Gas boiler

Abstract: In order to improve the performance of the flue gases exhaust from the tight chamber boiler, IABER S.p.A. uses a hooked pressure tube and a venturi tube, mounted inside the scroll. The location of the venturi and pressure tubes within the fan scroll allow pressure detectors not be affected by the intake air flow, caused by the natural draught of the stack, when the boiler is off. Also the venturi tube alone is useful to this purpose; actually, the solution providing for the only presence of the venturi tube allows a higher stability of the pressure signal reaching the pressure switch and assures that the boiler is shut-off in case of abnormal machine operation.

Description: The present invention relates to a gas boiler. In particular, the present invention relates to a gas boiler comprising a tight combustion chamber; an air intake duct connected to the combustion chamber; a gas exhaust duct connected to the combustion chamber; a pressure switch for detecting the flow of the gas exhaust; a tube for acquiring the stationary pressure in the gas exhaust duct; a venturi tube for acquiring the dynamic pressure in the gas tube; and a fan comprising a fan scroll located along the gas exhaust duct. A gas boiler of the above described type is disclosed in EP 790,465, in which the tubes for respectively relieving the dynamic pressure and the static pressure are located along the exhaust duct downwardly from the fan. The above described boiler is efficient in detecting eventual blockage of the gas exhaust duct but it is not particularly reliable in detecting the pressure since the latter is influenced by the natural draught of the exhaust duct and cannot fulfil the requirements of the gas boilers provided with tight combustion chamber. The object of the present invention is to provide a gas boiler having a tight combustion chamber improving its performance and passing the test required by PrEN483, according to which gas boiler of the above mentioned type shall be submitted to a 2 mbar vacuum. Under this condition the gas boiler shall light regularly and the flame shall remain steady According to the present invention there is provided a gas boiler according to claim 1. Description of the solution FIME fans type GR00680P, used for Basic boilers, incorporate the venturi tube (see Fig. 6) and the hooked pressure tube (see Fig. 7) into the scroll. The venturi tube reads a pressure, which is lower than the static pressure present in the scroll and is proportional to the speed of flue gases at that point The choice of the pressure tube position has been of the utmost importance; actually measurements are read by a pressure switch detecting pressure changes. The pressure switch reading shall be stable under normal operating conditions and shall decrease in abnormal operating conditions, in order to assure that the boiler is switched off. The correct signal decrease depends upon the position of the venturi and hooked tubes inside the fan's scroll. Therefore, the location of the two pressure detectors is crucial and required long testing efforts. The location of the venturi tube and of the hooked tube within the fan scroll, as shown by Figure no. 8, enables to pass C5 tests (as per standard prEN 483/1998), since pressure detectors are not affected by the air flow of the suction caused by the natural draught of the stack, when the boiler is off. This represents a remarkable advantage as compared to the tubes inside the flue gases connection. Actually in this case, if a suction is imposed (as provided to pass C5 tests), the venturi tube, being at the center of the fluid vein, shall read a vacuum, thus making it difficult to pass the test. On the contrary, if it is located inside the fan scroll, the venturi tube is protected from the intake air flow thus allowing to pass the test. Therefore, the venturi shall not be very sensitive to the flows imposed by simulating a suction when the boiler is off (test C5), but shall be highly sensitive to the speed changes of the fluid vein when the fan is operating, thus enabling the boiler to automatically shut-off, in case of either fan malfunctioning or incidental closure of the flue gases exhaust tube. Actually, tests carried out prove that emissions remain below 2000 ppm CO, corrected before the boiler is put off by the action of the pressure switch and below 1000 ppm CO, corrected at re-start as provided by standard prEN483/1998. In addition to the above advantages, this solution allows a significant cost saving. II. Purpose of the invention. Purpose of the invention is to improve the performance of the tight chamber boiler, passing the tests required by prEN483 standard for C5 configuration. PrEN483. Standard covering Type C (tight) boilers equipped with atmospheric burner, with rated thermal power equal to or less than 70 Kw. This standard specifies the requirements and test methods for the construction, safety, performance, rational use of power, classification and marking of gas-fired boiler, designed for central heating. C5 configuration. C5 configuration is defined by