GB2456881A

GB2456881A - Improvements in immersion heaters and their control

Info

Publication number: GB2456881A
Application number: GB0801933A
Authority: GB
Inventors: Nicholas Julian Jan Francis Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-02-04
Filing date: 2008-02-04
Publication date: 2009-08-05
Anticipated expiration: 2028-02-04
Also published as: GB2456881B; GB0801933D0

Abstract

A thermal store, electrical boiler or hot water tank, is provided with at least one immersion heater for insertion into a corresponding immersion heater boss. Each immersion heater comprises a plurality of individually controlled electric heating elements 1, 2. The total electrical load of each immersion heater is split between the elements, thus reducing the switching load of the immersion heater. The immersion heater elements are switched on/off by relays or thyristors (solid state relays) 19A, 19B under thermostatic control 16, 17. The thermostatic control incorporates an electrical "crowbar" circuit 21, triggered by a temperature limit thermostat 17, which actuates a normally latched closed contact relay device 20, such as a miniature circuit breaker (MCB). This generates an open circuit and provides electrical isolation of the immersion heater(s) and their relay/thyristor controls.

Description

THIS INVENTION RELATES TO:-

IMPROVEMENTS IN ELECTRIC IMMERSION HEATERS AND THEIR CONTROL

FOR THERMAL STORES

With the increased understanding of the advantages of thermal storage boilers and more especially electric thermal storage combi boilers of the type disclosed in patents GB91 18985.2 GB2423569A demand for them has increased. This increase in demand is because of better understanding of their flame, monoxide, and flue free, safe, economical operation. It is also because of their green credentials of reducing electrical generation wastage by enabling better load levelling and better base load use together with an ability to accept and store as heat the intermittent output of most alternative energy sources.

Demand for larger, higher output models has also increased to enable their use with larger properties.

To meet the higher output demands multiple immersion heaters are often used to heat the thermal store. However, multiple immersion heaters involve increased costs of the immersion heaters themselves together with the increased cost of providing more immersion heater tappings within the thermal store. Increased numbers of tappings also creates an increase in the risk of defects and leaks from the greater number of manufactured joints and immersion heater threaded joints in the thermal store.

An alternative to increasing the number of immersion heaters with their attendant increased cost and risk of leaks is to increase the wattage of each immersion heater. This typically involves increasing the standard domestic immersion heater output from 3kWatt to 6k Watt or more. However 6k Watt immersion heaters cannot be switched by standard domestic immersion heater thermostats but generally require thermostatic switching via relays that can cope with the heavier load. Such heavier load relays have to be generally housed separately from the immersion heaters. Such relays can be noisy in operation so they need to be sited away from noise sensitive areas. This is not always possible in a domestic environment as the typical favoured location to minimise dead leg draw off wastage from bathroom taps often dictates their location close to bathrooms that are close to bedrooms that are extremely noise sensitive.

Thyristor controls, or solid state relay (SSR) controls as they are commonly known, are a * silent answer to the problem of noise but they can carry the risk of failing in conducting *. state with an attendant risk of uncontrolled overheating damage and concomitant danger of injury. They also present problems for function checking by standard household :.. electricians test equipment often leading to diagnostic circuits being included by * manufacturers with their attendant cost, complication and service confusion. ***

It is the intention of the present invention to improve on or overcome the above *:*. mentioned problems.

This invention refers to twin or multi element immersion heaters. They are specifically side entry i.e. positioned in the vertical wall of the cylinder or thermal store and should

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not be confused with the commonly known dual immersion heaters having elements of dissimilar length specifically located in a top immersion heater boss. The dissimilar lengths of the elements enables standard domestic hot water cylinders to be bulk heated with a long element or a smaller amount of water at the top of the cylinder to be heated faster with the short element.

According to the present invention there is provided at least one immersion heater as may be suitable for insertion into at least one immersion heater boss of a thermal store said immersion heater being provided with at least two electrically heated elements said electrically heated elements being individually controlled so that the total electrical load of each immersion heater is split between each element reducing the individual load of its control.

Preferably the said individual elements are controlled by at least one relay contact whose coil is actuated by at least one thermostatic control being integral with or remote from the immersion heater.

Conveniently where loads permit the said individual elements may be switched by at least one thermostatic control having its sensing pocket integral with the immersion heater.

Advantageously the said individual elements are controlled by a thyristor control commonly known as a solid state relay actuated by at least one thermostatic control integral with or remote from the immersion heater.

Preferably any/all of the above control configurations incorporate an "electrical crowbar" circuit that actuates a residual current protection device causing it to open circuit and provide shut off protection additional to relay or thyristor controls.

Although the application of multi element immersion heaters is referred to in its application the thermal storage electric combi boilers this does not preclude its application to other electrical fluid heating applications for example large commercial hot water cylinders. * S.

