Method and apparatus for determining an air quality level

Abstract: For accurately determining air quality level even when the temperature and humidity are varied , predefining formula used for obtaining output value of air quality level sensor according to conditions of temperature and humidity at clean state, calculating output value at clean state of the air quality level sensor on a temperature and humidity at air quality detection using the formula, taking as correction amount a difference between the calculated output value and an output value at clean state of the air quality level sensor in conditions of temperature and humidity providing absolute determination reference of air quality level, correcting threshold value predetermined in the conditions of temperature and humidity providing an absolute determination reference , by adding the correction amount to the threshold value, and determining an air quality level by comparing an output of the air quality sensor upon the air quality detection , with the corrected threshold value.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for determining an air quality by detecting an air quality in an accommodation space. 2. Related Art of the Invention From WO 89/12 269 a control method of an air conditioner for maintaining comfortability in a room is known which controls the comfortability of the temperature, humidity and air current in the room. The aforementioned parameters are detected and are compared with comfortable levels, and if there is a difference between the detected values and the reference values, the air conditioner is controlled respectively for changing temperature, humidity and air current in the room. The state of the art disclosed in this document is the starting point of the invention as set forth in the preambles of claims 1 and 4, respectively. From EP-A-0 405 149 a room condition maintaining apparatus is known comprising surrounding detectors for detecting room temperature, humidity and air quality, outdoor temperature, humidity and lighting. Differences between the temperatures and humidities are detected. The collected data is input into a fuzzy controller which operates on the basis of fuzzy reasoning to determine output levels for an air regulator, a humidity regulator, a lighting apparatus and a fan. By continually adjusting the above output levels, the condition in a room is made more comfortable for anyone entering the room from outdoors. From EP-0-518 327 an air quality conditioning system is known for adjusting an environmental air quality in an accommodation space, comprising a detection device for detecting the air quality, a detection device for detecting the temperature and humidity, a signal processor for identifying the causes for the change in the air quality of the accommodation space based on the outputs of said detection devices, and also determining the degree of the change based on discomfort degree data for the air quality with another function of correcting the output of said detection means for the temperature and humidity. This system is based on the concept that the air quality is constituted by three elements, i.e. the presence of human beings in the accommodation space, smoking and background bad odour. By detecting these elements by respective sensors, the air quality is precisely judged. In the system, the temperature and humidity are used for correcting the output of each gas sensor, because the gas sensors are usually dependent on temperature and humidity so that a respective correction of the gas sensor outputs dependent on the ambient temperature and humidity is necessary. Today, as sealings of doors and windows of office buildings as well as residences are rather airtight, efficiency and energy saving in air conditioning are increased. On the other hand, however, carbon dioxide and various odors are accumulated as a result, and this causes problems in human health, while increasing discomfort by reduction of air quality in an accommodation space. As a means for dealing with such circumstances, various air conditioning apparatuses and air quality regulating apparatuses such as ventilators and air cleaners are being introduced. However, an air quality determination apparatus used in a conventional air quality regulator merely determines air quality by reference to an initially predetermined condition, that is, a set value corresponding to plural temperature stages or humidity stages. Thus, the air quality regulator operated on the basis of such a determination results in providing an operation control only in accordance with the predetermined set value. It thus becomes almost impossible to obtain a control in response to actual changes of air quality in an accommodation space. Specifically, if air quality itself is changed by a variation of temperature and humidity in an accommodation space, discomfort to residents results therefrom. Particularly, in the case where odor is present, an air quality regulator is required which operates in consideration of both temperature and humidity, because it may be felt uncomfortable, when only the humidity is changed, even if it is comfortable in certain conditions of temperature and humidity. However, an effective determination against the influence of such temperature and humidity is a problem and is almost impossible to achieve by conventional air quality determination apparatus. SUMMARY OF THE INVENTION Hence, in the light of such problems associated with conventional