FURNACE WITH PRIMARY AND SECONDARY HEAT EXCHANGERS
A furnace that includes a heater configured to heat a fluid and discharge a heated fluid flow, a first heat exchanger at least partially positioned in a air duct and in fluid communication with the heater to receive the heated fluid flow, and a second heat exchanger at least partially positioned in the air duct and in fluid communication with the first heat exchanger so that the heated fluid flow flows through the second heat exchanger after flowing through the first heat exchanger. The first heat exchanger and the second heat exchanger are arranged in the air duct so that the flow of air travels through the first heat exchanger to transfer heat between the heated fluid flow and the flow of air, and then through the second heat exchanger after the first heat exchanger to transfer heat between the heated fluid flow and the flow of air.
The present invention relates to a furnace that is utilized to heat a flow of air.
Furnaces can be used to heat a flow of air partially drawn from outside air and partially drawing from the space conditioned or heated by the furnace. The flow of air is passed through a heat exchanger to heat the flow of air. The heat exchanger can receive heated combustion air from a burner to heat the flow of air. After passing through the heat exchanger the heated flow of air is discharged to a conditioned space while the combustion air can be discharged to the atmosphere.
SUMMARYIn one embodiment, the invention provides a furnace configured to heat a flow of air and discharge the heated flow of air into a conditioned space. The furnace includes an air duct including an air inlet and an air outlet, and the air duct defines an air flow path from the air inlet to the air outlet. The air duct is configured to direct the flow of air along the air flow path from the air inlet to the air outlet. The furnace further includes a heater configured to heat a fluid and discharge a heated fluid flow, a first heat exchanger at least partially positioned in the air duct and in fluid communication with the heater to receive the heated fluid flow, and a second heat exchanger at least partially positioned in the air duct and in fluid communication with the first heat exchanger so that the heated fluid flow flows through the second heat exchanger after flowing through the first heat exchanger. The first heat exchanger and the second heat exchanger are arranged in the air duct so that the flow of air travels through the first heat exchanger to transfer heat between the heated fluid flow and the flow of air, and then through the second heat exchanger after the first heat exchanger to transfer heat between the heated fluid flow and the flow of air.
In another embodiment the invention provides a method of operating a furnace including heating a fluid with a heater, directing the heated fluid through a first heat exchanger, directing a flow of air through the first heat exchanger, transferring heat from the heated fluid to the flow of air in the first heat exchanger, directing the heated fluid through a second heat exchanger after directing the heated fluid through the first heat exchanger, directing the flow of air through the second heat exchanger after directing the flow of air through the first heat exchanger, transferring heat from the heated fluid to the flow of air in the second heat exchanger.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
Also, it is to be understood that phraseology and terminology used herein with reference to device or element orientation (such as, for example, terms like “central,” “upper,” “lower,” “front,” “rear,” and the like) are only used to simplify description of the present invention, and do not alone indicate or imply that the device or element referred to must have a particular orientation. In addition, terms such as “first” and “second” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance.
Referring to
The air duct 14 forms an air flow path to direct a flow of air from the inlet 26 and through the first heat exchanger 20 and the second heat exchanger 22 and then through the outlet 28. In the illustrated embodiment, the air inlet 26 is positioned outside the building or structure so that all (i.e., 100 percent) of the air that flows through the air duct 14 is outside or ambient fresh air. In other embodiments, a majority (i.e., greater than 50 percent) of the air that flows through the air duct 14 is outside air and the remainder of the air that flows through the air duct can be air that is circulated from the conditioned space (i.e., inside air). The outlet 28 is positioned so that the air duct 14 discharges the flow of air into the conditioned space or building. Additional ducts or the like can be attached to the outlet 28 to facilitate transporting the flow of air into the conditioned space or building.
With continued reference to
Referring to
Referring to
The illustrated second heat exchanger 22 is a fin tube heat exchanger including tubes 58 and fins 60 located between the tubes 58. The tubes 58 each include an inlet end 64 (
Referring to
With reference to
In operation, the air handling unit 16 draws a flow of air through the air inlet 26. The air duct 14 directs the flow of air through the first heat exchanger 20 and then through the second heat exchanger 22 generally in the direction of arrows 96 in
As the heated gas is cooled by the flow of air in the first heat exchanger 20 and the second heat exchanger 22, condensation may be formed. For example, in one embodiment, the heated gas is cooled by the flow of air in the second heat exchanger 22 from a first temperature above a dew point temperature of the heated gas to a second temperature below the dew point temperature of the gas, which causes condensation to form in the second heat exchanger 22. The condensate travels by gravity through the condensate outlet 72 and then through the traps 76 where it is discharged from the furnace 10. In the illustrated embodiment, the flow of air is first heated by the primary heat exchanger 20 which is directly downstream from the burners 40 and then the flow of air is heated by the secondary heat exchanger 22, which is downstream from the primary heat exchanger 20. Such an arrangement inhibits condensate from forming and then freezing in the primary heat exchanger 20 due to the relatively high temperatures adjacent the burners 40. When the flow of air drawn through the air inlet 26 is at or below 0 Celsius or the freezing temperature of water this arrangement may be particularly beneficial. Any condensate that forms in the secondary heat exchanger 22 is inhibited from freezing because the flow of air has already been heated to a temperature above the freezing temperature of water by the first heat exchanger 20. Such an arrangement is particularly useful in applications where a majority of the air drawn through the air inlet 26 is ambient or outdoor air, which may be at temperatures below the freezing temperature of water.
