WO2020193983A1

WO2020193983A1 - A water heating system

Info

Publication number: WO2020193983A1
Application number: PCT/GB2020/050817
Authority: WO
Inventors: Peter Armstrong; Christopher Randall
Original assignee: Mixergy Limited
Priority date: 2019-03-27
Filing date: 2020-03-26
Publication date: 2020-10-01
Also published as: GB2582596B; GB201904219D0; GB2582596A

Abstract

The present invention provides a water heating system (10) comprising: a tank (12) for holding a quantity of water and having a cold-water inlet (14) and a hot water outlet (16) and having a first upper zone (Z1) and a second lower zone (Z2); a heat exchanger (18) having a first side (20) for receiving heat (H) from a heat source (A) and a second side (22) for transmitting heat (H) to water to be stored within the tank (12); wherein said heat exchanger (18) includes an inlet (18a) into said second side (22) of said heat exchanger (18) and an outlet therefrom (18b); and wherein said system (10) further includes a water draw pipe (90) having an inlet (92) within said second zone (Z2) and an outlet (94) connected to said inlet (18a) to the second side (22) of the heat exchanger (18) for supplying water from zone Z2 to the heat exchanger (18) for heating therein; and wherein said heat exchanger (18) is external to the tank (12) and wherein said system (10) further includes a flow director (11) for directing flow of water from said outlet (18b) of second side (22) of said heat exchanger (18) to said second lower zone Z2.

Description

A WATER HEATING SYSTEM

The present invention relates to a hot water heating system having a storage tank and relates particularly but not exclusively to a heating system which is able to define and heat water within zones within the water tank itself and may also be able to improve the Coefficient of Performance too. Such a system may lend itself to use in domestic or commercial water heating systems where it is necessary or desirable to have a stored quantity of heated water for immediate use.

Presently, it is known to have hot water storage tanks for storing a quantity of heated water for immediate use. Such systems have a means for introducing cold mains water into the tank and also a heating system for heating the water within the tank itself. This heating system may comprise any one of a number of means but, conventionally, comprises a coil of pipe extending inside at least a portion of the length of the tank through which hot water heated in a boiler system is passed. Such an arrangement will cause the boiler heated water to pass heat to the water within the hot water tank and such arrangements are commonly used in domestic and industrial situations, particularly where there is a separate need for a boiler such as will be required to provide heat to the rooms of a building through radiators or the like. Whilst such systems are relatively energy efficient, they do tend to heat the water in a general manner, and it is generally necessary to heat the entire contents of the tank to the desired use temperature before hot water of a useful temperature and quantity can be drawn off. Modern demands on such hot water systems are very variable and may comprise a need for a relatively small quantity of hot water for one task but then a relatively large quantity of hot water for another task. When just a small quantity of water is needed the overall efficiency of heating that quantity of water is low and the time-lag in producing that relatively small quantity of water at the required temperature is high, both of which are extremely undesirable. The measure of water heating efficiency is known as the Coefficient of Performance or COP for short and is referred to herein as COP.

In more detail, it will be appreciated from figure 1 which shows an example of the hot water tank arrangements well known in the art, that hot water from a boiler is passed from top to bottom of the heating coil within the tank such as to cause heat from the boiler heated water to be passed to the water within the tank itself. As the boiler water heats the water in the tank it will cool so whilst the COP associated with heating the water at the top of the tank is high it will reduce rapidly as the boiler water passes heat to the water in the tank. The COP associated with heating water at the top of the tank may be as high as 4 whilst the COP associated with heating water at the bottom of the tank may be as low as 2. It will be appreciated from the above that modern hot water tank arrangements and hot water usage is not wholly conducive to optimising the COP for each particular use. The present invention, therefore, aims to address one or other or both of the issues raised so as to at least improve on the COP in one or more of the usage situations.

Accordingly, the present invention provides s water heating system comprising: a tank for holding a quantity of water and having a cold-water inlet and a hot water outlet and having a first upper zone and a second lower zone; a heat exchanger having a first side for receiving heat from a heat source and a second side for transmitting heat to water to be stored within the tank; wherein said heat exchanger includes an inlet into said second side of said heat exchanger and an outlet therefrom; and wherein said system further includes a water draw pipe having an inlet within said second zone and an outlet connected to said inlet to the second side of the heat exchanger for supplying water from zone to the heat exchanger for heating therein; and wherein said heat exchanger is external to the tank and wherein said system further includes a flow director for directing flow of water from said outlet of second side of said heat exchanger to said second lower zone.

The arrangement may include a diffuser within said second region for causing the gentle diffusion of heated water introduced thereinto.

