GB2195173A - Hot water container; self priming of primary water circuit - Google Patents

Abstract

A hot water container 1 has an upper interior divided into adjacent upper and lower chambers C,B defined by a base 2, partitioning wall 3 and the container roof 4, a primary duct 6 extending upwardly of the partitioning wall allowing communication between the upper and lower chambers and at least one secondary duct 5 extending downwardly of the partitioning wall allowing communication between the upper chamber and the remaining container compartment A. The lower chamber B has a vent 11 to atmosphere and can be connected at 10 to a primary water heating circuit including the indirect heat exchanger 16. The upper chamber has a hot water draw-off 8. The present container may be incorporated within a domestic hot water and central heating system particularly a combined unvented system with one set of safety controls serving both hot water and heating services. A further secondary duct 7 induces natural convection flow through the other secondary duct 5 into the upper chamber C. <IMAGE>

Description

1

SPECIFICATION

Hot water container and system GB2195173A 1 This invention concerns domestic hot water 70 storage containers, such as tanks or cylinders and heating systems incorporating such con tainers.

The principle of heating water for domestic purposes has in the majority of residences be- 75 come merged with heating the rooms by water-filled radiators by a single heat source.

The medium of water serves to heat both (1) the domestic hot water, and (2) the central heating radiators. It is necessary to keep the 80 water in these services physically separate by e.g. means of a heat exchange device. The water in the domestic services is to be kept clean and uncontaminated by the normally dirty radiator water. Similarly the central heat- 85 ing water should be kept inert and unaffected by dissolved air normally present in the do mestic water services.

The principle of physical separation of these water services is well known and largely at tained by having two independent water ser vices served by a single heat source and con nected for the transfer of heat from one to another by a heat exchanger. Contemporary practice is founded on heating the domestic hot water supply in a storage container such as a metal cylinder conventionally, but not essentially, of copper. This is referred to an an indirect cylinder. The bulk of stored water is heated, in use, by a heat exchanger coil (although other forms may be employed) con nected to the primary central heating system, both services being heated by one central boiler.

This contemporary practice has the disadvantage that two separate water systems leads to duplication of technical components and a consequent higher cost. The traditional method in the United Kingdom is based on both domestic hot water and the central heating water services requiring a separate high level cold water supply cistern and each with its own mains input supply, overflow discharge pipe, feed connecting pipe and open vent safety pipe.

GB-A-2 001 740 provided a system for avoiding this duplication so that one set of services could be utilised for both (1) the domestic hot water, and (2) the central heating system.

The patented system relies upon dissolved air naturally found in water and its release upon heating. The air is collected in a vessel to keep the secondary domestic water sepa- rate from the primary central heating water.

There exists a demand for 'unvented' domestic heating systems in which the intermediate storage cistern within the domestic residence is eliminated and the public reservoir is used instead as a direct feed supply to the hot water system.

In 'unvented' systems the domestic hot water services are no longer supplied from a high level cold water storage cistern, which has an open vent to atmosphere. As 'unvented' systems do not have an open vent it is necessary to introduce safety measures or devices., if not sold with the cylinder then certainly prior to actual operation, to make the system safe and to accommodate normal operation and malfunction.

Domestic hot water storage and central heating systems may now require (a) an inlet water pressure regulating valve, (b) a pressure relief valve, and (c) a temperature relief valve (preferably including an anti-vacuum function). These principal safety controls can be supplemented by an expansion vessel to accommodate thermal expansion and/or contraction of the bulk of stored hot water as it heats and cools.

Such mechanical safety controls form part of the 'unvented' domestic hot water system, the primary central heating system being phy- sically and mechanically separate.

The "sealed" central heating system has been in use in this country for some time with certain drawbacks. This type of system, because it has no open vent to atmosphere, re- quires an expansion vessel to accommodate expansion and contraction of the primary heating system. Pressure exerted within the primary system seeks out the weakest points of minor leakage, e.g. the packing gland of radia- tor valves. The sealed system hitherto used does not have a permanent facility for replen ishing lost water. The primary system only has to lose a "cup" of water per week to be a failure.

If the unvented domestic water heating sys tem were to be used together with the sealed central heating system this would involve du plication of all the mechanical safety control devices previously described.

The present invention seeks to provide a container, e.g. a cylinder and system in which the "unvented' domestic hot water system can be combined with the sealed central heat ing system. The mechanical safety control mechanisms may serve both services with savings in initial cost and subsequent maintenance.

