State of the art
[0001] The invention relates to a method of heating domestic water in a water heater having
a heat exchanger whose primary side is supplied with hot water, and whose secondary
side is supplied with colder water where the water on the secondary side is tapped
directly from the heat exchanger without being mixed with water already heated. A
method according to the preamble of claim 1 is already known from document DE 199
60527. Hot domestic water, particularly in major systems, is frequently of a poor
quality, as bacterial growth and formation of slime occur because of physical/bacterial
conditions.
[0002] The bacterial growth may cause diseases, and where legionella occurs, there is a
risk of legionnaire's disease.
[0003] This disease is a bronchial infection, which may be lethal when it occurs at hospitals,
etc. with immuno compromised patients.
[0004] The factors having the greatest influence on the bacterial growth in the water are
the temperature, the residence time of the water in the piping and the area of the
internal surfaces. The bacterial growth takes place particularly at temperatures between
20° and 50°C, with long residence times and large surfaces.
[0005] The traditional way of obviating the risk of bacterial growth is to maintain a relatively
high water temperature, or discharging all the heated water in the container and optionally
flushing out formations of slime, as needed. However, it is a problem that the heated
water from the container and in the piping to the tapping point frequently stands
still between the tappings and thereby loses temperature, thus involving the risk
of bacterial growth.
[0006] To remedy this drawback it is known from Japanese Patent Application
101 959 45 to sterilize the hot water in a heat exchanger, an electric water heater, in a container,
from which a limited amount of sterile water may be tapped.
[0007] The drawback of this is that, outside the tapping periods, the stagnant water constitutes
a relatively large amount of water corresponding to the volume of the container, and
this water has to be sterilized before it can be tapped. This requires both time and
energy, to which should be added the risk of scalding injuries.
[0008] Furthermore,
EP 621 450 A2 discloses a water heating system for heating domestic water through a heat exchanger
having a water supply via a buffer container.
[0009] This buffer container is necessary where the source of heating is limited such as
in solar heating systems. To ensure a suitable domestic water temperature from the
beginning of the tapping at the tapping point, circulation for the domestic water
is provided for. As a result, in the circulation line there will always be a temperature
of about 40°C, precisely the temperature which is the optimum temperature for the
multiplication of legionella bacteria. Since the circulation line has a length at
least corresponding to twice the distance between the exchanger and the tapping point,
this means that a relatively large amount of water, which must constantly be kept
heated to about 40°C, will constitute a considerable danger of infection. It should
be recalled in this connection that the bacterial growth is at least doubled every
two hours under these conditions.
[0010] Another water heating system is disclosed in
DE19960527 by Samson AG. This system has feed and return connections for heat carrier medium
for a room heating device (44) and a heat exchanger for heating drinking water, with
a regulator controlling the flow through the room heating circuit and a drinking water
heating circuit and a differential pressure regulator for maintaining the required
pressure difference between the feed and return connections. However, the technique
disclosed by Samson AG does not provide means for the control of for example bacterial
growth, which may cause disease.
Object of the invention
[0011] It is an object of the invention to remedy these defects and drawbacks, and this
is achieved accordingly to the invention by a method wherein, as stated in claim 1,
the secondary side of the heat exchanger is frequently flushed with domestic water
in order to keep the temperature of the secondary side of the heat exchanger below
a desired temperature, e.g. 20°C.
[0012] The risk of bacteria in the tapped hot domestic water is reduced in this simple manner
for the simple reason that the multiplication of the legionella bacteria in the periods
between the tappings cannot take place, since the heating and the tapping take place
at the same time, and thus no water is left standing in which the bacteria can thrive.
[0013] The installation may therefore be made so compact and the piping so direct that a
high water rate, low supply pipe temperature and return pipe temperature as well as
minimum storage of stagnant water may be achieved. In addition to low costs of installation,
this also results in a low consumption of energy.
[0014] The heating takes place when the tapping is initiated, and it takes place right up
at the actual tapping point. This provides the greatest possible certainty that the
water does not contain the feared legionella bacteria.
[0015] When, as stated in claim 2, the secondary side of the heat exchanger is flushed with
the cool domestic water immediately after the tapping is terminated, a particularly
efficient cooling of the secondary side and a further reducing of the possibility
of growing of legionella bacteria is achieved.
[0016] As stated in claim 3, the flushing water is preferably led out directly to the sewers
through an extra magnet valve, which is open during flushing and closed during normal
tapping. The normal tapping valve is closed during flushing and only opens during
tapping.
[0017] It is also possible to heat the secondary side of the heat exchanger to a desired
temperature, e.g. 60 - 70°C by letting the hot water flow through the primary side
in a period after terminating the tapping, as stated in claim 4, whereby the possibility
of growing legionella bacteria is further reduced.
