WO2005045327A1

WO2005045327A1 - An improved electric boiler

Info

Publication number: WO2005045327A1
Application number: PCT/GB2004/004581
Authority: WO
Inventors: Brian Hammond
Original assignee: Heatrae Sadia Heating Limited
Priority date: 2003-10-31
Filing date: 2004-10-29
Publication date: 2005-05-19
Also published as: GB0325399D0; EP1687574A1

Abstract

An electric boiler has a heat exchange unit (10) in which a heat transfer medium, usually water, is heated. Energy for the heating is through heating elements (13), whose activation is governed by a control means (14) operating on switches. The switches are either electromechanical, triacs or a combination thereof. The heating elements (13) comprise elements of at least two different power ratings, with elements of the same rating being combined together in a bank. The activation sequence of the heating elements (13) is controlled to minimise the sudden increased load applied to the power supply of the premises on which the boiler is located. In order to reduce the risk of excess heat being applied, the elements can be activated by a burst firing sequence in which power is supplied to the element for only a short period of time.

Description

AN IMPROVED BOILER

Field of the Invention

The present invention relates to electric boilers and improved means of controlling the activation of the heating elements within a boiler.

Background to the Invention

In order to heat a fluid, normally water, domestic and industrial boilers primarily utilise either combustion within the boiler of a fuel such as gas, oil, coal etc. or the heating of elements through passage of an electric current. Fuel combustion however brings with it problems relating to the efficient oxidation of the fuel and subsequent removal of waste combustion products. Moreover care must be taken to ensure that the lines feeding the combustion fuel to the boiler do not leak.

Boilers utilising electric heating elements pose therefore fewer safety problems. However, such electric boilers normally have a high heating output and consequently require a high energy input. The high energy input is not required constantly but only when demanded by the temperature control system.

Switching the elements on however results in a sudden load being put onto the electric supply for the premises in which the boiler is located, resulting in a drop in voltage at the point where the supply enters the premises.

The drop in voltage can be so large that the output of, for example, light from an incandescent lamp can be temporarily reduced, by a level sufficient for the drop to be noticeable by the user. Furthermore, if the boiler is switched on and off several times in rapid succession, the resultant flickering of the lamp can be irritating. Moreover, regulations and International Standards set levels for an acceptable amount of flicker.

It is therefore an object of the present invention to provide a boiler whose energy demands are such that the above problem is alleviated. Summary of the Invention

According to the invention, there is provided an electric boiler, the boiler including a heat exchange unit comprising an inner volume wherein heating elements heat a transfer medium to a desired temperature, the unit having an inlet port and an outlet port through which the medium respectively enters and leaves the unit;

a control means to govern the activation of the heating elements;

at least two of the heating elements having different power ratings,

switch elements to activate the heating elements and obtain the required loads.

The heating elements can be activated in a sequence determined by the control means, the sequence minimising flicker yet affording sufficiently rapid heating of the medium.

The switch element preferably comprises an electromechanical relay, which is highly durable. Alternatively, the switch, element includes a triac which has no moving parts and so reduces the electrical noise produced during activation and deactivation of the elements. The minimisation of electrical noise is encouraged by European Standards which set limits on the amount of radio frequency (RF) noise which is permissible.

Conveniently, a switching element comprises an electromechanical relay having a triac across the contact. The noise of the contact is therefore reduced. Optionally, the relay and triac are so configured that after current flow is initiated, the electromechanical relay is on, and the triac is off.

The elements are conveniently in banks each bank comprising elements sharing the same power rating. The wiring for the arrangement is thereby simplified. Optionally, the power rating of the higher power element is an integer multiple of that of the lower power element. This arrangement facilitates stepwise increase and decrease of the power output of the elements.

Preferably the heating elements are activated or deactivated sequentially to produce a stepwise increase or decrease in the rate of heating.

Preferably, the elements can be activated by a burst firing sequence, controllable by the control means. The burst firing sequence allows the heating of the medium to be fine tuned.

The boiler includes temperature sensors at the inlet and outlet port. The sensors relay the temperature to the control unit, which processes the data through an algorithm and determines the rate of flow of medium through the heat exchange. The flow calculation can be used as a safety device. For example, where the temperature difference between the sensors is higher than a certain pre-set level, this indicates that the flow of medium is too low. The elements can then be switched off to prevent localised overheating.

According to a further aspect of the invention there is provided a heat exchange unit, the unit having an inner volume in which a fluid medium can be heated by means of heating elements and which the medium respectively enters and leaves the heat exchange unit; switching elements to activate the heating elements; a control means to govern activation of the heating elements, the heating elements including at least two elements having different power ratings.

Brief Description of the Drawing

The invention will now be described with reference to the accompanying drawing which shows by way of example only one embodiment of an electric boiler. In the drawing:

Figure 1 is a diagram showing the operation of heating elements within a heat exchange unit.

Detailed Description of the Drawings

Referring to Figure 1, the electric boiler (not illustrated) includes a heat exchange unit 10 to increase the temperature of water to a desired value. The heated water can then go into, for example, a domestic hot water supply or central heating system.

