[0001] The invention relates to a device as described in the heading of claim 1.
[0002] When hot tap-water is required in such a device, the heating water coming from the
central heating boiler is carried via the tap-water heat exchanger, where incoming
cold mains water is heated to hot tap-water.
[0003] When the central heating boiler is at the required temperature hot water can be supplied
very quickly. However, when the boiler is not at the required temperature at the moment
when hot tap-water is required, as happens particularly in the summer, it takes a
long time before hot tap-water is available, since the central heating boiler and
the heating water must first be brought up to operating temperature.
[0004] In order to obviate this drawback it is known to give the tap-water heat exchanger
a relatively large capacity and to insulate it well, so that a buffer supply of hot
heating water remains in the heat exchanger. With such a system hot water is supplied
directly the hot water tap is turned on. However, since in the circumstances described
the heating water is at first still cold, the temperature of the heating water present
in the heat exchanger falls and thus also the temperature of the tap-water. Only
after considerable time, when the central heating boiler is at the required temperature
and has supplied hot heating water for a period of time such that the entire content
of the heat exchanger has been brought once again up to temperature, is the temperature
of the tap-water finally at the desired level.
[0005] Another improvement of this system is described in the European patent 0.178.351.
Provisions have been hereby made in the tap-water heat exchanger which ensure that
the initially incoming cold water does not mix with the hot water already present
in the exchanger. This system thus supplies hot water at the desired temperature very
rapidly. However, after some time, depending on the capacity of the heat exchanger,
the cold boiler water which entered initially and which is only partially mixed with
later supplied hot water will come into contact with the actual heat exchanging coil,
so that the hot tap-wa ter, after initially having had the desired temperature, suddenly
falls slightly in temperature, to then again definitively reach the desired high temperature
shortly afterward. Such temperature behaviour, whereby some time after the hot water
tap has been turned on a "dip" occurs in the temperature of the water, is extremely
undesirable, especially in the case the hot water is being used to have a shower.
[0006] The invention therefore has for its object to provide a device of the type described
in the preamble which has none of the above named drawbacks and which is able to supply
tap-water that is rapidly at the desired temperature, even when the central heating
boiler is not at operational temperature at the moment hot water is required, and
that afterward retains this temperature.
[0007] This object is attained with a device according to the invention in that a hot water
reservoir is arranged between the tap-water heat exchanger and the return pipe. When
the hot water tap is opened the water is at first still cold. Through simultaneous
switching on of the central heating boiler and the associated circulation pump hot
water is carried from the hot water reservoir via the return pipe to the central heating
boiler. The latter is immediately heated up by the hot water from the hot water reservoir,
so that it very rapidly begins to supply hot heating water and therefore also rapidly
begins to heat up the cold mains water in the tap-water heat exchanger. It has been
found that with a normal central heating installation and with a hot water reservoir
of a capacity of 10 litres, the tap-water reaches the required temperature within
half a minute.
[0008] An economical embodiment of the device according to the invention is characterized
in claim 2.
[0009] An especially favourable construction of this embodiment is characterized in claim
3.
[0010] It is noted that a tap-water heat exchanger consisting of an outer tank, an inner
tank arranged therein and having one closed end wall and a tap coil arranged around
the inner tank is per se known from the above-mentioned European patent specification
0.178.351. As already described the function of this unit differs from that according
to the invention. The heating water supply hereby runs out into the inner tank, while
the heating water outlet debouches outside the inner tank.
[0011] With the embodiment as characterized in claim 4 is achieved that a minimum amount
of hot water can be present between the inner tank and the outer tank and therefore
a maximum amount of hot water is available for the heating up of the central heating
boiler. In this embodiment a helical channel for the heating water is moreover created
in a favourable manner between the helical windings of the tap-water coil, which is
favourable for good heat transfer.
[0012] The invention will be further elucidated in the following description with reference
to the embodiments shown in the figures.
Fig. 1 shows schematically a device according to a first embodiment of the invention.
Fig. 2 shows a diagram of a preferred embodiment of the invention corresponding with
fig. 1.
Fig. 3 shows a partially broken away and partially sectional tap-water heat exchanger
and hot water reservoir combined into one unit according to the preferred embodiment
of the invention.
