HEATING SYSTEM FOR NON-DRINKING WATER

Abstract: A heating system for non-drinking water has a heat-exchanger (1), the primary part (2) of which is supplied with a heat transfer medium and the secondary part (6) of which is connected to a circulation pipe (9). The circulation pipe comprises at least one draw-off point (12) for hot non-drinking water, a circulation pump (13) and a cold water in-feed (15). A control device (19) comprises a first temperature sensor (20) at the initial section (10) of the circulation pipe (9) and a primary-side adjustment means (motorized valve 23), influenced by the temperature sensor, for the amount of heat transfer medium to be let through. A second temperature sensor (21), which influences the adjustment means, is arranged at the end section (17) of the circulation pipe (9) downstream of the cold water in-feed (15). In particular, the second temperature sensor (21) is a significant distance (a) from the heat exchanger inlet (8). The temperature of the non-drinking water is therefore subject to fewer fluctuations.

Description: Heating system for non-drinking water The invention relates to a heating system for non- drinking water, having a heat-exchanger, the primary part of which is supplied via a forward flow pipe and a return pipe with a heat transfer medium, and the secondary part of which is provided with a circulation pipe, which comprises at least one draw-off point for hot non-drinking water, a circulation pump and a cold water in-feed, and having a control device which comprises a first temperature sensor at the initial section of the circulation pipe and a primary- side adjustment means, influenced by the temperature sensor, for the throughput of heat transfer medium. In a known system of that kind (DE 38 09 893 C2) , the primary part of the heat exchanger is connected to a remote heating supply network, with a control valve being inserted in the return line. The temperature sensor arranged at the secondary-side heat exchanger outlet acts on the control valve and is intended to hold the temperature of the non- drinking water at a pre-set value. Nevertheless, the temperature of the non-drinking water fluctuates considerably. Both water that is too hot and water that is too cold is considered to be vexing, especially in a shower installation. The invention is based on the problem of providing a heating system for non-drinking water, in which fluctuations in the temperature of the non-drinking water can be kept at a low level. That problem is solved in accordance with the invention in that a second temperature sensor influencing the adjustment means is arranged at the end section of the circulation pipe, downstream of the cold water in-feed. The second temperature sensor detects the drop in water temperature that is effected at the start of drawing-off behind the cold water in-feed before this colder water enters the heat exchanger. The supply of heat transfer medium to the primary part of the heat exchanger can accordingly be increased much earlier than previously, so that the non-drinking water is prevented from cooling down too much. The end of the drawing-off operation is also ascertained early, so that, by reducing the primary-side supply of heat, too high a temperature of the non-drinking water is avoided. It is especially favourable for the second temperature sensor to be a significant distance from the heat exchanger inlet. This distance makes allowances for the fact that a heat exchanger has heat-storing properties, and therefore the transition from one steady stationary state to a different steady state requires a certain a time. The fluctuations in the non-drinking water temperature can be kept even smaller in this way. With particular advantage, provision is made for the distance to be such that the thermal energy that is required to heat up the amount of cold water present at the end of a drawing-off operation in the circulation pipe between the second temperature sensor and the heat exchanger inlet is substantially the same as the surplus energy, relative to the state in which no water is being drawn off. This permits a largely constant temperature of the non-drinking water. Furthermore, it is advisable for the volume of the circulation pipe between cold water in-feed and heat exchanger inlet to be approximately as large as the volume of the secondary part of the heat exchanger. This adaptation also contributes to keeping the temperature of the non-drinking water constant following the end of water draw-off. The second temperature sensor is advantageously arranged close to the cold water in-feed. The distance can be, for example, 2 to 20% of the length of the circulation pipe between cold water in-feed and heat exchanger inlet. In this way, for a given matching of the position of the cold water in-feed to the heat exchanger, the start and end of a drawing-off process can be detected at the earliest possible moment. The circulation pipe between cold water in-feed and/or second temperature sensor and heat exchanger inlet is preferably 3 to 4 metres long. Such values are typical for household draw-off points. Even if other lengths should be more favourable for different systems, it is nevertheless significant that comparatively long pipe lengths, that is, of more than 1 metre, should be the aim. A further advantage is obtained in that a third temperature sensor influencing the adjustment means is arranged on the return pipe. By means of this third temperature sensor, the primary-side return temperature and hence the input supplied to the heat exchanger can be limited, thereby avoiding too high a temperature of the non- drinking water. The adjustment means is preferably a motorized valve. Such a valve enables the throughput of heat transfer medium to be changed quickly and within comparatively wide limits. It is also advantageous for a non-return valve closing in the direction of the circulation pump to be provided in the circulation pipe between the last draw-off point and the cold water in-feed. This non-return valve safeguards the through-flow direction of the circulating medium, and also the mode of operation of the control device. It is further of advantage that the temperature sensors are electronic resistance sensors and an electronic control device is used. The temperature sensors can be connected to the control device so that they act on the adjustment means with a pre-determined weighting. The invention is explained in detail hereinafter with reference to a preferred exemplary embodiment illustrated in the drawing. The single drawing shows a circuit diagram of a heating system according to the invention for non-drinking water. A heat exchanger 1 is connected, with its primary part 2, by way of an inward flow pipe 3 and a return pipe 4 to a heat source 5, especially a remote heating supply network, and is supplied by this with a heated heat transfer medium. The secondary part 6 of the heat exchanger 1 has an outlet 7 and an inlet 8 that are connected to one another via a circulation pipe 9. Following an initial section 10 of the circulation pipe 9 is a draw-off section 11, having several draw-off points 12, a circulation pump 13, a non-return valve 14 closing in the direction towards this pump, a cold water in-feed 15, via which cold water is introduced from a pipe 16 every time water is drawn off, and an end section 17. A control device 19 provided with a setpoint adjuster 18 is connected to a first temperature sensor 20 at the initial section 10 of the circulation pipe 9, to a second temperature sensor 21 at the end section 17 of the circulation pipe 9 and to a third temperature sensor 22 at the primary-side return pipe 4. On the basis of the temperature signals, the control device controls an adjustment means 23 in the form of a motorized valve, which determines the amount of primary heat transfer medium flowing through the heat exchanger 1. A control circuit that is to keep the temperature of the non-drinking water at a desired value is accordingly produced. The first temperature sensor 20 detects the temperature of the non-drinking water emerging from the heat exchanger 1; this temperature is furthermore to remain as constant a possible even as water is being drawn off. The second temperature sensor 21 is located at the end section 17, so that the admixture of cold water occurring at the start of drawing off is detected before this cold water enters the heat exchanger 1, and the adjustment means 23 can be opened correspondingly further. Moreover, the second temperature sensor 21 should be a distance a (corresponding to a specific pipe length) from the heat exchanger inlet 8, so that the presence of cold water at the start of drawing off, or the termination of cold water as drawing off ceases, is detected some time before the change in temperature reaches the heat exchanger 1, and in this way the delays caused by heat storage in the heat exchanger 1 are at least partially compensated. The distance a is in most cases comparatively large, and can be typically 3 or 4 metres, or possibly 1 to 5 metres. The signals of the second temperature sensor 21 are superimposed in the control device 19 on the signals of the first temperature sensor 20 in a specific relationship, so that the adjustment means 23 is additionally influenced. In particular, the distance a should be large enough for the thermal energy that is needed to heat up the amount of cold water present at the end of a drawing off operation in the circulation pipe 9 between the second temperature sensor 21 and the heat exchanger inlet 8 to be substantially the same as the surplus energy available in the heat exchanger 1 at this time, relative to the state in which no water is being drawn off. The surplus energy is provided by the heated-up construction of the heat exchanger 1 and the amount of heat-transfer medium located in the primary part. The third temperature sensor 22 sets an upper limit to the return temperature, so that overheating cannot occur. The cold water in-feed 15 is likewise a comparatively large distance from the heat exchanger inlet 8. The volume of the circulation pipe 9 between the cold water in-feed 15 and the heat exchanger inlet 8 should be approximately as large as the volume of the secondary part 6 of the heat exchanger 1. This ensures that the entire non-drinking water content of the heat exchanger 1 at the end of a drawing-off operation is delivered into the circulation pipe and is replaced by the following non-drinking water still containing cold water. Overall, immoderate cooling down of the non-drinking water at the start of drawing off and immoderate heating of the non-drinking water at the end of drawing off is therefore avoided.

