GB2248674A

GB2248674A - Waterheating apparatus

Info

Publication number: GB2248674A
Application number: GB9120539A
Authority: GB
Inventors: Richard Martyn Griffiths
Original assignee: IMI RANGE Ltd
Current assignee: IMI RANGE Ltd
Priority date: 1990-09-29
Filing date: 1991-09-27
Publication date: 1992-04-15
Anticipated expiration: 2011-09-27
Also published as: GB9120539D0; GB2248674B; GB9021248D0

Abstract

A domestic hot water/central heating system of the thermal storage type comprises a cylinder 1 containing primary hot water 2 heated by a boiler 3. Domestic, ie secondary, hot water is generated, on demand, by the passage of mains cold water through finned tubing 7, 7' immersed in the primary hot water 2 and the central heating circuit is heated by pumping primary hot water 2 around the circuit. In order to improve the year round efficiency of the system, the primary hot water 2 is maintained at about 80 DEG C when the central heating is operative, for example during the winter, but at a lower temperature, for example around 65 DEG C, when the central heating is not required, for example in the summer. Maintenance of the primary hot water temperature at the respective desired values is controlled by a thermistor 5 whose output is fed to a control unit 17 which in turn controls operation of the boiler 3. <IMAGE>

Description

Waterheating Apparatus This invention relates to waterheating apparatus of the type comprising a vessel containing, in use, a thermal storage ("primary") medium, for example water, and heating means to heat the thermal storage medium, the storage medium having immersed in it, or otherwise associated with it, a high efficiency heat exchanger through which, on demand, cold ("secondary", ie. usable) water, usually at or driven by mains pressure, passes whereby the cold water is instantaneously heated by heat exchange with the thermal storage medium and is fed, usually via a thermostatic or other type of mixing valve, to a point of use such as a sink, bath or shower installation. The thermal storage medium is also used to heat a "wet" space (central) heating circuit by being pumped around the circuit.Hereinafter, such apparatus is referred to as "waterheating apparatus of the type described". The thermal storage medium may be heated by any suitable heating means, for example directly (or possibly indirectly) by a gas, oil or coal fired boiler or, less often, by one or more electric immersion heaters. Usually, the heating means will comprise a gas-fired boiler which may be located internally of externally of the vessel.

Waterheating apparatus of the type described is known in the form of, for example, our successful FLOWMAX product (FLOWMAX is a registered trade mark of IMI Range Limited). In order to render it suitable for use in heating a wet space heating circuit, it is necessary for the thermal storage medium to be heated to a relatively high temperature, typically of the order of 80 to 85 "C and it has hitherto been conventional practice continually to maintain the medium at such a temperature, even when there is no significant demand for space heating, for example in the summer. In that circumstance, the apparatus tends to be less running cost-effective because of heat loss from the vessel, even when it is well-lagged.

We have discovered that, with the use of a suitable high efficiency heat exchanger, secondary water of quite acceptable temperature may be generated from heating apparatus of the type described wherein the thermal storage medium is continually maintained at a significantly lower temperature, say between 45 and 70 "C, preferably around 60 "C, at which temperature such heat losses become smaller and at which the tendency of the boiler to "cold cycle" tends to be smaller. The present invention takes advantage of this whereby the year-on-year efficiency of heating apparatus of the type described may be improved.

According to one aspect of the present invention, therefore, there is provided waterheating apparatus of the type described including thermostat means for controlling the temperature of the thermal storage medium and arranged to cause the heating means to be switched off when the medium has risen to a pre-determined temperature, as sensed by the thermostat means, characterised in that said pre-determined temperature has selectable, different first and second values, the apparatus including means to select said first value when the space heating circuit is in use and to select said second value, being lower than said first value, when the space heating circuit is not in use.

Preferably, the thermostat means includes a single temperature sensor for sensing the temperature of the thermal storage medium and connected to a control unit, the control unit being adapted, when the space heating circuit is in use, to switch off the heat source when the temperature of the thermal storage medium, as sensed by the sensor, reaches said first value and, when the space heating circuit is not in use, to switch off the heat source when said temperature, as sensed by the sensor, reaches said second value. Alternatively, for example, there may be a pair of thermostat sensors for use in controlling the temperature of the thermal storage medium, in accordance with, respectively, said first and second values, and means to select the appropriate "active" one of the pair of thermostat sensors depending on whether or not the space heating circuit is in use.

The or each sensor is preferably a thermistor, although, especially where there is a pair of sensors as just described, the thermostat means may comprise conventional electro-mechanical devices.

