[0001] The invention relates to a method for controlling the temperature of a liquid which
is supplied by a non-controllable heating appliance to a take-off point. The invention
relates particularly to such a method for use with water coming from a heating appliance
powered by natural, for instance solar, energy.
[0002] Appliances which are powered by natural energy such as solar energy can generally
not be controlled, or hardly so, as their performance is related to a quantity which
cannot be influenced by the user, such as for instance the number of hours of solar
radiation, the number of hours that the wind exceeds a determined strength or the
like. In the use of such appliances it is however important that a form of control
is nevertheless applied. This applies in particular to hot water appliances operated
on solar energy, since when solar radiation is strong the temperature of the water
in such appliances can rise so high that this forms a danger to the user. For auxiliary
heating apparatus which will generally be used in combination with such a hot water
appliance operated on solar energy to provide additional heating when the solar radiation
is insufficient, it is also the case that this may not be exposed to water with too
high a temperature. A water temperature of 90°C at the inlet is generally considered
a safe limit for such auxiliary heating apparatus, while for a user the water temperature
may preferably not be higher than 80°C.
[0003] There therefore exists a need for a method of controlling the temperature of the
water coming from a hot water appliance operated by solar energy. Since the object
of the application of solar energy is to limit as far as possible the consumption
of other types of energy, particularly that obtained through burning fossil fuels,
the sought after control method must also result in a low consumption of energy (and
water). What must be particularly prevented is that water heated by the heating appliance
is drained without being used in order to limit the temperature of the water supplied
to the user or to the auxiliary heating apparatus.
[0004] According to the invention this is achieved by a method of the above described type
which comprises the steps of measuring the temperature of a liquid supplied to at
least one take-off point by a non-controllable, in particular a natural energy powered
heating appliance, by measuring the temperature of the liquid prior to the take-off
point, admixing to the liquid flow from the heating appliance a second liquid flow
with a determined lower temperature when the measured temperature exceeds a determined
target value, and continuously adapting the quantity of the second liquid flow for
admixing such that in each case the measured temperature approaches as closely as
possible the determined target value.
[0005] Because the temperature of the liquid coming from the heating appliance is controlled
by admixing a second liquid at lower temperature, no wastage of heated liquid occurs.
[0006] The liquid flows are preferably brought into mutual heat-transferring contact prior
to mixing. The temperature of the liquid coming from the heating appliance is hereby
already slightly decreased, whereby the device where mixing takes place will be exposed
to lower temperatures.
[0007] When one of the liquid flows is collected and stored for a short time prior to mixing,
excessive fluctuations in the temperature of the liquid coming from the heating appliance
are already damped somewhat, whereby temperature control is further simplified.
[0008] The invention also relates to a device for performing the above described method.
Such a device is provided according to the invention with a first inlet conduit for
connecting to the heating appliance, a second inlet conduit for connecting to a source
of liquid with a determined lower temperature and provided with controllable shut-off
means, a mixing chamber connected to the first and second inlet conduit, an outlet
conduit connected to the mixing chamber and provided with means for measuring the
temperature of the liquid flowing therethrough, and control means connected for transmitting
signals to the shut-off means, wherein the temperature measuring means are connected
for transmitting signals to the control means.
[0009] Preferred embodiments of this device are described in the dependent claims 7-12.
[0010] Finally, the invention relates further to a heating system equipped with a control
device of the above described type.
[0011] The invention is elucidated on the basis of a number of embodiments, wherein reference
is made to the annexed drawing in which corresponding parts are designated with the
same reference numerals, and wherein:
fig. 1 shows a schematic view of a heating system with a control device according
to the invention;
fig. 2 is a partly cut away perspective view of the control device shown in fig. 1;
fig. 3 is a partly cut away perspective view of an alternative embodiment of the heat
exchanger shown in fig. 2; and
fig. 4 is a partly sectional perspective view of a second alternative embodiment of
the heat exchanger.
