Field of the invention
[0001] The invention relates to an electric heater for heating liquids circulating mainly
in heating circuits of residential buildings and in particular in systems with a closed
circuit of the heat transfer liquid.
Prior art
[0002] Electric heaters used for heating liquids in heating circuits of residential buildings,
such as instantaneous water heaters, back-up electric heaters for heating the heat
transfer medium in heat pump systems, and other similar devices, have heating elements
generally constructed of resistance wires insulated with a magnesium oxide layer and
housed in a stainless steel casing. Their basic feature is that the heating elements
provide the power proportional only to the supply voltage and the structure of such
a heater is simple.
[0003] On the other hand, the actual use of such simple heating elements for heating the
heat transfer medium requires a sophisticated safety concept involving control of
the heating based on outputs from temperature sensors, flow sensors, safety temperature
limiters and other necessary components, since the temperature of the heating elements
can reach temperatures of up to 800°C.
[0005] Newer electric liquid heaters use other suitable elements to heat the heat transfer
medium, preferably so-called PTC heating elements (PTC = positive temperature coefficient).
[0006] The PTC elements are elements that are electrically conductive at low temperatures,
but after a certain temperature barrier is reached, the electrical conductivity drops
sharply. Thus, when the temperature of the PTC element increases, its resistance increases.
Negative feedback is used, acting on the actual heating of the PTC element due to
the passing current. When powered from a constant voltage source, this will cause
a drop in power on the PTC element, counteracting further temperature rise. The result
is simple heating with stabilization of the temperature of the heated space.
[0007] Heating with the PTC elements is therefore safe due to the automatic temperature
control and the fact that the maximum temperature of the heated element is below 300°C.
Independent power regulation does not require thermostat control.
[0008] The PTC elements can be made of ceramics or organic polymers, they are mainly produced
as plates with two electrically conductive electrodes to connect the supply voltage,
heating assemblies made of the PTC elements can contain insulating film and other
components, such as electrically conductive adhesives.
[0009] EP 3910260 A1 discloses an electric water heater for a closed-loop heating water system comprising
a water tank connected to a flange, at least one heating element extending from the
flange to the water tank, and a concentric wall arranged in the water tank, with the
water tank being connected to a cold water inlet and a hot water outlet. The water
tank housing comprises a cylindrical part attached to the flange at the top and a
conical part, which is connected to the cylindrical part of the water tank housing
at the bottom, with the shape of the concentric wall corresponding to the cylindrical
part of the water tank. The water tank housing is placed inside the water tank so
that an external circulation channel is defined between the water tank housing and
the concentric wall. The electric water heater integrates a filter function for solid
impurities, which are mainly formed on the heating elements during electric heating,
but can also be formed elsewhere in the heating system, by separating the solid particles
from the liquid flow when they hit the concentric wall and slowing them down to fall
into the conical part of the water tank where they can be settled. The sediments are
removed by a drain valve.
[0010] The concentric wall can be made, together with the cylindrical part of the tank housing
as an integral part thereof, by moulding from plastic.
[0011] Resistance coils and a safety temperature limiter are used and heating control by
an electronic control unit is assumed in the disclosed document.
[0012] The task of the invention is to make an electric heater of similar dimensions and
power using PTC elements, so that the function of the integrated filter for solid
impurities is preserved.
[0013] In the state of the art, liquid heaters with the PTC heating elements embedded in
the tank designed to heat the liquid are known. The existing PTC liquid heating devices
generally contain a PTC heating element with a heat transfer structure that is typically
very complex and therefore has disadvantages such as a low heat transfer rate and
uneven heat transfer.
[0014] The solution published in
EP3716730 A2 improves the uniformity of heat transfer, while the particular components of the
structure are bonded with conductive adhesive and require placement in a sleeve. However,
the heater does not provide the function of a filter integrated in the heated liquid
tank, and the manufacturing of the PTC heating assembly is complicated and expensive.