The arrangement may further include a diverter valve for directing water from the second side of the heat exchanger to said first or said second of said zones.

Said tank includes an upper portion and a lower portion and preferably said first zone is in the upper portion of said tank.

Said tank includes an upper portion and a lower portion and preferably said second zone is in the lower portion of said tank.

Said diverter valve may include an inlet for receiving heated water from said second side of said heat exchanger and a first outlet and a second outlet.

The arrangement may further include a first hot water supply pipe having an inlet connected to the first outlet of the heat exchanger and an outlet within the second zone of the tank. The heating system may further include a second hot water supply pipe having an inlet connected to the second outlet of the heat exchanger and an outlet within said first zone of said tank.

Said heating system may also include a cold-water supply pipe having an inlet for receiving cold water from a supply thereof and an outlet within said second zone of said tank.

The arrangement may further include a water pump for drawing water into said water draw pipe and supplying said water to said inlet to said heat exchanger.

Said heat exchanger may comprises a water-to-water heat exchanger and wherein said first side includes an inlet for receiving heated water and an outlet for expelling water from said first side after heat has been passed to the second side of said heat exchanger. In the alternative, the heat exchanger may include a gas heating system having a hot gas-to-water heating element for heating water circulating within said first side thereof. In the alternative, said heat exchanger may comprises an electric heating system including an electric heating element forming said first side thereof.

The arrangement may include a renewable energy generation system for generating electricity to be supplied to said electric heating system.

According to a further aspect of the present invention there is provided a method of operating a water heating system as claimed in any one of claims 1 to 13 including the steps of: a) drawing water from within the second zone and supplying it to the second side of said heat exchanger;

b) supplying heat to said first side of said external heat exchanger;

c) heating water within said second side of said external heat exchanger and diverting said hearted water by operation of said first diverter valve to either one or other of said first zone or said second zone.

The present invention will now be more particularly described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of a typical known hot water tank of the prior art; Figure 2 is a schematic representation of a hot water tank having various elements of the present invention;

Figure 3 is a detailed cross-sectional view of the lower zone of the tank shown in figure 2; Figure 4 is a more detailed schematic representation of a the heat exchanger and shows various options for heating that may be used individually or in combination with each other; and

Figure 5 is a Coefficient of performance graph which is referred to when explaining the operation of the present system.

Referring now briefly once again to figure 1 , a tank 1 of a water heating system 2 comprises a cold-water inlet 3 and a hot water outlet 4. A water heating coil in the form of a coiled pipe is passed through the inside of the tank and has an inlet 5 which receives heated water from a source thereof such as a boiler and an outlet 6 for passing spent heating water back to the boiler. Generally, the inlet is at a top zone Z1 and the outlet is at a bottom zone Z2, but other arrangements are possible. In operation, heated water from the boiler enters the inlet 5 at approximately 65 deg C and passes downwardly heating the water within the tank as it goes. Whilst the heating water is at 65 deg C and the water in the tank immediately surrounding the inlet end is at a low or the mains supply temperature the COP is high and may be as much as 4 but as the heating water passes downwardly and passes its heat to the water in the tank it looses temperature and is less effective in passing heat to the water in the tank and the COP drops progressively towards the bottom zone Z2, where it may be as low as 2. Clearly the water at the top of the tank will be heated first and once this has achieved the desired maximum temperature which matches the temperature of the heating water there will be no further heat transfer in the upper zone Z1 and the water lower down the tank will become more progressively warmed until the entire content of the tank is at the same temperature. If one were to average the COP it would be about 3 but the bigger issue is the time it takes to get the water in the tank to a usable temperature which can be very frustrating if the user just needs a relatively small amount of water.

The present invention is aimed at making better use of the heated water and improving the COP of the heating process and does so by amending the location of the heat exchanger and also the way water within the tank interacts with the heat exchanger and how the water to be heated is contained and circulated within the tank and heat exchanger itself. Details of the present invention are best seen in figure 2 which discloses a water heating system 10 having a tank 12 for containing water to be heated and having a cold-water inlet 14 and a hot water outlet 16 and an upper zone Z1 and a lower zone Z2. The heat exchanger 18 in this arrangement may be located external of the tank 12 and includes a first side 20 for receiving heat H from a heat source (A) and a second side 22 for transmitting heat H to the water to be stored within the tank 12. It will be appreciated that the heat exchanger 18 may take any one of a number of forms such as a simple plate heat exchanger or a heating water coil contained within a container arrangement. Further alternatives include electrical heating elements which extend into the second side 22 of the heat exchanger 18 so as to heat any water that may be contained therein. The source of heat is not particularly important, but it is important to note that the arrangement of the present invention does lend itself to the use of low temperature heat sources such as may be available from a ground source or air source heat pump arrangement (not shown) or solar PV (not shown) whilst also lending itself to use with high temperature but possibly less environmentally friendly sources of heat such as gas boilers or mains powered electrical heating elements. Mixes of each of these alternatives are possible and may, in some situations, be beneficial.

