machine, one above and one below the mandrel 30. As
shown in Figure 5, this inward movement is limited by
stops 39 located both above and below the mandrel 30.
Since an end of a core is about to ~e formed, the lower
sheet is a plain sheet 10' and the upper one is a noduled
sheet 10, a flange 15 of the lower sheet 10' and a flange
14 of the upper sheet 10 projecting beyond an enlargement
30' that forms the edge of the mandrel 30 into a work area.
The cylinders 23 and 32 are then operated to move the
parts to the clamped position o Figure 6B and a top hold
down frame 40 is lowered and clamped in place. Most
details of this frame have been omitted, since it is
conventional, but, as can be seen from Figure 4, it
consists essentially of a pair of main arms 41 pivoted at
g~
the rear of the machine about a horizontal axis and a
toggle mechanism 42 whereby the frame can be readily
manually moved to~ and locked in, a hold down position.
In this hold down position a bar 43 on the underside of
each arm ~1 presses down on the upper sheet 10 immediately
above the mandrel enla~gement 30' to hold the sheets 10
and 10' firmly down in the work position. On its underside
the lower sheet 10l is supported by a lip 45 of a bottom
mandrel 46 that extends along the slide assembly 21.
Consideration will now be given to the nature of the
tool ~ which is shown in detail in Figures 7A to 7D. This
tool consists of two parts, a side forming die 50 and a
bottom forminy die 51 both mounted in the forming block
27.
The side forming die 50 has a leading, steeply
inclined, underside surface 50a followed by a less steeply
inclined, underside surface 50b and a sideways inclined,
side surface 50c. At the rear of the surface 50b it is
formed with a straight groove 50d along its edge nearer
the bottom forming die 51. The inclined surface 50b leads
into a straight undersurface 50e extending beside the
groove 50d.
The bottom forming die 51 has a plane leading surface
51a extending along a side edge and a groove 51b in its
undersurface. Approximately in alignment with the trailing
edge of the surface 50b of the side forming die 50l the
bottom forming die 51 has a sharp, forwardly projecting
ramp 51c whose undersurface 51d is straight but whose
upper surface 51e inclines rearwardly outwardly and
upwardly. The ramp 51c ends at a location 51f in alignment
with the trailing edge 50f of the side forming die 50.
Immediately rearwardly of the ramp end 51f, the bottom
forming die 51 has a projection 51g that serves to present
a rearwardly outwardly and downwardly inclined sur~ace
51h, the degree of downward inclination of this surface
51h diminishing to zero by the time it reaches the trailing
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edge Sli of the projection 519. The projection Slg has a
flat undersurface Sls that, as can be seen from Fig. 7C is
raised slightly above the upper level of the groove 51b.
Rearwardly of the projection Slg the bottom forming die Sl
S has a further projection 51j that presents a rearwardly
outwardly and upwardly inclined surface 51k formed at its
leading edge with a short, shallow groove 51p. In
addition, the projection Slj has a straight groove Slm in
its outer undersurface.
It will be noted that the upper surface of the forming
block that supports the tool 28 (dies S0 and 51 collectively)
has a groove 52 that engages a corresponding track 53 on the
undersurface of the upper part of the slide assembly 21.
The effect of advancing the tool 28 from rear to
lS front, i.e. into the work area, with a pair of sheets
clamped in position as shown in Figure 6B is shown in the
series of diagrams of Figure 8A to 8F. The sections on
which these views are taken relative to the part of the
tool 28 responsible for each action are identified by
corresponding numbers in Figure 7B. In fact, of course,
the flanges 14 and 15 are folded progressively as the tool
moves towards the front of the machine.
Figure ~A shows the initial effect of the surface 50c
of the side for~ing die 50 in bending the flange 14 of the
sheet 10.
Figure 8B shows the situation a moment later when the
flange 14 has been bent by the die surface 50e into inner
and outer portions 14a, 14b that are at right angles to
each other. The surface 51e of the ramp 51c of the bottom
forming die 51, sliding in a groove 47 of the bottom
mandrel 46, has also started to bend up an outer portion
15a at the edge of the flange 15, while leaving an inner
portion 15b of this flange flatly underlying the flange
portion 14b.
Figure 8C shows the situation at line ~C in Figure 7B,
i.e. just before the trailing edge 51f of the ramp 51c and
~9~
g
the aligned trailing edge 50f of the side forming die 50
are reached. By this time the die 51 has bent the flange
portion 15a fully at right angles to the portion 15b.
Figure 8D shows the result of passing beyond the
trailing edge 50f of the side forming die 50 and the
action of the projection 51g of the bottom forming die 51
in ~olding the flange portion 15a over and down on top o~
the flange portions 14b and 15b, to form an assembly in
which the outer portion 14b is sandwiched between the
portions 15a and 15b.
