GB2208914A - Storage water heaters - Google Patents

Abstract

A semi-storage calorifier for heating water comprises a tank (A), an in-built non-storage heat exchanger (B), a pump (C) for delivering water via the heat exchanger (B) into an upper part of the tank (A), and a water velocity reduction device (I) located within the tank (A) adjacent to a cold water inlet, the velocity reduction device serving to reduce mixing of the stored hot water with incoming cold water (Q). <IMAGE>

Description

Calorifiers This invention relates to calorifiers. It has particular relevance to semi-storage calorifiers which are equipped with an in-built non-storage heat exchanger.

According to one aspect of the invention we provide a calorifier having a storage region and incorporating a heat exchanger from which the secondary heated fluid is supplied to an inlet to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, said draw-off outlet having associated with it a fluid velocity reduction mechanism, said mechanism being located within said storage region closely adjacent to said outlet.

According to a second aspect of the invention we provide a calorifier having a storage region and incorporating a heat exchanger from which the secondary heated fluid is supplied to an inlet to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, said storage region having an inlet in its lower part for cold fluid to be heated, said inlet having associated with it a fluid velocity reduction mechanism, said mechanism being located within such storage region and closely adjacent to said inlet. The purpose of the velocity reduction mechanism adjacent the inlet is to reduce the velocity of the cold fluid as it enters the storage region thereby creating as little disturbance as possible to the remainder of the stored volume of heated fluid.The purpose of the velocity reduction mechanism adjacent the draw-off outlet of the storage region is to encourage acceleration of the flow of fluid into the outlet whilst creating minimum disturbance to the stored volume of secondary fluid. Each or either mechanism may comprise a plate which may be flat or curved and may be spaced from the inlet by between 1/8 and i the diameter of the inlet or outlet. The plate may be curved such that it runs parallel to a curved surface of the storage region adjacent the inlet or outlet. The plate may be substantially circular or square with its diameter or square side having a dimension between 4 and 8 times the diameter of the respective inlet or outlet. Typically such dimension is about six diameters.

According to a third aspect of the invention we provide a calorifier having a storage region and incorporating a heat exchanger from which the secondary heated fluid is supplied to an inlet to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, incorporating a control valve which controls the flow of primary fluid into or out of the heat exchanger so as to maintain constant the temperature of the secondary heated fluid leaving the heat exchanger.

According to a fourth aspect of the invention we provide a calorifier having a storage region and incorporating a heat exchanger from which the secondary heated fluid is supplied to an inlet to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, incorporating a regulating valve between the output of secondary fluid from the heat exchanger and its inlet into the storage region which operates to admit secondary fluid to the storage region only at a pre-set temperature.

According to a fifth aspect of the invention we provide a calorifier having a storage region and incorporating a heat exchanger from which the secondary heated fluid is supplied to an inlet to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, in which the inlet to the storage region comprises a pipe extending into the storage region having at least one slot running parallel to the axis of the pipe. Preferably there are two parallel slots spaced radially by at least 90".

The secondary fluid is typically water as is the cold fluid introduced from the bottom of the storage region. The primary fluid may be steam.

One embodiment of the invention will now be described by way of example only with reference to the accompanying schematic drawing.

The calorifier typically has a baffled heat exchanger B with a 2-pass shell which provides an efficient compact unit which is considerably smaller than a conventional storage heater battery.

A pump C circulates secondary water between the storage region A and the heat exchanger. The interconnecting pipes are typically so arranged that the entire volume quickly reaches full storage temperature.

This not only assures a maximum reserve of hot water but also eliminates any areas of cool water, which may promote the growth of Legionalla pneumophila.

The maximum demand from a boiler associated with the calorifier can be regulated by adjusting the circulation rate through the heat exchanger B and offers a flexibility of control not possible with a simple storage battery. Demands for hot water are promptly sensed by a control system which immediately starts the heat recovery process. Low draw off rates only generate low demands from the boiler service. High draw off rates will only generate a demand from the boiler equal to the limit fixed by the control. The reserve of stored water in the storage region A provides the extra supply of hot water required for peak flows and the heat exchanger B continues to make up the deficit after the surge has ended.The calorifier is therefore able to handle peak flow rates in excess of its hourly rating without overloading the boiler, an advantage over the various forms of instantaneous heaters available.

