Automatic temperature and humidity regulation – Ventilator type – Electrically actuated
Reexamination Certificate
1999-01-29
2002-06-04
Wayner, William (Department: 2736)
Automatic temperature and humidity regulation
Ventilator type
Electrically actuated
C073S031050, C165S248000, C454S257000
Reexamination Certificate
active
06398118
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the art of conditioning indoor living and working and other enclosed public spaces. More particularly, this invention relates to a system in which the carbon dioxide (CO
2
) level is monitored and controlled by apparatus in which the CO
2
sensor and support circuitry is integral with a thermostat which also serves to conventionally control the temperature range within the conditioned space.
BACKGROUND OF THE INVENTION
The ever increasing cost of energy has resulted, in recent years, in the construction of homes and buildings which are very well insulated and, further, which carefully provide for keeping the air within the home or building well isolated from the encroachment of outdoor air. This latter feature serves to limit the adverse effect of outdoor air on the desired temperature intended to be maintained within the building occasioned by direct mixing with the indoor air, an effect which is in addition to and independent of the limitation of adverse conduction effects afforded by insulating the conditioned spaces.
However, it has been observed that these highly-efficient, substantially closed, environmental conditioning systems have a serious drawback which can even reach dangerous levels. Because of the natural breathing processes of the occupants of a closed conditioned space and, in some instances, because of the effects-of combustion or similar processes, the concentration level of oxygen (O
2
) decreases while the concentration of carbon dioxide (CO
2
) increases. It has been found that when the concentration of CO
2
in a conditioned space reaches on the order of 1000 parts per million, breathing becomes noticeably more labored and difficult, particularly for those with breathing problems. Higher concentrations exacerbate these problems and can reach dangerous levels.
Accordingly, recommended maximum allowable concentrations of CO
2
for living and working spaces have been formulated and promulgated, and, in some instances, various government agencies have imposed requirements that specify the maximum concentration of CO
2
which will be allowed in public conditioned spaces.
Commercial CO
2
detectors have been both bulky and have required fairly sophisticated support circuitry because the voltages (or other electrical parameter) generated by or measured across the conventional CO
2
sensors, which vary in accordance with changes in CO
2
concentration, do so only across a very narrow, low level range. One commonly used CO
2
sensor in CO
2
detectors constitutes an IR light source directed at an IR light sensor such that the CO
2
concentration between the source and sensor subtly affects the response of the source. As a result, the support circuitry has to be able to interpret a suitably compensated signal (for example, for temperature and/or humidity variations) which may change only be a few microvolts across the entire measurement range. It will be apparent that such a CO
2
sensor and its support circuitry cannot be integrated with a temperature sensing and control system in a single, compact environmental control unit housing. It will also be apparent to those skilled in the art that such a CO
2
sensor cannot be integrated with substantially all the circuitry and components of both the CO
2
detection subsystem and the temperature sensing and control subsystem into a single integrated circuit.
It is to overcoming these drawbacks of prior art space conditioning control systems which incorporate a CO
2
concentration control feature that the present invention is directed.
OBJECT OF THE INVENTION
It is therefore a broad object of this invention to provide an improved CO
2
detector which is sufficiently compact and simple as to be suitable for integration with a thermostat in a single housing.
It is a more specific object of this invention, in a presently preferred embodiment, to incorporate a small, heated, electro-chemical CO
2
sensor in such an improved CO
2
detector.
SUMMARY OF THE INVENTION
Briefly, these and other objects of the invention are achieved in a system for monitoring and modifying the quality and temperature of air within a conditioned space which includes a blower unit, a damper unit for selectively admitting outside air into the conditioned space, a temperature moderating unit and a control unit. The control unit includes a thermostat including a conventional, manually operable, temperature set point adjustment and temperature control apparatus for selectively activating the temperature moderating unit when the temperature of the conditioned space deviates by a predetermined amount from the established temperature set point. The control unit further incorporates integrated CO
2
concentration measuring and control apparatus for the conditioned space which includes a small CO
2
sensor. In a presently preferred embodiment, the CO
2
sensor consists of a cathode disposed on a substrate, an anode disposed on the substrate spaced from the cathode and a solid electrolyte disposed on the substrate intermediate and electrically in contact with each of the cathode electrode and the anode to effect a primary electrical cell. A heater and a heater thermostat are also disposed on the substrate and are connected to a source of electrical energy to maintain the primary electrical cell within a predetermined temperature range on the order of 250° C. The metals from which the cathode and anode are fabricated and the chemical composition of the electrolyte being further selected such that the voltage established between the cathode and the anode varies in accordance with the CO
2
concentration at the primary electrical cell when the temperature of the cell is within the predetermined temperature range. CO
2
concentration modifying apparatus is responsive 1) to the measurement of at least a first voltage level between the cathode and the anode, representing a first predetermined CO
2
concentration, for turning on the blower unit; and 2) to the measurement of at least a second voltage level between the cathode and the anode representing a second predetermined CO
2
concentration, higher than the first predetermined CO
2
concentration, for actuating the damper unit to admit outside air into the conditioned space.
In more simple, alternative configurations, either a blower unit only or a damper unit only may be the elements employed to control the CO
2
concentration in the conditioned space. In addition, the use of CO
2
concentration sensors (e.g., semiconductor CO
2
concentration sensors), suitable for integration with the thermostat, are contemplated in place of the electro-chemical cell.
REFERENCES:
patent: 4211362 (1980-07-01), Johnson
patent: 4326200 (1982-04-01), Bushman
patent: 5775406 (1998-07-01), Ghitea, jr.
patent: 5971067 (1999-10-01), Rayburn
S. Azad, S.A. Akbar, S.G. Mhaisalkar, L.D. Birkefeld and K.S. Goto, Journal of the Electrochemical Society, 139, 3690-3704 (1992).
Dushane Steven D.
Rosen Howard B.
Bracken David T.
Wayner William
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