The heat exchanger 18 effectively forms a container 18c having an inlet 18a into the second side 22 and an outlet therefrom shown at 18b. A water draw pipe 90 has an inlet 92 within the second zone Z2 of the tank 12 and an outlet 94 connected to the inlet 18a of the second side 22 of the heat exchanger 18 which, in operation, supplies water from zone Z2 to the heat exchanger 18 for heating therein. A flow director shown generally at 11 is provided for directing the flow of heated water from the outlet 18b of the second side 22 of the heat exchanger 18 back to the second zone Z2 of the tank 12. In one arrangement the flow director 11 may comprise a single return pipe 1 1a having an inlet 11 b connected to the outlet 18b of the heat exchanger 18 and an outlet 11 c terminating within the second zone Z2. A diffuser shown generally at 130 may be used to slowly and gently diffuse any heated water exiting the flow director 1 1 as it enters the second zone Z2 such as to minimise any turbulence associated with the re-introduction thereof. Such turbulence being undesirable as it tends to mix the water within the second zone Z2, which may decrease the efficiency of warming the totality of water within said zone Z2. The diffuser 130 may also include a portion 130a which shields the cold- water inlet 14 and / or the inlet 92 of the water draw pipe 90 as the flow therethrough will also benefit from being calmed thereby.

The above arrangement is able to draw water gently from the bottom zone Z2, heat it in heat exchanger 18 and return it gently to zone Z2 and, thus, create a relatively small quantity of heated water within the lower zone of the tank 12. Such an arrangement could be used with any source of heat but is particularly effective if a low energy or low heat temperature source of heat is being used. Such may be the case with geo-thermal or ground-source heat pump arrangements or solar PV or wind powered electrical generation. Indeed, any one of these sources could be used to create low energy heating of a volume of water within zone Z2 which, whilst not likely to quickly produce water of a temperature suitable for use, is perfectly capable of producing a volume of significantly warmed water which may be created slowly in the background in advance of the demand for hot water. Prolonged use of such“low energy” or renewable energy sourced heat will, eventually, be abler to raise the temperature of the entire volume of water within the tank 12 but it is anticipated that this arrangement will be used in combination with a“high energy” source of heating such as may be provided by, for example, a mains powered electrical heating coil or a gas boiler arrangement. Such an arrangement is shown generally in figure 2 and in more detail in figure 4 which shows alternative heat sources which could be used individually or in combination with each other.

The arrangement of figure 2 may further include means for causing heated water to be directed to a second zone Z2 within the tank 12. Such a zone may be anywhere within the tank but it is preferable to provide such second zone Z2 at the top portion P1 of the tank 12, as this is where the hot water is drawn from and contains the first quantity of water to be used. Heated water may be directed by means of a diverter valve 40 having an inlet 42 connected to receive heated water H W from the second side 22 via outlet 18b of the heat exchanger 18. The diverter valve 40 may include a first outlet 44 and a second outlet 46, each of which may be connected to a respective supply pipe 50, 60 which will each now be described in more detail. Supply pipe 50 includes an inlet 52 connected to the first outlet 44 of the diverter valve 40 and an outlet 54 within the second zone Z2, as mentioned above in more general terms. The second supply pipe 60 includes an inlet 62 connected to the second outlet 46 of the diverter valve 40 and an outlet 64 terminating within said first zone Z1 of said tank 12. Whilst the operation of this valve 40 will be described in detail below, it will be appreciated that it can be used to cause the diversion of heated water HW to one or other or both of said zones Z1 , Z2 as and when desired. Indeed, an actuator 44 and controller 46 may be provided for the purpose of controlling said valve 40 and these may be connected to a central control system shown generally at 200. Also shown in figure 2 is the cold-water supply pipe 70 which has an inlet 72 for receiving cold water from, for example, the mains water supply and an outlet 74 which, in this arrangement, terminates within the second zone Z2 of the tank 12. A water pump 100 is positioned for receiving water through said water draw pipe 90 and for supplying it to the inlet 18b of the heat exchanger 18. The controller 200 may also be connected to this pump 100 for controlling the speed and on/off status thereof as and when required or as and when desired or as and when appropriate as determined by the availability of the various sources of low energy or high energy heat.