The first, higher, temperature value may, for example, be within the range 70-95 "C, preferably between 75 and 90 "C and advantageously between 80 and 85 "C and the second, lower value, may, for example, be within the range 45 to 75 "C, preferably between 55 and 70 "C and advantageously between 60 and 65 "C.

By the expression "in use" when used herein in relation to the space (central) heating circuit, we mean, principally, that that circuit will operate in dependance upon the state (ie. "on" or "off") of any room thermostat used to control the space heating and/or any time switch. On the other hand, by "not in use" we mean that that circuit is inoperative, regardless of the state of the room thermostat and time switch. Thus, user-operable controllers used to control hot water/central heating installations almost invariably include a manually-operable switch moveable, by the user, between "central heating on" and "central heating off" positions, the central heating function being rendered operative (in response to a room thermostat and/or a time switch) by selecting the former position, but being rendered inoperative by selecting the latter position.Usually, such a position will be selected during the summer months, or during other periods of sustained warm weather during which the central heating is not required. On the other hand, the switch will usually be in the "central heating on" position throughout the winter months or during other periods of sustained cold weather.

Accordingly, the first or second temperature value may be automatically selectable in response to the selected mode of such a switch.

However, although less preferred, the second, lower temperature value may in addition or alternatively be automatically selectable in response to other criteria notwithstanding the fact that the central heating is latently 'on' eg. the aforementioned user-operable switch, if present, is in the "central heating on" position but the central heating is not actually operating in response to the state of the room thermostat and/or time switch. For example, in such a case, selection of the second, lower temperature value for the thermal store could be arranged to occur in response to a sustained, but unexpected, period of warm weather as sensed, for example, by a room thermostat or other temperature-sensing device. Equally, selection of the lower temperature value could be arranged to occur in response to 'central heating off' cycles dictated by a time switch.

According to another aspect of the present invention, there is provided a user-operable controller adapted for use with apparatus of the invention, said controller including a manually operable central heating on/off switch which, when in its "on" position, causes the heating means continually to maintain the thermal storage medium at about said first temperature value and which, when in its "off" position, causes the heating means continually to maintain the medium at about said second value.

An embodiment of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Fig 1 is a diagram of such embodiment; and Fig 2 is a detailed wiring diagram suitable for use in the embodiment of Fig 1.

Referring to Figure 1 of the drawings, the apparatus includes a well lagged cylinder 1 containing, in use, a primary, liquid thermal storage medium 2, such as water. The thermal storage medium 2 is heated by a boiler 3 through which the medium is circulated, via flow and return pipework, by a pump 4. The temperature of the medium 2 is controlled in response to a temperature sensor 5 as described in more detail below. Expansion and replenishment of the thermal storage medium 2 may be dealt with by a remote feed and expansion tank (not shown), as is conventional, connected by a pipe to the cylinder at 6. Alternatively, the feed and expansion tank may be of the integral type.

Within an upper region of the cylinder 1 is located a pair of high efficiency, finned tube heat exchange coils 7,7' made for example of INTEGRON tube (a registered trade mark of our sister company, IMI Yorkshire Alloys Limited). The adjacent inlets of the two coils 7,7 are connected in parallel to a cold water mains pipe 8, optionally via a pressure regulating valve (not shown), and their adjacent outlets are connected in parallel to the domestic hot water supply pipe 9 which distributes hot secondary water to the various points of use such as sinks, baths, basins and showers via a thermostatic mixer valve 10 where the hot water generated within the coils 7,7 may mix with mains cold water fed to the valve 10 by a pipe 11.There is also provided, in known manner, a sealed expansion vessel 12 for accommodating expansion of water within the coils 7,7' as it heats up under static conditions.

The cylinder 1 is connected to the flow and return pipes 13, 13' of a wet space ("central") heating circuit, the thermal storage medium 2 being circulated therearound by a pump 14 in response to the state of a room thermostat 15.

A pocket 16 is formed in the cylinder 1 adacent to the heat exchange coils 7, 7 for receiving the temperature sensor 5. The temperature sensor 5 is a thermistor and is capable, under steady state conditions, of maintaining the temperature of the thermal storage medium, at least adjacent to the location of the sensor, to within about 2 "C of the desired value.

Operation of the apparatus is controlled by a controller designated generally by reference numeral 17.

In Fig 1, the various electrical connections (shown by dashed lines) are purely schematic, but in Fig 2 one form of wiring diagram is shown in detail. The general nature of such a diagram will be familiar to those skilled in the art.