Storage Volume The optimum storage capacity for the calorifier is typically 25% of the peak hourly consumption. This capacity normally provides sufficient buffer volume to cope with the fluctuations in demand while the heat exchanger B continues at a steady input.

For some applications the hourly demand is concentrated into a few minutes. Under these conditions either the storage region A must be increased to meet the full demand or the heat exchanger B sized accordingly.

Flow Distributors The cold feed inlet at the very bottom of the storage region A is fitted with a flow spreader or velocity reducer I to reduce the incoming velocity and so minimise any disturbance of the stored hot water.

Similarly discharge from the heat exchanger B into the storage region A incorporates a spreader pipe K having long slots which introduce heated water with very little disturbance. The draw-off outlet M at the top of the cylinder has a velocity reduction device J to maintain stratification.

Peak Draw Off With the aid of the flow distributors there is very little mixing of hot and cold water within the storage region A. This allows flow rates greatly in excess of the hourly rate for short periods without loss of temperature.

Heater Output The heat exchanger B is normally rated 20% above the hourly demand to provide a margin of cover during sustained periods of heavy draw-off. However the maximum output can be reduced by throttling the pump C delivery to the heat exchanger. Since the thermostat D maintains a constant flow temperature from the heater, the output is automatically reduced in proportion to the circulation rate. Installations which are particularly critical to boiler load can be fitted with a tapped orifice for flow measurement on site. A lockshield valve F is fitted as standard for adjusting the flow.

Pump Unit The bronze circulating pump C may be an integral part of the calorifier and is independent of any external recirculating system. It is a low head, high output pump designed for low power consumption and continuous operation. The standard motor is totally enclosed, fan cooled, 3 phase, 50 Hz and supplemented with a flow switch which can be incorporated into a display or alarm system.

Control Valve For primary hot water supply a 3-port valve is normally fitted to minimise pressure and flow changes within the main system. However for a tight shut off in installations where there are long periods of no draw-off and no circulatory losses, a 2-port valve is recommended.

When steam is the primary medium a 2-port valve E is fitted, which is normally sized for critical pressure drop at the design load. This gives finer control over the operating range.

With both forms of heating the valve is controlled by a direct acting thermostat D. This is located in the flow pipe from the heat exchanger and the temperature setting is manually adjustable.

Heat Exchanger The heat exchanger B comprises a multi-pass U-tube assembly mounted in a 2-pass shell. The heat exchanger shell fits inside the storage cylinder for heat retention and economy of space. The primary medium is contained within the tubes to meet the requirements of BS 853 and accommodates high pressure primary services without undue pressure on the shell side. A bursting disc is fitted on the secondary side for high pressure primary hot water services. The U-tube battery is removable for cleaning and inspection like any conventional storage calorifier.

Finned tubes are normally fitted for their compactness and high output but plain tubes are available for hard water applications.

Safety Controls Due to the reduced storage capacity of the calorifier some form of thermal protection is recommended to supplement the temperature control system. The standard calorifier protection is a temperature/pressure relief valve L fitted to the main shell and designed to limit the storage temperature below 100etc.

Additional protection can be provided in the form of a thermal trip on the control valve E. Alternatively a completely independent valve can be fitted in series with the control valve to isolate the unit. Both of these systems have adjustable temperature limits. The high temperature sensor is located in the main shell.

Mention has already been made of the pump flow switch.

If the high temperature trip is also an electric switch it can be incorporated into an alarm system and form part of the starting sequence.

Access An inspection opening is provided on all sizes of calorifier for examination of the storage region interior. A single drain valve H is so positioned that the entire system can be drained down. Alternatively the heat exchanger B, control thermostat D and pump C can be isolated by means of a valve G from the storage region A and drained down without losing the main storage volume.

Condensate Cooling Due to the high performance of the 2-pass heat exchanger B it is possible to offer condensate cooling below 100"C. This cooling takes place in the battery before the steam trap and without any external pipework.

Steam consumption is reduced by the amount of additional heat extracted from the condensate. There are no problems with flash steam and losses from the condensate return lines are reduced.

