GB2250580A

GB2250580A - Waterheating system

Info

Publication number: GB2250580A
Application number: GB9125391A
Authority: GB
Inventors: Richard Martyn Griffiths
Original assignee: IMI RANGE Ltd
Current assignee: IMI RANGE Ltd
Priority date: 1990-12-05
Filing date: 1991-11-29
Publication date: 1992-06-10
Anticipated expiration: 2011-11-29
Also published as: GB9125391D0; GB2250580B

Abstract

A group waterheating system for a block of flats comprises one or more central boilers and pipework 4, 5 which conveys communal hot water or steam to the primary side of each of a plurality of plate-to-plate type heat exchangers 7, 7', one such heat exchanger being located on a boundary wall of each flat. Hot water generated in the secondary side of each heat exchanger 7, 7' is piped into its associated flat by pipework 9 and is used directly or indirectly therein for central heating and/or domestic hot water purposes. Because the communal hot water or steam pipework is located substantially entirely outside the flats, problems related to safety and to responsibility for the communal pipelines are avoided. Apportionment of each flat's central heating/hot water running costs is also made easier. <IMAGE>

Description

Waterheating System This invention relates to group waterheating systems, that is to say systems in which one or more 'central' gas, oil or coal-fired boilers provide a common source of primary hot water (or steam) for heating and/or domestic (ie usable) hot water purposes in each of a plurality of adjacent dwellings or other buildings, for example a block of flats.

In known schemes of this type, it is usual for the primary hot water to be pumped, under relatively high pressure, into each dwelling where it is used directly to heat space hating radiators and indirectly to generate domestic hot water. A number of problems arise from this arrangement, including responsibility for safety, maintenance etc of the primary circuit especially in the case of owner-occupied (as distinct from rented) dwellings, apportionment of space heating/hot water costs between the dwellings and the inherent dangers of having, within the dwellings, primary pipework conveying pressurised, very hot water or steam. It is an object of the present invention to solve, or at least mitigate, these problems.

According to one aspect of the present invention, therefore, there is provided a group waterheating system, for serving a plurality of dwellings or other units, including: a) at least one boiler for generating hot fluid, for example water or steam, and b) flow and return pipework for conveying the said fluid from the boiler to one side of each of a plurality of heat exchangers, one of which is located at or adjacent to the boundary, for example an external wall, of each dwelling or other unit, and back to the boiler, the other side of each heat exchanger being connectable or connected to pipework that serves, in use, to convey water, heated by means of heat exchange with said fluid, into its respective dwelling or other unit for utilisation therein.

In a system according to the invention, therefore, the "communal" hot fluid piped through the flow and return pipework is located substantially entirely externally of the dwellings or other inhabited buildings and the thermal energy contained in it is extracted, for use within the dwellings, via the heat exchanger associated with each dwelling. This not only substantially eliminates the potential hazards referred to above, but also it makes it easier to define questions of responsibility for maintenance etc of the flow and return pipework on the one hand and, on the other hand, of each dwelling's space heating and hot water system which is entirely self-contained.Further, as will become apparent below, conventional space heating and domestic hot water technology may be employed and it should be easier fairly to apportion heating/hot water costs as between the respective demands of the dwellings.

The flow and return pipework, which is in essence in the form of a "ring main", may be a single or two pipe system, with the one ("primary") side of each heat exchanger being connected thereto in parallel. However, it could comprise a single pipe system with the heat exchangers being connected in series without.

Usually, the boiler and the flow and return pipework will constitute a sealed system and the fluid conveyed to the heat exchangers will be hot water pumped through the system at relatively high pressure, or alternatively steam.

Each heat exchanger is preferably a high efficiency heat exchanger having mutually isolated primary and secondary sides. By way of example, each heat exchanger may be of the plate-to-plate type or of the coaxial tube type (eg YORCO-AX heat exchangers - Registered Trade Mark of IMI Yorkshire Alloys Limited).

In use, each heat exchanger has connected to it pipework which conveys water, heated in the other ("secondary") side of the heat exchanger by virtue of heat exchange with the hot fluid flowing through its primary side, into its associated dwelling. Once conveyed into the dwelling, the hot water may be utilised in a number of ways.For example: a) it could be used directly to heat radiators of a wet space heating system for the dwelling; b) it could be fed to the primary side of a conventional, indirect domestic hot water storage cylinder or to a conventional direct hot water storage cylinder; c) it could be used directly as a source of "instantaneous" domestic hot water; d) it could be used as the primary heat source for a so-called thermal storage system such as, for example, our FLOWMAX (Registered Trade Mark) system, for generating mains pressure domestic hot water and, optionally, for heating space heating radiators.

