GB2468015A

GB2468015A - Immersion heat exchanger with a shroud and insulated return conduit

Info

Publication number: GB2468015A
Application number: GB1002244A
Authority: GB
Inventors: Richard Bell
Original assignee: Solmatix Ltd
Current assignee: Solmatix Ltd
Priority date: 2009-02-19
Filing date: 2010-02-10
Publication date: 2010-08-25
Also published as: IE20100073A1; GB0902709D0; GB201002244D0

Abstract

An immersion heat exchanger (shown in an exploded view) for insertion into a hot water tank has a return conduit 116 extending from a distal end 114 of helical heat exchanger coils 102 and terminating adjacent to a fluid inlet 112; the return conduit 116 formed from, covered or coated with a thermally insulating or non-heat conductive material 118; and the coil 102 being within a coaxial tubular shroud 104. The heat exchanger fits an aperture of a central heating hot water tank, such as for a threaded electric immersion heater, and is mounted near-vertically for natural convection. Fluid in the coils may be solar heated, and an electric element may also be within the shroud 104. In one embodiment an outlet opening (208, fig 11) can close with temperature responsive actuation, such as a bi-metal strip to prevent reverse symphonic flow.

Description

Immersion Heat Exchanger for a Hot Water Tank This invention relates to an immersion heat exchanger for a hot water tank and in particular to an immersion heat exchanger for retrofitting to an existing hot water tank of a domestic central heating system.

When heating water in a water tank, domestic or commercial, the heat is typically transferred to the 1. the tank 1 will contain a coil 2 of material through which the hot liquid flows and transfers its heat through the walls of the coil 2 into the liquid in the tank, as shown in Figure 1 2. an external heat exchanger 4 is configured in parallel with the tank 1, as shown in Figure 2, where the hot fluid from a heat source passes through one side 5 of the exchanger 4. The heated fluid 6 on the other side of the external exchanger 4 rises and creates a thermal symphonic action between the lower outlet 7 and the upper inlet 8 of the tank 1.

With configuration 1, the complete tank of water is elevated at a constant temperature. The problem is that when the hot water demand only requires a proportion of the total volume of the tank 1, the whole tank must be heated to the required temperature. When the heating capability is intermittent (e.g. with a solar system when clouds reduce the heating capability) this configuration results in a tank of water at a low temperature throughout.

With configuration 2 the heat is exchanged at a high temperature to a smaller volume of water via the external heat exchanger 4. This hot water rises and draws cold water from the bottom of the tank 1 in a syphonic action. The result is that the tank fills with hot water from the top of the tank. For the user, the result is that there is very quickly produced a volume of hot water at the required temperature in an upper region 9 of the tank 1. This configuration is particularly suitable for a solar heating system, particularly in the climate in the British Isles, because, with each period of sunshine during the day, hot water builds up incrementally from the top of the tank. Such external heat exchangers are well known, both electric and solar plate exchangers, tube tank exchangers. In the US they are known as side arm exchangers.

Installing configuration 1 is relatively simple and is typically done at the point of manufacture of the tank. In the case where solar or other alternative energy systems are being retrofitted to a domestic dwelling, a 2-coil system is required (one for the existing central heating arrangement and an additional coil for the alternative energy system). It has not been possible until recently to retrofit an additional internal coil to a tank.

Installing configuration 2 is more suited to retrofitting of an additional heat exchanger. However, such side arm exchangers are relatively expensive and time consuming to install, require full draining of the system and approximately 3 -4 hours labour.

The ideal system would be capable of being retrofitted to existing tanks without the need for full draining and would create an efficient syphonic action in the tank as per the description of configuration 2 above.

In a domestic hot water systems, hot water tanks 1 are typically provided with an aperture 10 fitted with a large threaded flange to allow the fitting of an electric immersion heater, as shown in Figure 3.