How It Works The calorifier typically has a fixed speed centrifugal pump C which circulates secondary water through the heat exchanger B and into the storage cylinder. The flow rate through the heat exchanger B is normally set approximately 20% above the calculated peak hourly demand. The heat exchanger B is sized to raise the tempeature of the secondary water from cold to design temperature in a single pass through the exchanger.

When the unit is first commissioned the content is cold. The pump C draws water from the bottom and returns it hot through the spreader K into the top half of the storage region A. Here the hot water mixes with the cold storage gradually raising the entire contents to the design temperature.

When the demand for hot water is less than the peak hourly rate the cold feed Q is drawn directly into the heat exchanger B by the pump together with some hot water from the bottom of the storage region A so the water passing through the heat exchanger B is already partially warmed and only sufficient heat is added to reach the design temperature.

When the demand for hot water exceeds the pump rate cold feed is still drawn into the heat exchanger B but the excess cold feed enters the bottom of the storage region A without disturbing the layer of hot water above. The heat exchanger B now generates hot water at the maximum design rate and flow from the draw-off outlet M is supplemented by hot water from the heat exchanger B. After a heavy demand the heat exchanger B continues to work at high output until the storage temperature in the bottom of the storage region A is restored.

In order to make full use of the stored hot water it is advisable to fit a non return valve on the secondary return N. This will prevent cold water entering the secondary system via the return leg. It will be appreciated that even under severe overload conditions the heat exchanger B will maintain full power output giving a moderate mix temperature until such time as normality returns.

Claims (14)

CLAIMS:

1. - A calorifier having a storage region for secondary, heated fluid that is circulated therearound and by means of a pump via a heat exchanger for heating said secondary fluid, from which heat exchanger the secondary heated fluid is fed to the upper part of said storage region, said secondary heated fluid being drawn off on demand from said storage region through a draw-off outlet in the uppermost part of said storage region, said storage region having an inlet in its lower part for cold fluid to be heated and said inlet having associated with it a fluid velocity reduction device located within said storage region closely adjacent to said inlet.

2. A calorifier according to claim 1 wherein said draw-off outlet has associated with it a fluid velocity reduction device located within said storage region closely adjacent to said outlet.

3. A calorifier according to claim 1 or claim 2 wherein the or each said velocity reduction device comprises a flat or curved plate, one of the two major surfaces of which faces its associated inlet or outlet in spaced relationship thereto.

4. A calorifier according to claim 3 wherein the or each plate is spaced from the inlet or outlet by between 1/8 and 1/3 the diameter of the inlet or outlet associated therewith.

5. A calorifier according to claim 3 or claim 4 wherein the or each plate is substantially circular or square.

6. A calorifier according to claim 5 wherein the diameter or square side, as the case may be, of said plate has a dimension between 4 and 8 times the diameter of the inlet or outlet associated therewith.

7. A calorifier according to any one of claims 1 to 6 including a control valve for controlling the flow of primary fluid into or out of the heat exchanger so as to maintain substantially constant the temperature of the secondary heated fluid leaving the heat exchanger.

8. A calorifier according to any one of claims 1 to 7 including a manually adjustable valve between the output of secondary fluid from the heat exchanger and its inlet into the storage region for controlling the feed rate of secondary fluid to the upper part of said storage region.

9. A calorifier according to any one of claims 1 to 8 wherein said secondary heated fluid is fed into the upper part of the storage region by a pipe extending within the storage region and having in its wall at least one fluid outlet slot running substantially longitudinally of the pipe.

10. A calorifier according to claim 9 wherein the pipe wall has therein at least two such slots lying in radial planes that are at an angle of at least 90" to one another.

11. A calorifier according to any one of claims 1 to 10 wherein the heat exchanger includes an at least two-pass passageway, for example a tube, for the primary heating fluid.

12. A calorifier according to claim 11 wherein said passageway is a four-pass passageway.

13. A calorifier according to claim 11 or claim 12 wherein the heat exchanger is adapted to utilise steam as said primary heating fluid optionally together with a condensate cooling function.

14. A calorifier substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

14. A calorifier according to any one of claims 1 to 13 wherein the secondary fluid inlet side of the heat exchanger is teed off the cold fluid supply pipeline connected to the inlet in the lower part of the storage region.

15. A calorifier according to claim 14 wherein the pump is located between said tee and the heat exchanger.