Accordingly, the present invention also provides a group waterheating system as defined above and further including, within one or more of the dwellings or other units within the group, means for utilising hot water heated by its, or their, associated heat exchanger(s), for example any of the means selected from a), b), c) and, especially, d) referred to above.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings of which Fig 1 is a schematic diagram of one system of the invention as applied to a block of flats wherein the space heating and domestic hot water, in each flat, are provided by a thermal storage unit located in each flat.

Fig 2 is a diagrammatic view of the pipework and thermal storage unit in one of the flats of the system shown in Fig 1; Fig 3 is a diagrammatic view similar to that of Fig 2 but wherein the space heating and domestic hot water are provided within each flat by more conventional means; and Fig 4 is a diagrammatic view similar to those of Figs 2 and 3 but wherein the space heating and domestic hot water are provided in each flat by alternative means Referring firstly to Fig 1 of the drawings, this depicts the space heating/domestic hot water system in part (nine units) of a multi-storey block of flats.The primary hot water source for the block of flats is provided by two "central" boilers 1, 2 from and to which hot water, typically at 90"C or above, is, during selected hours of the day and night, continuously pumped by an electric pump 3 through flow pipe work 4 and return pipework 5. This primary system is sealed and includes a conventional expansion vessel 6 for accommodating expansion of the primary water as it heats up.

Each flat is provided, on the outside of an external wall, with a high efficiency plate-to-plate heat exchanger, two of which are designated 7, 7'.

Conveniently, each heat exchanger 7, 7' may be housed in a 'meter' box 8 whereby it is readily accessible for servicing purposes; the box 8 may also house a metering device 8 (see Fig 2) whereby space-heating/domestic hot water energy consumption for each flat may be determined, say at calendar quarterly intervals, without the need to enter the premises. The box 8 may likewise house a water consumption meter 8'' plumbed into the mains water 16 supply pipe. One side of each heat exchanger 7, 7 is connected in parallel to the flow and return pipework 4, 5 as shown. The other side of each heat exchanger 7, 7' is connected by flow and return pipework 9, 10, 9', 10' to the primary side of a thermal storage unit 11, 11 located in each flat.The general nature of such thermal storage units is well known and we refer the reader to, for example, our FLOWMAX range of thermal storage units.

Briefly, however, and with reference in particular to Fig 2, the unit comprises a well-lagged cylinder 12, for example of copper, which is filled with primary water.

The primary water is circulated by a pump 13 through the heat exchanger 7 via the pipework 9, 10 and becomes heated by virtue of heat exchange within the heat exchanger 7, typically to a temperature of about 80"C.

The temperature of the primary water in the thermal storage unit 11 is controlled by a thermostat (not shown) which in turn controls operation of the pump 13. Thus, when the mass of primary water in the thermal store has reached the predetermined temperature set on the thermostat, say 80 C, the pump 13 will be switched off, and if it drops much below that temperature, it will be switched on, and so on. The cylinder 12 includes an integral feed and expansion tank 14 in known manner.

Within the cylinder 12 (or otherwise associate with it), and immersed in the hot primary water, is a high efficiency heat exchanger, for example a coiled length of externally finned and preferably internally rifled tubing 15, eg INTEGRON tubing - INTEGRON is a Registered Trade Mark of IMI Yorkshire Alloys Limited. One end of the tubing 15 is connected to a source of mains cold water 16 (optionally via a pressure reducing valve, not shown) and the other end is connected to pipework 17 which, on demand, distributes hot water to the various points of use within the flat, eg. a basin, bath, sink and/or shower installation.More particularly, when there is a demand for hot water, the mains cold water 16 passes through the finned tubing 15 and becomes instantaneously heated, by virtue of heat exchange with the hot primary water within the cylinder 12, whence it is delivered, via a thermostatic mixing valve 15 to the point of demand at, or under the influence of, mains pressure. In other words, the finned tubing 15 and the distribution pipework 17 constitute the secondary ("domestic") hot water circuit of the system.

The hot primary water in the cylinder 12 is also used to heat space heating radiators within the flat, the hot water being circulated around the space heating circuit by a pump 18 in response to a room thermostat (not shown) in conventional manner. The space heating/waterheating installation may be controlled, in conventional manner, by a time controller (not shown).

