Chapter 25

EVALUATION OF THE EFFICIENCY OF MEANS ADOPTED TO IMPROVE
THE CLIMATIC CONDITIONS IN DEEP MINES

J. Drenda
Technical University of Silesia Gliwice, Poland

ABSTRACT

The parameter used to evaluate climatic conditions in working environments is the thermal discomfort index “δ”. This index is a dimensionless number which may assume both positive and negative values. Positive values are characteristic of warm environments while negative values are associated with cold ones. The thermal discomfort index can be calculated with nomographs dependant on climate, velocity of air-flow, worker's expenditure of energy and his acclimatisation. In the article nomographs are presented, allowing the calculation of the index of thermal discomfort in the following conditions and assumptions: workers with and without clothes and where the average temperature of radiation is equal to the air temperature.

For thermal comfort the thermal discomfort index is zero. In consequence, the closer to zero the thermal discomfort index is the more effective than the improvement of climatic conditions has been. Improving the climatic conditions does not, however, have to lead to the ideal thermal comfort level. Acceptable levels are those defined as safe climatic conditions in which the thermal discomfort index is lower than one (δ<1). Thus, safe climatic conditions exist in warm environments when thermal discomfort indicator lies within the interval (0÷1). This interval has been divided into smaller intervals describing climatic conditions as follows:

δ<0.2 favourable climatic conditions

0.2≤δ<0.5 satisfactory climatic conditions

0.5≤δ<0.8 difficult climatic conditions

0.8≤δ<1 very difficult climatic conditions

Considering different methods of improving climatic conditions, such as decreasing air temperature, reducing air humidity, increasing air-flow speed or lowering the average energy expenditure of a worker during the working day, we are able to evaluate in numbers the effectiveness of such an improvement. Basing on the thermal discomfort index we are enabled to choose the best method for improving climatic conditions, evaluate possible improvements or evaluate necessary corrections of parameters influencing climatic conditions in order to obtain a measure of the efficiency of the improvement. In the article many examples of using the thermal discomfort index in order to evaluate the effectiveness of improving the climatic conditions are elicited.

KEYWORDS

Climate, thermal comfort, thermal discomfort, climatic conditions

THERMAL DISCOMFORT INDEX

Thermal discomfort index “δ” is a parameter indicating the climatic conditions in environment. It has been created on the basis of Fanger's thermal comfort equation [Fanger, 1972] and boundary magnitudes of the WBGT index, called the reference magnitudes, stated within the international standards ISO 7243-1982 (in Poland PN-85/N-08011).

Thermal discomfort index “δ” takes into consideration the following parameters concerning environment and man:

• climatic parameters (temperature, relative humidity and the velocity of the air),

• environment radiation - average temperature,

• the worker's energy expenditure,

• the clothing - thermal resistance of the clothing,

• acclimatisation of the workers.

Air temperature, relative humidity, air velocity and radiation temperature, we can measure. Energetic expenditure i.e. the metabolic rate of the man depends on the type and intensity of the work. Energy expenditure is expressed in watts per square meter of the human body surface (W/m²=J/m²s), which may be called density of metabolic rate.

Energy expenditure depends on the nature of the human's actions and is as follows:

1. rest M=65 W/m²,

2. light work 65< M ≤ 130 W/m², M_m = 100 W/m²

3. moderate work 130< M ≤200 /m², M_m = 165 W/m²

4. hard work 200< M ≤ 260 W/m², M_m = 230 W/m²

5. The clothing of the worker is to be understood as the thermal resistance of the clothing .I_cl as illustrated in the unit “clo”.

I_cl=0- without clothes I_cl=0

I_cl=1- a men wearing ordinary working suits

The level of acclimatisation is based on the assumption that the man is either acclimatised or non-acclimatised. It is assumed, that acclimatisation is achieved after two weeks of working in a hot environment.

The thermal discomfort index ”δ” is a dimensionless number, which may assume both positive and negative values. It is calculated with the equation: (Drenda, 1993)

where:

t_s - air temperature measured with a dry-bulb

thermometer,

t_comf - temperature of thermal comfort in the environment. It is a temperature calculated on the basis of the Fanger's equation of thermal comfort related to the humidity of the air in the environment,

t_WBGT - the temperature which assumes the boundary magnitude of the WBGT index stated in ISO-7243 - 1982, depending on energy expenditure, clothing and the acclimatisation of the worker.

