DK2815196T3 - Heat exchange to heat or central heating system - Google Patents

Description

HEAT EXCHANGER FOR A HEATING SYSTEM OR A HEAT SUPPLY SYSTEM

The invention relates to the use of a heat exchanger as a heat sink for a heating system or a heat supply system according to the preamble of the patent claim 1. Such a heat exchanger is known, for example, from DE 35 193 15 A1.

Heating systems or heat supply systems often utilize renewable energy sources. Therefore, there is often the need to provide, from the media arriving with different parameters in terms of quantity and media temperature, a medium that is adapted to the requirements of the connected consumers. The different heat sources can be, for example, conventional heating boilers, thermal solar collectors, downhole heat exchanger or the like.

Usually, heat sinks are used for this object, and heat exchange between the media is achieved by means of separate line circuits. The general task for this individual case of use is that from the arriving heat quantities, a heated heating medium is generated in the shortest possible time which meets the requirements with respect to media temperature and quantity.

It has been known for a long time that on the part of energy generation, there are significant differences in terms of the media parameters. Thus, conventional heating boilers deliver media having temperatures of 40 °C and higher. Solar thermal collectors need their own separate media circuit. Downhole heat exchangers deliver media having temperatures between 30 °C and higher than 100 °C. A heating circuit of the consumer can require temperatures between 35 °C and 80 °C while service water having temperatures of higher than 55 °C has to be provided.

In addition, certain line circuits have to remain separated from other line circuits. For example, the circuit of a thermal solar collector contains a frost-proof medium whereas this is not required in a circuit of a heating boiler. On the part of consumers, there are also differences between a line circuit for heating purposes and a line circuit for service water which needs to have drinking water quality and therefore has to be supplied with fresh water.

Since bringing together the different media likewise having different heat contents is not possible and conveying certain media directly into connected heating system is also excluded, the primary energy sources in heating supply systems are combined in a so-called heat sink and a heat exchange from the primary media into a secondary medium is carried out in this heat sink. In order to compensate for greatly varying heat quantities, a larger fluid volume is provided at the secondary side.

The above-described object is to be achieved by a heat exchanger as a central element.

For example, a tubular heat exchanger could be considered for this purpose. However, known heat exchangers of this kind such as the one described, for example, in DE 36 41 139 C2 are not suitable due to their inertia.

For a type of a tube bundle heat exchanger according to DE 35 19 315 A1, the volume ratio can be configured such that no unnecessary storage volume is present in such a heat exchanger and, moreover, that the separator surface is increased by using corrugated tubes. This type of an air-water heat exchanger is not suitable for use as a heat sink in heat supply systems since, in order to recover heat quantities from exhaust gases of a heating boiler, it encloses the heating boiler’s exhaust pipe and is not designed for operation with two liquid media.

These objects can be achieved with a highly effective plate heat exchanger. However, due to its construction, the latter has disadvantages in heat supply systems. Thus, in areas with drinking water supplies of high hardness, there is the need to treat the operating media of the heat supply system with chemical-physical methods. Ultimately, this is necessary even in the case of small refilling quantities.

If no treatment of the media is carried out, the heat exchanger is plugged within a short period of time resulting in a significant loss in efficiency, flow-rate and dynamics.

In plate heat exchangers, calcination in the portion which serves for service water supply and is permanently filled with fresh water is unavoidable. Chemical cleaning of plugged plate heat exchangers ultimately results in material degradation and therefore in reduced service life. For the aforementioned reasons, plate heat exchangers are rarely used in heat supply systems.

In order to avoid the described problems in plate heat exchangers, so-called combination storages having a large container and a tube coil arranged therein are implemented in heat supply systems. These combination storages have a comparatively large storage volume and, at the same time, a small separator surface of the heat exchanger. Due to the heat layers which inevitably occur in the combination storage, a temperature gradient from top to bottom occurs in these heat layers.

If the equilibrium in such a combination storage is disturbed by extracting heat quantities, this naturally takes place via extraction possibilities arranged at the top of the combination storage, as a result of which significant cooling occurs in the upper region of the combination storage. The cooled medium begins to move downwards and mixes with colder layers so that ultimately a mixing temperature is generated which possibly no longer allows extracting heat quantities.

In some combination storages, a torus consisting of cold water is formed, which, by sinking, significantly disturbs the temperature conditions within the combination storage.