[0018] By controlling these operations, such as opening and closing of the magnet valves
in the system by a microprocessor, as stated in claim 5, it is made possible to automatize
and optimize the tapping and flushing processes.
The drawing
[0019] An example of an embodiment of an installation for use in the method according to
the invention will be described more fully below with reference to the drawing, which
shows a water heater in perspective and with a cabinet partially cut away.
Description of the embodiment
[0020] According to the invention, the example of an embodiment of a water heater 1 shown
in the drawing is constructed on a rear plate 3, which may be secured to the wall
right above the tapping point so that the tapped water 18 leaves the water heater
through the outlet line 17 directly and not through valves, outlet spouts and the
like.
[0021] The hot medium 5, which may either be district heating system water or an existing
hot water supply, is fed to the primary side of the heat exchanger 4 through a stub
6, a pipe 15 and a magnet valve 12.
[0022] Fresh domestic water 7 is fed to the secondary side of the exchanger 4 through a
stub 8 and a regulator 9.
[0023] The regulator 9 is preferably of the type which is described in Danish Utility Model
Registration No.
2000 00320.
[0024] The tapping of the heated domestic water 18 from the secondary side of the exchanger
4 takes place via a temperature sensor 13, which is connected with the regulator 9
via a capillary pipe 14 and with a magnet valve 11 inserted in the outline line 17.
[0025] The heated and now cooled medium is discharged from the primary side of the exchanger
4 through the regulator 9 to an outlet line, as illustrated by the arrow 16.
[0026] A switch 19 switches on the current to the water heater, including the magnet valves
11, 12, and a microprocessor (not shown) and various control lamps 20 on the front
of the cabinet 2. Finally, a water temperature regulator 10 is provided on the regulator
9 for determining the temperature of the hot domestic water 18.
[0027] The regulator 9 and the valves 11, 12 are made of materials approved for drinking
water. The exchanger 4 is preferably soldered of pure copper or silver, and the exchanger
is preferably made of acid-proof stainless steel AISI 316. The exchanger and the pipes
may be cleaned and be supplied with chlorine in a reasonably high concentration without
corrosion and are made with a minimum pipe dimension and exchanger size, such that,
at each tapping, there is a strong flow and great replacement of the water with a
predetermined quantity, temperature and time, which in turn results in a less favourable
environment for the formation of bio films, protozoans and thereby multiplication
of the legionella bacteria.
[0028] Outside the tapping periods, about 3 dl of stagnant water remains in the exchanger
4. In contrast to containers and/or long pipes of larger diameter with many times
greater amounts of stagnant water and thereby a potential, much greater risk of legionella
problems. If necessary, the exchanger 4 may be flushed automatically solely as far
as the domestic water is concerned x-number of times/time/days, so that the limited
amount of stagnant domestic water in the exchanger is replaced according to the concrete
need, which depends on concrete multiplication conditions for the legionella bacteria.
[0029] The temperature of the stagnant domestic water must be lower than 20 °C or higher
than 50-60 °C to prevent multiplication of the legionella bacteria. The exchanger
4, which, as mentioned, is soldered with pure copper or silver, releases copper or
silver ions to the stagnant water in the exchanger 4 to a minimum extent, which can
also contribute to restricting the multiplication environment of the bacterium and
reducing the number of bacteria.
[0030] District heating system water 5 is usually used for heating the primary side of the
exchanger, but, according to the invention, it is also possible to use the domestic
water on the secondary side, which has already been heated to 50 °C, and which is
present in the existing hot water piping, as the heating medium. This heating method
may provide domestic water of 40-45 °C°. Precipitation of lime and scalding, e.g.,
are avoided hereby.
[0031] To use the already heated domestic water as a heating medium, which frequently contains
an undesirable amount of legionella bacteria, may be of extreme practical importance
in case of repair and not least where old, long pipe installations are involved, as
the water heater 1 may merely be mounted directly above - and still use - e.g. the
existing wash basin and be connected with the existing hot water tap as a heating
medium source irrespective of the content of legionella bacteria. This simplifies
and reduces the costs of the installation.
[0032] There is no need for a mixer tap or other facility for mixing the domestic water
with "old", possibly legionella-infected, heated domestic water - only a tapping pipe.
[0033] In the water heater 1, there is just one tapping point for cold and/or hot domestic
water that comes directly from the exchanger 4 to the point of use. A tap/water valve
is not needed. The heated domestic water must be fed to the area of use as rapidly
and directly as possible. The system may thus replace previously used fittings.