EVALUATION OF CLIMATIC CONDITIONS

On the basis of the thermal discomfort index magnitudes we can evaluate the climatic conditions in different environments in which a man is working. (Drenda, 1993, 1996)

When:

δ < 0 discomfort the cold environments,

δ = 0 thermal comfort,

δ > 0 discomfort in a hot and warm environment,

0 <δ< 1 thermal discomfort, yet still safe for human health,

δ ≥ 1 thermal discomfort hazardous for human health.

A magnitude of the thermal discomfort index equal to one is the boundary magnitude of thermal safety of man in a hot environment. In worksites where
δ ≥ 1 man should neither be present nor work, because of the risk of elevating the core body temperature. Environments in which 0 <δ< 1 are safe for human health. The conditions for this range of thermal discomfort index are divided into:

0 <δ< 0,2 favourable climatic conditions.,

0,2 ≤δ< 0,5 satisfactory climatic conditions,

0,5 ≤δ< 0.8 difficult climatic conditions,

0,8 ≤δ< 1 very difficult climatic conditions.

THERMAL DISCOMFORT INDEX NOMOGRAPHS

For calculating the thermal discomfort index nomographs were created (Fig. 1; 2; 3; 4; 5). Each nomograph concerns the different magnitudes of relative humidity of the air.

Fig. 1 - ϕ = 20%

Fig. 2 - ϕ = 40%

Fig. 3 - ϕ = 60%

Fig. 4 - ϕ = 80%

Fig. 5 - ϕ = 100%

Nomographs have been designed for men without clothes and men wearing normal working clothes, I_clo=1clo. It is assumed that the average environmental radiation temperature is equal to the air temperature. Each nomograph consists of four areas and four axes. The air temperature is placed on the top, vertical axis; the bottom, vertical axis represents the thermal discomfort index magnitudes. The horizontal axes represent the effective American temperature. In the top right and top left areas lines are placed to represent stable airflow velocity. In the bottom right and bottom left areas are drawn lines to represent stabilised energy expenditure for rest, light, moderate and hard work for acclimatised and unacclimatised men.

THE USE OF THE NOMOGRAPH

The thermal discomfort index is calculated from the nomograph in the following manner: Through measurement we obtain data concerning the temperature, relative humidity and velocity of the air. The values in the example below have been assigned for the purpose of illustrating the use of the nomogram. We choose the nomographs on the basis of air humidity ϕ = 80% (Fig. 4).

On the vertical axis we mark the resultant air temperature 25°C, point A. Then we project a horizontal line to the left for people without clothes or to the right for people with clothes, towards point B(B'), which is placed on the proper air velocity line w=1m/s. After reaching point B(B'), a vertical line is drawn. This represents energy expenditure M=165 W/m² for men acclimatised point C(C'). From this point, we draw a horizontal line and on the vertical axis at point D(D') we find the thermal discomfort index magnitude.

Figure 1. Nomogram for evaluating thermal discomfort indeks for relative humidity j= 20%

Figure 2. Nomogram for evaluating thermal discomfort indeks for relative humidity j= 40%

Figure 3. Nomogram for evaluating thermal discomfort indeks for relative humidity j= 60%

Figure 4. Nomogram for evaluating thermal discomfort indeks for relative humidity j= 80%

Figure 5. Nomogram for evaluating thermal discomfort indeks for relative humidity j= 100%

Table 1

No	Method of improving the climatic condition	Air dry tempera- ture ts [°C]	Air wet tempe- rature tw [°C]	Relative humidity ϕ [%]	Air enthalpy i [kJ/kg]	Air velocity w [m/s]	Metabo- lic rate M [W/m^2]	Clothe Icl [clo]	Acclimatisation	Thermal discomfort index δ
I	The primary conditions	33	26.4	60	82	0,5	165	0	accl.	0,78
II	Decreasing the temperature without changing the air humidity	25	24,4	95	74	0.5	165	0	accl.	0,25
III	Decreasing the air humidity without changing the temperature	33	22,4	40	66	0,5	165	0	accl.	0,64
IV	Increasing the air velocity	33	26.4	60	82	1,5	165	0	accl.	0.7
V	Decreasing the average energy expenditure with work-breaks	33	26,4	60	82	0,5	100	0	accl.	0,54

For the assumptions of the example, the thermal discomfort index for people without clothes is δ=0,12, for people with clothes δ=0,83. It is possible to calculate thermal discomfort indices for middle magnitudes of relative air humidity ϕ=70% and clothes I_cl=0,5clo, from the nomographs through the process of interpolation.