[0015] Another invention with simple integration of a PTC heating assembly is published
in
CN 210267475. The heating element is made of a hollow body with a passage for liquid, the body
has a cross-section of a regular hexagon or square. The body is heated by surfaces
equipped with PTC elements. The surfaces are connected with the installation cavities
for inserting the PTC elements, during assembly, the PTC heating component is firstly
inserted into the installation cavity successively, and then a press for the PTC deformation
pressing is used. The outer surface of the heating element is pressed together to
form the final product.
[0016] The disadvantage of this solution is that the pressing can damage the PTC heating
component. The arrangement of the continuous cavity with reinforcing ribs throughout
the entire volume of the liquid passage causes significant pressure losses as well.
[0017] The present invention addresses the shortcomings of the known state of the art. It
is based on the design of an electric heater with an integrated filter function published
in
EP 3910260 A1, and features thereof are disclosed in the preamble of the Independent Claim, with
the concentric wall being conveniently used as an electrical insulator. The electric
heater uses a simple PTC heating assembly with an innovative flexible wire arrangement
to heat the liquid.
Summary of the Invention
[0018] According to the present invention, the electric heater comprises a plastic liquid
tank comprising an upper cylindrical part and a lower conical part, which are watertightly
connected to each other, e.g. by a screwed or welded joint; inside the plastic tank
there is basically cylindrical plastic concentric wall arranged, defining the internal
circulation channel for supplying the liquid to be heated and the external circulation
channel for discharging the heated liquid, which is cleared of impurities at the same
time. The external circulation channel is arranged between the concentric wall and
the cylindrical part of the housing, with the external circulation channel being connected
to the heated liquid outlet. In the lower conical part of the tank there is a space
for sedimentation of solid impurities, which are separated from the liquid flow by
hitting barriers and falling into the area with the lowest flow rate. The conical
part has a connection to connect a drain valve to remove the impurities.
[0019] The electric heater includes also a hollow heating module arranged in the internal
circulation channel (along the axis of the upper cylindrical part of the water tank).
The heating module is equipped with a connection piece for the supply of the liquid
to be heated to the heater and a continuous cavity for the liquid routing and heating.
[0020] The hollow heating module is made of metal material, conducting heat and electric
current well. Of the suitable materials, extruded aluminium is preferably used for
the module due to its light weight, but other materials are also possible. The hollow
heating module has surfaces bordered by projections arranged on its outer surface.
On its inner surface (in the continuous cavity), it has ribs arranged in the preferable
design to increase the heating surface and thus the heating efficiency.
[0021] After the hollow heating module is inserted into the internal circulation channel,
installation gaps are created between the plastic concentric wall and the outer surfaces
of the hollow heating module for insertion of the PTC heating assembly.
[0022] The concentric plastic wall has pairs of projections arranged on its inner surface,
facing the internal circulation channel, which are shaped so that the projections
arranged on the outer surface of the hollow heating module shape-fit between these
projetions.
[0023] The PTC heating assembly has a layered structure known in the prior state of the
art. The PTC plates are arranged in long strips, with the length and number of the
strips used determining the power of the heater (e.g. to use a PTC heater as a backup
electric heater in heat pump systems, power from 6 to 12 kW is required.
[0024] Each PTC heating assembly in the present invention includes two electrical conductors
(the first electrical conductor and the second electrical conductor) that are connected
to two opposing surfaces of the PTC layer. The PTC layer is made of PTC plates, with
a graphite pad sandwiched between the PTC layer and each electrical conductor to improve
electrical and thermal conductivity. The pad can be glued with electrically conductive
adhesive, its role is to ensure the best possible contact between the PTC plate and
the conductor, eliminating any unevenness on both materials at the point of contact.
[0025] It is an improvement of the prior state of the art that instead of a conventional
electrical conductor or conductive strip, a spring, for example a shaped electrically
conductive flexible strip, is used as the first electrical conductor in the present
solution. The first electrical conductor touches the concentric wall with its flexible
part.
