GB2493753A - Heat cable for preventing water freezing in pipes - Google Patents

Abstract

The invention relates to an electric heat cable 2 which prevents water freezing in pipes. The heat cable is dimensioned to fit within a pipe with an internal diameter of from about 9mm to about 15mm without substantially restricting flow in the pipe and capable of emitting sufficient heat to prevent freezing of water in the pipe in freezing conditions. The heat cable has a protective insulative and waterproof outer sheathing 22, and may have two conductors 23 for conducting electricity, a heating wire 14 with an insulating sheath layer separating the conductors from the heating wire, and at least one contact point 25 between the heating wire and each of the conductors. Later embodiment relates to a system comprising said heat cable, a temperature sensor (6 figure 1) and a thermostat (4 figure 1).

Description

Freeze Protection

Field of the Invention

[0001] The present invention relates to preventing water freezing in pipes. More particularly, the invention relates to a heat cable which can be placed into a water pipe to provide sufficient heating within the pipe to prevent water freezing in cold temperatures.

Background to the Invention

[0002] It is a common problem in many parts of the world that cold weather can lead to the freezing of pipes. Most vulnerable are those pipes which run externally of the building, for example to a mains supply. Mains supply pipes, which provide mains water supply to homes and businesses, tend to be sufficiently large and with sufficient flow to prevent complete freezing. However a take-off pipe from the mains is used to supply water to individual premises and is typically much smaller in diameter and therefore has a greater tendency to freeze. It is also typically a non-flowing system for much of the time, especially during the night when the lowest daily temperatures occur. At least part of the pipe typically runs underground from a junction with the mains, for example at a stop cock, to the interior of the building, for example a water tank The pipe has a greater tendency to freeze where it is above or close to ground surface so for example it will tend to freeze where it comes above the surface to enter the interior of the building. Frozen pipes prevent water from reaching taps and in the most severe case, frozen pipes can lead to the pipes becoming cracked and broken as the water in the pipes expands upon freezing. Once thawed severe leaks can occur, so the supply has to be turned off.

[0003] A known measure to prevent pipe freezing is pipe insulation. Insulating sleeves are designed to slide over the pipe to be protected. Such insulation is most suitably installed when the water supply is being installed. The solution can also be retro-fitted to pre existing pipes but it is considerably more difficult. When retro-fitting, the insulating sleeve must be cut along its length and then resealed with adhesive tape or other bonding substance. Resealing in this manner makes the insulation less effective than an uncut sleeve. Gaps in the insulation can lead to cold areas in pipes which can freeze quickly in cold weather and cause blockages. Such insulation sleeves are made from a variety of materials and come in many thicknesses. Many such solutions offer a very low level of insulation and do not afford protection against freezing in prolonged cold weather conditions.

[0004] Active frost protection, in the form of trace heating, is another method of protection preventing freezing pipes. Trace heating uses electrical cable, which heats up when an electrical current is passed through it. The cable is wound around the exterior circumference of pipes to prevent them freezing or to keep them at correct working temperature. Both the pipe and cable are then wrapped in insulation. The trace heating is usually switched on and off by a thermostat, which can be adjusted up or down. Other such systems operate as always on' with the amount of current passed through the cable rising and falling in response to temperature changes. This is not an efficient use of energy and can also lead to overheating of the pipes as well as melting or burning of the insulation. As with sleeve insulation, a trace heating system is ideally fitted when the piping to be protected is installed. Retro-fitting of such a system can be costly, especially when pipes have been buried for example beneath paved surfaces such as beneath concreted areas, and will often require expertise in wiring and installation.

[0005] Another method of preventing freezing in pipes is to place a heating element! often in the form of an electrical cable, into the pipe to be protected. GB 2470519 discloses a device which is placed into a condensate drain pipe and is heated to prevent liquid in the pipe from freezing.