In the system depicted in Figs 1 and 2, it will be appreciated that the integrated volume flow of primary hot water through the cylinder 12 and the primary flow and return pipework will be approximately proportional to the thermal energy consumed in generating the secondary domestic hot water and by the space heating system, including any heat losses which may be reduced by appropriate lagging. Accordingly, the energy bill for each flat may be reasonably accurately calculated, over say a calendar quarter, by determining the total primary flow volume during the quarter for the flat in question. To that end, a suitable flow meter 8', eg a conventional water meter, may be located in the flow or return pipework of each flat, preferably within the meter box that houses the heat exchanger 7, 7', whereby the meter may be read without the need to have access to the property.The accuracy of such calculation depends however on the differential between the hot fluid flow and return temperatures in the primary side of each heat exchanger 7, 7' remaining, on average, substantially constant during operation of the pump 13 and preferably, therefore, this is arranged to be the case. This may be achieved (bearing in mind that the hot fluid flow temperature will remain substantially constant as determined by the operating temperature of the boilers 1, 2) by varying the throughput of the pump 13 in dependence upon the return temperature of the hot fluid. To that end, a temperature sensor 23 such as a thermistor is provided to sense the return temperature of the hot fluid immediately it has left the primary side of the heat exchanger 7, the sensor 23 providing an electrical signal having a value indicative of the temperature sensed.

This signal is compared, in a microprocessor 24, with a reference value corresponding to a pre-determined, substantially constant return temperature of the hot fluid, the differential (if any) between the signal value and the reference value being used to vary the throughput of the pump 13 appropriately such that the hot fluid return temperature will continually adjust to about the pre-determined temperature. The throughput of the pump 13 may be varied by, for example, varying the speed of the pump 13 (for which purpose it is preferably an infinitely variable speed pump) and/or by incorporating an electrically operated proportional control valve (not shown) in the domestic primary hot water circuit, for example in the return pipe 10.By way of further explanation, and ascribing T1 to the hot fluid flow temperature and T2 to the hot fluid return temperature, T1 will in any event remain substantially constant and so for T1-T2 to be substantially constant, T2 needs to be maintained substantially constant at, say, T2c, the aforesaid reference value corresponding to a temperature of T2C. During operation of the pump 13 (as dictated by the thermostat referred to earlier), if T2 differs significantly from T2c, the microprocessor 24 causes variation of the throughput of pump 13 whereby an appropriate variation in the rate of heat exchange in the heater exchanger 7 occurs and T2 tends to T2c. More particularly, if T2 > T2C the throughput of the pump 13 is temporarily increased appropriately by increasing its speed or opening up the aforesaid proportional control valve, thereby increasing the rate of heat exchange If, however T2 < T2c, the pump throughput is temporarily reduced appropriately (by decreasing the pump speed or closing down the control valve), thereby decreasing the rate of heat exchange in 7. Needless to say, there will be a degree of hysteresis in these processes, but for all practical purposes T2 will be maintained approximately equal, on average, to T2C. Accordingly, the integrated volume flow through the flat's primary system, as measured by the water meter 8', will be approximately proportional to the thermal energy utilised in that flat, ie a 'Datagas' metering system, for example, could be used.Alternatively, the aggregate electrical power consumption of the pump 13 could be measured and this too would be more or less proportional to the flat's energy usage.

"Communal" costs, such as those associated with heat loss from the boilers 1,2 and the pipework 4, 5, could of course be defrayed over all the dwellings in an appropriate manner, eg as a flat rate per dwelling or in proportion to the respective amounts of energy consumed by the flats.

Fig 3 of the drawings shows an alternative domestic hot water/space heating arrangement within the flats of Fig 1, the "external" features (ie boilers 1, 2, pump 3, pipework 4, 5 and heat exchangers 7, 7') being identical. Here, rather than being a thermal storage system, the domestic hot water/space heating system is a conventional, low pressure indirect system the nature of which also will be very familiar to those skilled in the art. Briefly, the flow and return pipework 9 and 10 connected to the heat exchanger 7 is connected to a heat exchange coil 19 located in a copper cylinder 12' and hot water is circulated, by an electric pump 13, through the circuit comprising the pipework 9, 10, the coil 19 and the heat exchanger 7. As is conventional, that circuit may be vented to a feed and expansion tank or it may be sealed, in which latter case it would incorporate an expansion vessel. Thus, secondary domestic water in the cylinder 12 becomes heated and it is, on demand, fed to points of use, via the domestic hot water distribution pipework 17 by virtue of the head of water in an integral feed and expansion tank 14. The temperature of the secondary hot water in the cylinder 12 is controlled by a cylinder thermostat (not shown), as usual.

The space heating radiators (if present) are fed, under the action of the pump 13 with hot water, in response, as usual, to a room thermostat, directly from the flow pipework 9, via a motorised valve 20. Again, the thermal energy consumption for each flat can be determined using a flow meter 8' and more accurate calculation of that consumption may be achieved by employing the means described above with reference to Figure 2.