[0012] A device 1 (fig. 1) for controlling the temperature of a liquid supplied to at least
one take-off point by a non-controllable, in particular a natural energy heating appliance
2 powered is provided with an inlet conduit 3 joined to a connection 22 of the heating
appliance and a second inlet conduit 4 connected to a source 7 of liquid with a determined
lower temperature. The regular water supply system can for instance function as source
of liquid at low temperature. The first and second inlet conduits 3,4 come together
in a mixing chamber which in the embodiment shown forms part of a thermostatic mixing
valve 5. An outlet conduit 6 is connected to the mixing valve 5. The thermostatic
mixing valve comprises means for measuring the temperature of the liquid delivered
to the outlet conduit 6 and means for opening and closing at choice the second inlet
conduit 4. The shut-off means are controlled by control means which receive control
signals from the temperature measuring means.
[0013] The non-controllable heating appliance 2 is formed in the shown embodiment by a solar
boiler which consists of a transparent plate 8 which is arranged in the outside wall
or the roof of a building and behind which a water reservoir 10 is arranged with interposing
of an air cavity 9. Water reservoir 10 is enclosed on all sides by an insulation layer
11. Under the influence of the incident solar radiation S the water present in reservoir
10 is heated, wherein it flows slowly from the lower connection 23 in the direction
of the upper connection 22. The water for heating is transported via water conduit
7 and a non-return valve 13 to the connection 23 of solar boiler 2. An adjustable
pressure-sensitive valve 14 serves to prevent the pressure in reservoir 10 becoming
too high, for instance when the water present therein begins to boil. In that case
a part of the water present is drained via valve 14 to a sewer connection 15.
[0014] When a user needs water and opens a tap somewhere in the building, a flow of water
begins from reservoir 10 to the take-off point where the user is located. In order
to protect the user against excessive temperature of the water from heating appliance
2, this water is mixed if necessary with cold water from water conduit 7, which water
is guided via a non-return valve 12 to the second inlet conduit 4. In the thermostatic
mixing valve 5 this mains water, the temperature of which in general only varies a
little from for instance 5 to 15°C, is mixed with the hot water from the heating appliance
which can reach temperatures of a maximum of 135°C.
[0015] The mixing is preferably performed such that the water which flows via the outlet
conduit 6 to the take-off point is not hotter than 80°C, which is the maximum safe
temperature for human users. There will however often be an auxiliary heating apparatus
present between the outlet conduit 6 and the take-off point, for instance an electrical
or gas-fired boiler, for additional heating of the water when the solar radiation
contains too little energy (for example during the winter or on cloudy days). Such
an auxiliary heating apparatus may not generally be exposed to a supply flow with
a temperature of more than 90°C, so that interposing of the control device 1 is also
necessary in this case.
[0016] In order to protect the mixing valve 5 itself against excessive inlet temperatures
and also to prevent possible larger temperature fluctuations as far as possible, the
flow of hot water from heating appliance 2 is placed in heat-transferring contact
with the flow of cold water from the water supply system 7 before reaching mixing
valve 5. This takes place in a heat exchanger 16.
[0017] The non-return valves 12, 13 otherwise serve to prevent that, when the water in the
heating appliance 2 reaches a determined very high temperature of for instance 135°C,
hot water flows back into the mains supply system 7 as a result of the associated
pressure.
[0018] Together with the so-called inlet combination (consisting of non-return valve 13
and pressure valve 14) the control device 1 can be assembled into a single cabinet
17 (fig. 2) for simple connection. This cabinet 17 can be placed by a fitter in the
vicinity of heating appliance 2 and be connected up rapidly by interconnecting the
conduits 3,4,6,7 and 15. Cabinet 17 will generally be placed in an attic as the solar
boiler 2 has to be placed obliquely for optimum performance, and the only sloping
surfaces in a building are generally to be found on the roof. When the attic area
is heated this moreover ensures that the connections 22,23 of solar boiler 2 remain
frost-free, whereby frost damage to the solar boiler is prevented.
[0019] In the embodiment shown the heat exchanger 16 is formed by a storage container 19
which is arranged in the first inlet conduit and the content of which is greater than
that of the first inlet conduit 3 and through which the second inlet conduit 4 is
guided. In order to obtain the greatest possible heat exchanging surface area, the
cold water inlet conduit 4 is wound to a spiral 20. Large temperature fluctuations
are damped by the thermal mass of the water situated in storage container 19. This
is important since the thermostatic mixing valve 5 generally requires a certain response
time before it admixes sufficient cold water to the hot water from the first inlet
conduit 3. Sudden temperature increases of the hot water supplied to mixing valve
5 could thus result in water of too high a temperature being passed through mixing
valve 5 before sufficient cold water is admixed.
