The present invention relates to a heating system with a condensing boiler comprising a number of mainly uniform smoke gas/water heat exchanger sec¬ tions, each provided with an internal flue and a sur- rounding water jacket, said sections being series- coupled with respect to the smoke gas flow from a burner unit in connection with a first section to a smoke gas outlet with induced draught in connection with a last section. From DE-B-22 27 070 a heating system is known, in which a number of horizontally disposed parallel heat exchanger sections are superposed. The smoke gas flows through the sections in series in their longitudinal direction and with opposed flow direc- tions in adjacent sections, while the water flow takes place in the upward direction transversely to the longitudinal direction of the sections.

With this configuration the efficiency of the system will be limited by the fact that the highest water temperature occurs in the uppermost section where the smoke gas temperature is lowest. As the smoke gas must then have a discharge temperature that is higher than the desired supply water temperature for the radiator system, a complete utilization of the heat content of the smoke gas for heating the supply water for the radiator system cannot be obtained.

The same applies to a system known from US-A-2,587,530 in which, even though an improved heat transfer has been provided between the flue and the water jacket each individual section by causing the smoke gas and water to pass through each section in counterflow in the longitudinal direction of the section, the flow of smoke gas as well as water is

effected in parallel in various sections.

According to the present invention a consider¬ ably improved utilization of the heat content of the smoke gas and thereby an optimum efficiency is obtained for a heating system with a condensing- boiler in that the heat exchanger, sections are disposed vertically in juxtaposed relationship, the smoke gas discharge being connected with the upper end of the last section, and in that the sections are moreover series-coupled with respect to the water flow through said water jackets with an inlet for return water from a radiator circuit at the upper end of the last section and an outlet for supply water to the radiator circuit at the first sec¬ tion, condensate discharge means being provided in connection with transitional flues connecting the lower ends of adjacent sections.

Since in this configuration smoke gas as well as water flow in series through all sections in the longitudinal direction of each section and in full counterflow in each section, the return water from the radiator circuit will enter the boiler at the point where the smoke gas temperature is lowest, and the sup¬ ply water for the radiator circuit will leave the boiler at the point where the smoke gas temperature is highest.

Moreover, the boiler structure is simple so that the sections can be produced at comparatively low costs and with good possibilities of cleaning and maintenance, inasmuch as the flues in the individual sections may be connected at their upper ends through detachable caps. Moreover, due to the transitional flues between the lower ends of some of the sections an effective discharge of condensate is obtained.

In a preferred embodiment according to which a hot water supply system is further connected with the boiler an additionally increased efficiency is obtained

for the whole heating system including the radiator circuit and the hot water supply system, in that a cold water inlet for the hot water supply system is coupled to water pre-heating means positioned in the water jacket. of the last section and having its water discharge con¬ nected with a water/water heat exchanger heated by the supply water to the radiator circuit.

Thereby, the supply of cold water to the hot water supply system will be pre-heated by the return water from the radiator circuit before being supplied to said water/water heat exchanger.

As it will appear in detail from the following description such an aggregate heating system may comprise a control unit to actuate valve members so as to obtain during summer operation a tap water temperature for the hot water supply that is higher than the temperature of the supply water from the first boiler section.

Besides controlling the temperature of the hot tap water such a control unit that may comprise a microprocessor is capable of controlling the burner unit in dependence of a program caring for day and night • control of the supply water temperature and for survey¬ ing the smoke gas temperature, the supply water temper¬ ature, the return water-temperature, the fuel consump- tion and the condensate discharge.

In the following the invention will be more fully explained with reference to the accompanying drawings, in which

Fig. 1 is a schematical diagram of an embodiment of a heating system according to the invention.

Fig. 2 is a perspective view of a modified design to more fully illustrate details of a practically suitable construction, and

Figs. 3 and 4 are diagrams of two different em- bodiments of a hot water supply system in connection with the heating system.

The heating system schematically shown in Fig. 1 has a boiler comprising a "number of vertically dis¬ posed sections 1 to 5 each of which is formed as a smoke gas/water heat exchanger with an internal tubular flue 6 from which an effective heat transfer is effected through a wall 7 to a surrounding water jacket 8 of annular cross-section.