Recently a heat exchanger coil 12 has become available on the market, as shown in Figure 4, which can be retrofitted into the aperture 10 provided for an electric immersion heater, as shown in Figures 5a and 5b, wherein the diameter of the coil is arranged such that the coil 12 may be inserted through the aperture 10. An upper end of the coil is connected to a threaded flange 13 to be received within the aperture 10 and through which an inlet and outlet of the heat exchanger coil 12 pass.. This configuration provides one of the solutions, namely it can be quickly retrofitted to existing domestic hot water tanks. When tested however it does have several shortcomings as follows: 1. as with other in-tank coils the heat exchanger coil 12 attempts to heat the water in the tank from the bottom up requiring much more energy to create useable' hot water; 2. the return pipe 14 extends from the bottom of the coil 12, through the centre of the coil in contact with the water in the tank 1 and thus re-gains heat as the water flows back up the pipe 14 inside the tank 1 thus reducing the heat transfer efficiency of the heat exchanger.

According to a first aspect of the present invention there is provided an immersion heat exchanger for a hot water tank adapted for insertion into said hot water tank, said heat exchanger comprising a heat exchange conduit having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, a return conduit extending from said second end of the heat exchange conduit to said first end to terminate adjacent said heat exchange fluid inlet, wherein said return conduit is formed from, or is covered or coated with, a thermally insulating or non-heat conductive material.

Preferably the heat exchanger is adapted for insertion into an aperture provided in an upper region of the tank typically provided for insertion an electric immersion heater. Preferably said fluid inlet and return conduits extend through a plug adapted to be received within and close said aperture.

Preferably the heat exchange conduit is disposed within a coaxial, preferably substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect of the heat exchange fluid within said heat exchange conduit causes the water being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the heating coil.

Preferably the shroud is coated in or formed from a thermally insulating or non-heat conductive material.

Preferably said shroud comprises at least one lower inlet opening for allowing water to flow into a lower end of the shroud and at least one upper outlet opening for allowing water to flow out of an upper end of the shroud. Said inlet opening may comprise an open lower end of the shroud. The upper outlet openings may be defined by apertures provided in the side of the shroud adjacent an upper end thereof.

Where said heat exchanger is provided with a plug adapted for insertion into an aperture provided in an upper region of the tank for an electric immersion heater, an upper end of said shroud may be mounted on an inner surface of said plug. Preferably the plug is threaded to be received in a corresponding threaded aperture provided in the tank.

In an alternative embodiment, said at least one upper outlet opening may be closable. Preferably said closable outlet opening is openable by means of an actuation system in response to the temperature of the water adjacent the upper end of the shroud. In one embodiment, the actuation system may comprise a bi-metal strip or similar temperature responsive actuator, such that the at least one upper outlet opening is automatically opened when the temperature of water adjacent the upper end of the shroud exceeds a predetermined level.

Preferably the heat exchange conduit comprises an elongate tube wound in a helical or near-helical fashion to define a heat exchange coil. Preferably said return conduit is disposed coaxially within said heat exchange coil.

According to a further aspect of the present invention there is provided a fluid heating apparatus comprising a body defining a chamber for containing a volume of fluid to be heated, the chamber having a fluid inlet and a fluid outlet spaced apart in a first axial direction; a first heat exchange coil being located in said chamber between said fluid inlet and fluid outlet through which a heating medium may be passed to heat said fluid contained within the chamber by means of a primary heat source, an aperture being provided in an upper region of the chamber into which is inserted a second heat exchange coil, said second heat exchange coil having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, a return conduit extending from said second end to said first end to terminate adjacent said heat exchange fluid inlet, wherein said return conduit is formed from or is covered or coated in a thermally insulating material.

The volume of fluid contained within the body may comprise water for use in a domestic water heating and/or central heating system.

Preferably the second heat exchange coil is disposed within a substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect causes the medium being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the second heat exchange coil.

Preferably the second heat exchange coil comprises a elongate tube wound in a helical or near-helical fashion, said return conduit being disposed coaxially within said coil.