The heat exchanger 18 is best seen with reference to figure 4 which shows it in combination with one or more sources of heat which may be used to heat the water on the second side 22 thereof. The first source of heat may be a“high energy” gas heating system 120 feeding heating water to a water-to-water heat exchanger in the form of, for example a coiled pipe 300 within the heat exchanger 18 and exposed to cold water CW passing therethrough such as to heat said cold water before it exits via outlet 18b. an alternative source of heat may be a“low energy” water-to-water heat exchanger in the form of, for example, a second coiled pipe 400 within the heat exchanger 18 and exposed to cold water CW passing therethrough such as to heat said cold water CW before it exits via outlet 18b. Such a“low energy” heat source 140 may, for example, comprise a source of geo-thermal energy or a source of wind derived power or a source of photo-voltaic derived electricity. A third alternative source of energy may comprise an electrical element 500 which is also or alternatively exposed to cold water CW passing therethrough such as to heat said cold water CW before it exits via outlet 18b. Such electrical heating coils may be connected to either“low energy” or“high energy” sources so as to provide heat into the cold-water CW. Each of the sources 300, 400, 500 may be controlled via the controller 200 and may be used individually or in combination with each other as and when desired or as and when appropriate depending on the availability of the various sources of heat / power.

Reference is now made to figure 3, which illustrates in more detail the arrangement of the various pipes within zone Z1 and from which it will be appreciated that the cold-water supply pipe 70 may terminate within said zone in relatively close proximity to each of the inlet 92 of the water draw pipe 90 and the outlet 54 of the first hot water supply pipe 50. This arrangement will allow for the relatively gentle exchange of water between the three pipes and, thus, will assist with the reduction of circulation within the tank itself. This effect may be further enhanced by the use of a diffuser 130 as mentioned above.

Operation of the above-described arrangement will now be described with reference to the figures in general but with particular reference to figure 2.

Once the tank 12 is filled with cold water supplied via cold water inlet 14, the water may be heated by drawing water from zone Z2 by operating pump 100 controlled by, for example, controller 200. Water so drawn will be passed to the inlet 18a of the heat exchanger 18 before being exposed to one or other of the various sources of heat energy 300, 400, 500, each of which may be used individually or in combination with each other and each may be controlled by controller 200 in accordance with pre-defined or other operating conditions or processes. The drawn water is then heated either via a“low energy” or“high energy” source and is then sent to one or other of zones Z1 or Z2. If sent to zone Z2 this will result in heated or warmed water being returned to the bottom of the tank 12 and in close proximity to the cold-water inlet 14 and the inlet 92 to the water draw pipe 90 and, hence, the baffle 130 and 130a may be used to ensure that diffusion around the tank is minimised. Heating of the water in zone Z2 is likely to pass around the tank 12 by virtue of the normal thermal convection currents but the baffle 130 will help reduce this to some extent. Heating by directing heated water to zone Z2 will result in a more general heating of the water within the tank and may best be performed by“low energy” or renewable sources of heat energy. The alternative is to direct heated water to zone Z1 which is towards/ at the top of the tank in portion P1. This is the portion of water that is first drawn when a user requests hot water and it is, therefore, possible that the use of the“high energy” sources of heat may be most used when heating the water in this portion. Since heated water will always rise to the top of the tank, any heat injected into the water already within portion P1 will generally remain there and, hence, it will be possible to very rapidly heat an initial quantity of water for relatively speedy use as it is the water at the top of the tank which will be drawn first.

From the above, it will be appreciated that one may operate the controller 200 or system 10 such as to cause the rapid heating of an initial quantity of water within zone Z1 which may be relatively small compared with the entire volume of the tank 12. It will also be appreciated that a larger volume of water may be heated in zone Z2 by means of heat from“low energy” or “high energy” means. It will also be appreciated that the“low energy” means may be used to supplement the heating of water or used to commence initial background heating of water when there is surplus“low energy” available but, potentially, little or no demand for heated water by the consumer. Still further, the“low energy” or“high energy” sources may be used to heat water in either or both of zones Z1 and Z2 individually or in combination with each other or sequentially to each other so as to meet the demand whilst using as little“high energy” source of heat as possible.