[0020] The cold water from water supply system 7 is fed as according to arrow CI to the
control device 1 and fed for the greater part through non-return valve 13 in the direction
of arrow CO to the lower connection 23 of solar boiler 2. The hot water coming from
the solar boiler is fed as according to arrow H from the upper connection 22 to control
device 1 and flows through an inflow opening 21 in storage container 19 which also
functions as heat exchanger 16. When a user needs water at a take-off point this is
supplied via the first inlet conduit 3 to mixing valve 5 where as much cold water
is then admixed from the second inlet conduit 4 that the water exiting as according
to arrow M has a temperature such as is chosen by the user by means of the adjustment
knob 18. This target temperature can for instance be set to any desired value between
30 and 70°C. As a result of interposing the heat exchanger 16 the inlet temperature
of the water supplied to mixing valve 5 via the first inlet conduit 3 is limited,
whereby a comparatively inexpensive mixing valve can be used.
[0021] A better heat transfer can be achieved in heat exchanger 16 when the hot water is
supplied not axially but tangentially to the storage container 19. For this purpose
the injection aperture 21 can be arranged close to the cylindrical side wall of the
storage container, practically parallel to a tangent to the cylindrical surface (fig.
3).
[0022] In an embodiment which is simpler and which can thereby be manufactured at lower
cost, the heat exchanger 16 is formed by a double-walled tube. An optimum heat transfer
is herein obtained when the inner tube forms part of the first inlet conduit 3 for
the hot water and the outer tube forms part of the second inlet conduit 4 for the
cold water. In order to embody the heat exchanger 16 as compactly as possible it can
be wound to a spiral (fig. 4).
1. Method for controlling the temperature of a liquid which is supplied to at least one
take-off point by a non-controllable, in particular a natural energy powered heating
appliance, by measuring the temperature of the liquid prior to the take-off point,
admixing to the liquid flow from the heating appliance a second liquid flow with a
determined lower temperature when the measured temperature exceeds a determined target
value, and continuously adapting the quantity of the second liquid flow for admixing
such that the measured temperature of the mixture approaches as closely as possible
the determined target value.
2. Method as claimed in claim 1, characterized in that prior to mixing the liquid flows are brought into mutual heat-transferring contact.
3. Method as claimed in claim 1 or 2, characterized in that one of the liquid flows is collected and stored for a short time prior to mixing.
4. Method as claimed in claims 2 and 3, characterized in that the other liquid flow is brought into heat-transferring contact with the stored liquid
flow.
5. Method as claimed in any of the foregoing claims, characterized in that the target value of the temperature is adjusted prior to delivery of liquid from
the heating appliance.
6. Device for controlling the temperature of a liquid which is supplied to at least one
take-off point by a non-controllable, in particular a natural energy powered heating
appliance, provided with a first inlet conduit for connecting to the heating appliance,
a second inlet conduit for connecting to a source of liquid with a determined lower
temperature and provided with controllable shut-off means, a mixing chamber connected
to the first and second inlet conduit, an outlet conduit connected to the mixing chamber
and provided with means for measuring the temperature of the liquid flowing therethrough,
and control means connected for transmitting signals to the shut-off means, wherein
the temperature measuring means are connected for transmitting signals to the control
means.
7. Control device as claimed in claim 6, characterized in that the first and second inlet conduit are mutually connected for heat transfer over
at least a part of their length.
8. Control device as claimed in claim 6 or 7, characterized by a storage container which is arranged in one of the inlet conduits and the content
of which is greater than that of the associated inlet conduit.
9. Control device as claimed in claims 7 and 8, characterized in that the other inlet conduit is carried through the storage container.
10. Control device as claimed in claim 7, characterized in that one of the inlet conduits is enclosed over at least a part of its length by the other
inlet conduit.
11. Control device as claimed in claim 10, characterized in that the inlet conduits are wound spirally over at least a part of their mutually enclosing
length.
12. Control device as claimed in one or more of the claims 6-11, characterized in that the control means are adjustable.
13. Heating system provided with a non-controllable, in particular a natural energy powered
heating appliance, at least one take-off point for heated liquid connected to the
heating appliance, and a control device as claimed in one or more of the claims 6-12
interposed between the heating appliance and the at least one take-off point.
14. Heating system as claimed in claim 13, characterized in that the heating appliance is a so-called solar boiler.