Air heater control

• US 6,431,457 B1
• Filed: 09/13/2000
• Issued: 08/13/2002
• Est. Priority Date: 09/28/1999
• Status: Expired due to Term

• Current Assignee: Roberts-Gordon, LLC (Specified Air Solutions LLC)
• Original Assignee: Rapid Engineering Inc.
• Inventors: Dirkes, James V. II
• Primary Examiner(s): WAYNER, WILLIAM E
• Application Number:
  US09/660,800
• Time in Patent Office: 699 Days
• Field of Search: 236/91.F, 236/91.R, 236/11, 165/249, 165/212, 454/229, 237/46, 126/110.C, 126/80
• US Class Current: 236/11
• CPC Class Codes: F24D 19/1084 for air heating systems
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 2110/00 Control inputs relating to air properties
• CPC Class Codes: F24F 2110/10 Temperature
• CPC Class Codes: F24F 2110/12 of the outside air
• CPC Class Codes: F24F 2140/40 Damper positions, e.g. open or closed
• CPC Class Codes: F24H 15/20 characterised by control inputs
• CPC Class Codes: F24H 15/208 Temperature of the air after heating
• CPC Class Codes: F24H 15/254 Room temperature
• CPC Class Codes: F24H 15/258 Outdoor temperature
• CPC Class Codes: F24H 15/33 Control of dampers
• CPC Class Codes: F24H 15/36 of burners
• CPC Class Codes: F24H 9/2085 using fluid fuel
• CPC Class Codes: G05D 23/1931 to control the temperature of one space

Abstract

A heater control system is operable to modulate a heater of a building or warehouse or the like, in order to maintain the temperature rise of air passing through the heater at or below a maximum allowable temperature rise value. The maximum allowable temperature rise value is determined by a percentage or proportion of outside air being inducted into the heater and the type of heater, in order to limit the accumulation of carbon dioxide within the building. The control system is operable to modulate the heater in response to an outside air temperature, an inside or return air temperature, and the proportion of outside air to return air being inducted into the heater. Preferably, the proportion of outside air is determined by a position of a damper, which is operable to vary the relative flows of outdoor air and return air which are inducted into the heater. The control system monitors the temperature of the discharge air from the heater and modulates the heater to maintain the discharge air temperature below a value based on the maximum allowable temperature rise, the indoor and outdoor air temperatures, and the proportion of outdoor air being inducted into the heater. Optionally, the control may adjust a position of the damper to maintain the temperature rise below the maximum allowable temperature rise. The present invention thus provides a low cost control system which ensures that the temperature rise of air passing through the heater is maintained below the maximum allowable value for any given proportion of outdoor air being inducted therein.

Claims

1. A direct fired recirculating air heater, comprising:

a burner;

an outdoor air path to said heater and a return air path to said heater;

a first temperature sensor which is operable to measure outdoor air temperature and a second temperature sensor which is operable to measure return air temperature; and

a control which is operable to control said heater in response to at least said first and second temperature sensors and an amount of outdoor air being inducted to said heater via said outdoor air path.

2. The direct fired recirculating air heater in claim 1 further including a damper which is movable to adjust relative flows through said outdoor and return air paths, said control being operable to control at least one of said burner and said damper in response to said first and second temperature sensors and a position of said damper.

3. The direct fired recirculating air heater in claim 2 further including a discharge air path from said heater and a third temperature sensor measuring a discharge air temperature at said discharge air path.

4. The direct fired recirculating air heater in claim 3, wherein said control is further responsive to said third temperature sensor.

5. The direct fired recirculating air heater in claim 4, wherein said control is operable to control said at least one of said burner and said damper such that a temperature rise of air passing through said heater does not exceed a maximum allowable temperature rise determined by a position of said damper.

6. The direct fired recirculating air heater in claim 5, wherein the maximum allowable temperature rise is determined by the position of said damper and an error associated with said damper.

7. The direct fired recirculating air heater in claim 5 including a position sensor which is operable to sense a position of said damper.

8. The direct fired recirculating air heater in claim 7, wherein said control is operable to calculate a maximum discharge air temperature in response to said position sensor and said first and second temperature sensors.

9. The direct fired recirculating air heater in claim 5, wherein said control is operable to control said burner and maintain the discharge air temperature according to the following equation:

10. The direct fired recirculating air heater in claim 9, wherein the maximum allowable temperature rise and the percentage of outdoor air are determined by a position of said damper.

11. The direct fired recirculating air heater in claim 10, wherein the maximum allowable temperature rise is determined by said percentage of outdoor air and said percentage of outdoor air is determined by the equation:

12. The direct fired recirculating air heater in claim 11, wherein said control is operable to control said burner and maintain the discharge air temperature according to the following equation:

13. A method of controlling a direct fired recirculating air heater having a burner, an outdoor air path to the heater, a return air path to the heater, and a discharge path from the heater, said method comprising:

determining a proportion of outdoor air being inducted to said heater;

measuring outdoor air temperature and return air temperature; and

controlling said heater as a function of at least the measured outdoor air temperature and return air temperature and the proportion of outdoor air being inducted to said heater.

14. The method of controlling a direct fired recirculating air heater in claim 13, wherein said heater includes a damper which is movable to adjust relative flows through said outdoor and return air paths, said method including determining a position of said damper and controlling at least one of said burner and said damper as a function of the measured outdoor air temperature and return air temperature and the position of said damper.

15. The method of controlling a direct fired recirculating air heater in claim 14 further including measuring discharge air temperature at said discharge air path.

16. The method of controlling a direct fired recirculating air heater in claim 15 further including controlling said at least one of said burner and said damper as a function of the measured discharge air temperature.

17. The method of controlling a direct fired recirculating air heater in claim 16 including controlling said at least one of said burner and said damper such that a temperature rise of air through the heater does not exceed a maximum allowable temperature rise determined by a position of said damper.

18. The method of controlling a direct fired recirculating air heater in claim 17 including providing a position sensor which senses a position of said damper.

19. The method of controlling a direct fired recirculating air heater in claim 18 including controlling said burner such that the discharge air temperature does not exceed a maximum allowable discharge air temperature determined by said position sensor and the measured outdoor air temperature and return air temperature.

20. The method of controlling a direct fired recirculating air heater in claim 17 including controlling said burner to maintain the discharge air temperature according to the following equation:

21. The method of controlling a direct fired recirculating air heater in claim 20, wherein the maximum allowable temperature rise is determined by the percentage of outdoor air and the percentage of outdoor air is determined by the equation:

22. The method of controlling a direct fired recirculating air heater in claim 21 further including providing a first temperature sensor to measure the outdoor air temperature and providing a second temperature sensor to measure the return air temperature.

23. The method of controlling a direct fired recirculating air heater in claim 22, wherein the step of controlling said burner to maintain the discharge air temperature is performed according to the following equation: