NL2001108C2 - Solar water heating system, has control unit controlling valve system to release from disinfection mode, when temperature of water in storage vessel satisfies predetermined criterion - Google Patents

Abstract

The system has a solar collector (10) connected to a storage vessel (12) for heating tap water stored in the vessel. A valve system is switchable between a release mode in which the water is release from the output of the storage vessel and disinfection mode in which disinfection of water is carried out. A temperature sensor (122) measures temperature of the tap water in the storage vessel, and a control unit (14) controls the valve system to release from the disinfection mode, when the temperature of the water in the vessel satisfies a predetermined criterion.

Description

P83496NL00

Title: Solar water heating system with thermal disinfection

The invention relates to a solar boiler system. Solar water heater systems commonly used in the Netherlands include a pre-heater. Such a system contains a storage tank with tap water that is directly or indirectly heated with solar heat.

5

The temperature in the vessel varies depending on the sun supply and demand. The more sun there is, the warmer the water in the barrel and the more hot water is drained, the colder the water will be. It is known to use water after heating, for example with a gas burner 10, to bring the water to the desired tap temperature.

There is a risk that the water in the solar boiler system becomes contaminated with bacteria such as legionella bacteria. Depending on the temperature variation of the water in the storage vessel, periods of growth (T between 25 and 50 C), and periods of decay (T above 50 C) of the legionella bacteria alternate. ISSO publication 55.1 states that, in order to be "Legionella risk neutral", the periods between 25 and 50 C may not be longer than a total number of days.

With insufficient sunlight there is a danger that legionella or other microorganisms are present in the water in dangerous amounts.

This problem can be solved with a thermal disinfection step, ie by heating the tap water for a sufficient time above 60 ° C. However, the use of gas or electricity for this thermal disinfection step cancels out part of the energy gain of the solar boiler.

2

It is inter alia an object of the invention to provide a solar boiler system in which the risk of contamination of the water is reduced, without the energy consumption having to be greatly increased as a result.

5

A solar boiler system is provided according to claim 1. Herein, a control unit detects whether a time course of a temperature in a storage vessel prior to detection meets a predetermined criterion. This criterion has been chosen to establish a risk of development and persistence of bacteria, such as legionella. For this purpose, it can be detected, for example, whether the temperature has been in a range for more than a predetermined period of time, going back from the time of detection, in which the bacteria can develop. However, it is also possible, for example, to use a model that calculates a predicted amount of bacteria as a function of the temperature variation, the criterion being whether the predicted amount is above a threshold. In response to detection that the criterion is met, the control unit switches the system from a release state to a disinfection state. In the release position, water is fed from the outlet of the storage tank to a tap water outlet. In the disinfection mode, a bypass is realized in which water is fed from the water supply to the tap water outlet without passing through the storage tank. This makes it feasible to heat the water in the storage tank exclusively with solar energy. In the disinfection mode, the water in the storage vessel can be further heated under the influence of the solar collector to remove contamination.

Brief description of the drawings

These and other objects and advantages will be apparent from a description of embodiments with reference to the accompanying Figure 1 which shows a solar water heater system.

Detailed description of embodiments Figure 1 shows a solar boiler system

Figure 1 shows a solar boiler system provided with a solar collector 10, a water supply 11, a storage vessel 12, a control unit 14, a three-way valve 16 and a post-heater 17.

Solar collector 10 is coupled to storage tank 12 via a heating circuit. The heating circuit comprises a heating coil 120 in storage tank 12 and a pump 124 for pumping water through heating coil 120 and solar collector. Although a heating coil is shown by way of example, other ways can be used to heat water with solar energy. Post-heater 17 is, for example, gas or electrically fired.

Water supply 11 is, for example, connected to a drinking water supply network. Water supply 11 is successively coupled via a first and second non-return valve 190, 194 to a supply at the bottom of storage tank 12. A drain at the top of storage tank 12 is coupled to a first connection of three-way valve 16. A second connection of three-way valve 16 is coupled to a connection between first and second non-return valve 190.194 and a third connection of three-way valve 16 is coupled to an input of post-heater 17. An output of post-heater 17 is coupled to tap water taps 18. Discharge valves 192, 196 are coupled to traps (not shown) to the sewer from the connection between first and second check valve 190, 194 and the connection between second check valve 194 and storage tank 12, respectively.

4

Control unit 14 has an input coupled to a temperature sensor 122 in storage vessel 12 and an output coupled to a control input of three-way valve 16. Control unit 14 comprises, for example, a microcomputer and is arranged to switch three-way valve 16 between a release position in which water is fed from storage vessel 12 to post-heater 17 and a disinfection position in which water is fed from water supply 11 to post-heater 17 without passing through storage vessel 12. Control unit 14 is arranged around three-way valve 16 between the release position and the disinfection position depending on a criterion indicative of the development of legionella bacteria, as a function of the time course of the temperature indicated by the temperature sensor. To that end, the microcomputer can for instance be provided with a stored program with instructions to periodically evaluate the criterion and to switch between the different positions depending on the result of the evaluation.

Temperature sensor 122 is preferably arranged at the top of storage vessel 12, approximately at the level of vessel, the tap point for water flowing to three-way valve 16. This draw-off point is at the top, for example at less than 10% of the maximum height of storage vessel 12. As shown, temperature sensor 122 protrudes into storage vessel 12, but temperature sensor 122 can also be placed on storage vessel 12. It is not necessary that the temperature of the tap water is measured immediately. Any measurement that provides information about the temperature can be used, such as, for example, a measurement of the temperature of the inner wall of storage tank 12.

Control unit 14 can be provided with a control board with a 230 V AC output that can directly control a 230 V valve motor in three-way valve 16. Of course, three-way valve 16 can also be controlled in a different way.

5

In normal operation, water is taken from storage tank 12 via three-way valve 16 and post-heater 17 to taps 18. If necessary, post-heater 17 is activated to bring the water to a desired temperature.

In operation, thermal disinfection is used, i.e. disinfection by keeping water above a predetermined temperature for at least a predetermined time. Protection to remain intrinsically “Legionella risk neutral” is achieved according to the following operating principle. If, after the last thermal disinfection storage tank 12, a total of 5 (or 7) days has been between 25 and 50 C, the control unit 14 switches three-way valve 16 to the disinfection position.

Thus, three-way valve 16 functions as part of a bypass through which cold water from water supply 11 is fed to post-heater 17, bypassing the storage vessel. Three-way valve 16 now blocks the discharge from storage vessel 12. Because storage vessel 12 is further closed, no more water flows to storage vessel 12 from water supply 11. As long as the vessel is bypassed, there is no cooling of storage vessel 12 as a result of refreshing, as a result, the temperature in storage tank 12 can rise without being inhibited by refreshing with cold water. In this way a safe situation is immediately created, while thermal disinfection with the available solar heat can also start immediately. If water is tapped via tap taps 18 during this time, post-heater 17 is activated to bring the water to the required tap water temperature.

Control unit 14 detects the rising temperature after the water 25 in storage tank 12 has been above a threshold value for a predetermined time (e.g. above 60 ° C for at least one hour, or another combination of time and temperature suitable for disinfection) switches control unit 14 back to the release position and the hot water supply goes again via the solar boiler barrel.

6

Preferably, the thermal disinfection device must meet the following requirements: intrinsically safe, no comfort reduction, so post-heater 17 must always be able to supply tap water, disinfection system itself must have as little extra energy consumption as possible, and preferably be carried out with solar energy . In the system the protection according to the aforementioned principle and requirements is realized by (see figure) equipping the pre-heater with a bypass line between tap water-in and tap-water out of storage tank 12 and a 2-way three-way valve that is controlled on the basis of time and temperature in the tank.

10 The three-way valve has two positions with the following intended effect. In the release position normal solar boiler operation is involved and the tap water can flow freely through the solar boiler tank, the bypass AB is then closed. In the disinfection mode, tap water cannot flow via the solar boiler tank, but cold water is sent directly to the post-heater 15 via bypass AB. The tank is then heated by solar heat, and no longer cooled by tapping. Thermal disinfection then takes place as follows: after passing the limit temperature of approx. 60 C, actual killing will occur and after sufficient time above 60 C (approx. 1 hr) the disinfection is complete, and normal operation can resume.

The valve is controlled by control unit 14 as follows: Temperature sensor 122 must indicate the temperature of the most Legionella critical zone, for example at the top of storage tank 12. Control unit 14 counts the total time tso temperature sensor 122 indicates a temperature below 50 ° C ( starting from time 0 after last 25 disinfection). If a disinfection occurs prematurely, that is, if the temperature remains above a threshold value for a predetermined time (for example at least one hour above 60 degrees C) then the tso count is reset to zero. Optionally, time below 25 ° C is not included, because then no significant Legionella growth is possible.

30 Control unit 14 maintains "release" tilt position to tso <N, where N

7 is a predetermined number of days, for example 5 or 7 days, and switches to the disinfection mode if tso> N days.

After switching to “disinfection”, control unit 14 counts for a time period t6o for which Tsensor> 60 C. applies. From disinfection position control unit 14 switches to release mode if t6o> 60 min.

Although specific criteria have been mentioned, it will be clear that the necessary variation in the criterion is possible. For example, it is possible to use a circle that, more often than described, leads to switching to the disinfection mode. The safety is thus not compromised, but the energy consumption can thus become higher. For example, switching can take place as before, before the limit of Legionella danger is reached. The energy consumption is preferably minimized. This is done, for example, by not counting the length of time that the water is below 25 ° C. This means that it is less often possible to switch to the disinfection mode, without reducing safety. Counting this length of time that the water is below 25 C is also possible, but requires more energy. Something similar applies to the criterion of switching back from the disinfection mode to the release mode: staying longer in the disinfection mode is not a safety issue, but to minimize energy consumption, the shortest possible time in the disinfection mode is preferred .

Another possibility is to make use in control unit 14 of a calculation model for growth behavior and death behavior of the legionella and / or temperature-dependent decimal times for growth and killing. With this, control unit 14 can calculate a predicted amount of bacteria as a function of the measured temperature variation. By comparing this prediction with a threshold value, control unit 14 can also calculate the moment at which disinfection is desired, or can be interrupted, according to such models and thus create a safe situation with minimal energy consumption through as few disinfection moments as possible. From the literature, models for growth behavior and death behavior of the legionella as a function of the temperature are known per se. The criterion with tso is in fact an application of a simple model, in which the comparison is implicitly performed by comparing tso with a threshold 5.

In addition to temperature sensor 122, further sensors can be used to make a more accurate prediction. For example, a plurality of temperature sensors at different locations in storage vessel 12 can be coupled to control unit 14, or use can be made of a flow sensor in storage vessel 12, or a flow sensor for flow to or from storage tank 12, or optical transparency measurements and so on. Use can be made of a calculation model that calculates the prediction of the quantity bacteria partly as a function of flow data.

Optionally use can be made of a back flow protection.

As a result of heating the water, it will expand, and a few cc of water will flow back into it. This is in principle undesirable and prohibited in various countries. Backflow protection can be implemented in various ways. Different requirements are set for this in 20 different countries.

In the example of the figure, two inlet combinations are included with valves 192, 194, 196 to prevent backflow to supply 11. The added value of the valves between supply 11 and point A is limited and limited, and this can easily be omitted. However, it will be clear that the implementation of the backflow protection is optional and has no influence on thermal disinfection.

However a three-way valve is shown, it will be clear that other valve systems can also be used, such as valves in combination with T-pieces to realize the same function. The point is that the water from storage tank 12 in the disinfection mode does not flow away, or at least not with a substantial flow, for use as tap water, but instead water is used that is used outside the storage tank. This gives the solar collector time to heat up the water sufficiently for thermal disinfection even with little sunlight. As long as a substantial amount of water does not flow out of storage tank 12, in the sense that not enough flows out that the effect of heating with solar collector 10 is canceled out, this makes thermal disinfection possible. In a preferred embodiment, B is set higher for a substantial amount, for example that no more than half of the said effect is undone, or that no more than a fraction of, for example, 10% of the tap water in the disinfecting position from storage tank 12 flows. The limit is chosen at least so that a sufficient heating effect for thermal disinfection in storage tank 12 is maintained and it is prevented that the bacterial concentration in the final tap water 15 can rise above a safe threshold.

Although three-way valve 16 is shown at position B, it can also be included at point A, that is to say in the connection between supply 11 and storage vessel 12, with a branch to a T-piece in the connection between storage vessel 12 and post-heater 17. In the disinfection position, the passage to storage vessel 12 is then blocked and passage to the T-piece is made possible. Furthermore, because storage vessel 12 forms a closed system, no substantial amount of water can flow from storage vessel 12 to post-heater 17. Additional valves can of course be used for this. In the release position, the three-way valve in this embodiment passes water to the storage tank. Three-way valve 16 at position B has the advantage that by using an inlet combination in the line between A and the tank, water can be prevented from flowing back out of the tank, (in the disinfection phase, due to expansion when temperature rises in the tank, some 1 water is pressed out of the tank, this "expansion water" should preferably not end up in the tap water pipes).

10

With the solar water heater, an inlet combination (valves 190, 192) is always installed in the cold water pipe with discharge pressure PI (usually 8 BAR). By including the additional inlet combination (with outlet pressure P2 lower than PI, for example 6 BAR), a safe drain is now given to the "expansion water".

In the event of a defect in the three-way valve 16 or its control, the three-way valve 16 should preferably remain in the "disinfection" safe position. This can be achieved by, among other things, a motor valve with automatic return by means of a spring and / or a limit switch on three-way valve 16 which triggers alarm function 10 if the valve does not reach the disinfection position.

It will be apparent from the foregoing that a pre-heater for tap water that is intrinsically legionella safe is provided by immediately switching to a safe situation with the 3-way valve in an unsafe situation (temperature-time curves). Thermal disinfection can only be achieved with the addition of solar heat. Alternatively, a heater can be used in a storage vessel, for example on the basis of electricity or gas, to support heating with solar collector 10. Preventing substantial drainage from storage tank 12 makes it possible to realize the heating only with a solar collector. Only thermal disinfection if necessary (time-temp curve) and this only with the solar collector, minimizes the output of the solar boiler.

Claims (11)

1. Zoimboiler system, comprising - a storage tank for tap water with an input and output for the tap water; - a solar collector which is coupled to the storage tank for heating the tap water; 5. a water supply coupled to the entrance of the storage vessel; - a tap water outlet; - a valve system with connections coupled to the water supply, the output of the storage vessel and the tap water output, and switchable to a release position and a disinfection position, wherein in the release position water is fed from the output of the storage vessel to the tap water output and in the disinfection mode a bypass is realized in which water is fed from the water supply to the tap water outlet without passing through the storage tank and substantial flow of water from the storage tank is prevented; 15. a temperature sensor for measuring information about a temperature of the tap water in the storage vessel; a control unit adapted to detect whether a time lapse of the temperature meets a predetermined criterion and to switch the valve system from the release position to the disinfection position in response to detection that the criterion is met. Solar water heater according to claim 1, adapted to heat the tap water in the storage tank exclusively with the solar collector. 3. Solar water heater according to claim 1 or 2, wherein the criterion is that a period of time in which the temperature has been below a predetermined threshold value has exceeded a maximum. Solar water heater according to claim 3, wherein the duration is reset in response to detection that the temperature curve meets a further criterion. Solar water heater according to claim 3 or 4, wherein during the period of time periods 5 in which the temperature is below a further threshold value are not counted. 6. Solar water heater according to claim 1 or 2, wherein in the evaluation of the criterion the control unit uses a calculation model for predicting an amount of bacteria as a function of the time course of the temperature. 7. Solar water heater as claimed in any of the foregoing claims, wherein the control unit is adapted to further detect whether the change in temperature after switching from the release position to the disinfection position satisfies a further criterion and in response to detection of compliance with the further criterion depends on the further criterion. switch from disinfection mode to switch to release mode. 8. Solar water heater according to claim 7, wherein the further criterion is that a further period of time in which the temperature has been above a further predetermined threshold value has exceeded a further maximum. 9. Solar water heater as claimed in any of the foregoing claims, with a connection between the water supply and the entrance of the storage vessel, wherein an entrance of the valve system is coupled to the water supply via a branch of said connection. 10. Solar water heater as claimed in any of the foregoing claims, provided with a non-return valve between the water supply and the entrance of the storage vessel. A method for supplying tap water, comprising - heating the tap water in a storage tank with a solar collector; detecting whether a time lapse of a temperature of the tap water in the storage tank meets a predetermined criterion; - in response to detection that the criterion of a release state has been met, switch to the disinfection state, wherein in the release state water is fed from an outlet of the storage vessel to a tap water outlet and in the disinfection state a bypass is realized in which water from the water supply is fed to the tap water outlet without passing through the storage tank and substantial flow of water from the storage tank is prevented.