Fig 4 of the drawings shows yet a further possible arrangement in accordance with the invention. Here, the secondary side of the heat exchanger 7 is split into two mutually isolated sections 21, 22. The section 21 is connected to a supply of mains cold water 25 and, upon demand, instantaneously produces domestic hot water which is piped, at mains pressure, to the point of demand via a thermostatic mixing valve 17' and pipework 17''. The other section 22 feeds the space heating system, through which hot water is circulated by a pump 18', again in response to a room thermostat. In such an arrangement, however, it would be necessary to separately meter the volume flow through each section in order to determine the billings for each particular flat.

In conclusion, it will be seen that the heat exchanger 7, 7 can be regarded as the respective flats own "boiler" and that the occupier, for example, can simply connect up his own choice of domestic hot water/space heating system, be it a very conventional one as shown in Fig 3 or otherwise. However, regardless of the system he chooses, the primary supply of thermal energy in the form of pressurised, very hot water circulated from the central boilers 1,2 and through the pipework 4, 5 will be substantially wholly outside his premises thereby giving rise to safety advantages and solving the problem of responsibility for maintenance of the primary heat supply. As noted also, fair and simple apportionment of domestic hot water/space heating costs can also be readily realised with a system of the invention.

Whilst the specific embodiments described above refer to use of a group heating system in a block of flats, it will be appreciated that a system of the invention could be used to advantage in other contexts such as, for example, an office block occupied by a number of unrelated companies/people who might have different internal hot water/space heating requirements and who, of course, will require separate billings proportionate to their energy use.

Claims

CLAIMS:

1. A group waterheating system, for serving a plurality of dwellings or other units, including: a) at least one boiler for generating hot fluid, for example hot water or steam, and b) flow and return pipework for conveying the hot fluid from the boiler to one side of each of a plurality of heat exchangers, one of which is located at or adjacent to the boundary, for example an external wall, of each dwelling or other unit, and back to the boiler, the other side of each heat exchanger being connectable or connected to domestic pipework that serves to convey hot water, heated in the heat exchanger by means of heat exchange with the hot fluid, into its associated dwelling or other unit for utilisation therein.

2. A system according to claim 1 wherein said heat exchangers are each of the plate-to-plate type.

3. A system according to claim 1 wherein said heat exchangers are each of the coaxial-tube type.

4. A system according to any one of claims 1 to 3 wherein said domestic pipework serves to convey said hot water directly to wet space heating radiators located in the dwelling or other unit.

5 A system according to any one of claims 1 to 4 wherein said domestic pipework serves to convey domestic hot water to points of use in the dwelling or other unit, said domestic hot water being generated by the instantaneous heating, in said heat exchanger, of mains cold water fed to said other side of the heat exchanger.

6. A system according to any one of claims 1 to 5 wherein the other side of each heat exchanger comprises two mutually isolated sections, each section being provided with separate domestic pipework arranged to convey central heating hot water and domestic hot water respectively into its dwelling or other unit in the manner set out in claims 4 and 5.

7. A system according to any one of claims 1 to 3 wherein said domestic pipework serves to circulate, under the action of a pump, hot water to and from the primary circuit of vented or mains pressure unvented indirect hot water storage cylinder and, optionally, wet central heating radiators, located in the dwelling or other unit.

8. A system according to any one of claims 1 to 3 wherein said domestic pipework serves to circulate, under the action of a pump, hot water to and from the primary thermal store of a thermal storage type of water heater.

9. A system according to claim 7 or claim 8 wherein said domestic pipework includes in it a volume flow meter for measuring the volume flow of hot water through said domestic pipework.

10. A system according to claim 9 wherein temperature measuring means is provided to measure the return temperature of the hot fluid immediately it has left each heat exchanger, or the differential between the flow and return temperatures of said hot fluid adjacent to each heat exchanger, and the measured temperature or temperature differential is used to vary, as appropriate,-the throughput of the pump so as to render said temperature or temperature differential substantially constant, on average, during operation of the pump, whereby the measured volume flow through the pipework will be substantially proportional to the thermal energy consumed by the associated dwelling or other unit.

11. A system according to claim 11 wherein the throughput of the pump is varied by varying the pump speed.

12. A system according to claim 11 wherein the throughput of the pump is varied by a proportional control valve located in said domestic pipework.

13. A group waterheating system substantially as hereinbefore described with reference to Figure 1 and Figure 2 or Figure 1 and Figure 3 or Figure 1 and Figure 4 of the accompanying drawings.