GB2407859A

GB2407859A - Condensing boiler assembly with pressure sensor

Info

Publication number: GB2407859A
Application number: GB0325772A
Authority: GB
Inventors: Martin Hodgson
Original assignee: Worcester Heat Systems Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 2003-11-04
Filing date: 2003-11-04
Publication date: 2005-05-11
Also published as: GB0325772D0

Abstract

A condensing boiler assembly 10 comprises a boiler body 12 having a flue gas outlet 22, a heat exchanger 14 which is housed in the boiler body 12, a burner 16 for heating the heat exchanger 14, a condensate collector 20 for collecting condensation formed by the heat exchanger 14 and having an outlet which is connectable for fluid-communication to a drain which is external of the boiler body 12, a fan 18 for directing flue gas from the heat exchanger 14 to the flue gas outlet 22, and a pressure sensing device P for sensing the pressure or a change in pressure of the flue gas leaving the heat exchanger 14. The sensing device P, in use, provides an indication of a blockage or partial occlusion of a flow path of the flue gas.

Description

CONDENSING BOILER ASSEMBLY

This invention relates to a condensing boiler assembly.

The detection of a blockage or partial occlusion of the intended flow path of flue gas is especially important where the flue gas flow path could divert, and thus discharge from the boiler assembly at a different, and potentially hazardous, place.

One example of this is the use of a U-bend trap condensate collector within the boiler assembly. If the intended flue gas flow path is sufficiently obstructed, the water seal in the U-bend trap can be breached, leading to discharge of flue gas from the condensate collector and not the flue.

The present invention seeks to provide a solution to this problem.

According to one aspect of the present invention, there is provided a condensing boiler assembly comprising a boiler body having a flue gas outlet, a heat exchanger which is housed in the boiler body, a burner for heating the heat exchanger, a condensate collector for collecting condensation formed by the heat exchanger and having an outlet which is connectable for fluid-communication to a drain, a fan for directing flue gas from the heat exchanger to the flue gas outlet, and a pressure sensing device for sensing the pressure or a change in pressure of the flue gas leaving the heat exchanger, the sensing device, in use, providing an indication of a blockage or partial occlusion of a flow path of the flue gas.

Preferable and/or optional features of the present invention are set forth in claims 2 to 13, inclusive.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawing, which shows a diagrammatic sectional view of a simplified condensing boiler assembly, in accordance with the present invention.

Referring to the drawing, there is shown a condensing boiler assembly 10 which comprises a boiler body 12, a condensing heat exchanger 14 housed in the boiler body 12, a burner 16 also housed within the boiler body 12 and mounted above the heat exchanger 14, a fan 18 for drawing air into the burner 16, and a condensate collector 20 positioned below the heat exchanger 14 to collect condensate.

The boiler body 12 has a flue gas outlet 22, typically in its upper surface, and a pipe 24 connects a flue gas outlet 26 of the condensate collector 20 and the flue gas outlet 22 of the boiler body 12. The flue gas outlet 22 of the boiler body 12 is connectable to a common external flue 28 in the usual manner.

When the boiler assembly to is installed, a flue gas flow path from the heat exchanger 14 is thus defined by the condensate collector 20, pipe 24, and flue 28.

The condensate collector 20 includes, at its lower end, a common U-bend trap which has an outlet 32 for the discharge of collected condensate. The condensate outlet 32 is, in usual fashion, connectable through a wall of the boiler body 12 to an existing, typically domestic, drain (not shown) which resides externally of the boiler assembly 10.

The U-bend trap 30 of the condensate collector 20, in normal operation of the boiler assembly 10, maintains a sufficient head of liquid to prevent flue gas passing through the trap and discharging into the external drain.

To enable monitoring of the flue gas flow path, a pressure sensing device P is positioned in the boiler body 12, downstream of the heat exchanger 14. The sensing device P can be mounted at any position between the heat exchanger 14 and the flue gas outlet 22 of the boiler body 12. However, it is generally desirable to mount the sensing device P in the condensate collector 20, at or adjacent to the U-bend trap 30.

The sensing device P. in use, senses the pressure of the flue gas at the U-bend trap 30 as the fan 18 forces the flue gas out of the heat exchanger 14 and along the flue gas flow path. If the flue gas flow path becomes obstructed, for example by the flue 28 or pipe 24 connected to the flue gas outlet 22 of the boiler body 12 becoming blocked or partially occluded, the flue gas pressure upstream of the obstruction, i. e. towards the heat exchanger 14, will tend to rise. This rise in flue gas pressure will tend to cause the head of liquid in the U-bend trap 30, on the flue side, to decrease. If the flue gas pressure rises sufficiently, the trap 30 will open allowing flue gas to discharge to the external drain.

The present European (EN) standard is that a U-bend trap operating in a condensing boiler assembly should have at least a 25mm water seal on the Due side.

As such, known U-bend traps have a typical height in excess of 75 millimetres (mm), and can be as much as 150 mm in height or more. These sizes are necessary to allow for evaporation while still complying with the European standard.

In the present invention, to prevent flue gas pressure from reaching a value whereby the head of water on the flue side in the U-bend trap drops below the required 25 mm, the sensing device P is set to operate at a predetermined value. The predetermined value is dependent on the size of the U-bend trap being used, and thus the head of liquid it produces. For example, when using a 75 mm U-bend trap, the predetermined value would, typically, be set at less than or equal to 5 mbar, which generally corresponds to a head of water approaching or reaching the 25 mm minimum seal level. However, if using a 150 mm U-bend trap, the predetermined value would, typically, be set at less than or equal to 12.5 mbar, which, for this particular trap, generally corresponds to a head of water approaching or reaching the mm minimum seal level.