[0013] The device 1 in fig. 1 is a combined central heating device and tap-water heating
device. In the usual manner the heat source is a central heating boiler 2 which comprises
a burner 3 and a heat exchanger 4 in which heating water from a return pipe 5 is heated
and after heating is carried away via an outlet heating water pipe 6. The central
heating boiler 2 is provided with a control device 7 which controls the burner 3 and
has as entrance quantity in the case shown the temperature of the heating water in
the heating water pipe 6 and the temperature of the heating water in a tap-water
heat exchanger 11. Arranged in the return pipe 5 is a circulation pump 8.
[0014] As shown schematically in fig. 1, radiators and/or convectors 9 are connected between
the heating water pipe 6 and the return pipe 5. These generate heat from the heating
water in the space in which they are disposed.
[0015] In addition to these radiators and convectors 9 a tap-water heat exchanger 11 is
arranged between the heating water pipe 6 and the return pipe 5. Mounted for this
purpose in the heating water pipe 6 is a three-way valve 10, which can carry the heating
water at choice to the tap-water heat exchanger 11 or to the radiators 9.
[0016] Arranged in the tap-water heat exchanger 11 is a tap-water coil 12 through which
water from the mains water supply 13 can flow. The feed connection of the tap coil
12 is connected to this mains water supply via respectively a main cock 14, a non
return valve 15 and an adjusting tap 16.
[0017] The hot water from the tap coil 12 can be discharged directly via the connection
18. The hot water connection of the tap coil 12 is likewise connected to a control
valve 17, which is connected at a second inlet to the mains water supply 13, and which
can deliver hot water at a controlled temperature via connection 19.
[0018] In the situation where the central heating boiler 2 is at operating temperature,
that is, usually during the winter period, as soon as hot tap-water is required, for
instance through opening of a draw-off tap in the connecting pipe 18 or 19, the three-way
valve 10 is switched over in order to send hot water from the pipe 6 to the tap-water
heat exchanger 11. Hot water can then be drawn immediately from the connection 18
or 19.
[0019] In the situation where the central heating boiler is not at operating temperature,
as is usual in the summer period, hot tap-water is not immediately available. As soon
as hot tap-water is again required, the central heating boiler 2 is switched on.
The control device which provides this switch-on is per se commonly known and will
consequently not be further described here.
[0020] In this situation, after the central heating boiler 2 has been switched on, the water
leaving the heat exchanger 4 is initially cold. The cold mains water is therefore
not yet heated.
[0021] According to the invention however a hot water reservoir 20 is arranged between
the tap-water heat exchanger 11 and the return pipe 5. This hot water reservoir 20
is filled with hot heating water. When the central heating boiler 2 and the circulation
pump 8 are switched on, this hot water comes out of the hot water reservoir 20 via
the return pipe 5 into the central heating boiler 2, which results in it being rapidly
heated and moreover in the temperature of the water in the outlet pipe 6 increasing
rapidly. The hot water from the pipe 6 flows to the tap-water heat exchanger 11 and
can thus heat the tap-water rapidly.
[0022] An important aspect of the invention is therefore that a quantity of hot water is
stored in the hot water reservoir 20 and is used to bring the installation quickly
up to operating temperature, this instead of the usual practice of generating heat
directly to the water in the water pipe. The installation and the tap-water thus reach
the operating temperature rapidly, and this operating temperature, particularly of
the tap-water, remains high for unlimited time afterward.
[0023] Fig. 2 shows a device 25 which largely corresponds with the device 1 in fig. 1. The
tap-water heat exchanger 11 and the hot water reservoir 20 shown in fig. 1 are combined
in the device 25 into a heat exchanger unit 26. The other elements of the device are
designated with the same reference numerals as in fig. 1 and do not require further
description.
[0024] The heat exchanger unit 26 comprises a closed outer tank 27 in which is arranged
an inner tank 28 with one closed end wall 29. A helically wound tube forming the tap
coil 32 is arranged around the inner tank 28. The ends of the tap coil 32 are guided
in sealed manner through the wall of the outer tank 27.