Various features and advantages of the invention are set forth in the following claims.
Claims
1. A furnace configured to heat a flow of air and discharge the heated flow of air into a conditioned space, the furnace comprising:
- an air duct including an air inlet and an air outlet, the air duct defining an air flow path from the air inlet to the air outlet, the air duct configured to direct the flow of air along the air flow path from the air inlet to the air outlet;
- a heater configured to heat a fluid and discharge a heated fluid flow;
- a first heat exchanger at least partially positioned in the air duct and in fluid communication with the heater to receive the heated fluid flow; and
- a second heat exchanger at least partially positioned in the air duct and in fluid communication with the first heat exchanger so that the heated fluid flow flows through the second heat exchanger after flowing through the first heat exchanger,
- wherein the first heat exchanger and the second heat exchanger are arranged in the air duct so that the flow of air travels through the first heat exchanger to transfer heat between the heated fluid flow and the flow of air, and then through the second heat exchanger after the first heat exchanger to transfer heat between the heated fluid flow and the flow of air.
2. The furnace of claim 1, wherein a majority of the flow of air entering the air inlet is outdoor air.
3. The furnace of claim 1, wherein the flow of air is discharged from the air outlet into a building.
4. The furnace of claim 1, wherein the first heat exchanger is positioned outdoors.
5. The furnace of claim 1, wherein the second heat exchanger is positioned outdoors.
6. The furnace of claim 1, further comprising at least one condensate reservoir fluidly coupled to the second heat exchanger and positioned to receive condensate from the heated fluid flow in the second heat exchanger.
7. The furnace of claim 1, further comprising an air handling unit including a motor and a centrifugal fan, the motor is configured to rotate the centrifugal fan and the centrifugal fan is configured to direct the flow of air along the air flow path.
8. The furnace of claim 1, wherein the heater includes at least one burner.
9. The furnace of claim 8, wherein the at least one burner is an inshot burner, and wherein the first heat exchanger includes a plurality of tubes in which the heated fluid flows.
10. The furnace of claim 9, wherein the second heat exchanger includes a plurality of tubes and a plurality of fins, and wherein the heated fluid flows through the plurality of tubes of the second heat exchanger and the flow of air flows through the plurality of fins.
11. The furnace of claim 1, wherein the first and the second heat exchangers are positioned outdoors, and wherein the air inlet is positioned outdoors.
12. A method of operating a furnace comprising:
- heating a fluid with a heater;
- directing the heated fluid through a first heat exchanger;
- directing a flow of air through the first heat exchanger;
- transferring heat from the heated fluid to the flow of air in the first heat exchanger;
- directing the heated fluid through a second heat exchanger after directing the heated fluid through the first heat exchanger;
- directing the flow of air through the second heat exchanger after directing the flow of air through the first heat exchanger; and
- transferring heat from the heated fluid to the flow of air in the second heat exchanger.
13. The method of claim 12, further comprising inhibiting freezing of condensate from the flow of air in the second heat exchanger by transferring heat from the heated fluid to the flow of air in the first heat exchanger prior to directing the flow of air through the second heat exchanger.
14. The method of claim 12, further comprising moving outdoor air into the first heat exchanger prior to directing the flow of air through the first heat exchanger.
15. The method of claim 12, further comprising discharging the flow of air into a building after directing the flow of air through the second heat exchanger.
16. The method of claim 12, wherein the flow of air through the second heat exchanger is warmer than the flow of air through the first heat exchanger.
17. The method of claim 12, wherein the fluid in the first heat exchanger is warmer than the fluid in the second heat exchanger.
18. The method of claim 12, further comprising positioning the first heat exchanger outdoors.
19. The method of claim 12, further comprising positioning the second heat exchanger outdoors.
20. The method of claim 12, further comprising fluidly coupling at least one condensate reservoir to the second heat exchanger to receive condensate from the heated fluid in the second heat exchanger.
21. The method of claim 12, wherein heating the fluid with a heater includes igniting a gas in a burner.
22. The method of claim 12, wherein transferring heat from the heated fluid to the flow of air in the first heat exchanger includes raising a temperature of the flow of air from a first temperature less than or equal to 0 degrees Celsius to a second temperature above 0 degrees Celsius.
23. The method of claim 12, wherein the heated fluid has a dew point temperature in the second heat exchanger, wherein transferring heat from the heated fluid to the flow of air in the second heat exchanger includes lowering a temperature of the heated fluid from a first temperature above the dew point temperature to a second temperature below the dew point temperature.
Type: Application
Filed: Jan 31, 2012
Publication Date: Aug 2, 2012
Inventor: Kevin Alphs (Racine, WI)
Application Number: 13/362,831