According to a further aspect of the present invention, there is provided an immersion heat exchanger for a hot water tank, said immersion heat exchanger being adapted to be inserted into said hot water tank, said heat exchanger comprising a heat exchange conduit having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, the heat exchange conduit being disposed within a coaxial, preferably substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect causes the medium being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the heat exchange conduit, said shroud comprising at least one lower inlet opening for allowing water to flow into a lower end of the shroud and at least one upper outlet opening for allowing water to flow out of an upper end of the shroud, wherein said at least one upper outlet opening may be closable.

Preferably said closable outlet opening is openable by means of an actuation system in response to the temperature of the water adjacent the upper end of the shroud. In one embodiment, the actuation system might be a bi-metal strip or similar temperature responsive actuator, such that the at least one upper outlet opening is automatically opened when the temperature of water adjacent the upper end of the shroud exceeds a predetermined level.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-Figure 6 is a perspective view of an immersion heat exchanger according to a first embodiment of the present invention; Figure 7 is an exploded view of the immersion heat exchanger of Figure 6; Figure 8 is a perspective view of a lower end of the immersion heat exchanger of Figure 6; Figure 9 is a detailed sectional view of a lower end of the immersion heat exchanger of Figure 6; Figure 10 is a detailed sectional view of an upper end of the immersion heat exchanger of Figure 6; Figure 11 is a perspective view of an upper section of an immersion heat exchanger according to a second embodiment of the present invention shown in an open configuration; Figure 12 is a perspective view of the upper section of the immersion heat exchanger of Figure 11 in a closed configuration.

An immersion heat exchanger 100 according to a first embodiment of the present invention is shown in Figures 6 to 11. The immersion heat exchanger 100 has an outer diameter dimensioned to be inserted through the standard threaded aperture 10 provided in a hot water tank 1 of a central heating system for insertion of an electric immersion heater, as shown in Figure 3. Thus the immersion heat exchanger 100 can be easily retrofitted to an existing hot water tank ito enable connection of an auxiliary heat source to the hot water tank 1, such as a solar heater or a heat pump or any other additional source of heat. In this way, the immersion heat exchanger 100 is similar to the known auxiliary heat exchanger coil i2 shown in Figure 4. Where the tank is not provided with such a threaded aperture or such aperture is in use, a hole may be cut into an upper region of the tank and a suitable flange may be attached to the resulting hole, for example by means of a clamping arrangement or by welding or brazing, said flange being provided with a threaded aperture adapted for receiving the immersion heat exchanger.

The immersion heat exchanger 100 comprises heat exchange coil 102 is disposed within a coaxially arranged substantially vertically or near-vertically arranged tubular shroud 104 such that a natural convection current generated by the heating or cooling effect of a heat exchange fluid passing through the coil 102 causes the water within the tank to flow through the shroud from a lower to an upper end thereof while being confined by the shroud to the vicinity of the heating coil.

The shroud 104 has an open lower end defining an inlet opening 106 for allowing water to flow into a lower end of the shroud 104 and a plurality of apertures 108 provided in the side of the shroud adjacent an upper end thereof defining outlet openings allowing heated water to pass out of the upper end of the shroud 104. Alternatively an outlet opening may be defined by an open upper end of the shroud.

An upper end of the shroud 104 may connected to a plug 110 adapted for insertion into the aperture provided in an upper region of the tank 1 for an electric immersion heater, the plug 110 is provided with a threaded portion adapted to engage a corresponding threaded region of the aperture of the tank 1. The tubular shroud 104 is made from a thermally insulating or heat non-conducting material, such as a high temperature elastomeric material. Alternatively the shroud may be mounted directly onto the heat exchange coil of the heat exchanger.

The second heat exchange coil 102 comprises a elongate tube wound in a helical or near-helical fashion, the heat exchange coil 102 having a heat exchange fluid inlet 112 at a first end and a heat exchange fluid outlet 114 at a second, distal end, a return conduit 116 extending from said second end of the heat exchange coil 102 to said first end to terminate adjacent said heat exchange fluid inlet 112. The return conduit 116 is disposed coaxially within the heat exchange coil 102. Preferably the return conduit 116 is thermally insulated to prevent heating of the fluid within the return conduit by hot water in an upper region of the tank.