The predetermined value is also based on a consideration of acceptable margin of error and operating tolerances.

Consequently, if the flue gas pressure at the sensing device P reaches the predetermined value, the sensing device P outputs a signal to a control unit (not shown) of the boiler assembly 10, which shuts off the boiler assembly 10.

The sensing device P can be a transducer-type pressure sensor or a diaphragm- type pressure sensor. Any other suitable type of sensor could also be used.

The sensing device P could also be positioned in the outlet of the heat exchanger 14, or the inlet of the condensate collector 20.

In a modification to the invention, the control unit may simply output a warning signal, when receiving the signal from the sensing device that the flue gas pressure equals and/or exceeds the predetermined value. However, this would not necessarily prevent the flue gas pressure from reaching a magnitude which would cause the water seal of the U-bend trap to be breached.

As another alternative, the signal output from the sensing device could cause the control unit to moderate the speed of the fan, thereby lowering the flue gas pressure. This is not preferable, however, since changing the fan speed will alter the flow rate of air into the burner unit, adversely effecting the power output.

Being able to monitor the flue gas pressure, and control the boiler assembly accordingly, allows a U-bend trap to be used which maintains a head of liquid, under normal operating conditions, which is closer to the European standard. This U-bend trap can thus have a smaller height than presently used in corresponding applications and, as a consequence, enables internal space savings and/or a reduction in the overall height necessary for the boiler body. It also prevents or limits the possibility of the flue gas flow path being diverted through the U-bend trap of the condensate collector, and thus discharging flue gas to an external drain.

A further advantage lies in the fact that the fan can be up-rated in terms of power output. A more powerful fan is beneficial due to the flow restrictions inherent in a modern condensing boiler assembly. For example, due to the conduits and channels in the heat exchanger. A more powerful fan can increase power output of the boiler assembly, but will increase the flue gas pressure on the head of liquid in the U- bend trap of the condensate collector. Monitoring the flue gas pressure therefore allows the fan to be rated and operated at or closer to an optimum power output, such that the required 25 mm minimum head on the flue side is not exceeded.

The boiler assembly described above can be incorporated as part of any condensing boiler, including a combination boiler, a water heater-type boiler, and a standalone boiler. Furthermore, the said heat exchanger may be a condensing secondary heat exchanger which is used in conjunction with a primary heat exchanger.

The primary heat exchanger is, typically but not necessarily, noncondensing.

Although the burner is gas-fired, it may equally be oil-fired. It may also be down-firing, up-firing or side-firing.

The sensing device can, alternatively, sense a predetermined change in pressure, instead of a predetermined pressure value. Once the change in pressure is reached, the signal is output to the control unit, as described above.

The sensing device can be applied to any condensing boiler assembly in order to detect flue gas flow path obstruction. However, the sensing device is particularly suitable for application in a boiler assembly having a U-bend trap condensate collector.

The embodiments described above are given by way of examples only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, if the European (EN) standard is altered, the sensing device can be recalibrated or changed to detect a flue gas pressure corresponding to the new European standard.

Claims

A condensing boiler assembly comprising a boiler body having a flue gas outlet, a heat exchanger which is housed in the boiler body, a burner for heating the heat exchanger, a condensate collector for collecting condensation formed by the heat exchanger and having an outlet which is connectable for fluid-communication to a drain, a fan for directing flue gas from the heat exchanger to the flue gas outlet, and a pressure sensing device for sensing the pressure or a change in pressure of the flue gas leaving the heat exchanger, the sensing device, in use, providing an indication of a blockage or partial occlusion of a flow path of the flue gas.
2. A condensing boiler assembly as claimed in claim 1, wherein the sensing device is positioned downstream of the heat exchanger.
3. A condensing boiler assembly as claimed in claim 2, wherein the sensing device is positioned between an outlet of the heat exchanger and a flue gas outlet of the condensing boiler assembly.
4. A condensing boiler assembly as claimed in claim 2 or claim 3, wherein the sensing device is positioned in the condensate collector.
5. A condensing boiler assembly as claimed in claim 4, wherein the sensing device is positioned at the inlet of the condensate collector.
6. A condensing boiler assembly as claimed in claim 1, wherein the sensing device is positioned in the outlet of the heat exchanger.
A condensing boiler assembly as claimed in any one of the preceding claims, wherein, when a predetermined pressure or pressure difference is detected by the sensing device, an output of the sensing device operates a control unit to output a warning signal and/or to turn off the boiler assembly.
8. A condensing boiler assembly as claimed in any one of the preceding claims, wherein the sensing device is a diaphragm-type pressure sensor.
9. A condensing boiler assembly as claimed in any one of claims I to 7, wherein the sensing device is a transducer-type pressure sensor.
10. A condensing boiler assembly as claimed in any one of the preceding claims, wherein the condensate collector comprises a U-bend trap which discharges to the drain, the sensing device preventing or limiting the escape of flue gas through the trap.
11. A condensing boiler assembly as claimed in claim 10, wherein the sensing device detects a predetermined pressure corresponding to a head of liquid held in the U-bend trap of the condensate collector being at least equal to or less than the European (EN) standard.
12. A condensing boiler assembly as claimed in claim 10 or claim 11, wherein the sensing device detects a predetermined pressure corresponding to a head of liquid held in the U-bend trap of the condensate collector being at least equal to or less than 25 millimetres.
13. A condensing boiler assembly as claimed in any one of the preceding claims, further comprising a secondary heat exchanger which is housed in the boiler body and which pre-heats liquid flowing into the boiler body.
14. A condensing boiler assembly substantially as hereinbefore described with reference to the accompanying drawings.