In the illustrated embodiment, the first boiler section 1 is connected at its lower end with a burner unit for a liquid or gaseous fuel such as oil or natural gas. The burner unit 9 which is not shown in detail may be of conventional design and provided with fuel pre-, heating means as known in the art to reduce fuel consump¬ tion. The sections 1 to 5 are series-coupled both with respect to the smoke gas flow effected from burner unit 9 through the first section 1 to the upper end of the flue 6 in the heat exchanger section 2 and from there further on through' the flues in sections 3, 4 and 5 to a smoke gas discharge 10 connected with the upper end of the section 5, an induced draught fan 11 being mounted in said discharge, and with respect to the water flow effected from an inlet 12 for return water from a radiator circuit not shown, connected with the upper end of the section 5 through the annular water jackets 7 in sections 5, 4, 3, 2 , and 1 in said order, of succession on to a discharge 13 for supply water to the radiator circuit connected with the water jacket in section 1. An expansion tank 14 is further connected with the water jacket in section 1. In sections 2 , 3, 4, and 5 the heat transfer sur¬ face between the flue and the water jacket has been enhanced by forming the heat transfer wall 7 to be wave-shaped such as known from US-A-2,587,530.

In order to force the smoke gas .flow through the internal flues 6 of the individual sections into effective contact with the wave-shaped heat transfer

walls 7, rod-like cylindrical displacement members 15 may be arranged in the flues of the sections coaxially with the tube walls 7, such as known from DE-A-22 27 070. During the passage of the flow of smoke gas through the heat exchanger sections 2 to 5 condensate deposits which is collected in the transitional flues 16 and 17 connecting the lower ends of the flues in adjacent sections 1 to 3 and 4 to 5, respectively, and is removed through condensate outlets 18. In the perspective view shown in Fig. 2 of a practically suitable embodiment of. the same structure as schematically illustrated in Fig. 1 members corres¬ ponding to those illustrated in Fig. 1 are designated by the same reference numerals.. The figure serves particularly to illustrate a practically suitable design of the smoke gas and water connections between the flues and water jackets of the individual sections. Between the upper ends of the heat exchanger sections 1 and 2, the upper ends of heat exchanger sections 3 and 4 and from the upper end of heat exchanger section 5 to the discharge, duct 10 the transitional flues extend in caps 19,20 and 21 connecting the adjacent ^' sections and section 5 and discharge duct 10, respectively, and being- provided 'with detachable covers 22 in alignment with the internal flues of the indidual sections.

Similarly, the lower ends of the heat exchanger sections 2 and 3 and the lower ends of the heat exchanger sec¬ tions 4 and 5 are connected through transitional members 23 and 24, in which the transitional flues 16 and 17 shown in Fig. 1 extend.

As a water connecting duct Fig. 2 only shows a short piece of tube 25 between the lower ends of the water jackets in sections 4 and 5, but corresponding water connecting ducts are provided between the upper ends of the water jackets in sections 4 and 3, the lower ends of the water jackets in sections ^* 3 and 2 and the upper ends of the water jackets in sections 2 and 1.

A water connecting tube 26 extending between the upper ends of the sections 1 and 5 serves control purposes with respect to a hot water supply system associated with the heating system, as further explained in the following.

Heating coils 27 and 28 arranged in the water jackets of the heat exchanger sections 5 and 1 form part of a design of such a hot water supply system described in the following with reference to Fig. 4. A box 29 beneath the heat exchanger sections accommodates a neutralization unit for the condensate discharged through the outlets 18. The neutralization unit may for instance comprise an exchangeable bag containing crushed marble receiving the condensate through a water seal not shown. The condensate thus percolates through the crushed marble, thereby being neutralized, e.g. so that its pH-value which generally is about 2,5 increases to about 7. The box 28 is pro¬ vided with a detachable cover 29 to be used when replacing the neutralization bag.

In the diagrams shown in Figs. 3 and 4 of two different embodiments of a hot water supply system in connection with the heating system according to the in¬ vention the heat exchanger sections 1 to 5 of the boiler and the burner unit 9 are only illustrated purely schematically.