Such pipes are used to dispose of condensate resulting from the operation of devices such as boilers, freezers, refrigerators and air-conditioners. Condesate pipes are quite short in length, generally running from an outlet of a device to the exterior of a building. There is no suggestion that such an arrangement would be suitable for preventing freezing in much longer lengths of pipe.

[0006] The prior art devices also designed to operate at mains (240V) voltage which represents a substantial risk to any person who inadvertently is exposed to such a voltage.

[0007] A device or system which provided heat to prevent freezing of pipes in cold temperatures would be an improvement over the state of the art. A further advantage would be if the device or system was easily pre-installed or just as easily retro-fitted to existing pipes.

Summary of the Invention

[0008] The present invention comprises a heat cable surrounded by a protective electrically insulative and waterproof outer sheathing layer and being dimensioned to fit within a pipe with an internal diameter of between 9mm and 15mm without substantially restricting flow in the pipe and capable of emitting sufficient heat to prevent freezing of water in the pipe in freezing conditions. None of the devices of the prior art are suitable for such an application because the cables dimensions provide a particular advantage of the invention. The cable has the advantage of being able to be fed or retro-fitted through a pipe with a relatively small (internal) diameter.

The cable can be fitted into pipes having internal diameters of less than 15mm, most preferably having diameters between about 9 mm and about 12 mm. The cable can be fitted into pipes with a hydraulic diameter of 6.5mm. This has the advantage of allowing the cable to operate in very narrow pipes without substantially restricting the flow of water through the pipes or the pressure at taps fed by the pipes. The cable would fit in a narrow gauge pipe (so called 1/2 inch pipe" of 12mm approx.) common for water supply some regions e.g. in Republic of Ireland and United Kingdom.

[0009] The cable may further comprise within the protective electrically insulative and waterproof outer sheathing layer: two conductors for conducting electricity; an insulating sheath layer separating the conductors from a heating wire; a heating wire; a plurality of contact points between the heating wire and the conductors wherein the heating wire is wound about the insulating sheath of the conductor. The outer layer prevents water from entering the inside of the cable and making contact with the heating wire. The two conductors will typically be two sheathed wires. Desirably the sheathed wires are each sheathed in a single sheath arrangement which holds the wires side-by-side but electrically insulated from each other.

[0010} Each conductor or wire of the cable may comprise a plurality of conducting strands.

[0011] Each conductor of the cable may be comprised of a single conducting strand, for example a single wire. This has the advantage of providing greater rigidity to the heat cable to allow for easier retro fitting into a pipe.

[0012] The cable is desirably constructed to have a maximum dimension of about 4mm to about 9mm.

[0013] The cable is desirably constructed to have a maximum dimension of about 5mm to about 7mm. The maximum dimension is defined by the maximum width or height from one external surface of the cable to the opposing external surface of the cable. The maximum dimension does not include the length of the cable, which may be varied according to its use in different pipes.

[0014] The cable is desirably constructed to have an operating wattage of from about 3W to about 40W per metre. The wattage of the cable may from about 6W to about 15W per metre.

The wattage of the cable may be about 7W per metre. This has the advantage of allowing the cable to effectively prevent pipes from freezing for a range of wattages.

[00151 The heat cable may have a range of operating voltages. Operating the cable at a low voltage (c75V) provides the advantage of allowing the cable to operate without an earth braiding layer typical of high voltage (-240V) heat cables. Constructing the heating cable of the invention without an earth braid and for operating at relatively low voltages is very significant as compared to a high voltage 240V electric mains heating cable it is significantly smaller in diameter. The diameter of a cable of the invention is sufficiently small to allow it fit into relatively narrow piping without significantly obstructing water flow in the pipe but at the same time preventing freezing. It would not be viable to operate a mains (240 Volt) heating cable as removing the earth braid would render the cable unsafe to users. By operating at a low voltage, it is possible to operate the cable safely even though it is constructed with no earth braid.

[0016] By operating at a low voltage, it is possible to construct and operate the cable of the invention safely without an earth braid but also, omitting the earth braid also allows the construction of the cable of the invention without a layer of insulation found in priol art constructions that protects the earth braid from the conductors and the heating element wire.