prEN 483 as a system where a type C (tight) boiler is connected, though separate ducts, to two terminal units located in areas having a different pressure. In practice, the following two conditions occur: air intake on a wall and exhaust on another wall (not on the opposite one) at different pressures (see Fig.1) wall air intake and roof exhaust. PrEn 483 states that the exhaust of flue gases for a boiler installed according to this configuration shall be submitted to a 2 mbar vacuum; under these conditions, the machine shall light regularly and the flame shall remain steady. Present situation. IABER boilers are not able to pass this test. Pressure and venturi tubes are mounted inside the fan connector (see Fig.2). The pressure tube reads a vacuum, changing with the change of the air speed passing through it. These two components are connected to a pressure switch (see Fig.5) reading any pressure change. The pressure switch is an electromechanical device with a ON position at 100 +/-6 Pa and an OFF position at 72 +/-5 Pa. Upon boiler's start-up, and for safety reasons, the software controlling the boiler operation, checks the pressure switch position. Consent to boiler's start-up is granted only when the pressure switch is in the OFF position. Under C5 configuration testing conditions, the 2 mbar vacuum applied to flue gases exhaust, generate an air flow causing a pressure change within the boiler, such as to bring the pressure switch to the ON position. Therefore the software does not agree to the boiler's start-up. Description of the solution. FIME fans type GR00680P, used for Basic boilers, incorporate the venturi tube into the scroll (see Fig.8). The venturi tube reads the pressure intake proportionally to the speed of flue gases, at that point; the vacuum signal thus generated is then detected by the pressure switch. Therefore, it "perceives" a pressure change (PD) generated by two pressure signals coming from the venturi tube and from a static pressure tube (see Fig. 4). In the previous solutions, the static pressure tube consisted of a straight tube (see Fig.4) taking the signal from flue gases exhaust. Now the static pressure tube consists only of the positive tube of the pressure switch, reading the vacuum existing in the boiler's air box (see Fig. 3). The minimum PD to be assured during boiler's operation is 120 Pa, in the worst conditions (i.e. tubes of the maximum width and operation at the maximum power). Such PD could be generated by working both on the location of the venturi tube inside the scroll and on the diameter of the venturi throat, which is presently 4.6 +/-0,1 mm. Thanks to these adjustments, the venturi generates a vacuum signal of approx. 150 Pa. Under these conditions, the second pressure sensor of the pressure switch perceives a vacuum of approx. 30 Pa. The PD value detected by the pressure switch is therefore 120 Pa (150 Pa of the venturi - 30 Pa of the direct intake = 120 Pa). The advantages of this solution are mainly reflected on a higher stability of the pressure signal. The signal reaching the pressure switch shall be stable under the normal operating conditions and shall decrease in abnormal operating conditions, in order to assure that boiler goes off. The correct reduction of the signal is typical of the venturi positive action. Moreover, the venturi location inside the fan scroll, as shown by Fig. 8, enables to pass the C5 tests (as per standard prEN483/1998); actually in that position, it is not affected by the air flow caused by the natural draught of the stack, when the boiler is off. This constitutes a remarkable advantage; actually , inside the fan scroll, the venturi is located in a position protected from the flow thus allowing to pass the C5 test (2 mbar vacuum suction). Therefore, the venturi shall not be sensitive to the flows imposed by simulating a suction , when the boiler is off (C5 test), but shall be highly sensitive to the speed changes of the fluid vein when the fan is operating, thus enabling the boiler to automatically shut-off, in case of either fan malfunctioning or incidental closure of the flue gases exhaust. Tests carried out at the IABER R & D laboratory prove that emissions remain below 2000 ppm CO, corrected before the boiler is put off by the action of the pressure switch, and below 1000 ppm CO, corrected at re-start, as provided by standard prEN 483/1998.

Claims: Gas boiler comprising a tight combustion chamber; an air intake duct connected to the combustion chamber ; a gas exhaust duct connected to the combustion chamber; a pressure switch for detecting the flow of the gas exhaust; a tube for acquiring the stationary pressure in the gas exhaust tube; a venturi tube for acquiring the dynamic pressure in the gas tube; and a fan comprising a fan scroll located along the gas exhaust duct; the boiler being characterized in that the tube and the venturi tube are located inside the fan scroll.

Inventors: PASTORINO GIORGIO ING, PASTORINO, GIORGIO, ING.
Applicants: RIELLO SPA, RIELLO S.P.A.
Application year: 2000
Main classification: F23N5
IPC codes: F23N5