In use, hot water from a source of heat, such as a solar heater, is passed into the heat exchange fluid inlet 112 of the heat exchange coil 102 and heats the water within the shroud 104. This in turn cools the water within the heat exchange coil 102 which passes out of the heat exchange fluid outlet 112 at the lower end of the heat exchange coil 102 and into the return conduit 114 to pass back out of the tank through the plug 110. As the cooled water passes back up the return conduit 114, there is a risk that it will extract heat from the heated water in the upper region of the shroud 104, which may be at a higher temperature than the water in the return conduit 114 due to the temperature stratification of the water within the tank 1. To avoid this, the return conduit 114 may be covered in a sleeve 116 of thermally insulating material to prevent heat transfer between the water in the return conduit 114 and the water in the shroud 104. In an alternative embodiment, the return conduit 114 may be formed from a thermally insulating or non-heat conductive material.

An electrical heating element (not shown) may be provided within the shroud 104, alongside or within the heat exchange coil 102 to provide additional electrical heating of the water within the shroud 104.

In an alternative embodiment, the outlet opening 208 at the upper end of the shroud 204 may be closable to prevent reverse syphonic flow where the fluid temperature is the heat exchanger becomes less than that of the fluid within the tank (or vice versa where the device is being used for cooling). Preferably said closable outlet opening 208 is openable by means of an actuation system in response to the temperature of the water adjacent the upper end of the shroud 204. In one embodiment, the actuation system may comprise a bi-metal strip or similar temperature responsive actuator, such that the upper outlet opening 208 is automatically opened when the temperature of water adjacent the upper end of the shroud exceeds a predetermined level. The actuation system may be associated with the plug 210 or the shroud 204 and may act against the shroud, or between the shroud 204 and the plug 210 to open and close the opening 208.

An immersion heat exchanger in accordance with an embodiment of the present invention creates a convective action within the tank thus immediately heating the water at the top of the tank to the maximum possible transferred temperature the hot water from the source enters the coil of the exchanger from the top and exits at a position further down the tank -preferably close to the bottom of the tank i.e. the hottest water in the coil is at the hottest region of the tank the return pipe from the coil is coated in an thermally insulating material (or could be formed from a thermally non conductive material) to ensure less heat-pick up as the water leaves the tank and therefore better performance and efficiency from the device there is an outer tube on the device made from a thermally insulated or non conductive material to encourage convective flow. The outer tube may or may not be touching the heat exchange coil 35. the complete device is not integral to the tank. It is introduced through an existing aperture in the tank and thus can be readily and easily retrofitted to an existing tank without requiring draining of the existing tank.

The apparatus may incorporate an electrical heating element to perform as an electrical immersion heater. Whilst aimed at domestic installation, particularly retro-fit applications, the invention could be used in any liquid tank where the temperature of the fluid therein is to be controlled. The tubular components of the heat exchanger coil may be made of copper. Alternatively other materials, such as brass, stainless steel or plastics, may be used to allow the device to be used in other liquid situations, such as food or chemical production. In addition to being used with a hot fluid in the heat exchanger coil, the device could have cold fluid in the coil and thus be used to reduce the temperature of the fluid in the tank.