Thus, the cable diameter is reduced further as compared to the prior art.

[OOIT} The heat cable may have an operating voltage of up to about 75V.

[0018] The heat cable may have an operating voltage from about 1OV to about 60V.

[0019] The heat cable may have an operating voltage from about 24V to about 55V.

[0020] The heat cable may have an operating voltage of about 48V. Such operating voltages mean that the cable of the invention has the advantage of being a safe level for humans to be in contact with without the risk of death or serious injury from electrical shock. This safety feature is particularly important for cables that are inside a water pipe that is already buried in the ground. It is also safe from the perspective of human interaction with the water that is supplied to the user from the water mains supply. A further advantage of allowing the cable to operate at a low voltage or less than mains voltage is that it saves on energy costs. The risk of the cable overheating is also reduced. Nowhere in the prior art has it been appreciated that such a cable can be constructed and operated with the voltages/wattages of that of the present invention, all while achieving the desired aim of freeze prevention without substantially restricting water flow in the pipe.

[0021] The operating voltage of the heat cable may be AC.

[00221 The operating voltage of the heat cable may be DC.

[0023] The heat cable may have an operational length without substantial power loss of up to SUm. Typically a cable of the invention will be from about 2 to about 50 metres.

[0024] The heat cable may have an operational length without power loss of 35m. This allows the system to effectively prevent pipes from freezing over a considerable length. The cable of the invention can be constructed to be from about 2 to about 50 metres, for example from about 3 to about 40 metres, for example from about 4 to about 37 metres.

[0025] The heating cable of the invention will be constructed to be sufficiently rigid to allow insertion into a pipe of the desired length without having it fold or bend upon itself. As stated above the cable of the invention can be constructed to be from about 2 to about 50 metres, for example from about 3 to about 40 metres, for example from about 4 to about 37 metres so it will be constructed to allow insertion from one end of the pipe length and for the cable to be heated along sufficient length to prevent freezing.

[0026} Desirably the outer sheathing layer is made from polyethylene. Typically the outer sheathing layer is from about 0.5mm to 2mm in thickness with 1mm being preferable.

[0027] The present invention also provides a system for preventing freezing of water in pipes.

The system may comprise a temperature sensor for sensing the air temperature; a heater for heating the pipe; a thermostat for activating the heater when the temperature sensed by the sensor falls below a threshold value and a transformer for controlling the operating voltage of the heater wherein the heater is a cable of the present invention dimensioned for insertion and operation within the pipe. This has the advantage of conserving power by allow the system to operate at a low voltage and by only passing current through the cable at temperatures cold enough to require freeze protection.

Brief Description of the Drawings

[0028] Figure 1 shows a circuit diagram of the system [0029] Figure 2 shows the system installed on a mains water connection to a tap [0030] Figure 3 shows the heat cable placed within a pipe [0031] Figure 4 shows the component parts of the heat cable

Detailed Description

[0032] The present invention will now be described with reference to the accompanying drawings.

[0033] Figure 1 shows a circuit diagram of a system for preventing freezing of water in pipes.

The system 1 will be described with reference to this diagram. The system 1 consists of a heat cable 2, a transformer 3, a switching thermostat 4 and a temperature probe 5 A sensor 6 at the tip 7 of the temperature probe 5 monitors the external temperature. A switching thermostat 4 controls the circuit 8. A display 9, e.g. LCD display, shows the temperature at the sensor 6. If the air temperature falls below a threshold temperature (which can be preset or adjusted by a user), for example 1 degree Celsius, the thermostat 4 switches on. With the thermostat 4 on, current 10 flows through the circuit 8. An amp fuse, for example a 3.15 amp fuse 11, limits current 10 in the circuit 8. A transformer 3 drops the mains voltage of 240V down to a suitable low operating voltage, for example 48 V. The heat cable 2 is operated at this low operating voltage. The heat cable 2 is located inside a take off pipe 12 which connects the external mains water supply 13.