[0026] Electrically insulating film (e.g., Kapton film) is applied between the second electrical
conductor and the hollow heating module to provide insulation for the second electrical
conductor while not preventing heat transfer from the PTC heating assembly to the
hollow heating module.
[0027] At least one PTC heating assembly generating heat is arranged on the outer surfaces
of the hollow heating module; each PTC heating assembly includes a flexible metal
electrical conductor for supplying electrical voltage and for pressing the PTC assembly
against the concentric wall and also against the heating module.
[0028] The flexible conductor ensures tight contacts between the layers of the PTC heating
assembly. Using a flexible electrical conductor, the entire PTC heating assembly is
pressed against the hollow heating module on one side and the plastic concentric wall
on the other side. Basically, there is no need for pressing or gluing to ensure good
contact of all layers of the PTC heating assembly with each other and to ensure good
contact with the heating module and the plastic concentric wall.
[0029] Heating of liquid is accomplished by applying voltage (of appropriate height and
polarity) to the two conductors of the PTC heating assembly to generate heat in the
PTC plates, which is transferred through the hollow heating module to the liquid.
[0030] In the preferred design, an electrically conductive body of the hollow heating module
is used as the second electrical conductor.
Brief description of the Drawings
[0031] The invention is further explained using the figures below, without limitation thereto.
[0032] They show the following:
Fig. 1 - Electric PTC liquid heater - exploded view
Fig. 2 - Layers of the PTC heating assembly - exploded view
Fig. 3 - Drawing of the hollow heating element and its cross-section
Fig. 4 - Cross-section of the assembled PTC electric heater, with detail of the PTC
heating assembly inserted in the installation cavity
Fig. 5 - Schematic diagram of the connection of three-phase electrical voltage to
PTC heating assemblies - wiring example
Examples of Embodiment
Example 1
[0033] Fig. 1 shows an electric heater according to the present invention. This includes
a plastic liquid tank comprising an upper cylindrical part 1 and a lower conical part
2, which are watertightly connected to each other, with a screwed joint of flanges
24 and 25 and a gasket 22. Inside the plastic tank there is basically cylindrical
plastic concentric wall 5 arranged, defining the internal circulation channel 31 for
routing the liquid to be heated and the external circulation channel 32 for discharging
the heated liquid, which is cleared of solid impurities at the same time. The external
circulation channel 32 is arranged between the concentric wall 5 and the cylindrical
part of the housing 1, with the external circulation channel 32 being connected to
the heated liquid outlet 4. In the lower conical part 2 of the tank there is a space
for sedimentation of solid impurities, which are separated from the liquid flow by
hitting barriers and falling into the area with the lowest flow rate. The conical
part 2 of the tank has a connection for connecting a drain valve 7, which is used
to remove the settled impurities from the heater.
[0034] The electric heater includes also a hollow heating module 6 (shown in Fig. 3 and
Fig. 1) arranged in the internal circulation channel 31 (along the axis of the upper
cylindrical part of the water tank). The heating module 6 is provided with a connection
piece 61 with an external thread for the inlet of the liquid to be heated into the
heater, a continuous cavity for routing and heating the liquid, and a connection piece
62 with an internal thread for the outlet of the heated water.
[0035] The hollow heating module 6 is watertightly connected to the heater tank by a coupling
nut 21, a connection piece 62 and O-rings 23.
[0036] The hollow heating module 6 and its cross-section are shown in Fig. 3. It has arranged
surfaces 64 bordered by projections 63 on its outer surface. On its inner surface,
the continuous cavity 65 has conveniently arranged ribs 66 to increase the heating
surface area.
[0037] The concentric plastic wall 5 has pairs of projections 51 arranged on its inner surface,
facing the internal circulation channel 31, which are shaped so that the projections
63 arranged on the outer surface of the hollow heating module 6 shape-fit between
these projetions 51. A detail of the arrangement is shown in Fig. 4. The pairs of
projections 51 are arranged for shape connection of the projections 63, which are
arranged on the outer surface of the hollow heating module 6.