Referring to Fig 2, the connection 18 serves to transmit a central heating "on" or "off" signal, as the case may be, from a manually operable switch 19 that (as is conventional) forms part of the controller 17, to circuit A which comprises a temperature set point controller which serves to feed a temperature set point signal to a comparator circuit, also comprised in A, being a signal which corresponds to the first or second temperature value, as required, for the thermal storage medium 2. More particularly, such signal will correspond to the first, higher value when the switch 19 is in its 'on' position and to the second, lower, value when the switch 19 is in its 'off' position. Typically, these values will be about 85 "C and 60 OC respectively.

The thermistor 5 also feeds a signal to the circuit A having a value corresponding the temperature sensed by it. If the temperature of the thermal store 2 as sensed by the thermistor 5 is below the pre-determined value dictated by the position of the switch 19, the comparator circuit causes relay contacts 20 to close whereupon the boiler 3 fires and the pump 4 operates. The thermal storage medium 2 thus becomes heated until such time as the thermistor 5 senses that the medium has reached its predetermined temperature, whereupon the comparator circuit causes the contacts 20 to open whereupon the boiler 3 and pump 4 switch off.This cycle will continually be repeated, in dependance upon the output from thermistor 5, whereby the thermal storage medium 2 is continually maintained at about the appropriate pre-determined temperature, being either the first, higher temperature when the switch 19 is in the "on" position or the second, lower temperature when the switch 19 is in the "off" position Needless to say, it will be necessary to provide a power input to the circuitry contained in A in order to enable it to function.

Accordingly, the temperature of the thermal storage medium may be controlled in dependance upon the mode of the switch 19 and will be maintained at its lower temperature of about 60 "C, when the switch 19 is off, eg during the summer, and at its higher temperature of about 85 "C when the switch is on, eg during the winter. The heat losses from the medium 2 during a summer/winter cycle will therefore be less than if the medium were at all times maintained at the higher temperature of, say, 85 "C, whilst still being able to supply a plentiful amount of secondary hot water.

Whilst the specific embodiment described above with reference to the drawings illustrates the use of coiled, externally finned tubing 7,7' immersed in the thermal storage medium 2, the domestic secondary hot water may be generated alternatively by heat exchange between the incoming cold water and the thermal storage medium 2 in a high efficiency heat exchanger located internally or externally of the vessel 1 and through the primary side of which the medium 2 is pumped. Such heat exchanger may be, for example, of the plate-to-plate or coaxial tube type, for example a YORCO-AX heat exchanger manufactured by IMI Yorkshire Alloys Limited.

Claims

CLAIMS:

1. Waterheating apparatus of the type described including thermostat means for controlling the temperature of the thermal storage medium and arranged to cause the heating means to be switched off when the medium has risen to a pre-determined temperature, as sensed by the thermostat means, characterised in that said pre-determined temperature has selectable, different first and second values, the apparatus including means to select said first value when the space heating circuit is in use and to select said second value, being lower than said first value, when the space heating circuit is not in use.

2. Waterheating apparatus according to claim 1 wherein said first temperature value is within the range from 70-95 OC.

3. Waterheating apparatus according to claim 2 wherein said first temperature value is within the range of from 75 to 85 "C.

4. Waterheating apparatus according to any one of claims 1 to 3 wherein said second temperature value is within the range of from 45 to 75 "C.

5. Waterheating apparatus according to claim 4 wherein said second temperature value is within the range of from 60 to 65 "C.

6. Waterheating apparatus according to any one of claims 1 to 5 wherein the first or second temperature value, as the case may be, is automatically selectable in dependence upon the position of a user operable "central heating on/off switch" incorporated into a control unit of the apparatus.

7. Waterheating apparatus according to any one of claims 1 to 6 wherein said thermostat means includes a single sensor for sensing the temperature of the thermal storage medium and adapted to produce a temperature-dependant electrical output signal that is fed to a comparator circuit which compares said output signal with a selected one or other of two electrical set-point signals corresponding respectively to said first and second temperature values, the output of said comparator circuit operating a switch thereby to control operation of the heating means.

8. Waterheating apparatus according to claim 7 wherein said sensor comprises a thermistor.

9. Waterheating apparatus according to any one of claims 1 to 6 wherein said thermostat means includes a pair of sensors for sensing the temperature of the thermal storage medium and respective switches associated therewith for controlling operation of the heating means in accordance with, respectively, said first and second temperature values, the appropriate active one or other of said sensors/switches being selectable in dependence upon whether or not the space heating circuit is in use.

10. Waterheating apparatus substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.