METHOD AND UNIT FOR CONTROLLING THE BACTERIAL CONDITIONS IN WATER SYSTEMS

Abstract: Method and unit for controlling bacterial conditions in domestic water systems comprising a cold water system (1, 3) and a hot water system (5, 8, 9, 10) wherein periodical temperature reductions and/or cleansings for fighting bacterial occurrences are applied. Under a general control (11) and on the basis of temperature measurements (16, 17, 18, 19) and/or consumption measurements (23, 24) periodical and/or consumption-dependent temperature reductions, cleansings, pasteurisations and/or flushings of the domestic water system are carried out.

Description: METHOD AND UNIT FOR CONTROLLING THE BACTERIAL CONDITIONS IN I WATER SYSTEMS The invention relates to a method and a unit for controlling bacterial condi- tions in domestic water systems, said water systems comprising a cold water system and a hot water system. Parts of such a domestic water system may under normal operating conditions form the basis of unhealthy bacteria, the reason why it is important to be able control the state of the system such that the various types of bacteria are killed to the greatest possible extent before the occurrence thereof assumes critical proportions. Thermophilous bacteria give rise to formation of slime in the system which besides skin problems and obnoxious smells may form the basis of additional bacterial species and may influence negatively on the heat transmission. For limiting this slime formation it is known now and then to apply a regular, e.g. nightly, temperature reduction in combination with for example a weekly-monthly manual cleansing of the hot-water tank, whereby domes- tic hot water is tapped off at the bottom of the hot-water tank, whereas domestic cold water is continuously supplied to same. This method will unstick and remove part of the formed slime coating in the tank whereby the amount of nutrient medium for other bacteria is reduced. For reasons of economy and energy consumption many domestic water systems operate at temperatures of about 50-55°C, which may give rise to growth of the unhealthy bacteria Legionelle causing legionaire's disease. A temperature reduction and cleansing as described above may give rise to improved growth conditions of this species, for which reason it is of great importance, particularly in hospitals, rest homes, old people's homes, hotels and in apartment blocks, also to protect against an increased occurrence of Legionelle. Moreover, stagnant water in cold as well as hot water pipes may assume favourable conditions of growth of Legionelle which may cause problems at tap off points with a sporadic consumption and in connection with vacations/holidays etc. Various systems for fighting bacterial growth in domestic water systems are known. Accordingly, EP 0 594 020 B1 , EP 0 391 508 A2 and DE 195 24 079 A1 describe systems wherein the fight against the harmful bacteria takes place by periodical or as occasion requires heating, pasteurisation, of the water in the unit. The object of this temperature increase of the hot-water tank and the circulation system for the domestic hot water is to fight the growth of the harmful bacteria including the Legionelle bacteria. These known systems, however, have the drawback that due to the periodical temperature increase there will first and foremost be generated improved growth conditions of the thermophilious bacteria and thus an increase in their numbers. Moreover, the heating will promote lime precipitation and hence the sludge formation due to the precipitation of lime in the limy water, which is for example used in Denmark. Directly contrary to the object, these circumstances will cause the bacterial growth to form nutrient medium in the sludge for bacteria including Legionelle and accordingly unintentionally cause an increase in the growth conditions of such bacteria. It is the object of the invention to provide a method and a device for actively fighting bacterial growth in domestic water systems and, if desired, for giving the alarm in cases of increased risk of harmful bacterial occurrence in the domestic water in that said fighting may preferably take place in an automated manner. This is achieved by a method of the type disclosed in the introduction and which is characterised in that under a general control and on the basis of temperature measurements and/or consumption measurements, periodical and/or consumption-dependent temperature reductions, cleansings, pasteurisations and/or flushings of the domestic water system are carried out. By this method the constituent parts of the domestic water system may at predetermined points of time or according to recorded requirements be subjected to a fixed temperature cycle intended to fight thermophilous bacteria as well as Legionelle. At the same time, the device may be designed in such a manner that it is capable of warning an increased risk of bacterial occurrence due to stag- nancy, alternatively to prevent stagnancy through forced tapping off at dead ends in the hot water as well as the cold water system, and by an automatic cleansing of the hot-water tank. Finally, the device is prepared for connection of equipment for analysing bacterial growth. Advantageous embodiments of the method will appear from the dependent claims 2-6. According to the invention a unit of the type described in the introduction is characteristic in that the unit comprises a central control unit which on the basis of temperature measurements and/or consumption measurements, may carry out periodical and/or consumption-dependent temperature re- ductions, cleansings, pasteurisations and/or flushings of the domestic water system. In this manner, it is possible to adjust the unit for applying, preferably in a fully automated way, one or more of the options disclosed in connection with the method, perhaps in combination, and at a fixed frequency or at a frequency as required. Furthermore, the control unit may be adjusted for varying strategies dependent on the existing sensors, measuring instruments and actuators available. Advantageous embodiments of the unit according to the invention will appear from the dependent claims 8-10. The invention will be further described in the following with reference to the drawings, wherein fig. 1 is a generally known domestic water system, and fig. 2 is a domestic water system according to an embodiment of the invention. Fig. 1 shows a commonly known domestic water system such as it may generally be designed. A cold water supply 1 in the form of a pipe or hose connection is connected to a cold water inlet 2 of a hot-water tank 5 and to a number of tap off points 3 for domestic cold water, whereof solely three are shown in the figure, in that said tap off points 3 may be situated in various places within the area or the building which the system services. Furthermore, the system comprises a heating circuit 4 for the hot-water tank 5, said heating circuit 4 comprising a heating coil or the like 6 within the hot- water tank 5. As shown, a thermostatic valve 7 has moreover been inserted in the heating circuit 4. From the hot-water tank 5 the domestic hot water is circulated by means of a circulating pump 8 for domestic hot water through a circulating loop 9 for domestic hot water, and from this circulating loop 9 the domestic hot water may be drawn off at a number of tap off points 10 for domestic hot water. As is generally known, domestic cold water will be supplied to the hot-water tank 5 via the cold water inlet 2 when domestic hot water is tapped off, and heating water controlled for example as shown by a thermostatic valve 7 or another regulating unit will flow in the heating circuit 4 in such a manner that heating water will only flow in the heating circuit 4 when there is a need for heating the domestic water. As is also generally known, the circulating pump 8 serves to circulate the domestic hot water such that a suitable temperature thereof is maintained, also of the part circulating in the circulating loop 9 and partly in the supply pipes for the tap off points 10. As mentioned above, slime formations and bacterial occurrences may be generated in such a unit, which as mentioned entail numerous drawbacks. An example of a domestic water system designed according to the inven- tion and whereby the method according to the invention may be carried out is shown in fig. 2. This domestic water system comprises the same components as shown in fig. 1 , such components being designated with the same reference numerals. Accordingly, these components will not be described again. In addition, the system shown in fig. 2 comprises a central control unit 11 which as shown is connected to the circulating pump 8 via a speed control link 12, and which is connected to a link 13 for transmitting control signals from an analysis equipment 14. This analysis equipment 14 may via a wa- ter-sampling valve 15 be connected to the circulating loop 9 for domestic hot water. Moreover, the central control unit 11 may be connected to other sensors, control components etc, whereof some will be mentioned in the following. The connections to these sensors, control components etc from the control unit are not shown in fig. 2, but the existence thereof will be obvious to a person skilled in the art. In this manner the system is provided with several temperature sensors, namely as shown a temperature sensor 16 for the supply-pipe temperature of the domestic hot water in the circulating loop 9, a temperature sensor 17 in the hot-water tank 5, temperature sensors 18 for the pipe temperature of the domestic hot water as well as temperature sensors 19 for the pipe temperature of the domestic cold water. In series with the thermostatic valve 7 there is arranged a blocking valve 20, and in parallel with this assembly there is arranged a regulating valve/shunt valve 21. Furthermore, the hot-water tank 5 is provided with a controlled cleansing valve 22. For registering the domestic water consumption the system is provided with a meter 23 arranged by the cold water supply 1 for registering the consumption of domestic cold water as well as with a meter 24 for registering the consumption of domestic hot water. Moreover, in this part of the system there is arranged a blocking valve 25 for domestic hot water and a blocking valve 26 for domestic cold water. In the system for the domestic hot water there is arranged a flushing valve 27, and in the system for the domestic cold water there is similarly arranged a flushing valve 28. It will be understood that more of the said flushing valves 27 and 28 may be arranged in the system such that it is possible to carry out an efficient flushing of the entire unit and the constituent parts thereof. Finally, in the hot-water tank 5 there is arranged an additional heater 29 for low temperature units. The functioning of this system will be further explained in the following. The control unit 11 is equipped with a works or a timer function which may be used individually or in combination with demand registration from the sensors and measuring instruments connected to the control unit for starting pasteurisation, cold shock, cleansing and/or flushing of the domestic water system as will be described in the following. A cold shock is regularly carried out, for example once a day, in that for a predetermined period of time the control unit 11 will lower the domestic water temperature measured by means of the temperature sensor 17 to a predetermined temperature, e.g. 20°C. This is done by blocking the service thermostat 7 of the unit by means of the blocking valve 20, while the pump control 12 from the control unit 11 keeps the circulating pump 8 in operation such that the heat loss in the circulation loop 9 will contribute to a quick cooling off. Following a suitable, pre-selected exposure, the control unit 11 will again open the blocking valve 20 such that the domestic water system may resume normal temperature regulation and operation. Such treatment will restrict the growth of themnophilous bacteria in the system. Under circumstances where the natural heat loss is insufficient to ensure the necessary cooling off during the time available, control unit 11 may provoke a supply of domestic cold water by opening the flushing valve 27 and/or the cleansing valve 22. Under extreme conditions a refrigerating plant (not shown) may moreover be used for reducing the water temperature under the control of the control unit 11. Furthermore, it is possible to regularly carry out a cleansing, for example monthly or after a determined consumption, said consumption being deter- mined by means of the meter 23 for registering cold water consumption and/or by means of the meter 24 for registering hot water consumption. The cleansing is carried out by the control unit 11 stopping the heat supply by closing the blocking valve 20, whereas the pump control 12 keeps the cir- culating pump 8 stopped and the cleansing valve 22 is kept open by the control unit 11 for a predetermined period of time. Rather than carrying it out for a predetermined period of time or in combination herewith, the cleansing may be carried out until the temperature measured by means of the temperature meter 17 in the hot-water tank reaches a pre-selected low value or until the flow measured by means of the consumption meter 24 since the beginning of the cleansing reaches a pre-selected high value. Following completed cleansing, the control unit 11 will again close the cleansing valve 22 and open the blocking valve 20, whereas the pump control 12 will allow the circulating pump 8 to return to normal operating speed in such a manner that the domestic water unit may again return to normal temperature regulation and operation. This treatment will remove organic sludge being a nutrient medium of bac- teria. Finally, it is possible to regularly carry out a pasteurisation, for example once a day, in that for a predetermined period of time the control unit 11 will increase the domestic water temperature measured by means of the tem- perature meter 16 of the supply-pipe temperature to a predetermined temperature, for example 65°C. This is done by blocking the service thermostat 7 of the unit by means of the blocking valve 20 and regulating the heat supply by a suitable opening of the shunt valve 21 , while at the same time the pump control 12, if possible, forces the circulating pump 8 to take its high- est speed such that the temperature difference across the circulating loop 9 is reduced as much as possible, whereby the pasteurisation becomes ef- fective in its entire length. In this phase and according to a predetermined pattern or according to requirements registered by means of the temperature sensor 18 of the domestic hot water, the control unit 11 may pasteurise 'dead' ends of the system by opening the flushing valves 27 of the domestic hot water whereby the entire pipe system is raised to a temperature which will kill Legionelle. In connection with low temperature units and/or poor heat supply conditions the control unit 11 may activate a heater 29 as an additional energy source such that a temperature suitable for pasteurisation may be obtained. Following a suitable, pre-selected exposure, the control, unit 11 will again shut off the flushing valves 27, the shunt valve 21 and open the blocking valve 20 as well as set the circulating pump 8 at its normal speed such that the domestic water unit may revert to normal temperature regulation and operation. Flushing of the cold water system is carried out by the control unit 11 according to requirements registered by means of the meter 23 for registering the cold water consumption and/or by means of the temperature meter 19 of the cold domestic water. The flushing takes place by opening the flushing valves 28 for a predetermined period of time or until a predetermined amount of cold water has run through as registered by means of the meter 23 for registering the cold water consumption or until for a predetermined period of time a suitably low, pre-selected temperature has been existing measured by means of the temperature meter 19 of the cold domestic water. Where a flushing is not possible or has been deselected, the control unit 11 will in stead give a warning of an increased risk of bacterial occurrence alternatively (if pre-selected) block the supply of cold domestic water by shut- ting off the blocking valve 26 while at the same time giving the alarm. Sampling for the analysis equipment 14 may be made by the control unit 11 by a short opening of the valves 15 at predetermined points of time. The result of the analysis made is transmitted by the analysis equipment 14 to the control unit via the link 13 on the basis whereof the control unit may allow continued operation of the domestic water system or - in case this has been selected - block further operation by shutting off the blocking valves 25 and 26 while at the same time giving the alarm. The control unit 11 may be set to apply one or more of these options in combination, at fixed frequencies or according to requirements, just as same may be set to apply varying strategies dependent on the currently available sensors 13, 14, 16, 17, 18, 19, 23 and/or 24 and actuators 12, 15, 20, 21 , 22, 25, 26, 27, 28 and/or 29.