[0038] After the hollow heating module 6 is inserted into the internal circulation channel
31, installation gaps 19 are created between the plastic concentric wall 5 and the
surfaces 64 of the hollow heating module 6 for insertion of at least one PTC heating
assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6. The above example allows the use of up
to six PTC heating assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6, the number of assemblies
is not limited to this number (in other designs).
[0039] Each PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 in the present invention
includes two electrical conductors (11, 15), the first electrical conductor 11 and
the second electrical conductor 15, that are connected to two opposing surfaces of
the PTC layer 13. The PTC layer 13 is made of PTC plates, with a graphite pad 12,
14 sandwiched between the PTC layer 13 and each electrical conductor 11, 15 to improve
electrical and thermal conductivity. The pad 12, 14 can be glued with electrically
conductive adhesive, its role is to ensure the best possible contact between the PTC
layer 13 and the electrical conductor 11, 15; the pad 12, 14 eliminates any unevenness
on both materials at the point of contact.
[0040] A spring, e.g. a shaped electrically conductive flexible strip, is used as the first
electrical conductor 11 in the present solution. The first electrical conductor 11
with its flexible part touches the concentric wall 5.
[0041] Electrically insulating film 16 (e.g., Kapton film) is applied between the second
electrical conductor 15 and the hollow heating module 6 to provide insulation for
the second electrical conductor 15 while not preventing heat transfer from the PTC
heating assembly to the hollow heating module 6.
[0042] At least one PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 generating heat
is arranged on the outer surfaces 64 of the hollow heating module; each PTC heating
assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 includes a flexible metal electrical conductor
11 for supplying electrical voltage and for pressing the PTC assembly PTC1, PTC2,
PTC3, PTC4, PTC5, PTC6 against the concentric wall 5 and also against the heating
module 6.
[0043] Basically, there is no need for pressing or gluing to ensure good contact of all
layers of the PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 with each other
and to ensure good contact with the heating module 5 and the plastic concentric wall
6.
[0044] The pair of projections 51 is also shape connected to the projection 63 in order
to insulate the electrically conductive parts of the PTC heating assembly PTC1, PTC2,
PTC3, PTC4, PTC5, PTC6.
[0045] After insertion of the PTC heating assembly into the installation gap 19, an unfilled,
free space, generally filled with air, remains in it. In the preferred solution, the
free space between the first electrical conductor 11 and the concentric wall 5 and
in the installation gap 19 is filled with a thermally conductive and at the same time
electrically insulating filler material.
[0046] Heating of the liquid is accomplished by applying voltage (of appropriate height
and polarity) to two electrical contacts 17, 18 of conductors 11, 15 of the PTC heating
assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 to generate heat in the PTC layer and
the heat is transferred through the hollow heating module 6 to the liquid in the internal
circulation channel 31. The ribs 66 are arranged to increase the heating area.
[0047] The plastic concentric wall 5 is also partially heated, and the heat is transferred
to the liquid in the external circulation channel 32. Thus, the generated heat is
used in the present solution as efficiently as possible and the heated liquid is cleared
of solid impurities before leaving the heater.
[0048] The electric heater is preferably used as an electric back-up heater in heat pump
systems, for heating less pure liquids, even with glycol content, where applicable.
[0049] Fig. 5 shows an example schematic of the Y- wiring of three-phase voltage to the
connection contacts 17,18 of the electrical conductors 11 and 15 of the PTC heating
assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6. The phase voltage L2 is connected to
the contacts 17 of the first electrical conductor 11 of the heating assemblies PTC1
and PTC2, the phase voltage L3 is connected to the contacts 17 of the first electrical
conductor 11 of the heating assemblies PTC3 and PTC 4, and the phase voltage L1 is
connected to the contacts 17 of the first electrical conductor 11 of the heating assemblies
PTC5 and PTC 6. The contacts 18 of the second electrical conductor 15 on all heating
assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 are connected to zero potential.