Although for ease of description twinned 3kWatt element immersion heater units (ie each * immersion heaters having a 6kWatt total load comprising two 3kWatt elements) are described this does not preclude other multiples of element per immersion heater or other * :* element loads where circumstance requires/permits.

* Although for ease of description a single immersion heater application is described it should be understood that more than one immersion heater is commonly used and *:*. therefore multiple immersion heater use should not be precluded.

The invention will now be described by example with reference to the accompanying drawing in which:-* 3 DRAWING 1. Is a diagrammatic representation of a twin element immersion heater embodying a form of the present invention.

DRAWING 2. Is a diagrammatic representation of a typical thermostatic control arrangement that would be integral with the immersion heater.

DRAWING 3 Is a diagrammatic representation of a typical thermostatic control arrangement that would be remote from the immersion heater and would switch each element via at least one relay contact or thyristor solid state relay.

DRAWING 4 Is a diagrammatic representation of a "Crowbar Circuit" utilising the existing residual current device/s as may be incorporated with any of the thermostatic control systems of the immersion elements that form the present invention. This to provide an extra stage of safety shut off in the event of overheating occurring.

Preferred embodiments of the present invention are now described by example referring to the accompanying drawings in which: Figure 1 is a diagrammatic view of a twinned element immersion heater having heater elements I and 2 passing through threaded base plate 9 and having electrical connections 3 and 4 and earth connection 5, thermostat phial picket entries 6 and 7 pass through base plate and could be used to house thermostats integral with the immersion heater to sense the temperature of the fluid in the store at 6A and 7A.

Figure 2 is a diagrammatic representation of the integrated thermostat control of one element and one thermostatic control of the twinned heaters shown in Figure 1 where line shown by L passes through the control limit thermostat of thermostatic control 10 that has a sensor phial rod 11 as would be inserted in phial pocket 6 or 7 of Figure 1. When the thermostatic control calls for heat live is conducted to live connection 12 of the heater element 13 and emits via neutral conductor connection 14 to complete the circuit to neutral at N. Figure 3 is a diagrammatic representation of a thermostatic control remote from the immersion heater together with a relay or contactor arrangement as would be needed if * the thermostats (integral as shown in Figure 2 or remote as shown in Figure) have insufficient current carrying capacity for an element. Inside a thermostat housing 15 are control thermostat 16 and manual reset thermostat 17 actuated by sensor phials 16A and 17A in sensor phial pocket 18. When the thermostats are both calling for heat power is * fed from live at L through the closed contacts of the thermostats 16 and 17 to energise the *. coil 19 causing the contacts 19A and 19B to close energising the immersion heaters I and 2 on threaded immersion heater base page 9. I. S

Figure 4 shows the arrangement of Figure 3 with the additional safety cut off of an MCB or equivalent t safety cut off 20 triggered to off by the off contact 21 of the manual reset thermostat 17 of the thermostats 15 of Figure 3.

It should be understood that the MCB or equivalent safety cut off 20 may be triggered by a further manual reset thermostat (not shown) additional to that shown in Figures 3 and 4.

It should be understood that the thermostats and relays described above may be replaced b solid state devices for example thermisters and thyristors.

To avoid large current switching causing parasitic voltage spikes multiple relay sets may conveniently incorporate time delays between each relay set (or their solid state equal) to create delayed sequential switching of each element on each group of immersion heater/s to reduce and/or eliminate such spikes. * .* * * S * S. S... * S 5.. S. * a * * . S.. S. * * * . * S.

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Claims

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Claim 1. A thermal store or electrical boiler or hot water tank provided with at least one immersion heater as may be suitable for insertion into at least one immersion heater boss.

Said immersion heater/s being provided with at least two electrically heated elements said electrically heated elements being individually controlled so that the total electrical load of each immersion heater is divided between the elements reducing the switch load of each immersion heater control The relay/s or thyristor/s controlling the immersion heater/s element1s are under thermostatic control which incorporates an "electrical crowbar" circuit triggered by at least one temperature limit thermostat that actuates a normally lached closed contact relay device causing it to open circuit and provide electrical isolation of the immersion heater relay/s or thyristor/s controls as well as the immersion heaters.
Claim 2. A thermal store or electrical boiler or hot water tank of claim 1. where the said individual electrically heated elements are controlled by at least one relay contact whose coil is actuated by at least one thermostatic control being integral with or remote from the immersion heater.
Claim 3. A thermal store or electrical boiler or hot water tank of claim 1. where, when loads permit, the said individual electrically heated elements may be switched by at least one thermostatic control having its sensing pocket integral with the immersion heater.
Claim 4. A thermal store or electrical boiler or hot water tank of claim 1. where the said individual electrically heated elements are controlled by a thyristor control commonly known as a solid state relay actuated by at least one thermostatic control integral with or remote from the immersion heater. * S * S S. S

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