Different manufacturers of such combination storages try to avoid this disadvantageous effect by installing transverse bulkheads and overflow channels in the combination storages. In a known system CTC Eco Zenith I 550 of CTC AB, 341 26 Ljungby, Sweden, a transverse bulkhead is installed in such a combination storage and is provided in the upper and the lower region in each case with an overflow channel having multiple holes.

In the Spiro combination storage of FEURON AG, 9430 St. Margrethen, Switzerland, the attempt is made to maintain a layering of the medium according to the natural temperature layers as long as possible by using a spiral heat exchanger arranged distributed over the entire volume of the combination storage.

In both above-described combination storages, the medium of a solar thermal collector that is mostly supplied at the highest temperature is supplied by a separate heat exchanger within the combination storage, and the separate heat exchanger is arranged in both cases at the bottom of the container. In the combination storage of CTC Eco Zenith I 550 system, the heat exchange takes place with the cold medium that is present in the lower chamber, while in the Spiro combination storage of FEURON AG, a narrow spirally wound heat exchanger is additionally enclosed in a separate housing, and rising of the heated medium into the upper region of the combination storage is preferably to take place by means of a riser duct.

Both systems have the disadvantage that they operate with large volumes and have a complicated inner structure. The inevitably forming temperature layering and the technical precautions for preventing unintended mixing processes result at the same time in inert behavior of the combination storages. The technical complexity and therefore the manufacturing costs are high.

However, in order to ensure a heat exchanger having low inertia, it is essential to ensure a highly efficient heat exchange.

For this purpose, the combination storage of FEURON AG is provided with a tube coil which is composed of a corrugated tube and, according to the technical description of the combination storage, is intended to generate a turbulent flow in the interior of the corrugated tubing so as to achieve effective heat exchange. However, effective heat exchange cannot be achieved because there is no turbulent flow in the medium surrounding the corrugated tube, and special precautions for achieving this flow type are not provided.

Therefore, there is a need to replace the combination storages by heat exchangers which, with significantly reduced inertia, enable the heat exchange between a primary and a secondary medium while, at the same time, avoiding the susceptibility to failure of the above-described plate heat exchangers. Previously known operating conditions including their different temperature ranges have also to be considered.

It is therefore an object of the invention to propose a use for the heat sink of a heating system or a heat supply system which does not have the disadvantages of the combinations storages commonly used in the prior art, which has high transfer capacity at low volume, which, without much inertia, transfers the heat quantities of arriving media from primary line circuits to a secondary medium which is also present in the heat exchanger and thus enables a quick response to changing heat demands, which is durable and, in addition, can be constructed in a simple and cost-effective manner and thereby reduces at the same time the total costs for heating systems and/or heat supply systems and, apart from that, improves the heat utilization rate of such systems.

In the following description, the exemplary embodiments and the patent claims, the terms listed below are used with the following meaning:

Heat exchanger - a tubular heat exchanger having at least one tube coil arranged in a container and connectors extending to the outside for the tube coil and the container interior.

Tube coil - a helically and/or spirally wound tube, the pitch of which can be uniform or different in different regions.

Tube - metallic tube having a profiled wall, preferably a corrugated tube having a parallel or a helical corrugation.

Separator - a solid partition wall that is impermeable to fluids and is arranged between different media. It is formed by the tube wall.

Medium - fluid that can contain and transport heat quantities.

First medium - fluid that can be heated by any heat source and transfers these heat quantities in a heat exchanger to a second medium.

Second medium - a fluid that absorbs heat quantities from the first medium in a heat exchanger and transports the heat quantities to consumers or storage units present in the system.

The object above is achieved with a use having the features of the characterizing part of claim 1 in connection with the features of the preamble of this claim. Independent and subordinate claims describe embodiments of the heat exchanger according to the invention.

According to the invention, the object is achieved with a heat exchanger of the type of a tubular heat exchanger. The latter is designed in such a manner that its container volume is filled with the first medium and a second medium flows through a coil tube that likewise is arranged in the container.

In this way it is achieved that a sufficiently large quantity of heated first medium is always available, and the second medium transporting heat quantities is able to absorb these heat quantities as required and within a short time and at a high flow rate.