[0034] One, two or more magnet valves 11, 12 are mounted on the system. Basically, one on
the secondary side and one on the primary side, which are controlled by a microprocessor
separately and independently.
[0035] On the domestic water side, the magnet valve 11 is provided with a pressure-controlled
regulator 9 - also for reasons of safety. In those cases where just a magnet valve
is mounted, and the magnet valve perhaps fails e.g. because of impurities or other
faults, the domestic water will undesirably continue to flow in such cases. Here,
however, the pressure-controlled regulator 9 becomes operative, as the pressure-controlled
regulator will always operate with an on/off function when starting and terminating
the tapping.
[0036] Further, it is possible to supplement with a magnet valve (not shown) in those cases
where it is desired that part of the domestic water on the primary side and/or the
secondary side should be fed e.g. to the sewer system for a shorter or longer period
of time or after terminated tapping, cf. the following.
[0037] For example, the system may optionally be set for activation with simultaneous opening
of the primary and the secondary side. Here, however, there may be a short waiting
period, e.g. if the domestic water is heated to 40 °C, because the heating medium
must heat the piping and the exchanger and/or be set for activation of first the secondary
side x-number of units of time and/or quantity and/or temperature-dependent such that
fresh water is fed to the exchanger until the "old" stagnant water has been flushed
away, before the primary side is connected. With an extra magnet valve, the secondary
side may optionally convey directly to the sewers instead of to the basin until the
primary side becomes operative, and/or until the desired domestic water temperature
has been achieved, and/or is set for activation of first the primary side x-number
of units of time and/or quantity and/or temperature-dependent such that the heated
domestic water in the exchanger has the desired temperature before opening the tapping
point or starting the primary and the secondary side simultaneously, and such that
the secondary side first conveys directly to the sewers until the desired domestic
water temperature has been reached, and then directly to e.g. the basin.
[0038] This ensures that the secondary side is flushed with/for pure, cold domestic water,
and also that the domestic water temperature has the desired temperature when the
tapping point becomes operative and/or is set for activation solely on the secondary
side with a predetermined interval of time for x-number of units of time or quantity
per time, irrespective of whether the water heater 1 has been affected by an operator
for use or not in the short or long term, or correspondingly automatically activated
x-number of time units after the latest tapping so that the secondary side always
contains domestic water of an optimum quality irrespective of whether the system has
been activated by an operator or not in the short or long term and/or is set for activation
such that when the desired tapping is terminated, the primary side stops immediately,
while the secondary side continues the flow in the exchanger for x-number of units
of time and/or quantity and/or temperature-dependent optionally to the sewers to thereby
cool the exchanger 4 immediately and thus also the "stagnant" water in the exchanger
4 to the desired temperature below 20 °C e.g. to prevent legionella bacteria from
multiplying.
[0039] The process may also be reversed so that, after terminated tapping, the primary side
is activated solely for x-number of units of time/quantity and/or temperature-dependent,
whereby the temperature of the domestic water, the "stagnant" water in the exchanger
of 3 dl, is raised to the desired temperature of e.g. 60-70 °C to thereby destroy
any legionella or other bacteria. This, however, involves a waste of water and may
cause scalding and/or scaling of the exchanger. The latter, however, is a minor problem,
as the exchanger may be descaled like a coffee machine and/or be set for activation
such that, irrespective of activation of the tapping point, the temperature range
in the exchanger on both the primary side and the secondary side is always e.g. min.
50 °C and optionally below 50 °C after commenced tapping because of e.g. the scalding
risk, so that the multiplication capacity of the legionella bacteria is restricted
or eliminated also in the standstill period of the water heater.
[0040] According to the combination of components used, including the microprocessor, there
are numerous alternative possibilities of combination and security which may be set
for activation such that the domestic water in e.g. a buffer container is given an
optimum temperature and/or time horizon for e.g. killing bacteria and the like, which
is placed directly in front of the water heater 1, and then the domestic water from
the buffer container is subsequently cooled, if the exchanger 4 - instead of being
supplied with e.g. district heating system water 5 on the primary side like before
- in this case is supplied with cold/cooled water that may be recirculated and thereby
bring the container domestic water first optimally heated and stored down to the desired
tapping temperature.
[0041] The temperature of the domestic water is generally controlled by a thermostat 10,
which may be connected with a pressure-controlled domestic water part to achieve an
optimum solution in terms of security as well as temperature. The thermostat 10 may
readily be adjusted to the desired approximate temperature.
1. A method of heating domestic water in a water heater (1) having a heat exchanger (8)
whose primary side is supplied with hot water (5), and whose secondary side is supplied
with colder domestic water (7), where the water (18) on the secondary side is tapped
directly from the heat exchanger (4) without being mixed with water already heated,
characterized in that the secondary side of the heat exchanger is frequently flushed with domestic water
in order to keep the temperature of the second side of the heat exchanger below a
desired temperature, e.g. 20°C.