[0034] If the external temperature rises above a threshold temperature, for example 5 degrees Celsius, the thermostat 4 switches off. With the thermostat 4 off, no current 10 flows through the circuit 8. No current 10 is provided to the heat cable 2 and thus no heating is provided to the pipe 12.

[0035] Figure 2 shows the system in place at a take off pipe 12 from the mains water 13 connection to a building 15. The circuit 8, including the thermostat 4 and the transformer 3 are located within an enclosure 28. The temperature probeS is placed outside the building 15 and connects through an external wall 16 of the building 15 to the switching thermostat 4 which is generally placed inside the building 15. The cable 2 may be inserted into the pipe 12 at a junction 17 between the external pipe 12 (which connects to the external water mains 13) and a pipe 18 connecting the thermostat 4 to a tap 19. A particular advantage of the system 1 is that it is straightforward to install the cable 2 by feeding it into the external water mains pipe 12. This prevents removal of floors 20 and prevents the need for earthworks if the pipe 12 is substantially beneath the floor 20 of the dwelling and/or under the ground 21.

[0036] Figure 3 shows a close up of the cable 2 placed within the pipe 12. The cable 2 is sufficiently narrow to fit into narrow gauge pipes commonly used for mains water supply 13 in the UK and Ireland. However, the cable 2 also occupies a sufficiently low amount of space to prevent the water supply from being substantially restricted. When placed inside of a pipe 12, the cable 2 will not cause a substantial restriction in the flow of water through the pipe.

Therefore, there is not appreciable loss in water pressure at the taps 19 fed by the pipe 12. The percentage of the pipe cross sectional area which is consumed by the cable is preferably less than 60%, for example 40% to 60%, or 20% to 40% or for example 22%. In a particular embodiment, a cable 2 with an oval shaped cross sectional area of 27.5mm2 placed in a pipe 12 of with a circular cross sectional area of 122.7 mm2 will result in a flow cross sectional area of 95.2 mm2 or 78% of the pipe cross sectional area, i.e. the cable occupies the remaining 22% of the cross sectional area. The hydraulic diameter of such a system is 6.5mm.

[0037] A hydraulic diameter of 6.5 mm is derived as follows: A cable has an oval cross section with major and minor dimensions of 7mm by 5 mm and is to be fitted into a pipe with circular cross section of internal diameter 12.5mm.

Area of an oval shape is lt*A*B where A is half the major dimension and B is half the minor dimension.

For 7mm by 5mm oval, A = 3.5 and B = 2.5 Thus n(3.5)(2.5) = 27.5mm2 (cross-sectional area of cable) The perimeter of an oval is r j3(A + B) -(3A + B)(A + 3B) } In this case, m + 2.5)-(3(3.5) + 2.5)(3.5 + 3(2.5))} = 19.0 mm (cable perimeter) Hydraulic diameter = 4 * flow cross-sectional area I wetted perimeter Flow cross-sectional area = [pipe area -cable area] Wetted perimeter = [Pipe circumference + cable circumference] For pipe of internal diameter 12.5 mm: (m14)(l2.5) = 122.7 mm2 (Pipe cross-sectional area) m(l2.5) = 39.3 mm (Pipe Perimeter) [122.7-27.5] = 95.2 mm2 (Flow cross-sectional area. Note: 78% of pipe area) [39.3+19.0] = 58.3 mm (Wetted perimeter) Therefore hydraulic diameter = 4(95.2/58.3) = 6.5 mm [0038] In such a case, with a hydraulic diameter of 6.5mm, flow tests indicate a flow reduction of 20% over 35 metres given the cross sectional dimension ratio of the cable inside the pipe. In accordance with the present invention a flow reduction of 50% or more would result in an appreciable loss in water pressure, for example at taps, and would be considered a substantial restriction in flow.

[0039] Figure 4 shows the component pads of the cable 2. The cable 2 comprises an outer insulation layer 22, heating wire 14 and two conductors 23 each with an insulating layer 24 which is unitary and holds the heating wires_14 together and in a side-by-side arrangement.