In doing so, the heat exchanger achieves a conversion efficiency of at least 90 percent based on the heat quantities supplied with the first medium and discharged with the second medium under the temperature conditions existing in heat supply systems.

In order to achieve this, the heat exchanger has at least the following parameters: A ratio of the volumes of the container and the volume of the coil tube is targeted that lies at a value of 5 or below.

The container of the heat exchanger is greatly thermally insulated.

The coil tube is made from a metallic material.

The wall thickness of the tube of the coil tube is very small.

The coil tube is movable in the container to a limited extent.

The shape of the container is selected such that the container has a small surface.

Through the measures described above it is achieved according to the invention that the container of the heat exchanger is always filled with a sufficient quantity of the heated first medium. If there is a need for heat, the second medium flows through the coil tube, and intensive heat exchange takes place.

Particularly preferred here is a coil tube that is composed of a thin-walled corrugated tube. Such types of corrugated tubes have wall thicknesses in the range of a just a few tenths of a millimeter. Thus, the tube wall forms an extremely thin separator through which intensive heat exchange can be achieved.

According to the invention, corrugated stainless steel tubes are used for the coil tube. The reduced heat transition through stainless steels is compensated by the small wall thickness.

The helically wound coil tube made from a corrugated tube already effects the transition into a turbulent flow at a comparatively low flow velocity, as a result of which the exchange process is intensified to a significant degree.

The coil tube is able to move in the container to a limited extent, for example in the form of thermal expansion. As a result and due to the predominantly turbulent flows, no deposits can form in the region of the separator.

The container of the heat exchanger preferably has a cylindrical shape. The length thereof can be up to 6 times the diameter.

On the other hand, the comparatively low container volume effects that the first medium also has to be constantly re-supplied and therefore also has a high flow velocity within the container. Thus, on this side of the separator, there is also a largely turbulent flow and the exchange process is additionally intensified.

With the measures described above it is prevented that temperature layering of the first medium occurs in the interior of the container. Thus, tori are prevented in the first medium and temperature fluctuations are prevented in the second medium.

Thus, with a comparatively small volume of approximately 60 I, an inlet temperature of the first medium of approximately 90 °C, a volume flow of the first and second media of in each case approximately 3000 l/h and a temperature gradient of approximately 40 °C, the heat exchanger according to the invention is capable of achieving a specific capacity of 750 W per 100 cm2 of separator surface.

Thus, the capacity parameters of the heat exchanger meet those of plate heat exchangers.

Furthermore, it is possible to configure the heat exchanger according to the invention in such a manner that the coil tube in the container interior is subdivided to form a multiarrangement. In this way, the volume ratios between the first medium and the second medium in the heat exchanger can be influenced in favor of the second medium. The majority of coil tubes can either be fed with their connectors to the outside and can be connected outside of the container or can be branched out within the container.

In the case that more than one coil tube is arranged in the container and their connectors are fed to the outside, one of the coil tubes can also be connected to another heat source.

Likewise, one of the coil tubes can be connected to a circuit of a heat supply system which requires a different temperature level. A preferred embodiment provides that at least one second coil tube serves for connecting a third medium from a heat source or from a heat consumer to the heat exchanger if the third medium, due to its particular properties, must not be mixed with the first or second media.

Depending on the actual configuration of the heat supply system in which the heat exchanger according to the invention is used, the latter can be provided with a coil tube for service water supply so that provision of hot water can be enabled in this manner.

Likewise, depending on the configuration of a heat supply system in which the heat exchanger according to the invention is used, the latter can be provided with an electrically operated heating cartridge which can take on the function of supplying heat quantities or of merely ensuring the frost protection.

Due to the profiled wall of the coil tube, on the one hand, the surface area serving for heat exchange and thus the so-called separator surface increases. Furthermore, due to the profiled wall, the second medium to be heated in the coil tube is subjected to a turbulent flow which intensifies the heat exchange.

According to the invention, the heat exchanger is configured in such a manner that, with regard to the heat requirements in the heating circuit, it has the lowest possible inertia during the heat transfer. In order to achieve this, the heat exchanger is designed in such a manner that it has a conversion efficiency of at least 90 percent.

The invention is explained in more detail below by means of some exemplary embodiments and drawings. In the figures:

Fig. 1 shows a schematic illustration of the heat exchanger according to the invention.