Figure 8E shows how the surface 51k of the projection
51j then bends this assembly upwardly until the vertical
position shown in Figure 8F is eventually reached, namely
a completed substantially air tight fold of the flanges,
referred to below as a lap joint 54.
When a pair of such lap joints 54 has thus been formed
on opposite sides of a pair of sheets 10, 10', the hold
down frame 40 is released and raised, and the cylinders 23
and 32 are retracted to allow the slide assemblies 21 and
the mandrels 30 to move to the relaxed condition, the
cylinders 29 are retracted to withdraw the tools 28, thus
enabling the operator to slide the now-joined pair of
sheets forwardly and off the mandrels 30. He then turns
this pair of sheets through 90 about a vertical axis and
reinserts it into the machine except that the sheet 10,
which was formerly above the mandrels 30, is now
immediately below them. The 90 turn thus brings the
larger flanges 15 of this sheet 10 into the working area of
the tools 28. The operator also inserts another noduled
sheet 10 into the machine above the mandrels 30 with its
smaller flanges 14 to the side7 i.e. in the working area.
Thus these flanges 14 and 15 bear th~ same relationship to
each ~ther as did the flanges 14 and 15 of the first pair
of sheets, and reactivation of the tools 28, after first
bringing the slide assemblies 21, mandrels 30 and hold down
frame 40 to the clamped position, will form another pair of
lap joints 54, this time between the second and third
sheets.
-- 10 --
This procedure is repeated to build up a series of
sheets interconnected along their opposite edges by air
tight lap joints 54, the pairs of edges so joined
alternating down the stack. The result is a core 60
providing one set of air passages extending from front
right to rear left and another set extending from front
left to rear right as seen in Figure 9, each such set of
air passages being isolated from the other, except that
they are in close thermal contact through the thin aluminum
sheets between them. To maintain the correct spacing
between the sheets each corner of the core 60 is co~pleted
by means of a corner post 61 which, as shown in Figures lOA
and lOB, is an elongated, angled section of aluminum with
two arms carrying rows of teeth 62 staggered so as to enter
between alternate pairs of sheets.
Figures 11, 12 and 13 illustrate two alternative ways
of arranging the sheets 10. If they are placed with
upwardly projecting nodules llc on one sheet 10 aligned
with downwardly projecting nodules lld on the sheet :L0
above, then the effect will be to divert the air flow
around the constrictions lle thus formed, as demonstrated
by the arrows C in Figure 12~ Alternatively, if upwardly
projecting nodules llc on one sheet 10 are aligned with
upwardly projecting nodules lOf on the sheet above, as in
Figure 13, the undulations of the air flow Cl tend to be
in a plane perpendicular to the sheets 10, in contrast to
Figures 11 and 12 where they are more parallel to the
planes of the sheets. In either case the effect is to
create some turbulence and break up boundary layers in the
air flow, hence increasing heat transfer between the air
and the sheets.
The core 60 is rigidly mounted in a frame 63 (Figures
14 and 15) that includes side flanges 64 whereby the
assembly can be slidingly received in and supported by a
pair of U-tracks 65 extending from front to rear in a
lefthand compartment 66 of a heat exchanger housing 67.
~ 89~6~:
-- 11 --
The frame 63 includes a bent up front edge 68 that acts as
a handle for inserting and removing the core assembly from
the housing. In addition, the frame 63 includes vertical
side flanges 69 and top and bottom horizontal flanges 70
that effectively extend around the entire frame as a
peripheral border. When the core assembly is in position
in the housing, these 1anges 69, 70 engage corresponding
flanges 71 projecting inwardly from the wal:Ls of the
compartment 66 to form a border around the opening for
receiving the frame 63.
The effect of this arrangement is perhaps best
appreciated from the diagrammatic representatives of the
interior of the housing 67 provided by Figure 16A which
sees it from above, Figure 16B which sees it from the front
and Figure 16D which sees it from the left hand end. The
engagement of flanges 64 and tracks 65 will be sufficiently
air tight taken together with the front and rear shelves
73, 72 which respectively abut the closed door 74 and rear
panel 75 of the housing to divide the compartment 66
between top and bottom, while the cooperating flanges 69,
70 and 71 similarly divide it from front to rear. Hence
four chambers are formed 66a (upper front), 66b (~pper
rear), 66c (lower front) and 66d (lower rPar).
The right hand compartment of the housing 67 is divided
by a fixed vertical panel 76 and a fixed horizontal panel
77 into a rear chamber 78, an upper front chamber 79 and a
lower front chamber 80. Fans 81 and 82 powered by a common
motor 83 are located in chambers 78 and 79 respectively.
Chamber 78 also houses an electric heater 84 and chamber 80
contains circuit elements 85 connected to external controls
86 and to a thermostat tnot shown) sensing the temperature
of the fresh air entering the building. Ports 87, 88, 89
and 90 are shown communicating with chambers 79, 78, 66d
and 66c respectively.