There are a number of contact points 25 along the conductor 23 where a gap 26 in the respective insulating layers 24 of the conductors 23 allows contact between one conductor 23 and the heating wire 14 at any given contact point 25. This allows heating of the heating wire 14 as current 10 is passed through the conductors 23. The preferred distance between the contact points 25 is 50 cm. The length of the gap 26 in the insulating layer 24 which forms the contact points 25 is preferably from 2 to 12mm, for example 4 to 10 mm or 6 to 9 mm for example about 8mm. A length of 15mm is standard on higher voltage cables. Reducing the length to 8mm results in increased rigidity of the cable. In a particular embodiment, the cable has an oval shaped cross sectional area with external dimensions of 5mm diameter on the minor axis and 7mm diameter on the major axis. In a particular embodiment, the outer nsulation layer 22 consists of Polyethylene (PE) or PVC. PE is preferred as it has more suitable waterproofing and electrical insulating properties. PE insulation provides sufficient rigidity for retro fitting of the cable 2.The conductors 23 of the cable 2 may be, for example, Tinned copper 0.75 mm2. In one embodiment, each conductor 23 of the cable may be comprised of a plurality of conducting strands 27 with seven strands being preferable. In another embodiment, the plurality of conducting strands may be replaced with a single conducting strand having the same diameter as the plurality of conducting strands. The single conducting strand provides greater rigidity to the cable 2 making it more suitable for fitting into pipes over longer distances, for example over metres. The heating wire 14 of the cable 2 may be, for example, Nickel-Copper. The conductor insulation 24 of the cable 2 may be, for example, silicon elastomer.

[0040] Prior art heating cables would have an earth braiding layer around the cable. Also in the prior art there may also be a further outer layer consisting of plastic or another shield material.

In the present invention however, the earth braiding layer and the outer layer are desirably omitted as this substantially reduces the dimensions of the cable 2 and allow it to be fit into more narrow piping than if the layers remained on. By operating at a low voltage, it is possible to construct and operate the cable 2 safely without an earth braid thereby reducing the diameter of the cable 2, allowing it to be fitted into more narrow gauge piping. Omitting the earth braid also allows the construction of the cable of the invention without a layer of insulation that protects the earth braid from the conductors and the heating element wire. Thus, the cable 2 diameter is

reduced further as compared to the prior art.

[0041] In a particular embodiment, the cable can tolerate a temperature of from -50°C to +80°C.

When placed in a pipe, current passing through the cable 2 heats the heating wire 14 of the cable which prevents water from freezing as it is passing through the pipe, and thus flowing around the cable 2.

[0042] A sealed end on the cable 2 protects the cable 2 from damage resulting from pressure due to the water flowing in the pipes. The sealed end may be made from an epoxy high resistant polymer. In a particular embodiment, the pressure on the cable 2 due to water flowing in the pipe may be 3 bar (300kPa) and the cable of the invention is designed to withstand immersion in water at such pressures for many years.

[0043] The cable 2 may be adapted to have a range of wattage values. It may be 3W to 40W per m, but suitably from 5W to 30W per m. A range of 6W to 15W per m is suitable. An operating wattage per linear meter of cable of 7W per metre is easily achievable.

[0044] The cable 2 may be adapted to operate at a number of different voltages. The operating voltage may be up to 75V but suitably from 1OV to 60V and for example, 24V or48 V. The cable 2 may be adapted to operate on AC or DC voltage.

[0045] The cable 2 may be adapted to operate for a range of lengths. At 24 V, the cable 2 may be adapted to operate for a length of up to 25m but 15m is preferred as beyond this length the voltage starts to drop and the cable stars to lose power per linear meter. At 48 V, the cable 2 may be adapted to operate for lengths of up to SUm but 35m is preferred as beyond this length the voltage starts to drop and the cable 2 starts to lose power per linear meter. In a particular embodiment, the operating voltage is 48 V. [0046] The cable 2 may be adapted to operate in pipes 12 with a range of dimensions. The cable 2 of the system may be fitted into pipes 12 with an internal diameter of less than 22 mm.