Fig. 2 shows an embodiment of the heat exchanger according to the invention in which all coil tubes are connected in parallel.

Fig. 3 shows an embodiment of the heat exchanger according to the invention in which all coil tubes within the heat exchanger are connected in parallel.

The heat exchanger 1 according to the invention is composed at least of one container 2, insulation 3 surrounding the container 2 und a coil tube 4.

In contrast to the embodiment of heat exchangers for heating systems or heat supply systems from the prior art, a heated first medium provided by heat generators is present in the interior chamber 7 of the container 2, and a second medium which is heated through exchange processes and supplies the heat consumer flows through the coil tube 4.

The coil tube 4 is connected via its outwardly fed connectors 5 and 6 to a line circuit in which the heat consumers are situated. The first medium is contained in the interior chamber 7 of the container 2, wherein the container 2 is connected via the connectors 8 and 9 to the first line circuit in which the heat generators are arranged. In this context, heat generators can be thermal solar collectors, heat pumps, heating boilers, downhole heat exchangers or units which recover process heat.

In the heat exchanger 1 according to the invention, a second coil tube 10 and a third coil tube 11 can be arranged, which, with their connectors 12 and 13 as well as 14 and 15 can also be connected to heat consumers.

The coil tubes 4, 10 and 11 can be connected to one and the same line circuit. They can also supply a heated medium to various line circuits.

In the simplest case, only one coil tube 4 is arranged in the heat exchanger 1.

Such an arrangement has the following advantages if a heat exchanger 1 having a volume of 60 I is taken as a basis:

The ratio between the first medium in the interior chamber 7 of the container 2 and the second medium in the coil tube 4 ranges between 1:2 to 1:4. For a heat exchanger 1 having a volume of 60 I, this means that up to 24 I of the second medium can be contained in the coil tube 4.

At a volume flow of = 1000 l/h, an inlet temperature of 60 °C and an outlet temperature of 40 °C, the heat exchanger 1 has a capacity of 24 kW.

In the described case, the transfer capacity of the separator/the separator wall is 125W/100 cm2.

At a volume flow of Qi = 470 l/h, an inlet temperature of 50 °C and an outlet temperature of 10 °C, the heat exchanger 1 has a capacity of about 23 kW.

The specific capacity of the separator can then be 150 W/100 cm2.

After heating up, the heat exchanger 1 achieves properties which correspond to those of a plate heat exchanger. The inertia resulting from the volume flows at the inlet and outlet of the heat exchanger 1 occurs only during the heating-up cycle.

After heating up is completed and under the same conditions, a volume of about 500 I of heated second medium at a temperature of 50 °C can be extracted for any desired time period.

The heat exchanger 1 has a calculated peak capacity of 120 kW, based on a throughput of 3000 l/h.

In the event of an interruption of the supply of heated first medium, the heat exchanger can maintain the exchange process for a period of about 1 min at a capacity of about 100 kW.

At an increased throughput of 3000 l/h, at an inlet temperature of 90 °C, an outlet temperature of 50 °C at the separator/the separator wall, the heat exchanger 1 has a specific capacity of 750 W/100 cm2.

Independent of the actual size of the heat exchanger 1 according to the invention, furthermore, the following applies:

The transferred capacity is directly proportional to the surface area of the separator and thus to the surface area of the corrugated coil tube and ultimately also to the number of corrugated coil tubes. Likewise, the transferred capacity is directly proportional to the volume flow on the primary and secondary sides and to the temperature gradient At.

The coil tube 4 is composed of a corrugated stainless steel tube.

The corrugated stainless steel pipe is profiled in a parallel or helical manner.

The wall thickness of the corrugated stainless steel tube lies between 0.1 mm and 0.5 mm. Thus, the heat transfer in stainless steel, which is less favorable compared to base steel materials, is largely offset by the small wall thickness.

The coil tube 4 is suspended in the interior chamber 7 of the container 2 to be movable to a limited extent. As a result of temperature changes, the coil tube can expand and/or slightly change its shape.

Due to the use of corrugated tubes, the flow in the coil tube is already turbulent at low flow velocities and therefore ensures an intensive exchange process.

The volume ratios and the geometrical shape of the coil tube 4 are selected such that a turbulent flow also prevails in the interior chamber 7 of the container 2, and the exchange process on both sides of the separator is therefore equally intensive.