air quality determination apparatuses, it is an object of the present invention to provide a method and apparatus for determining an air quality level by taking temperature and humidity into consideration. This object is attained by the features of claim 1 and claim 4, respectively. Preferred embodiments are subject matter of the respective dependent claims. In the present invention, an output value at a clean state of air quality level sensing means based on a temperature and humidity at the air quality detection is calculated from a predefined formula, and as a correction amount a difference between the calculated value and an output value at the clean state of the air quality level sensing means at conditions of temperature and humidity which provides an absolute determination reference of air quality level, is calculated, and a threshold value which is determined under temperature and humidity of the absolute determination reference of air quality level is corrected by adding the correction amount to the threshold value, and an output upon air quality detection of the air quality sensing means and the corrected threshold value are compared. In the present invention, the air quality sensing means detects a state of the air quality, and the temperature and humidity sensing means detects temperature and humidity. The reference value output means has preliminary relational information established between different temperatures and humidities and output values of the air quality in a reference air quality , and the computing means obtains a threshold value for air quality determination upon air quality detection by amending a predetermined threshold value of an absolute determination reference of the air quality level, referring to the relational information, on the basis of the detected temperature and humidity. The computing means determines an air quality by comparing an output upon air quality detection of the air quality sensing means with the obtained threshold value for air quality determination at the actual temperature and humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the structure of an air quality level determination apparatus according to an embodiment of the present invention. Fig. 2 is a flowchart representing a procedure for determining an air quality level in accordance with an embodiment of the present invention. Fig. 3 is a characteristic diagram showing a temperature-humidity characteristic of voltage outputs of a gas sensor used in the embodiment. Fig. 4 is an explanatory drawing for explaining output correction in determining an air quality level according to the embodiment. PREFERRED EMBODIMENTS An embodiment of the present invention is described below by reference to the drawings. Fig. 1 is a block diagram showing an embodiment of an air quality level determination apparatus of the present invention. In Fig. 1, numeral 11 is an air quality sensing means for sensing a state of the air quality, and 12 a temperature and humidity sensing means for sensing temperature and humidity, wherein the state of the air quality, temperature and humidity obtained by both means 11, 12 are provided to computing means 14, and the computing means 14 is adapted to control an air quality regulator 15 on the basis of the state of the air quality, temperature and humidity by referring to memory means 13. The memory means 13 stores threshold values that provide an absolute determination reference of the air quality level, an output value (first output value) of the air quality sensing means 11 that corresponds to a clean state in conditions of temperature and humidity under which the threshold values are derived ,and a temperature and humidity correction formula correlated with output values of the air quality sensing means 11, respectively. The memory means 13 can be considered as a reference value output means, and the temperature and humidity correction formula established between various kinds of temperatures and humidities prestored in the memory means 13 and output values of the air quality sensing means 11 in an air quality that provides the determination reference ,for example the air quality in a clean state, is considered as relational information. The computing means 14 , referring to the memory means 13, calculates from the temperature and humidity correction formula an output of the air quality sensing means corresponding to a clean state at a temperature and humidity upon air quality detection. And the computing means 14 calculates and takes as an output correction amount a difference between the calculated value (second output value) and the output value (first output value) of the air quality sensing means 11 corresponding to a clean state at a temperature and humidity providing an absolute determination reference of the air quality level, the first output value being prestored in the memory means 13 . And then the computing means 14 adds the output correction amount calculated to an output value of the threshold value for an air quality determination at the temperature and humidity providing the absolute determination reference of the air quality level, the output value of the treshold value being prestored in the memory means 13 , thereby the output value of the threshold value is corrected. Further the computing means 14 determines an air quality level by comparing the output of the air quality sensing means 11 at an air quality detection with the corrected output value of the threshold value for air quality determination, and outputs the result as a control signal for controlling the air quality regulator 15. In the noted embodiment, as the air quality sensing means 11, an SnO 2 semiconducting gas sensor (hereinafter called as a gas sensor) capable of sensing such organic solvents as alcohols, volatile sulfides and nitrogen-containing compounds is used. In addition, a ceramic thermistor (hereinafter thermistor) is used as a temperature sensor, and a ceramic humidity sensor (hereinafter humidity sensor) as a humidity sensor of the temperature and humidity sensing means 12. The operation of the embodiment is described below. Fig. 2 is a flowchart showing a procedure for determining an air quality. When the air quality level determination apparatus is activated, an output of the temperature and humidity sensing means 12 and an output of the air quality sensing means 11 are measured (step 21), and an output value of the air quality sensing means 11 that corresponds to a clean state at the temperature and humidity of the air quality detected is calculated by the temperature and humidity correction formula (step 22). Succeedingly, a difference between the calculated value and an output value of the air quality sensing means 11 ,prestored in the memory means 13, corresponding to a clean state at the temperature and humidity providing an absolute determination reference of the air quality level is calculated ,and is regarded as an output correction amount (step 23). Then, by adding the output correction amount to an output value of the threshold value for the air quality level determination at the temperature and humidity that provide the absolute determination reference of the air quality level, the output value of the threshold value for the air quality level determination is corrected (step 24). In succession, by comparing an output of the air quality sensing means 11 and the corrected output value of the threshold value for the air quality level determination (step 25), an air quality level is determined (step 26), and a control signal for controlling the air quality regulator 15 is outputted on the basis of the result. In order to confirm the operation of the air quality level determination apparatus, an air quality was measured in a laboratory room of approximately 1.5 × 2 × 2.2 m in size that is provided with an air conditioner having ventilating and air cleaning functions (hereinafter air quality regulator). The gas sensor, thermistor and humidity sensor were attached in a mutual vicinity on a wall of the room at a level of approximately 1.2 m. Fig. 3 illustrates the temperature and humidity characteristics of a voltage output (used as a sensor output in the embodiment, and hereinafter referred to as a sensor output) of the gas sensor used in the embodiment, and a relation between humidities and sensor outputs is shown in a graph with temperature as a parameter. In figure 3, temperature and humidity characteristics at 15°C (line a), 25°C (line b) and 35°C (line c) are shown, respectively, as examples. As can be seen from figure 3, with the gas sensor, the humidity and sensor output (V) are in a proportional relationship in a humidity range of 20 to 80%RH, and can be expressed by a general formula (Formula 1). Formula 1 V = A × [%RH] + B In the case of the gas sensor, since the characteristic lines are parallel with each other, a constant A: 1.7 × 10 -2 (V/% RH) represents an inclination and parameter B is 0.07 V (15°C), 0.86 V (25°C) and 1.02 V (35°C), respectively. In Fig. 4, correction of the sensor output in the air quality level determination is explained. In the case of the embodiment, as shown in the figure, a portion within a range of temperatures between 15 and 35°C and humidities between 30 and 70%RH that is enclosed by straight lines is regarded as a temperature and humidity correction range. Furthermore, the temperature and humidity correction range is divided into five sections referred to as sections 1 ○, 2 ○, 3 ○, 4 ○ and 5 ○, delimiting the ranges 1,2,3 and 4 at temperatures of 19, 23, 27 and 31°C. The delimiting temperatures 15, 19, 23, 27 and 31°C are regarded as belonging to the sections 1 ○, 2 ○, 3 ○ and 4 ○, respectively, and temperature 35°C to the section 5 ○. In the embodiment, a temperature and humidity that provide an absolute determination reference of the air quality level are set at 25°C and 50% RH, respectively (shown by an ○ in figure 4). Therefore, at this temperature and humidity, a sensor output value corresponding to a clean state is 1.39 V, and a threshold value for the air quality level determination is 1.5 V. This threshold value for the air quality level determination of 1.5 V is an experimental value obtained from a correlation between the sensor output of the air quality sensing means 11 with an air quality load (odor) at 25°C and 50 % RH and a discomfort impression (report) of a subject man. On the other hand, the temperature and humidity at an air quality detection in an experiment for confirming operation of the air quality level determination apparatus were set at 30°C and 65% RH, respectively. Thus, in the laboratory room, as a result of setting the temperature and humidity at 30°C and 65% RH, respectively, and measuring a sensor output by applying some air quality load (odor), the sensor output of the air quality sensing means 11 was 1.85 V. As shown in Fig. 4, the temperature and humidity conditions of 30°C and 65%RH belong to the section 4 ○. And a temperature and