2. A method according to claim 1, characterized in that the secondary side of the heat exchanger is flushed with domestic water immediately
after a tapping is terminated.
3. A method accordingly to claims 1 or 2, characterized in that the domestic water used for flushing is led directly to the sewers through an extra
magnet valve, which is open during flushing and closed during tapping.
4. A method accordingly to claim 1, characterized in the further feature that the primary side of the heat exchanger is flushed with hot
water in a period after terminating tapping in order to heat the water, reminding
in the secondary side of the water exchanger to a desired temperature of e.g. 60 -
70°C.
5. A method accordingly to claims 1 - 4, characterized in that the various operations of the valves are controlled by a microprocessor in accordance
with signals from temperature- and/or pressure transducers in the system.
1. Verfahren zum Erwärmen von Brauchwasser in einem Wassererwärmer (1) mit einem Wärmetauscher
(8), dessen primäre Seite mit Heißwasser (5) beschickt wird und dessen sekundäre Seite
mit kälterem Brauchwasser (7) beschickt wird, wobei das Wasser (18) auf der sekundären
Seite direkt von dem Wärmetauscher (4) abgezapft wird, ohne dass es mit bereits erwärmtem
Wasser gemischt würde, dadurch gekennzeichnet, dass die sekundäre Seite des Wärmetauschers häufig mit Brauchwasser gespült wird, um die
Temperatur der zweiten bzw. sekundären Seite des Wärmetauschers unter einer gewünschten
Temperatur von beispielsweise 20 °C zu halten.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die sekundäre Seite des Wärmetauschers unmittelbar nach Beendigung eines Abzapfung
mit Brauchwasser gespült wird.
3. Verfahren nach Ansprüchen 1 oder 2, dadurch gekennzeichnet, dass das zum Spülen verwendete Brauchwasser über ein zusätzliches Magnetventil, das während
des Spülens offen und während des Abzapfens geschlossen ist, direkt in die Abwasserleitung
geleitet wird.
4. Verfahren nach Anspruch 1, gekennzeichnet durch das weitere Merkmal, dass die primäre Seite des Wärmetauschers während einer Zeitspanne
nach Beendigung einer Abzapfung mit Heißwasser gespült wird, um das auf der sekundären
Seite des Wassertauschers bzw. Wärmetauschers befindliche Wasser auf eine gewünschte
Temperatur von beispielsweise 60 bis 70 °C zu erwärmen.
5. Verfahren nach Ansprüchen 1 bis 4, dadurch gekennzeichnet, dass die verschiedenen Betriebshandlungen der Ventile von einem Mikroprozessor entsprechend
Signalen aus Temperatur- und/oder Druckwandlern in dem System gesteuert werden.
1. Procédé pour chauffer de l'eau domestique dans un chauffe-eau (1) ayant un échangeur
de chaleur (8) dont le côté principal est alimenté avec de l'eau chaude (5) et dont
le côté secondaire est alimenté avec de l'eau domestique plus froide (7), où l'eau
(18) du côté secondaire est exploitée directement de l'échangeur de chaleur (4) sans
être mélangée à l'eau déjà chauffée, caractérisé en ce que le côté secondaire de l'échangeur de chaleur est fréquemment rincé avec de l'eau
domestique afin de maintenir la température du second côté de l'échangeur de chaleur
au-dessous d'une température souhaitée, par exemple, 20 °C.
2. Procédé selon la revendication 1, caractérisé en ce que le côté secondaire de l'échangeur de chaleur est rincé avec de l'eau domestique immédiatement
après qu'un prélèvement a été terminé.
3. Procédé selon les revendications 1 ou 2, caractérisé en ce que l'eau domestique utilisée pour le rinçage est amenée directement des égouts par une
vanne magnétique supplémentaire, qui est ouverte pendant le rinçage et fermée pendant
le prélèvement.
4. Procédé selon la revendication 1, caractérisé par la caractéristique supplémentaire qui réside dans le fait que le côté principal de
l'échangeur de chaleur est rincé avec de l'eau chaude pendant une période, après avoir
terminé le prélèvement afin de chauffer l'eau restant dans le côté secondaire de l'échangeur
de chaleur, à une température souhaitée par exemple de 60 - 70 °C.
5. Procédé selon les revendications 1 à 4, caractérisé en ce que les différentes opérations des vannes sont contrôlées par un microprocesseur selon
des signaux provenant des capteurs de température et/ou de pression dans le système.