From the above, it will also be appreciated that the average COP associated with heating the relatively small volume of water in the upper zone Z1 is likely to be high as there is a relatively small amount of water to heat. It will also be appreciated that the COP associated with using “low energy” sources of heat to heat the rather larger volume of water in zone Z2 or the water in zone Z2 which is then gently re-distributed around the tank 12 is also likely to be relatively high. It will also be appreciated that the use of “low energy” heat when there is a surplus thereof is likely to be very energy efficient and will result in the general temperature of the water in the tank being increased in advance of any demand which can then be more easily or speedily met by using the“high energy” sources of heat which will be used for less time and, hence, more efficiently.

Claims

CLAIMS:

1. A water heating system (10) comprising: a tank (12) for holding a quantity of water and having a cold-water inlet (14) and a hot water outlet (16) and having a first upper zone (Z1) and a second lower zone (Z2); a heat exchanger (18) having a first side (20) for receiving heat (H) from a heat source (A) and a second side (22) for transmitting heat (H) to water to be stored within the tank (12); wherein said heat exchanger (18) includes an inlet (18a) into said second side (22) of said heat exchanger (18) and an outlet therefrom (18b); and wherein said system (10) further includes a water draw pipe (90) having an inlet (92) within said second zone (Z2) and an outlet (94) connected to said inlet (18a) to the second side (22) of the heat exchanger (18) for supplying water from zone Z2 to the heat exchanger (18) for heating therein; and wherein said heat exchanger (18) is external to the tank (12)and wherein said system (10) further includes a flow director (11) for directing flow of water from said outlet (18b) of second side (22) of said heat exchanger (18) to said second lower zone Z2.

2. A water heating system (10) as claimed in claim 1 and including a diffuser (130) within said second region (Z2) for causing the gentle diffusion of heated water introduced thereinto.

3. A water heating system (10) as claimed in claim 1 or claim 2 and further including a diverter valve (40) for directing water from the second side (22) of the heat exchanger (18) to said first or said second of said zones (Z1 , 7.7).

4. A water heating system (10) as claimed in claim 3 and wherein said tank (12) includes an upper portion (P1) and a lower portion (P2) and wherein said first zone (Z1) is in the upper portion (P1) of said tank (12).

5. A water heating system (10) as claimed in claim 3 or claim 4 and wherein said tank (12) includes an upper portion (P1) and a lower portion (P2) and wherein said second zone (Z2) is in the lower portion (P2) of said tank (12).

6. A water heating system (10) as claimed in any one of claims 3 to 5 and wherein said diverter valve (40) includes an inlet (42) for receiving heated water (HW) from said second side (22) of said heat exchanger (18) and a first outlet (44) and a second outlet (46) and wherein said heating system (10) further includes a first hot water supply pipe (50) having an inlet (52) connected to the first outlet (44) of the heat exchanger (18) and an outlet (54) within the second zone (Z2) of the tank (12).

7. A water heating system (10) as claimed in any one of claims 1 to 6 and wherein said heating system (10) further includes a second hot water supply pipe (60) having an inlet (62) connected to the second outlet (46) of the heat exchanger (18) and an outlet (64) within said first zone (Z1) of said thank (12).

8. A water heating system (10) as claimed in any one of claims 1 to 7 and wherein said heating system (10) further includes a cold-water supply pipe (70) having an inlet (72) for receiving cold water (CW) from a supply thereof and an outlet (74) within said second zone (Z2) of said tank (12).

9. A water heating system (10) as claimed in claim 8 and including a water pump (100) for drawing water into said water draw pipe (90) and supplying said water to said inlet (18a) to said heat exchanger (18).

10. A water heating system (10) as claimed in any one of claims 1 to 9 and wherein said heat exchanger (18) comprises a water-to-water heat exchanger and wherein said first side (20) includes an inlet (20a) for receiving heated water and an outlet for expelling water from said first side (20) after heat has been passed to the second side (22) of said heat exchanger (18).

1 1. A water heating system (10) as claimed in claim 10 and including a gas heating system (120) having a hot gas-to-water heating element (122) for heating water circulating within said first side (20) thereof.

12. A water heating system (10) as claimed in any one of claims 1 to 11 and wherein said heat exchanger (18) comprises an electric heating system (110) including an electric heating element (112) forming said first side (20) thereof.

13. A water heating system (10) as claimed in claim 12 and including a renewable energy generation system for generating electricity to be supplied to said electric heating system (110).

14. A method of operating a water heating system as claimed in any one of claims 1 to 13 including the steps of: d) drawing water from within the second zone (Z2) and supplying it to the second side (22) of said heat exchanger (18);

e) supplying heat to said first side (20) of said external heat exchanger (18);

f) heating water within said second side (22) of said external heat exchanger (18) and diverting said hearted water by operation of said first diverter valve (30) to either one or other of said first zone Z1 or said second zone Z2.