GB2235966A

GB2235966A - Water heating systems

Info

Publication number: GB2235966A
Application number: GB9018328A
Authority: GB
Inventors: David Edwin Steade
Original assignee: Worcester Heat Systems Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 1989-08-31
Filing date: 1990-08-21
Publication date: 1991-03-20
Anticipated expiration: 2010-08-21
Also published as: GB9018328D0; GB8919654D0; GB2235966B

Abstract

A water heating system comprises a primary circuit in which primary water is circulated between a boiler 10 and a heat exchanger 13, and a secondary circuit in which secondary water from the mains is passed through the heat exchange 13 and delivered to a hot tap 18. A bypass 20, controlled by a valve 21, is provided across the heat exchanger 13 in the secondary circuit. The valve 21 is controlled by a temperature sensor 15 in the primary circuit so as to be open if the primary water is below a predetermined temperature. Thus, cold mains water is bypassed directly to the tap 18 until the heat exchanger has reached the operating temperature, thus preventing the waste of partially heating secondary water during the warm-up period. In an alternative arrangement the bypass is in the primary circuit. <IMAGE>

Description

"Improvements in or relatina to Water Heating Systems The invention relates to water heating systems of the kind comprising a primary water circuit in which primary water may be circulated between a boiler and a water-to-water heat exchanger, and a secondary circuit in which secondary water from a supply, usually the mains supply, is passed through the heat exchanger and delivered to a point of use.

Usually, when therm is no demand for hot water in the secondary circuit all the components within the system are at ambient temperature. When a flow of secondary water is initiated, indicating a demand for the water to be heated, a suitable flow sensing device detects this flow and causes the boiler to be ignited as well as, usually, starting up a circulating pump to force primary water around the primary circuit and through the heat exchanger. After a period of time the primary water heats up and, in turn, heats the secondary water passing through the heat exchanger.

Since heating of the primary water depends on flow of secondary water being detected, it is at present necessary to let the secondary water run to waste during the warm-up period, until it reaches a temperature where it is suitable for use. However, during the warm-up period the secondary water is partly heated so that this heat energy is wasted.

The object of the present invention is to provide a form of water heating system which prevents this partial heating taking place during the warm-up period, thus saving energy and reducing the length of the warm-up period.

According to the invention there is provided a water heating system of the kind comprising a primary circuit in which primary water may be circulated between a boiler and a water-to-water heat exchanger, and a secondary circuit in which secondary water from a supply is passed through the heat exchanger and delivered to a point of use, wherein at least one of said circuits includes means bypassing said heat exchanger and a bypass valve controlling the flow of water through said bypass.

Preferably the bypass valve is adapted to be open when the temperature of the primary water is below a predetermined value, and is automatically closed when the temperature exceeds that value.

Thus, where the bypass is in the secondary circuit, the secondary water bypasses the heat exchanger until the primary water has sufficiently warmed upt and is therefore not partially heated during the warm-up period. In the case where the bypass is in the primary circuit, the secondary water continues to pass through the heat exchanger but the heat exchanger does not receive primary water and thus does not transfer any heat to the secondary water during the warm-up period.

The bypass valve should have a low resistance to flow and the normal resistance to flow in the heat exchanger may then be sufficient to ensure that most of the water flows through the bypass rather than through the heat exchanger when the bypass valve is open.

Preferably, however, there is provided in said one of the circuits a flow controlling device which is in series with the heat exchanger and through which water passes to the heat exchanger when the bypass valve is closed.

The flow controlling device may be in the form of a flow restrictor which provides a greater resistance to flow than the bypass valve, so that when the bypass valve is open substantially all the water flowing in the circuit flows through the bypass.

Alternatively, the flow controlling device may be in the form of a further valve which is controlled so as to be closed when the bypass valve is open and open when the bypass valve is closed. This ensures that all the water in the circuit flows through the bypass valve when it is open and none flows through the heat exchanger.

The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a water heating system in accordance with the invention, and Figure 2 is a similar representation of an alternative form of system.

t Referring to Figure 1: a boiler 10 is connected by a supply conduit 11 and a return conduit 12 to a water-to-water heat exchanger 13. A pump 14 effects circulation of primary water around the circuit. The circuit comprising the boiler 10, conduits 11, 12, pump 14 and heat exchanger 13 constitutes the primary circuit.. A temperature sensor 15 detects the temperature of the primary water flowing around the primary circuit.

The secondary circuit comprises a delivery conduit 16 which delivers cold mains water to the waterto-water heat exchanger 13 and an outlet conduit 17 which delivers secondary water from the heat exchanger 13 to a point of use, typically a tap 18. A flow sensor 19 is provided in the delivery conduit 16. In parallel with the heat exchanger 13 is a bypass conduit 20 which connects the delivery conduit 16 to the outlet conduit 17 and is controlled by a bypass valve 21. The bypass valve 21 is controlled by the temperature sensor 15.

The valve is normally open but is arranged to close when the temperature sensor 15 detects a predetermined temperature of the primary water in the primary circuit, typically in the region of 70-80iC.