Claims: Patent Claims 1. A heating system for non-drinking water, having a heat-exchanger, the primary part of which is supplied via an inward flow pipe and a return pipe with a heat transfer medium, and the secondary part of which is provided with a circulation pipe, which comprises at least one draw-off point for hot non-drinking water, a circulation pump and a cold water in-feed, and having a control device which comprises a first temperature sensor at the initial section of the circulation pipe and a primary-side adjustment means, influenced by the temperature sensor, for the amount of heat transfer medium to be let through, characterized in that a second temperature sensor (21) influencing the adjustment means (23) is arranged at the end section (17) of the circulation pipe (9) downstream of the cold water in-feed (15) . 2. A heating system for non-drinking water according to claim 1, characterized in that the second temperature sensor (21) is a significant distance (a) from the heat exchanger inlet (8) . 3. A heating system for non-drinking water according to claim 2, characterized in that the distance (a) is such that the thermal energy that is required to heat up the amount of cold water present at the end of a drawing-off operation in the circulation pipe (9) between the second temperature sensor (21) and the heat exchanger inlet (8) is substantially the same as the surplus energy, relative to the state in which no water is being drawn off. 4. A heating system for non-drinking water according to any one of claims 1 to 3 , characterized in that the volume of the circulation pipe (9) between cold water in-feed (15) and heat exchanger inlet (8) is approximately as large as the volume of the secondary part (6) of the heat exchanger. 5. A heating system for non-drinking water according to any one of claims 1 to 4 , characterized in that the second temperature sensor (21) is arranged close to the cold water in-feed (15) . 6. A heating system for non-drinking water according to any one of claims 1 to 5, characterized in that the circulation pipe (9) between cold water in-feed (15) and/or second temperature sensor (21) and heat exchanger inlet (8) is 3 to 4 metres long. 7. A heating system for non-drinking water according to any one of claims 1 to 6, characterized in that that a third temperature sensor (22) influencing the adjustment means (23) is arranged on the return pipe. 8. A heating system for non-drinking water according to any one of claims 1 to 7, characterized in that the adjustment means (23) is a motorized valve. 9. A heating system for non-drinking water according any one of claims 1 to 8, characterized in that a non-return valve (14) closing in the direction of the circulation pump (13) is provided in the circulation pipe (9) between the last draw-off point (12) and the cold water in-feed (15). 10. A heating system for non-drinking water according to any one of claims 1 to 9, characterized in that the temperature sensors (20, 21, 22) are electronic resistance sensors and an electronic control device (19) is used.

Inventors: STEENBERG BJOERN KIM, STEENBERG, BJOERN, KIM
Applicants: DANFOSS AS, STEENBERG BJOERN KIM, DANFOSS A/S, STEENBERG, BJOERN, KIM
Application year: 1999
Main classification: F24D17
IPC codes: F24D10, F24D17