[0050] The electrical wiring may be different, depending on the requirements for heating
power.
[0051] The electric PTC heater integrates a solid impurity filter function, the solid impurities
are separated from the liquid stream by hitting the ribs 66 arranged in the continuous
cavity 65 of the hollow heating module 6 and settle in the conical part 2 of the tank.
A drain valve 7 is connected to the tank to drain impurities.
Example 2 (not shown)
[0052] In the other design of the invention, the electrically conductive body of a hollow
heating module 5 is used as the second electrical conductor 15.
[0053] In this case, the PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 includes
the first electrical conductor 11, the PTC layer 13 and the graphite pads 12,14, and
the conductive surface of the hollow heating module 5 as the second electrical conductor
15.
[0054] Such an arrangement is suitable for use in a pure water instantaneous heater, as
a module for measuring the conductivity of the water as well as other safety measures
are the mandatory parts of instantaneous heaters.
Industrial applicability
[0055] The electric PTC heater for heating liquids according to the present invention is
designed for heating liquids circulating mainly in heating circuits of residential
buildings. The PTC electric heaters provide many advantages over resistance wire based
systems and simplify heating control.
1. An electric liquid heater, comprising
a plastic liquid tank, wherein the tank comprises an upper cylindrical part (1) and
a lower conical part (2), watertightly connected to each other and wherein a basically
cylindrical plastic concentric wall (5) is firmly arranged inside the tank,
a hollow heating module (6), with outer surfaces (64) and with a continuous cavity
(65) for directing the liquid to be heated, wherein the hollow heating module (6)
is provided with a connection piece (61) for supplying the liquid to be heated,
and wherein the plastic concentric wall (5) defines an internal circulation channel
(31) and an external circulation channel (32) connected to the outlet (4) of the heated
liquid,
characterized in that
the hollow heating module (6) is arranged in the internal circulation channel (31),
at least one PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) generating
heat is arranged on the outer surfaces (64) of the hollow heating module (6),
each PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) comprises a flexible
metal electrical conductor (11) for supplying electrical voltage and for pressing
the PTC heating assembly against the concentric wall (5) and against the hollow heating
module (6).
2. The electric liquid heater, according to claim 1,
characterized in that
the PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) is assembled as a layered
structure of the layers of the first flexible electrical conductor (11), a first graphite
pad (12), a layer (13) of PTC plates, a second graphite pad (14), a second electrical
conductor (15) and an electrical insulator (16).
3. The electric liquid heater, according to claim 1,
characterized in that
the PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) is assembled as a layered
structure of the layers of the first flexible electrical conductor (11), the first
graphite pad (12), a layer (13) PTC plates and a second graphite pad (14) and the
hollow heating module (6) is connected as the second electrical conductor.
4. The electric liquid heater, according to any one of the claims 1 to 3,
characterized in that
the surfaces (64) are defined by projections (63) arranged on the outer surface of
the hollow heating module (6) and ribs (66) are arranged in the continuous cavity
(65) to increase the heating area.
5. The electric liquid heater, according to any one of the claims 1 to 4,
characterized in that
the concentric plastic wall (5) has pairs of projections (51) arranged on its inner
surface, facing the internal circulation channel (31), for the shape connection with
the projections (63) arranged on the outer surface of the hollow heating module (6).
6. The electric liquid heater, according to any one of the claims 1 to 5,
characterized in that
installation gaps (19) are arranged between the heating module (6) and the plastic
concentric wall (5) for inserting at least one PTC heating assembly (PTC1, PTC2, PTC3,
PTC4, PTC5, PTC6).
7. The electric liquid heater, according to any one of the claims 1 to 6,
characterized in that
a free space between the first electrical conductor (11) and the concentric wall (5)
in the installation gap (19) is filled with a thermally conductive and electrically
insulating filler material.