The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims

Claims 1. An immersion heat exchanger for a hot water tank adapted for insertion into said hot water tank, said heat exchanger comprising a heat exchange conduit having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, a return conduit extending from said second end of the heat exchange conduit to said first end to terminate adjacent said heat exchange fluid inlet, wherein said return conduit is formed from, or is covered or coated with, a thermally insulating or non-heat conductive material.
2. An apparatus as claimed in claim 1, wherein the heat exchanger is adapted for insertion into an aperture provided in an upper region of the tank, such aperture typically being provided for insertion of an electric immersion heater.
3. An apparatus as claimed in claim 2, wherein said fluid inlet and return conduits extend through a plug adapted to be received within and close said aperture.
4. An apparatus as claimed in claim 3, whererin the plug is threaded to be received in a corresponding threaded aperture provided in the tank.
5. An apparatus as claimed in any preceding claim, wherein the heat exchange conduit is disposed within a coaxial substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect of the heat exchange fluid within said heat exchange conduit causes the water being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the heat exchange conduit.
6. An apparatus as claimed in claim 5, wherein the shroud is coated in or formed from a thermally insulating or non-heat conductive material.
7. An apparatus as claimed in claim 5 or claim 6, wherein said shroud comprises at least one lower inlet opening for allowing water to flow into a lower end of the shroud and at least one upper outlet opening for allowing water to flow out of an upper end of the shroud.
8. An apparatus as claimed in claim 6, wherein said inlet opening comprises an open lower end of the shroud
9. An apparatus as claimed in claim 7 or claim 8, wherein the at least one upper outlet opening is defined by apertures provided in the side of the shroud adjacent an upper end thereof and/or by an open upper end of the shroud.
10. An apparatus as claimed in any one of claims 7 to 9, wherein at least one of said at least one upper outlet openings is closable.
11. An apparatus as claimed in claim 10, wherein said closable outlet opening is openable by means of an actuation system in response to the temperature of the water adjacent the upper end of the shroud.
12. An apparatus as claim in claim 11, wherein the actuation system comprise a bi-metal strip or similar temperature responsive actuator, such that the at least one upper outlet opening is automatically opened when the temperature of water adjacent the upper end of the shroud exceeds a predetermined level.
13. An apparatus as claimed in any preceding claim, wherein the heat exchange conduit comprises an elongate tube wound in a helical or near-helical fashion to define a heat exchange coil.
14. An apparatus as claimed in claim 13, wherein said return conduit is disposed coaxially within said heat exchange coil.
15. A fluid heating apparatus comprising a body defining a chamber for containing a volume of fluid to be heated, the chamber having a fluid inlet and a fluid outlet spaced apart in a first axial direction; a first heat exchange coil being located in said chamber between said fluid inlet and fluid outlet through which a heating medium may be passed to heat said fluid contained within the chamber by means of a primary heat source, an aperture being provided in an upper region of the chamber into which is inserted a second heat exchange coil, said second heat exchange coil having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, a return conduit extending from said second end to said first end to terminate adjacent said heat exchange fluid inlet, wherein said return conduit is formed from or is covered or coated in a thermally insulating material.
16. An apparatus as claimed in claim 15, wherein the volume of fluid contained within the body comprises water for use in a domestic water heating and/or central heating system.
17. An apparatus as claimed in claim 16, wherein the second heat exchange coil is disposed within a substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect causes the medium being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the second heat exchange coil.
18. An apparatus as claimed in claim 17, wherein the second heat exchange coil comprises a elongate tube wound in a helical or near-helical fashion, said return conduit being disposed coaxially within said coil.
19. An immersion heat exchanger for a hot water tank, said immersion heat exchanger being adapted to be inserted into said hot water tank, said heat exchanger comprising a heat exchange conduit having a heat exchange fluid inlet at a first end and a heat exchange fluid outlet at a second, distal end, the heat exchange conduit being disposed within a coaxial, preferably substantially vertically or near-vertically arranged shroud such that a natural convection current generated by the heating or cooling effect causes the medium being heated or cooled to flow within the shroud while being confined by the shroud to the vicinity of the heat exchange conduit, said shroud comprising at least one lower inlet opening for allowing water to flow into a lower end of the shroud and at least one upper outlet opening for allowing water to flow out of an upper end of the shroud, wherein said at least one upper outlet opening may be closable.
20. An immersion heat exchanger as claimed in claim 19, wherein said closable outlet opening is openable by means of an actuation system in response to the temperature of the water adjacent the upper end of the shroud.
21. An immersion heat exchanger as claimed in claim 20, wherein the actuation system might be a bi-metal strip or similar temperature responsive actuator, such that the at least one upper outlet opening is automatically opened when the temperature of water adjacent the upper end of the shroud exceeds a predetermined level.