humidity correction formula associated to sensor outputs in the section 4 ○ can be defined as shown in a formula 2 by setting A = 1.07 × 10 -2 (V/% RH), B = 0.92 V (which corresponds to a straight line shown by a bold line in figure 4). Formula 2 V = 1.07 × 10 -2 × [%RH] + 0.92 Meanwhile the temperature and humidity correction formula 2 is established at an intermediate value (mean value) of temperatures in the divided temperature sections. Therefore, it represents a sensor output at a temperature of 29°C, and is regarded as a temperature and humidity correction formula for calculating a correction amount of the sensor output in section 4. An air quality value corresponding to a clean state at 30°C, 65% RH (shown by a o ○ in figure 4) is calculated to be 1.62 V from the formula 2. As a result, a correction amount of the sensor output is calculated as 1.62 - 1.39 = 0.23 V, and an output of the threshold value for air quality level determination is corrected to 1.50 + 0.23 = 1.73 V, accordingly. Succeedingly, the sensor output of 1.85 V at air quality detection was compared with the output of the threshold value for air quality level determination of 1.73 V, and it was determined, as a result, that the air quality level is significantly degraded, because 1.85 V > 1.73 V. On the other hand as a result of experiment at this time , a discomfort report showed a significant discomfort, and the report was consistent with a determination result based on a sensor output of the air quality level determination apparatus. As described above, by using a method of determining an air quality level and air quality level determination apparatus utilizing the method according to the present invention, a sensor output can be easily corrected on the basis of temperature and humidity changes, and the air quality level can be accurately determined. Although conditions of the section 4 ○ are described as an example in the embodiment, correction of a sensor output and determination of an air quality level can be easily performed in the same manner in other sections as well by changing the value of parameter B in the temperature and humidity correction formula, respectively. The parameter B in sections 1 ○, 2 ○, 3 ○ and 5 ○ of the embodiment is in the order 0.13 V, 0.79 V, 0.86 V and 0.99 V, respectively. In the embodiment of the present invention, where the temperature and humidity correction range is divided into 5 sections in terms of temperature is described, by further increasing the number of divisions, a threshold value for air quality level determination can be corrected more in detail, and precision of air quality level determination can be increased thereby. Additionally, although the temperature and humidity correction range is divided into plural sections in terms of temperature as described in the above embodiment of the present invention, a similar result to that of the embodiment can be obtained by using such a method of dividing the temperature and humidity correction range into plural sections in terms of humidity, and defining a temperature and humidity correction formula by which an output of the air quality sensing means 11 is expressed by a linear expression of temperature. Moreover, in the embodiment of the present invention where lines representing the temperature and humidity correction formula are parallel to each other, value of A in the temperature and humidity correction formula may differ, depending on the gas sensor, and the inclination of the lines in the lower and higher temperature ranges. In such a case, by setting A and B independently in each section, respectively, a similar correction to that of the embodiment can be achieved. The present invention can utilize a table equivalent to the above-mentioned formula. In addition, in the embodiment, although an SnO 2 semiconductive gas sensor is utilized as an air quality sensing means of the present invention, an equivalent of various gas sensors may be alternatively be used. Moreover, plural gas sensors having different gas selectivity may be used, in such a case, a factor that causes degradation of air quality can be identified, and air quality can be adjusted more finely at the same time. Also, it is not limited to a semiconductive gas sensor, and such an air quality sensing means as an optical gas sensing means and a chemical gas sensing means can be used according to the particular purpose and size. Furthermore, the temperature and humidity sensing means of the present invention is not limited to such ceramic sensor and ceramic humidity sensor of the embodiment, and arbitrary means may be employed as far as it is capable of sensing temperature and humidity and outputting a signal. As appreciated by the above description, according to a method for determining an air quality level of the present invention, a threshold value that provides an absolute determination reference of the air quality level is corrected in response to a temperature and humidity of the air quality detected, and an air quality level is determined, so that the air quality is accurately determined. Additionally, according to an apparatus for determining an air quality level of the present invention, even when temperature and humidity are varied, a level of air quality can be easily and accurately determined, and the air quality can be maintained and controlled at a comfortable level by applying the determination result to an air quality regulator, and properly controlling the air quality regulator.