THE EVALUATION OF THE IMPROVEMENT OF THE CLIMATIC CONDITIONS

The thermal discomfort index is a very good tool for the evaluation of improvement or deterioration of the climatic conditions. On the basis of changes in it's magnitude we can effectively evaluate the effectiveness of different methods used to improve climatic conditions. After applying different methods, their effectiveness and the cost of implementing them enables a best solution to be chosen in a given situation. The basic ways in which improvement of the climatic conditions in hot environments may be effected are:

1. Decreasing the air temperature t_s

2. Lowering the humidity of the air

3. Increasing the velocity of the air

4. Decreasing the average energy expenditure of the worker by introducing rest-periods, or breaks from work

Each of these methods leads to a decrease of the thermal discomfort index and this indicates that the climatic conditions in the environment have improved. The thermal discomfort values obtained while planning a specific method of improving the climatic conditions or a combination allow the effectiveness of the improvement to be evaluated. The closer to zero the thermal discomfort index, the more efficient and effective the climatic conditions improvement will be. examples of improving the climatic conditions at the workface are presented in Table 1. Line I contains the parameters of the microclimate in the workface. Lines II to V represent the parameters of the microclimate and the worker after implementing the above-mentioned methods of improving the climatic conditions.

CONCLUSION

The analysis and evaluation of the climatic conditions in a working environment on the basis of a thermal discomfort index is simple and convenient. The index provides objective information about climatic comfort and safety. It also allows the effectiveness of different methods used to improve the climate conditions to be evaluated. It helps the choice the most efficient and profitable method or combination of methods to achieve this outcome to be chosen.

Combined with air temperature and humidity forecasts, it allows the climatic conditions, which will prevail in the planned workface to be predicted.

LITERATURE

Drenda J. (1993) Thermal discomfort in working environments of deep mines. Zeszyty Naukowe Politechniki Śląskiej Z.213, Gliwice (in polish)

Drenda J.(1993) Bewertung der Klimatischen Arbeitsbedingungen mit Hilfe des Wärmediskomfortkoeffizienten. Gluckauf - Forschungshefte Nr 2. s. 86-89.

Frycz A. Drenda J.(1994) Bewertung der Effektivitat der Angewandten Methoden zur Verbesserung der Klimatischen Verhaltnisse zwecks Sicherung des Warmekomforts in tiefen Gruben. Proceedings, 16-th World Mining Congress, 12 ÷16 Sept. 1994. Sofia, Bułgaria.

Drenda J.(1996) Urawnienie predelnogo tepłowogo diskomforta trudjaszczichsja Proceedings, National Bureau of Thermophysics Sofia 16-20 września 1996. Bułgaria.

Drenda J.(1996) Thermal safety of workers in warm and hot work conditions. Proceedings, 5^th International Conference on Air Distribution in Rooms ROOMVENT-96 Yokohama, July 17-19. 1996 r. Japonia.

Drenda J., Domagała L., Jaromin M., Musioł D. (1998). Prostoj graficzeskij sposob ocenki biezopasnosti klimaticzeskich usłowij w szachtnych zabojach. Proceedings, International Scientific and Technical Conference „Occupational safety in underground and open pit mines and quarries Warna 08-11. 06. 1998. Bułgaria.

Frycz A., Sułkowski J., Drenda J.(1998). Klimaticzeskije usłowja - priczina zapozdanija gorno cpasatielnoj operacji. Proceedings, VIII Plenary session International Bureau of Mining Thermophysics, Saint - -Petersburg 14-18. 09. 1998 r.

Drenda J. Wieprzycki H.(1999). The hazard of thermal shocks for miners. Proceedings, Międzynarodowa konferencja naukowa nt. Najnowsze osiągnięcia w zakresie przewietrzania kopalń oraz zwalczania zagrożeń pożarowych, gazowych i klimatycznych. Szczyrk, 22. 04. 1999.

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EVALUATION OF THE EFFICIENCY OF MEANS ADOPTED TO IMPROVE

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