IE47820B1 - A wrap-around back boiler - Google Patents

Abstract

A wrap-around back boiler (1) for mounting in an open hearth fire comprises a rear tank (2) and outwardly projecting side tanks (3) with three additional transverse water tanks, namely a front tank (7), a back tank (8) and an intermediate tank (9) defining three substantially vertical flues. The rear tank (2) and intermediate tank (9) are interconnected by a top bridging member while the bottom of the back water tank (8) and the front water tank (7) are connected by a bottom bridging member to define a combustion gas passageway having a first rising leg (17), a falling leg (18) and a second rising leg (19). A refractory fire brick is mounted behind the grate (35) to provide a hot surface 39 for additional burning of combustion gases.

Description

The present invention relates to a wrap-around back boiler t One problem with conventional wrap-around back boilers, and in particular domestic back boilers, is that they are particularly inefficient in use and a considerable amount of the available heat of combustion is lost up the flue. Various constructions of boilers have been developed to overcome this problem. For example, back boilers are constructed with side water tanks and one or two spaced apart transverse water tanks joining the side tanks and mounted above the firebed to increase the available heat transfer surface area. Back boilers in which flues are provided in the rear and side water tanks have also been developed. However, while these boilers extract some of the available heat a considerable amount of heat is still lost up the flue.

One object of the present invention is to provide a wrap-around back boiler which will offer improved heat transfer efficiency over presently known boilers.

According to the invention there is provided a wrap20; - around back boiler for fitting in a domestic fireplace comprising a transverse rear tank, a pair of outwardly directed side tanks forming extensions of the rear tank a-n'd de.fi nin‘g therewith a channel-shaped firebed enclosure, arid at least three additional tanks mounted transversely -3between and interconnecting the side tanks to form a plurality of parallel substantially vertical flues, the flues, when the boiler is in use, communicating at alternate upper and lower ends to form a successively rising and falling continuous passageway for combustion gases from an entry aperture near the firebed to an exhaust flue, a top bridging member extending, in use, between at least one pair of alternate transverse tanks at their upper ends to define a portion of the flue gas passageway.

Preferably, the entry aperture is adjacent the rear tank and preferably there is a bottom bridging member which extends in use, between at least one pair of alternate transverse tanks at their lower ends.

The top bridging member may be in the form of a plate or a fire brick. Conveniently, the top of one additional tank is disposed below the level of adjacent transverse tanks. There are preferably three additional tanks. Preferably, the additional tanks are mounted forwardly of the upper portion of the rear tank, above the firebed.

Preferably, a refractory member is situated below the rear tank adjacent the entry aperture to the passageway, the top face of the refractory member extending upwardly rearwardly towards the rear tank to direct combustion gases into the passageway and provide a hot face to burn the combustible gases 7 8 2 0 -4passing thereover.

Typically, the discharge outlet of the passageway is closable by a damper plate.

The invention will be more clearly understood from the 5 following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawi ngs , in whi ch: Fig. 1 is a perspective, partly cut-away, view of a domestic wrap-around back boiler, in accordance with the invention, Fig. 2 is a sectional side view of the boiler of Fig. 1, Fig. 3 is a plan view, from the top, of the boiler of Fig. 1, and Fig. 4 is a cross sectional plan view along the line IV-IV in Fig. 2.

Referring to the drawings, there is provided a domestic wrap-around back boiler according to the invention indicated generally by the reference numeral 1. The back boiler 1 comprises a rear water tank 2 and a pair of outwardly directed side water tanks 3 forming extensions of the rear tank 2 and defining therewith a channel shaped firebed -5enclosure 4. The water tanks 2 and 3 are manufactured from metal plate material welded together. A water inlet 5 and a water outlet 6 are provided to and from one of the side tanks 3.

The boiler 1 also includes at least three, and in this case three, additional water tanks, namely a front water tank 7, a back water tank 8 and an intermediate water tank 9, mounted transversely between and interconnecting the side tanks 3. The transverse tanks 7,8 and 9 are of metal plate material welded together and welded to the side tanks 3. As can most clearly be seen from Fig. 2 the additional tanks 7, 8 and 9 together with the rear tank 2 and side tanks 3 form three parallel, substantially vertical, flues forming a successively rising and falling passageway for combustion gases from an entry aperture 11 adjacent the firebed 4 to a discharge outlet 12 for exhaust to a chimney flue (not shown).

The flue gas passageway comprises a first rising leg 17, a falling leg 18 and a second rising leg 19. A top bridging member 21 provided by a refractory fire brick directs the flue gases from the first rising leg 17 of the flue gas passageway to the falling leg 18. The top of the additional back water tank 8 is dropped below the level of the top of the rear water tank 2 and the intermediate water tank 9 to allow free passage of 7 8 2 0 -6combustion gases between the first rising leg 17 and the falling leg 18. A lower removable bridging member 26 of flat cast iron plate material mounted between the bottom of the front water tank 7 and the back water tank 8 directs the flue gases from the falling leg 18 of the combustion gas passageway to the second rising leg 19. Again, the bottom of the intermediate tank 9 is spaced apart from the bridging member 26 to allow passage of combustion gases. A lug 24 extending the width of the bottom bridging member 26 engages a lip 27 extending the width of the lower edge of the back additional water tank 8 while an upper edge 28 of the bridging member 26 engages a lip 29 projecting from the front water tank 7 thereby retaining the bridging member 26 in position. The bottom bridging member 26 can be readily removed by moving it upwardly in the direction of the arrow A to disengage the lug 24 from the lip 27.

A damper 30 to close the discharge outlet 12 to the chimney flue is slidably mounted in guides (not shown) welded to the side tanks 3. The damper 30 has an upwardly projecting lip 32 which abuts a complementary lip 33 extending the width of the intermediate transverse additional water tank 9. A handle 34 on the damper 30 is provided to open and close the damper as desired.

A grate 35 to support the firebed 4 is slidably removable -7on supports 36 mounted on the side tanks 3. A refractory fire brick 38 extends between the side tanks 3 and has an upwardly rearwardly directed top face 39 to deflect combustion gases through the entry aperture 11 into the combustion gas passageway. The top face 39 presents a hot face to assist in the additional burning of the combustion gases before they enter the passageway.

In operation, when it is desired to pass the combustion gases through the tortuous passageway the damper plate 30 is moved at least partially into the open position illustrated by interrupted lines in Fig. 2 to uncover the discharge outlet 12 from the passageway. In this position the combustion gases are drawn into the combustion gas passageway through the entry aperture 11 and heat is transferred from the combustion gases to the water tanks.

In the fully open position the damper plate 30 substantially prevents the combustion gases from passing directly from the firebed 4 on the grate 35 to the exhaust chimney. Accordingly, a major portion of the combustion gases pass over the surfaces of the additional tanks 7,8 and 9. When it is desired to bypass the tortuous passageway, for example when starting a fire, the damper 30 is moved into the closed position illustrated by continuous lines in Fig. 2 and the combustion gases rising from the firebed pass directly into the exhaust chimney.

To clean the passageway the bottom bridging member 26 is -8removed which provides access to the falling and second rising legs of the passageway 18 and 19. Access for cleaning the first rising leg 17 of the combustion gas passageway is provided through the entry aperture 11.

It has been found that by drawing the flue gas over the additional tanks 7, 8 and 9 through the passageway a considerable improvement in thermal efficiency in the back boiler can be achieved.

In the wrap-around back boiler just described the flue gases are led through the successively rising and falling passageway from the back towards the front. We have found that when the gases are led from the back to the front a good draught may be maintained because, as the gases are cooled down on their travel through the passageway they are heated up again by contact with hot faces. In addition if the inlet is at the back it is difficult for cold ambient air to enter the passageway. On the other hand, in the case where the gases are led through a successively rising and falling passageway from the front towards the back the gases are taken from what is generally the coldest part of the fire and it is possible that they may stagnate in the passageway as they are not speeded up by contact with a hot face. In addition unless a large firebed is maintained cold air may rush into the inlet at the front, cooling down the gases and making the boiler less efficient than if the gases are led from the back towards the front. 7820 -9It is envisaged that in addition to the refractory fire brick at the back of the grate a secondary air supply may be provided in this region to assist in the secondary combustion of combustible volatiles. Indeed, the secondary air supply and/or hot face may be provided at any other suitable point in the passageway, for example at the top of the first rising leg.

It will be appreciated that while the embodiment described has referred to three additional tanks a greater number of additional tanks may be employed, the flues communicating at alternate upper or lower ends to form a successively rising and falling combustion gas passageway.

It will also be appreciated that any of the water tanks may be replaced by another member such as a metal plate.

It will further be appreciated that while the embodiment described has shown the wrap-around boiler incorporated in an open hearth fire, such a boiler could also be incorporated in an enclosed fire appliance. For example, the front of the fire may be closed off by a removable door hingedly mounted adjacent one of the side tanks and closed for increased efficiency of water heating.

It will also be appreciated that although the boiler has been described as being manufactured of metal plate material 8 20 -10welded together, it could also be formed by a single or any number of castings.

Claims (5)

1. A wrap-around back boiler for fitting in a domestic fireplace comprising:a transverse rear tank, 5 a pair of outwardly directed side tanks forming extensions of the rear tank and defining therewith a channel-shaped firebed enclosure, and at least three additional tanks mounted transversely between and interconnecting the side tanks to form a 10 plurality of parallel substantially vertical flues, the flues, when the boiler is in use, communicating at alternate upper and lower ends to form a successively rising and falling continuous passageway for combustion gases from an entry aperture near the firebed to an exhaust flue, 15 a top bridging member extending, in use, between at least one pair of alternate transverse tanks at their upper ends to define a portion of the flue gas passageway.

2. A boiler as claimed in claim 1 in which the entry aperture is adjacent the rear tank. 20

3. A boiler as claimed in claim 1 or 2 in which a bottom bridging member extends in use, between at least one pair of alternate transverse tanks at their lower ends. -124. A boiler as claimed in any of claims 1 to 3 in which the bridging members are removable. 5. the A boiler as claimed top bridging member in any of claims is provided by a 1 to

4. In which plate member. 6. A boiler as claimed in any of claims 1 to 4 in which the top bridging member is provided by a refractory fire brick. 7. A boiler as claimed in any preceding claim in which the top of one additional tank is disposed below the level jq of adjacent transverse tanks. 8. A boiler as claimed in any preceding claim in which there are three additional tanks. 9. A boiler as claimed in any preceding claim in which the additional tanks are mounted forwardly of the upper 15 portion of the rear tank, above the firebed. 10. A boiler as claimed in any of claims 2 to 9 in which a refractory member is situated adjacent the bottom of the rear tank and the entry aperture to the passageway, the top face of the refractory member extending upwardly 20 rearwardly towards the rear tank to direct combustion gases into the passageway and providing a hot face to burn combustible gases passing thereover. -13Π. A boiler as claimed in any preceding claim in which the discharge outlet is closable by a damper plate. 12. A boiler substantially as described herein with reference to and as illustrated in Figs. 1 to 4 of the

5. Accompanying drawings.