By selecting a coil tube 4 made from stainless steel in connection with the coil tube’s changes of shape and the turbulent flows, deposits on the separator are avoided and the exchange process can be maintained with the same intensity over a long period of time.

Due to the selected volume ratios between the interior chamber 7 and the coil tube 4 and due to their shape, no temperature-dependent layerings of the first medium can occur in the interior chamber.

This ensures that the heat exchanger 1 implements in each operating state an exchange process that is designed for the achievable maximum and thereby achieves in any case an efficiency of over 90 %.

The effectively conducted exchange process further results in the fact that a set-point temperature of 50 °C is reached in a tenth of the time that a combination storage known from the prior needs.

The extraordinarily low inertia of the heat exchanger 1 is achieved, besides through the measures already mentioned above, in that the separator surface implemented with the coil tube 4 exhibits a value of between 150 cm2 - 700 cm2 per liter of container volume.

Achieving such a high value can also be enabled in that further coil tubes 10 and 11 are arranged in the container 2.

The coil tubes 4, 10 and 11 can be configured as helical coils, as spiral coils or as a combination of both forms.

Specific embodiments of the heat exchanger 1 according to the invention can be created in that the coil tubes 4, 10 and 11 are connected to a connection 16 outside of the insulation 3.

It is also possible to establish the connection 16 only between two of the existing coil tubes 4, 10 and 11 while the remaining coil tube is associated with a separate line circuit. This is, for example, the preferred variant if a service water treatment has to be provided in addition to the heating or heat supply system.

The interconnection of the coil tubes 4, 10 and 11 can also be established with a connection 17 in the interior chamber 7 of the container 2. In this case, the interconnection is established in the region enclosed by the insulation 3, and only the connectors of the coil tube 4 are fed outwards through the insulation. In this manner, an effective heat exchanger having a large separator surface is created.

Such a heat exchanger according to the invention ultimately provides the possibility to design various embodiments similar to a modular system and therefore to adapt the heat exchanger to certain operating conditions.

The arrangement described above can be implemented with known means as a standing or suspended arrangement or as a combination of both possibilities.

Furthermore, it is possible to configure the heat exchanger according to the invention in pre-assembled form with the necessary line connections and optionally combined with valves and circulation pumps.

The insulation 3 of the heat exchanger 1 can be designed from the viewpoints of optimal energy utilization. Furthermore, it can include lines, valves and circulation pumps. Likewise, it can be configured to be removable.

Thus, the invention has the advantage that it proposes heat exchangers for heating or heat supply system which operate efficiently, the dimensions of which are compact, which provide heated media while having low inertia and, apart from that, can be produced in a cost-effective manner and with low material and production expenses.

REFERENCE LIST 1 heat exchanger 2 container 3 insulation 4 coil tube 5 connector 6 connector 7 interior chamber 8 connector 9 connector 10 coil tube 11 coil tube 12 connector 13 connector 14 connector 15 connector 16 connection 17 connection

Claims (6)

Use of a tube heat exchanger for a heat exchanger (1) for heat receivers in a heat exchange or heat supply system, consisting of a closed container (2), a spiral or helical coiled tubing (4) located in the container (2) of a corrugated pipe or corrugated tubing and an insulation (3) enclosing the container (2), a first heat-carrying medium filling the inner space (7) of the container (2), the tubing (4) containing a second heat-carrying medium, characterized by , a the volume of the first medium in the interior space (7) of the container (2) is at most equal to 6 times the volume of the second medium in the tube hose (4), and the tube hose (4) has a separator surface of at least 150 cm2 based on is liter of container contents. Use of a heat exchanger (1) according to claim 1, characterized in that it has a volume of approx. 60 I. Use of a heat exchanger (1) according to claim 1, characterized in that the pipe hose (4) is divided into several strands and that at least one outer and an inner pipe hose are located coaxially relative to each other. Use of a heat exchanger (1) according to claim 1, characterized in that at least one additional pipe hose, such as one connected to an independent wiring circuit, which carries a third medium, is placed in the container. Use of a heat exchanger (1) according to claim 1, characterized in that the medium carried in the further tube hose is fed into an open circuit. Use of a heat exchanger (1) according to claim 4, characterized in that the third medium feeds heat quantities to and / or from the heat exchanger.