Claims: PATENT CLAIMS 1. Method for controlling bacterial conditions in domestic water systems comprising a cold water system and a hot water system, said method being carried out by applying periodical temperature reductions and/or cleansings, characterized in that under a general control and on the basis of temperature measurements and/or consumption measurements periodical and/or consumption- dependent temperature reductions, cleansings, pasteurisations and/or flushings of the domestic water system are carried out. 2. Method according to claim 1, characterized in that temperature reductions are carried out by blocking, e.g. once a day, heat admission and/or temperature control of the hot water system, and that a circulation in the hot water system and/or a flushing is/are carried out until the domestic water temperature reaches a predetermined temperature, for example about 20°C. 3. Method according to claim 1 or 2, characterized in that cleansing are carried out by flushing the hot water system for a predetermined period of time until the domestic water temperature has reached a predetermined value or until a predetermined value for the circulation of domestic water has been registered. 4. Method according to claim 1, 2 or 3, ch a racte rized in that a pasteurisation is carried out by raising, e.g. once a day, the domestic water temperature, preferably measured as the supply- pipe temperature, to a predetermined value, for example about 65°C, and that a circulation in the hot water system and/or a flushing is/are carried out, for example for a predetermined period of time. 5. Method according to claim 1,2, 3 or 4, characterized in that a flushing of the cold water system is carried out for a predetermined period of time and/or until a predetermined value for the circulation has been registered and/or until a predetermined minimum temperature of the cold water system has been exceeded for a predetermined period of time. 6. Method according to claim 1, 2, 3, 4 or 5, characterized in that an analysis of the domestic water is made at predetermined points of time and that on the basis of the result thereof an alarm may be given and, if desired, a close-down of the domestic water system. 7. Unit for controlling bacterial conditions in a domestic water system comprising a cold water system (1 , 3) and a hot water system (8, 9, 10) with a hot-water tank (5), characterized in that the unit comprises a central control unit (11) which on the basis of temperature measurements (16, 17, 18, 19) and/or consumption measure- ments (23, 24) may carry out periodical and/or consumption-dependent temperature reductions, cleansings, pasteurisations and/or flushings of the domestic water system. 8. Unit according to claim 7, characterized in that the unit com- prises a blocking valve (20) arranged in a heating circuit (4) for the system, and that a shunt valve (21) may moreover be arranged in parallel with the said blocking valve (20) and a control device (21) for the heating circuit arranged in the heating circuit (4). 9. Unit according to claim 7 or 8, characterized in that the unit comprises one or more flushing valves (27, 28) for the hot domestic water and the cold domestic water, respectively, and preferably a controlled cleansing valve (22) for the hot water system (5, 8, 9). 10. Unit according to claim 7, 8 or 9, characterized in that the unit comprises equipment for analysing (14) the domestic water, said equipment being controlled by the central control unit (11) which on the basis of signals from the analysis equipment (14) may activate an alarm and/or other functions, such as e.g. a close-down of the domestic water system.

Inventors: NIELSEN ERIK, NIELSEN, ERIK
Applicants: DANTAET ELECTRONICS AS, NIELSEN ERIK, DANTAET ELECTRONICS A/S, NIELSEN, ERIK
Application year: 2001
Main classification: F24D17
IPC codes: F24D17