The present invention relates to an indirect fired heat exchanger.
Indirect fired heaters and furnaces are commonly used in heating residential, commercial and industrial spaces.
Unlike direct fired heaters, in indirect fired heat exchangers and furnaces, the burner is fired into a drum and tube type heat exchanger and the products of combustion do not come in contact with the process air within the work chamber. Process air or gas is forced by a combustion blower into the heat exchanger and travels through the heat exchanger drum and tubes and the air that passes over the heat exchanger is heated and then directed to its destination via externally attached duct work.
Government regulations surrounding efficiency of indirect fired heat exchangers has become increasingly stringent. Fuel costs and environmental considerations also lead to increased demand for high efficiency heat exchangers.
Attempts have been made in the past to improve heat exchanger efficiency, which is measured as the percentage of energy input by the heat exchanger's burner that is translated to energy output from the existing flue gas. The energy input from the fuel is typically measured by thousands of BTU's per hour (MBH).
In some cases the materials of construction have been varied to optimize heat transfer or to insulate from heat losses. In other cases, fins have been added to the tubes of the heat exchanger to increase heat transfer.
In other cases, configuration of the tubes of the furnace has been altered in an effort to improve efficiencies.
U.S. Pat. No. 5,322,050 and related U.S. Pat. No. 5,406,933 teach a fuel-fired condensing furnace having a number of modifications thereto. These include a smaller than typical outside diameter of the combustion tubes, specifically an outside diameter OD of from 1⅛″ to 1½″ and correlating the firing rate of the furnace to the flame tube size in a manner such that the firing rate per unit inner cross-sectional area of the flame tubes is within the range of from about 9,000 to 13,000 Btu/hr/in2.
However there is still a need in the art to find means for improving heat exchanger efficiencies.
An indirect fired heat exchanger is provided, comprising an arcuate airflow pattern.
The present invention will now be described in greater detail, with reference to the following drawings, in which:
The invention provides an indirect fired condensing heater having a novel heat exchanger. The present heat exchanger has shown high performance efficiencies of up to 95.7% when fins are present on the last one or more passes of the heat exchanger tubes.
With reference to
A plurality of first heat exchanger tubes 46 are positioned in the heat exchanger assembly 42 and a plurality of final pass heat exchanger tubes 46 are positioned in the final pass section 40 before discharge of combustion products as flue gasses.
The arrangement of the heat exchanger containment plates 7A/7B is illustrated in more detail in
The present heat exchanger comprises a larger number of heat exchanger tubes and radiator tubes than typically seen in the art. Preferably, the number of tube passes in the heat exchanger assembly 42 is increased from that typically seen in known heat exchangers in the art. Further preferably the number of tube passes in the final pass section 40 is also increased from that typically seen in known heat exchangers in the art.
In a preferred embodiment, and as illustrated in
The present inventors have found that the combination of semi-offset and random stagger pattern, creating a three pass tube exchanger arrangement of the first heat exchanger tubes 46 allows for maximum heat transfer with minimal loss of airflow across the heat exchanger assembly section 42.
In further a preferred embodiment, the present heat exchanger comprises twenty four final pass heat exchanger tubes 46. More preferably the final pass heat exchanger tubes 46 are aligned in a horizontal in-line stack configuration. Most preferably, the final pass heat exchanger tubes 46 are 1″ to 1.5″ in diameter and are made of 409 stainless steel. The final pass heat exchanger tubes 46 may have external fins or they may be finless.
In a preferred embodiment, the final pass section 40 of the present heat exchanger is a two pass section illustrated as sections 40a and 40b in
The present inventors have found that the present size, number and arrangement of final pass heat exchanger tubes 46 provide minimal pressure drop from the process air supply fan. As well the present inventors have found that locating final pass section 40a/40b proximal the inlet of air to be heated, as seen in
Most preferably, the first heat exchanger tubes 46 have internal turbulators to cause turbulent flow through the first heat exchanger tubes 46. Sizing of the final pass heat exchanger tubes 46 advantageously provides turbulent flow without the need for internal turbulators or similar devices.
A process air supply fan (not shown), which may or may not be provided as part of the heat exchanger of the present invention, supplies process air to be heated to a process air inlet on the heat exchanger. In a preferred embodiment as illustrated in
In a preferred embodiment, airflow through the heat exchanger follows an arcuate flow path. In a more preferred embodiment, the airflow pattern creates horseshoe pattern. In a most preferred embodiment air flows through the heat exchanger in an “omega” (Ω) shaped airflow, as illustrated by the curved arrows in
The present heat exchanger preferably comprises one or more baffles, and more preferably three interconnected baffles 30, 31 and 32 that form a process airflow diversion within the heat exchanger. The baffles 30, 31 and 32 direct airflow into the omega (Ω) flow pattern. The present inventors have found that this omega (Ω) flow pattern provides a significant increase in heat exchanger efficiency over traditional S-shaped flow patterns commonly seen in the art.
As heat is removed from combustion gasses traveling through the primary drum 2, first heat exchanger tubes 46 and radiator tubes 42, moisture in the combustion gas condenses to form condensate. Combustion gas condensate is typically acidic and can cause internal fouling and corrosion of the heat exchanger tubes and primary drum if not properly drained and discharged. The acidic condensate is not deemed acceptable by plumbing code to be disposed of directly into a drainage system. A condensate neutralization system may be used in conjunction with the present invention for condensate neutralization and acceptably safe disposal. Preferably, the heat exchanger tubes and radiator tubes as well of the present heat exchanger are oriented to optimize gravity drainage of condensate to the condensate neutralization system.
While the above mentioned invention is described for typical horizontal air flow delivery to the building space, alternate approaches to air flow delivery are also possible and encompassed by the scope of the current invention.
For example, the heat exchanger can be designed for vertical air delivery to a building space to be heated. Such configuration is illustrated in
In the present alternate embodiment, a process air supply fan (not shown), which may or may not be provided as part of the heat exchanger of the present invention, supplies process air to a process air inlet on a shell side of the heat exchanger. Preferably the process air enters the heat exchanger at the final pass section 40a/40b travels over the final pass heat exchanger tubes 46 and then over the first heat exchanger tubes 46 and exits the heat exchanger with final pass across primary drum 2 through a process air outlet in the form of a discharge opening 50 in the heat exchanger.
With reference to
Airflow through the heat exchanger in this alternate embodiment also follows an arcuate flow path, more preferably the airflow pattern creates horseshoe pattern and most preferably air flows through the heat exchanger in an “omega” (Ω) shaped airflow, as illustrated by the curved arrows in
The baffles (30, 31, 32) of the heat exchanger of this alternate embodiment the invention still form a process airflow diversion within the heat exchanger. The baffles 30, 31 and 32 direct airflow into the omega (Ω) flow pattern, however, in the alternate embodiment the omega pattern is shifted by 90°. The omega (Ω) flow pattern has shown to provide significant increases in heat exchanger efficiency regardless of orientation.
The alternate embodiment illustrated in
In the foregoing specification, the invention has been described with a specific embodiment thereof; however, it will be evident that various modifications and changes may be made thereto without departing from the broader scope of the invention.
Number | Date | Country | Kind |
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PCT/CA2013/000847 | Oct 2013 | CA | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CA2014/000370 | 4/24/2014 | WO | 00 |