The heat exchanger 10 has an input port 11 through which cold or cool water enters. After the water has been heated the water exits the exchanger 10 via the output port 12 which is connected to the taps or radiator system where the hot water is required. In order to effectively heat the water, heating elements 13 are provided. In the exemplified arrangement, the elements comprise two 1 Kilowatt

(KW) heating elements AB and three KW elements C,D,E. Where elements of the same rating are included together in a single bank array then wiring for the elements is simplified. The elements are individually and collectively controlled by the control unit 14. In order to determine the temperature of the water as it enters and leaves the heat exchanger 10, temperature sensors 15,16, connected to the control unit 14, are included at the input port 11 and output port 12 respectively.

The elements in the disclosed embodiment are capable, if activated correctly, of providing an output of up to 1 lkW in steps of 1WK. This is illustrated in Table 1 below in which the steps from OkW to 11KW are illustrated, with V indicating that the particular heater is active and X that it is inactive. It will be appreciated that elements having ratings different from 1KW can be used to achieve a stepwise change in heating and power consumption, without departing from the scope of the invention.

In use, the user or boiler installer programs into the control unit 14, either directly or through a separate interface, the desired temperature of the output water. The control unit 14 determines the energy required by processing the input, output and pre-set desired temperature through an algorithm and activates the heating elements accordingly.

The data from the temperature sensors can be used to determine the flow of water through the boiler and in particular across the heating elements. For example, should the temperature difference between the output water and the input water be higher than a pre-set value, then the control unit can be programmed to take this as an indicator that the flow rate of the water is too low. Power supplied to the heating elements can be reduced.

In order to minimise the risk of a sudden change in energy requirements, the heating elements are activated sequentially as illustrated above. The sequence ensures that the change in energy requirements does not vary by more than lkW in each step. Activation of an element will typically extend over a period of 1 Vz to 2 seconds.

The reduction in the rate of energy input to the water is also reduced in similar fashion by reduction in 1 kW steps of activation of the heating elements, essentially the reverse of that shown in Table 1.

The power within the IkW elements A,B can be further modulated by a technique known as burst firing. In this technique, the IkW element B is activated in short bursts so that smaller pockets of energy can be delivered to the water. This technique is used primarily once the water has reached the desired temperature, normally from 40-90C. Typically, the element will be activated for only a few cycles per second. The temperature of the water can be controlled to a higher degree of accuracy than would be the case if the power was adjustable in IkW blocks. The burst firing sequence is normally controlled through an electronic circuit, governed by software and/or a microprocessor.

The process of switching the elements on and off can generate electrical noise. In order to minimise this, triacs are normally preferred to electromechanical relays. However, in the situation here, triacs are not suitable as they themselves are a source of heat, this requiring cooling means. Moreover, triacs do not always behave in a consistent manner. An arrangement is considered therefore which combines electromechanical relays and triacs. In this combination, a triac forms a bridge across the contacts of the relay.

In order to turn the heating on, the triac is turned on. When current is flowing the electromechanical relay is turned on and the triac is turned off. When switching off heating, the triac is first turned on, the electromechanical relay turned off, then the triac turned off. These sequences also reduce the wear on the electromechanical relay contacts and prolongs the life of the relay. By switching the triac at the point in the a.c. cycle where the voltage is close to zero (a technique known as zero voltage crossover switching) electrical noise is minimised.

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible with the scope of the appended claims.

Claims

1. An electric boiler, the boiler including a heat exchange unit comprising an inner volume wherein heating elements heat a transfer medium to a desired temperature, the unit having an inlet port and an outlet port through which the medium respectively enters and leaves the unit; a control means to govern the activation of the heating elements; at least two of the heating elements having different power ratings, switch elements to activate the heating elements and obtain the required loads.

2. A boiler according to Claim 1, wherein one or more of the switch elements comprises an electromechanical relay.

3. A boiler according to Claim 1 or Claim 2, wherein one or more of the switch elements comprises a triac.

4. A boiler according to Claim 2 or Claim 3, wherein one or more of the switching elements comprises an electromechanical relay having a triac across the contact.

5. A boiler according to Claim 4, wherein the relay and triac are so configured that after current flow is initiated, the electromechanical relay is on, and the triac is off.

6. A boiler according to any preceding Claim wherein the heating elements are arranged in banks each bank consisting of elements of the same power rating.

7. A boiler according to any preceding Claim, wherein the power rating of the higher power element is an integer multiple of that of the lower power element.

8. A boiler according to any preceding Claim, wherein heating elements are activated or deactivated sequentially to produce a stepwise increase or decrease in the rate of heating.

9. A boiler according to any preceding Claim wherein the elements can be activated by a burst firing sequence, controllable by the control means.

10. A boiler according to any preceding Claim including temperature sensors at the inlet and outlet port.

11. A boiler according to Claim 10, wherein the control means, processes the data from the temperature sensors through an algorithm and determines the rate of flow of medium through the heat exchange unit.

12. A heat exchange unit, having an inner volume in which a fluid medium can be heated by means of heating elements and an inlet port and an outlet port through which the medium respectively enters and leaves the heat exchange unit; switching elements to activate the heating elements; a control means to govern activation of the heating elements, the heating elements including at least two elements having different power ratings.

13. A boiler substantially as herein described with respect to the accompanying drawing.