摘要：It is a fundamental task of HVAC to provide occupants a healthy and comfort environment. By far more and more attention has been paid to indoor air quality(IAQ). Excellent indoor air ensures health of occupants. It has become a worldwide problem and caused many sick building syndromes(SBS) and building related illness(BRI), which can not be ignored. Indoor air quality would be one of the most important problems which developers, owners, proprietors care more about before entering 21st century.

关键词：indoor air quality　　sick building syndromes　　building related illness

ABSTRACT

It is a fundamental task of HVAC to provide occupants a healthy and comfort environment. By far more and more attention has been paid to indoor air quality(IAQ). Excellent indoor air ensures health of occupants. It has become a worldwide problem and caused many sick building syndromes(SBS) and building related illness(BRI), which can not be ignored. Indoor air quality would be one of the most important problems which developers, owners, proprietors care more about before entering 21^st century.

But up to now, due to lack of accepted international specific standard and uniform method of assessment on indoor air quality, in many cases, some index and standards in assessment on outdoor atmosphere have to be employed when assessing indoor air quality. Stressing on this point, a new assessment system, based on fuzzy mathematics, is put forward in this paper. A full-scale assessment on indoor air quality of 6 high-rise buildings in Shanghai is carried through. All data are from measurement on site.

1.INTRODUCTION

There are thousands of pollutants in building. We can not measure every pollutant that can impat occupant health and comfort, but we can select some representative pollutants as indicator for different sort of indoor contamination. The indicator and its reference value can provide a broad assessment of IAQ. The reasons for selecting indicators and their reference value are discussed as follows:

CO₂: Indoor CO₂ s produced by the occupants and can be an useful indicator of the human bioeffluents. ASHRAE Standard 62-1989 provides a recommended maximum CO₂ level of 1000 ppm, according to ASHRAE, this level is not a health risk but is a surrogate for odors produced by humans.

CO: CO is an indicator of combustion activities because it is produced by combustion processes associated with some activities such as cooking, smoking and so on. If the building has an underground garage, motor vehicle operation is a potential source of CO for the occupied portion of the building. There are no standards for maximum CO levels for office environments, but other guidelines are available. A maximum CO concentration of 10 ppm was selected for assessment based on the continuous exposure level recommended by the World Health Organization. If indoor levels of CO exceed 10 ppm it could indicate a significant indoor source.

Inhalable Particles: Particles that are less than 10 micron in diameter (referred to as PM10) are of concern in terms of human health. Particles is also an indicator for occupant activities. The reference value of a maximum short-term concentration of 0.15 mg/m³ is based on the Nation Ambient Air Quality Standards set forth by EPA. This reference value applied to inhalable particles that are less than or equal to 10 micron in diameter.

When we need investigation more detailed, other parameters can be added, such as SO₂, NO_x, and bacteria, so as to investigate the indoor combustion activities in detail.

Indoor air pollution is a major occupational health problem in occupied environments. The objective assessment of indoor air quality is usually difficult due to the cocktail effect of various pollutants. IAQ problems are often multi-factorial and difficult to analyze independent effect. Now a new objective assessment system, based on fuzzy mathematics, is put forward in this paper.

The definition of fuzzy itself is indefinite. There is no specific finitude between two opposite concepts, but some quantitative difference belonging to artificialness. The instances are very common, such as “young” and “old”, “tall” and “short”, “fat” and “thin”, “cleanness” and “pollution”, etc.. Fuzzy cases in measurement of Indoor Air Quality (IAQ) are shown in the following table.

According as criterion of CO₂ of Japan, there is some explicit but illogical finitude after careful analysis among the parameters above, such as, because the criterion of NO₂ is 50ppb, concentration of indoor NO₂ of 50.01ppb, exceeding the standard, belongs to be polluted, which can not be accepted by most people.

Indoor environment includes a lot of pollutants, so definite evaluation can’t come from one pollutant. If concentration of CO is 701vppm, between the first and the second grade, and at the same time, another pollutant lies between the second and the third grade, then how we can evaluate the indoor air synthesizing all pollutants correctly?

Fuzzy mathematics figures out this question. Now the mathematics model of fuzzy mathematics evaluation is introduced first.

