US20070149109A1 - Occupancy based ventilation system - Google Patents

Abstract

An occupancy based ventilation system for indoor air quality that uses a counter to count the number of persons in a specific indoor room or other area, wherein the number of persons determines the degree of ventilation from the room's ventilation system. The counter would keep track of both the number of persons and the length of time each is present in the room. A feedback control algorithm between the counting device and the ventilation management controls provides for automatic control of the amount of ventilation needed to insure a comfortable and efficient environment.

Description

FIELD OF THE INVENTION
• The present invention relates to room ventilation systems. More particularly, the invention relates to an occupancy based system in which the amount of ventilation is determined by the number of persons in the area under consideration, such as a meeting room and the like.
BACKGROUND OF THE INVENTION
• With the energy crisis looming and with expectations that energy costs will be increasing, efficient indoor air quality control is highly desired. A well controlled room allows the occupants to be comfortable and thus more efficient. In a meeting room, for example, as the meeting proceeds, the temperature, CO₂ concentration, humidity, and body odor all increase with time. Working efficiency in this environment can be low as discomfort increases.
• One possible solution to this concern would be to assemble an array of sensors that would provide data as to each parameter, and have a controller adjust ventilation and heat or cooling as needed. This would involve a large expense, of course, since each sensor would have to be installed in the room and a microprocessor or other controller would then adjust the flow of air and the temperature as indicated by the sensors.
• Another factor in room air quality is the number of people in the room at any one time. More persons means more CO₂ being produced as the people breathe. Typical sensor based solutions do not take into account the number of persons in the room.
• It would be a great advantage in the art if a simpler, more economic solution to the concerns over room quality could be provided.
• Yet another advantage would be if an energy efficient indoor air quality control solution could be provided that uses a sensor that adjusts the amount of ventilation based on a simple measurement such as the number of persons in the room.
• A particular advantage in room ventilation control would be a system that takes into account the number of persons entering and leaving a room as well as the degree of activity in the room.
• Other advantages will appear hereinafter.
SUMMARY OF THE INVENTION
• It has now been discovered that the above and other advantages of the present invention may be obtained in the following manner. Specifically, instead of sensing a plurality of variables, it has been discovered that a correlation between the number of people in a room and the length of time they are present provides an accurate picture of the ventilation requirements of the room.
• This discovery is based on the knowledge that the metabolism of an average person is more or less the same as any other average person. Thus, it has been discovered that the number of people correlates closely to the CO₂ that they generate. A feedback control algorithm between the counting device and the ventilation management device allows the system to tune ventilation of the room to the number of people present at any given time.
• The occupancy based ventilation system for indoor air quality of a predetermined area adjusts the room ventilation system for providing outdoor air to the predetermined area as needed and as determined by the CO₂ concentration in the room as it is used by the number of people in the room.
• The system includes a counter for counting the number of persons in the area and the amount of time each person remains in the area. The counter produces a signal representing the sum of the number of persons times the amount of time for each person. The counter is positioned by the entrance to the area. The counter may use any sensor that is capable of identifying the entrance or egress of a person. Preferred sensors are selected from photo cells, IR detectors, RF detectors, pressure plates and a turnstile.
• The system also includes a processor that adjusts the ventilation system for the area based on the signal produced. The processor determines the amount of ventilation needed to maintain the CO₂ concentration in the room air at a predetermined level. The preferred CO₂ concentration is 500 ppm or less. In a preferred embodiment, the processor is further adapted to adjust the amount of ventilation based on the outside air temperature or based on the air temperature in the room.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• The present invention operates as a system in which the amount of CO₂ present in the room is determined as a function of the number of people in the room and the length of time each is present. The sum of person-time is directly proportional to the increase in CO₂ that the persons produce simply by exhaling. Presented below in Table I, the amount of CO₂ produced per individual is shown for an enclosed area or room depending on the activity of the person. More work produces more CO₂.

  	TABLE I
  	Activity	Metabolic Rate (W)	CO2

  	Sedentary work	100	0.004
  	Light work	100-300	0.006
  	Moderate work	300-500	0.012
  	Heavy work	500-650	0.020
  	Very heavy work	650-800	0.026

• The present invention regulates the amount of outside air that the ventilation management system brings into the room. Ventilation air or outside air has a CO₂ concentration normally of about 300 ppm. The maximum desirable concentration in the room should be 500 ppm or lower a counter for counting the number of persons in said area and the amount of time each person remains in said area, said counter producing a signal representing the sum of the number of persons times the amount of time spent in the room for each person. The processor adjusts the ventilation system controls based on the signal produced according to an algorithm, such as: $\frac{d{P}_{\mathrm{CO}2}}{dt}=\frac{j_{\mathrm{CO}2}*N\left(t\right)-v_{\mathrm{CO}2}\left(t\right)}{\mathrm{Vol}}$
  where dP_CO2/dt is the rate of CO₂ partial pressure change in the room, V_CO2 (t) is the rate of 300 ppm CO₂/air ventilation into the room, N(t) is the number of people in the room as a function of time, and j_CO2 is the average CO₂ respiration rate of a person (assumed to be constant and independent of specific individuals).
• The particular processor will be programmed to make the appropriate calculations and send a signal to the ventilation system for the room. Using the present invention allows the elimination of many sensors that would otherwise be needed to sense temperature, CO₂ concentration, humidity, body odor and the like. By simply counting each and every time a person goes into and out of the room, and since the metabolism of an average person is more or less the same, the summed number of person/time units is correlated to the CO₂ generation rate and the room can be maintained at an efficient and comfortable atmosphere.
• While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.