This means that the cable 2 can operate in very narrow pipes without significantly restricting the flow of water through the pipes. In a particular embodiment, the cable 2 is capable of being placed inside a pipe 12 of internal diameter 11mm to 12.1mm e.g. "Quality Plastics (CP) 1/2 inch Heavy Gauge". In another embodiment, the cable 2 is capable of being paced inside a pipe 12 of internal diameter 12.1 mm to 12.35 mm e.g. Quality Plastics (CP) 1/2 inch Normal". In another embodiment, the cable 2 of the system 1 is capable of being paced inside a pipe 12 of internal diameter 12.5mm e.g. "Wavin 1/2 inch Heavy Gauge". The preferred internal diameter of the pipe is 10.8mm to 13mm. This is particularly advantageous as it allows the cable 2 to operate effectively in the narrow gauge piping used for water supply in some regions e.g. Republic of Ireland and United Kingdom.

[0047] The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0048] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims (1)

1. <claim-text>Claims 1. A heat cable comprising a heating wire surrounded by a protective electrically insulative and waterproof outer sheathing layer and being dimensioned to fit within a pipe with an internal diameter of between about 9mm and about 15mm without substantially restricting flow in the pipe and capable of emitting sufficient heat to prevent freezing of liquid in the pipe in freezing conditions.</claim-text> <claim-text>2. The cable of claim 1 wherein the cable further comprises within the protective electrically insulative and waterproof outer sheathing layer: two conductors for conducting electricity; an insulating sheath layer separating the conductor from a heating wire; a heating wire; at least one contact point between the heating wire and each of the conductors; wherein the heating wire is wound about the insulating sheath.</claim-text> <claim-text>3. The cable of claim 2 wherein the conductor is comprised of a plurality of conducting strands.</claim-text> <claim-text>4. The cable of claim 2 wherein the conductor is comprised of a single conducting strand.</claim-text> <claim-text>5. The cable of any preceding claim wherein the maximum dimension of the cable is from about 4mm to about 9mm.</claim-text> <claim-text>6. The cable of any preceding claim wherein the maximum dimension of the cable is from about 5mm to about 7mm.</claim-text> <claim-text>7. The cable of any preceding claim where wattage of the cable is from about 3W to about 40W per metre.</claim-text> <claim-text>8. The cable of any preceding claim where wattage of the cable is from about 5W to about 30W per metre.</claim-text> <claim-text>9. The cable of any preceding claim where wattage of the cable is from about 6W to about 15W per metre.</claim-text> <claim-text>10. The cable of any preceding claim where wattage of the cable is about 7W per metre.</claim-text> <claim-text>11. The cable of any preceding claim where the operating voltage of the cable is up to 75V.</claim-text> <claim-text>12. The cable of any preceding claim where the operating voltage of the cable is from about by to about 60V.</claim-text> <claim-text>13. The cable of any preceding claim where the operating voltage of the cable is from about 24V to about 55V.</claim-text> <claim-text>14. The cable of any preceding claim where the operating voltage of the cable is 48V.</claim-text> <claim-text>15. The cable of any preceding claim where the operating voltage of the cable is AC voltage.</claim-text> <claim-text>16. The cable of any preceding claim where the operating voltage of the cable is DC voltage.</claim-text> <claim-text>17. The cable of any preceding claim where operational length of the cable without substantial power loss is up to 50m.</claim-text> <claim-text>18. The cable of any preceding claim where operational length of the cable without substantial power loss is 35m.</claim-text> <claim-text>19. A system for preventing freezing of water in pipes comprising: a temperature sensor for sensing the temperature; a heater for heating the pipe; a thermostat for activating the heater when the temperature sensed by the sensor falls below a threshold value; wherein the heater is the cable of any of the preceding claims.</claim-text>