GB2270369A - Electric instantaneous water heater - Google Patents

Abstract

A heat exchanger for an instantaneous water heater has one or more coiled electric heating elements 2, 3 in a tank 1 provided with an inlet deflector 8 at one end for producing swirling movement of water through the tank 1 and an outlet deflector 11 at the other end for directing outflowing water over a thermal cut-out switch 10 for the heating elements 2, 3. The heat exchanger has a pressure relief valve 17, a flow sensor whereby elements 2, 3 are switched on only when there is a predetermined water flow through the tank 1, and means for maintaining constant the water flow rate. In an alternative construction, the heating elements may be located side by side or concentrically. <IMAGE>

Description

HEAT EXCHANGER This invention relates to heat exchangers, particularly heat exchangers for use in instantaneous electric water heaters for ablutionary appliances such as showers.

In an instantaneous electric water heater, water is heated as it flows through a heat exchanger containing one or more heating elements and the user selects the power input to the heat exchanger and adjusts the water flow rate to obtain the desired outlet water temperature.

For application to ablutionary appliances such as showers, it is desirable for the heat exchanger to have a low volume relative to the surface area of the heating elements for efficient heat transfer and fast response to adjustments to the flow rate and/or power input.

It is already known to provide compact heat exchangers by the use of one or more coiled heating elements. A disadvantage of such heat exchangers is that fluctuations in the temperature of the outflowing water can occur due to thermal currents rising of the heating elements. Such temperature fluctuations may be noticeable by the user and create problems in siting a thermal switch for interrupting the power supply to the heating elements if an unsafe water outlet temperature is obtained, for example due to malfunction.

Another disadvantage of compact heat exchangers is that there is only a small volume of water to absorb the residual heat in the heating elements when the water flow is stopped which can result in the accumulation of very hot water that is discharged first when re-starting the water flow as a hot-shot which the user may not expect. This is a particular problem if there is only a short delay between stopping and re-starting the water flow.

The present invention has been made from a consideration of the problems and disadvantages above-discussed.

According to the present invention there is provided a heat exchanger for an instantaneous water heater having a water inlet, a water outlet, at least one coiled heating element, and a deflector for at least one of the inlet and outlet.

Preferably, the inlet and outlet each have an associated deflector for the inflowing and outflowing water respectively. Advantageously, the inlet deflector is arranged to direct the inflowing water around the heat exchanger. In this way, the water is stirred as it flows through the heat exchanger so that fluctuations in the outlet water temperature are reduced and, on stopping water flow, the residual heat in the heating element(s) is dissipated more evenly so that the effects of hotshot on re-starting are reduced.

Preferably, the outlet deflector is arranged to collect outflowing water over a wide area and direct it over a surface on which a thermal safety cutout switch for the heating element(s) is mounted. In this way, inaccuracies in the response of the switch to the water outlet temperature are reduced.

Conveniently, the outlet deflector is outwardly flared with a peripheral rim portion located adjacent to a surface of the heat exchanger on which the switch is located opposite the outlet.

The invention will now be described in more detail by way of example only with reference to the accompanying drawing wherein: FIGURE 1 is a longitudinal section through a heat exchanger embodying the present invention; and FIGURE 2 is a section on the line 2-2 of Figure 1.

The heat exchanger shown in the drawings comprises a generally cylindrical tank 1 containing upper and lower coaxial coiled heating elements 2 and 3 respectively each comprising a conductor surrounded by an insulating sheath.

The tank 1 is formed by securing flanged end plates 4,5 to the opposite ends of a length of copper tube, for example by soldiering.

The terminals 23,3a of the upper and lower heating elements 2,3 extend through the top and bottom plates 4,5 respectively for connection to the electrical supply and are secured to the associated plate, for example by soldering.

The bottom plate 5 is pierced by an inlet pipe 6 for connection to the cold water supply, and by an outlet pipe 7 for connection via a hose (not shown) to a spray head, shower handset or other ablutionary appliance (not shown).

Each pipe 6,7 is offset from the central longitudinal axis of the tank 1 as shown in Figure 2 and is secured to the bottom plate 5, for example by soldering.

The inlet pipe 6 terminates adjacent to the bottom plate 5 and is provided with a deflector 8 to direct the inflowing water around the tank 1.

In this embodiment, the deflector 8 is formed integrally by cutting, flattening and bending the end of the inlet pipe 6 but it will be understood that this is not essential and that the deflector 8 could be a separate element secured to the end of the inlet pipe 6.

The outlet pipe 7 extends through the centre of the heating elements 2,3 and terminates adjacent to the top plate 4 opposite a raised platform 9 on which a thermal safety cut-out switch 10 for the heating elements 2,3 is mounted.

The free end of the outlet pipe 7 is provided with an outwardly flared deflector 11 to collect the outflowing water over a wide area. The deflector 11 has an annular rim 12 that is received in a recess 13 formed by the raised platform 9 and is located by three circumferentially spaced lugs 14.

In this embodiment, the deflector 11 is formed by a funnel 15 secured to the free end of the outlet pipe 7, for example by soldering, but it will be understood that this is not essential and that the deflector 11 could be formed integrally by flaring the end of the outlet pipe 7.

The heat exchanger is suitable for use in an instantaneous water heater having user operable controls (not shown) for selectively energising one or both of the heating elements 2,3 to vary the power input and for adjusting the water flow rate to heat the water flowing through the tank 1 to a selected temperature with the thermal switch 10 being operable to interrupt the power supply to the heating elements 2,3 at a pre-determined water outlet temperature higher than that for comfortable showering to reduce the risk of the user being scalded.

The inlet deflector 8 imparts a swirling motion to the inflowing water promoting turbulence and stirring of the water flowing through the tank 1. In this way, hot thermal currents are mixed with cooler water within the tank 1 so that oscillations in the temperature of the outflowing water are reduced.

The swirling action of the inlet deflector 8 is also beneficial in reducing the problem of hot-shot by ensuring that stirring of the water continues for a while when the water flow is stopped and the heating elements 2,3 switched off. In this way, the residual heat in the heating elements 2,3 is dissipated more evenly preventing the accumulation of a small volume of very hot water at the top of the tank 1.

The outlet deflector 11 collects the heated water at the top of the tank 1 over a wide area and causes the water to flow over the surface 16 of the raised platform 9 on which the thermal switch 10 is mounted. In this way, the surface 16 is substantially at the same temperature as the outflowing water so that inaccuracies in the temperature sensed by the thermal switch 10 are reduced.

The heat exchanger is also provided with a pressure relief valve 17 mounted in a recessed portion of the tank 1 for relieving excess pressure within the tank 1, for example if the heating elements 2,3 are switched on with outlet blocked or with insufficient water flow.

Yet another safety feature may be provided by a flow sensor (not shown) arranged to control the power input to the heat exchanger so that the heating elements 2,3 are switched on only when there is sufficient water flow through the tank 1.

An additional safety feature may be provided by a flow stabiliser (not shown) arranged to maintain constant a selected flow rate so that the outlet water temperature is unaffected by fluctuations in the water supply pressure.

As will be appreciated from the foregoing description of the exemplary embodiment of the invention, the provision of the deflectors 8,11 on the inlet and outlet pipes 6,7 enables the volume of the tank 1 to be kept small for obtaining a fast speed of response to changes in the water flow rate and/or power input whilst providing the desired operating characteristics of steady outlet temperature, moderate hot-shot and accurate response of the thermal switch 10 to the outlet temperature.

It will be understood that the invention is not limited to the embodiment above-described. For example, only one of the inlet and outlet pipes may be provided with a deflector. Also, the heat exchanger tank may be of any suitable construction with one, two or more coiled heating elements arranged in any desired configuration such as twin coiled heating elements located side by side or concentrically.

Claims (12)

Claims

1. A heat exchanger for an instantaneous water heater comprising a water inlet, a water outlet, at least one coiled heating element, and a deflector for at least one of the inlet and outlet.

2. A heat exchanger according to Claim 1 wherein the inlet and outlet are arranged at opposite ends of the heat exchanger.

3. A heat exchanger according to Claim 1 or Claim 2 further comprising a respective deflector for each of the inlet and outlet.

4. A heat exchanger according to any one of the preceding Claims wherein the or each deflector is provided at the end of an inlet pipe and/or an outlet pipe for the inlet and outlet respectively.

5. A heat exchanger according to any one of the preceding Claims wherein the inlet deflector is arranged to direct inflowing water around the heat exchanger.

6. A heat exchanger according to any one of Claims 1 to 4 wherein the outlet deflector is arranged to direct outflowing water over a thermal safety cut-out switch for the heating element(s).

7. A heat exchanger according to Claim 6 wherein the outlet deflector is outwardly flared with a peripheral rim portion located adjacent to a surface of the heat exchanger on which the switch is located opposite the outlet.

8. A heat exchanger according to any one of the preceding Claims further comprising a pressure relief valve for relieving excess pressure.

9. A heat exchanger according to any one of the preceding Claims further comprising a flow sensor arranged to control the power input to the heat exchanger.

10. A heat exchanger according to any one of the preceding Claims further comprising a flow stabiliser arranged to maintain constant a selected flow rate.

11. A heat exchanger for an instantaneous water heater substantially as hereinbefore described with reference to the accompanying drawing.

12. An instantaneous water heater incorporating a heat exchanger according to any one of the preceding Claims.