Claims (21)

1. An occupancy based ventilation system for indoor air quality of a predetermined area, comprising:

a room ventilation system for providing outdoor air to said predetermined area;

a counter for counting the number of persons in said area and the amount of time each person remains in said area, said counter producing a signal representing the sum of the number of persons times the amount of time for each person; and

a processor for adjusting said ventilation system for said area based on the signal produced, said processor being adapted to determine the amount of ventilation needed to maintain the CO₂ concentration in the room air at a predetermined level.

2. The system of claim 1, wherein said CO₂ concentration is 500 ppm or less.

3. The system of claim 1, wherein said counter is positioned by the entrance to said area.

4. The system of claim 1, wherein said counter includes a sensor selected from photo cells, IR detectors, RF detectors, pressure plates and a turnstile.

5. The system of claim 1, wherein said processor is further adapted to adjust the amount of ventilation based on the outside air temperature.

6. The system of claim 5, wherein first detector further includes a first filter that passes only said first IR band and said second detector further includes a second filter that passes only said second IR band.

7. The system of claim 1, wherein said processor uses the algorithm:

$\frac{d{P}_{\mathrm{CO}2}}{dt}=\frac{j_{\mathrm{CO}2}*N\left(t\right)-v_{\mathrm{CO}2}\left(t\right)}{\mathrm{Vol}}$

where dP_CO2/dt is the rate of CO₂ partial pressure change in the room, V_CO2 (t) is the rate of 300 ppm CO₂/air ventilation into the room, N(t) is the number of people in the room as a function of time, and j_CO2 is the average CO₂ respiration rate of a person.

8. An occupancy based ventilation system for indoor air quality of a predetermined area, comprising:

room ventilation system means for providing outdoor air to said predetermined area;

counter means for counting the number of persons in said area and the amount of time each person remains in said area, said counter producing a signal representing the sum of the number of persons times the amount of time for each person; and

processor means for adjusting said ventilation system for said area based on the signal produced, said processor being adapted to determine the amount of ventilation needed to maintain the CO₂ concentration in the room air at a predetermined level.

9. The system of claim 8, wherein said CO₂ concentration is 500 ppm or less.

10. The system of claim 8, wherein said counter means is positioned by the entrance to said area.

11. The system of claim 8, wherein said counter means includes a sensor selected from photo cells, IR detectors, RF detectors, pressure plates and a turnstile.

12. The system of claim 8, wherein said processor means is further adapted to adjust the amount of ventilation based on the outside air temperature.

13. The system of claim 8, wherein said processor means is further adapted to adjust the amount of ventilation based on the air temperature in the room.

14. The system of claim 8, wherein said processor means uses the algorithm:

$\frac{d{P}_{\mathrm{CO}2}}{dt}=\frac{j_{\mathrm{CO}2}*N\left(t\right)-v_{\mathrm{CO}2}\left(t\right)}{\mathrm{Vol}}$

where dP_CO2/dt is the rate of CO₂ partial pressure change in the room, V_CO2 (t) is the rate of 300 ppm CO₂/air ventilation into the room, N(t) is the number of people in the room as a function of time, and j_CO2 is the average CO₂ respiration rate of a person.

15. A method for controlling indoor air quality of a predetermined area having a room ventilation system for providing outdoor air to said predetermined area, comprising the steps of:

positioning a counter for counting the number of persons in said area and the amount of time each person remains in said area, and producing a signal representing the sum of the number of persons times the amount of time for each person; and

adjusting said ventilation system for said area based on the signal produced using a processor, said processor being adapted to determine the amount of ventilation needed to maintain the CO₂ concentration in the room air at a predetermined level.

16. The method of claim 15, wherein said CO₂ concentration is 500 ppm or less.

17. The method of claim 15, wherein said counter is positioned by the entrance to said area.

18. The method of claim 15, wherein said counter includes a sensor selected from photo cells, IR detectors, RF detectors, pressure plates and a turnstile.

19. The method of claim 15, wherein said processor adjusts the amount of ventilation based on the outside air temperature.

20. The method of claim 15, wherein said processor adjusts the amount of ventilation based on the air temperature in the room.

21. The method of claim 15, wherein said processor uses the algorithm:

$\frac{d{P}_{\mathrm{CO}2}}{dt}=\frac{j_{\mathrm{CO}2}*N\left(t\right)-v_{\mathrm{CO}2}\left(t\right)}{\mathrm{Vol}}$

where dP_CO2/dt is the rate of CO₂ partial pressure change in the room, V_CO2 (t) is the rate of 300 ppm CO₂/air ventilation into the room, N(t) is the number of people in the room as a function of time, and j_CO2 is the average CO₂ respiration rate of a person.