According to this invention there is provided a container such as a cylinder suitable for e.g.

domestic hot water storage, which in an upright position has an upper interior divided into adjacent upper and lower chambers defined by a base, partitioning wall and the container roof, a primary duct extending upwardly of the partitioning wall allowing communication between the upper and lower chambers, at least one secondary duct extending downwardly of the partitioning wall allowing communication between the upper chamber and the remaining container compartment, said lower chamber GB2195173A 2 having a vent to atmosphere preferably by means of an automatic air vent and means suitable for connection to a water heating cir cuit. The invention includes a hot water sto rage and central heating system incorporating such a container.

This invention eliminates the need for a se parate expansion vessel by providing integral chambers for accommodating expansion and contraction of both the domestic store of hot 75 water, and also the primary central heating system. The invention may provide 'make-up' water to the primary heating system which may be required from e.g. minor leakages.

The invention may allow the pressure exerted 80 on both the domestic stored water and the primary heating circuits to be equal. Both ser vices may be influenced equally by the pres sure entering from the street mains through a pressure reducing valve. This valve may be preset at any required input pressure, e.g.

0.45 BAR (7 Ibs. per square inch) This operating pressure will enable a normal BSS 1566 GRADE 3 copper hot water cylin der to be utilised as one form of storage con- 90 tainer, with cost savings. The pressure relief valve when fitted to the cylinder may be set at any required break pressure, e.g. only 1 BAR (14 Ibs. per square inch). In practice this means that the normal operating pressure on both the domestic hot water service and also the central heating system would be equiva lent to an ordinary two storey house, tradi tionally with a high level storage cistern in the attic. The invention is designed to exploit the 100 release of -dissolved air- naturally found in water and to use this as a functional compo nent. The invention may render the primary system inert, removing the dissolved air from the central heating system, and maintaining such status. The release of dissolved air from the secondary hot water storage is consider able being some 2% of water volume. In prac tice this means there is about 1/2 gallon of dissolved air in every 25 gallons of stored hot 110 water. This means that there is in normal use a consistant rejuvenatory discharge of dissolved air from the domestic stored hot water into the functional air collecting chamber(s). 50 In embodiments of the present invention the 115 physical volume of the vessel capable of maintaining an air seal is substantially enhanced compared to the system described in GB-A-2 001 740. 55 Suitable cylinders for use in the present invention include, for example, a standard BSS1566 Indirect Cylinder, or BSS699 Direct Cylinder. It will be appreciated from the detailed description of embodiments that the up- per part of a standard hot water cylinder can be modified to contain the air collecting chamber(s).

In order that the invention may be illustrated and readily carried into effect, an embodiment thereof applied to an indirect cylinder will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a view of a domestic cylinder showing selected internal and external features, Figure 2 is a corresponding further external fittings, and Figure 3 illustrates the cylinder and chambers containing water during initial priming or use.

Referring to Figs 1 and 2 of the drawings which show parts of an 'unvented' domestic hot water storage and central heating system, the storage cylinder 1 is fed by direct mains through stop valve 20 and strainer 19 to pressure regulating valve 13.

The pressure regulating valve can be preset to the required output pressure. This is fol- lowed by a cold water supply outlet 17 which has the advantage of equalising the input pressure to both the hot and cold household supply- with a resulting advantage in the function of these services, particularly the operation of a hot and cold shower. Just before entering the normal cold feed supply point 15 in the hot storage cylinder 1, there is positioned a non-return valve 14. This is to prevent back-pressure into the main supply, which would result from expansion of the stored hot water during heating.

The bulk of the hot water is contained within the storage cylinder compartment Constructed integrally within the upper interior of the cylinder are the two adjacent chambers-the lower serving as the primary expansion chamber---13-, the upper expansion cham ber---Wserving as secondary domestic supply service. Lower chamber -B- is defined by the cylinder space contained between base 2 extending the full internal width of the cylinder and partitioning wall 3 also extending the full width of the cylinder 1. The upper chamber ---Wis defined by the cylinder space between partitioning wall 3 and the internal roof 4, comprising a conventional domed top. The chambers are in communication but in a manner to separate the primary from the secondary water supply. The internal pressure on both sides of these 'separating' chambers being equal, and not requiring to sustain any pressure differential between them.

The whole of the hot water storage vessel is contained within the cylinder 1. This will usually be constructed to the pressure requirements of BS1566 or 13SS699- in accordance with the grade calling for respective operating pressure. The main water storage compartment -A- is in communication with the upper chamber---Wby means of a secondary duct 5, which transcommunicates from compartment -A- to chamber---W,without communicating with the intervening lower chamber ---B -.

A primary duct 6 extends upwardly from view showing 11k 3 GB2195173A 3 the partitioning wall 3 to open communication with the top of chamber -C- and spaced from the roof 4. A further secondary duct 7 extends downwardly from the partitioning wall 3 through chamber -B- but not in communi cation therewith towards the cylinder base within main storage compartment---A-.

The upper chamber -C- comprises domes tic hot water storage/supply, being intercom municated through duct 5 being an open tube 75 to the main (domestic) storage compartment ---A-. This upper chamber provides a hot water draw-off 8 to the household fittings at a point adjacent the partitioning wall. There is also on or near the same horizontal plane to80 wards the bottom of chamber -C- a pressure relief valve 9 incorporating external discharge pipe and preferably also an anti-vacuum de vice. Also on or near this horizontal plane there may be an automatic air vent of the type Trade Mark "Purg-0-Mat" ga which will release any surplus of dissolved air accumu lated in chamber -C- which is not otherwise discharged through the hot water draw-off 8.

Chamber -B- provides primary central heat- 90 ing supply. Adjacent base 2 is the connection suitable for primary heating circuit, see Fig.

2. Also on the same horizontal plane as adja cent base 2 is an automatic air vent 11, for example, the type sold under the Trade Mark 95 "Purg-0-Mat". Towards the top of compart ment -A- there is a temperature and pressure relief valve 12, incorporating an anti-vacuum function and external discharge pipe.

A coiled copper tubular heat exchanger is shown at 16 (Fig. 1) for connection to the primary heating circuit, incorporating pump 18 (Fig. 2), boiler flow line -F-, boiler return line -G-, heating flow line -D- and heating return line---E-.

The filling and operation of the system is described with reference to Figs. 1 and 3. Water enters the cylinder compartment -Aby way of the cold feed inlet 15 at the bot- tom, being connected from pressurised street mains, and passes through the stop valve 20, strainer 19, pressure regulating valve 13 preset to a pressure acceptable to the primary and secondary circuits, and the non- return valve 14. The pressure reduced cold water enters the main storage compartment -Aand proceeds to fill the entire cylinder and the major part of upper chamber---C-. The autoair vent 11 in chamber -B- is wide open, as is the air vent 9a when deployed in chamber -C-, so that as cold water enters the storage cylinder air is automatically expelled. Compartment -A- continues to fill and the water rises through secondary duct 5 into chamber---C-.

The air vent 11 continues to vent air and the water level in chamber -Crises until it reaches the top of the primary duct 6, the automatic air vent 9a having closed. This water then spills over primary duct 6 and pours into the lower (primary water) chamber 130 -B-. The water in the primary chamber -Bcontinues to fill, and water from here pours through the primary connection 10 to fill the entire primary central heating system, which includes the boiler and radiator system (not shown). The primary heating system continues to fill while the automatic air vent 11 continues to expel air. Eventually the water fills the entire primary system and the water level then rises in the primary chamber---13-, so that water then enters the auto-vent 11 raising the automatic air vent float control and so preventing further air expulsion. The instant the auto-vent closes the water which was pouring over the primary duct 6 from -C- stops at the lip of this duct, having trapped atmospheric air in chamber -B- from the watiSr level set by the auto-vent, Air is trapped in (i) chamber "B", from this water level to the partitioning wall 3, in (ii) the primary duct 6, and (iii) above the end of this duct to the cylinder roof 4. The level of the domestic stored water in chamber -C-, at this stage, is at the top of the primary duct 6.

The entire system is then ready for normal operation, and the boiler can be switched on enabling the primary circuit to heat up. Before doing this, however, the chamber -C- can be primed with atmospheric air by a manual process, e.g. the cold water control stop valve from the street mains is temporarily turned off. The pressure relief valve 9 in -C- is then manually opened, being fitted with a manual operating lever for this purpose. The water in -C- then drains out through the discharge pipe attached to the pressure relief valve, while simultaneously the anti-vacuum valve opens and draws atmospheric air into---C-. Once chamber -C- is fully primed with atmo- spheric air the street mains control stop valve can then be turned on. The effect of this manual action is to artificially fill the upper section of -C- with a cushion of air. This atmospheric air having been trapped in the up- per portion of the chamber -B- is cornpressed to the pressure set by the incoming pressure-reduced setting of the system. It should be noted that chamber -C- is designed to accumulate air expelled from the water which would otherwise be continually present in the stored domestic hot water in compartment---A-. At this stored hot water is continually heated and replaced there is a continuous release of dissolved air which rises by its own buoyancy from compartment -A-, and passes through the secondary duct 5 into ---C-. The accumulation of this air in "C", together with the previously 'trapped' atmospheric air in the lower chamber "B", is im- portant to functional operation.