Stale air from the building (represented by solid arrows
D) will be dra~n by the fan 82 through the port 87 into the
chamber 79 and hence discharged by this fan through the
~9~6~
main dividing panel 91 between the left and right com-
partments of the housing into the upper front chamber 66a.
From here it passes through one set of air passages in the
heat exchange core 60 to the lower rear chamber 66d and out
of the port 89. Fresh air from the exterior of the house
(represented by broken arrows E) is drawn by the fan 81
through the port ~8 and over the preheater 84 into the
chamher 78, and is discharged through the panel 91 into the
upper rear chamber 6~b. From here it passes through the
other set of air passages in the heat exchange core to the
lower front chamber 66c and out of the port 90. It will be
noted that the two ports 88 and 89 that are required to
communicate with the exterior of the building, to bring in
fresh air and expel stale air, respectively, are arranged
at the rear of the housing 67 so that the latter can
conveniently be mounted in a wall 92 of the building. The
ports 87 and 90 for removing stale air from, and supplying
fresh air to, the building, are located at forward
locations in respective ends of the housing.
An alternative embodiment is illustrated in Figures 17A
to 17E. In this instance the core 60 requires no frame,
although one can be provided if desired. It is shown in
Figure 17B with its four corner posts 61 arranged to slide
in tracks 100 extending from front to rear in a housing
101. When in position as shown in Figure 17C, the top edge
of the core 60 is contacted by a flexible gasket 102 on the
lower edge of a panel 103 that divides the upper part of
the houG.ing in the front to rear direction into a front
chamber 104 and a rear chamber 105. Stale air D drawn into
the housing through a port 106 by a fan 107 is forced into
the chamber 104 and downwardly through the forward half of
one set of air passages in the core 60 into a lower chamber
108, from where it flows upwardly through the rear half of
the same set of air passages to the chamber 105 and hence
out of a port 109 at the rear of the housing 101 to the
exterior of the building.
~ ~390~2
- 13 -
In a like manner, as shown in Figure 17E, a side edge
of the core 60 is contacted by a flexible gasket 110 on the
vertical edge of a panel 111 that d;vides the right hand
side of the housing 101 in the front to rear direction into
a front chanber 112 and a rear chamber 113. Fresh air E
drawn into the housing through a port 114 into a chamber
115 is driven by a fan 116 into the rear side chamber 113.
From here it passes horizontally through the rear half of
the second set of air passages in the core 60 into a left
hand chamber 117, from where it flows back horizontally to
the right through the front half of this second set of air
passages to the chamber 112 and out of a port 118 into the
building.
Thus, the core ~0 serves as two heat exchangers in
series, although this effect is achieved without the need
to have two cores. A first "higher temperature" exchanger,
which consists of the front half of the core 60, takes in
stale building air at a temperature Tlf discharging it at a
lower temperature T2. A second "lower temperature"
exchanger, which consists of the rear hal of the core 60,
takes in this partly cooled air at temperature T2 and
discharges it to the exterior of the building at a still
lower temperature T3. The cold incoming fresh air~ on the
other hand, comes in at a temperature T4 and is heated by
the second exchanger to a temperature of T5 and subsequently
by the first exchanger to a temperature T6. The maximum
temperature drop across the first exchanger is this Tl-T5
and that across the second exchanger is T2-T4. Each of
these temperature drops is less than the total difference
Tl-T4 between the inside and the outside air. This is an
important advantage, because this total temperature
difference is the main factor determining the necessary
amount of preheating of the outside air. When the outside
air is below 0C, heat exchangers of the present type can
be expected to experience the formation of frost arising
from moisture in the stale house air that is subjected to a
- 14 -
freezing temperature, and it is to avoid this problem that
preheaters, such as the heater 84, are provided. Generally
speaking, the greater the total temperature difference
across such a heat exchanger, the more the preheating
required to prevent the formation of frost sufficient to
impair the operation of the device. Hence, by effectively
dividing the core 60 into two heat exchangers and providing
counter flow so that an upstream portion of one flow is in
heat exchange relationship with a downstream portion of the
other flow, and vice versa, each heat exchange relationship
has a drop less than the total temperature difference. The
result is a reduction in the need for preheating. If the
device needs to be equipped to handle the most extreme
climatic conditions, say below -20C, a preheater (not
shown) can nevertheless be provided, if desired, but its
capacity can be comparatively small and its utilisation can
be expected to be relatively infrequent.
As an alternative or an addition to the use of a
preheater that contacts the incoming cold air, either of
the embodiments described above can include a make up
heater located to heat the incoming air but on the
downstream (warm) side of the heat exchanger. Such a make
up heater is shown at 119 in Figure 17E which also shows
controls 120.