2.MATHEMATICS MODEL OF FUZZY MATHEMATICS EVALUATION

(1)Assorting Factors

In the following equation; j=1,2,…,n；k=1,2,…,p；

If there are n factors in the factors unit U: U={u₁,u₂,…,u_n}。

(2)Results Unit

Results unit is aggregate of all possible results coming from final evaluation. If there is p possible results, the results unit may be : V＝(v₁,v₂,……,v_p)

(3)Factors Magnitude Value Unit

According to the importance of all factors in the factors unit, corresponding magnitude (value changing from 0~1) is given to every factor. If the magnitude value of the j factor u_j is a_j, there is factors magnitude unit: A＝(a₁,a₂,……,a_n)。

The sum of all factors magnitude value is 1 and all of them can not be negative.

(4)Subject Value and Subject Function

If an evaluated object belongs to the factor k, v_k, of results unit, its subject value is r_jk.

(5)The First Degree Fuzzy Synthetical Evaluation

Synthetical evaluation is carried out by all factors from factors unit. Evaluated by the factor j, u_j in the factors unit, and If the evaluated object belongs to the factor k, v_k, of results unit, its subject value is r_jk, so the matrix of the first degree fuzzy synthetical evaluation is:

R=

there are n factors and p results

The first degree fuzzy synthetical evaluation unit is B＝A°R

“°” is synthesis of fuzzy relationship.

3.THE FIRST DEGREE FUZZY SYNTHETICAL EVALUATION OF IAQ

When evaluating indoor air quality, it is the most important that factors unit, subject function and magnitude value are built first.

(1) Factors Unit

Because of the real testing condition, we only choose PM10 (u₁), CO₂ (u₂), CO (u₃), NO₂(u₄), and bacteria（u₅）as synthetical evaluation factors, so the factors unit is: u={u₁,u₂,u₃,u₄ , u₅}。

(2) Subject Function

Subject function has several form, such as triangle, trapezoid, and bell, etc., so we can choose one by experience. Now we choose the simple and visual triangle function.

In the left graph, there is:

Variable X₁----The concentration of cleanness;

Variable X₂----The concentration of pollution;

Point A----random point, that is, this point can be considered as cleanness or pollution.

The subject function F₁(x), F₂(x) are:

F₁(x)＝ F₂(x)＝

Now except Japanese criterion of CO₂ and bacteria (showing in Tab. 2 and Tab. 3), most criterion of indoor air pollutants have only one standard between polluted and unpolluted, which is not suit for fuzzy evaluation. So on the basis of Chinese Atmosphere Quality Standard-- GB3095-96 (Tab. 4) and effect on human health of some main pollutants, combined with the four- degree criterion put forward by World Health Organization in 1963, the three-degree criterion of Chinese Atmosphere Quality Standard, and Atmosphere Quality Standard (Tab.4), 定义各室内污染物的X₁、X₂ of every indoor pollutants are defined as the following:

Table2 Criterion of CO2 in Japan DEGREE CO2 (ppm) fine 700以下 good 700～1000 common 1000～2000 bad 2000～5000 polluted slightly 5000以上 Polluted seriously 10000以上

Table3 Criterion of CO2 in Japan DEGREE BACTERIACFU/9cm*5min） fine 1～2 clean <30 common 31~75 polluted 150 polluted slightly <300 Polluted seriously >301

(3) Factors Magnitude Value Unit

That is the magnitude of every pollutant in indoor air quality.

a_pm10=1/3、a_co2=1/3、a_co=1/9、a_no2=1/9、a_cfu=1/9。

According to harm on human health, we consider that the most important pollutant are PM10 and CO₂, next is NO₂、CFU、CO.

4.THE FIRST DEGREE FUZZY SYNTHETICAL EVALUATION OF TESTING BUILDINGS

Six buildings are tested in July and Autumn, 1999. The testing focus on the indoor air quality and many valuable data are collected. The following is the first degree fuzzy synthetical evaluation of testing buildings.

Evaluation result from calculating program: Building D, E, F are polluted, and the other three are clean.

5.CONCLUSION

From the first degree fuzzy synthetical evaluation on six office buildings in Shanghai, the merit of fuzzy mathematics evaluation is obvious, it can synthesize all undefinite elements in evaluation. But it has some shortcomings, for example, the result can not be classified into several degrees for lack of clear degree standard, except for CO₂ and bacteria. So, if the corresponding degree standard of several pollutants, such as NO_X, SO_2, O₃, CO, TSP, PM10, can be built, the fuzzy mathematics evaluation method for IAQ will be improved greatly.

REFERENCE

1) Wang Fan, Fuzzy and Engineering Mathematics, Ha’ebin shipping Engineering Institute Publisher, 1988

2) Shen Jinming, Mao J., Objective Assessment on IAQ in Shanghai Office Building, Journal of Ventilation and Dust Control, 1995.4, p14-17