Initially, when there is no flow of secondary water, the boiler is not alight, the pump 14 is inoperative, and all components of the system are at ambient temperature.

When the tap 18 is opened there is a flow of mains water along the delivery conduit 16 which is detected by the flow sensor 19. The flow sensor causes the boiler 10 to ignite and the pump 14 to operate, circulating primary water from the boiler 10 through the heat exchanger 13. However, secondary water in the delivery conduit 16 is bypassed through the valve 21 to the outlet conduit 17 and tap 18, without passing through the heat exchanger 13. The valve 21 may be normally open, or may be arranged to be opened in response to the flow of secondary water. The secondary water remains therefore unheated as it flows to waste.

When the temperature sensing device 15 detects that the primary water has reached the predetermined temperature, it causes the valve 21 to close and secondary water then flows through the heat exchanger 13 which has now reached its correct operating temperature. During the warm-up period, not only has there been no waste of partially heated secondary water, but the time taken for the heat exchanger to reach the operating temperature has been significantly reduced.

The normal resistance to flow through the heat exchanger 13 may itself be sufficient to ensure that substantially all the secondary water flows through the bypass 20. Although a very small quantity of water may still pass through the heat exchanger, this may not be significant.

However, in order to ensure that substantially all the secondary water flows through the bypass a flow controlling device 22 is preferably provided in the secondary circuit in series with the heat exchanger 13.

The device 22 may take the form of- a flow restrictor which creates a sufficient resistance to flow through the heat exchanger to ensure that substantially all the secondary water will flow through the bypass.

Alternatively, the device 22 may be in the form of an electrically or mechanically operated valve which remains closed while the valve 21 is open and is opened electrically or by other means when the valve 21 is closed. To achieve this operation the valve 22 may be electrically or mechanically coupled to the valve 21, or may be controlled by the temperature sensing device 15. Alternatively, the two valves 21 and 22 may be combined into a single diverting valve having a single entry port and two delivery ports through which the flow may be selectively diverted.

Figure 2 shows a modified arrangement and corresponding components of the water heating system-are given the same reference numerals.

In this case a heat exchanger bypass conduit 23 is provided in the primary circuit rather than in the secondary circuit, and is controlled by a bypass valve 24. The valve 24 is controlled by the temperature sensing device 15, as in the previously described arrangement, and a flow restrictor or valve 25, corresponding to the device 22, is provided in series with the heat exchanger.

In this arrangement the valve 24 remains open during the initial warm-up period so that during this period no primary water passes to the heat exchanger.

The heat exchanger 13 is therefore not pre-heated and therefore transfers no heat to the secondary water.

Although, in this arrangement, the heat exchanger itself is not pre-heated, considerable benefit is still obtained since there is pre-heating of the boiler, circulating pump and other components of the primary circuit.

As mentioned with reference to the Figure 1 arrangement, the valves 24 and 25 may be combined into a single diverting valve having a single entry port and two delivery ports through which the flow may be selectively diverted.

In some cases it may be simpler and cheaper to adopt the arrangement of Figure 2 in view of the less severe pressures etc. normally present in the primary water circuit.

Claims

1. A water heating system comprising a primary circuit in which primary water may be circulated between a boiler and a water-to-water heat exchanger, and a secondary circuit in which secondary water from a supply is passed through the heat exchanger and delivered to a point of use, wherein at least one of said circuits includes means bypassing said heat exchanger and a bypass valve controlling the flow of water through said bypass.

2. A water heating system according to Claim 1, wherein the bypass valve is adapted to be open when the temperature of the primary water is below a predetermined value, and is automatically closed when the temperature exceedsgthat value.

3. A water heating system according to Claim 1 or Claim 2, wherein the bypass is in the secondary circuit.

4. A water heating system according to Claim 1 or Claim 2, wherein the bypass is in the primary circuit.

5. A water heating system according to any of Claims 1 to 4, wherein the bypass valve has a low resistance to flow and the normal resistance to flow in the heat exchanger is sufficient to ensure that most of the water flows through the bypass rather than through the heat exchanger when the bypass valve is open.

6. A water heating system according to any of Claims 1 to 5, wherein there is provided in said one of the circuits a flow controlling device which is in series with the heat exchanger and through which water passes to the heat exchanger when the bypass valve is closed.

7. A water heating system according to Claim 6, wherein the flow controlling device is in the form of a flow restrictor which provides a greater resistance to flow than the bypass valve, so that when the bypass valve is open substantially all the water flowing in the circuit flows through the bypass.

8. A water heating system according to Claim 6, wherein the flow controlling device is in the form of a further valve which is controlled so as to be closed when the bypass valve is open and open when the bypass valve is closed, so that all the water in the circuit flows through the bypass valve when it is open and none flows through the heat exchanger.

9. A water heating system according to Claim 8, wherein the bypass valve and the further valve are combined in a single diverting valve having a single port and two delivery ports through which the flow may be selectively diverted.

10. A water heating system substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.