[0025] As shown in fig. 2, near to the closed end wall 26 of the inner tank 28, the heating
water outlet 31 is located in the inner tank 28 and the heating water feed 30 outside
this inner tank.
[0026] After the central heating boiler 2 has been switched on, because hot tap-water is
required, the hot water present in the inner tank 28 flows via the outlet 31 to the
return pipe 5 and the central heating boiler 2 to heat up the latter. The water from
the pipe 6, at this moment cold, flows via the feed 30 into the space between the
outer tank 26 and the inner tank 28, along the tap coil 32.
[0027] It will be apparent that the cold water supplied via the feed 30 can mix with the
initially hot water in the space between the outer tank 27 and the inner tank 28.
As a result the average temperature of this water falls, rendering it no longer effective
in heating up the central heating boiler 2.
[0028] Fig. 3 shows a further developed embodiment of the heat exchanger unit in which this
disadvantageous effect is minimalised. This heat exchanger unit 35 comprises in the
manner already described an outer tank 36 assembled from a tubular wall closed off
with end covers 37 and 38, in which is arranged an inner tank 39 likewise comprising
a cylindrical wall, which however is only closed off at one end, in fig. 3 the upper
end, with an end wall 40. The lower end of the inner tank 39 is entirely open. Close
to the closed end wall 40 the feed 41 runs into the outer tank 36, and the outlet
42 into the inner tank 39. This outlet 42 leads through the end cover 38 to a connection
43 with the return pipe, onto which also runs out a connection 44 which is connected
to the outlet of the radiators.
[0029] The diameter of the inner tank 39 is such that the space between the inner tank 39
and the outer tank 36 has a breadth substantially equal to the diameter of the tube
of the tap coil 45. The helically wound tube of the tap coil 45 therefore lies substantially
against both the outer wall of the inner tank 39 and the inner wall of the outer tank
36. A similarly helical space 46 is thus separated off between the successive windings,
through which space the heating water from the feed 41 is constrained to flow.
[0030] The heat exchanger unit 35 according to the invention shown in fig. 3 has on the
one hand the advantage that the effective quantity of hot water it can contain is
maximal while on the other a very good heat transfer results from the hot water supplied
via the feed 41 to the water in the tap coil 45, so that a pure counterflow heat exchange
takes place. The hot water leaving the tap coil 45 at the upper side therefore has
practically the same temperature as the heating water supplied via the feed 41, so
that with this embodiment the heating speed is optimal.
[0031] The heat exchanger unit according to the invention can be applied in both lying and
standing position. In the latter case the closed end wall of the inner tank can be
situated at the top or at the bottom. Because when the central heating boiler 2 and
the circulation pump 8 are switched on the contents of the unit 45 are renewed very
rapidly, the effects of the force of gravity on the mixing of the supplied cold water
and the hot water present in the inner tank are relatively insignificant. It has
been found that a capacity for the unit of approximately 10 litres is optimal for
a domestic central heating installation.
1. Device for heating tap-water in a central heating device comprising a central heating
boiler with an outlet heating water pipe and an incoming return pipe, heating radiators
and/or convectors and a tap-water heat exchanger arranged between these pipes and
a circulation pump arranged in one of these pipes, characterized in that a hot water reservoir is arranged between said tap-water heat exchanger and said
return pipe.
2. Device as claimed in claim 1, characterized in that the tap-water heat exchanger and the hot water reservoir are integrated into a unit.
3. Device as claimed in claim 2, characterized in that said unit comprises an outer tank with closed end walls, an inner tank arranged therein
having one closed end wall, a helically wound tube arranged around said inner tank
and forming a tap coil, the ends of which tube are guided in sealed manner through
the wall of said outer tank and whereby close to the closed end wall of said inner
tank, a heating water outlet runs out into said inner tank and a heating water feed
debouches outside said inner tank.
4. Device as claimed in claim 3, characterized in that side walls of the outer tank and the inner tank are coaxially cylindrical and have
an intermediate space corresponding substantially with the thickness of the helically
wound tube, so that the tube lies substantially against said inner tank and said outer
tank.
5. Device as claimed in any of the foregoing claims, characterized in that the capacity of the hot water reservoir or the outer tank amounts to less than 10
litres.