In both embodiments of the hot water supply system the cold water inlet 31 thereof is coupled to water pre-heating means 32 arranged in the water jacket of the last heat exchanger section 5 in the form of a heating coil, e.g. designed as shown at 27 in Fig. 2. The water discharge 33 from the water pre-heating means 32 is connected with a water/water heat exchanger heated by the supply water to the radiator circuit dis- charged from the section 1.

In the embodiment shown in Fig. 3 this water/ water heat exchanger comprises a hot water tank 34 having a heating coil 35, the water inlet 36 of which is coupled to the discharge 13 for supply water from the 5 section 1 through a controlled valve member 37, by means of which the. water discharge 13 may be coupled either to the radiator system or to the heating coil 35. The water discharge 38 from the heating coil 35 is connected with another controlled valve member 39, 10 by means of which it can be coupled either to the radiator circuit through a communication 40 or to the return water inlet 12 at the water jacket in the heat exchanger section 5 through a by-pass connection 41. The valve members 37 and 39 may be three-way •15 magnet valves controlled from a central control unit 51, which for instance may include a microprocessor, in dependence ori the temperature of the supply water for the radiator system at water discharge 13 measured by a temperature measuring device 42 and the temperature... 20 of the tap water at the water discharge 44 from the water tank 34 to the hot water supply system.' measured by a temperature measuring device 43. By means of the control unit 51 a desired tap water temperature, for instance between 35 and 60 C, may be adjusted. When 25 the water in the hot water tank 34 measured by the measuring device 43 has attained the desired temperature, the supply water is caused by valve 37 to by-pass the hot water tank 34 and flow directly to the radiator sy¬ stem. If, on the contrary, the tap water temperature 30 measured by the measuring device 43 is lower than the desired temperature, whereas the supply water tempera¬ ture at the measuring device 42 exceeds the desired tap water temperature, the supply water is caused by valves 37 and 39 to pass through the hot water tank 34 and from 35 there further on to the radiator system. If, for instance, during summer operation, the supply water has a lower

temperature than the desired tap water temperature, the control unit 51 actuates, however, the valve 39 i such a manner that the supply water subsequent to having passed through the heating coil 35 is conducted through the by-pass conduit 41 to the return water inlet 12 of the last heat exchanger section 5. A direct recircula- tion of the supply water through the boiler is thereby established and the control unit 51 which also controls the burner unit 9 is adapted or programmed so as to maintain the burner unit in a state of full output in this situation till the tap water has attained the desired temperature.

Due to the pre-heating of the tap water for the hot water supply in connection with the above described control an optimum efficiency is obtained also with respect to the tap water heating, allowing the hot water tank 34 to have a smaller capacity than otherwise neces¬ sary.

In the embodiment of the hot water supply sy- ste shown in Fig. 4 the water/water heat exchanger con- : nected with the water, discharge .33' of the water pre- heater 32' is constituted by a heating coil 45 located in the water jacket of the section 1 and having its water discharge 46 connected with the hot water supply system. The tap water temperature measured by a temperature measuring device 47 is in this case controlled by mixing the water passed through the heating coil 45 with cold water supplied from the cold water inlet 31 ' of the water pre-heater 32 through a controlled valve member 48. The water discharge 1.3 for the supply water from the water jacket of the transitional section is connected with another controlled valve member 49 by means of which the supply water may be coupled either directly to the radiator system or through a by-pass connection 50 to the return water inlet 12 for the water jacket in the last heat exchanger section 5. As in the embodiment

illustrated in Fig. 3 this allows establishment of a direct recirculation of the supply water through the boiler to be used for instance during summer operation or, in the embodiment shown in Fig. 4, also in case of peak load, in which case the radiator circuit is switched off and only tap water heating is effected. The control unit 51 and 51 * , respectively, for the valve members 37, 39 and 48, 49, respectively, may further be connected with a surveying device in the form of a pH-measuring device 52 and 52', respect¬ ively, for controlling the acidity of the condensate passing through the neutralization unit in Fig. 2 and with an alarm device 53 and 53', respectively, so as to produce an alarm signal when the pH-value falls below a prescribed threshold value, for instance 6, as a warning that the aforementioned neutralization bag is to be replaced.

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