Claims: A method determining the quality level of air in an environment, comprising the steps: A) predefining a formula as a function of temperature and humidity of clean air to obtain an output value of clean air quality, B) predefining an absolute determination reference value of clean air quality at a given temperature and humidity, C) predefining an air quality threshold value at said given temperature and humidity, D) measuring the air quality in said environment and outputting a respective measurement value, E) deriving the clean air quality value at the temperature and humidity of the air in said environment by means of the formula of step A), F) calculating the difference between the air quality value derived in step E) and the reference value defined in step B) to obtain a correction value, G) adding said correction value calculated in step F) to the air quality threshold value derived in step C) to obtain a corrected threshold value, and H) determining the actual air quality level in said environment by comparing the measurement value measured in step D) with the corrected threshold value obtained in step G. The method of claim 1, wherein said reference values are expressed by a linear expression of humidity in each of a plurality of ranges of a range of reference values from which a correction range of temperature and humidity is divided by temperature conditions. The method of claim 1, wherein said reference values are expressed by a linear expression of temperature in each of the pluralities of ranges of said range of reference values from which a correction range of temperature and humidity is divided by humidity conditions. An apparatus for determining the quality level of air on an environment comprising: air quality sensing means (11) for detecting the quality level of air in the environment and providing a respective output signal, temperature and humidity measuring means (12) for detecting the air temperature and humidity in said environment and providing respective output signals, reference value output means (13) providing clean air quality output values dependent on a predefined relation of a plurality of temperature and humidity values, characterized by further comprising computing means (14) connected to said air quality sensing means (11), said temperature and humidity sensing means (12) and said reference value output means (13), said computing means (14) comprising, means for calculating a difference between a predefined absolute air quality value defined at a given air temperature and humidity and a clean air quality value predefined by said relation at the temperature and humidity of said environment, means for adding said difference to an air quality threshold value predefined at said given temperature and humidity to obtain a corrected threshold value, and means for comparing said corrected threshold value with the output signal of said air quality sensing means (11). The apparatus of claim 4, wherein said reference value output means comprises memory means (13) for storing threshold values that provide and absolute determination reference of the air quality level, a first output value indicative of the clean state of the air quality sensing means (11) as a condition of temperature and humidity under which the threshold values are divided, and a formula for an output value of the air quality that is correlated with various values of temperature and humidity, and said computing means comprises correction means (14) for computing a second output value indicative of a clean state of the air quality on the basis of temperature and humidity at the temperature and humidity conditions measured by said temperature and humidity sensing means (12) during air quality detection by using said formula, and computing means (14) for determining an air quality level by comparing the composite threshold value with the output of said air quality sensing means (11) and for outputting a control signal for controlling an air quality regulator (15). An apparatus as set forth in claim 4 or 5, wherein the air quality sensing means (11) includes a gas sensor. An apparatus as set forth in any one of claims 4 to 6, wherein the temperature and humidity sensing means includes a ceramic thermistor and ceramic humidity sensor.

Inventors: TACHIBANA HIROKAZU, YOSHIIKE NOBUYUKI, TACHIBANA, HIROKAZU, YOSHIIKE, NOBUYUKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: F24F11
IPC codes: F24F11, G01N27, G01N25, G01W1