Method and controller for determining carbon dioxide emissions from a recirculating air heater

• US 7,104,460 B2
• Filed: 07/30/2004
• Issued: 09/12/2006
• Est. Priority Date: 07/31/2003
• Status: Expired due to Fees

• Current Assignee: Maxitrol Company
• Original Assignee: Maxitrol Company
• Inventors: Masen, Mark Geoffrey, Schlachter, John James, Sundberg, David Ray, Mimick, Frank Phillip
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US10/903,575
• Publication Number:
  US 20060118646A1
• Time in Patent Office: 774 Days
• Field of Search: 236/10, 236/11, 236/15.BR, 236/15.BD, 236/15.E, 236/26.A, 236/49.3, 236/91.R, 236/91.F, 431/12, 431/14, 431/75, 431/76, 700/274, 702/100
• US Class Current: 236/11
• CPC Class Codes: F23N 2225/20 entrant temperature
• CPC Class Codes: F23N 2225/21 outlet temperature
• CPC Class Codes: F23N 2235/06 at the air intake
• CPC Class Codes: F23N 3/002 using electronic means F23N3/02 - F23N3/08 take precedence
• CPC Class Codes: F23N 5/003 using detectors sensitive to combustion gas properties F23N5/02, F23N5/18 - F23N5/26 take precedence
• 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 11/63 Electronic processing
• CPC Class Codes: F24F 11/74 for controlling air flow rate or air velocity
• CPC Class Codes: F24F 11/745 the air flow rate increasing with an increase of air-current or wind pressure
• CPC Class Codes: F24F 2110/30 Velocity
• CPC Class Codes: F24F 2110/50 Air quality properties
• CPC Class Codes: F24F 2140/40 Damper positions, e.g. open or closed
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A method of determining the amount of air flowing through an outside air damper of a recirculating air heater includes the steps of sensing an amount of airflow flowing through the damper, recording the amount of airflow and a damper position value at a plurality of damper positions, and interpolating a curve relating the amount of airflow to the damper position for all damper positions between a minimum damper position and a maximum damper position. Once the amount of air flowing through the outside air damper is determined from a position on the curve, the concentration of carbon dioxide (CO₂) within a building space can be calculated and/or determined to be within acceptable limits.

Claims

1. A method of determining a concentration C of carbon dioxide (CO₂) in air discharged from a recirculating air heater having a burner, an outside air damper, and a recirculating air damper inversely interlocked with the outside air damper, said method comprising the steps of:

adjusting the outside air damper to a plurality of outside air damper positions;

sensing an amount of airflow flowing through the outside air damper at each of the plurality of outside air damper positions;

recording the amount of airflow and an outside air damper position value at each of the plurality of outside air damper positions;

interpolating a curve relating the amount of airflow to the outside air damper position for all possible outside air damper positions between a minimum damper position and a maximum damper position;

determining an amount of airflow through the outside air damper of the heater based on a current outside air damper position and utilizing the curve relating the amount of airflow to the outside air damper position;

calculating a proportion P of outside air brought through the burner based on the current outside air damper position;

determining a temperature difference Δ

T between a supply air temperature T_S of air before the burner and discharge air temperature T_D of air after the burner;

receiving a factor K based on a type of fuel used in the heater; and

determining the concentration C of CO₂ with an equation utilizing the temperature difference Δ

T, the factor K, and the proportion P of outside air brought through the burner.

2. A method as set forth in claim 1 wherein said step of determining the concentration C of CO₂ with an equation utilizing the temperature difference Δ

T, the factor K, and the proportion P of outside air brought through the burner is further defined as the step of determining the concentration C or CO2 with the equation C=(19.63×

K×

Δ

T)/P.

3. A method as set forth in claim 2 wherein the minimum damper position is further defined as about 15% open.

4. A method as set forth in claim 3 wherein the maximum damper position is further defined as about 100% open.

5. A method as set forth in claim 4 wherein the plurality of damper positions is further defined as being at about 5% increments between the minimum and maximum damper positions.

6. A method as set forth in claim 1 wherein the step of calculating a proportion P of outside air brought through the burner is further defined as dividing the amount of airflow at the current outside air damper position by the amount of airflow at the maximum damper position and multiplying by 100.

7. A method as set forth in claim 1 further comprising the step of calculating the supply air temperature T_S using the equation T_S=(T_O·

P·

0.01)+(T_R·

(100−

P)·

0.01), where To is defined as the outside air temperature of air flowing through the outside air damper and T_R is defined as the return air temperature of air flowing through a return air damper inversely interlocked with the outside air damper.

8. A controller for controlling and maintaining a concentration C of carbon dioxide (CO₂) in air discharged from a recirculating air heater having a burner, an outside air damper, and a recirculating air damper inversely interlocked with the outside air damper, said controller comprising:

an airflow measuring sensor for determining an amount of outside air flowing through the outside air damper;

a position sensor operatively connected to the outside air damper for sensing an outside air damper position of the outside air damper;

an outside air temperature sensor for sensing an outside air temperature T_O of air flowing through the outside air damper;

a return air temperature sensor for sensing a return air temperature T_R of air flowing through the recirculating air damper;

a discharge air temperature sensor for sensing a discharge air temperature TD of air flowing through the discharge air damper; and

a processor electrically connected to said sensors for recording the amount of airflow through the outside air damper and the outside air damper position value at a plurality of outside air damper positions, interpolating a curve relating the amount of airflow to the outside air damper position for all possible outside air damper positions between a minimum damper position and a maximum damper position, determining an amount of airflow through the outside air damper based on a current outside air damper position and utilizing the curve, calculating a proportion P of outside air brought through the burner based on the current outside air damper position, calculating a supply air temperature T_S utilizing the outside air temperature T_O, the return air temperature T_R, and the proportion P of outside air, determining a temperature difference Δ

T between the supply air temperature T_S and discharge air temperature T_D, receiving a factor K based on a type of fuel used in the heater, and determining the concentration C of CO₂ with an equation utilizing the temperature difference Δ

T, the factor K, and the proportion P of outside air brought through the burner.

9. A controller as set forth in claim 8 further comprising an analog-to-digital converter electrically connected to said sensors and said processor for converting analog signals generated by said sensors to digital signals usable by said processor.

10. A controller as set forth in claim 8 further comprising a communications port electrically connected to said processor for connecting a user interface to said controller.