Air is compressible, and this acts as an air cushion, to accommodate the expansion and contraction in both the primary and secondary water systems. The physical size of chambers 'B- and "C" can be varied by an accommo- 4 GB 2195 173A 4 dation in the height of the cylinder wall. The actual dimensions can be determined by an assessment of the amount of expansion vol ume which will result from heating both the primary central heating system, and also the stored domestic hot water in compartment ---A-. It has been assessed that both the pri mary and secondary water volumes have to allow for an increase in volume due to heating of some 4% of volume. Since air is compres- 75 sible, while water is not, it is therefore a func tion of the air cushion in both chambers -B and---Wto accommodate this expansion in volume. An assessment requires to be made to take account of all modes of operation. For purposes of example, the pressure relief valve 9 in---Wis set to open when the pressure reaches 10 pounds per square inch. Similarly the temperature and pressure relief valve 12 is set to open at a slightly higher pressure of 12 pounds per square inch. It will be observed that both these relief valves are set to operate at a pressure slightly below the maximum pressure required by the grade of cylinder for normal operation (i.e.-13SS1566-Grade 3=14 pounds per square inch).

The normal mode of operation would as sume that when the boiler starts to heat, the primary central heating system, including the radiators, will heat and expand first. Shortly afterwards heat transferred through the pri mary heating coil in the indirect cylinder will begin to heat and expand the secondary stored water. Immediately the domestic hot water draw-off tap at the household fittings 100 was used this would instantly relieve and equalise all expansion pressure within the sto rage vessel. For the purpose of assessment, however, it should be assumed that during the initial mode of operation this draw-off tap will not be used. The primary central heating water, which is the content of the boiler, the primary pipe-work, and the radiators will ex pand, upon heating, some 4% of volume. The size of the primary chamber -B- can accom modate such volumetric expansion. As the pri mary water heats, the water level previously set by the auto-vent. 11 rises in chamber -B and pushes the air previously trapped therein upwards through the primary duct 6 into chamber---C-. This air is compressed in pro portion to the primary system volumetric ex pansion and taking account of its initial volu metric capacity. It should be noted the air content already accumulated in chamber---W had previously been manually increased.

After a time interval the primary heating coil in -A- will heat the stored domestic hot water, and depending upon the initial stored volume of the cylinder, will also expand some 4% of volume. It would be possible to design the communicating air cushions to accommo date the maximum expansion of both the pri mary and secondary water simultaneously.

However, since normal domestic applications run the draw-off to the household taps, this immediately relieves and equalises the internal pressure due to expansion of both systems. Minor relief of pressure through the pressure relief valve 9 under maximum operational mode may be permitted. There are two pressure relief valves in the embodiment described as manual relief valves which can stick when they are not occasionally functional.

In a normal operational mode, both the primary and secondary water is free to expand and contract as it heats and cools. The physical size of chamber -B- can be sufficient to permit expansion and contraction of even the largest primary central heating system, without fear of intermixing primary water with secondary storage supply. Similarly the stored domestic hot water is free to expand and contract as its heats and cools, and there is a continual release of dissolved air from the water in cylinder compartment -A- as this water is heated. It is estimated that some 2% of the volume of cold water from the street mains is dissolved air, and this is released by the act of heating the water. By its normal buoyancy this dissolved air accumulates in chamber---C-. Eventually this chamber provides an optimum air cushion and any surplus of air can be discharged mildly through the draw-off outlet to the taps, or released through the automatic air vent 9a. Should both, or either, of the primary or secondary water systems be in a fully heated state and at maximum expansion, then upon the boiler being switched off allowing the systems to cool and contract, the anti- vacuum function preferably in both pressure relief valves comes into operation. Upon the volume in the main compartment contracting, the anti- vacuum valves open and admit atmospheric air to the cylinder, thus enhancing the air cushion. The normal mode of operation of the system is to continually maintain and enhance this air cushion. The water to air interface of the primary system within -B- is free to rise and fall therein as the primary heats and cools, and oxygenated air cannot enter the primary water system through this interface.

A supplementary function is attributed to the further secondary duct 7 as shown in Fig. 1 or 3. This duct is to induce natural convection flow through the other secondary duct to ensure the hottest water is always available in the upper chamber---W,where it can then be drawn off to the household taps.

It is equally important to consider any possible malfunction of the system. In the event of failure of the incoming pressure regulating valve 13, allowing mains pressure to bear upon the storage cylinder, there are two pres sure relief valves to accommodate this, the upper valve 9 set to open at e.g. - 10 psi, and the lower valve 12 set to open at 12 psi. Under malfunction consideration should be given to an event such as the boiler -boiling 1 1 i 1 GB2195173A 5 Although normally the present system would be fitted with a -protected- boiler, i.e. a boiler fitted with a -high-limit- thermostat, if excess pressure caused an accidental -boil ing- of the boiler, this excess pressure should 70 be relieved through either of the two pressure relief valves 9 and 12, both of which are inde pendently discharged to atmosphere. Once the cause of malfunction was corrected, the air seal within the chambers would automatically 75 re-establish, to restore operation to normal mode. The temperature and pressure relief valve 12 in compartment -A- can take ac count of the need to relieve pressures which could result from temperature increases be yond preset level. This could occur by failure of an electric immersion heater fitted with an automatic thermostat. This relief valve 12 will open on both temperature and pressure mal function.

Fig. 2 shows a substantial part of a domes tic hot water storage and central heating sys tem according to the invention. It can be seen that one set of pressure regulating and relief valves may serve both the domestic hot water 90 services and the central heating system simul taneously with resulting saving in costs.

The Figs. 1 to 3 illustrate how a standard BSS1566 indirect cylinder, manufactured to normal dimensions, and founded on a dia meter of 450 mm will have a height which is the standard height plus 350 mm, accounted for by the assessed physical dimension and height of both chambers -Band---C-. This design criteria may apply to all BSS Copper Cylinders of 450 mm diameter. It is possible to construct other containers and systems to these principles for any other selected internal width, while taking account of the physical volume required in the chambers -B- and ---C-.

Claims (14)

1. A container suitable for hot water sto- rage which in an upright position has an upper 110 interior divided into adjacent upper and lower chambers defined by a base, partitioning wall and the container roof, a primary duct extend ing upwardly of the partitioning wall allowing communication between the uper and lower 115 chambers, at least one secondary duct extending downwardly of the partitioning wall allowing communication between the upper chamber and the remaining container compart- ment, said lower chamber having a vent to atmosphere and means suitable for connection to a water heating circuit.

2. A container as claimed in Claim 1 in communication with a mains pressure regulat- ing valve, stop valve and non-return valve.

3. A container as claimed in Claim 1 or 2, in which the container comprises a metal direct or indirect cylinder optionally including a domeshaped roof.

4. A container as claimed in any preceding 1 claim in which the lower chamber vent cornprises an automatic air vent, the upper chamber optionally also incorporating an automatic air vent.

5. A container as claimed in any preceding claim in which the lower chamber is constituted by the container space bounded by the base extending the full internal width of the container and the partitioning wall also extending the full internal width of the container.

6. A container as claimed in any preceding claim in which the upper chamber is constituted by the container space bounded by the partitioning wall extending the full internal width of the container and the interior roof thereof.

7. A container as claimed in any preceding claim in which the upper and lower chambers are in communication whereby a primary water supply can be separated from a secondary water supply, the remaining container compartment communicating with either or both other chambers when required.

8. A chamber as claimed in any preceding claim including two secondary ducts, one being extended towards the bottom of the container.

9. A container as claimed in any preceding claim including pressure relief valve and optionally anti-vacuum device with discharge means in communication with the upper and/or lower chamber.

A container as claimed in any preceding claim including temperature and pressure relief valve optionally incorporating an anti-vacuum function with discharge means.

11. A container as claimed in any preceding claim which, in use, maintains or can maintain communicating air cushions in the up- per and lower chambers through release of dissolved air from heated water.

12. A hot water storage and heating system incorporating a container as claimed in any preceding claim.

13. A container suitable for hot water storage, substantially as herein described with reference to and as illustrated in the accompanying drawings.

14. A hot water storage and heating system substantially as herein described and illustrated.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.